Rare earth reduction using a novel variable magnetomotive force flux-intensified IPM machine

This paper presents a novel variable magnetomotive force flux-intensifying interior permanent-magnet (IPM) (VFI-IPM) machine, which uses only low-coercive force magnets to reduce usage of rare earth metals. The VFI-IPM machine is designed with a characteristic of L_d > L_q, which is typical for FI-IPM machines and uses low-coercive force magnets with magnetization level control. A theoretical magnet operating point analysis was conducted to investigate the design methodology. A proof-of-principle prototype machine was then designed based on these principles. Simulation and experimental results show that the VFI-IPM prototype can achieve a wide torque-speed envelope and variable torque-speed characteristics while not requiring high-coercive force magnets that would include far more expensive rare earth materials, such as dysprosium.