Analysis of Open-Circuit Performances in Flux-Reversal Permanent Magnet Machines by Superposition Methods

In this paper, superposition methods including the superposition of a single stator tooth and the superposition of a single rotor tooth, are proposed to predict the open-circuit performances of flux-reversal permanent magnet (FRPM) machines. By the proposed superposition methods, the electromagnetic performances, such as air-gap flux density, electromotive force, cogging torque, and unbalanced magnetic pull (UMP) are investigated and verified by 2D finite element analysis (FEA). Further, according to the superposition methods, cogging torque reduction techniques can be acquired from both stator side and rotor side. In addition, the influence of stator-slot/rotor-pole-pairs (slot/pole) combination on UMP is also studied, and consequently, a reasonable slot/pole combination rule is suggested to avoid UMP. Then, an improved configuration for UMP reduction is also investigated and verified by FEA. Finally, the prototype machines are manufactured and tested to further verify the theoretical analysis and FEA predictions.