Common mode voltage in DC-fed motor drive system and its impact on the EMI filter

Common mode (CM) choke saturation is a practical problem in common-mode filter applications. It´s generally believed that the leakage inductance of common-mode chokes makes the core saturated. This paper analyzes two new mechanisms for common-mode choke saturation due to common-mode voltage, and these mechanisms are verified in experiment. Common-mode choke saturation is particularly important for motor drive systems, which have a high common-mode voltage and comparably higher stray grounding capacitance. A model is established to describe the relationship between the common-mode voltage and the volume of the common-mode magnetic components. According to the analysis, LISNs (line impedance stabilization networks) play an important role in the design of CM magnetic components.