Two kind of nonuniform slot distribution models, the unit machine shift model (Model 1) and the single slot shift model (Model 2), are proposed for reducing cogging torque of surface-mounted permanent magnet(SPM) machines. Further, based on exact subdomain model and Maxwell stress tensor, an analytical model is further built for calculating cogging torque in SPM machines with nonuniformly distributed stator slots. Its accuracy and feasibility have been validated by finite element (FE) method. With the analytical model, effects of slot shift angle on cogging torque are investigated for an 8-pole/12-slot SPM machine. Meanwhile, coupling relationships between shift angle and other design parameters (slot/pole number, pole arc coefficient and slot opening) are analyzed. In addition, influences of slot shift on back-EMF and electromagnetic torque are also studied. Conclusions are drawn from the analysis and indicate that Model 1 is much better than Model 2 in improving the performances of SPM machine.
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