PWM impact on CM noise and Ac CM choke for variable-speed motor drives

This paper analyzes the common-mode (CM) current and CM filter size for the variable-speed motor drives with different PWM methods. The principle of CM current and CM choke saturation are studied. Some previous proposed CM deduction PWM methods such as active zero states PWM (AZSPWM) and near state PMW (NSPWM) can reduce the CM voltage peak value, However, they may not obviously reduce the CM current and CM choke volt-seconds, due to increased 3^rd order switching harmonics and CM loop parameters. PWM methods should work properly with the CM loop impedance. Also, new CM volt-seconds relationship with PWM methods is proposed with consideration of CM modulation signals. Simulation and experimental results are presented to verify the analysis.