Integrated CM Inductor for Both DC and AC Noise Attenuation in DC-Fed Motor Drive Systems

Using passive electromagnetic interference (EMI) filter to suppress the common mode (CM) noises on the dc and ac side of motor drive systems is a common filtering method. Shrinking the volume of CM inductors is the key to the miniaturization of EMI filters. In order to reduce the volume, this article proposes a new method to integrate the dc and ac CM inductors by magnetic coupling. The principle of the filter and the design constraints of coupled CM inductors are analyzed. The filter volume reduction advantage gained by using the proposed method is illustrated. A model is built to describe the relationship between the coupling coefficient and filtering performance. Finally, the procedures for design of coupled inductors are addressed and the results are verified by experiments. In the comparative case study, the volume of coupled inductor is 90% of that of discrete inductor.