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Electrical Machines and Power Electronics

The Electrical and Electronic Power Engineering Group is actively engaged in research into power electronic systems, novel electrical machines, and drives. There is a blend of interests and skills amongst the academic and research staff, providing a rare multidisciplinary strength to the Group; including expertise in very high voltage and current, novel magnetic design and power systems. The aim of the research is to make significant contributions to the understanding and development of power electronics,machines and derived systems.

Electrical Machines and Drives - Power Electronics and Pulsed Power - Publications

Centre for Advanced Electronically Controlled Machines and Drives

   Director - Dr. Paul Lefley

Recent work in the field of electrical machines has lead to the development of a new type of electric motor that is energy efficient, electronically controlled and of a low cost to manufacture, with the intention to make OEM manufacturers aware of an alternative to the world’s reliance on inefficient single phase induction motors. These energy efficient motors are based on new patented designs and are essentially permanent magnet based brushless DC motors with very low electronic component count. The new designs have been developed for low torque ripple and quiet operation. The new motors are attracting growing commercial interest worldwide.

Nexa fuel cell; part of the electric vehicle traction drive system developed in the Electrical and Electronic Power Engineering Group (Photo courtesy of Ballard)

Traditionally Dr. Lefley has developed electric motors for electric and hybrid vehicles. However, recently has also developed new bespoke motor/generator technologies for aerospace applications where high power densities at very high speeds are essential. Such machines are designed for directly coupled gas-turbine applications, where a combined high speed starter coupled with a generator capability is required. This is a new field and is of considerable interest not only in aerospace but in military applications as well. Further work on energy efficient motors for industrial fan and pump applications is also on-going and is currently being spun-out through Synchropulse Ltd (see below). Dr. Lefley has developed in conjunction with colleagues from the Electrical and Electronic Power Engineering Group a complete fuel cell based electric vehicle drive system using a Nexa fuel cell, ultra-capacitors for energy storage, and an energy efficient permanent magnet brushless DC motor. 

Shell Springboard Winners, SynchroPulse - Lord Wade, Dr Paul Lefley and Andrew Hogbin, SynchroPulse Ltd., and James Smith, Shell UK Chairman.

Power Electronics and Pulsed Power

Dr. Lefley has had considerable experience in development of power electronic based systems including recently, the application of pulsed power both at very high currents and high voltages.

A 20 kW ultra-rapid battery recharger, for charging fork-lift truck and submarine batteries at currents of up to 2,500 amps

The work on ultra-rapid battery recharging stemmed from fundamental work on how a rechargeable battery may accept charge at a high rate without causing deleterious effects to the battery such as overheating, gassing, active material shedding, etc. The purpose of this research was to investigate and develop new ways of rapidly recharging batteries by taking into account the electrochemistry and physical effects of rapid  recharging on the battery. The Group has had considerable success in developing a new ultra-fast charging technique using pulsed power electronics to enable lead-acid batteries to be rapidly charged without overcharging, excessive gassing, or overheating. A real-time electronic charge management system prevents overcharging by controlling the rate at which the charge pulses are injected. This system substantially reduces gassing until a level of almost 90% state of charge is reached. A 24 kW charger has been developed to rapidly recharge large battery installations of between 24 to 72 volts at 800 Ahr capacities in under an hour.

Scanning electron micrographs of the surface of battery plates showing: (left) a healthy new battery, and (right) an aged battery charged with a low current density.

The very high current power electronics (up to 2,500 amps) is applicable to all large scale energy storage media, and interested parties are encouraged to contact Dr. Lefley. Much of the ultra-rapid battery recharging work is currently seeing commercial interest. The work on electrostatic precipitation was an application of modern high frequency switched mode power electronics to replace the traditional low frequency transformer/rectifier set, but also to improve the dust collection efficiency in the precipitator by applying a controllable pulsed waveform from the new power supply. This system was implemented in a pilot project at Didcot B power station in Oxfordshire, UK.  

