Investigation of Rotor Designs of Variable-Flux Interior Permanent Magnet Synchronous Machines for Traction Applications

Abstract

This paper presents a comparative study of rotor designs in variable-flux interior permanent magnet (VF-IPM) machines to understand their characteristics and potential for reducing cost and improving high-speed efficiency. A new optimization model is proposed with the consideration of designing maximum 50% magnetization state (MS) variation range at all operating conditions and increasing torque density. It identifies the main design tradeoff between torque density and MS controllability. Limiting MS variation range also significantly reduces inverter current rating requirement in traditional VF-IPM machines and reduces system cost. Finite element analysis results show the proposed method significantly reduces MS control current, achieves high torque output, and reduces heavy rare-earth usage in optimal VF-IPM machines.