Journal publications
- Novel generic fault model considering fundamental and PWM current components of PM machines with inter-turn short-circuit
IEEE Transactions on Power Electronics, 2024
Y. Qin, G. J. Li, Z. Q. Zhu, M. P. Foster. D. A. Stone, C. J. Jia & P. McKeeverThis paper proposes a novel analytical fault model for permanent magnet machines with inter-turn short-circuits that considers the influence of various factors on the fault current. These factors include (1) mutual inductances between the faulted turns and the remaining healthy windings (faulted and healthy phases), (2) load current, and (3) PWM harmonics introduced by the drives. These three factors have been largely neglected by the published methods in literatures but could have significant influence on fault current depending on operating conditions. The investigation in this article shows that, without using the proposed fault model, the conventional fault model that only considers the back-EMF in the short-circuited loop and the self-impedance of the short-circuited turns, would underestimate the fundamental fault current by more than 45%. In addition, the proposed model establishes the relationship between the PWM ripple current in the short-circuited turns and that in the faulted phase. By doing so, the fault current including both the fundamental and PWM ripple components can be accurately predicted. The accuracy of the proposed method has been fully validated by a series of experiments
https://doi.org/10.1109/TPEL.2024.3383495 - Techno-economic planning of a fully renewable energy-based autonomous microgrid with both single and hybrid energy storage systems
MDPI Energies, 2024
M. Naderi, D. Palmer, M. J. Smith, E. E. F. Ballantyne, D. A. Stone, M. P. Foster, D. T. Gladwin, A. Khazali, Y. Al-Wreikat, A. Cruden & E. FraserThis paper presents both the techno-economic planning and a comprehensive sensitivity analysis of an off-grid fully renewable energy-based microgrid (MG) intended to be used as an electric vehicle (EV) charging station. Different possible plans are compared using technical, economic, and techno-economic characteristics for different numbers of wind turbines and solar panels, and both single and hybrid energy storage systems (ESSs) composed of new Li-ion, second-life Li-ion, and new leadacid batteries. A modified cost of energy (MCOE) index including EVs unmet energy penalties and present values of ESSs is proposed, which can combine both important technical and economic criteria together to enable a techno-economic decision to be made. Bi-objective and multi-objective decision-making are provided using the MCOE, total met load, and total costs in which different plans are introduced as the best plans from different aspects. The number of wind turbines and solar panels required for the case study is obtained with respect to the ESS capacity using weather data and assuming EV demand according to the EV population data, which can be generalized to other case studies according to the presented modelling. Through studies on hybrid-ESS-supported MGs, the impact of two different global energy management systems (EMSs) on techno-economic characteristics is investigated, including a power-sharing-based and a priority-based EMS. Single Li-ion battery ESSs in both forms, new and second-life, show the best plans according to the MCOE and total met load; however, the second-life Li-ion shows lower total costs. The hybrid ESSs of both the new and second-life Li-ion battery ESSs show the advantages of both the new and second-life types, i.e., deeper depths of discharge and cheaper plans.
https://doi.org/10.3390/en17040788 - Planning a Hybrid Battery Energy Storage System for Supplying Electric Vehicle Charging Station Microgrids
MDPI Energies, 2024
A. Khazali, Y. Al-Wreika,E. J. Fraser, S. M. Sharkh,A. J. Cruden, M. Naderi, M. J. Smith,D. Palmer,D. T. Gladwin, M. P. Foster, E. E. F. Ballantyne, D. A. Stone and R. G. WillsThis paper presents a capacity planning framework for a microgrid based on renewable energy sources and supported by a hybrid battery energy storage system which is composed of three different battery types, including lithium-ion (Li-ion), lead acid (LA), and second-life Li-ion batteries for supplying electric vehicle (EV) charging stations. The objective of this framework is to determine the optimal size for the wind generation systems, PV generation systems, and hybrid battery energy storage systems (HBESS) with the least cost. The framework is formulated as a mixed integer linear programming (MILP) problem, which incorporates constraints for battery ageing and the amount of unmet load for each year. The system uncertainties are managed by conducting the studies for various scenarios, generated and reduced by generative adversarial networks (GAN) and the k-means clustering algorithm for wind speed, global horizontal irradiation, and EV charging load. The studies are conducted for three levels of unmet load, and the outputs are compared for these reliability levels. The results indicate that the cost of hybrid energy storage is lower than individual battery technologies (21% compared to Li-ion, 4.6% compared to LA, and 6% compared to second-life Li-ion batteries). Additionally, by using HBESS, the capacity fade of LA batteries is decreased (for the unmet load levels of 0, 1%, 5%, 4.2%, 6.1%, and 9.7%, respectively), and the replacement of the system is deferred proportional to the degradation reduction.
https://doi.org/10.3390/en17153631 - Fully-Integrated Transformer With Asymmetric Primary and Secondary Leakage Inductances for a Bidirectional Resonant Converter
IEEE Transactions on Industrial Applications, 2023
S. A. Ansari, J. N. Davidson & M. P. FosterTypically, inserted-shunt integrated transformers have symmetric primary and secondary leakage inductances. However, bidirectional resonant converters typically operate more efficiently with different primary and secondary series inductances. In this paper, a new topology for an inserted-shunt integrated transformer which can provide tunable, asymmetric leakage (series) inductances on the primary and secondary sides is presented. Two magnetic shunts, with appropriate air gaps, are inserted between two E-cores and the primary and secondary windings are separated by being placed at opposite sides of the shunts. The proposed transformer is analysed in detail and modelling and design guidelines are provided. It is shown that the magnetising inductance and the primary and secondary leakage inductances are decoupled from each other, and they can be determined separately. The design has the advantage of using planar E-cores and magnetically permeable sheets that are commercially available. The theoretical analysis is verified by simulation and experimental results. In addition, to demonstrate the performance of the proposed integrated transformer in practice, an exemplar bidirectional CLLLC resonant converter is designed, constructed and tested using the new integrated transformer.
https://doi.org/10.1109/TIA.2023.3252525 - Soft Switching Voltage Regulation for Inductorless Piezoelectric Transformers: A Cyclic-Mode Analysis
IEEE Transactions on Power Electronics, 2023
Z. Yang, J. Forrester, J. N. Davidson, M. P. Foster & D. A. StoneThis article describes a novel methodology for predicting the ability of an inductorless-driven piezoelectric transformer (PT)-based H-bridge inverters to simultaneously achieve zero-voltage switching (ZVS) and output regulation. A new idea for output voltage regulation by controlling deadtime interval is presented. A model is derived using cyclic-mode analysis to estimate the state-variable parameters of the circuit for a given operating condition. The model is then used to demonstrate operation in the ZVS region and to estimate the deadtime period, load, and operating frequency along the ZVS boundary. The output voltage regulation profile is presented and regions where voltage regulation can be continuously achieved while still obtaining ZVS are shown. Both SPICE simulation and experimental results taken using a ring-dot radial-mode PT are presented as verification. The proposed method for an H-bridge PT-based inverter is able to achieve a 5-V output from 15 to 60 V input with simultaneous ZVS and voltage regulation.
https://doi.org/10.1109/TPEL.2023.3305558 - Inductorless Step-Up Piezoelectric Resonator (SUPR) Converter: A Describing Function Analysis
IEEE Transactions on Power Electronics, 2023
J. Forrester, J. N. Davidson & M. P. FosterA model for an inductorless step-up piezoelectric-resonator-based dcdc converter is presented. A describing function approach is used to determine the equivalent circuit of the mosfet power stage and resonator, allowing the duty cycles of both mosfets to be accurately estimated. The model provides a method for estimating the output voltage and resonant current of the converter during operation. The accuracy of the model is verified against experimental and simulation results, with a less than 1.5% mean absolute percentage error in voltage gain estimation, compared with experimental measurements. Design guidelines for optimal operation of the converter are also presented.
https://doi.org/10.1109/TPEL.2023.3294802 - Real-Time Comprehensive Condition Monitoring Technique for SiC MOSFET-Based Inverters in EV Applications
Transport Research Procedia, 2023
J. Naghibi, K. Mehran & M. P. FosterReliable performance in various system operating modes is a substantial requirement in the new power electronics systems and applications. Wide Bandgap-based devices are favorable and appropriate choices for the new EV applications, specially inverter circuits which demands low loss and low parasitic performance in high voltage switching operation. A comprehensive condition monitoring system can have a major contribution in enhancing system reliability and solve the problem of reliability by observing the deterministic parameters in system failure and maintenance. In this paper, a comprehensive condition monitoring technique with a special focus on two major failure mechanisms of SiC MOSFETs is proposed. The results of evaluation tests show that broadening the condition monitoring vision into package-related as well as chip-related domains leads to having a more realistic and accurate monitoring data of the health of the switch during operation.
https://doi.org/10.1016/j.trpro.2023.11.043 - Circuit Simulator Compatible Model for the Ring-Dot Piezoelectric Transformer
Journal of Microelectromechanical Systems, 2023
J. Forrester, J. N. Davidson, M. P. Foster & D. A. StoneA lumped-element equivalent circuit model for the ring-dot piezoelectric transformer (PT) is derived based on a one-dimensional analysis of the radial vibration mode. Initially, equations for the magnitudes of force, vibration velocity at the boundaries of each Section of the device are derived based on the piezoelectric constitutive equations and using Kirchhoff plate theory. Similarly, equations for the amplitudes of input and output currents are derived from the electric displacement field and Gauss law. From this analytical approach, an equivalent circuit model is developed and, using a Taylor expansion, approximated as the Mason equivalent circuit. A key contribution of this work is the development of a circuit simulator compatible model which can be used by electronic engineers, without in-depth knowledge of the underlying material science, to design ring-dot PTs for power conversion applications. The resulting model is verified against both COMSOL finite element simulations and experimental impedance measurements. Compared to COMSOL, the model estimates the resonant circuit elements to within 1% and the input and output capacitance are estimated to within 10%. Experimental results match the simulation to within 10% for most parameters, and 1% for resonant frequency. [2022-0154]
https://doi.org/10.1109/JMEMS.2022.3220042 - A Position Error Correction Method for Sensorless Control of Dual Three-Phase Permanent Magnet Synchronous Machines
IEEE Transactions on Industry Applications, 2022
T. Liu, Z. Q. Zhu, X. Wu, Z. Wu, D. Stone & M. P. FosterIn this paper, an online rotor position error correction method is proposed to eliminate the impact of parameter mismatch in sensorless control for dual three-phase (DTP) permanent magnet synchronous machines drives. The rotor position error production mechanism is firstly derived and shows that the error changes with the trend of current variation when there is a parameter mismatch. Based on this mechanism, by injecting sinusoidal current signals with low frequency and small amplitude into both sets of three-phase windings, the presence of parameter mismatch and its level can be revealed from the corresponding sinusoidal responses of the estimated speed of sensorless observers, which do not depend on the inertia of the machine. Since the amplitudes of these responses decrease as the parameter mismatch level reduces, with the help of the least mean square algorithm, the parameters can be adaptively adjusted to the actual values, and the position error can be thus corrected. Moreover, with the extra freedom of DTP machines, the detrimental effects on torque production due to current signal injections can be eliminated through adjusting the phase between the two injected signals. The effectiveness of the proposed method has been validated through simulation and experimental results.
https://doi.org/10.1109/TIA.2022.3152682 - Inserted-shunt Integrated Planar Transformer with Low Secondary Leakage Inductance for LLC Resonant Converters
IEEE Transaction on Industrial Electronics, 2022
S. A. Ansari, J. N. Davidson & M. P. FosterThe leakage inductance of an integrated transformer is usually utilised as the series inductor of an LLC topology. However, leakage inductance exists on both primary and secondary sides of an integrated transformer and secondary leakage inductance leads the control and design of the converter to difficulty. In this paper, a novel topology for inserted-shunt integrated transformers is proposed which has low secondary leakage inductance. The inserted shunt of the proposed topology is not segmental and can be located conveniently within the transformer. In addition, the inserted shunt does not require low permeability core material, simplifying its manufacture. The design and modelling of the proposed transformer topology are presented and verified by finite-element analysis and experimental implementation. The proposed topology is also compared with a recently published inserted-segmental-shunt integrated transformer. It is shown that the proposed transformer provides higher efficiency and lower AC resistance. Finally, an LLC resonant converter is implemented to examine the performance of the proposed integrated transformer in practice.
https://doi.org/10.1109/TIE.2022.3165259 - A Monte Carlo simulator to investigate cell-to-cell deviation in a grid-tied battery pack
IET Power Electronics, 2022
Z. Wang, J. N. Davidson, M. P. Foster & D. T. GladwinBattery energy storage systems (BESSs) are commonly used in smart grids. Voltage deviation or imbalance among cells generally exists in multi-cell battery packs. This work presents a study of the voltage deviation-related phenomena observed during the operation of a grid-tied BESS, Willenhall Energy Storage System (WESS), including the voltage deviation changes during full range cycle and the cut-off mechanism activated by it. Electroimpedance spectroscopy measurements and equivalent circuit modelling were conducted on the same type of cell as that used in WESS to obtain cell-equivalent circuit parameter distributions (the standard deviation and mean). Cell voltage deviation in a WESS-sized battery pack (> 21k cells) was studied using Monte Carlo simulation through a proposed cell level battery simulator. Both experiments and simulations reveal that high cell voltage deviation emerges at the low and high state-of-charge zones where the cell internal resistance has a large value and large extent of deviation.
https://doi.org/10.1049/pel2.12289 - Enhancing energy management of a stationary energy storage system in a DC electric railway using fuzzy logic control
International Journal of Electrical Power & Energy Systems, 2022
H. H. Alnuman, D. T. Gladwin, M. P. Foster & E. M. AhmedacIn DC electric railways, energy storage systems (ESSs) have been addressed to assist in the energy efficiency improvement, which is achieved by exploiting the captured excess braking energy of decelerating trains in order to reduce the traction energy demand of the accelerating trains. Conventionally, stationary ESSs are assumed to have access to the substations and grid, which is being a significant shortcoming since the ESS in many locations such as the London Underground has neither access to the traction substations nor external sources. Since ESSs cannot have infinite capacity and have practical restrictions on the state of charge (SOC), much of the regenerative energies during braking are being lost, which reduces the benefits of ESSs in enhancing energy efficiency of electric railways. In this paper, boosting the energy efficiency of the system is achieved by proposing a new adaptive control method based on fuzzy logic control (FLC) to dynamically control a stationary ESS connected to a DC track system. Therefore, the power flow between the track and the ESS with respect to the storage capacity is managed without affecting the benefits yielded by the system. The proposed control method is simulated and tested experimentally on a real prototype including a supercapacitor ESS. Three traffic scenarios are applied to evaluate the feasibility and the performance of the proposed controller with respect to the undefined traffic scenarios matching the case in the London Underground. The proposed control method applied to three traffic scenarios have achieved energy savings of 39.241.4%. The experimental results are compared against the simulation results, showing a percentage error ranging from 1.8 to 3.6%.
https://doi.org/10.1016/j.ijepes.2022.108345 - Gate Oxide Degradation Condition Monitoring Technique for High Frequency Applications of Silicon Carbide Power MOSFETs
IEEE Transactions on Power Electronics, 2022
J. Naghibi, S. Mohsenzade, K. Mehran & M. P. FosterGate oxide degradation, which considerably affects turn-on/-off dynamics of the switch, embraces a large percentage of chip-related failure modes both in Silicon and Silicon Carbide power MOSFETs. The gate oxide layer is thinner in Silicon Carbide power MOSFETs in comparison to their Silicon-based counterparts. Consequently, the problem of gate oxide degradation has become a more crucial impediment in achieving reliable performance in Silicon Carbide power MOSFETs. This problem is even more severe in high frequency applications due to higher EMI signature and complicated and costly measurement. In this paper, a reliable fully analogue cost-effective gate oxide degradation condition monitoring technique is proposed and validated. High order harmonics magnitudes of drain-source voltage are used to produce a DC signal as the ageing precursor of gate oxide region. Using a dedicated degradation set-up, the credibility of the developed condition monitoring technique was examined at different rates of gate oxide degradation for 650V/22A Silicon Carbide discrete MOSFET. In 200 kHz, 217V switch operation, the proposed precursor showed 68% change in comparison to its initial value. This brings a high resolution assessment on the reliability level of the switch gate oxide region.
https://doi.org/10.1109/TPEL.2022.3198291 - Comparison of BSPT and PZT Piezoelectric Ceramic Transformers for High Temperature Power Supplies
Advanced Engineering Materials, Wiley-VCH, 2022
J. Forrester, L. Li, Z. Yang, J. N. Davidson, D. C. Sinclair, I. M. Reaney, M. P. Foster & D. A. StoneHigh temperature power electronics is an advancing area of research, especially given the widespread availability of wide bandgap semiconductors. In this work a suitability analysis of (1?x)BiScO3xPbTiO3 (BSPT) as a material for high temperature piezoelectric transformers (PTs) is presented and compared to state-of-the-art Pb(Zr1?xTix)O3 (PZT). Initially, both materials will be compared using a variety of metrics to prove the suitability of BSPT as a material for constructing PTs specifically for high temperature applications. PTs based on the two materials are designed and fabricated, and then subsequently characterised using impedance measurements. Finally, half-bridge resonant inverters are constructed using both PTs and the performance of each inverter measured over a range of ambient temperatures. The result of these experiments confirm the suitability of BSPT for PT applications and show the excellent performance of BSPT PTs at temperatures in excess of that possible with PZT based PTs.
https://doi.org/10.1002/adem.202200513 - A Space Vector Modulation Strategy for PMSMs Operating at Low Switching-to-Fundamental Frequency Ratio
IEEE Transaction on Industrial Electronics, 2022
J. Riedemann, Z. Q. Zhu, D. A. Stone, M. P. Foster, J. Greenough, K. Takemoto, D. Ivanovic & B. BatemanA novel space vector modulation (SVM) strategy for a permanent magnet synchronous machine drive, operating at low switching-to-fundamental frequency ratio, is presented in this article. The proposed strategy is based on applying more than two active vectors in a switching period, aiming to consider the expected rotation and possible movement from one sector to another of the voltage reference vector within that period. The method is simple as the calculation of the duty cycles is still based on the expressions for a conventional SVM. Current distortion and efficiency calculations are also provided, comparing the proposed SVM with conventional SVM and six-step modulation. The results show that the proposed method generates a current distortion similar to the conventional SVM at high frequency ratios but much lower at low frequency ratios. Moreover, comparing with six-step modulation, the current distortion generated by the proposed SVM is always lower, independent of the frequency ratio. On the other hand, the efficiency of the inverter obtained with the proposed SVM is higher than the one obtained with conventional SVM. The effectiveness of the proposed strategy is validated via simulations and experiments.
https://doi.org/10.1109/TIE.2022.3225804 - Electrical modelling of a metro system
Electric Power Systems Research, 2022
H. Alnuman, D. T. Gladwin, M. P. Foster, E. M. Ahmed, M. Aly & A. AlshahirSimulation tools allow changes in electrical network, timetabling, and train speed profiles, which is fundamental for the planning and development of electric railways. When simulating electric railways, it may be challenging to adequately represent their nonlinear characteristics resulting from the rectifier substations, overvoltage protection circuits, and the continuous changes of the load according to the train position. The power exchange between trains and the change of the rail resistance between them require high temporal resolution and thus results in high computational complexity. Given these goals and challenges, the main objective of this work is to develop a sufficiently simple, fast to simulate, yet accurate, simulation method based on real-world assumptions. Further, the simulation method should be extendable to energy storage systems (ESSs) and control to allow designing control methods for energy management to maximise the energy efficiency of electric railways. This article describes the development of a framework for modelling the power flow within an electric rail network referenced to a case study example. In this article, a test scenario is presented comprising of eight trains running on a double rail track in order to verify the model against expected observations. The simulation model includes two DC traction substations separated by 2 km and three passenger stations separated by 1 km. The model operation requirements and parameters are based on the Yizhuang Line in Beijing Metro. The simulation methodology developed for this work differs from other methods reported in pertinent literature as it facilitates modifications to the model by avoiding the common approach of forming iterative methods for solving the power flow. The proposed test scenario allows the model to be verified for accuracy. The verification is accomplished via different methods and the obtained results confirm that the proposed modelling approach is accurate as the error between the supplied and consumed energy is only 0.11%.
https://doi.org/10.1016/j.epsr.2022.108680 - Improved Sensorless Control Method and Asymmetric Phase Resistances Determination for Permanent Magnet Synchronous Machines
IEEE Transactions on Industry Applications, 2022
T. Y. Liu, Z. Q. Zhu, Z. Y. Wu, D. A. Stone & M. P. FosterThis article proposes an improved sensorless control method for permanent magnet synchronous machines under phase resistance asymmetry. The proposed method acquires positive sequence current and voltage signals by applying a sequence component extractor and a double synchronous reference frame current control strategy. These signals can, then, be applied to improve the extended electromotive force based sensorless observer to eliminate the undesired second-order fluctuation in position and speed estimation due to asymmetric phase resistances. In addition, the resistance deviations, which may be due to asymmetric resistances and temperature variation, could introduce dc offset error in rotor position estimation. Therefore, a model reference adaptive system based resistance estimation is employed to compensate for inaccuracy of resistances. Moreover, from the information contained in the negative sequence voltages, the specific values of all asymmetric phase resistances can be estimated as well. Experimental and simulation results are provided to validate the proposed method.
https://doi.org/10.1109/TIA.2022.3155479 - Comparative Study of Dual PM Vernier Machines
World Electric Vehicle Journal, 2021
H. Qu H, Z. Q. Zhu, T. Matsuura, D. Ivanovic , T. Kato, K. Sasaki, J. Greenough, B. Bateman, D. A. Stone, M. P. Foster & J. RiedemannIn this paper, two types of dual permanent magnet (PM) machines, i.e., stator slot dual-PM (SSDPM) machine and split-tooth dual-PM (STDPM) machine, are investigated and compared. Both machines have consequent pole structure with Halbach array PMs. Their difference lies in the position of stator PM. The SSDPM machine has Halbach array PMs in the stator slots, while the STDPM machine has PMs between the split teeth. Torque characteristics, i.e., average torques and torque ripples, of different slot/pole number combinations of the two machines are compared. The 24 stator slots/20 rotor slots/4 armature pole pair (24S20R4Pa) SSDPM machine with distributed windings and the 24 stator slots/10 rotor slots/4 armature pole pair (12S20R4Pa) STDPM machine with concentrated windings are compared under both open-circuit and on-load conditions. The results show that the SSDPM machine is more competitive by delivering higher torque density and higher power density.
https://doi.org/10.3390/wevj12010012 - Single active switch high?voltage gain DC DC converter using a non coupled inductor
IET Power Electronics, 2021
A. Mizani, S. A. Ansari, A. Shoulaie, J. N. Davidson & M. P. FosterA single active switch high voltage gain non coupled inductor DC DC converter is presented. The introduced converter achieves high step up gain without using any coupled inductors or transformers, provides high efficiency, and has a simple control system. The converter also achieves low voltage stress on the switch and diodes without clamping circuits, reducing cost, conduction losses, and complexity. The input current of the introduced converter is continuous with low ripple, and is therefore suitable for renewable energy applications in which the fast dynamic response of the converter is necessary. The principle of operation and design considerations of the introduced converter are investigated. A 200 W prototype circuit with 40 kHz switching frequency, 40 V input voltage, and 250 V output voltage is implemented. The prototype operates at 93.2% efficiency, with voltage and current error of less than 4% compared to theoretical values.
https://doi.org/10.1049/pel2.12007 - Evaluation of silicon MOSFETs and GaN HEMTs in soft?switched and hard?switched DC?DC boost converters for domestic PV applications
IET Power Electronics, 2021
S. A. Ansari, J. N. Davidson & M. P. FosterHard?switched high?gain DC?DC converters such as the boost converter play an important role in renewable energy systems. Research to increase their efficiency is important and can be achieved using soft?switching techniques; however, that approach requires an auxiliary circuit. The auxiliary circuit decreases power density and reliability while increasing the cost. Moreover, soft?switching topologies usually cannot improve the efficiency for all power and voltage ranges. Wide bandgap (WBG) devices, such as gallium nitride (GaN), result in lower switching losses than silicon (Si), can be used while retaining the simple structure of a hard?switched topology. However, the high cost of these devices is problematic for their frequently cost?sensitive applications. To quantify the cost and efficiency, this study compares soft?switching techniques and WBG?based switches in DC?DC boost converters for a photovoltaic (PV) energy application. The performance of four prototypes including the soft?switched and hard?switched DC?DC converters with both state?of?the?art Si and GaN switches are evaluated in terms of cost, power density, efficiency, and reliability using theoretical analysis, simulation and experimental results. It is shown that the GaN?based hard?switched converter provides higher efficiency and power density; it is more expensive than its Si?based counterpart, yet is cheaper than soft?switched converters.
