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. 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. 

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.

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.  
 

Publications

Transformers in Practice, Lopez-Fernandez, Turowski, Kazmierski, Lesniewska, Ertan, Lefley, et al, monograph ISBN 978-84-609-9515-9, 2007.

A New Simplified Sensorless Control Method For A Single Phase SR Motor Using HF Signal Injection, Ahmed S, Lefley P W, 42nd International Universities Power Engineering Conference 2007, Brighton, pp890-894.

A New Breed of Power Supply for ESPs, Lefley P W, Parker K, SAIEE Energize Power Journal, July 2006, pp 56-61.

Breathe Easy, Lefley P W and Parker K, IEE Power Engineer, vol.20, (issue 1 February/March), 2006, pp39-43

Transformer Design for High Voltage, High Frequency, High Power, Lefley P W, Fothergill J C, Devine P J, Advanced Research Workshop on Modern Transformers (ARWtr 2004), Vigo Spain, October 2004

Is Lead Dead? Starkey J P, Lefley P W, IEE Power Engineering Journal Dec/Jan 2003/04, pp 30-35

A Novel High Current, Short Pulse Battery Charging System Using a Variable Pulse Frequency Resonant Converter, Starkey J P, Lefley P W, 10th European Conference on Power Electronics and Applications, Toulouse, September 2003

Finite Element Analysis Of Three Dimensional Current Distribution In Pasted Grid Plates For Lead Acid Batteries, Starkey J P, Lefley P W, 37th International Universities Power Engineering Conference 2002, pp890-894.