Reducing Cogging Torque in Permanent-Magnet Synchronous Motors by Auxiliary Teeth Method

Cogging torque in permanent-magnet motors is one of the most important problems to be considered in high performance applications especially in low speed and direct drive applications. In this paper, the analytical expression for cogging torque in permanent-magnet synchronous motors (PMSM) with auxiliary teeth is derived by the energy method and the Fourier series analysis, based on the air gap permeance and the flux density distribution in an equivalent slotless machine. Analytical method was proposed to determine an appropriate scope of auxiliary tooth width. In order to reduce cogging torque to the maximum extent, cogging torque corresponding to different slot openings was analyzed. To determine the auxiliary teeth width accurately, finite element method (FEM) which considered the effects of flux leakage and saturation was proposed. And then on this basis auxiliary teeth height was determined by analyzing the distribution of the radial component of the flux density in the air gap. Finally, calculation results of cogging torque corresponding to different distributions of the auxiliary teeth, the auxiliary teeth width as well as the auxiliary height were discussed.