Hysteresis loss in NdFeB Permanent Magnets in a Permanent-Magnet-Synchronous Machine

Abstract

Most permanent-magnet (PM) loss studies consider only eddy current loss and neglect hysteresis. In this paper, the hysteresis behavior of two NdFeB PM grades with different magnetic properties is assessed when applied in a PMSM. Data from vibrating sample magnetometer measurements and hysteresis modelling are used as a base. In addition to the main magnetic phase the samples contained magnetic phases with reduced coercivity. Such phases may contribute to hysteresis losses in a PM material. A new model is introduced to simulate the hysteresis of rare-earth magnets of any geometric shape in the 2nd and 1st quadrants of the intrinsic BH-plane. The magnetic field strength distribution in the permanent magnet material of an electrical motor was analyzed by 2D finite-element method (FEM). The results are used as the input data for an analytical hysteresis model. The results indicate that the hysteresis loss resulting from the structural imperfections and geometry of the magnet may introduce a considerable loss in NdFeB PMs applied in rotating electrical machines.