Power Factor Analysis of Dual-Stator Permanent Magnet Vernier Motor With Consideration on Turn-Number Assignment of Inner and Outer Stator Windings

Abstract

Permanent magnet vernier motors (PMVMs) are extremely attractive in low-speed large-torque (LSLT) and direct-drive (DD) applications, due to high torque density and simple structure. However, they suffer from low power factor (PF). The existing research has shown that dual-stator PMVM (DS-PMVM) is an effective topology to improve the PF. This article focuses on the PF analysis of DS-PMVMs to maximize the PF. The analytical perspective is not trying to propose new topologies of DS-PMVMs but to consider the turn-number assignment of the inner and outer stator windings. In this article, both the analytical and the operational procedures are elaborated; by combining the 2-D finite element method (FEM) with the mathematical method, two DS-PMVMs are used to verify the theoretical analysis. The simulation results agree well with the results obtained by the theoretical analysis. The results also showed that 1) if the inductances of single-turn inner and outer stator windings are close or equal, the equal turn-number of inner and outer stator windings will make the PF of DS-PMVM maximum; otherwise, the PF will reach maximum with the unequal turn-number assignment and 2) the turn-number assignment can not only maximize the PF of DS-PMVMs but also meet the torque requirement.