Cogging Torque Reduction in External-rotor Permanent Magnet Torque Motor Based on Different Shape of Magnet

The external-rotor permanent magnet torque motor is widely used in electric vehicles and mobile robots. In order to improve its working accuracy, the cogging torque needs to be reduced. Cogging torque results from the interaction of permanent magnet magnetomotive force harmonics and air-gap permeance harmonics due to slotting. In this paper, the finite element analysis (FEA) has been conducted on the external-rotor surface-mounted permanent magnet motor. Cogging torque can be reduced by optimizing the shape of the permanent magnet (PM) according to the theoretical analysis. And three types of PM pole shape are adopt to reduce the cogging torque. By optimizing the dimension parameters of PMs, each of these three shapes can reduce the cogging torque effectively.