Improvement of Field-Weakening Performance of IPM Machines with Salient Pole Shoe Rotors

Interior permanent magnet (IPM) machines, with high torque density and strong rotor robustness, have been widely employed as traction machines in electric vehicles (EVs). However, due to the machine armature reaction, IPM machines suffer from voltage distortion in the field-weakening region, which may influence the machine field-weakening capability and lead to a higher DC-link voltage requirement in the EV traction system. This paper investigates the terminal voltage distortion of IPM machines with three different magnet configurations in the rotor. The Nissan Leaf electric vehicle traction machine is studied as a benchmark machine. Experimental results of this machine are used to validate the analysis presented in this paper. The rotor surface shaping impacting the machine voltage is also studied. Therefore, a salient pole shoe machine is proposed and designed, which achieves an improved field-weakening performance compared to the conventional cylindrical rotor IPM machines.