Fast Prediction of Transient Magnet Temperature Distribution for SPMSMs Considering PWM Effect

The pulsewidth modulation (PWM) effect plays a critical role not only in permanent magnet (PM) loss but also in PM temperature distribution. This article proposes an analytical method to fast predict transient PM temperature distributions in surface-mounted PM synchronous machines (SPMSMs) accounting for the PWM effect. The proposed method is obtained by solving the transient conduction heat transfer equation, in which the coordinate transform is employed to simplify the mathematical expressions, and a PM loss factor is introduced to consider nonuniform PM loss distributions caused by low- and high-frequency current harmonics. Meanwhile, it can be further integrated with a lumped-parameter thermal model to predict PM temperature distribution considering different load and/or thermal conditions with a minor computation burden compared to the finite element (FE) method. Furthermore, the proposed method is applied to investigate the influences of the PWM effect on the PM temperature distribution. By evaluating the asymmetric PM temperature distributions caused by different current harmonics, it is shown that the high-frequency current harmonics due to the PWM effect may lead to significant PM temperature rises on both sides of each PM pole. It will further superimpose the PM temperature rise caused by the low-frequency current harmonics, resulting in a pronounced nonuniform PM temperature distribution. The proposed integrated analytical and LPTM method can consider both the nonuniform PM loss and temperature distributions due to the PWM effect for the first time to avoid temperature overheating. Finally, the FE method and experiments are used for validation based on a prototype SPMSM.