Nonlinear Analytical Model for Predicting Magnet Loss in Surface-Mounted Permanent-Magnet Motors

Abstract

This article develops a nonlinear analytical model (NAM) for predicting the magnet loss of surface-mounted permanent-magnet (PM) motors considering nonlinearity effect and slotting effect. The analytical expression of vector magnetic potential in the PM region is derived from Hague’s equation for slotless air-gap, and then, it is extended for slotted air-gap based on the conformal mapping method. The PMs, iron nonlinearity, and winding current contributing to the eddy current are all represented by equivalent current in the analytical model. The key of the proposed model is to solve the equivalent current of iron nonlinearity from the improved magnetic circuit model (IMCM) of iron region, where the air flux source is proposed to replace the air reluctance. It is found that the iron saturation can decrease the amplitude of flux density and therefore reduce the magnet loss. Based on the NAM, the magnet loss can be obtained with high accuracy and high efficiency, which is a powerful tool for the optimization of magnet loss in the motor design. The effectiveness of the proposed model is verified by the finite-element method.