Alleviation Technique for Thermal Concentration on Power Devices Driving a PMSM under Zero-Speed and High-Torque Condition

Abstract

This work is concerned with a technique to alleviate thermal concentration on specific switching devices that drive a permanent magnet synchronous motor (PMSM) under zero-speed and high-torque condition. In this condition, e.g., start or stop of an elevator or hill-start of an electric vehicle, a large DC current flows in the PMSM, and the heat generated in the specific switching devices is locally concentrated. The proposed technique uses a zero-sequence voltage in a three-level inverter, and the polarity of the zero-sequence voltage is switched according to the magnetic pole position of the PMSM. The proposed technique can change the current paths in the inverter, and the loss concentrations in specific devices can be alleviated. The simulation results show that the amplitude and the time ratio of the zero-sequence voltage that depend on the magnetic pole position of the PMSM affect the temperature rise of the power device with the maximum temperature. In the experiment, the effectiveness of the proposed technique is evaluated using a small power inverter. This three-level inverter consists of discrete power devices so that the surface temperature of each device can be observed with a thermal camera. The experimental results show that the temperature rise of the device with the maximum temperature is reduced by about 31%.