Current feedback based hybrid common-mode EMI filter for grid-tied inverter application

In this paper, a current feedback based hybrid common-mode EMI filter is presented for grid-tied inverter application, which employs passive filter with parallel damping branch. A current transformer is used to sense the target common-mode (CM) current, and the active circuit injects cancelation CM current via coupling capacitor. In particular, the proposed hybrid EMI filter with 2^nd order high pass filter characteristic equivalently enhances the filter capacitance at high frequency range. Standalone and offline experimental results based on grid tied three-phase inverter system show that the proposed hybrid filter can improve the EMI attenuation by 10~20 dB beyond 150 kHz.