Design and Optimization of a Novel Dual-Rotor Hybrid PM Machine for Traction Application

The objective of this paper is to investigate the design and optimization of a novel dual-rotor hybrid permanent magnet machine for traction application. The proposed dual-rotor hybrid synchronous PM machine synthesizes the synchronous reluctance and surface permanent magnet rotors into a single machine with the common shaft by using “inner-out” configuration. One feature of this hybrid machine is to explicitly separate the magnet torque and reluctance torque components so that the two rotors can be designed individually with more flexibility. Instead of using expensive rare-earth magnets, the hybrid machine is demonstrated to achieve similar performance as the Toyota Prius motor with only ferrite magnets arranged in a Halbach array structure. Design principles including structure configuration, sizing equation, and alternative topologies using N-N and N-S types are elaborated. Multi-objective optimization is implemented in the electromagnetic finite element analysis for the traction motor design, and Pareto line of the results is identified. Structural analysis is also used to validate the mechanical integrity at high-speed conditions. The optimized machine demonstrates almost the same torque profile as the Prius motor.