Cost reduction of vernier permanent-magnet machine with ferrite magnets

This paper presents a novel five-phase fault-tolerant vernier permanent-magnet (VPM) machine for direct-drive applications, which has hybrid magnet materials in both rotor and stator. By adopting surface mounted unipolar NdFeB in rotor, the flux leakage between PMs is much reduced, and the addition of unipolar ferrite material between flux-modulation poles (FMPs) can effectively improve the flux in stator teeth. Besides, the air-gap circle is unequally divided by FMPs in the proposed machine, which in return further improves the torque density. The time-stepping finite element method is used to evaluate the proposed VPM machine as compared with existing ones. The results verify the theoretical analysis, showing that the proposed VPM machine has higher PM utilization rate and lower manufacturing cost.