Modelling of the Bearing Breakdown Resistance in Bearing Currents Problem of AC Motors

Abstract

With the wide application of pulse width modulation (PWM) technology in motor driving, the bearing current problem has become more and more severe. The most complicated problem in analyzing bearing currents is modeling the equivalent circuit of the bearing and determination of the equivalent parameters of the model. During the process of bearing current breakdown, the bearing undergoes a transition from the capacitor state to the resistor state. The previously used equivalent model, which only consists of a capacitor parallel with a constant resistor, cannot reveal the real breakdown process. In this paper, an improved equivalent bearing model is derived from the waveform analysis of the experiment. The variable breakdown resistance model of the bearing is put forward and the calculation method of the breakdown resistance is given. The circuit simulation results from the variable resistance bearing model were much closer to the results of the experiment than those from the constant resistance model.