Recent Publications:

• Optimal Design of a Novel Single Phase PM BLDC Motor Using Genetic Algorithm, Lefley P, Ahmed S, EPE-PEMC 2012, Novi-Sad, September 2012.

• Cogging Torque Minimization in the Double Stator Cup Rotor Machine, Diryak E, Lefley P, 4th Symposium on Applied Electromagnetics SAEM'12, 3rd to 6th June 2012, Sopron Hungary.

• High Voltage, High Frequency Transformer Design, Lefley P, Devine P. Transformers Analysis Design and Measurement, CRC Press, Monograph Ch 21, ISBN 9781466508248.

• Synthesis and Analysis of a High-performance Low-cost Permanent Magnet Brushless DC Motor, Lefley P,  International journal for Computation and Mathematics in Electrical and Electronic Engineering (COMPEL).

• Fault Detection of a Series Compensated Line during the Damping Process of Inter-area Mode of Oscillation, Lami F, Lefley P. IET DPSP 2012 - Protecting the Smart Grid. The 11th International Conference on Developments in Power System Protection. 23-26 April 2012.

• Rechargeable batteries – Part 4: Battery graveyard,  Energize April 2012  Lefley P, Soge A, Starkey J

• Rechargeable batteries – Part 3: Lithium-ion batteries, Energize April 2012  Lefley P, Soge A, Starkey J

• Rechargeable Batteries Part 2: Nickel based batteries,  Energize March 2012  Lefley P, Soge A, Starkey J

• Rechargeable Batteries – The Evolution and Beyond, Energize Jan/Feb 2012  Lefley P, Soge A, Starkey J

• A New Design of Low Cost Energy Efficient Single Phase Brushless DC Motor, Lefley P, Ahmed S, Journal of Electrical Research Review, ISSN 0033-2097, 2/2012.

• Static Characteristics of a Novel Low Cost Brushless DC Permanent Magnet Motor, Lefley P, Journal of Electrical Research Review, ISSN 0033-2097, R88 NR 1a/2012.

• A Novel Three-Phase Buck-Boost Power Quality Converter, Lefley P, Starkey J, Seventh Mako/CIGRE Conference October 2 – 4, 2011.

• Synthesis and Analysis of a High Performance Low-Cost Permanent Magnet Brushless DC Motor L. Petkovska, P. Lefley, G. Cvetkovski  XV International Symposium on Electromagnetic Fields in Mechatronics, Electrical and Electronic Engineering – ISEF'2011 Funchal, Madeira September 2011.

• Optimisation of the Design Parameters of an Asymmetric Brushless DC Motor for Cogging Torque Minimisation, Lefley P, Petkovska L, Cvetkovski G, European Power Electronics Conference EPE 2011, Birmingham, September 2011.

• From Dynamic Modelling to Experimentation of an Induction Motor Powered by a Doubly-Fed Induction Generator by Passivity based Control,  Electrical Machines and Drives, InTech, Monograph Ch 7, ISBN 978-953-307-548-8. 

• Design and Control of the Brushless Doubly Fed Twin Induction Generator (BDFTIG) - Part 2, Bensadeq A, Lefley P, IEEE 14th International Power Electronics and Motion Control Conference 6th to 8th September 2010, (EPE-PEMC 2010), Ohrid.

• Finite Element Analysis of a Novel Single Phase Permanent Magnet Brushless DC Motor, Lefley P, Ahmed S, IEEE 14th International Power Electronics and Motion Control Conference 6th to 8th September 2010, (EPE-PEMC 2010), Ohrid.

• Study of the Impact of Asymmetrical Stator Pole Arc on the Cogging Torque for Single Phase Permanent Magnet BLDC Motor, Ahmed S, Lefley P, IEEE International Conference on Electric Power and Energy Conversion Systems 10th to 12th November 2009, (EPECS09), Al Sharjah.

• Design and Control of the Brushless Doubly Fed Twin Induction Generator (BDFTIG), Bensadeq A, Lefley P, IEEE 11th Spanish Portuguese Conference on Electrical Engineering 1st to 4th July 2009, (11CHLIE), Zaragoza.

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