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 2nd 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.