Technology trends, challenges, and opportunities of reduced-rare-earth PM motor for modern electric vehicles

Abstract

Nowadays, with increasing concerns about environmental pollution and energy crisis electric vehicles are rapidly developing owing to their significant environmental-friendly benefits. To meet the diverse driving requirements of electric vehicles, the PM motors with high-performance rare-earth PMs have been widely employed in electric vehicle powertrains, which shows the performance merits of high power density and high efficiency. Yet, rare-earth PMs, as non-renewable strategic resources, usually suffer from unstable supply and fluctuation prices, which increases the potential risks of further large-scale application of rare-earth PM motors. And this also poses a negative factor for the long-term sustainable development of electric vehicles or other applications that rely heavily on rare-earth PM materials. Under this background, a type of less-rare-earth PM motors, which aims to effectively alleviate the dependence of high-performance PM motors on rare-earth PMs, has recently drawn increasing attention from experts and scholars. It implies that the investigation and development of less-rare-earth PM motors without compromising performances is becoming a new and hot research direction in the motor field. This paper reviews the existing main alternatives for less-rare-earth PM motors. Based on the dominated torque component, the less-rare-earth PM motors are divided into two types, which are the less-rare-earth PM-dominated motor and less-rare-earth PM-assisted motor. The operation principle, design considerations and restrictions of each type of less-rare-earth PM motor is sequentially discussed. Finally, combined with the potential electric vehicle application, the key problems of less-rare-earth PM motor are summarized and the corresponding technological means are prospected.