Investigation of Dy-Free Hybrid PM Motor Based on Spoke-Type Rotor for Automotive Applications

Abstract

NdFeB permanent magnets (Nd-PM) can achieve a coercivity of up to 21 kOe without dysprosium due to the development of manufacturing technology. However, due to the high-temperature operation characteristics of vehicle traction motors, Nd-PM over 25kOe is mainly applied. In this paper, 21kOe Nd-PM and 5.5kOe ferrite-PM (Fe-PM) are simultaneously applied, and a hybrid PM motor (HPMM) suitable for environmental temperature conditions of vehicle traction motors is proposed. HPMM is divided into serial configuration and parallel configuration according to the arrangement of each PM. This paper compares the pros and cons of each configuration and presents rotor structures that can improve demagnetization durability and torque characteristics. After comparing the performance characteristics of each rotor structure through 2D-FEM, finally, an HPMM suitable for vehicle traction motors is proposed. Also, the proposed HPMM shows the same torque and power density as the traction motor of TOYOTA PRIUS 4th-generation hybrid electric vehicle (HEV), the target motor. At the same time, the proposed HPMM reduced the usage of Nd-PM by 47% and the total PM cost by 10% compared to the target motor.