Small-Signal Stability Boundary Analysis of Grid-Following Inverters under Weak Grids by Applying Nonlinear Modeling and Lyapunov's First Method

Grid-following inverter contains highly nonlinear parts such as the PLL, the frequency coupling and so on. The accurate stability analysis is very important. In this study, a high-order nonlinear model of grid-following inverter is established by considering the current control, phase-locked loop and frequency coupling. Then, focusing on the small-signal stability under weak grid, the high-order nonlinear model is carefully linearized, through which the impact of different system and control parameters on the small-signal stability are evaluated with the aid of Lyapunov's first method. The small-signal stability boundaries for different grid parameters and control parameters are depicted for achieving high robustness. Detailed simulations verify the accuracy of the modeling and stability analysis results.