Methods for cogging torque reduction of directly driven PM wind generators

This paper deals with several methods for the reduction of cogging torque in case of low speed permanent magnets wind generators. The first analyzed method consists in asymmetrical spacing of the permanent magnets on the rotor outer surface. The second method consists in using close stator slots that determines a nearly isotropic magnetic stator structure. The last investigated method consists in stator skewing. The smallest cogging torque results however were obtained by combining closed stator slots with the other two studied methods. The proposed solutions for cogging torque reduction are analyzed by means of 2D/3D finite element models developed using the professional Flux software package. The numerical results are discussed and compared with experimental measurements.