Failure analysis on Nd-Fe-B under the multi-physical field coupling of permanent-magnet synchronous machines

Abstract

In this paper, the Tesla meter and magnetic force microscope were used to study the open-circuit remanence and magnetic domain structure of Nd-Fe-B permanent magnets (PMs) in high-power density permanent magnet synchronous motors (PMSMs). An experimental platform was built to simulate the internal demagnetization environment of PMSM. Nd-Fe-B PMs were subjected to high temperature, DC demagnetizing field and alternating demagnetizing field. The results show that even when the working point of Nd-Fe-B PM is higher than the knee point, demagnetization still occurs in the simulated motor environment. The relationship between macroscopic magnetic properties and magnetic domain structure is investigated. With the decrease of open-circuit remanence, the average width and the magnetization of the magnetic domain in the magnetization direction decrease. Due to the width of the magnetic domain decreasing, the number of magnetic domains increases, and the area of the domain wall increases. As a transition region with weak magnetism, the increase of the domain wall area will lead to a decrease in magnetic properties. This work is helpful to understand the demagnetization mechanism of Nd-Fe-B magnets in the PMSMs.