Reducing Cogging Torque in Surface-Mounted Permanent-Magnet Motors by Nonuniformly Distributed Teeth Method

This paper proposed a novel method for reducing cogging torque in surface-mounted permanent-magnet (PM) motors with nonuniformly distributed teeth. In this method, the width of one tooth tip is different from that of the others while all slot openings are the same. By suitable selection of the teeth width ratio, i.e., the width ratio of the one tooth tip to others, the cogging torque can be greatly reduced. First, the analytical expression of cogging torque was deduced and used to analyze the cogging torque qualitatively. Based on the above, analytical method was proposed to determine the teeth width ratio. To determine the teeth width ratio accurately, numerical method was proposed. Calculation of cogging torque by finite element method (FEM) shows that cogging torque can be greatly reduced by teeth width ratio determined by analytical method, and the teeth width ratio determined by numerical method can reduce the cogging torque further, which proved the effectiveness of the proposed methods. At last, the influences of the stator asymmetry resulted by this method on PM motors were discussed.