A Comparison between Hybrid Excited Permanent Magnet and Wound Rotor Motor

Abstract

This paper deals with the comparison between Hybrid Excited Permanent Magnet (HEPM) and Wound Rotor (WR) machines. These motors are suitable for EV application due to their high torque and power density and their enhanced flux weakening capabilities. In this study, two similar machine topologies are proposed: a WR and a HEPM motor, obtained from the WR geometry adding Permanent Magnets (PMs) within salient poles core. Thus, PMs assist the excitation current (PMaEXC) to generate the rotor flux. Main design purposes are to maximize the mean torque and minimize the torque ripple. Finite-element method is employed to analyze PMaEXC motor and WR motor electromagnetic and mechanical performance. Simulation results show the comparison of flux density, flux regulation capability, back-electromagnetic force, torque and power characteristics and efficiency maps of the two motors. The magneto static analysis shows advantages and drawbacks of adding a low amount of rare-earth magnetic material to a traditional PM-less machine. The proposed PMaEXC machine can achieve high torque density at low speed and great flux-weakening capability at high speed.