Analysis and Reduction of Cogging Torque for Flux-Switching Permanent Magnet Machines

In this article, a new modeling approach is proposed to investigate cogging torque and the corresponding reduction techniques of flux-switching permanent magnet (FSPM) machines. First, based on the superposition of each single rotor tooth, an analytical expression of cogging torque in FSPM machines is derived and confirmed by the finite-element analysis (FEA). Then, three feasible techniques, i.e., successively shifting rotor teeth, alternately shifting rotor teeth, and stepped skewing rotor blocks, are proposed for cogging torque minimization of FSPM machines. Correspondingly, generally analytical expressions of these three methods are deduced, through which the analytically optimal shifting angles can be determined. Besides, the cogging torque harmonics are analyzed by both analytical expressions and FEA, and then, the multidimensional techniques, namely three rotor-based reduction methods combined with the optimal stator tooth width, are introduced and studied to further suppress cogging torque. Finally, prototyped machines are manufactured and tested, and the corresponding experiments verify the effectiveness of the reduction methods.