A modified LLCL-filter with the reduced conducted EMI noise

For a transformerless grid-tied converter using Pulse Width Modulation (PWM), the harmonics of grid-injected current, the leakage current and the Electromagnetic Interference (EMI) noise are three important issues during design of the output filter. In this paper, the Common-Mode (CM) and the Differential-Mode (DM) EMI noises are investigated for the LCL- and LLCL-filters based single-phase full-bridge grid-tied inverter. Based on this, a modified LLCL-filter topology is proposed to provide enough attenuation on the conducted EMI noise as well as to reduce the DC-side leakage current. The parameter design method of the filter is also developed. The comparative analysis and discussion on four filter cases (the conventional LCL-filter, the conventional LLCL-filter, the modified LCL-filter, and the modified LLCL-filter) are carried out and verified through simulations and experiments on a 0.5 kW, 110 V / 50 Hz single-phase full-bridge grid-tied inverter prototype.