Rotor design techniques for reducing the cogging torque in a novel dual-rotor axial field flux-switching permanent magnet machine

Dual-rotor axial field flux-switching permanent magnet (DRAFFSPM) machine is a novel permanent magnet (PM) machine which incorporates the merits of both the flux-switching PM machine and the axial field PM machine. The cogging torque of the DRAFFSPM machine is high due to the flux focusing which is caused by the double salient structure. In order to reduce the cogging torque, the influence of the rotor pole width and shape on the cogging torque is analyzed based on the 3D finite element (FE) method. The cogging torque reduction methods, such as the rotor skewing, rotor notching, and rotor pole displacement, etc., are investigated. The results show that increasing the rotor pole width and adopting fan-shaped rotor pole can decrease the cogging torque greatly. The cogging torque can be reduced by ~77% when the rotor pole width and rotor fan-shaped angle are optimized to 15.5 deg. and 3 deg., respectively. The cogging torque can´t be decreased by the rotor skewing for DRAFFSPM machine. However, the cogging torque can be reduced by rotor notching and rotor pole displacement.