Design and Analysis of Novel Modular Stator Axial-Flux Permanent Magnet Vernier Machine With Improved Power Factor

Permanent magnet Vernier machines (PMVMs) have drawn increasing attention in recent years due to the advantage of high torque density. However, the inherent low power factor issue of PMVMs remains a key challenge. In this paper, a novel axial-flux permanent magnet vernier machine (AFPMVM) with modular stator is proposed. Benefiting from the unique separation slot structure, the proposed machine can obtain not only the improved power factor but also the higher electromagnetic torque, and this is explained theoretically by air-gap field modulation theory. A magnetomotive force (MMF)-permeance model is established to predict the air-gap field harmonics modulated by the stator slots. Moreover, by quantifying the contribution of air-gap field harmonics to the torque generation, the working and non-working harmonic components of the air-gap field in the proposed machine can be determined. Meanwhile, the relationship between electromagnetic torque and power factor of the proposed AFPMVM is revealed from the perspective of the air-gap field harmonics. Then, the power factor of the proposed machine is significantly improved due to the lower non-working harmonic contents of armature reaction field. The analysis results show that the proposed AFPMVM can achieve 4.1% higher electromagnetic torque and 6.9% higher power factor than the existing AFPMVM. Finally, the influences of some key design parameters on electromagnetic torque and power factor of the proposed AFPMVM are analyzed and verified by finite element analysis.