Optimization of Modular SPM Machines Considering Stator Modularity

This paper presents the global optimization of modular surface-mounted permanent magnet machines considering the effect of stator modularity on machine electromagnetic performances. In order to optimize the electromagnetic performance, the multi-objective genetic algorithm is adopted and 2D finite element method is used. Variables such as stator yoke height, tooth width, flux gap width, split ratio and rotor yoke thickness have been selected for the optimization. The objectives are to achieve maximized average torque, minimized torque ripple, copper loss and total machine mass. Amongst all the variables, the flux gap width is a key parameter which has significant impact on machine electromagnetic performance, but has not been included in the optimization process in the literature. The results in this paper have shown that considering the flux gap width in the optimization will lead to further improvement in machine electromagnetic performance. In addition, for machines with lower slot number than rotor pole number, the optimization process shows that an appropriate flux gap width is needed for optimal electromagnetic performance. However, for machines with higher slot number than pole number, the flux gap width tends to be zero, leading to non-modular machine having the optimal performance.