Optimal split ratio and torque comparison of surface-mounted permanent magnet machines having inner or outer rotor

Permanent magnet (PM) machines are widely used in many applications. They can have inner (IR) or outer rotor (OR). These two configurations are optimized individually and compared in this paper based on surface-mounted PM (SPM) machines. The optimal split ratio and flux density ratio are derived analytically for both topologies. The analytical models are verified by finite element (FE) analyses. Their optimal designs are compared when they have the same overall size and copper loss. It shows that the OR designs have significantly higher split ratio while the IR designs require much higher flux density ratio for the maximum torque. For SPM applications, the OR designs exhibit higher torque than IR designs.