Phasor Analysis-Based Design Method for Active Common-Mode EMI Filter in DC/AC Converters

Active EMI filter (AEF) mitigates common mode (CM) electromagnetic interference by injecting a compensation current of the opposite phase with CM noise current. Due to AEF’s nonideality, the phase difference between compensation and noise current varies with frequency and hardly maintains 180°. Thus, the phase difference determines AEF’s noise compensation performance, and it changes with AEF key parameters. The adjustment of phase difference is key to AEF design. However, the traditional insertion loss (IL) based design method does not exhibit the phase information, which hinders the improvement of AEF performance. To address the issue, this article proposes an AEF design method based on phasor analysis. First, the traditional IL-based design method is introduced, and the effect of phase difference is emphasized. Then, the phasor analysis is conducted that contains the phase difference between compensation and noise currents. Therefore, the phasor analysis-based AEF design method is proposed, which guides to change key parameters to adjust the phase difference and improve AEF performance. Experiment shows that the proposed method can improve AEF’s noise suppression by around 10 dB with no additional hardware or software.