A Novel Methodology for the Demagnetization Analysis of Surface Permanent Magnet Synchronous Motors

A surface permanent magnet synchronous motor (SPMSM) using ferrite magnet represents small air gaps and high stack lengths relatively. Thus, it has small edge effects on the performance of the motor, and a 2-D finite-element analysis (FEA) method is largely used to design it. In the case of the demagnetization analysis in the SPMSM, however, it is difficult to neglect fringing effects in air gaps, because the permeability of the permanent magnet is the same as air and the direction of the armature reaction is opposite to the magnetization direction. Therefore, the accuracy of the 2-D FEA is significantly degraded. In this paper, the edge effect of SPMSM on the demagnetization analysis is analyzed. For achieving it, the opposing magnetic field that contributes to the demagnetization is analyzed by two different elements, such as permanent magnet and armature reaction. In addition, a simplification model of the yz plane that can consider the edge effect is proposed to increase the accuracy of the conventional 2-D FEA, which is analyzed on the xy plane, and correction factors are also induced. Finally, its validity is verified by applying the proposed method to the conventional motors.