High Pole Number Outer-Rotor SPM Machine for Sustainable 150kW High-Speed EV Traction

The ambitious roadmaps of electric vehicle (EV) powertrains are pushing traction motors to achieve step-change performance improvements in power density, efficiency, and cost by 2035. Limited by technology bricks such as materials, manufacturing and thermal management, the widely adopted interior permanent magnet (IPM) machine solutions are reaching their performance boundaries in multi-physics domains. This digest will introduce a feasibility study of outer rotor surface mounted PM (OR-SPM) motor against these leading performance KPIs for high speed EV traction. Through comparison with state of the art interior PM (IPM) machine solutions under the same torque-speed requirements, active material properties as well as converter specifications, it is found that an OR-SPM motor with high pole number is a promising topology from sustainability perspective. Global optimisation of a down-sifted 72-slot, 24-pole OR-SPM motor is then conducted based on finite element tools. It is revealed that compared with a benchmark 150kW IPM motor, >20% magnet usage reduction can be achieved. Meanwhile, the study also identifies the challenge in the relatively low partial load efficiency of the optimised design. Methods to improve the efficiency based on core material selection are then investigated. It is found that for the proposed OR-SPM solution, amorphous steel with ultra-low iron loss behaviour is a promising candidate material for significant efficiency improvement.