Cost-Effective Vernier Permanent-Magnet Machine With High Torque Performance

This paper presents a cost-effective five-phase vernier permanent-magnet (VPM) machine with fault tolerance for direct-drive applications, which has hybrid magnet material in both stator and rotor. By adopting unipolar rare-earth PM in rotor, the amount of rare-earth PM is reduced by half and the flux leakage between PMs is much reduced. Besides, the unipolar ferrite PM is assisted between flux-modulation poles to further improve the flux in stator teeth. Moreover, the torque performance and PM utilization rate are further improved due to the optimization of stator teeth in the proposed machine. The time-stepping finite-element method is used to evaluate the performance of proposed VPM machine in comparison with bipolar and unipolar ones. The results show that the proposed VPM machine not only remains the advantage of fault tolerance, but also significantly improves the torque density and reduces torque ripple simultaneously with considerable less consumption of rare-earth PM.