Filippov-Based Stability Analysis of Digitally Controlled Single-Phase Grid-Tied Inverter

Filippov’s method has been extensively used to evaluate stability in dc–dc converters. However, its application to dc–ac converters, which operate at both the switching frequency and the grid frequency, has rarely been studied. In this article, the stability of a digitally controlled single-phase grid-tied inverter (GTI) is investigated via extended Filippov’s method, which fully accounts for multifrequency dynamics and digitization effects. The closed-form expression of the monodromy matrix for the digitally controlled single-phase GTI is established. Using the obtained monodromy matrix, the stability boundary concerning various control bandwidths and grid impedances is assessed, and the oscillation frequency in unstable cases is predicted. Finally, experiments are carried out to validate the theoretical analysis.