Reduction Methods Using Canceling Effect for Cogging Torque in Dual-Stator PM Synchronous Machines

This paper investigates cogging torque reduction methods using canceling effect for dual-stator permanent magnet synchronous machines (PMSM). The cogging torque in dual-stator PMSMs can be calculated by the superposition of both cogging torque components from outer and inner stator parts neglecting the saturation effect. If out and inner parts have the same least common multiple of pole/slot number combination, both cogging torque components share the same harmonic contents. Therefore, the cogging torque harmonics from both components can be cancelling or additive, which depends on their phase angle difference. In addition to the relative position shift between inner and outer stators, this paper proposes more options using the canceling effect, such as relative position shift between inner/outer magnet poles, inner/outer slot number pairing, size pairing of inner/outer slot openings, and size pairing of inner/outer pole-arc to pole-pitch ratios. The investigation shows all these methods can effectively reduce the cogging torque. The analysis is verified by direct finite element results.