Reduction of Magnet Usage in Flux-Reversal Permanent Magnet Machine for Electric Vehicle

In this paper, a new topology of magnet usage reduction for flux-reversal permanent magnet (FRPM) machines used in electric vehicles is proposed and verified by comparing the corresponding electromagnetic performances with a conventional FRPM machine. Firstly, the topology of the proposed machine as well as its working principle is introduced and studied by air-gap field modulation theory. Then, the feasible slot/pole combinations for the novel FRPM machine are investigated, taking the back electro-magnetic-force (EMF) quality, magnetization methods and unbalanced magnetic pull (UMP) into consideration. Correspondingly, in order to investigate the electromagnetic performances of the proposed FRPM machine, a comparison with the conventional FRPM machine is made, including the working harmonics, back-EMF, winding inductance, UMP and torque characteristics. Besides, in order to optimize the back-EMF and reduce the UMP, a further improved topology with PM rearrangement is investigated. Finally, two prototype machines are manufactured and tested to verify the analytical analyses.