A unified Impedance-based Stability Criterion (UIBSC) for paralleled grid-tied inverters using global minor loop gain (GMLG)

In this paper a unified Impedance-based Stability Criterion (UIBSC) has been proposed for paralleled grid-tied inverters. Compared to the traditional Impedance-based Stability Criterion (IBSC) which needs to evaluate all minor loop gains (MLGs) of each individual inverter, the UIBSC only checks the derived global minor loop gain (GMLG) once to determine system stability. As a result, the computation efforts can be significantly reduced when system contains a large number of inverters. In addition, a stability-oriented design guideline based on the GMLG has been developed for the paralleled grid-tied inverters. Therefore, the grid impedance, inverter filter parameters, time delays of digital control and control parameters can be analyzed or designed to meet the system stability requirement. Theoretical analysis and simulation results have been presented to verify the proposed methods.