Reduced Dysprosium Permanent Magnets and Their Applications in Electric Vehicle Traction Motors

Permanent magnet (PM) machines employing rare-earth magnets are receiving increasing interest in electrical vehicle (EV) traction applications. However, a significant drawback of PM machine-based EV tractions is the extremely high cost and volatile supply of rare-earth materials, especially for dysprosium (Dy), whose price is almost 6 times higher than neodymium. This paper describes a new Dy grain boundary-diffusion process for sintered Nd₂Fe₁₄B magnets to maximize its effect on coercivity enhancement. The new process gains an 81% reduction in Dy consumption normally required by the conventional Nd₂Fe₁₄B magnets for the equivalent performance and 17% higher remanence. The investigation into the application in an interior PM (IPM) machine for a small-sized EV traction shows that compared with the conventional Nd₂Fe₁₄B magnets, despite the relatively low coercivity, the low-Dy-content magnets still withstand the thermal and demagnetization challenge over various driving operations. In addition, with the magnet´s high remanence and energy product, the machine gains significant torque and energy efficiency improvements. The analysis results are validated by a series of tests carried out on a prototype IPM machine with the new magnets.