https://doi.org/10.1049/pel2.12085 - Generalized Predictive DC-Link Voltage Control for Grid-Connected Converter
IEEE Journal of Emerging and Selected Topics in Power Electronics, 2021
T. Wang, Z.Q. Zhu, N. M. A. Freire, D. A. Stone & M. P. FosterThe main function of the grid-connected converter in many applications is to control the DC-link voltage with high performance, i.e. strong disturbance rejection capability and good dynamic response. Take the grid connected PWM rectifier of a motor drive system as an example, good disturbance rejection capability is essential for the DC-link voltage control to address the varying loads on the motor side, and the dynamic process of the DC-link voltage control is preferred to be fast and overshoot-free, so as to adaptively adjust the DC-link voltage according to the motor speed and reduce the switching losses. However, the performance of the conventional PI-based DC-link voltage control is not always satisfying and can be further improved. In this paper, the generalized predictive control (GPC) method is applied to the DC-link voltage control of a grid-connected converter for the first time, which can provide both good disturbance rejection capability and satisfying dynamic performance. Moreover, stability analysis of the proposed GPC-based DC-link voltage control strategy is theoretically studied, and a parameter tuning guideline is provided. The effectiveness and advantages of the proposed method are validated with experimental results.
https://doi.org/10.1109/JESTPE.2021.3060725 - An Online Position Error Correction Method for Sensorless Control of Permanent Magnet Synchronous Machine With Parameter Mismatch
IEEE Power Electronics, 2021
T. Y. Liu, Z. Q. Zhu, B. Shuang, Z. Y. Wu, D. A. Stone, M. P. FosterTo eliminate the influence of parameter mismatch for fundamental model based sensorless methods, an effective online position error correction method is proposed for permanent magnet synchronous machines in this paper. Based on the derived position error mechanism, i.e. the error varies proportionally to the dq -axis currents, the proposed method injects a sinusoidal current signal with a small amplitude and low frequency into the d - or q -axis current for a short period. During injection, the corresponding sinusoidal response for current injection can be acquired from the estimated speed of the sensorless position observer. It is found that the amplitude of the response in the estimated speed decreases as the parameter mismatch reduces, and eventually reaches a minimum if there is no parameter mismatch. Thus, by applying the least mean square (LMS) algorithm, the amplitude of the response in the estimated speed can be minimised as the parameters are adaptively adjusted to the actual values, and then the position error can be corrected. The proposed method is validated through experiments on a permanent magnet generator drive system.
https://doi.org/10.1109/ACCESS.2021.3116515 - High-Frequency Non-Invasive Magnetic Field-Based Condition Monitoring of SiC Power MOSFET Modules
Energies, 2021
J. Naghibi, K. Mehran 1 & M. P. FosterCurrent distribution anomaly can be used to indicate the onset of package-related failures modes in Silicon Carbide power MOSFET modules. In this paper, we propose to obtain the wire bonds magnetic field profile using an array of Tunnel Magneto-Resistance (TMR) sensors, and characterise the small changes in the current density distribution to find the onset of the wire bond degradation processes, including wire bond lift-off, wire bond cracking, and wire bond fracture. We propose a novel condition monitoring technique where a non-galvanic high-bandwidth sensing and a reliability model monitor the health of the power switches. We designed a dedicated calibration set-up to examine the sensor array and calibrated to demonstrate the adequate sensitivity to a minimum 5% current anomaly detection in a single wire bond of the switching devices operating with 50 kHz switching frequency. We use a hardware-in-the-loop (HIL) experimental set-up to replicate wire bond-related failures in a 1200 V/55 A SiC MOSFET power module of a DC/DC Boost converter. Signal conditioning circuits are further designed to amplify and buffer the sensor readings. Experimental results showed the proposed technique is able to detect a wide range of package-related failures.
https://doi.org/10.3390/en14206720 - Fully-integrated Planar Transformer with a Segmental Shunt for LLC Resonant Converters
IEEE Transactions on Industrial Electronics, 2021
S. A. Ansari, J. N. Davidson & M. P. FosterThis paper presents two topologies which provide high leakage inductance in shunt-inserted integrated magnetic transformers. These differ from conventional designs by replacing the low-permeability magnetic shunt of a planar transformer with high-permeability magnetic shunt segments, separated by many small air gaps. This approach results in a shunt with the same bulk permeability as the conventional design, while using lower cost and readily available magnetic materials such as ferrite. A modelling and design approach which can estimate the leakage and magnetising inductances precisely is provided for each topology. Theoretical analysis is presented and verified using finite-element analysis and experimental implementation. AC resistance analysis for both transformer topologies is also presented. In addition, an LLC resonant converter is built to verify the performance of the proposed fully-integrated magnetic transformers in practice. It is shown that the proposed topologies can integrate all three magnetic components of an isolated LLC resonant converter in a single planar transformer, which reduces the converters volume and cost.
https://doi.org/10.1109/TIE.2021.3116574 - Fully-Integrated Solid Shunt Planar Transformer for LLC Resonant Converters
IEEE Open Journal of Power Electronics, 2021
S. A. Ansari, J. N. Davidson & M. P. FosterA new topology for achieving high leakage inductance in inserted-shunt integrated magnetic planar transformers is proposed. In the proposed topology, two one-segment shunts are placed across the planar E-core air gap and between the primary and secondary windings. The proposed topology benefits using solid inexpensive ferrite shunts, making manufacturing easier. A detailed mathematical model is derived from which a design methodology is developed, providing accurate estimation for the leakage and magnetising inductances. The theoretical analysis has been verified using finite-element analysis and experimental implementation. AC resistance analysis and efficiency comparison are also presented for the proposed topology and a recent topology with inserted-segmental-shunt, which shows the proposed topology provides higher efficiency because of lower AC resistance. In addition, an isolated LLC resonant converter is designed and built to investigate the performance of the proposed topology in practice. The three magnetic components needed for the designed LLC resonant converter is integrated in a single planar transformer using the proposed topology and the converter operates properly.
https://doi.org/10.1109/OJPEL.2021.3137016 - A Low Cost, Rapid Impedance Measurement Technique Suitable for Li-ion Health Diagnosis in Battery Energy Storage Systems
International Journal of Smart Grid and Clean Energy, 2020
D. A. Stone, M. P. Foster, E. E. F. Ballantyne & H. PriceBattery energy storage is becoming a vital part of green energy systems. Prediction of the state of health of energy storage systems is difficult as it relies on a number of parameters. Pseudo Random Binary Sequence (PRBS) excitation of energy storage batteries has been shown to be a valid method of battery parameter identification for lead acid batteries [1]. The purpose of this work is to validate PRBS test data from a 3Ah LiFePO4 cell forming part of an EV battery-pack cell against Electrochemical Impedance Spectroscopy (EIS) data obtained from an industry-standard potentiostat (Solartron 1480). PRBS results are obtained in under 200 seconds on easily reproducible equipment which can be built into a green energy battery management system, while the EIS process takes over two hours on prohibitively expensive laboratory equipment. This work validates PRBS as a fast and portable method of obtaining the impedance spectrum of Lithium Ion cells, which can then be used to obtain information about SoH of the BESS.
https://doi.org/10.12720/sgce.9.2.346-356 - Equivalent circuit parameter extraction of low-capacitance high-damping PTs
IET Electronics Letters, 2020
J. Forrester, L. Li, J. N. Davidson, M. P. Foster, D. A. Stone, D. C. Sinclair & I. M. ReaneyExisting equivalent circuit extraction techniques are inaccurate for piezoelectric transformers (PTs) with low-input capacitance or high damping. A new method is presented, offering improved accuracy in both damping resistance and resonant frequency extraction compared with state-of-the-art methods. Effectiveness is evaluated on two sample PTs, with the proposed method achieving up to 84% decrease in error compared with previous methods.
https://doi.org/10.1049/el.2019.3887 - Resonant current estimation and phase-locked loop feedback design for piezoelectric transformer-based power supplies
IEEE Transactions on Power Electronics, 2020
Z. Yang, J. Forrester, J. N. Davidson, M. P. Foster & D. A. StoneA control system to achieve zero-voltage switching (ZVS) for an inductorless half-bridge piezoelectric transformer-based resonant power supply is presented. Both the phase and frequency of the resonant current are locked to the switching waveform using an analogue phase-locked loop (PLL) to ensure ZVS operation. We present two resonant current estimation circuits which generate the reference signals for the PLL. We also present three PLL feedback designs to produce the in-phase gate drive signals with adequate deadtime. The operating principle of the control system and its ability to achieve ZVS operation is discussed. Experimental results of the PLL circuit verify the successful operation of the proposed system. The six permutations of current estimation and feedback are contrasted and conclusions for application-specific usage are made.
https://doi.org/10.1109/TPEL.2020.2976206 - Influence of Spurious Modes on the Efficiency of Piezoelectric Transformers: a Sensitivity Analysis
IEEE Transactions on Power Electronics, 2020
J. Forrester, J. N. Davidson, M. P. Foster & D. A. StoneAn analysis of the efficiency degradation resulting from spurious modes in piezoelectric transformers (PTs) is presented. Circuit analysis is performed on PT equivalent circuit models with both a single resonant branch and with two resonant branches (spurious mode included), allowing the efficiency degradation from a spurious mode to be analysed. Multiple sensitivity analyses were then performed, highlighting frequency difference (between modes) and characteristic impedance of the spurious resonant circuit [?(L2/C2)], as critical design parameters for minimising efficiency degradation from spurious mode. These two parameters are further analysed to determine optimum design conditions to ensure minimal efficiency degradation. Results of this analysis provide a method of estimating the whether a spurious mode will degrade efficiency and consequently provides a method for improving PT designs.
https://doi.org/10.1109/TPEL.2020.3001486 - Multivariable Generalized Predictive Control with Measurement Noise Rejection and Speed Ripple Mitigation for PMSM Drives
IET Power Electronic, 2020
T. Wang, Z. Q. Zhu, N. M. A. Freire, Z. Wu, M. Odavic, M. P. Foster & D. A. StoneGeneralized predictive control (GPC) is known for its good dynamic performance and long prediction horizon, but the performance can be severely deteriorated when measurement noises exist due to the wide control bandwidth of GPC. Meanwhile, the unmodeled periodic disturbances can cause ripples to the output variables. In this paper, a practical PMSM drive system with speed measurement noise and periodic disturbances is considered, for which a novel multivariable GPC method is proposed to achieve both good dynamic performance and speed ripple mitigation. The proposed method hasasimple structure, since the traditional cascaded speed and current control loops are replaced by a non-cascaded one. To rejectthe measurement noise without jeopardizing the system stability, an internal low-pass filter (LPF) is embedded in the GPC. Meanwhile, external resonant loops are added to the GPC to mitigate the low-order speed ripplescaused by the periodic disturbances. Furthermore, a deadbeat-based current constraint method is proposed to avoid overcurrent during transient processes.Theoretical stability analysis of the proposed method is presented.Experimental results show that the proposed method has good steady-state and dynamic performances, including measurement noise rejection and speed ripple mitigation.
https://doi.org/10.1049/iet-pel.2020.0246 - Modelling of phase-shift modulated bidirectional CLLC resonant converter
IET Power Electronics, 2020
L. F. Martins, D. A. Stone & M. P. FosterThe study proposes the application of two modelling techniques for analysis of bidirectional CLLC resonant converters. The state-variable and cyclic-averaging techniques are applied for converters operating under two types of phase-shift modulation: single-phase-shift and pulse-phase modulation. The converter is analysed considering forward and reverse power flow directions and a state-variable equation description is obtained for both modes. The models are first validated through simulation, comparing the state-variable and cyclic-averaging results to a simulation program with integrated circuit emphasis (SPICE)-based simulation. Additionally, a low power prototype is built, experimental results are presented and the influence of parasitic elements and system delays is discussed. Simulation and experimental results show the models can accurately represent the behaviour of CLLC converters for both types of phase-shift modulation. In addition, using the cyclic-averaging technique results in a considerably faster execution compared to state-variable and SPICE-based models.
http://dx.doi.org/10.1049/iet-pel.2018.5672 - Performance Investigation of Consequent-Pole PM Machines with E-core and C-core Modular Stators
IEEE Transactions on Energy Conversion, 2020
R. Zhou, G.-J. Li, K. Zhang, Z. Q. Zhu, M. P. Foster & D. A. StoneThis paper investigates some novel modular consequent pole PM machines (CPMs) with E-core and C-core stators. Different slot-pole number combinations including 12-slot/10-pole (Ns>2p) and 12-slot/14-pole (Ns<2p) have been investigated. Their static and dynamic electromagnetic performances have been compared, e.g. the phase back-EMF, on-load torque, torque-speed curves, power factor-speed curves and also efficiency maps are compared. It is found that the existence of flux gaps (FGs) can improve the average torque of the 12-slot/14-pole E-core modular CPMs while the C-core structure can be a better candidate where relatively low torque ripple is desirable. Moreover, by selecting proper FG width, the 12-slot/14-pole E-core modular CPMs can achieve better flux-weakening capability and higher efficiency while the 12-slot/10-pole C-core modular CPMs can have higher power factors over the whole speed range. The finite element simulation results have been validated by a series of experiments using 12-slot/14-pole modular CPMs with both C-core and E-core stators.
http://doi.org/10.1109/tec.2020.3027366 - A Simple Sensorless Position Error Correction Method for Dual Three-Phase Permanent Magnet Synchronous Machines
IEEE Transactions on Energy Conversion, 2020
T. Liu, Z. Q. Zhu, Z.-Y. Wu, D. A. Stone & M. P. FosterIn this paper, a simple position error correction method is proposed to minimize the influence of parameter deviation on the model-based rotor position estimation, with the help of two sets of windings in a dual 3-phase permanent magnet synchronous machine (PMSM). In the proposed method, when each set of 3-phase windings is individually used for sensorless rotor position estimation, the nominal parameters that are set in each observer are identical but inaccurate, which leads to errors in the estimated rotor position from both observers. Since the error is varied according to the current level, small current pulses are injected respectively into d- or q-axis of one set (or both set) of 3-phase windings, which causes the difference between the rotor position estimation errors from two sets of 3-phase windings. This difference is subsequently used as the input of an updated controller to minimize the parameter deviation and the corresponding rotor position error. The proposed method is experimentally validated on a dual 3-phase PMSM system.
https://doi.org/10.1109/TEC.2020.3023904 - Suppressing Leakage Current for Cascaded H-Bridge Inverters in Renewable Energy and Storage Systems
IEEE Transactions on Industrial Electronics, 2020
I. Gunsal, D. A. Stone & M. P. FosterLeakage current in a transformerless cascaded H-bridge inverter is a problem that deteriorates the system performance and causes safety concerns. In this paper, a common-mode equivalent circuit is established for analyzing the occurrence of leakage current in an m-level cascaded H-bridge inverter with either asymmetrical or symmetrical inductance output filter configurations. The analysis provides a comparison between traditional phase shifted pulse width modulation, phase disposition pulse width modulation and the proposed leakage current reduction pulse width modulation. It is reported that grid leakage current cannot be suppressed in an asymmetrical inductance filter configuration solely based on modulation methods. The proposed LCRPWM pulse width modulation can effectively reduce the grid leakage current in a symmetrical filter configuration nine-level cascaded H-bridge inverter. Simulation and experimental studies for aforementioned methods are provided and their performances are evaluated
https://doi.org/10.1109/TIE.2020.3031524 - Study on noise and disturbance issues of generalized predictive speed control for permanent magnet synchronous machines
IET Electric Power Applications, 2020
T. Wang, Z. Q. Zhu, N. M. A. Freire, Z. Wu M. P. Foster & D. A. StoneGeneralized predictive control (GPC) is promising for permanent magnet synchronous machine drive systems, due to its outstanding dynamic performance and disturbance rejection capability. However, the speed measurement noise introduced by the encoder and the unmodelled disturbances introduced by the non?ideal machine characteristics deteriorate the performance of GPC. The noise and disturbance issues are studied in detail, and an enhanced GPC method is proposed to address them. For the noise issue, the mathematical model of the speed measurement noise is derived, and the noise spectra at different speeds are analysed. Then, a novel GPC with internal low?pass filter is proposed to reject the influence of the noise. For the disturbance issue, the influence of the unmodelled disturbances on the speed performance is assessed when applying different noise rejection methods, and a resonant controller?based speed ripple mitigation method is proposed and integrated to the GPC. Experimental results show that the proposed methods can effectively deal with the noise and disturbance issues, as well as providing better dynamic performance than the conventional PI based speed control.
https://doi.org/10.1049/elp2.12009 - Using power factor to limit the impact of energy storage on distribution network voltage
International Journal of Smart Grid and Clean Energy , 2020
D. Strickland, S. Morley, D. A. Stone, S. J. Royston, S. Nejad, D. T. Gladwin & M. P. FosterThe introduction of embedded renewable generation and energy storage into the electricity grid may result in increased complexity to the Distribution Network Operator (DNO) in managing the voltage within statutory limits. This paper investigates how the voltage at the point of common coupling between the grid and an energy storage system could be adapted such that the charging and discharging of a battery energy storage system has a neutral impact on the voltage at that point. The paper uses measured results from the Willenhall Energy Storage System to show that a seagull shape curve of Power and corresponding Var setting could be used to mitigate against voltage rise or fall on the Network caused by the Energy Storage System.
http://doi.org/10.12720/sgce.9.4.727-736 - Using power factor to limit the impact of energy storage on distribution network voltage
International Journal of Smart Grid and Clean Energy, 2020
S. J. Royston, D. Strickland, D. A. Stone, D. T. Gladwin, M. P. Foster & S. NejadFast acting battery energy storage systems are able to swing power very quickly between maximum import and maximum export in less than 50ms based on operational experience of a 2MW energy storage system. However, this can result in nuisance tripping of the unit through the operation of the loss-of-mains protection (LoM). This paper looks at data captured during power swings of up to 4MW during typical operation and discusses the potential for nuisance tripping, and suggests potential settings for improved operation.
http://doi.org/10.12720/sgce.9.3.473-484 - Practical observations of loss-of-mains nuisance tripping of fast acting energy storage
International Journal of Smart Grid and Clean Energy, 2020
S. J. Royston, D. Strickland, D. A. Stone, D. T. Gladwin, M. P. Foster& S. NejadFast acting battery energy storage systems are able to swing power very quickly between maximum import and maximum export in less than 50ms based on operational experience of a 2MW energy storage system. However, this can result in nuisance tripping of the unit through the operation of the loss-of-mains protection (LoM). This paper looks at data captured during power swings of up to 4MW during typical operation and discusses the potential for nuisance tripping, and suggests potential settings for improved operation.
https://dio.org/10.12720/sgce.9.3.473-484 - Scaling Effect on Electromagnetic Performance of Surface-Mounted Permanent-Magnet Vernier Machine
IEEE Transactions on Magnetics, 2020
D. K. Kana Padinharu, G. J. Li, Z. Q. Zhu, M. P. Foster, D. A. Stone, A. Griffo, R. Clark & A. ThomasThis article investigates the impact of scaling on the electromagnetic performance of surface-mounted permanent-magnet Vernier (SPM-V) machines with a main focus on open-circuit induced Electro Motive Force (EMF). Three different power ratings, i.e., 3 kW, 500 kW, and 3 MW, have been chosen for this article. For each power rating, the SPM-V machines are analyzed for different slot/pole number combinations to compare their optimal performance with a conventional SPM machine. Step-by-step development of an analytical equation is presented for the prediction of induced EMF taking into account the interpole leakage of rotor permanent-magnets. 2-D finite-element analysis (FEA) has been used to validate the analytical equation across different power ratings. The analytical equation is thereafter utilized to study the influence of different geometric parameters on the performance of the SPM-V machines. It reveals that the back EMF and torque of SPM-V machines, for a given normalized pole pitch (rotor pole pitch to magnetic airgap length), are unaffected by the increase in airgap length due to scaling. However, the power factor of SPM-V, unlike the conventional SPM, reduces significantly with the increase in electrical loading due to the scaling effect. The analytical model for induced EMF and the 2-D FEA predicted results are validated by experiments using conventional SPM and SPM-V machine prototypes.
https://doi.org/10.1109/TMAG.2020.2980500 - A PLL controller for achieving zero voltage switching (ZVS) in inductorless half-bridge drive piezoelectric transformer resonant power supplies
The Journal Of Engineering, 2019
M. P. Foster, J. N. Davidson, D. A. Stone & R. S. YapaInductorless half-bridge, piezoelectric transformer (PT) resonant power supplies require careful control if zero voltage switching of the MOSFETs is to be achieved. Here we describe how a phase-locked loop may be used to achieve this by ensuring adequate deadtime exists between the two MOSFETs to allow the PT input voltage to fully charge to the DC link. Experimental results demonstrate the operation of the system.
https://doi.org/10.1049/joe.2018.8063 - Automated design tools for piezoelectric transformer-based power supplies
Journal of Engineering, 2019
J. Forrester, J. N. Davidson, M. P. Foster , E. L. Horsley & D. A. StoneThis paper proposed a design approach for piezoelectric transformer-based power supplies. Initially, an analytical approach is used to derive the Mason equivalent circuit parameters of a PT. This is coupled with a semi-automated procedure to decide the appropriate physical dimensions of the PT. The procedure is applied to a typical low-power power supply specification, whereupon a specific transformer is design, verified using COMSOL and used as a simulated converter in SPICE. Results show that the design can be successfully implemented while maintaining efficient zero-voltage switching operation.
https://doi.org/10.1049/joe.2018.8065 - Quantitative power loss analysis and optimisation in Nth-order low-voltage multilevel converters
IET Power Electronics, 2019
A. Petersen, D. A. Stone, M. P. Foster & J. N. DavidsonFocusing on cascaded H-bridge converters for grid-tie battery energy storage, a practical, analytical method is derived to evaluate the switching-associated power loss in multilevel converters, evaluated from a number of sources of loss. This new method is then used to find performance trends in the use of converters of increasing order over a range of switching frequencies. This includes an experimental analysis into predicting the performance of MOSFET body diodes. Authors' analysis with this model shows that a multilevel converter can have lower losses than the equivalent single-bridge, three-level converter, particularly at higher switching frequencies, due to the availability of suitable switching devices. It also has interesting implications for enabling the use of cutting-edge non-silicon power switching devices to further improve potential efficiencies.
https://doi.org/10.1049/iet-pel.2018.5928 - Performance comparison between consequent-pole and inset modular permanent magnet machines
The Journal of Engineering, IET, 2019
B. Ren, G. J. Li, Z. Q. Zhu, M. P. Foster & D. A. StoneThis paper proposes some consequent-pole (CP) modular permanent magnet (PM) machines with different flux gap(FG) widths and slot/pole number combinations. The corresponding inset modular PM machines having the same magnetvolume are also presented for comparison. It has been demonstrated that the output torques of the consequent pole modularmachines are always higher than those of the inset modular machines regardless of FG widths and slot/pole numbercombinations. Other electromagnetic performances such as back-EMF, cogging torque, and iron losses etc. are calculated by2D FEA software and compared as well. The advantages and disadvantages of consequent and inset modular PM machinesare summarised here.
http://dx.doi.org/10.1049/joe.2018.8200 - Comparative investigation of stator-mounted permanent magnet machines under fault conditions
The Journal of Engineering, IET, 2019
P. Taras, G. Li, Z. Zhu, M. P. Foster & D. A. StoneHere, machines having permanent magnets (PM) mounted in the stator are compared during fault operations such as armature winding short circuits. The magnet potential irreversible demagnetisation is also investigated due to the fact that the PMs are placed close to the armature coils (heat sources) and hence are prone to temperature-related demagnetisations. It is found that the doubly salient and flux reversal machines have inherently higher fault tolerant capabilities when compared with the switched-flux one. To the point of view of demagnetisation withstand capability, the doubly salient topology stands out as the most robust one while the switched flux is the weakest one.
