Analysis of Two-dimensional Cogging Torque of Permanent Magnet Spherical Motor with Soft Magnetic Composite Material Core

Abstract

The use of soft magnetic composite materials (SMCM) core in the permanent magnet spherical motor (PMS_pM) can increase the air gap magnetic flux density and torque density. However, it will also cause the distortion of the magnetic flux density, leading to the generation of cogging torque. In this paper, an analytical model of cogging torque for PMS_pM with iron core is proposed. Firstly, based on the spatial distribution of the air gap, the distribution function characterizing the tooth slot structure in both the longitude and latitude direction is obtained through Fourier expansion. Secondly, an analytical model of air gap magnetic flux density is obtained based on the distribution function of the tooth slot structure. Next, an analytical model for the rotation and yaw cogging torque is established based on the virtual work method. Finally, the analytical results are verified by finite element analysis and experimental results. The model can quickly obtain the relationship between the cogging torque and structural parameters such as permanent magnet thickness, air gap length, and stator slot opening angle, which lays a certain theoretical foundation for the structural optimization design of the PMS_pM with SMCM cores.