A High Power Factor Permanent Magnet Vernier Machine With Modular Stator and Yokeless Rotor

Abstract

Permanent magnet vernier machines (PMVMs) have drawn increasingly more attention due to their high torque density. However, they suffer from low power factor due to the large harmonic inductance caused by abundant no-working harmonics. This paper proposes a high power factor PMVM endowed with modular stator and yokeless halbach-PM-array rotor. Benefited from the unique structure, the magnetic circuits of low order no-working harmonics are interrupted and their amplitudes can be effectively decreased. Meanwhile, multiple working harmonics are produced by the modulation effects of un-evenly distributed stator permeance. Thus, both the high power factor and average torque can be achieved. Moreover, the influence of critical dimension parameters, including slot bottom width, flux barrier width and PM thickness on average torque and power factor are comprehensively analyzed. Finite element analysis (FEA) and experimental results verify that at current density 10 A/mm2, the power factor and active volume torque density of proposed PMVM with 9-slot-stator 14-pole-pair PM rotor can be improved to 0.9 and 26 Nm/L, while regular PMVM counterpart is corresponding to 0.84 and 22 Nm/L, respectively.