https://doi.org/10.1049/joe.2018.8203 - State-variable and cyclic-averaging analysis of bidirectional CLLC resonant converters
The Journal of Engineering, IET, 2019
L. Farias-Martins, D. A. Stone & M. P. FosterThe study proposes the application of state variable and cyclic-averaging modelling techniques for analysis of bidirectional, dual active bridge, CLLC resonant converters. The techniques are applied for converters operating under single phase-shift modulation in forward and reverse modes and the equation description is obtained for both models. The design of the converter is presented and the simulation results obtained are compared to a Spice-based simulation to verify the accuracy of the proposed models. Results show the models are suitable to represent the behaviour of CLLC converters under single phase-shift modulation. In addition, when using the cyclic-averaging technique integration is not required to solve the model, which results in a considerably rapid analysis when compared to the execution times of state variable and Spice-based models.
https://doi.org/10.1049/joe.2018.8072 - Demagnetization Withstand Capability Enhancement of Surface Mounted PM Machines Using Stator Modularity
IEEE Transactions on Industry Applications, 2018
G. J. Li, B. Ren, Z. Q. Zhu, M. P. Foster & D. A. StoneThe flux gaps in alternate stator teeth of the modular permanent-magnet machines can have a significant impact on the total magnet flux density, and hence the potential magnet reversible/irreversible demagnetization under flux weakening operations or short-circuit conditions. Such a problem has not been studied in literature and will be investigated in this paper. The influence of flux gaps on the d-axis inductance and the potential peak short-circuit current is analyzed for different slot/pole number combinations. It is found that the flux gaps will affect both d-axis inductance and open-circuit flux linkage, and hence reduce short-circuit current of machines with pole number (2p) smaller than slot number (Ns), while they will increase the short-circuit current of machines with 2p > Ns . However, the opposite phenomena can be observed for demagnetization withstand capability. For machines having 2p <; Ns, the flux gaps tend to lower withstand capability, while for machines having 2p > Ns, this capability can be improved. Other parameters such as magnet thickness and temperature have also been accounted for in the demagnetization analysis. Tests have been carried out to validate the predictions of inductances and short-circuit current, as well as performance such as phase back electromotive force, cogging torque, and static torque for machines with one defective magnet, which represents the case of partially demagnetized magnets.
https://doi.org/10.1109/TIA.2017.2777922 - A Battery Energy Management Strategy for UK Enhanced Frequency Response and Triad Avoidance
IEEE Transactions on Industrial Electronics, 2018
B. M. Gundogdu, S. Nejad, D. T. Gladwin, M. P. Foster & D. A. StoneThis paper describes a control algorithm for a battery energy storage system (BESS) to deliver a charge/discharge power output in response to changes in the grid frequency constrained by the National Grid Electricity Transmission (NGET) - the primary electricity transmission network operator in the UK - whilst managing the state-of-charge (SOC) of the BESS to optimise the availability of the system. Furthermore, this paper investigates using the BESS in order to maximise Triad avoidance benefit revenues whilst layering other services. Simulation using a 2 MW/1 MWh lithium-titanate BESS validated model are carried out to explore possible scenarios using the proposed algorithms. Finally, experimental results of the 2MW/1MWh Willenhall Energy Storage System (WESS) verify the performance of the proposed algorithms.
https://doi.org/10.1109/TIE.2018.2818642 - A Battery Energy Management Strategy for U.K. Enhanced Frequency Response and Triad Avoidance
IEEE Transactions on Industrial Electronics , 2018
B. M. Gundogdu, S. Nejad, D. T. Gladwin, M. P. Foster and D. A. StoneThis paper describes a control algorithm for a battery energy storage system (BESS) to deliver a charge/discharge power output in response to changes in the grid frequency constrained by the National Grid Electricity Transmission (NGET)the primary electricity transmission network operator in the U.K.while managing the state of charge of the BESS to optimize the availability of the system. Furthermore, this paper investigates using the BESS in order to maximize triad avoidance benefit revenues while layering other services. Simulation using a 2 MW/1 MWh lithiumtitanate BESS validated model is carried out to explore possible scenarios using the proposed algorithms. Finally, experimental results of the 2 MW/1 MWh Willenhall Energy Storage System verify the performance of the proposed algorithms.
https://doi.org/10.1109/TIE.2018.2818642 - Electrical Modelling of a DC Railway System with Multiple Trains
MDPI energies, 2018
H. H Alnuman, D. T. & M. P. FosterElectrical modelling of rail tracks with multiple running trains is complex due to the difficulties in solving the power flow. The train positions, speed and acceleration are constantly varying resulting in a nonlinear system. In this work, a method is proposed for modelling DC electric railways to support power flow analysis of a simulated metro train service. The method exploits the MathWorks simulation tool Simscape, using it to model the mechanical and electrical characteristics of the rail track system. The model can be simulated to provide voltages at any position in the track and additionally, the voltages seen by any train. The model includes regenerative braking on trains, this is demonstrated to cause overvoltage in the feeding line if it is higher than the power demand of the other trains at that time. Braking resistors are used to protect the network from overvoltage by burning the excess energy. Through the implementation of Energy Storage Systems (ESSs), it will be possible to improve the energy efficiency and remove timetabling restrictions of electric railways by effectively controlling the rail track voltage. The paper proposes several methods to validate the model.
https://doi.org/10.3390/en11113211 - Combined multi-physics model of switched flux PM machines under fault operations
IEEE Transactions on Industrial Electronics, 2018
P. Taras P, G.J.Li, Z. Q. Zhu, M. P. Foster & D. A. StoneIn this paper, the transient thermal response of a conventional double layer switched flux permanent magnet machine is studied for both healthy and fault conditions such as inter-turn short-circuit. A highly optimized and accurate co-simulation model for different operating conditions is developed requiring low computation and time resources. The electro-mechanical models for both healthy and faulty operation are implemented in Matlab/Simulink while the thermal model is implemented using 3D FEM software. Both models are dynamically coupled to enable the influence of temperature rise on the electromagnetic performance and vice versa to be predicted. Operation under various conditions are investigated and it is found that the temperature rise under fault conditions and high speed can lead to irreversible demagnetization of the permanent magnets. The superposition principle is used to accurately estimate the impact of short-circuit currents on the temperature rise. A series of dynamic tests are carried out to validate the transient thermal response prediction when operating during both the healthy and fault conditions.
https://doi.org/10.1109/TIE.2018.2877089 - Comparative Investigation of Stator Mounted Permanent Magnet Machines under Fault Conditions
The Journal of Engineering, 2018
P. Taras, G.-J. Li, Z. Q. Zhu, M. P. Foster & D. A. StoneIn this paper, machines having permanent magnets (PM) mounted in the stator are compared during fault operations such as armature winding short-circuits. The magnet potential irreversible demagnetization is also investigated due to the fact that the permanent magnets are placed close to the armature coils (heat sources), and hence are prone to temperature related demagnetizations. It is found that the doubly salient and flux reversal machines have inherently higher fault tolerant capabilities when compared with the switched-flux one. To the point of view of demagnetization withstand capability, the doubly salient topology stands out as the most robust one while the switched flux is the weakest one. - Performance Comparison between Consequent-Pole and Inset Modular Permanent Magnet Machines
The Journal Of Engineering, 2018
B. Ren B, G.-J. Li G, Z. Q. Zhu, M. P. Foster & Stone DAThis paper proposes some consequent-pole modular permanent magnet machines with different flux gap widths and slot/pole number combinations. The corresponding inset modular permanent magnet machines having the same magnet volume are also presented for comparison. It has been demonstrated that the output torques of the consequent pole modular machines are always higher than those of the inset modular machines regardless of flux gap widths and slot/pole number combinations. Other electromagnetic performances such as back-EMF, cogging torque, and iron losses, etc. are calculated by 2D FEA software and compared as well. The advantages and disadvantages of consequent and inset modular permanent magnet machines are summarized in this paper. - The Largest Lithium Titanate Battery in Europe (Willenhall Energy Storage System)
IET Engineering & Technology Reference, 2017
D. Rogers, D. T. Gladwin, D. A. Stone, D. Strickland & M. P. FosterThe Willenhall Energy Storage System is one of the largest research-led lithium titanate, grid-tied electrical storage systems in Europe. It took nearly 2 years from procurement through to final commissioning and cost 3.3 M. From its location in the West Midlands it forms a test bench for current and future grid support methodologies not possible previously with co-generation methods such as diesel and pumped-hyro. This study details the logistical challenges of construction, initial results from commissioning trials and the technical obstacles to the wider adoption of such systems.
http://dx.doi.org/10.1049/etr.2016.0121 - Novel Dual-Phase-Shift Control With Bidirectional Inner Phase Shifts for a Dual-Active-Bridge Converter Having Low Surge Current and Stable Power Control
IEEE Transactions Power Electronics, 2017
X. Liu, Z.Q.Zhu, D. A. Stone, M. P. Foster, W. Q. Chu, I. Urquhart and James GreenoughTo transmit constant powers particularly at light load, the isolated dual active bridge (DAB) with conventional dual-phase-shift (DPS) control exhibits large variations of currents, losses, and efficiencies if there is a small change of outer phase shift ratio, which is caused by the change of command to adjust power transmission. This is mainly because of the narrow operation region of outer phase shift ratio if the conventional DPS modulation is used. To solve this problem, a novel DPS control with bidirectional inner phase shifts for the DAB is developed to reduce the current surge in the high-frequency transformer, which can stabilize the output power with high efficiency. From the analysis of operation modes and power characteristics of the proposed DPS control, it is shown that due to wider operation region of outer phase shift ratios compared with the conventional DPS control in which the inner phase shifts of both the primary and secondary H-bridges are in the same direction, lower surge current can be obtained in the change of phase shift command, which results in stable power transmission particularly at light load without scarifying the efficiency. Moreover, the DAB of using the proposed DPS control can transmit bidirectional energy with the inner and outer shift ratios of 01. For experimental verifications, the test results are also presented in this paper.
https://doi.org/10.1109/TPEL.2016.2593939 - On the impact of current generation commercial gallium nitride power transistors on power converter loss
IET Electronic Letters, 2017
A. Petersen, D. A. Stone & M. P. FosterThe enormous potential benefits of gallium nitride based power switching devices, only commercially available very recently, in terms of power switching device loss are highlighted. This is first demonstrated through a simulated prediction of loss in multilevel converters, followed by experimental validation. While the simulations focus on losses in multilevel converters, the observations made are relevant in a broad range of applications.
https://doi.org/10.1049/el.2017.3183 - Measurement and Characterization Technique for Real-Time Die Temperature Prediction of MOSFET-Based Power Electronics
IEEE Transactions Power Electronics, 2016
J. N. Davidson,D. A. Stone, M. P. Foster & D. T. GladwinThis paper presents a technique to predict the die temperature of a MOSFET based on an empirical model derived following an offline thermal characterization. First, a method for the near-simultaneous measurement of die temperature during controlled power dissipation is presented. The method uses a linear arbitrary waveform power controller which is momentarily disconnected at regular intervals to allow the forward voltage drop of the MOSFET's antiparallel diode to be measured. Careful timing ensures the power dissipation is not significantly affected by the repeated disconnection of the power controller. Second, a pseudorandom binary sequence-based system identification approach is used to determine the thermal transfer impedance, or cross coupling between the dice of two devices on shared cooling using the near-simultaneous measurement and control method. A set of infinite impulse response digital filters are fitted to the cross-coupling characteristics and used to form a temperature predictor. Experimental verification shows excellent agreement between measured and predicted temperature responses to power dissipation. Results confirm the usefulness of the technique for predicting die temperatures in real time without the need for on-die sensors.
http://dx.doi.org/10.1109/TPEL.2015.2476557 - Analysis and design of LLC resonant converters with capacitor-diode clamp current-limiting
IEEE Power Electronics, 2015
C. Tsang, M. P. Foster, D. A. Stone & D. T. GladwinThis paper presents a design methodology for LLC resonant converters with capacitor-diode clamp for current limiting in overload conditions. A new fundamental harmonic approximation (FHA) based equivalent circuit model is obtained through the application of describing function techniques, by examining the fundamental behaviour of the capacitor-diode clamp. An iterative procedure to determine the conduction point of the diode-clamp is also given. The behaviour of this type of converter is analysed and guidelines for designing the current limiting characteristics are discussed. The characterisation of a 90 W converter design using the proposed methodology is presented. The converter voltage gain and the voltage-current characteristics under different overload conditions and operating frequencies are predicted using the proposed model, which accuracies are validated against the prototype with good correlation.
http://dx.doi.org/10.1109/TPEL.2014.2317653 - Spatially Resolved Measurements of Magnetic Fields Applied to Current Distribution Problems in Batteries
IEEE Instrumentation & Measurement, 2015
J. E. Green, D. A. Stone, M. P. Foster & A. TennantThis paper presents a novel instrumentation system for spatially resolved measurements of steady-state and slowly time-varying magnetic fields. The instrumentation system has a measurement area of 400 mm 200 mm consisting of 256 magnetic pixels each measuring the magnetic field crossing the center of the pixel area as three orthogonal vectors. The specified minimum resolution of our chosen sensor is approximately 1.0 10-7 T and the maximum specified measurable magnetic field is 8.0 10-4 T. Magnetic field data can be recorded at approximately one frame per second. This paper also reports the application of this instrumentation system to measurements on lead acid batteries and hybridized battery ultracapacitor combinations. The objective of this paper is to infer, for the first time, the moving charge distribution inside the battery volume by measuring the magnetic field resulting from the moving charge. Empirical tests are reported which show the current distribution as a function of increasing distance down the plate away from the terminal is highly likely to be exponential in nature, with most current flowing in the uppermost portion of the battery.
http://dx.doi.org/10.1109/TIM.2014.2362432 - Modular Permanent Magnet Machines with Alternate Teeth Having Tooth Tips for Performance Improvement
IEEE Industrial Electronics, 2015
G.-J. Li, Z. Q. Zhu, M. P. Foster & D. A. StoneThis paper presents single layer modular permanent magnet machines with either wound or unwound teeth with tooth tips. The structures with wound teeth having tooth tips are suitable for modular machines with slot number higher than pole number to compensate for the drop in winding factor due to the flux gaps in alternate stator teeth, accordingly to maintain or even to increase their average torques. However, the structures with unwound teeth having tooth tips are suitable for modular machines with slot number lower than pole number to increase the winding factor and hence to further improve the machine performance. The phase back-EMF, on-load torque, iron and copper losses as well as efficiency have been calculated using finite element analysis for different slot/pole number combinations, and for different flux gap and tooth tip widths. It is found that by properly choosing the flux gap and tooth tip widths, both the on-load torque performance and the efficiency can be optimized for the investigated machines with different slot/pole number combinations. Experiments have been carried out to validate the finite element results.
http://dx.doi.org/10.1109/TIE.2015.2427112 - Critical design criterion for achieving zero voltage switching in inductor-less half-bridge driven piezoelectric transformer based power supplies
IEEE Power Electronics, 2015
M. P. Foster,J. N. Davidson, E. L. Horsley & D. A. StoneA methodology for predicting the ability of inductor-less driven piezoelectric transformer (PT) based power supplies to achieve zero voltage switching (ZVS) is presented. A describing function approach is used to derive an equivalent circuit model of the PT operating in the vicinity of ZVS and the subsequent application of the model provides a quantitative measure of a PT's ability to achieve ZVS when driven by an inductor-less half-bridge inverter. Through detailed analysis of the analytical model, the limitations of the inductor-less half-bridge driven PT are exposed from which guidelines for designing both the PT and inverter are derived.
http://dx.doi.org/10.1109/TPEL.2015.2481706 - Investigation on operational envelops and efficiency maps of electrically excited machines for electrical vehicle applications
IEEE Magnetics, 2015
W. Q. Chu, Z. Q. Zhu, J. Zhang, X. Liu, D. A. Stone & M. P. FosterIn this paper, the operational envelops and efficiency maps of an electrically excited (EE) machine with/without employing flux weakening control via armature current and/or with/without the field excitation regulating are obtained and comprehensively compared for electric vehicle applications. It shows that even in EE machines, only using the field excitation regulating but without the flux weakening armature current control, the maximum power at high speed is not constant but inversely proportional to the machine speed. Only by employing the flux weakening armature current control, the maximum constant power operation at high-speed region can be achieved while the operational high-speed region can be greatly extended. The maximum efficiency in this extended high-speed region can be achieved when both the field excitation and flux weakening d-axis armature current change proportionally. The main benefit of the field excitation regulating is that the efficiency in low-torque region can be significantly improved. All the analyses are validated analytically.
http://dx.doi.org/10.1109/TMAG.2014.2359008 - Real-Time Prediction of Power Electronic Device Temperatures Using PRBS-Generated Frequency-Domain Thermal Cross Coupling Characteristics
IEEE Power Electronics, 2015
J. N. Davidson, D. A. Stone and M. P. FosterThis paper presents a technique to predict the temperature response of a multielement thermal system based on the thermal cross coupling between elements. The complex frequency-domain cross coupling of devices is first characterized using a pseudorandom binary sequence technique. The characteristics are then used to predict device temperatures for a known input power waveform using a discrete Fourier transform-based technique. The resulting prediction shows good agreement with an example practical system used for evaluation. To reduce the computational complexity of the initial method, a digital infinite impedance response (IIR) filter is fitted to each cross coupling characteristic. A high correlation fit is demonstrated that produces a near-identical temperature response compared to the initial procedure while requiring fewer mathematical operations. Experimental validation on the practical system shows good agreement between IIR filter predictions and practical results. It is further demonstrated that this agreement can be substantially improved by taking feedback from an internal reference temperature. Additionally, the proposed IIR filter technique allows the efficient calculation of future device temperatures based on simulated input, facilitating future temperature predictions.
http://dx.doi.org/10.1109/TPEL.2014.2331285 - Modified switching-table strategy for reduction of current harmonics in direct torque controlled dual-three-phase permanent magnet synchronous machine drives
IET Electric Power Applications, 2015
K. D. Hoang, Y. Ren, Z. Q. Zhu & M. P. FosterThe switching-table-based direct torque control (ST-DTC) strategies of dual-three-phase permanent magnet synchronous machine (PMSM) drives are investigated in this study. Owing to its inherited advantage of suppression of sixth harmonic torque pulsation, dual-three-phase machine has attracted more and more interests among various sorts of multiphase machines. However, unexpected stator harmonic currents are often observed in the classical ST-DTC strategy for dual-three-phase PMSM drives, which cause large losses and decrease the efficiency of the drive system. An optimised ST-DTC strategy which consists a two-step process to determinate the most appropriate inverter voltage vector is proposed to reduce the stator harmonic currents. The merits of the classical DTC, that is, simple structure and good dynamic performance, are still preserved. The experimental results verify that the proposed method can significantly reduce the current harmonics.
http://dx.doi.org/10.1049/iet-epa.2013.0388 - Real-time temperature estimation in a multiple device power electronic devices
IEEE Power Electronics, 2015
J. N. Davidson, D. A. Stone, M. P. Foster & D. T. GladwinThis paper presents a technique to estimate the temperature of each power electronic device in a thermally coupled, multiple device system subject to dynamic cooling. Using a demonstrator system, the thermal transfer impedance between pairs of devices is determined in the frequency domain for a quantised range of active cooling levels using a technique based on pseudorandom binary sequences. The technique is illustrated by application to the case temperatures of power devices. For each cooling level and pair of devices, a sixth order digital IIR filter is produced which can be used to directly estimate temperature from device input power. When the cooling level changes, the filters in use are substituted and the internal states of the old filters are converted for use in the new filter. Two methods for filter state conversion are developeda computationally efficient method which is suited to infrequent changes in power dissipation and cooling, and a more accurate method which requires increased memory and processing capacity. Results show that the temperature can be estimated with low error using a system which is suitable for integration on an embedded processor.
http://dx.doi.org/10.1109/TPEL.2015.2443034 - Improved Bandwidth and Noise Resilience in Thermal Impedance Spectroscopy by Mixing PRBS Signals
IEEE Power Electronics, 2014
J. N. Davidson, D. A. Stone, M. P. Foster & D. T. GladwinThis paper presents a method of mixing pseudo-random binary sequences (PRBSs) to form a new signal that can be used to obtain the thermal impedance spectrum of power electronic systems. The proposed technique increases the useful frequency range of a PRBS by mixing two identical sequences at different frequencies. The new signal incorporates the frequency responses of both contributions. Mixing can be performed using a number of mathematical operators and analysis reveals that AND is the operator of choice since it has the lowest average input power for the same effectiveness. The bandwidth, frequency-domain representation, and noise resilience of PRBS signals are also reported. It is shown that the noise floor is significantly reduced under the mixed technique, which allows lower impedances to be measured under noisy measurement conditions. For a typical 8-bit PRBS, mixing reduces the noise floor by a factor of 10.5. Simulated and experimental validation are performed and results show the mixed scheme offers increased bandwidth, reduced computation and improved noise resilience compared to single PRBS techniques.
http://dx.doi.org/10.1109/TPEL.2013.2288936 - Required Cauer network order for modelling of thermal transfer impedance
IET Electronics Letters, 2014
J. N. Davidson, D. A. Stone & M. P. FosterImpedance spectroscopy, a technique for analysing electroceramics, is applied to the two-port form of the Cauer network which is commonly used as a thermal circuit analogue. The transfer impedance spectra of the Cauer network representations of a single material are presented as Nyquist plots for a range of network orders. The results demonstrate that a model with four or more resistor-capacitor elements is required to accurately model a single material. The effect of taking a measurement at different points within a single material is then reported and four elements are similarly required between the heat source and the measurement. The existing modelling techniques, which often use only one element per material block, are shown to be especially inaccurate. By using these findings, a design engineer can produce a better thermal model of a complete system by making an informed compromise between the model's accuracy and complexity.
http://dx.doi.org/10.1049/el.2013.3426 - Experimental investigation of a Recursive Modelling MPC system for space heating within an occupied domestic dwelling
Elsevier Building and Environment, 2014
D. Rogers, M. P. Foster & C. M. BinghamA key contributor to excessive energy usage in UK domestic dwellings is the poor temperature regulation of fluid filled heat emitters that form the most common constituent of central heating systems. This is in-part due to oversizing of the heat emitters, and deficiencies in localised closed-loop temperature control. In an attempt to address this, Controllable Radiator Valves (CRVs) are becoming an increasingly popular domestic technology with the ability to allow previously unrealisable control schemes to operate the traditional central heating system with minimal mechanical modification. Following previous reported work, therefore, this paper presents a new family of Recursive Modelling Model Predictive Controllers (RM-MPCs) for use with low cost thermic CRVs. The ability of the presented control methodologies to maintain superior temperature regulation despite the use of oversized heat emitters, is a key contribution of the paper. Furthermore, unlike previously reported techniques, the underlying recursive modelling method has been reformulated so that traditional parameter matching calculations do not now require a computationally intensive curve fitting stage. A comparison of techniques is included using experimental measurements from both an oversized oil filled heat emitter within a test chamber, and also from BS EN 442 water-filled heat emitters within an occupied dwelling. Results show the proposed methodologies can be realised using more cost-effective thermoelectric valves, whilst providing superior set point tracking.
http://dx.doi.org/10.1016/j.buildenv.2013.11.014 - Estimation of Transportation Battery Second Life for Use in Electricity Grid Systems
IEEE Sustainable Energy, 2014
D. Strickland, L. Chittock, D. A. Stone, M. P. Foster & B. PriceThis paper presents research from part of a larger project focusing on the potential development of commercial opportunities for the reuse of batteries on the electricity grid system, subsequent to their primary use in low and ultra-low carbon vehicles, and investigating the life cycle issues surrounding the batteries. The work has three main areas; examination of electric vehicle fleet data in detail to investigate usage in first life. Batteries that have passed through a battery recycler at the end of their first life have been tested within the laboratory to confirm the general assumption that remaining capacity of 80% after use in transportation is a reasonable assumption as a basis for second-life applications. The third aspect of the paper is an investigation of the equivalent usage for three different second-life applications based on connection to the electricity grid. Additionally, the paper estimates the time to cell failure of the batteries within their second-life application to estimate lifespan for use within commercial investigations.
