An approach to eliminating high-frequency shaft voltage and leakage current from an inverter-driven motor

This paper proposes a small-sized passive EMI filter for the purpose of eliminating high-frequency shaft voltage and ground leakage current from an AC motor driven by a voltage-source PWM inverter. The filter requires access to the neutral point of the motor. A common-mode inductor is connected between the inverter and the motor. The neutral point of the motor is connected to the DC bus mid-point via a resistor. The DC bus mid-point is created by using two capacitors in series across the DC positive and negative buses. This unique circuit configuration makes the common-mode inductor effective in reducing the common-mode voltage appearing at the motor terminals. The validity and effectiveness of the EMI filter is verified by experimental results obtained from a 5-kVA laboratory system.