Winding Factor of Vernier Permanent Magnet Motor

Several studies have been reported on vernier permanent magnet synchronous motors (VPMSMs) using spatial harmonics in air-gap flux density owing to their low-speed high-torque characteristics. However, coefficients that can predict the performance of VPMSMs in motor design processes have not been extensively researched. The gear ratio indicates the degree of amplification of the spatial harmonics, but there is a big difference between the performances predicted using the gear ratio and the actual performance of VPMSMs. The winding factor can estimate the magnitude of the electromotive force (EMF) of the motor. Although the winding factor is suitable for conventional motors, it cannot be applied to VPMSM, which amplifies EMF through spatial harmonics. In this study, we investigated the winding factor of VPMSMs and proposed a winding factor calculation method suitable for VPMSMs. Based on the analytical method, the proposed calculation method could instantly and accurately estimate the winding factor of VPMSMs. With this method, the EMF performance of VPMSMs can be predicted according to the pole–slot combination. To verify the validity of the proposed method, we compared the gear ratio, the proposed winding factor, and the magnitude of the EMF obtained by the finite element method.