http://dx.doi.org/10.1109/TSTE.2014.2303572 - Influence of Flux Gaps on Electromagnetic Performance of Novel Modular PM Machines
IEEE Energy Conversion, 2014
G.-J. Li, Z. Q. Zhu, W. Q. Chu, M. P. Foster and D. A. StoneIn order to simplify manufacture processes and improve fault-tolerant capabilities, modular electrical machines, especially the ones with segmented stators, are increasingly employed. However, flux gaps between segments are often inevitable. In this paper, to take advantage of these flux gaps to enhance the machine performance, novel modular permanent magnet machines with different slot/pole combinations have been proposed. The influence of these flux gaps on the electromagnetic performance of modular PM machines, such as winding factor, open-circuit air-gap flux densities, back-EMFs, cogging torque, on-load torque, inductances, magnetic saturation and copper losses, are comprehensively investigated and general rules have been established. It is found that for modular machines having slot number higher than pole number, the flux gaps between stator segments degrade the electromagnetic performance due to the lower winding factor and the flux defocusing effect. However, for modular machines having slot number lower than pole number, the electromagnetic performances can be significantly improved using proper flux gap width due to the higher winding factor and the flux focusing effect. The finite element results are validated by experiments using two prototype modular machines.
http://dx.doi.org/10.1109/TEC.2014.2312429 - Comparative Studies of Modular and Unequal Tooth PM Machines Either With or Without Tooth Tips
IEEE Magnetics, 2014
G. J. Li, Z. Q. Zhu, M. P. Foster & D. A. StoneThis paper presents four types of three-phase permanent magnet (PM) machines, that is, modular and unequal teeth (UNET) machines either with or without tooth tips. Two-dimensional finite element (FE) modeling has been carried out to analyze the influences of flux gaps (in alternate stator teeth) and UNET widths. These influences are mainly on winding factors, air-gap flux density due to PMs, flux linkage, back-electromotive force, and electromagnetic torques. For UNET machines without tooth tips, it has been found that the UNET widths affect both winding factor and air-gap flux density due to PMs. However, for UNET machines with tooth tips, the UNET widths have no effect on machines' electromagnetic performance. Nevertheless, for modular machines, the flux gaps influence three parameters: winding factor, air-gap flux density due to PMs, and flux focusing/defocusing. Meanwhile, for different slot/pole number combinations, the influences of flux gap and UNET widths are different. Several general rules concerning these influences have been established. These general rules can be extended to other single or dual three-phase modular or UNET machines with different slot/pole number combinations. Prototypes of modular machines have been built, and the predictions and conclusions have been validated.
http://dx.doi.org/10.1109/TMAG.2014.2310179 - Iron Loss Calculation in Permanent Magnet Machines under Unconventional Operations
IEEE Magnetics, 2014
W. Q. Chu, Z. Q. Zhu, X. Liu, D. A. Stone & M. P. FosterThis paper investigates the iron loss calculation of permanent magnet (PM) machines undertaking unconventional operations, where the high-frequency alternating armature field is only a fraction of the constant PM field. It is found that the iron loss of PM machines undertaking such unconventional operations cannot be calculated reliably as the conventional summation of all the iron loss harmonics predicted by finite-element (FE) methods due to fake iron loss harmonics. Further investigation is conducted on the influence of current frequency and magnitude, FE mesh, and convergence tolerance on the FE predicted iron loss under unconventional operations. It is then proposed in this paper that the iron loss of PM machines undertaking unconventional operations can be calculated as the summation of only the iron loss harmonics, which are insensitive to the convergence tolerance. The analyses are validated by the experimental results.
http://dx.doi.org/10.1109/TMAG.2014.2317784 - Minimum gain identifiable when pseudorandom binary sequences are used for system identification in noisy conditions
IET Electronics Letters, 2013
J. N. Davidson, D. A. Stone & M. P. FosterA method to determine the minimum gain of the system is presented which can be identified by pseudorandom binary sequence (PRBS)- based approaches when noise is present in the output signal. A formula for the minimum gain is derived in terms of required noise resilience from the discrete Fourier transforms of the PRBS signals and white noise. The formula allows an engineer to discount noiseaffected low-gain portions of the transfer function. The calculated minimum gain is compared graphically with noisy Bode plots and good agreement is shown with the actual noise level, demonstrating the usefulness of the result.
http://dx.doi.org/10.1049/el.2013.1034 - A recursive modelling technique applied to the model predictive control of fluid filled heat emitters
Elsevier Building and Environment, 2013
D. Rogers, M. P. Foster & C. M. BinghamBased on the recent emergence of Controlled Radiator Valve (CRV) components, the paper considers the research, development, application and benefits of a modern control methodology to improve the heating efficiency of domestic dwellings. In particular, the problem of efficient temperature control, is formulated as a model predictive control scheme employing a parameter matching technique. A key contribution of the paper is the development of an on-line modelling method, which, in contrast to previously reported techniques, requires no prerequisite knowledge of the thermodynamic behaviour of a given controlled zone and a training period of only 48 h. Moreover, it is shown that excellent performance is obtained without the normal requirements for measurements of site weather or input from other external sources of weather data, thereby reducing system cost and complexity. The proposed techniques are applied in a controlled zone using a BS EN 442 oil filled heat emitter, whose input power is closely controlled using a PWM power converter within an instrumented test cell, and also in an occupied dwelling. Results demonstrated MPC can be implemented in a dwelling with minimal perquisite modelling and still achieve set point tracking when compared to more conventional solutions resulting in an energy saving of up to 22%.
http://dx.doi.org/10.1016/j.buildenv.2013.01.004 - Evaluation of UltraBattery Performance in Comparison with a Battery-Supercapacitor Parallel Network
Elsevier Journal of Power Sources, 2013
A. J. Fairweather, D. A. Stone & M. P. FosterThis paper examines the emerging technology of batteries incorporating carbon in the negative plate to affect a parallel capacitance within the battery itself. Using a frequency domain approach in conjunction with low frequency static tests and step responses an UltraBattery is examined. Initial examinations using the Randles' model lead to development of a modified model to better represent the battery parameters. These findings then expand the work to examine a similar conventional battery connected in a parallel network with a supercapacitor bank, allowing comparisons to be made and performance criteria to be established.
http://dx.doi.org/10.1016/j.jpowsour.2012.10.095 - Active current ripple cancellation in parallel connected buck converter modules
IET Power Electronics, 2013
C. Tsang, M. P. Foster, D. A. Stone & D. GladwinParallel connection of converters has become a popular method of improving efficiency. This study first presents a design technique for a buck converter with two parallelly connected power modules (PMs), where one PM is designed with large current ripple for high efficiency. This study then demonstrates an active current ripple cancellation technique, where the current waveform of the second PM is shaped to be the exact opposite to that in the first PM, to reduce the current ripple as seen by the output capacitor. The factors that affect the overall efficiency in a parallel connected converter and the calculation of the parameters that determine the effectiveness of the ripple cancellation are reported. A prototype parallel converter is designed based on the proposed converter design technique and the current ripple seen by the output capacitor is successfully reduced by 66% with the proposed ripple cancellation technique, under different line and load conditions.
http://dx.doi.org/10.1049/iet-pel.2012.0383 - Direct torque control of permanent magnet brushless AC drive with single-phase open-circuit fault accounting for influence of inverter voltage drop
IET Electric Power Applications, 2013
K. D. Hoang, Z. Q. Zhu & M. P. FosterThis study presents a novel direct torque control (DTC) of permanent magnet (PM) brushless AC (BLAC) drive under single-phase open-circuit fault (SOF) accounting for the influences of inverter voltage drop (IVD), together with novel current model-based and voltage model-based stator flux estimation schemes for post-fault operation. It is demonstrated that for accurately elaborating the modified mathematical model, the voltage induced in the stator open phase winding and its relevant flux linkage should be taken into account although they do not contribute to torque production in the post-fault operating mode. It is also proven that reconfiguration of the conventional six-switch three-phase inverter for the purpose of fault-tolerant control results in a significant magnitude imbalance between the ?- and ?-components of IVD. Thus, the influences of this unbalanced issue on performance of the two proposed stator flux estimation methods are investigated in details and a compensation method for the voltage model-based stator flux estimator is proposed and experimentally verified. It is shown that fault-tolerant control with high performance operation can be maintained for a DTC-based PM BLAC drive under SOF using the proposed modified mathematical model.
http://dx.doi.org/10.104/iet-epa.2012.0290 - Predicting the zero-voltage switching profiles of half-bridge driven inductor-less piezoelectric transformer-based inverters
IET Power Electronics, 2012
M. P. Foster, E. L. Horsley & D. A. StoneA methodology for predicting the ability of an inductor-less driven piezoelectric transformer (PT)-based inverter to achieve zero-voltage switching (ZVS) is presented. Cyclic-mode analysis is used to derive a model of the PT operating in the vicinity of ZVS. The output of the model is a normalised parameter that indicates the PT-based inverter's ability to achieve ZVS for a given operating condition. Subsequently, the model is employed to generate the ZVS profiles of a PT-based inverter that indicates regions where ZVS can be achieved and provides the loci of the operating frequency and dead-time when working at the ZVS boundary. The ZVS profiles of two PT-based inverters with different characteristics are presented to highlight the need to consider the ZVS loci when selecting a PT for a given application.
http://dx.doi.org/10.1049/iet-pel.2011.0344 - Analysis of Dual-Output Resonant Power Converters Through Use of Linear Load Approximations
IEEE Power Electronics, 2012
D. R. Williams, C. M. Bingham, D. A. Stone & M. P. FosterThis paper presents methodologies for the structured modeling and analysis of dual-output dc-dc resonant power converters. The work is underpinned by a generalization of classical fundamental mode analysis (the most prevalent technique for the analysis of single-output converters) with a progression of increasingly accurate linear load-modeling extensions (at the expense of computational complexity) to accommodate converter output asymmetry and component parasitics when a dual-output rectifier is employed. Application of the technique, and the benefits afforded by the proposed modeling methodologies, are demonstrated through the analysis of a prototype dual-output converter, with a comparison of the results from both theoretical predictions and simulation studies, and experimental measurements from the commissioned converter.
http://dx.doi.org/10.1109/TPEL.2012.2189135 - Modelling of VRLA batteries over operational temperature range using Pseudo Random Binary Sequences
Elsevier Journal of Power Sources, 2012
A. J. Fairweather, M. P. Foster & D. A. StoneThis paper continues previous work concerning the use of maximum length sequences within parameter estimation for batteries. Using the familiar Randles model batteries are examined over typical operational temperatures for variations in readily identifiable equivalent circuit parameters, using previously identified methods [1]. This analysis is used to present characteristics which can be subsequently used to inform the design of an online State-of-Charge (SoC) and State-of-Health (SoH) system for these batteries.
http://dx.doi.org/10.1016/j.jpowsour.2012.02.024 - Analysis of Inductorless Zero-Voltage-Switching Piezoelectric Transformer-Based Converters
IEEE Power Electronics, 2012
E. L. Horsley, A. V. Carazo, Nam Nguyen-Quang, M. P. Foster & D. A. StoneThe inductorless piezoelectric transformer (PT)-based resonant converter topology allows all the components between the half-bridge inverter and rectifier in a conventional LCC converter to be replaced with a single ceramic component. This offers potential savings in cost, size, and mass. However, zero-voltage switching (ZVS) becomes more difficult to achieve because the MOSFET output capacitances are augmented by the PT input capacitance. This paper presents an analytical model for the ZVS condition in inductorless PT-based converters. Unlike previously reported models, the proposed model is shown to offer a level of accuracy comparable to a SPICE simulation and to correlate well with experimental results. Using a normalization scheme and numerical optimization techniques, the criteria for achieving inductorless ZVS are found in terms of the equivalent circuit components. Both ac-output and dc-output variants are considered, and design charts for ensuring ZVS in five different topologies are presented. The results and design charts are applicable to any type of PT that can be represented by the standard PT equivalent circuit.
http://dx.doi.org/10.1109/TPEL.2011.2169431 - Arbitrary waveform power controller for thermal measurements of semiconductor devices
IET Electronics Letters, 2012
J. N. Davidson, D. A. Stone & M. P. FosterPresented is a simple and easy-to-implement design for an arbitrary waveform power controller. The power dissipation in an active semiconductor device is controlled by virtue of its current and voltage for any waveform. By measuring the heating effect on an electronic product, an engineer can evaluate the effectiveness of its design. The controller is demonstrated practically with a MOSFET using an arbitrary waveform, and power dissipated in the device agrees well with intended dissipation.
http://dx.doi.org/10.1049/el.2011.3927 - Describing function model of series resonant inverter with current limiting diode-clamp
IET Electronics Letters, 2011
M. P. Foster & D. A. StoneAn equivalent circuit model for predicting the steady-state behaviour of the series resonant inverter with a current limiting diode-clamp is derived using describing function techniques. An iterative procedure is employed to determine the conduction point of the diode-clamp. Experimental results taken from a prototype inverter are presented to validate the model.
http://dx.doi.org/10.1049/el.2011.2768 - Battery parameter identification with Pseudo Random Binary Sequence excitation (PRBS)
Elsevier Journal of Power Sources, 2011
A. J. Fairweather, M. P. Foster & D.A. StoneThis paper extends previous work on the use of maximum length sequences as tools for parameter estimation within electrochemical batteries. An improved technique using a simplified monopolar current pulse excitation strategy allows identification of Randles model equivalent circuit values, which can be subsequently employed in state-of-charge and state-of-health algorithms. Within the approach the problems associated with establishing bulk capacitance over a short time period are avoided. Instead, using readily identifiable parameters (surface capacitance, series resistance and charge transfer resistance) comparison of parameters for new and aged batteries is carried out, and a potential indicator for State of Health described. Experimental results are presented to verify the proposed technique.
http://dx.doi.org/10.1016/j.jpowsour.2011.06.072 - Low-cost solar emulator for evaluation of maximum power point tracking methods
IET Electronics Letters, 2011
D. M. L. Schofield, M. P. Foster & D. A. StonePresented is a design for a solar photovoltaic (PV) emulator optimised for the cost-effective evaluation of solar-array maximum point tracking (MPPT) methods and their associated power converters. The system design and component calculation methodology are reported with a practical comparison of the emulator output with measurements from an actual solar panel. Unlike previous work in this area the output of the emulator is compared with measurement from an actual PV array. The results show good agreement between the characteristics, demonstrating its suitability for the evaluation of static parameter based estimation and dynamic search based MPPT techniques.
http://dx.doi.org/10.1049/el.2010.2930 - Influence and Compensation of Inverter Voltage Drop in Direct Torque Controlled Four-Switch Three-Phase PM Brushless AC Drives
IEEE Power Electronics, 2011
K. Hoang, Q Zhu & M. P. FosterThis paper presents direct torque control (DTC) methodology for a four-switch three-phase (FSTP) inverter-fed permanent magnet brushless ac (PM BLAC) machine, with reference to a conventional six-switch three-phase (SSTP) inverter. It has been found that when derived from conventional voltage model flux estimation scheme, the predicted stator flux imbalance may be caused by unbalanced inverter voltage drop in the FSTP inverter, in which one phase winding is directly connected to dc-link midpoint. While this imbalanced problem does not adversely affect the performance of current-model-based DTC, it causes significantly nonsinusoidal current waveforms and considerably unbalanced current magnitudes in voltage-model-based DTC. A new compensation scheme taking into account the different forward voltage-drop values in the switching device and the freewheeling diode is proposed for the voltage-model-based DTC to correct for stator flux imbalance via the addition of corrective voltages to flux equations. The proposed scheme has significantly improved the shape of current waveforms with satisfactory balanced magnitudes, total harmonic distortion, and torque ripple factor, as verified by both simulation and experimental results. It has been shown that it is possible for an FSTP inverter to provide similar performance to an SSTP inverter when driving a PM BLAC machine.
http://dx.doi.org/10.1109/TPEL.2010.2096561 - Compensation of Non-Linearities in Diode-Clamped Multilevel Converters
IEEE Industrial Electronics, 2010
S. R. Minshull, C. M. Bingham, D. A. Stone, & M. P. FosterThe application of multilevel converters for exciting permanent-magnet machines with low-phase inductance to dc-link voltage ratios facilitates a reduction in high-frequency switching harmonics. However, converter nonlinearities and, in-particular, on-state device voltage drops, create additional low-frequency harmonics. This paper therefore proposes a generic compensation scheme to accommodate the effects of such converter nonlinearities and, in doing so, improve the harmonic quality of the machine phase currents. Experimental results gathered from a prototype five-level diode-clamped converter validate the benefits of the proposed scheme by showing quantitative reductions in low-frequency harmonics.
http://dx.doi.org/10.1109/TIE.2009.2023631 - Frequency reduction schemes for back-to-back connected, diode-clamped multilevel converters
IET Power Electronics, 2010
S. R. Minshull, C. M. Bingham, D. A. Stone & M. P. FosterTwo new switching schemes for back-to-back connected diode-clamped multilevel converters that reduce the devices switching frequency while maintaining capacitor balancing are presented. Comparisons are made between a previously reported optimal balancing strategy and the two proposed switching techniques using data gathered from a prototype five-level, back-to-back connected, diode-clamped multilevel converter. The proposed schemes are shown to allow as much as 35% reduction in switching frequency when compared to the optimal balancing case while also balancing the voltages across the series connected DC-link capacitors. The back-to-back connected, multilevel converter excites a permanent magnet synchronous motor to obtain the experimental data and verify the proposed switching schemes.
http://dx.doi.org/10.1049/iet-pel.2008.0215 - Hamel locus design of self-oscillating DC-DC resonant converters
IET Power Electronics, 2010
D. R. Williams, C. M. Bingham, M. P. Foster & D. A. StoneThe study presents a technique for analysing and controlling resonant DC-DC converters in a self-oscillating manner. Self-oscillating converters benefit from higher efficiency and higher power density than their non-self-oscillating counterparts since they can be operated closer to the tank resonant frequency. The analysis necessary to predict the behaviour of such converters, based on the construction of Hamel loci, is developed. The impact of parasitic circuit elements is also inherently accommodated. Operation is based on the behaviour of a relay with a negative hysteresis transition. The proposed self-oscillating mechanism is therefore simple and cost effective to implement. Results from a prototype converter are included in order to verify the underlying theoretical principles.
http://dx.doi.org/10.1049/iet-pel.2008.0263 - Self-oscillating control methods for the LCC current-output converter
IEEE Power Electronics, 2008
A. J. Gilbert, C. M. Bingham, D. A. Stone & M. P. FosterA strategy for self-oscillating control of LCC current-output resonant converters, is presented, based on varying the phase-angle between the fundamental of the input voltage and current. Unlike other commonly employed control methodologies, the proposed technique is shown to provide a convenient, linear system input-output characteristic suitable for the design of regulators. The method is shown to have a similar effect as controlling the DC-link supply voltage, in terms of output-voltage/current control. The LCC converter variant is used as an application focus for demonstrating the presented techniques, with simulation and experimental measurements from a prototype converter being used to show the practical benefits. Third-order small and large-signal models are developed, and employed in the formulation of robust output-voltage and output-current control schemes. However, notably, the presented techniques are ultimately generic and readily applicable to other resonant converter variants.
http://dx.doi.org/10.1109/TPEL.2008.925198 - Analysis of CLL voltage-output resonant converters using describing functions
IEEE Power Electronics, 2008
M. P. Foster, C. R. Gould, D. A. Stone & C. M. BinghamA new AC equivalent circuit for the CLL voltage-output resonant converter is presented, that offers improved accuracy compared with traditional FMA-based techniques. By employing describing function techniques, the nonlinear interaction of the parallel inductor, rectifier and load is replaced by a complex impedance, thereby facilitating the use of AC equivalent circuit analysis methodologies. Moreover, both continuous and discontinuous rectifier-current operating conditions are addressed. A generic normalized analysis of the converter is also presented. To further aid the designer, error maps are used to demonstrate the boundaries for providing accurate behavioral predictions. A comparison of theoretical results with those from simulation studies and experimental measurements from a prototype converter, are also included as a means of clarifying the benefits of the proposed techniques.
http://dx.doi.org/10.1109/TPEL.2008.924835 - Analysis and Control of Dual-Output LCLC Resonant Converters with Significant Leakage Inductance
IEEE Power Electronics, 2008
C. M. Bingham, Y. Ang, M. P. Foster & D. A. StoneThe analysis, design and control of fourth-order LCLC voltage-output series-parallel resonant converters for the provision of multiple regulated outputs, is described. Specifically, state-variable concepts are developed to establish operating mode boundaries with which to describe the internal behavior and the impact of output leakage inductance. The resulting models are compared with those obtained from SPICE simulations and measurements from a prototype power supply under closed loop control to verify the analysis, modeling, and control predictions.
http://dx.doi.org/10.1109/TPEL.2008.925156 - Self-Oscillating Control of a DC-DC Resonant Converter Using a Hysteretic Relay
ISAST Trans. Electronics and Signal Processing, 2008
D. R. Williams, C. M. Bingham, M. P. Foster & D. A. StoneThe paper presents a technique for analysing and controlling resonant DC-DC converters in a self-oscillating manner. Self-oscillating converters benefit from higher efficiency and higher power density than their non-self-oscillating counterparts since they can be operated closer to the tank resonant frequency. The analysis necessary to predict the behaviour of such converters, based on the construction of Hamel loci, is developed. The impact of parasitic circuit elements is also inherently accomodated. Operation is based on the behaviour of a relay with a negative hysteresis transition. The proposed self-oscillating mechanism is therefore simple and cost effective to implement. Results from a prototype converter are included in order to verify the underlying theoretical principles. - Normalised analysis and design of LCC resonant converters
IEEE Power Electronics, 2007
J. Gilbert, C. M. Bingham, D. A. Stone & M. P. FosterA normalization of the LCC voltage-output resonant converter performance characteristics, in terms of the tank gain at resonance and the parallel-to-series-capacitor ratio, is presented. The resulting description is subsequently used for the derivation of a design procedure that incorporates the effects of diode losses and the finite charge/discharge time of the parallel capacitor. Unlike previously reported techniques, the resulting normalized behavior of the converter is used to identify design regions to facilitate a reduction in component electrical stresses, and the use of harmonics to transfer real power. Consideration of the use of preferred component values is also given. The underlying methodology is ultimately suitable for incorporation into a software suite for use as part of a rapid interactive design tool. Both simulation results and experimental measurements from a prototype converter are included to demonstrate the attributes of the proposed analysis and design methodologies.
http://dx.doi.org/10.1109/TPEL.2007.909243 - Automated design of LCC resonant converters using a genetic algorithm employing a describing function equivalent circuit converter model
ISAST Trans. Electronics and Signal Processing, 2007
M. P. Foster, A. J. Gilbert, C. R. Gould, D. A. Stone & C. M. BinghamThis paper describes how genetic algorithms can be applied to design LCC resonant converters. Operation of a binary genetic algorithm is described and an appropriate cost function is developed which is used in conjunction with a describing function based model to rapidly evaluate multiple candidate converters over a wide operating range. Simulation results demonstrate the versatility of the design tool. - Methodologies for the design of LCC voltage-output resonant converters
IEE Electric Power Applications, 2006
M. P. Foster, H. I. Sewell, C. M. Bingham & D. A. StoneThe paper presents five structured design methodologies for third-order LCC voltage-output resonant converters. The underlying principle of each technique is based on an adaptation of a FMA equivalent circuit that accommodates the nonlinear behaviour of the converter. In contrast to previously published methods, the proposed methodologies explicitly incorporate the effects of the transformer magnetising inductance. Furthermore, a number of the methodologies allow the resonant-tank components to be specified at the design phase, thereby facilitating the use of standard off-the-shelf components. A procedure for sizing the filter capacitor is derived, and the use of error mapping, to identify parameter boundaries and provide the designer with a qualitative feel for the accuracy of a proposed converter design, is explored - CCL resonant converters with output short-circuit protection
IEE Electric Power Applications, 2005
C. R. Gould, C. M. Bingham, D. A. Stone & M. P. FosterThe use of harmonic excitation of resonant converters as a means of limiting excessive electrical stresses on power switches, and tank components, in the event of over-current or output short-circuit fault conditions is investigated. It is demonstrated that the excitation of the primary tank resonance, by odd harmonics of the square-wave input voltage, facilitates reduced power dissipation for systems that are subject to long periods of standby operation. Due to the inherent limitations of traditional fundamental mode approximation techniques to predict sub-harmonic resonant peaks, an alternative, steady-state, cyclic-averaging methodology, is proposed, that is shown to provide accurate and rapid analysis of the resonances when the converter is operated under short-circuit conditions, thereby allowing the effects of high electrical components stresses to be mitigated, and eliminates the necessity for time-consuming integration-based simulations. Measurements from a prototype converter, along with simulation results from a derived state-variable model and a component-based simulation package, are used to demonstrate the accuracy of the proposed cyclic predictions, and the reduction in losses imparted by the use of harmonic excitation when compared to other previously published techniques for over-current/short-circuit protection.
