Reduction of common mode voltage and current in voltage source inverters by passive methods

High frequency common mode voltage (CMV) in voltage source inverter driven AC motors results in parasitic common mode current (CMC) in the motor. In this paper, the cause and the undesired effects of the CMV/CMC are reviewed, the improvements of the passive suppression techniques, the common mode inductor (CMI) and the pure sine filter (PSF), are progressively studied and their experimental performance is investigated in a 4kW motor drive. It is experimentally shown that employing the CMI reduces the CMC effectively, and employing the PSF eliminates all the negative effects caused at the motor side by the high frequency switching.