Demagnetization Performance Enhancement of Heavy Rare Earth Free Permanent Magnet Machines

This paper proposes a 90% HRE-free hybrid rotor concept to enhance the demagnetization performance of a 100 kW motor for traction applications. The demagnetization analysis is presented for three cases- for a motor with 100% HRE-free, 90% HRE-free, and finally with a 100%-HRE magnet. The proposed concept divides each magnet into several segments, and use HRE magnets at the most demagnetization prone top corners of a rectangular magnet. For the proposed hybrid rotor, magnets can be safe from irreversible demagnetization up to 150°C even at 100% negative d-axis current and three-phase short-circuit fault. The hybrid rotor uses approximately 90% HRE-free PM content. Moreover, the hybrid rotor reduces the magnet loss by 90%, which helps alleviate the challenging thermal management problem in a rotary environment.