Principle and Robust Impedance-Based Design of Grid-tied Inverter with LLCL-Filter under Wide Variation of Grid-Reactance

Currently, how the inductive grid impedance variation affects the stability of digitally controlled grid-tied inverters with a high-order (LCL or LLCL) filter has been numerously studied. Note that a distributed power system may contain the capacitive load, the Power Factor Correction (PFC) capacitor and the long cable. During the design of grid-tied inverters, we should address effects of the equivalent grid reactance, including both the inductive and capacitive impedance, on the stability of system. Nevertheless, up to now, to best knowledge of authors, the detailed parameter design method of the LCL- or LLCL-filter-based grid-tied inverter has not yet been introduced, when the capacitive grid impedance is addressed. In this paper, by using the passivity-based analysis, the detailed stability study on the LLCL-filter-based grid-tied inverter is carried out, when the grid reactance varies in a wide range. Based on the analysis, an exact and robust parameter design of system is proposed. Simulations and experimental results on a 220 V/2 kW prototype confirm that by using the proposed parameter design method, a high performance grid-tied inverter system can be achieved under the rigid grid condition.