Demagnetization proximity considerations of inverter-fed permanent magnet motors

This study provides a detailed guideline on how the demagnetization proximity of a permanent magnet synchronous motor has to be evaluated and incorporated into the design process of an inverter-fed machine. It is shown that the motor is subjected to a serious level of demagnetization risk even in the rated and flux-weakening modes, which are less demanding operations than the transient mode. A new analytical-computational approach is proposed to modify the existing finite element-based simulation process in which a constant current is always applied to different motor geometries, regardless of different magnetic loading levels and operating modes, to find the most robust design in terms of the demagnetization phenomenon. Instead of the current-based method, a torque-based simulation process based on which the correct electric loadings are calculated and applied to the motor is introduced. The obtained results indicate a significant distinction between the existing and the proposed approach in terms of the demagnetization study of a permanent magnet motor. Moreover, the effect of two different types of permanent magnet materials, i.e. rare-earth and ferrite magnets, is also addressed. As a very significant factor, the temperature-dependent PM and silicon steel material properties are also measured experimentally and incorporated into the simulation process handled by the FE package.