Multiphysics Design and Optimization of a Rare-Earth Free, Manganese Bismuth Based, Surface Mounted Permanent Magnet Machine

Abstract

This paper deals with the feasibility of rare earth (RE) free manganese bismuth (MnBi) permanent magnets as an alternative material in electric vehicle (EV) motor applications and performance evaluation at high temperature. Neodymium Iron Boron (NdFeB) permanent magnets are typically used in permanent magnet synchronous machines (PMSMs) for EV applications for achieving high power, high torque density and high efficiency due to high remanent flux density $(\boldsymbol{B}_{\boldsymbol{r}})$ and maximum energy product $(\boldsymbol{BH}_{\boldsymbol{max}})$. Market dominance of NdFeB is hindered significantly due to the supply chain limitations of rare-earth elements which also have the tendency to experience significant price fluctuations. This has triggered substantial efforts in investigating new, alternative magnetic materials containing rare earth free elements. Although ferrite magnets have been explored as alternative choices in the past, ferrites have inferior magnetic properties compared to the emerging MnBi magnets. In this paper, a finite element-based multi-physics design and optimization framework of a SPM machine is conducted evaluating MnBi and NdFeB magnets including electromagnetic performance at high temperatures with thermal and mechanical validation.