Comprehensive Experimental Study on Shaft Voltage of Traction Motor with Ceramic Bearing for Electric Vehicles

This study investigates the experimental analysis of shaft voltage, focusing on the variables of the inverter and motor in electric vehicles (EVs), applying ceramic bearings. The aim of the study is to analyze the tendencies of shaft voltage in the inverter-fed EV traction motor using experimental methods. The variables for trend analysis include the switching frequency of pulse width modulation (PWM), the oil temperature, and the usage of shaft ground ring (SGR) as variables. Moreover, the variables cover the rotational speed and the torque as load conditions. In order to investigate the stochastic shaft voltage data rigorously, the post-process method using the probability density function is proposed. Using the proposed method, the trends of shaft voltage are analyzed according to the variables above in terms of the mean value and the probability over certain value. The results are figured out that the switching frequency of PWM and the oil temperature influence the shaft voltage, while the rotational speed has little effect on the shaft voltage. Under the load condition, it is shown that the torque, proportional to the current, rather than the rotational speed affects the shaft voltage. The effect of SGR will be handled as a future work with test results of prototype applying SGR.