http://dx.doi.org/10.1049/ip-epa:20045157 - Design oriented analysis of fourth-order LCLC converters with capacitive output filter
IEE Electic Power Applications, 2005
Y. A. Ang, C. M. Bingham, M. P. Foster, D. A. Stone & D. HoweAn analytical methodology for the rapid steady-state analysis of fourth-order resonant power converters, with capacitive output filter, is proposed. The technique extends previously published work on LCC converters to the more common, but more complex, LCLC counterpart. The output filter/rectifier and load circuit are represented by multiple 'equivalent' passive components that permit the subsequent calculation of the steady-state voltage conversion ratio and the estimation of the voltage and current stresses on the resonant-tank components. The resulting methodology facilitates the derivation of four design synthesis procedures for LCLC converters based on various user-definable constraints. Simulation results and measurements from a prototype fourth-order converter are used to demonstrate the accuracy of the proposed methodology, whose computational requirement is comparable to that for classical fundamental-mode approximation.
http://dx.doi.org/10.1049/ip-epa:20045112 - Analysis of 4th-order LCLC Resonant Power Converters
IEE Electric Power Applications, 2004
Y. A. Ang, M. P. Foster, C. M. Bingham, D. A. Stone, H. I. Sewell & D. HoweA methodology is presented for the high-speed, steady state analysis of 4th-order LCLC resonant power converters. Both current-output and voltage-output variants are considered. State-variable dynamic descriptions of the circuits are derived and subsequently employed to rapidly determine the steady-state cyclic behaviour and the voltage and current characteristics of the resonant-tank and output-filter, and to estimate the voltage and current stresses on resonant components. Simulated and experimental results for two prototype 4th-order converters (inductive and capacitive output variants) confirm that the accuracy of the model is comparable with SPICE simulations, while requiring less than 10-4 of the computational time.
http://dx.doi.org/10.1049/ip-epa:20040218 - Analysis of voltage output LCC resonant converters, including boost mode operation
IEE Electric Power Applications, 2003
H. I. Sewell, M. P. Foster, C. M. Bingham, D. A. Stone, D. Hente & D. HoweA novel methodology for the high-speed analysis of LCC voltage output resonant power converters is presented. Termed rectifier transformed fundamental mode analysis, the procedure employs describing functions for determining equivalent passive circuit models for the combined rectifier, output filter and load circuitry. The resulting passive network is then used to predict voltages and currents throughout the converter. A refinement algorithm is also described that further enhances the accuracy of the analysis. Unlike previously published techniques, the proposed procedure is shown to accurately predict converter operation in the boost mode; a mode that normally requires the incorporation of an additional step-up transformer to realise output voltages that are higher than the input voltage in the converter topology under consideration. The accuracy of the procedure, and the enhancement that results from the refinement process, is demonstrated by comparing predictions of the maximum output voltage of LCC converters as a function of load, and the regulation at a fixed switching frequency as a function of the parallel rectifier capacitance with measurements from prototype converters, including operation in boost mode. The results confirm that the methodology is capable of correctly predicting the steady-state behaviour of voltage output LCC series resonant converters, particularly around the resonant frequency where previously published techniques can exhibit significant error.
http://dx.doi.org/10.1049/ip-epa:20030765 - Cyclic averaging for high speed analysis of resonant power converters
IEEE Power Electronics, 2003
M. P. Foster, H. I. Sewell, C. M. Bingham, D. A. Stone, D. Hente & D. HoweThe paper describes the development and application of a cyclic-averaging technique for the rapid analysis of high-order resonant power converters. To provide a focus to the paper, particular emphasis is given to a 3rd-order LCC voltage output converter topology. The proposed methodology predicts steady-state voltages and currents throughout the circuit, and provides estimates of the stresses on the resonant circuit components. State-space simulations and experimental results from a 350 V-input/150 V-output converter are used to demonstrate a prediction accuracy comparable with time-domain integration-based techniques is achievable, while requiring only 1/10,000th of the computation time. In addition, a comparison with Spice simulation results shows that cyclic averaging provides commensurate predictions of voltage and current stresses on the resonant circuit components. Issues arising from the stray capacitance associated with the resonant inductor, and the corresponding sensitivity of the predicted output voltage, are also considered.
http://dx.doi.org/10.1109/TPEL.2003.813763 - High Speed analysis of resonant power converters
IEE Electric Applications, 2003
M. P. Foster, H. I. Sewell, C. M. Bingham, D. A. Stone, D. Hente & D. HoweA methodology for determining the steady-state operation of resonant power-switching converters is described. The technique, based on cyclic averaging, employs a reduced-order harmonic analysis to obtain the switching transition times which separate different modes during each cycle in the steady state. The internal state variables of the system, in the steady state, are then immediately determined. In comparison with previously published techniques, the methodology has the advantage of allowing any piecewise-linear state-space model of a power converter to be used to predict the steady-state performance without the prerequisite of a transient-based simulation. The simulated and experimental results for a prototype third-order CLC current-output converter are compared to demonstrate that the prediction accuracy is comparable with that of state-variable-simulation models, and that the execution speed is of the same order as that for FHA (first-harmonic analysis).
http://dx.doi.org/10.1049/ip-epa:20030057 - Stress analysis of 4th order LLCC resonant converters
IEE Electronics Letters, 2002
Y. Ang, M. P. Foster, H. I. Sewell, C. M. Bingham & D. A. StoneA high-speed methodology for analysing fourth-order LLCC resonant converters is presented. Formula-based predictions of output voltage and, importantly, estimates of voltage and current stresses on resonant components, are derived. Comparison of predictions with those from SPICE demonstrate a high degree of correlation whilst requiring only 1/10,000th of the computation time.
http://dx.doi.org/10.1049/el:20021078 - State-variable modelling of LCC Voltage Output Resonant Converters
IEE Electronics Letters, 2001
M. P. Foster, H. I. Sewell, C. M. Bingham & D. A. StoneA state-variable model for third-order leadless chip carrier (LCC) voltage-output resonant converters has been derived. This is demonstrated to be at least 40 times faster to simulate than an `equivalent' SPICE simulation of the circuit. Comparison of simulation results with those from an experimental resonant converter show that accuracy commensurate with SPICE simulations is obtained.
http://dx.doi.org/10.1049/el:20010736
- Bidirectional inverting piezo resonator-based (BIPR) converter for cell balancing applications
2023 IEEE Energy Conversion Congress and Exposition (ECCE), 2023
J. Forrester, J. N. Davidson & M. P. FosterA novel piezo resonator-based resonant converter topology is presented, specifically tailored for active cell balancing applications. The bidirectional operation of the converter is presented, and the control requirements are discussed. Simulations are performed to determine the output voltage gain and output current of the converter. Finally, the cell balancing performance of the converter is simulated and compared to a passive balancing method, showing improved efficiency and balancing speed.
https://doi.org/10.1109/ECCE53617.2023.10362516 - Modelling and sizing sensitivity analysis of a fully renewable energy-based electric vehicle charging station microgrid
EVI: Charging Ahead Conference, 2023
M. Naderi, D. Palmer, M. Nunez Munoz, Y. Al-Wreikat, M. J. Smith, E. Fraser, D. T. Gladwin, M. P. Foster, E. Ballantyne & D. A. Stone - Predicting Energy Use of an Electric Vehicle using Vehicle Dashcam Telemetry Data
World Conference on Transport Research - WCTR 2023 Montreal, Canada, 2023
T. Stincesu, E, Ballantyne, D. A. Stone, R. Zhao & M. P. FosterPrior to the acquisition an electric vehicle, pre-evaluation of vehicle energy use is essential for assessing whether the intrinsic electrical storage capability is satisfactory. However, inconsistency in vehicle modelling may provide unreliable predictions concerning energy usage. In order to increase the prediction reliability, one potential solution may lie in use of city-specific driving cycle data and other geographical information. This paper presents a novel method of extracting driving data from archived dashcam videos without the need to deploy a fleet of test vehicles to log conventional telemetry. Utilising dashcam videos as input, employing last-generation image processing and recognition technology, textual in-route driving data embedded in the video can be extracted. The results from preliminary testing using real-life dashcam videos demonstrate negligible errors with regards to energy requirements and pollutants emitted from an EV operating on the modelled routes. Consequentially, the proposed solution opens up the possibility to employ a significant amount of new data in order to better assess the transport sectors energy requirements. This is especially important for situations where conventional telemetry is difficult to obtain. - Design and Analysis of a Voltage Controlled Current Source Gate Driver for an IGBT
PCIM Europe 2023 - International Exhibition and Conference for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management, 2023
A. L. Q. Parillo, M. P. Foster & D. A. StoneThis article presents a voltage controlled current source gate driver for an IGBT and compares its performance to a conventional voltage gate driver. Both gate drivers are designed using discrete com-ponents and evaluated using a double pulse test bench. The voltage gate driver is tested under differ-ent gate resistor conditions, while the proposed current source gate driver is tested under different gate current levels. The results show that the proposed gate driver reduces delay time and energy losses. Additionally, the proposed gate driver is tested under different gate current profiles during the turn-on and turn-off stages, and the results demonstrate that the dIc/dt and dVce/dt can be controlled.
http://doi.org/10.30420/566091155 - A Design Methodology for a CLLLC Bidirectional Resonant Converter with an Integrated Planar Transformer
PCIM Europe 2023 - International Exhibition and Conference for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management, 2023
S. A. Ansari, J. N. Davidson & M. P. FosterThe efficiency and power density of a bidirectional CLLLC resonant converter can be improved by integrating its magnetic components into a single transformer (known as integrated transformer). However, integrated transformers, especially integrated planar transformers, usually suffer from high parasitic capacitance. In the conventional design process of the CLLLC converter, the parasitic capacitance of the transformer is neglected while a high parasitic capacitance can affect the performance of the converter noticeably. Therefore, this paper presents a new design methodology for a bidirectional CLLLC resonant converter, which studies the effect of parasitic capacitance and guarantees ZVS conditions for the switches even when integrated planar transformers with high stray capacitance are used. Simulation results are presented to verify the theoretical analysis.
http://doi.org/10.30420/566091332 - Performance Of Pzt-based Piezoelectric Transformers For Use In High-temperature Converters
IET Power Electronics Machines and Drives Conference 2022, 2022
J. Forrester, L. Li, Z. Yang, J. N. Davidson, M. P. Foster, D. A. Stone, I. M. Reaney, D. C. SinclairPiezoelectric transformers (PTs) are ideally suited for resonant converter applications, owing to their inherent resonant tank circuit, high power density and efficiency. High temperature electronics is an area of research that is increasing in popularity, due to SiC and GaN devices. However, high temperature power electronic conversion is difficult to achieve using traditional passive components due to the novel materials required. In this paper, a PT made from lead zirconate titanate (PZT) is proposed for use in high temperature power conversion. - Cyclic-mode Modelling Of Class EF2 Inverters Featuring a Piezoelectric Resonator As The Auxiliary Network
IET Power Electronics Machines and Drive Conference 2022, 2022
Y. Wang, J. N. Davidson & M. P. FosterBy connecting an auxiliary network in parallel with the switch in a class E inverter, class EF resonant inverters are able to reduce the voltage stresses on the switch. This paper presents a cyclic mode model for predicting the behaviour class EF inverters that use a piezoelectric resonator in place of the resonant circuit. The performance of the proposed model is validated using a Class EF2 resonant inverter where the piezoelectric resonator is tuned to twice the main branch resonant frequency. - Fully-integrated Transformer With Asymmetric Leakage Inductances For A Bidirectional Resonant Converter
IET Power Electronics Machines and Drive Conference 2022, 2022
S. A. Ansari, J. N Davidson & M. P. FosterIn this paper, a new design for an integrated planar transformer is presented which can provide asymmetric leakage inductance in primary and secondary sides. Therefore, the proposed integrated transformer can be used in bidirectional resonant converters in which the primary and secondary inductors have different values. To achieve a precise, high leakage inductance for the primary and secondary sides, two magnetic shunts are inserted into a planar transformer. In the proposed topology, flexible magnetic sheets which can be cut easily are used as the magnetic shunts, leading the design process to high flexibility. The analysis, design and modelling of the proposed integrated transformer are presented in detail. It is shown that the magnetising inductance can be determined by regulating the length of an inserted air gap inserted between two E-cores. In addition, the leakage inductance of the primary and secondary sides can be regulated separately by the length of air gaps inserted within the magnetic shunts. The theoretical analysis is verified by finite element analysis and the operation of the proposed integrated transformer is demonstrated while it is used in a CLLLC bidirectional converter. - Parameterisation Methods For Piezoelectric Transformer Equivalent Circuit Models
IET Power Electronics Machines & Drives, 2022
H. OKeeffe, M. P. Foster & J. N. DavidsonThree techniques for extracting equivalent circuit parameters from piezoelectric transformers based on the Mason equivalent circuit model are explored, starting from a frequency domain analysis of the input and output impedance. Two optimisation techniques to improve the accuracy of the parameterisation are detailed and tested, each allowing multiple resonant modes to be modelled, with the aim of minimising the percentage error of the fit. - Resonant Current Estimation And Voltage Regulation For Piezoelectric Transformer-based Power Supply
IET Power Electronics Machines and Drives Conference 2022, 2022
Z. Yang , J. Forrester, J. N. Davidson , M. P. FosterThis paper proposes an output voltage regulation approach for a piezoelectric transformer (PT)-based power converter. The inductorless half-bridge configuration is employed to achieve zero-voltage switching. A resonant current estimation circuit is implemented at the output section of the PT, and it is used by a phase-locked loop (PLL) zero voltage switching (ZVS) controller to synchronise MOSFET switching to the zero crossings of the resonant current. Burst-mode control is employed to provide output voltage regulation of the DC/DC converter. Both experimental and simulation results demonstrate the operation of the system. - Package-related Degradation Condition Monitoring Of Sic Power Mosfets
Using Current Distribution Anomaly Detection
IET Power Electronics Machines and Drives Conference 2022, 2022
J. Naghibi, K. Mehran, K. N. Toosi & M. P. FosterAnomaly detection in current distribution of wire bonded connection of the Silicon Carbide power MOSFET module is proposed and examined as a comprehensive condition monitoring precursor for monitoring package-related failure modes. The simulation and experimental results show that both wire bond-related and solder layer-related degradation can be detected using the proposed technique. To capture the current distribution profile, magnetic field of the wire bonds is measured using the tunnel magneto-resistance sensors in the - Investigation of using BSPT for ring-dot piezoelectric transformers for use in high-temperature resonant power supplies
International Conference and Exhibition on HIGH TEMPERATURE ELECTRONICS NETWORK (HiTEN 2022), IMAPS - International Microelectronics Assembly and Packaging Society, 2022
J. Forrester, L. Li, J. N. Davidson, M. P. Foster, D. A. Stone, I. M. Reaney & D. C. SinclairSiC and GaN devices are gaining in popularity in both research and commercial applications. One of the many benefits of these devices is the possibility of power converter operation at temperatures in excess of that possible with Si-based devices (>200C). A bismuth scandium lead titanate (BSPT) piezoelectric transformer is analysed for use in high temperature (up to 250C), resonant converters using impedance spectroscopy and power converter measurements. The PT shows declining losses with temperatures during testing, translating into an improvement of 15% points in efficiency whilst more than doubling the output power across the temperature range. A peak performance of 0.7W output power and 53% efficiency at 225C was achieved, giving comparable performance to previous work but at higher temperatures. - Resonant current estimation and phase-locked loop control system for inductorless step-up single piezo element-based (SUPRC) DC-DC converter
IECON 2022 48th Annual Conference of the IEEE Industrial Electronics Society, 2022
J. Forrester, J. N. Davidson & M. P. FosterAn FPGA-based control system for the step-up piezo resonator-based DC-DC converter is presented. An all-digital phase-locked loop (ADPLL) is used to self-start the converter and locks on to the resonant current, which is extracted using a current estimator. The PLL and several analogue comparator outputs are used to generate the gate signals for both MOSFETS. A new method is presented for determining the optimal high side switch duty cycle, which ensures zero-voltage switching on both MOSFETS. A practical converter is constructed, and experimental results presented, showing the effectiveness of the converter across a range of operating conditions.
https://doi.org/10.1109/IECON49645.2022.9969043 - Critical design criterion for inductorless H-bridge driven piezoelectric-transformer-based power supplies
IECON 2022 48th Annual Conference of the IEEE Industrial Electronics Society, 2022
Z. Yang, J. Forrester, J. N. Davidson, M. P. Foster & D. A. StoneA methodology for predicting the ability of a piezoelectric transformer for achieving zero-voltage switching (ZVS) is presented. A describing function method is employed to obtain the PT equivalent circuit model operating under ZVS operation. This methodology is encapsulated within a critical criterion which, if fulfilled, guarantees efficient ZVS operation over a wide load range. The model provides a quantitative measure of a PTs ability to achieve ZVS using a H-bridge inductorless configuration. With the capacitance ratio profile provided by the analytical model, the limitations of the inductorless H-bridge driven PT-based inverters are indicated and guidelines for designing both PT and inverter control circuit are demonstrated.
https://doi.org/10.1109/IECON49645.2022.9968767 - On the Effect of SiC Power MOSFET Gate Oxide Degradation in High Frequency Phase Leg-Based Applications
2022 IEEE Energy Conversion Congress and Exposition (ECCE), 2022
J. Naghibi, S. Mohsenzade, S. Iqbal, K. Mehran & M. P. FosterSilicon Carbide power MOSFET is a promising option for high power high density applications in the next generation of power electronic applications. Investigating the reliability issues and concerns, however, is a pre-requisite for enabling this technology to be widely used. Gate oxide degradation is a major chip-related failure mode in MOSFETs. The problem of gate oxide degradation is even more severe in S iC MOSFETs because of the thin gate-oxide layer. Interface trapped charge at SiC-SiO 2 interface is much higher than Si counterpart. The main effect of gate oxide degradation is changes in Miller plateau and threshold voltage value of the switch. These changes usually lead to having a longer rise time and shorter fall time in the switch. Although extensive research has been carried out on proposing precursors and characterization for S iC MOSFET gate oxide degradation, a circuit-level study is lacking. In this paper, the effect of gate oxide degradation on the operation of a half-bridge converter is studied. It is shown that the deadtime between the high side and low side switches in phase leg structure has been increased. In high frequency applications with short pulsewidth, the main consequence is that the average load voltage will be decreased. To show the effect of gate oxide degradation on phase leg operation, simulation in PSpice and experimental set-up are used. Commercial discrete SiC MOSFET 650V/22A is degraded in gate oxide layer using an adjustable degradation set-up. The brand-new and degraded switches are examined in a phase leg structure with switching frequency of 115kHz. The results showed that a 45% increment in deadtime is detected, which leads to decrement in the average voltage of the load.
https://doi.org/10.1109/ECCE50734.2022.9947441 - Analysis of Test Methods for Measurement of Leakage and Magnetising Inductances in Integrated Transformers
2022 24th European Conference on Power Electronics and Applications (EPE'22 ECCE Europe), 2022
S. A. Ansari, J. N. Davidson, M. P. Foster & D. A. StoneThe attention in integrated transformers has increased recently. The operation of the converters with integrated transformers depends on their components' value significantly. Therefore, a sensitivity analysis is provided to find the most precise measurement method for characterization of integrated transformers, especially when they have different primary and secondary leakage inductances. The theoretical analysis is verified by simulation and experimental results.
https://ieeexplore.ieee.org/document/9907386 - A Position Error Correction Method for Sensorless Control of Dual Three-Phase Permanent Magnet Synchronous Machines
2021 IEEE International Electric Machines & Drives Conference (IEMDC), 2021
T. Y. Liu, Z. Q. Zhu, X. M. Wu, Z. Y. Wu, D. A. Stone D & M. P. FosterIn this paper, an online rotor position error correction method is proposed to eliminate the impact of parameter mismatch in sensorless control of dual three-phase (DTP) permanent magnet synchronous machines (PMSMs). The position error production mechanism is firstly derived, i.e., the error changes with the trend of current variation when there is a parameter mismatch. Based on this mechanism, by injecting sinusoidal current signals into both sets of three-phase windings, the presence of parameter mismatch and its level can be revealed through the corresponding sinusoidal responses from the estimated speed of sensorless observers. Since the amplitudes of rotor position error responses decrease as the parameter mismatch level reduces, with the help of the least mean square (LMS) algorithm, the parameters can be adaptively adjusted to the actual values, and the position error can be thus corrected. Moreover, through a simple technique and with the extra freedom of DTP machines, the detrimental effects because of current signal injection can be eliminated. The proposed method has been validated through simulation and experimental results.
https://doi.org/10.1109/IEMDC47953.2021.9449591 - Novel Liquid Cooling Technology for Modular Consequent-Pole PM Machines
2021 IEEE International Electric Machines & Drives Conference (IEMDC), 2021
R. Zhou, G. J. Li, Z. Q. Zhu, M. P. Foster, D. A. Stone, C. J. Jia & P. McKeeverIn this paper, a forced oil cooling scheme is proposed for a novel modular consequent-pole permanent magnet machine (CPM) with E-core stator. In this modular machine, flux gaps (FGs) that are normally used for improving electromagnetic performance and simplifying the winding process, can also be utilized as cooling channels for the oil to pass through, leading to significantly improved machine internal cooling. Computational fluid dynamics (CFD) analyses have been carried out and the results indicate that circa 15C reduction in the peak temperature can be achieved based on the initial design. Moreover, the influences of several other critical parameters such as inlet position and geometry have been investigated, and optimal inlet configurations have been identified to realize the temperature uniformity. Some useful design guidelines for thermal management in the modular CPMs have also been provided in this paper.
https://doi.org/10.1109/IEMDC47953.2021.9449533 - Matlab-based High-Performance Electric Motorbike Energy Model, Utilising Video Data
2021 Sixteenth International Conference on Ecological Vehicles and Renewable Energies (EVER), 2021
T. Stincescu, R. Zhao, E. E. F. Ballantyne, D. A. Stone & M. P. FosterThis paper presents a novel approach towards modelling energy usage of a high-performance, motorsport-purposed electric motorcycle (eBike) under racing use conditions. While the energy usage is assessed, the simulation robustness is also considered as it will confirm that the chosen modelling approach has a high degree of versatility. The presented research work showcases the presented modelling approach applied as a software model, indicates the chosen methodology for acquiring the required telemetry data and finally presents the results and related conclusions and interpretations and their meaning to the field of expertise and the related project.
https://doi.org/10.1109/EVER52347.2021.9456609 - Dashcam Video-Driven, Route Distinctive Energy Consumption Pre-Evaluation for Electrifying Public Services Fleets
2021 Sixteenth International Conference on Ecological Vehicles and Renewable Energies (EVER), 2021
R. Zhao, T. Stincescu, E. E. F. Ballantyne, D. A. Stone & M. P. FosterConventional evaluations prior to electrifying Public Services Vehicles (PSVs) generally provide macro conclusions based on urban layout and fleet magnitude. These inaccurate estimations could further result in recommendations to purchase unsuitable vehicles. Predicting the energy of replacement Electric Vehicles (EVs) using city-designated driving cycle data and geographical information could significantly enhance the accuracy, however, requires vehicle's en-route driving data (cycle) which challenging to obtain before the actually deploy of vehicles. In this paper, taking only dashcam videos as input, through an emergent image processing and recognition technology, textual en-route driving data can be extracted. Thus a vehicle model could simulate the driving of an EV and accurately predict the energy usage of each filmed route. The theories and technology presented in this paper were evaluated using real-life dashcam videos and results demonstrating a negligible error rate while energy requirement from operating an EV on the same route is predicted.
