A Novel Technique to Measure Parasitic Capacitances Affecting CM Noise Emissions

By utilizing wide-bandgap power devices, converters can operate at high switching frequency to increase power density without sacrificing efficiency. However, conducted electromagnetic interference (EMI) poses a challenge in the design of these high-frequency power converters. Common-mode (CM) noise is especially difficult to model and diagnose because it is determined by small distributed parasitic capacitances. This work evaluates the limitations of existing techniques to measure parasitic CM capacitances in power converters. Then, a new technique is presented to precisely quantify the parasitic capacitances affecting CM noise based on conducted EMI measurements. The measured capacitance values are demonstrated to accurately predict CM noise under several different converter operating conditions.