Analysis of Reduced Rare Earth PM-Assisted Synchronous Reluctance Motor Enabled with Iron Nitride for High-Speed Traction Application

This paper analyses the performance of reduced rare earth Permanent Magnet assisted Synchronous Reluctance Motor (PMaSynRM) with blended magnets for traction applications. The blended magnet approach utilizes two magnet combinations of Dysprosium-free (Dy-free) rare earth permanent magnet, Iron Nitride and Ferrite magnets which reduce the contribution of rare earth permanent magnets in the double layer rotor topology. The Iron Nitride magnet with comparable energy product of Ferrite magnet is employed for the design of the high-speed traction motor. Multi-physics multi-objective optimization algorithm (MP-MODE) based on differential evolution identifies the optimal designs satisfying the defined objectives and constraints based on a baseline traction motor with rare earth permanent magnets. The critical design objective of demagnetization risk is evaluated at extreme temperatures of -20℃ and 150℃ for both magnet combinations. The lower energy product variants of the rare earth free magnets increase the overall magnet volume which poses challenges to the rotor design at high speed. Hence ensuring the mechanical integrity of the rotor is necessary and the mechanical stress is evaluated dynamically using the multi-physics optimization process. The electromagnetic and mechanical performance of the optimal Iron Nitride-assisted design is compared to an optimal Ferrite-assisted design and baseline traction motor for validation.