Extracting the parameters of a common mode EMI equivalent circuit model for a drive inverter

This paper proposes a general device-based common mode (CM) model for inverter-fed motor system that able to describe the CM conducted electromagnetic interference (EMI) propagating mechanism in the system. Numerical parameters are derived using impedance measurements. The procedure of model elements extraction is introduced systematically and is convenient to implement. The derived model makes the CM EMI characteristic of the inverter is deduced from a circuit analysis viewpoint. Variable EMI noise propagation paths are evaluated and impedances along the propagation loops inside the inverter can be reconstructed for better EMI suppression. The transfer ratio calculations under different conditions show good agreement with experimental measurements verifying the proposed modeling methodology.