A Modified LLCL Filter With the Reduced Conducted EMI Noise

TLDR

Transformerless grid‑tied converters using PWM face significant challenges from grid‑injected current harmonics, leakage current, and EMI noise during output filter design. This study investigates common‑mode and differential‑mode EMI in LCL and LLCL filters and proposes a modified LLCL topology to attenuate conducted EMI and reduce dc‑side leakage current. The authors analyze EMI behavior in LCL and LLCL filters, design a modified LLCL filter, and develop a parameter‑design method for the filter. Simulations and experiments on a 0.5‑kW, 110‑V/50‑Hz inverter prototype confirm that the modified LLCL filter outperforms conventional LCL and LLCL filters in EMI attenuation and leakage current reduction.

Abstract

For a transformerless grid-tied converter using pulse width modulation, the harmonics of grid-injected current, the leakage current, and the electromagnetic interference (EMI) noise are three important issues during designing of the output filter. In this paper, the common mode and the differential mode EMI noises are investigated for the LCL- and LLCL-filter-based single-phase full-bridge grid-tied inverters. 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.