https://doi.org/10.1109/EVER52347.2021.9456625 - RadPTDesigner: A program for designing radial mode piezoelectric transformers for inductorless inverters
2021 23rd European Conference on Power Electronics and Applications, EPE 2021 ECCE Europe, 2021
J. Forrester, J. N. Davidson, M. P. Foster & D. A. StonePiezoelectric transformers (PTs) offer the possibility for designing compact and efficient power supplies featuring few components. PT power supplies are difficult to design owing to the fusion between resonant power conversion and materials science. This paper presents a program for designing radial-mode PTs.
https://ieeexplore.ieee.org/abstract/document/9570504 - Design and Analysis of a Fully-integrated Planar Transformer for LCLC Resonant Converters
2021 23rd European Conference on Power Electronics and Applications, EPE 2021 ECCE Europe. 06 Sep 2021, 2021
S. A. Ansari, J. N. Davidson, M. P. Foster & D. A. StoneThe isolated LCLC resonant converter needs five discrete passive components including two capacitors, two inductors and a transformer. In this paper, to cut down the number of components of this converter, a new design for a high-frequency transformer is proposed which integrates all the five magnetic and capacitive components in only a single magnetic device. The series capacitor and inductor are integrated into the primary winding and the parallel capacitor and inductor are integrated into the secondary winding. The design guideline for this transformer is presented in detail and theoretical analysis is confirmed by simulation results.
https://ieeexplore.ieee.org/abstract/document/9570666 - Improved Cooling in Modular Consequent Pole PM Machine Utilizing Flux Gaps
IEEE Energy Conversion Congress & Expo. IEEE-ECCE. 15 Oct 2020, 2020
R. Zhou, G.-J. Li, Z. Q. Zhu M. P. Foster & D. A. StoneIn this paper, a novel cooling method utilizing the flux gaps (FGs) as cooling channels in modular consequent pole PM machines has been proposed. With numerical calculations such as computational fluid dynamics (CFD) analyses, it is proven that the proposed forced air cooling method with inlets and outlets on the end-caps can take advantage of the FGs and a remarkable reduction of temperature rise can be achieved in modular machines. The optimal FG width for better cooling effect has been identified. Moreover, several design parameters of the inlets such as inlet position, inlet dimension have been investigated. Some design guidelines of such modular machines considering particularly the thermal performance are given at the end of this paper. - Improved Sensorless Control Method for Permanent Magnet Synchronous Machines Considering Resistance Asymmetry and Temperature Variation
2020 IEEE Energy Conversion Congress and Exposition (ECCE), 2020
T. Liu, Z. Q. Zhu, Zh. Wu, D. A. Stone & M. P. FosterThis paper aims to improve the sensorless control performance for permanent-magnet synchronous machines (PMSMs) under resistance asymmetry. The improved sensorless method can eliminate the undesired 2nd order fluctuation in position and speed estimation with the help of sequence component extractor (SCE) while the DC offset position error caused by asymmetric resistance and temperature variation can be compensated by applying a novel pulse injection method. Experimental and simulation results are provided to validate the proposed methods.
https://doi.org/10.1109/ECCE44975.2020.9235887 - An Online Failure Assessment Approach for SiC-based MOSFET Power Modules Using Iterative Condition Monitoring Technique
Twenty-first IEEE Workshop on Control and Modelling for Power Electronics (COMPEL), 2020
J. Naghibi, K. Mehran & M. P. FosterCharacterization and monitoring of the faults in Wide Bandgap-based power modules are the prerequisites to achieve robust and reliable high density power electronic design. Due to the basic differences between wide bandgap and Silicon -based power modules, applying the existing condition monitoring approaches - which are mostly designed for Silicon-based devices - does not necessarily provide the expected accuracy in these circuits. Comprehensive and accurate reliability assessment can be addressed using condition monitoring techniques, specialized for wide bandgap-based devices. Real-time observation of the switch junction temperature, as the main failure indicator, is considered in this paper, and it has led to a more accurate estimation of the switch failure rate. In this paper, employing an iterative failure rate assessment with the capability to monitor the device condition and renew the assessment in specific time intervals has addressed the required condition monitoring criteria in wide bandgap-based devices. A coupled simulation platform, consisting of PLECS, COMSOL, and MATLAB is developed to obtain the switch operational parameters during an iterative real-time process. Bayerer lifetime model is employed to estimate the switch failure rate based on the real-time switch parameters. The developed real-time iterative condition monitoring technique is tested for a 1200V/50A SiC MOSFET power module as the case study. DSPACE is employed in the experimental setup as a high bandwidth signal interface, and it was shown that by employing the proposed condition monitoring technique, the switch failure rate can be acquired based on a real-time process in order to achieve more accurate reliability assessment during the switch operation. - Analysis, Design and Modelling of Two Fully- Integrated Transformers with Segmental Magnetic Shunt for LLC Resonant Converters
IECON 2020 The 46th Annual Conference of the IEEE Industrial Electronics Society. IEEE. 18 Oct 2020, 2020
S. A. Ansari, J. N. Davidson & M. P. Foster - Impact of magnetic coupling in transverse flux permanent magnet machine for wind power application
IET PEMD 2020, 2020
R. Clark, A. Duke, R. Kumar, Zi-Q Zhu, D KK Padinharu, G-J Li, A. Griffo, M. Odavic, M. P. Foster, D. A. Stone, L. Huang & A. ThomasThis paper is devoted to three dimensional (3D) finite element method (FEM) based examination of the interphase magnetic coupling in a three-phase transverse flux machine (TFM). The comprehensive analysis shows that the axially stacked phases are magnetically coupled, which leads to an unbalanced contribution of torque from each phase and therefore a reduced value of resulting three-phase torque. This issue can be addressed by introducing an axial air gap in the rotor back-iron between the phase modules or selecting a proper magnet arrangement. Following a discussion of different magnet arrangements, it is found that the optimal combination is dependent on the flux patterns produced by the armature reaction and the magnets. - Comparative evaluation of Si MOSFET-based soft switching DC-DC converters and GaN HEMT-based hard switching DC-DC converters
IET PEMD 2020, 2020
S. Ansari, J. N. Davidson & M. P. Foster - A large-scale battery energy storage system simulation tool for studying cell variation
IET PEMD 2020, 2020
Z. Wang, J. Davidson & M. P. Foster - Multivariable generalized predictive speed control for permanent magnet synchronous machine with enhanced luenberger speed observer
IET PEMD 2020, 2020
T. Wang, Z. Zhu, M. P. Foster, D. A. Stone, A. Griffo, M. Odavic & G-J Li - Sensorless control for permanent-magnet synchronous machine drives considering resistance asymmetry
IET PEMD 2020, 2020
T. Liu, Z. Zhu, D. A. Stone, M. P. Foster, M. Odavic, A. Griffo, G. Li & Z. Wu - Output voltage regulation for piezoelectric transformer-based resonant power supplies using phaselocked loop control
IET PEMD 2020, 2020
Z. Yang, M. P. Foster & J. N. Davidson - Comparative Study of Parameter Mismatch on Different Model Predictive Controls for PMSM Drives
2020 IEEE 9th International Power Electronics and Motion Control Conference (IPEMC2020-ECCE Asia), 2020
T. Wang, Z. Q. Zhu, N. M. A. Freire, M. P. Foster & D. A. Stone All AuthorsModel predictive control (MPC) is known for its good dynamic performance, but the parameter mismatch issue has long been concerned. In order to help evaluating and improving the control performance of MPC, a comprehensive knowledge of the side-effects of a variety of possible parameter mismatches on different MPC types is highly required. In this paper, three main MPC types, i.e. the continuous-control-set MPC (CCS-MPC), the finite-control-set MPC (FCS-MPC), and the generalized predictive control (GPC), are considered for the permanent magnet synchronous machine (PMSM) drive. Three types of parameter mismatch are considered, i.e. mismatches of the stator resistance, stator inductance, and permanent magnet flux linkage. Their side-effects, including the steady-state control errors and the stability issues, on all the three MPC types are theoretically analyzed and compared. Simulation results are provided to validate the correctness of the comparison study.
https://doi.org/10.1109/IPEMC-ECCEAsia48364.2020.9368219 - Influence of Demagnetization on Selecting the Optimum Slot/Pole Number Combination for 3MW Surface Mounted Permanent Magnet Vernier Machine
22nd International Conference on Electrical Machines and Systems (ICEMS2019), 2019
D. Kumar, G.J. Li, M. P. Foster, D. A. Stone, A. Griffo, R. Clark & A. ThomasElectromagnetic performance of Vernier machines largely depends on choosing the correct slot/pole number combinations. For a given gear ratio, designs with different slot/pole number combinations are possible. This paper investigates the impact of these slot/pole number combinations on electromagnetic performance such as torque, power factor and demagnetization. The study is carried out through detailed finite element analysis on a 3MW outer rotor direct drive generator targeted at wind power application. The torque/cost, torque/mass and efficiency, which are critical parameters for this application, are compared with a conventional direct drive PM generator. The study shows that Vernier designs with lower values of slot/pole number combinations exhibit much better performance in terms of torque and power factor. However, the potential magnet demagnetization and also core saturation limit these designs and hence play a critical role in selecting the optimal slot/pole number combination.
https://doi.org/10.1109/ICEMS.2019.8921618 - Study of Manufacturing Tolerance of Modular Permanent Magnet Machines: Segment Radial Displacement
2019 IEEE International Electric Machines & Drives Conference (IEMDC), 2019
B. Ren, G.-J. Li, Z. Q. Zhu, M. P. Foster & D. A. StoneIn this paper, the investigation about the influence of manufacturing tolerance on the electromagnetic performance of modular PM machines with segmented stator has been carried out. Two typical slot/pole number combinations such as 12-slot/10-pole and 12-slot/14-pole have been chosen for case studies. The manufacturing tolerances scenarios are focused on the radial stator segment displacement. Firstly, the influence on the phase back-EMF as well as the on-load torque is investigated. By doing so, the cases where the influence of manufacturing tolerance are the most significant can be identified. This allows for further studying the influence of flux gap widths on the performance of the modular PM machines. Through the analyses of the back-EMF, the on-load torque, the cogging torque and the unbalanced magnetic force, the manufacturing tolerance withstand capability of the 12-slot/10-pole and 12-slot/14-pole modular PM machines can be assessed. It is found that the 12-slot/10-pole modular PM machines have better manufacturing tolerance withstand capability compared with the 12-slot/14-pole modular PM machines.
https://doi.org/10.1109/IEMDC.2019.8785073 - Coordinated Dispatch Performance of AC Grid-Connected Energy Storage Systems
2019 IEEE Milan PowerTech, 2019
R Todd, A. M. Pavan, T. Feehally, A. J. Forsyth, S. Nejad, D. T. Gladwin, D. A. Stone & M. P. FosterCommanding multiple energy storage systems (ESSs) to provide grid balancing services is a popular approach to manage the finite state-of-charge (SoC) of each asset. The communication between the individual assets can be a challenge due to their distribution throughout the land-based power network. Two battery-based ESS, a 240 kW 180 kWh lithium ion polymer (nickel manganese cobalt oxide (NMC)) based system located behind-the-meter on a 400 V power network, and a 2 MW 1 MWh lithium-titanate system, which is located at an 11 kV residential substation, are located 100 km apart. Their performance when delivering grid support services using simple time or frequency synchronised coordinated dispatch methods is evaluated in this research. Experimental results from the real and reactive power step profiles show both energy storage systems (ESSs) are correctly time dispatched, and operate according to the power profile. In the real power test, the 2 MW ESS had a larger SoC change at the end of the discharge period when compared to the 240 kW system, due to its higher power to energy ratio. The reactive power test demonstrated that both systems were able to influence their local voltage. The dynamic demand response profile shows the successful use of frequency to determine the dispatch, and both ESSs delivered or absorbed the correct real power for the frequency deviation, while achieving a 100% service performance measure.
https://doi.org/10.1109/PTC.2019.8810416 - Comparative Studies of Fractional/Integer-Slot Consequent Pole Permanent Magnet Machines
2019 IEEE International Electric Machines & Drives Conference (IEMDC), 2019
R. Zhou, G.-J. Li, Z. Q. Zhu, Y. X. Li, M. P. Foster & D. A. StoneThis paper compares several different consequent-pole permanent magnet machines (CPM) with fractional-slot (FS) concentrated-winding and integer-slot (IS) distributed-winding. The electromagnetic performance of the proposed machines such as the open-circuit air-gap flux density, back-EMF, cogging torque, on-load torque, inductances, losses and torque/power-speed characteristics are compared by 2D finite element analysis. The reason about the existence of the even-harmonics in the phase back-EMF of the CPMs is explained from the perspective of winding factor. It is also found that the FS-CPMs have better flux weakening capability compared with the IS-CPMs although their average torque might be slightly lower due to lower winding factor, which could be compensated by shorter end-winding.
https://doi.org/10.1109/IEMDC.2019.8785218 - Investigation of Integer/Fractional Slot Consequent Pole PM Machines with Different Rotor Structures
2019 IEEE International Electric Machines & Drives Conference (IEMDC), 2019
R. Zhou, G.-J. Li, Z. Q. Zhu, Y. X. Li, M. P. Foster & D. A. StoneThis paper investigates several integer and fractional slot consequent-pole permanent magnet machines (CPM) with different rotor structures. Besides the conventional SPM rotor, the most commonly used rotor structures for conventional IPMs such as the I-shape (I-IPM) and V-shape (V-IPM) are employed for comparison. The electromagnetic performance such as back-EMF, on-load torque, PM eddy current losses and dynamic characteristics are compared using 2D finite element analysis. In addition, the 3D thermal models including end-windings and end plates are established to predict the temperature variations in different machines. Then the demagnetization withstand capabilities of different CPMs are analysed by taking into account the temperature influence on magnet working point. It is found that the CPMs with IPM rotors have much better demagnetization withstand capabilities compared with their SPM counterparts.
https://doi.org/10.1109/IEMDC.2019.8785273 - Equivalent circuit parameter extraction methods for piezoelectric transformers
2019 European Conference on Power Electronics and Applications (EPE'19 ECCE-Europe), 2019
J. Forrester, J. N. Davidson, M. P. Foster & D. A. StoneThree methods for extracting the equivalent circuit components of a piezoelectric transformer areproposed. Each of the methods is presented in detail, describing both the measurement setup and thealgorithm used for extraction. A full comparison of the implementation complexity and extractionaccuracy is performed using experimentally measured data. Finally, the performance of each techniquein the presence of measurement noise is explored. The comparison presented allows the reader todetermine which technique is most suitable for their application.
https://doi.org/10.23919/EPE.2019.8915189 - Online electrolytic capacitor prognosis system for PWM drives
2019 European Conference on Power Electronics and Applications (EPE'19 ECCE-Europe), 2019
R. Rajapakse, Kankanamalge, M. P. Foster & J. N. DavidsonElectrolytic capacitors are ubiquitous in power electronic systems owing to their relatively large capacitance-to-volume ratio provided by virtue of their anodised electrode and electrolyte. As the capacitor ages, the electrolyte solution present in the capacitor is known to reduce and this leads to an increase in the equivalent series resistance (ESR) and a reduction in the capacitance. End-of-life for electrolytic capacitors is indicated by an increase in ESR by a factor of two. Here a prognostic system is proposed that can measure the ESR of a capacitor while it is operating in a PWM circuit. By using lock-in amplifiers synchronised to the PWM fundamental frequency, it is possible to extract precisely capacitor ripple voltage and ripple current. These signals are then combined to provide an estimate for the ESR. - Suppressing Leakage Current for Cascaded H-bridge Converters in Grid-Tie Renewable Energy Systems
2019 European Conference on Power Electronics and Applications (EPE'19 ECCE-Europe), 2019
I. Gunsal, D. A. Stone & M. P. FosterPhotovoltaic panels contain parasitic capacitance causing leakage currents in transformerless converters, which raises safety concerns and reduces system performance. This work presents a common-mode equivalent circuit for Cascaded H-Bridge (CHB) converters with symmetrical filter configuration. In this paper, we develop a novel modulation technique for CHB multilevel converter, which can suppress the leakage current. The simulation and experimental results for standard phase shifted pulse width modulation and novel leakage reduction pulse width modulation (LRPWM) are provided. It is found that LRPWM is more effective in suppressing leakage current. - Adaptive control method to manage SOC for energy storage in DC electric railways
IECON 2019 - 45th Annual Conference of the IEEE Industrial Electronics Society, 2019
H. Alnuman, D. T. Gladwin, M. P. Foster & T. FanthamIncorporating energy storage systems (ESSs) into electric railways has been shown to be advantageous for energy saving and power quality enhancement. For DC railways, the connection method of the ESS to the track may impose restrictions on charging and discharging the ESS to control the state of charge (SOC). Without management of the SOC, the ESS is shown in this study to reach minimum or maximum limits, reducing its effectiveness due to unavailability. Whilst it is possible to oversize the capacity of ESS, this incurs increased costs and requires more physical space. The main objective of this study is to propose and validate a control algorithm that prevents the ESS from reaching the maximum or minimum SOC limits whilst maintaining the benefits of the system. The main concept of the proposed control method is to dynamically update the voltage and current setpoints of the ESS to manage its SOC. The control algorithm is implemented in the MATLAB software and the simulation results are validated against experimental results, using a track emulator and supercapacitor. The findings demonstrate that, with appropriate dynamic charge/discharge control, the SOC levels can be adequately managed and no external load or source is required.
https://doi.org/10.1109/IECON.2019.8927602 - Modelling of Bidirectional CLLC Resonant Converter Operating under Frequency Modulation
2019 IEEE Energy Conversion Congress and Exposition (ECCE), 2019
L. F. Martins, D. A. Stone & M. P. FosterThis paper proposes the application of three modelling techniques for analysis of bidirectional resonant converters with capacitor-inductor-inductor-capacitor (CLLC) compensation network operating under frequency modulation. Fundamental Mode Approximation (FMA), state-variable and cyclic-averaging models are obtained and compared. The simulation results for forward and reverse power flow direction are verified against Spice simulation and results obtained from literature. All models could successfully predict the behavior of the converter but state-variable and cyclic-averaging techniques showed better accuracy. Execution time is compared confirming that cyclic-averaging is the method with fastest execution.
https://doi.org/10.1109/ECCE.2019.8913203 - Novel Control Method for Improving Energy Efficiency of DC Electric Railways
2019 IEEE 15th International Conference on Control and Automation (ICCA), 2019
H. Alnuman, D. T. Gladwin & M. P. FosterIn DC electric railways, trains dissipate excess regenerative braking energy in braking resistors. This energy cannot be recovered and increases the temperature inside the underground tunnels requiring further energy for cooling. Consequently, it is beneficial to use energy storage systems (ESSs) to capture the regenerative energy and release it back to the trains when needed. ESSs have been shown in literature to enable energy saving, reduce peak demand, and minimise voltage peaks and troughs. This paper focuses on the high power and high energy requirements of the ESS that exceed the capabilities (within physical and cost constraints) of the state of the art storage technologies such as batteries. In this study it is discussed how batteries can be combined with supercapacitors to create a Hybrid ESS (HESS) that has high energy and high power capability. The limitations of using such a system in this application are discussed and a novel control method is proposed to maximise potential gains. This novel control method is implemented as an electrical model of a DC electric railway that is designed using Matlab. The simulation results indicate that the proposed control methodology can increase the energy efficiency of the DC electric railway while minimising the ESS size, cost, and degradation.
https://doi.org/10.1109/ICCA.2019.8899576 - A transformerless single-phase multilevel converter for grid-tie renewable energy systems
4th Annual Conference in Energy Storage and Its Applications, 4th CDT-ESA-AC, 2019
I. Gunsal, D. A. Stone & M. P. FosterA multilevel converter produces a high quality output voltage waveform therefore requires less filtering in grid-tie systems. Cascaded H-bridge converter is a favourable topology for a hybrid renewable and storage system due to isolated DC source requirement. This converter is designed to interface a hybrid photovoltaic and battery system to the utility grid, making DC sources more accessible. In this study, a nine-level cascaded H-bridge converter is presented. A closed loop controller implemented in synchronous rotating frame is used to control active and reactive power independently. The control strategy is implemented in a simulation environment and then validated with experimental results. The generated output current waveforms are analysed when operated with various sinusoidal pulse width modulation techniques such as phase disposition pulse width modulation. It is found that the converter has a low total harmonic distortion that conforms to IEEE 1547 standard.
https://doi.org/10.1016/j.egyr.2020.02.029 - Performance comparison between consequent-pole and inset modular permanent magnet machines
IET PEMD 2018, 2018
B. Ren, G. J. Li, Z. Q. Zhu, M. P. Foster & D. A. Stone - Comparative investigation of stator-mounted permanent magnet machines under fault conditions
IET PEMD 2018, 2018
P. Taras, G. Li, Z. Zhu, M. P. Foster & D. A. Stone - A PLL controller for achieving zero voltage switching (ZVS) in inductorless half-bridge drive piezoelectric transformer resonant power supplies
IET PEMD 2018, 2018
M. P. Foster, J. N. Davidson, D. A. Stone & R Yappa - Automated design tools for piezoelectric transformer-based power supplies
IET PEMD 2018, 2018
J. Forrester, J. N. Davidson, M. P. Foster, D. A Stone & E. L. Horsley - State-variable and cyclic-averaging analysis of bidirectional CLLC resonant converters
IET PEMD 2018, 2018
L. Farias-Martins, D. A. Stone, M. P. Foster - A forecasting battery state of charge management strategy for frequency response in the UK system
2018 IEEE International Conference on Industrial Technology (ICIT), 2018
B. Gundogdu, D. T. Gladwin, M. P. Foster, and D. A. StoneFrequency regulation is an important part of ancillary services in the UK power system to mitigate the impacts of variable energy resources and uncertainty of load on system frequency. The National Grid Electricity Transmission (NGET), the main distribution network operator in the UK, have introduced various frequency response services which are developed to provide real-time response to deviations in the grid frequency. This paper aims to meet the balancing requirement of NGET for UK frequency response service. Flexible and fast response capabilities of battery energy storage systems (BESSs) make them an ideal candidate to provide grid frequency regulation. This paper presents a control algorithm that supplies a charge/discharge power output with respect to deviations in the grid frequency, whilst managing the state-of-charge (SOC) of the BESS to maximise the utilisation of the available energy capacity. In this paper, a forecasting battery SOC management and a battery charge/discharge management strategy have also been developed to maximize battery availability for grid frequency response delivery. A model of a 2MW/1MWh lithium-titanate BESS, that is experimentally validated, is used to simulate historical real-time frequency data obtained from NGET to verify the proposed algorithm based on the control of an experimentally validated battery model.
https://doi.org/10.1109/ICIT.2018.8352443 - Development of an electrical model for multiple trains running on a DC 4th rail track
IEEE International Conference on Environment and Electrical Engineering and 2018 IEEE Industrial and Commercial Power Systems Europe (EEEIC / I&CPS Europe), 2018
H. H. Alnuman, D. T. Gladwin and M. P. FosterThe electrical modelling of rail tracks with multiple running trains is complex due to the difficulties of solving the power flow. The trains' positions, speed, and acceleration change instantly which makes the system nonlinear. Additionally, the nonreversible substations are another reason for the nonlinearity of the system. These nonlinear characteristics of the rail system make the power flow analysis more complicated. In this paper, a simple method for modelling electric railways has been used to avoid complicated algorithms to solve the power flow. The method depends mainly on modelling the mechanical and electrical characteristics of the full rail track system using the simulation tool Simscape, which has been developed by MathWorks. The model is able to provide the track voltage and also the trains voltages. Through the implementation of Energy Storage Systems (ESS) it will be possible to improve the energy efficiency of electric railways by effectively controlling the rail track voltage and the trains contact voltages.
