Mechanism and Characteristics of Cogging Torque in Surface-Mounted PMSM: A General Airgap Field Modulation Theory Approach

In this article, the surface-mounted permanent magnet machine is regarded as a salient pole reluctance machine to take into account the effect of stator teeth. The field modulation behavior of the magnetizing field is firstly introduced, and the field model is then derived using the general airgap field modulation theory (GAFMT). The properties of the modulated field harmonics are explored based on the proposed field model. Subsequently, a general cogging torque model based on the virtual work method and the GAFMT is proposed to describe the relationship between the field harmonics and the cogging torque. On this basis, the mechanism of the cogging torque is studied, its frequency, effective field harmonics, and the contribution of each harmonic are revealed. The proposed model is then validated by comparing its results with those obtained from the Maxwell Stress Tensor method and the finite-element analysis, and a good agreement is observed, demonstrating the effectiveness of the proposed model. Furthermore, the experimental results also confirm the effectiveness of the proposed model.