Insertion Loss Analysis and Optimization of a Current Based Common-Mode Active EMI Filter

Active electromagnetic interference filter (AEF) is an effective method to handle common-mode (CM) electromagnetic interference (EMI). This article derives the accurate closed-loop transfer function of a feedback-type current-sensing current-compensating AEF. The attenuation factor (A(F)) is defined in this article, identified as a critical parameter influencing the suppression performance of the AEF. For practical systems where the CM impedance exhibits capacitive behavior in high band, a method using impedance-optimized inductor is proposed to enhance the CM impedance environment of the feedback AEF. This enhancement raises A(F), thereby expanding the bandwidth of AEF and improving the suppression effects. An optimization strategy for insertion loss of the AEF is also proposed. The insertion loss is predicted and verified through experiments. The proposed AEF exhibits outstanding suppression performance in the range of 100 kHz to several MHz, achieving nearly 40 dB of CM EMI suppression in the region.