A Review on Magnet Loss Analysis, Validation, Design Considerations, and Reduction Strategies in Permanent Magnet Synchronous Motors

Abstract

Eddy current losses in magnets are a major consideration in the rotor design of permanent magnet synchronous motors (PMSMs). Stator design choices and the use of modern inverters with high switching frequency introduce harmonics that can contribute to significant losses in the magnets, causing the rotor to heat up. In typical PMSMs, the lack of rotor cooling can cause the magnet’s performance to degrade at high temperatures and eventually demagnetize. This review examines a large number of studies analyzing magnet eddy current losses using analytical methods and finite-element analysis. In some of these studies, magnet segmentation is carried out to reduce the losses; however, their loss-reduction effects depend highly on the type of PMSM and the mix of stator harmonics. Magnet segmentation without considering these effects can, in fact, increase the magnet losses, in addition to the extra manufacturing efforts. Multiple design analysis show the influence of rotor–stator geometric features on magnet losses. Although measuring magnet eddy current losses for these motor designs is a tedious task, authors have proposed calorimetric and loss segregation-based techniques to provide validation. This paper addresses magnet loss modeling techniques, PM material considerations, magnet segmentation effectiveness, motor and stator design effects, and experimental validation to inform motor designers about the costs and benefits of rotor designs that minimize rotor losses.