Investigation of Cascade Connection Method to Improve the Insertion Loss of DM Active EMI Filters

In this article, a new kind of cascade connection method of differential mode (DM) active EMI filter (AEF) is put forward. Contrary to the conventional idea, it is found different kinds of cascade AEF connections show different insertion loss (IL). Based upon the mathematical analysis, among the eight potential connection methods, two cascade AEF-connection methods are more effective than the other six methods. The IL is much higher than the others. Therefore, the two effective topologies are further analyzed from several perspectives. And the best topology suiting the practical application is found. Several prototypes are fabricated and tested. Experimental results show good agreement with the theoretical calculation.