Study on cogging torque in PM motor with pole width modulation rotor

Cogging torque may causes torque oscillation and noise while motors running, which affects their performance indexes. Aiming at this problem and comparing with several common cogging torque reducing methods, the feasibility of reducing cogging torque with pole width modulation method was pointed out. The cogging torques of surface-mounted permanent magnet motor and pole width modulation permanent magnet motor were calculated separately by the model built with finite element method (FEM). The cogging torque experiment of two prototype with different structures were done by a cogging torque testing system consists of angle sensor, permanent magnet motor, torque wrenches and other equipment. The experimental result was consistent with the simulation results. The cogging torqueses were all reduced by 30% or more. It shows that the method of pole width modulation method can reduce cogging torque and it is a novel method to reduce cogging torque.