https://doi.org/10.1109/EEEIC.2018.8494511 - Effect of spurious resonant modes on the operation of radial mode piezoelectric transformers
PCIM Europe 2018; International Exhibition and Conference for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management , 2018
J. Forrester, J. N. Davidson, M. P. Foster & D. A. StoneThis paper analyses both the intentional and unwanted resonant modes of radial piezoelectric transformers (PTs). lnitially, finite element analysis is performed to discover the type of spurious modes prevalent is radial mode PTs. From this, analysis is performed on these modes and a relationship between resonant frequency and geometry is found. The effect of spurious modes on the efficiency of a typical PT is simulated using an equivalent circuit model in LTSpice and Simulink. A number of design rules are generated based on the findings. Results show that, in most cases and by careful design, spurious modes can be avoided. - An Experimental Investigation of MOSFET Intrisic Body Diode Performance
IEEE International Symposium on Industrial Electronics, 2018
A. Petersen, D. A. Stone & M. P. FosterIn order to enable evaluation of power loss during both forward and reverse conduction of intrinsic body diodes in power MOSFETs, an experimental series is performed to derive a set of expressions to approximate performance. A set of relevant performance metrics are selected, and then tested over a range of devices. Any correlation between these metrics and properties of these devices commonly provided by device manufacturers are investigated and quantified. A set of empirical expressions are derived from the closest correlations found, that therefore enable an estimation of performance of the body diode without any prior testing, with a predicted margin of error.
https://doi.org/10.1109/ISIE.2018.8433636 - A Unique Pulse Width Modulation to Reduce Leakage Current for Cascaded H-Bridge Inverters in PV and Battery Energy Storage Applications
Energy Procedia, 2018
I. Gunsal, D. A. Stone & M. P. FosterCascaded H-bridge (CHB) inverters operate with isolated DC sources, which makes them a favorable topology for hybrid-interfaced applications. Parasitic capacitance of grounded photovoltaics (PV) results in leakage currents that may deteriorate the system performance and raise safety concerns. In order to address this problem, a common-mode equivalent circuit for a multilevel CHB is illustrated. The study reveals that common modulation techniques such as phase shifted pulse width modulation fail to suppress the leakage current. A unique modulation scheme, based on considering the switching states is proposed in order to ensure that the topology conforms to the transformerless inverter regulations and standards such as VDE-0126-1-1. Simulation study results for conventional and proposed modulation methods are presented and analyzed in a symmetrical grid inductance filter circuit
https://doi.org/10.1016/j.egypro.2018.09.032 - Arc-Flash Calculation Comparison for Energy Storage Systems
Universities Power Engineering Conference (UPEC) , 2017
S. Royston, D. Strickland, D. A. Stone, D. T. Gladwin, M. P. Foster & S NejadThere is an increasing prevalence of energy storage systems on the electricity grid network. However, as of yet, there is no overriding standard on how to deal with DC arc-flash calculations and subsequent determination of the PPE requirements for a DC system within the UK. This paper compares various published DC arc-flash calculations using a case study based approach. The paper uses data available from the Willenhall Energy Storage System.
https://doi.org/10.1109/UPEC.2017.8232005 - Switching loss optimisation of cascaded H-bridge converters for bidirectional grid-tie battery energy storage systems
IECON 2017 - 43rd Annual Conference of the IEEE Industrial Electronics Society, 2017
A. Petersen, D. A. Stone, M. P. Foster & D. T. GladwinMultilevel converters are an emerging industrial technology and are the subject of a substantial amount of research. However, they are yet to find their way into many mainstream engineering applications. This paper presents a method of quantifying the benefits and disadvantages of multilevel converters of increasing order. The analysis focuses on the cascaded H-bride topology for grid-tie battery inverter applications. The analysis includes both semiconductors losses and semiconductor driver losses. It is shown that multilevel converters can have significant benefits over their conventional counterparts, but that more levels is not necessarily better. This paper's important result is to create a quantitative measure of the pros and cons of multilevel architecture.
https://doi.org/10.1109/IECON.2017.8216271 - Parameterisation and online states estimation of high-energy lithium-titanate cells
IECON 2017 - 43rd Annual Conference of the IEEE Industrial Electronics Society, 2017
S. Nejad, D. T. Gladwin, M. P. Foster & D. A. StoneIn 2013, the University of Sheffield commissioned a 1 MWh lithium-titanate (LTO) battery energy storage system (BESS), directly connected to the grid through an 11 kV feed. With a view to later on develop a comprehensive model structure for the whole battery pack - key to many online battery management system (BMS) operations - in this paper, an in-depth frequency-domain analysis is performed on one of the constituent 2.3 V 20 Ah LTO cells, using a potentiostatic sine-swept method. A first-order resistor-capacitor (RC) equivalent-circuit model is put forward, capable of representing the LTO cell's impedance magnitude with an error of less than 0.1 m?. Thereafter, the performance of the proposed one-RC model structure for online SOC estimation is experimentally verified using the Extended Kalman Filter (EKF). The verification test is performed on a dynamic pulsed-power profile, derived from a real grid frequency-support service that is offered by several BESSs in the UK.
https://doi.org/10.1109/IECON.2017.8217342 - Performance evaluation of SiC MOSFET in 5-level single phase converter
IET PEMD 2016, 2016
J. D. Gomez-Palomino, M. P. Foster, D. A. StoneThe use of silicon carbide (SiC) semiconductor power devices has been studied and evaluated in a wide variety of converters. The work presented in this paper shows the performance of C2M SiC MOSFETs compared to Si devices operating as switching elements in a 5-level, single phase, multilevel converter. The paper describes the multilevel converter platform used to undertake the evaluation study and experimental results for the operating temperature of the MOSFETs, and conversion efficiency are shown for frequencies ranging from 20 kHz to 80 kHz. Finally, a discussion of the results obtained to highlight the differences in the performance of the Si and SiC devices and the feasibility of using SiC in MLC.
https://doi.org/10.1049/cp.2016.0360 - Battery charger with a capacitor-diode clamped LLC resonant converter
IET PEMD 2016, 2016
C. W. Tsang, C. M. Bingham, M. P. Foster, D. A. Stone & J. M. Leach - Minimum charge-recovery time control with parallel connected
buck converters
IET PEMD 2016, 2016
C. W. Tsang, C. M. Bingham, M. P. Foster, D. A. Stone, J. N. Davidson & J. M. Leach - Repurposing ATX Power Supply for Battery Charging Applications
IET PEMD 2016, 2016
S. A. Abuzed, M. P. Foster & D. A. Stone - Electrolytic Capacitor Age Estimation Using PRBS-based Techniques
PCIM Europe 2016, 2016
D.A. Hewitt, J. E. Green, J. N. Davidson, M. P. Foster & D. A. Stone - Design procedure for pot-core integrated magnetic component
PCIM Europe 2016, 2016
M. P. Foster, A. J. Fairweather & G. Ashley - Multi-stage LLC resonant converters designed for wide output voltage ranges
PCIM Europe 2016, 2016
C-W. Tsang, C. M. Bingham, M. P. Foster, D. A. Stone & J. Leach - Examining Contrasting Excitation Modes within Battery Characterisation using Maximum Length Sequences
PCIM Europe 2016, 2016
A. J. Fairweather, D. A. Stone & M. P. Foster - Battery energy storage systems for the electricity grid: UK research facilities
IET PEMD 2016, 2016
T. Feehally, A. J. Forsyth, R. Todd, M. P. Foster, D. T. Gladwin, D. A. Stone & D. Strickland - Observations on Changes to Electrolytic Capacitor Electrical Properties Caused by Gamma Irradiation
9th International Workshop on Impedance Spectroscopy, 2016
D. Hewitt, J. Davidson, J. E. Green, M. P. Foster & D. A. StoneElectrolytic capacitors form an important part of most drive systems. This paper considers the effect of gamma irradiation on the electrical properties of electrolytic capacitors. To achieve this, electrolytic capacitors with capacitances ranging from 47 ?F to 1000 ?F are exposed to radiation levels ranging from 0 to 910 kGy. Measurements of the capacitors capacitance and equivalent series resistance are performed before and after exposure to radiation to determine the effect on the electrical properties. It is seen that the irradiation primarily impacts the equivalent series resistance, with some capacitors exhibiting as much as a 60% increase. - Measurement of Electrical Parameters of Electrolytic Capacitors Using Real-World Drive Waveforms for State-of-Health Determination
9th International Workshop on Impedance Spectroscopy, 2016
D. Hewitt, J. E. Green, J. N. Davidson, M. P. Foster & D. A. StoneElectrolytic capacitors form an important part of most drive systems. Consequently a method of determining the state-of-health of these capacitors without having to remove them from the system would be of value. In this paper a method of achieving this is proposed. This is achieved by measuring the current through and the voltage across the dc link capacitor within a brushless dc motor drive; from these values the impedance spectrum is calculated. From these measurements the capacitance and resistance values of the capacitor are calculated. This technique forms a useful prognostic tool for power electronic drive systems where changes to these electrical parameters are a good indicator of the state-of-health of the capacitor. Real-world results taken from an experimental system demonstrate that increases in capacitor resistance can be clearly observed. - A Model-based Predictive Current Controller for a back-to-back connected multilevel converter aerospace starter-generator
IECON 2016 - 42nd Annual Conference of the IEEE Industrial Electronics Society, 2016
R. H. Williams, M. P. Foster & D. A. StoneThe application of predictive current control to a multilevel converter is explored for application in an aerospace starter-generator system to investigate how such as system may be used to limit the harmonic distortion in the starter-generator's stator current waveform and also at the point of common connection with the aircraft supply system. The proposed system is analyzed, and a prototype converter and aerospace generator are used to provide experimental testing results. During testing a dynamometer is used to reproduce the turbines torque speed characteristics.
https://doi.org/10.1109/IECON.2016.7793150 - Observation of electrolytic capacitor ageing behaviour for the purpose of prognostics
IECON 2016 - 42nd Annual Conference of the IEEE Industrial Electronics Society, 2016
D. A. Hewitt, J. E. Green, J. N. Davidson, M. P. Foster & D. A. StoneElectrolytic capacitors are an important component within power electronics systems which are known to exhibit poorer reliability compared to other components within the system. In this paper, the changes in electrical parameters (capacitance and equivalent series resistance) which occur as electrolytic capacitors age are characterised at regular intervals over the life of the capacitors. Ageing is observed under three different bias conditions: no bias; constant voltage bias and square wave excitation and at two different ambient temperatures. The data captured within this work presents the changes in capacitor properties from new, reaching to a point which the capacitor parameters have changed sufficiently, such that the capacitor can be considered to have failed. Such data will prove valuable in the development of a system designed to determine the state of health of a capacitor, or could be used to predict its remaining useful lifetime.
https://doi.org/10.1109/IECON.2016.7793614 - Thermal Analysis Using 2-Dimensional Impedance Spectroscopy and Pseudorandom Binary Sequences
9th International Workshop on Impedance Spectroscopy, 2016
J. N. Davidson, M. P. Foster &D. A. Stone - Modelling the enhancement to the thermal performance of encapsulants using thermally conductive filler materials
PCIM Asia 2015, 2015
D. A. Hewitt, D. A. Stone & M. P. Foster - Practical Design Considerations of Cascaded Hybrid Battery Storage Systems
2015 17th European Conference on Power Electronics and Applications (EPE'15 ECCE-Europe), 2015
I. Mosely, A. Middleton, D. Strickland, N. Mukherjee, D. A. Stone, D. T. Galdwin, D. Rogers & M. P. FosterThe high cost of batteries has led to investigations in using second-life ex-transportation batteries for grid support applications. Vehicle manufacturers currently all have different specifications for battery chemistry, arrangement of cells, capacity and voltage. With anticipated new developments in battery chemistry which could also affect these parameters, there are, as yet, no standards defining parameters in second life applications. To overcome issues relating to sizing and to prevent future obsolescence for the rest of the energy storage system, a cascaded topology with an operating envelope design approach has been used to connect together modules. This topology offers advantages in terms of system reliability. The design methodology is validated through a set of experimental results resulting in the creation of surface maps looking at the operation of the converter (efficiency and inductor ripple current). The use of a pre-defined module operating envelope also offers advantages for developing new operational strategies for systems with both hybrid battery energy systems and also hybrid systems including other energy sources such as solar power.
http://dx.doi.org/10.1109/EPE.2015.7309434 - An experimental evaluation of thermally conductive filler loaded encapsulant composites
IET PEMD 2014, 2014
D. Hewitt, D A. Stone & M. P. FosterIn this paper, epoxy/aluminium oxide powder composites designed for use as encapsulants are produced and thermally characterised. Experimental results obtained for a variety of filler concentrations, sample thicknesses and manufacturing methods are presented and compared to analytical and empirical models from literature. Further to this the effects of modifying analytical models using experimental data are considered. This yields models which allow the bulk thermal conductivity of these composites to be predicted more accurately than when the models were used in a purely analytical manner. Furthermore, the effect on thermal conductivity of uneven filler distribution within the samples is considered.
http://dx.doi.org/10.1049/cp.2014.0403 - Real-time temperature monitoring and control for power electronic systems under variable active cooling by characterisation of device thermal transfer impedance
IET PEMD 2014, 2014
J. Davidson, D. A. Stone & M. P. FosterThis paper presents a technique for predicting the temperature response of a system to arbitrary power dissipation in its constituent elements under variable air-cooling. The thermal impedance is first characterised under the available range of cooling levels. This data is used to predict the thermal response directly. Practical results show good agreement with predicted temperature waveforms. The technique is extended provide active control to maintain steady device temperatures by using power dissipation data without reference to actual temperature. This successfully reduces thermal cycling without requiring additional sensors.
http://dx.doi.org/10.1049/cp.2014.0496 - ATX power supply derived MPPT converter for cell phone charging applications in the developing world
IET PEMD 2014, 2014
D. Rogers, J. E. Green, M. P. Foster, D. A. Stone, D. M. K. Schofield, A. Buckley & S. AbuzedRecently, a new method has evolved for the recovery of materials in Waste Electrical and Electronic Equipment (WEEE) namely, the repurposing of constituent components for second life. Such an approach is opposed to the traditional raw materials harvesting that is the norm, which in the majority of cases leads to the destruction of serviceable parts together with all other non-recycling materials. This paper presents a novel photovoltaic system suitable for disparate population centres in the developing world utilising repurposed components from discarded computer power supplies.
http://dx.doi.org/10.1049/cp.2014.0446 - Variable PWM step-size for modified hill climbing MPPT PV converter
IET PEMD 2014, 2014
S. A. Abuzed, M. P. Foster & D. A. StoneMaximum power point tracking (MPPT) converters are often used to continuously track the optimum operating point of a solar panel. Due to their low-cost and ease of implementation, hill climbing (HC) MPPT methods based on the perturbation principles are most commonly used to extract the maximum power (MP). However, the efficiency of these methods are highly influenced by the continued oscillation around the maximum power point. In order to circumvent the problem of continued oscillations and increase efficiency in steady-state and dynamic conditions a modified MPPT algorithm is proposed. The algorithm is simulated in Simulink/Matlab and validated with an experimental. Results from the experiment indicate higher efficiency and better performance in both steady-state and dynamic conditions.
http://dx.doi.org/10.1049/cp.2014.0489 - A low cost photovoltaic maximum power point tracking buck converter for cell phone charging applications
PCIM 2014 Nuremberg, 2014
D. Rogers, J. E. Green, M. P. Foster, D. A. Stone, D. M. K. Schofield, S. A. Abuzed & A. BuckleyAt present resource extraction techniques remain the priority among Waste Electrical and Electronic Equipment (WEEE) recyclers. As a result, fully functional components are often destroyed together with other nonrecyclable materials. Yet, another process stream is evolving, namely repurposing of specific types of WEEE for alternative uses after minimal modification. This paper presents a Maximum Power Point tracking (MPPT) buck converter suitable for cell phone charging in remote areas of the developing world utilising discarded computer power supplies. - Computationally Efficient Method and Investigation of Operational Envelopes of Hybrid and Electrically Excited Machines
Ninth International Conference on Ecological Vehicles and Renewable Energies (EVER) Vehicles and Renewable Energies (EVER), 2014
W. Q. Chu, X. Liu, Z. Q. Zhu, D. A. Stone, M. Foster, I. Urquhart & J. GreenoughIn this paper, an investigation on the operational envelopes of electrically excited (EE) and hybrid excitation (HE) machines for electric vehicles (EV) is highlighted. A computationally efficient calculation method utilising 2D scanning of finite element analyses (FEA) having different d- and q-axis currents is developed. Compared with the conventional method, which typically requires 3D scanning of FEA having different excitation, d- and q-axis currents, the proposed method significantly reduces the complexity and the computation time. The accuracy of the new method is validated by direct FE results. It is further found that even for EE and HE machines the maximum constant power operation in the high speed range is achieved by employing flux weakening control by the armature current instead of applying a lower excitation current, which is also validated by analytical analyses.
http://dx.doi.org/10.1109/EVER.2014.6844131 - Iron Loss Calculation in Permanent Magnet Machines under Unconventional Operations
IEEE International Magnetics Conference INTERMAG 2014, 2014
W. Q. Chu, Z. Q. Zhu, X. Liu, D. A. Stone & M. P. FosterIn order to reduce system weight, volume and cost, various integrated designs are being developed [1]-[3] in which permanent magnet (PM) machines are required to realize additional functions. Commonly this results in unconventional modes of operation where, for instance, the high frequency (e.g. 10kHz) alternating armature field is only a fraction (e.g. <2%) of the constant PM field. It is found in this paper that the iron loss of PM machines undertaking such unconventional operations cannot be calculated accurately using conventional finite element (FE) methods due to fake iron loss harmonics. Thereafter, further investigations are carried out to identify the causes and a new method of iron loss calculation is developed and validated by measurement. - Viability of second-life use of electric and hybrid-electric vehicle battery packs
IEEE IECON 2013, 2013
D. T. Gladwin, C. R. Gould, D. A. Stone & M. P. FosterIn order for successful second-life implementation of Electric Vehicle (EV) battery packs, the viability of the intended second-life use must be ascertained based on a cost-benefit analysis and technical appraisal of the estimated condition of the available battery packs. This paper discusses the issues in measuring State-of-Health (SoH) and other battery condition metrics of a battery pack. Measurements on real-life battery packs sent for recycling are taken that demonstrate a typical 85% SoH; slightly higher than predicted by Original Equipment Manufacturers (OEM). A model is introduced that can simulate the energy demand in a home/dwelling being met by a number of sources including mains (utility) power, photovoltaic generation (PV), and second-life battery storage. The model is applied to three scenarios using second-life battery storage, to create energy costs savings through time-shifting of energy using on-peak/off-peak electricity tariffs. For each scenario a cost-benefit analysis is produced, indicating that whilst energy costs savings can be achieved, excessive usage of the battery pack can cause the payback period of the capital investment to be longer than the predicted second-lifetime of the battery pack. However, the final scenario demonstrates that combining the battery pack with local generation, such as PV, yields cost savings that are significant at 75%, and the payback period is within the estimated lifetime of the battery pack.
http://dx.doi.org/10.1109/IECON.2013.6699425 - Second life of computer power supplies in PV battery charging applications
European Conference on Power Electronics and Applications (EPE 2013), 2013
D. Schofield, S. Abuzed, M. P. Foster, D. A. Stone, D. Rogers & J. E. GreenThis paper proposes and investigates the second life application of computer power supplies for PV applications. The emphasis is on reclamation and reuse of operational power supply components and circuits. Results shown verify operational limits of the power supply validating its suitability for PV-MPPT systems.
http://dx.doi.org/10.1109/EPE.2013.6634653 - Repurposing of ATX computer power supplies for PV applications in developing countries
IEEE International Conference on Renewable Energy Research and Applications (ICRERA 2013), 2013
D. Rogers, J. E. Green, M. P. Foster, D. A. Stone, D. M. K. Schofield, S. Abuzed & A. BuckleyTo date, the recycling process for most Waste Electrical and Electronic Equipment (WEEE) simply involves recovering materials using pyrometallurgy and similar techniques due to the difficultly of removal of their constituent components. Thus most components are incinerated with all other non-recyclable materials. However, for specific types of WEEE an alternative approach has evolved namely the reuse or repurposing of particular parts of the equipment suitable for second life. This paper presents a novel photovoltaic system suitable for disparate population centers in the developing world utilising the ubiquitous ATX computer power supply.
http://dx.doi.org/10.1109/ICRERA.2013.6749893 - A comparative study of on-board bidirectional chargers for electric vehicles to support vehicle-to-grid power transfer
IEEE 10th International Conference on Power Electronics and Drive Systems (PEDS 2013), 2013
C. R. Gould, K. Colombage, J. Wang, D. A. Stone & M. P. FosterIn order to provide stabilization of the utility power supply during peak-load times, the possibility for use of an Electric Vehicle's (EV) traction battery for energy buffering has been proposed, and an On-Board Bidirectional Charger is required to allow efficient battery charging regimes, whilst enabling power to be fed back to the grid pursuant to necessary standards. Here, an in-depth case-study comparison between the use of the EV motor inverter as the bidirectional charger with low frequency transformer (for galvanic isolation), and the use of a high frequency transformer with associated Dual Active Bridge topologies has been undertaken to identify the merits and issues associated with such technologies.
http://dx.doi.org/10.1109/PEDS.2013.6527097 - A robust state-of-function battery modelling technique for Li-ion battery chemistries developed for EV/HEV vehicles
Power Electronics, Intelligent Motion, Renewable Energy and Energy Management PCIM 2013 Asia, 2013
C. R. Gould, H. Price, J. Wang, D. A. Stone, M. P. FosterThree Li-ion battery cells of different manufacture and capacities, typically used in EV/HEV traction battery packs, are subjected to battery cycling derived from EV/HEV driving data, and are subsequently assessed for their State-of-Function by means of robust circuit-based battery model parameter estimation. - Bipolar Mode Pseudo Random Binary Sequence Excitation for Parameter Estimation in Lead-Acid Batteries
Power Electronics, Intelligent Motion, Renewable Energy and Energy Management PCIM 2013 Asia, 2013
A. J. Fairweather, D. A. Stone & M. P. FosterThis paper continues previous work using maximum length sequences in parameter estimation for batteries. Battery parameter estimation using a bipolar perturbation signal in the form of Pseudo Random Binary Sequences is explored. The work is supported with experimental investigations, and the correlations obtained are subsequently presented as the basis for a parameter estimation system which can be used to assess performance of the batteries in application. - Design of thermally integrated planar inductor utilising aluminium oxide as a winding insulation material
Power Electronics, Intelligent Motion, Renewable Energy and Energy Management PCIM 2013 Europe, 2013
D. Hewitt, D. A. Stone & M. P. FosterThis paper details an investigation into the production of planar inductors employing aluminium oxide as winding insulation. Aluminium oxide is an electrical insulator which offers superior thermal performance over conventional winding insulation materials such as plastic, therefore resulting in a reduced operating temperature within the inductor windings when under load. In this work the electrical properties of aluminium oxide are verified; methods for joining aluminium oxide insulated windings together are evaluated; and finally an inductor is produced; this inductor is tested thermally to confirm theoretical operating temperature predictions. - Parallel buck converter with non-identical power module for improved transient efficiency
Power Electronics, Intelligent Motion, Renewable Energy and Energy Management PCIM 2013 Europe, 2013
C. Tsang, M. P. Foster & D. A. StoneThis paper describes a new control methodology to improve the efficiency of a parallel connected buck converter during transient conditions, without unduly increasing the transient response. This is achieved by minimising the on-duration of the high-bandwidth power module of the parallel connected buck converters. The calculated efficiency during the transient condition is shown to improve by as much as 60% dependent on the load condition. A 35W prototype converter is built and its efficiency was measured to be 1.8% higher at step load of 2.4A. - Mixed PRBS technique for thermal impedance spectroscopy of power electronic systems
Power Electronics, Intelligent Motion, Renewable Energy and Energy Management PCIM 2013 Europe, 2013
J. N. Davidson, D. A. Stone & M. P. FosterA technique to increase the usable frequency range of a pseudo-random binary sequence (PRBS) by mixing multiple sequences for thermal impedance measurement is presented. This allows the complex thermal impedance to be determined in less time and with greater noise immunity compared to unmixed PRBS techniques. Practical results have shown good agreement with, and reduced noise over, equivalent unmixed PRBS techniques. - Application of maximum length sequences to battery charge programming for parameter estimation in lead-acid batteries
Power Electronics, Intelligent Motion, Renewable Energy and Energy Management PCIM 2013 Europe, 2013
A. J. Fairweather, M. P. Foster & D. A. StoneThis paper continues previous work using maximum length sequences in parameter estimation for batteries Implementation of designed charge current waveforms using Pseudo Random Binary Sequences as an excitation signal for battery state evaluation is explored. The work is supported with experimental investigations, and the correlations obtained are subsequently presented as the basis for a parameter estimation system which can be used on-line during battery charging - Prediction of device temperatures in an electric vehicle battery charger system by analysis of device thermal cross-coupling
European Conference on Power Electronics and Applications (EPE) 2013, 2013
J. N. Davidson, D. A. Stone, M. P. Foster & C. R. Gould - Nonlinear Effects in Piezoelectric Transformers Explained by Thermal-Electric Model Based on a Hypothesis of Self-Heating
IEEE IECON 2012, 2012
T. Andersen, M. A. E. Andersen, O. C. Thomsen, M. P. Foster & D. A. StoneAs the trend within power electronic still goes in the direction of higher power density and higher efficiency, it is necessary to develop new topologies and push the limit for the existing technology. Piezoelectric transformers are a fast developing technology to improve efficiency and increase power density of power converters. Nonlinearities in piezoelectric transformers occur when the power density is increased enough. The simple linear equations are not valid at this point and more complex theory of electro elasticity must be applied. In This work a simplified thermo-electric model is developed to explain nonlinearities as voltage jumps and voltage saturation and thereby avoid the complex theory of electro elasticity. The model is based on the hypothesis of self-heating and tested with measurements with good correlation.
