Selection of rare-earth-free permanent magnet machine for C-segment electric vehicle: Comparative analysis of different machine topologies

摘要

This paper deals with rare-earth-free permanent magnet traction machine design for C-segment electric vehicle (EV). Four different ferrite permanent magnet synchronous machine topologies having different magnets arrangement and pole-pair number, selected for their high potential, are presented and compared thanks to a computationally efficient finite-element based analysis tool that was developed purposely. It was found that flux focusing machine having 12 poles and 72 slots outperforms in terms of torque-speed requirement fulfillment, efficiency and power to weight ratio. Influence of the magnet grade on the resilience against demagnetization under symmetrical short-circuit condition of the selected machine was then investigated. It is shown that the machine is subject to complete demagnetization if low grade hard ferrite (Ceramic 8) is adopted, thereby fostering research of new and abundantly available magnet grades is key for penetration of new and cost effective electrical machines into EV powertrain market.