Research on Bearing Currents Negative Effect of PWM Variable Frequency Speed Regulation System

The research on variable frequency system mainly focuses on the developing of system performance, while the negative effects of the system is ignored. The bearing currents issues are a typical negative effect. In this paper, a lumped common mode system model of a variable frequency motor driven by PWM inverter is proposed and the formulas of the key parameters in the system are presented. By researching a 3kW variable frequency motor, the experiment platform is built, experimental results are consistent with the simulation results, which provides the system model and the calculation of key parameters are basically rational. By analyzing of the generation mechanism of shaft voltage and bearing current, as well, the relationship between common-mode voltage and the shaft voltage and bearing current, it has studied the impact of the carrier frequency and the motor running frequency to common mode voltage, shaft voltages and bearing currents. It has provided a theoretical basis for further studying the suppression measures of bearing currents and improving the stability and reliability of the PWM variable frequency speed regulation system.