Development of a Rare-Earth-Free SR Motor With High Torque Density for Hybrid Vehicles

• Published in: IEEE transactions on energy conversion Vol. 30; no. 1; pp. 175 - 182
• Main Authors: Chiba, Akira, Kiyota, Kyohei, Hoshi, Nobukazu, Takemoto, Masatsugu, Ogasawara, Satoshi
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.03.2015; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Carbon dioxide; Competition; Density; Efficiency; Hybrid electric vehicle (HEV); Hybrid vehicles; Iron; Motion control; Motors; Permanent magnet motors; Permanent magnets; Rare earth metals; rare-earth-free; Reluctance; Reluctance motors; Stator windings; Steel; switched reluctance motor (SRM); Torque; switched reluctance motor (SRM); Hybrid electric vehicle (HEV); rare-earth-free
• ISSN: 0885-8969; 1558-0059
• DOI: 10.1109/TEC.2014.2343962

The increased price and the limited supply of rare-earth materials have been recognized as a problem by the international clean energy community. Rare-earth permanent magnets are widely used in electrical motors in hybrid and pure electrical vehicles, which are prized for improving fuel efficiency and reducing carbon dioxide (CO 2 ) emissions. Such motors must have characteristics of high efficiency, compactness, and high torque density, as well as a wide range of operating speeds. So far, these demands have not been achieved without the use of rare-earth permanent magnets. Here, we show that a switched reluctance motor that is competitive with rare-earth permanent-magnet motors can be designed. The developed motor contains no rare-earth permanent magnets, but rather, employs high-silicon steel with low iron loss to improve efficiency. Experiments showed that the developed motor has competitive or better efficiency, torque density, compactness, and range of operating speeds compared with a standard rare-earth permanent-magnet motor. Our results demonstrate how a rare-earth-free motor could be developed to be competitive with rare-earth permanent-magnet motors, for use as a more affordable and sustainable alternative, not only in electric and hybrid vehicles, but also in the wide variety of industrial applications.