Research on the Large Disturbance Stability of Grid-connected VSC System Considering the Limiter Strategy of Outer Loop

The proportion of renewable energy generation with voltage source converter (VSC) as the interface is increasing. The existing researches only focus on the characteristics of the phase-locked loop (PLL) and other control loops while ignoring the influence of nonlinear loops such as limiter on the stability. To fill the gap, the effect of the VSC outer loop and its limiter on the large disturbance stability is of the main interest in this paper. Firstly, a simplified grid-connected VSC system is established to analyze the existence of equilibrium points, which takes the electrical quantity constrained by the limiter as the state variable. Secondly, based on the Poincaré theorem and Lyapunov’s second theorem, the deterministic condition of the fixed point is proved, which is a fixed position away from the outer loop limiter. The mechanism that the actual power is inconsistent with the command value under the large disturbance is revealed. Then, the limiter principle considering safety and stability is proposed, and based on this, the improved limiter strategy is designed. Finally, the analysis results based on the actual model show that a reasonable outer loop limiter can improve the stability of the grid-connected VSC system. ©2023 Chin.Soc.for Elec.Eng.