A cogging torque reduction method for surface mounted permanent magnet motor

A method to reduce the cogging torque in surface mounted permanent-magnet (PM) motors is proposed. In this method, some auxiliary grooves are put on the PM pole face, which reduce the harmonics of field function of PM contributing to the cogging torque. The cogging torque of such a motor is thoroughly analyzed. Based on this analysis the positions of the auxiliary grooves that can minimize the cogging torque are presented. FEM analysis confirms the effectiveness of this method and the optimum width of the auxiliary grooves is also discussed by numerical analysis. The paper also proposes the combined method of both auxiliary grooves and gradually inclined surface edge on PM to achieve better cogging torque reduction. The FEM result shows that this combined method can effectively reduce the cogging torque while keeping the high torque density of the motor.