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Performance Comparison of Different Permanent Magnet Motors for Traction Applications

With the increasing demand for traction applications, various permanent magnet motor topologies have been innovated recently to improve key aspects such as efficiency, power density, maximum motor speed, design cost, and reliability. This paper studies eight different motor topologies and compares their electromagnetic performance to investigate the current design trends and challenges. It includes a 3-phase and 5-phase rare-earth (RE) magnet-assisted inner rotor motor, 3-phase, and 5-phase ferrite magnet-assisted inner rotor motor, 5-phase ferrite, and RE magnet-assisted outer rotor motor, 3-phase, and 5-phase RE magnet axial flux motor. The motors are optimized by using the lumped parameter model and finite element analysis (FEA). The objective functions are developed by considering the characteristics of the individual motor model and key factors of traction application such as average torque, torque pulsation, demagnetization, losses, material cost, and DC-link voltage. For a fair comparison, the active volume, cooling system, and maximum current density limit are maintained the same for all motors. Performance characteristics such as torque profile, back-EMF, efficiency, power factor, power density, and torque/dollar are compared using intensive FEA simulation. Several optimized motors are prototyped and tested for no-load and loaded conditions for experimental validation using a dynamo setup. The measured back-EMF, cogging torque, and torque constant are presented.