Research on an Inverter Output Filter for Reducing Common-Mode Voltage at Motor Terminals in PWM Drive System

Pulse width modulated (PWM) inverter can generate common-mode voltage. Common-mode voltage can produce charge-discharge current at the distant of every insulated gate bipolar transistor (IGBT) high-speed switching. This current creates leakage current escaping to earth through stray capacitors inside motors. The large leakage current can create electromagnetic interference (EHI) and short the life of motor bearings, effect reliability of the whole system. A novel PWM inverter output filter is proposed for common-mode voltage reduction. A compensating voltage with the same amplitude but with the opposite polarity is imposed to the common-mode voltage generated by the PWM inverter. Analysis and experiment results confirm the validity of the proposed filter that the common-mode voltage at motor terminals is eliminated almost completely and the adverse effects of the commonmode voltage, such as shaft voltage and leakage current, are unobvious.