Abstract
As motor design is key to the development of electric vehicles (EVs) and hybrid EVs (HEVs), it has recently become the subject of considerable interest. Interior permanent magnet (IPM) motors offer advantages such as high torque density and high efficiency, benefiting from both permanent magnet (PM) torque and reluctance torque. However an obvious disadvantage of IPM motors is that operation at high speed involves difficulties in achieving the required flux-weakening capability and low vibration. This study focuses on optimizing the flux-weakening performance and reducing the vibration of an IPM motor for EVs. Firstly, flux-weakening capability, cogging torque, torque ripple, and radical vibration force are analyzed based on the mathematical model. Secondly, three kinds of motors are optimized by the genetic algorithm and analyzed, providing visible insights into the contribution of different rotor structures to the torque characteristics, efficiency, and extended speed range. Thirdly, a slotted rotor configuration is proposed to reduce the torque ripple and radical vibration force. The flux density distributions are discussed, explaining the principle that motors with slotted rotors and stator skew slots have smaller torque ripple and radical vibration force. Lastly, the design and optimization results have been validated against experiments.
Highlights
Due to the ever-increasing concerns with respect to the energy crisis and environmental pollution, the reduction of greenhouse gases and exhaust emissions of CO, HC, and NOX from the transportation sector has become an issue of worldwide relevance [1,2]
An obvious disadvantage of the interior permanent magnet (IPM) motor is that operation at high-speed ranges involves difficulties in achieving the required flux-weakening capability [8]
In order to improve flux-weakening capability, flat-type, V-type, and triangle-type IPM motors have been employed by Prius, for they have greater d-axis and q-axis inductance, and smaller flux linkage than surface mounted permanent magnet (SPM) motors [10,11,12]
Summary
Due to the ever-increasing concerns with respect to the energy crisis and environmental pollution, the reduction of greenhouse gases and exhaust emissions of CO, HC, and NOX from the transportation sector has become an issue of worldwide relevance [1,2]. The relatively important torque pulsation in the design of the IPM motor has received significant attention in recent years Design features such as asymmetric flux barriers [16] or sinusoidal profiling of the rotor surface [17], skew slots, and control techniques [18,19,20] have been proposed to reduce the torque ripple of the IPM motor. This study focuses on optimizing the flux-weakening performance and reducing the vibration of an IPM motor for EVs. In Section 2, an iterative comparative analysis of torque–speed characteristics with different flux linkage, d-axis inductance, and rotor saliency ratios is performed to demonstrate the design principle.
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