Ultra-efficient electrical machines and drives for EVs and HEVs

Lead Research Organisation: University of Sheffield
Department Name: Electronic and Electrical Engineering


The development of electric traction drive performance to achieve market expectations is fundamental to the acceptance and swift realisation of electric propulsion vehicles, be they pure electric, fuel cell or hybrid drive systems. The widely acknowledged basic requirements of an electrical machine for EV/HEV propulsion include (a) high torque and high power density (b) high torque at low speeds (c) high power at high speeds (d) high efficiency over a wide speed and torque range (e) high reliability and (f) low cost, etc. This project is limited to permanent magnet (PM) machines as they offer higher efficiency and higher torque density than currently available induction and switched reluctance machine alternatives.PM brushless electric traction machines can achieve 60-70% efficiency at partial loading (<35% of full load) which is typical for electric vehicle (EV) urban duty cycles. Whilst this is an improvement over current internal combustion engine (ICE) efficiency it is less than the typical rated operation efficiency for an existing PM machine and drive unit which is circa. 90%.The strategic importance of the project is that at the present time no cost effective solution exists that is able to maximise the high operating efficiency region of a PM machine in accordance with the requirements of a zero, or ultra-low carbon vehicle's duty cycle. Therefore, it is proposed to undertake a systematic programme of work which aims to significantly increase PM machine partial load efficiency and to achieve a wider high efficiency operating region by developing novel variable flux PM brushless machine topologies and control strategies, and to facilititate increased vehicle range and reduced battery requirements. The outcomes will be validated through CAD/CAE and scaled proof-of-concept prototypes to demonstrate the effectiveness of controlling the flux excitation by both mechanical actuation and electrical means, leading to a working demonstrator that will ultimately be packaged into an EV architecture and be commercially viable, with a route to market within 7 years.


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Urquhart I. (2013) Mechanically actuated variable flux IPMSM for EV and HEV applications in World Electric Vehicle Journal

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Zhu Z.Q. (2012) Novel switched flux permanent magnet machine topologies in Diangong Jishu Xuebao/Transactions of China Electrotechnical Society

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Zhu Z.Q. (2012) Recent advances on permanent magnet machines in Diangong Jishu Xuebao/Transactions of China Electrotechnical Society

Description Variable flux machines can significantly improve the system efficiency for electric vehicles.
Exploitation Route The variable flux concept can be utilised not only for electrical vehicles, but also for wind power generator design.
It is still at early stage, much effort and funding are required in order to realise its potential.
At Sheffield, the research are continued by direct industrial sponsorship and/or joint government and industries, including Siemens for wind power generator design, Dynex (via KTP) on system simulation and design.
Sectors Energy,Transport

Description Previously it was usually considered the electrical machines exhibit high efficiency already and there is not much scope for improvement. The developed variable flux machines provide significant system efficiency improvement, ~11%. This has result a wide awareness of the electric machine design based on variable flux concept.
First Year Of Impact 2017
Sector Education,Transport
Impact Types Societal

Description Technology Strategy Board
Amount £571,221 (GBP)
Funding ID 18886-135187 
Organisation Innovate UK 
Sector Public
Country United Kingdom
Start 10/2012 
End 03/2015