Comparison of Stator Slot Permanent Magnet Hybrid Excited Machine with Rotor Interior Permanent Magnet Machine for EV/HEV Application

Hybrid excited (HE) machines have synergies of high torque density of permanent magnet (PM) machines and flexible flux weakening of wound field (WF) machines, and are potentially promising candidate for electric vehicles (EVs) and hybrid electric vehicles (HEVs). This paper focuses on a fault tolerant hybrid excited (HE) machine with stator slot PMs and evaluates its electromagnetic performance. To demonstrate the feasibility, a commercial rotor interior PM (IPM) machine, equipped for Toyota Prius 2010, has been selected as the benchmark. The electromagnetic performances, including back-EMF, average torque, torque ripple, torque-speed envelope, efficiency, and fault tolerant capability have been compared comprehensively. It is revealed that the stator slot PM HE machine possesses similar torque density and overload capability with the IPM machine under the same frame length. Moreover, the output torque/power and fault tolerant capability of the HE machine at high speed operation are superior as the result of an additional degree to regulate the magnetic field. Although the torque-speed envelopes are extended, the operation efficiency is reduced for the HE machine due to doubly salient structure and stator PM allocation.