http://dx.doi.org/10.1109/IECON.2012.6388760 - EV/HEV li-ion battery modelling and state-of-function determination
2012 International Symposium on Power Electronics, Electrical Drives, Automation and Motion (SPEEDAM 2012), 2012
C. R. Gould, J. B. Wang, D. A. Stone & M. P. FosterThe paper describes the application of a realtime, adaptive battery modelling methodology to Li-ion batteries. This methodology allows accurate estimation of the State-of-Function (SoF) of batteries for an Electric or Hybrid-Electric vehicle. Through use of a Kalman Estimator and online battery model parameter estimation, the voltages associated with monitoring the State of Charge (SoC) of the battery system are shown to be accurately estimated, even given erroneous initial conditions in both the model and parameters. In this way, problems such as self-discharge during non-use of the cells and SoC drift (as usually incurred by coulomb-counting methods due to over-charging or ambient temperature fluctuations) are overcome. A further benefit of the adaptive nature of the parameter estimation allows battery ageing (State of Health - SoH) to be monitored and, in the case of safety-critical systems, cell failure may be predicted in time to avoid inconvenience to passenger networks. Moreover, the ability to accurately predict the SoF and changes in battery parameters allows charging scenarios to be optimized to extend lifetime and facilitate future Vehicle-to-Grid (V2G) implementation.
http://dx.doi.org/10.1109/SPEEDAM.2012.6264616 - The use of virtual flux estimation in aerospace starter-generator systems
2012 International Symposium on Power Electronics, Electrical Drives, Automation and Motion (SPEEDAM 2012), 2012
R. H. Williams, D. A. Stone, M. P. Foster & S. R. MinshullThis study explores how virtual flux estimation may be applied to the grid synchronization of an aerospace S/G system. This technique is used to make the converter more resilient to the grid distortion to be expected on an aircraft distribution bus. The performance of the proposed system is assessed in simulation and hardware. It is demonstrated how using the virtual flux technique the converter is able to maintain synchronization with the grid under the maximum distortion conditions permitted by aerospace power quality standards.
http://dx.doi.org/10.1109/SPEEDAM.2012.6264532 - Maximum Power Point Tracking Converters and Their Issue
All-Energy 2012 Exhibition and Conference, 2012
D. M. K. Schofield, M. P. Foster & D. A. Stone - State indicators for lead-acid batteries utilising pseudo random binary sequences
All-Energy 2012 Exhibition and Conference, 2012
A. J. Fairweather, M. P. Foster & D. A. Stone - A Review of Electrical Energy Storage (EES) Technologies for Stationary Grid Applications
All-Energy 2012 Exhibition and Conference, 2012
J. N. Davidson, H. R. Price, D. A. Stone & M. P. Foster - Modelling of VRLA batteries over operational temperature range using Pseudo Random Binary Sequences
Internation Conference on Lead Acid Batteries 2012, 2012
A. J. Fairweather, M. P. Foster & D. A. Stone - Impact of ripple current on the average output power of solar cells
All-Energy 2012 Exhibition and Conference, 2012
D. M. K. Schofield, M. P. Foster & D. A. Stone - New design approach for higher energy efficiency with parallel converter
IET PEMD 2012, 2012
C.-W. Tsang, M. P. Foster & D. A. StoneThis paper proposes a new design approach for two non-identical converters connected in parallel to obtain higher efficiency across the load range. This is achieved by allowing one converter to be designed for efficiency, without being constrained by system requirements, such as the transient response and current ripple, which will be met by the second converter. The efficiency of the proposed parallel converter is compared to an interleaved converter, both in theory and in practice.
http://dx.doi.org/10.1049/cp.2012.0225 - Impact of ripple current on the average output power of solar cells
IET PEMD 2012, 2012
D. K. Schofield, M. P. Foster & D. A. StoneThis paper presents an analysis of the effects of power converter induced ripple on solar cells. The majority of analysis presented on maximum power point tracking (MPPT) schemes and switched mode power converters (SMPCs) assume smooth DC current is drawn from the cell. In this paper, results from simulation and experimental work are presented to elucidate these effects, showing a significant degradation in the maximum average power when ripple current is accounted for. The effects of power converter switching frequency are also given showing an improvement in the average power from the PV module at greater frequencies.
http://dx.doi.org/10.1049/cp.2012.0333 - Optimum look-up table for reduction of current harmonics in direct torque controlled dual three-phase permanent magnet brushless ac machine drives
IET PEMD 2012, 2012
K.D. Hoang, Z.Q. Zhu & M. P. FosterThis paper presents an investigation into application of direct torque control (DTC) methodology to a dual three-phase (DTP) permanent magnet (PM) brushless AC (BLAC) machine drive. Fundamentally, DTP topology including two sets of three-phase windings shifted by 30 electrical degrees in space together with two isolated neutrals enables cancellation of the 6th harmonic torque component and therefore results in enhancement of torque production. However, since the stator phase current harmonic components which do not participate in electromagnetic torque production are let freely circulate inside the machine and only limited by values of the stator phase resistance and leakage inductance, the stator phase current waveforms under the DTP topology are seriously non-sinusoidal. Therefore, a voltage vector selection scheme together with an optimum look-up table (LUT) for DTC technique is proposed to minimize these useless current harmonic components. Simulation results confirm validity of the proposed method.
http://dx.doi.org/10.1049/cp.2012.0183 - Online optimized stator flux reference approximation for maximum torque per ampere operation of interior permanent magnet machine drive under direct torque control
IET PEMD 2012, 2012
K.D. Hoang, Z.Q. Zhu & M. P. FosterThis paper presents an online optimized stator flux reference approximation scheme for application of direct torque control (DTC) technique to interior permanent magnet (IPM) brushless AC (BLAC) drives with maximum torque per ampere (MTPA) operation. It is found that by considering dq-axis stator flux components instead of stator flux magnitude, straightforward mathematical functions for computing stator flux reference from the relevant torque reference to achieve MTPA operation can be derived. It is also demonstrated that by properly selecting initial value for approximating the proposed stator flux equation utilizing the Newton-Raphson method, a high degree of accuracy can be obtained utilizing only one computing step. It is shown that MTPA operation can be achieved for a DTC-based IPM BLAC drive using the proposed stator flux reference approximation scheme. Simulation results confirm validity of the proposed method.
http://dx.doi.org/10.1049/cp.2012.0266 - Reduction of passive filtering in aerospace starter/generator systems using a multilevel converter with predictive current control
IET PEMD 2012, 2012
R. H. Williams, D. A. Stone, M. P. Foster & S. R. MinshullThe application of predictive current control to a multilevel converter is investigated in an aerospace starter-generator system. The use of a multilevel inverter with predictive current control enables the system to reduce the harmonic distortion in the current waveform when compared to a conventional Field Orientated Controller. It is important that the power converter is optimized to control the current harmonics as aerospace starter-generators are typically low inductance machines. Experimental results taken from a prototype inverter show a substantial reduction in THD is achieved using the proposed controller.
http://dx.doi.org/10.1049/cp.2012.0250 - An investigation into the feasibility of using aluminium oxide to insulate aluminium planar windings
iPower2 Conference, 2012
D. A. Hewitt, D. A. Stone & M. P. Foster - A capacitive level shifter for high voltage (2.5kV)
2012 IEEE International Power Modulator and High Voltage Conference (IPMHVC), 2012
T. Andersen, M. A. E. Andersen, O. C. Thomsen, M. P. Foster & D. A. StoneA capacitive level-shifter as a part of a high voltage halfbridge gate driver is presented in this work. The level-shifter utilizes a differential capacitor pair to transfer the information from low side to high side. A thorough evaluation of the critical parts of the level-shifter is presented with focus on low power consumption as well as low capacitive load between the floating half-bridge node and ground (output capacitance). The operation of the level-shifter is tested and verified by measurements on a prototype half-bridge gate driver. Results conclude stabile operation at 2.44kV, 50kHz with a current consumption of 0.5mA. Operation voltage was limited by test equipment. The output capacitance isThis email address is being protected from spambots. You need JavaScript enabled to view it. .
http://dx.doi.org/10.1109/IPMHVC.2012.6518777 - The development of a solar photovoltaic test rig for the analysis of MPPT algorithms and power quality of attached converters
All-Energy 2011 Exhibition and Conference, 2011
D. M. K. Schofield, M. P. Foster & D. A. Stone - Utilizing Existing Aircraft Wound Field Generators for Starter-Generators
2011 IEEE 8th International Conference on Power Electronics and ECCE Asia (ICPE & ECCE), 2011
R. Williams, D. A. Stone, M. P. Foster & S. R. MinshullThis paper proposes an alternative method for starting an aerospace gas turbine, temporarily driving its existing low inductance wound-field generator as a starter-motor using back-to-back connected, diode clamped inverters. This approach will result in a net weight saving as the existing pneumatic starter is now not required. A prototype converter is constructed and tested upon an aerospace generator, using a dynamometer to reproduce the turbines torque-speed characteristics.
http://dx.doi.org/10.1109/ICPE.2011.5944641 - Simulation of a Scheduling Control Scheme for Domestic Central Heating Systems in the UK
IASTED International Conference on Applied Simulation and Modelling (ASM 2011), 2011
D. J. Rogers, M. P. Foster & C. M. BinghamGas fired space heating is responsible for 24% of the UK's energy consumption [1] and 14% of the UK's CO2 emissions [2]. This paper provides a brief overview of current domestic heating installation practice in the UK and introduces a novel simulation technique. Finally, the paper demonstrates that communicating radiator valves when used in conjunction with a reverse modulation control technique, represent an opportunity to achieve a reduction of 86.1kg of CO2 emissions per household per annum for an average UK household.
http://dx.doi.org/10.2316/P.2011.715-045 - A dynamic model of the LLC resonant converter for control response prediction
Power Electronics, Intelligent Motion, Renewable Energy and Energy Management PCIM 2011 Europe, 2011
M. P. Foster & D. A. Stone - State-of-charge indicators for VRLA batteries utilising Pseudo Random Binary Sequences (PRBS)
Power Electronics, Intelligent Motion, Renewable Energy and Energy Management PCIM 2011 Europe, 2011
A. J. Fairweather, M .P. Foster, D.A. Stone - Phase-locked loop (PLL) pulse-width modulator (PWM) based controller for LLC resonant converters
Power Electronics, Intelligent Motion, Renewable Energy and Energy Management PCIM 2011 Europe, 2011
M. P. Foster, D. A. Stone & J. K. Woo - Back-to-Back Connected Multilevel Inverters for Aerospace Starter-Generator Applications
Power Electronics, Intelligent Motion, Renewable Energy and Energy Management PCIM 2011 Europe, 2011
R. Williams, D. A. Stone, M. P. Foster, S. R. Minshull - State-of-function Determination for EV/HEV Battery Packs
25th World Battery, Hybrid and Fuel Cell Electric Vehicle Symposium (EVS 25), 2010
C. R. Gould, D. A. Stone, C. M. Bingham & M. P. Foster - MLS Testing of VRLA Batteries Using Pseudo Random Binary Sequences (PRBS)
25th World Battery, Hybrid and Fuel Cell Electric Vehicle Symposium (EVS 25), 2010
A. J. Fairweather, D. A. Stone & M. P. Foster - Evaluation of Thermally Efficient Mounting Techniques for Ferrite Cores
International Power and Energy Conference (IPEC) 2010, 2010
J. Holmes, D. A. Stone, M. P. Foster - Comparative Study of Current Vector Control Performance of Alternate Fault Tolerant Inverter Topologies Applied to Three-Phase PM Brushless AC machine with One Phase open-Circuit Fault
IET PEMD 2010, 2010
K. D. Hoang, Z. Q. Zhu, M. P. Foster & D. A. Stone - Effect of Inter-Layer Interface Quality on Electrical and Thermal Characteristics of IMS
IET PEMD 2010, 2010
J. Holmes, D. A. Stone & M. P. Foster - VRLA Battery Parameter Identification using Pseudo Random Binary Sequences (PRBS)
IET PEMD 2010, 2010
A. J. Fairweather, M. P. Foster & D. A. Stone - Device Temperature Projection Technique for IMS based Systems
IET PEMD 2010, 2010
J. D. Holmes, D. A. Stone & M. P. Foster - Multilevel cascaded H-bridge inverter with integrated battery management for alternative energy applications
EPE Wind Energy Chapter - 3rd Seminar: Wind Power to the Grid, 2010
K. D. Wilkie, D. A. Stone, M.P. Foster, C. M. Bingham - Low Computational Complexity Observer Based Modelling Techniques for Device Temperature Prediction in IMS based Systems
PEDS 2009, 2009
J. Holmes, M. P. Foster & D. A. Stone - Achieving ZVS in inductor-less half-bridge piezoelectric transformer based resonant converters
PEDS 2009, 2009
E. L. Horsley, M. P. Foster & D. A. Stone - A three-phase to single-phase matrix converter for high-frequency induction heating
European Conference on Power Electronics and Applications (EPE 2009), 2009
N. Nguyen-Quang, D. A. Stone, C. M. Bingham & M. P. Foster - Comparison between multilevel and classical 2-level inverters regarding stall torque improvements for driving brushless PM machines
European Conference on Power Electronics and Applications (EPE 2009), 2009
S. R. Minshull, C. M. Bingham, D. A. Stone & M .P. Foster - An automated design methodology for LLC resonant converters using a genetic algorithm
Power Electronics, Intelligent Motion, Renewable Energy and Energy Management PCIM 2009 Europe, 2009
M. P. Foster, D. A. Stone & C. M. Bingham - A lumped equivalent circuit model for the radial mode piezoelectric transformer
IEEE Applied Power Electronics Conference APEC 2009, 2009
E. L. Horsley, A. V. Carazo, M. P. Foster & D.A.StoneA lumped equivalent circuit model for the radial mode piezoelectric transformer is presented, based on a one-dimensional analysis of the radial vibration mode and the constitutive piezoelectric equations. The model allows each of the components in the piezoelectric transformer equivalent circuit to be calculated from the appropriate material properties and device dimensions, thereby facilitating the design and optimisation of transformers to meet a set of electrical specifications. Since the analysis treats the transformer as a composite, the effects of the isolation layer and copper electrodes on the electrical characteristics are also included.
http://dx.doi.org/10.1109/APEC.2009.4802906 - System-wide temperature estimation for IMS based power electronics circuits
Proceedings of the International Conference on Power Electronics and Drive Systems, 2009
J. D. Holmes, M. P. Foster & D. A. Stone - Digitally Controlled Converter with an Adaptive Step Size for Maximum Power Point Tracking for Photovoltaic Applications
IEEE IECON 2008, 2008
D. A. Stone, M. P. Foster, C. M. Bingham & P. G. Stewart - Characteristics of high-voltage capacitors when operating in high temperature environments
IEEE ESTC Electronics Systems-Integration Technology Conference 2008, 2008
N. Nguyen-Quang, M. P. Foster & D. A. Stone - A frequency-response-based characterisation methodology for piezoelectric transformers
IEEE ESTC Electronics Systems-Integration Technology Conference 2008, 2008
E. L. Horsley, M. P. Foster & D. A. Stone - On-line tuning of a feedback controller for a buck converter using a genetic algorithm
International Symposium on Power Electronics, Electrical Drives, Automation and Motion (SPEEDAM 2008), 2008
K. D. Wilkie, M. P. Foster, D. A. Stone & C. M. Bingham - Integrated multilevel converter and battery management
International Symposium on Power Electronics, Electrical Drives, Automation and Motion (SPEEDAM 2008), 2008
K. D. Wilkie, D. A. Stone, C. M. Bingham & M. P. FosterA cascaded H-bridge multilevel converter is proposed as a BLDC drive incorporating real-time battery management. Intelligent H-bridges are used to monitor battery cells whilst simultaneously increasing their performance by reducing the variation between cells and controlling their discharge profiles.
http://dx.doi.org/10.1109/SPEEDHAM.2008.4581251 - Phase Locked Loop (PLL) based self-oscillating controller for LCC resonant converters
IET PEMD 2008, 2008
A. J. Gilbert, M. P. Foster, D. A. Stone & C. M. Bingham - A genetic algorithm for designing LCLC resonant converters
IET PEMD 2008, 2008
D. R. Williams, M. P. Foster, C. M. Bingham & D. A. Stone - A New Switching Scheme for Reduced Switching Frequency and Balanced Capacitor Voltages for Back-to-Back Connected, Diode-Clamped Multilevel Converters
IET PEMD 2008, 2008
S. R. Minshull, C. M. Bingham, D. A. Stone & M.P. Foster - Hardware-in-the-loop tuning of a feedback controller for a buck converter using a GA
SPEEDAM 2008 - International Symposium on Power Electronics, Electrical Drives, Automation and Motion, 2008
K. D. Wilkie, M. P. Foster, D. A. Stone & C. M. BinghamThis paper presents a methodology for tuning a PID-based feedback controller for a buck converter using the ITAE controller performance index. The controller parameters are optimized to ensure that a reasonable transient response can be achieved whilst retaining stable operation. Experimental results demonstrate the versatility of the on-line tuning methodology.
http://dx.doi.org/10.1109/SPEEDHAM.2008.4581265 - GA tuning of Pitch Controller for Small Scale MAVs
World Scientific and Engineering Academy and Society (WSEAS) World Conference 2007, 2007
N. C. Essex, M. P. Foster, C. M. Bingham & C. Kuo - Analysis and control of dual-output LCLC resonant converters, and the impact of leakage inductance
PEDS 2007, 2007
Y. Ang, C. M. Bingham, M. P. Foster & D. A. Stone - Modelling and regulation of dual-output LCLC resonant converters'
IEEE IECON 2007, 2007
Y. Ang, C. M. Bingham, M. P. Foster & D. A. Stone - High power unity power factor supply for plastic pipe welding applications
IEEE IECON 2007, 2007
D. A. Stone, C. M. Bingham & M. P. Foster - A cascaded H-bridge BLDC drive incorporating battery management for HEV's
European Conference on Power Electronics and Applications (EPE 2007), 2007
K. D. Wilke, C. M. Bingham, M. P. Foster & D. A. Stone - A back to back multilevel converter for driving low inductance brushless AC machines
European Conference on Power Electronics and Applications (EPE 2007), 2007
S. R. Minshull, C. M. Bingham, M. P. Foster & D. A. Stone - Power factor control of the LCC current-output resonant converter
European Conference on Power Electronics and Applications (EPE 2007), 2007
A. J. Gilbert, C. M. Bingham, M. P. Foster & D. A. Stone - Design of an LCC current-output resonant converter for use as an aluminium anodising supply
European Conference on Power Electronics and Applications (EPE 2007), 2007
A. J. Gilbert, C. M. Bingham, M. P. Foster & D. A. Stone - Analysis of Self-Oscillating DC-DC Resonant Power Converters using a Hysteretic Relay
European Conference on Power Electronics and Applications (EPE 2007), 2007
D. R. Williams, C. M. Bingham, M. P. Foster & D. A. Stone - Comparison of single-phase matrix converter and H-bridge converter for radio frequency induction heating
European Conference on Power Electronics and Applications (EPE 2007), 2007
N. Nguyen-Quang, D. A. Stone, C. M. Bingham & M. P. Foster - State-of-the-art piezoelectric transformer technology
European Conference on Power Electronics and Applications (EPE 2007), 2007
E. L. Horsley, M. P. Foster & D. A. StoneTo date, piezoelectric transformers (PTs) have been extensively commercialised in step-up applications, such as cold cathode fluorescent lamp backlighting for LCDs. As step-down PT technology matures, PT-based converters are set to replace conventional transformers and power converters in a wide variety of applications that require relatively low power levels, low cost, high efficiency, high power density, small size and weight, low EMI, and high reliability. This paper examines the various types of piezoelectric transformer and provides an overview of the materials technology, converter designs, and control methods involved with their use.
http://dx.doi.org/10.1109/EPE.2007.4417637 - Rapid analysis & design methodologies of high- frequency LCLC resonant inverter as electrodeless fluorescent lamp ballast
Proceedings of the International Conference on Power Electronics and Drive Systems (PEDS) 2007, 2007
Y. A. Ang, D. A. Stone, C. M. Bingham & M. P. Foster - A novel AC equivalent circuit for the CLL voltage-output resonant converter using describing functions
ICEMS 2006, 2006
M. P. Foster, C. R. Gould, D. A. Stone & C. M. Bingham - Bandwidth-controlled Steady-state Design and Analysis of a 3kW CLL Resonant Converter with Rectified Mains Output Characteristics
ICEMS 2006, 2006
C. R. Gould, M. P. Foster, D. A. Stone & C. M. Bingham - Single Phase Matrix Converter As A Radio Frequency Induction Heater
SPEEDAM 2006, 2006
N. Nguyen-Quang, D. A. Stone C. M. Bingham & M. P. Foster - Digital control of dual-load LCLC resonant converters
European Conference on Power Electronics and Applications (EPE 2005), 2005
Y. A. Ang, C. M. Bingham, D. A. Stone & M. P. Foster - EKF-based output voltage estimation of 3rd order LCC resonant converters with significant load variations
European Conference on Power Electronics and Applications (EPE 2004), 2005
A. J. Gilbert, C. M. Bingham, B. S. Bhangu, M. P. Foster, D. A. Stone & D. Howe - Rapid steady-state analysis of CLL resonant power converters
IASTED 2004, 2004
C. R. Gould, C. M. Bingham, D. A. Stone, & M. P. Foster - Analysis & design of high-frequency LCLC resonant converters for electrode-less fluorescent lamp ballasts
IET PEMD 2004, 2004
Y. A. Ang, D. A. Stone, C. M. Bingham & M. P. Foster - State-variable modelling of CLL resonant converters
IET PEMD 2004, 2004
C. R. Gould, D. A. Stone, M. P. Foster & C. M. Bingham - Observer based feedback control of 3rd order LCC resonant converters
European Conference on Power Electronics and Applications (EPE 2003), 2003
M. P. Foster, H. I. Sewell, C. M. Bingham & D. A. Stone - Review of modelling methodologies to facilitate rapid simulation of high order resonant converters
European Conference on Power Electronics and Applications (EPE 2001), 2001
M. P. Foster, H. I. Sewell, D. A. Stone & C. M. Bingham