A General Design Approach of Surface-Mounted Permanent Magnet Vernier Machine

Permanent magnet vernier machines (PMVMs) have drawn increasing more attention due to their high torque density, which is promising for low-speed high-torque direct-drive applications. Nowadays, researches are mainly focus on machine optimization design under the specific size and working condition. However, the difference and relationship under different power ratings are few investigated. Thus, this paper is devoted to propose a general design approach of surface-mounted permanent magnet vernier machine (SPMVM), covering different power ratings. The closed-from per-unit formation is proposed to clarify how the pole numbers, pole ratios (the pole-pair ratios of rotor PM to stator winding) and normalized geometric variables, including the ratio of magnet thickness to air-gap length, stator slot opening ratio, length-radius ratio, and so on, are related to machine performance. It reveals that SPMVMs endowed with high pole ratio and low armature winding pole-pair can achieve high torque density and high efficiency simultaneously, while the power factor of which is lower than regular PM machines due to abundant harmonic inductances. Moreover, with the increase of power ratings, power factor is further decreased and efficiency difference is further increased. Taking torque, power factor and efficiency into consideration, the preferable slot/pole combinations and dimensional parameters under different power ratings are determined. And the analysis results have been validated by Finite element analysis (FEA) and experiments.