Quantitative Transient Stability Analysis for Parallel Grid-Tied Grid-Forming Inverters Considering Reactive Power Control

Transient stability of single grid-forming inverter (GFMI) system has been thoroughly analyzed in recent years, but quantitative transient stability analysis for parallel GFMI system considering reactive power control has not been studied. To bridge this gap, the equivalent large signal model of parallel GFMI system considering the interaction between inverters is newly established. Based on the model, the path-independent Lyapunov function (LF) considering the dynamic of reactive power control, damping dissipation, and interaction effect is newly constructed for quantitative transient stability analysis, which can obtain maximum attraction region for stability prediction, estimate critical clearing time, and characterize stability margin. Compared with traditional LF, the conservatism of attraction region and error of estimated critical clearing time is significantly reduced. Moreover, the effect of parameters on the transient stability of parallel system is revealed. Finally, experimental results verify the accuracy of attraction region and parameter analysis.