Suppression techniques of common-mode voltage generated by voltage source PWM inverter

Voltage source PWM inverters generate high frequency common-mode voltage, which induces high shaft voltage, leads to bearing current, and results in premature bearing failure. The generating mechanism of common-mode voltage of voltage source PWM inverters is discussed, which illustrates that common-mode voltage is ladder-type high dv/dt and high frequency step voltage, its amplitude varies with the states of switching devices. According to theoretical analysis and based on conventional sinusoidal output filter, common-mode connection is introduced, i.e., the neutral point of filter Y-connected RC network is connected to the midpoint of DC bus of the inverter. Thus, an improved common-mode sinusoidal output filter is achieved, which can eliminate over-voltage and suppress common-mode voltage, the differential-mode and common-mode problems can be solved synchronously. Simulations and experiments indicate the effectiveness of the proposed common-mode filter.