Robust Impedance Reshaping of Multiple Ongrid Inverters regarding Variable Grid Conditions

To avoid the cost of extra high-precision sensing circuit, single injected current feedback control scheme has been developed to complete both current regulation and active damping control of LCL-type filter-based grid-connected inverter. However, traditional single current feedback control method is sensitive to the variation of grid impedance. This paper will address this problem by reshaping the inverter output impedance with an added low-cost two-switch auxiliary circuit in the filter capacitor branch. Because the auxiliary circuit requires very low power rating, it does not sacrifice the efficiency of the inverter. Compared with the traditional single injected current feedback control method, the inverter output impedance with the proposed method possesses sufficient passivity and robustness in the frequency range of interest. To verify the validity and feasibility of the proposed method, comparative experimental waveforms are given in the paper.