Cogging Torque Analysis and Minimization of Axial Flux PM Machines With Combined Rectangle-Shaped Magnet

This paper introduces three indexes for the cogging torque waveform and analyzes the influence of machine parameters on these three indexes in the theory. The phase of cogging torque under different combinations of slot opening ratio and pole-arc ratio is analyzed. Based on this analysis, two techniques to minimize cogging torque of the axial-flux permanent-magnet (AFPM) machines are proposed and discussed. Using the quasi-3-D analysis method, the mechanism of cogging torque minimization for AFPM machines equipped with several special magnet shapes is revealed by elaborating the results of each slice. Then, a novel rectangle-shaped magnet arrangement is proposed and investigated for cogging torque minimization. Comparing with other cogging torque minimization techniques such as conventional skew on PM edges, this method is able to decrease cogging torque without comprising torque output. Finally, a prototype is built and the experiment is performed to validate the finite-element analysis results.