Conformal Mapping Based Investigation of Torque Density and Ripple in SPM Motors

Torque density and ripple content in torque are two important criteria to assess the suitability of a motor for a considered application. This paper provides an overview on correlation between torque per unit rotor volume (TRV), flux density components, electrical loading and magnetic loading for surface mounted permanent magnet motors. These expressions are derived using Maxwell stress tensor and conformal mapping. The torque expression presented here helps in faster development of torque related back-end models required during design optimization process. The discussion presented here gives an overview on typical effects of stator slots on slotless field distributions, and the associated effects on TRV and ripple in torque.