An Improved Method for Reduction of Voltage Distortion in IPM EV Motors for a Better Flux Weakening Capability

Abstract

There is a growing interest in interior type permanent magnet (IPM) with electric mobility transformation. High speed capability and power density are the main features of IPM motors. Special motor control techniques such as field weakening (FW) and maximum torque per voltage (MTPV) are applied to these motors for high speed operation. Motor terminal voltage is the most critical control parameter of these motor control techniques. Terminal voltage distortion is another important parameter in the literature. Especially in the FW and MTPV regions, the terminal voltage distortion increases with the effect of the armature reaction. In this study, the reduction of terminal voltage distortion in IPM motors has been analyzed for the first time in the literature in both FW and MTPV regions for e-mobility application. An improved method is proposed to reduce the terminal voltage distortion level of the reference IPM EV motor, which has a round rotor structure. This method proposes pole shoe rotor topology that directly affects the harmonics of the air gap field and the motor terminal voltage. Finite Element Analysis (FEA) is performed during the design phase. The proposed rotor structure is prototyped. Performance results are obtained to verify the FEA results. According to the experimental results, d-axis current ripple is reduced by nearly 10% at 6000 rpm and 5% at 12000 rpm, q-axis current ripple is reduced nearly 20% at 6000 rpm and 7% at 12000 rpm. The terminal voltage ripple is reduced by nearly 11% at 6000 rpm and 3% at 12000 rpm as a result of the proposed method.

Keywords

• Electric vehicle (EV)
• traction motor
• interior permanent magnet (IPM)
• terminal voltage distortion
• field weakening (FW)
• maximum torque per voltage (MTPV)