Novel Design Optimization Strategy using a Lumped Magnetic-Circuit Model for Surface Permenet Magnet Machine with Step-skewing Rotor

In this paper, a novel approximation strategy to three-dimensional(3-D) optimization design is proposed for surface permanent-magnet machines (SPMSM) with rotor overhang and step-skewing type motor using lumped magnetic circuit model. The rotor overhang method is applied to consider the tolerance of electric steel length in axial-direction and maintain the machine performances. The rotor step-skewing technique is used to reduce cogging torque, torque ripple value and THD of back-electro motive force (EMF). In general, the 3-D finite element method (FEM) analysis is requisite to analyze the performance of overhang and step-skewing SPM motor considering the additional flux on the overhang side and the leakage flux crossing section on the rotor magnet side. Moreover, to optimize the SPM topology for target performance, 3-D effect which are number of skew steps, shape of magnet and length of rotor, need to be considered. However, 3-D FEM optimization process requires abundant computation time and computing memory. To deal with this problem, main design variables is considered using lumped magnetic-circuit model. In addition, effective of this method is validated through comparison of 2-D, 3D and test results.