Dynamic Modeling and Stability Analysis for Repeated LVRT Process of Wind Turbine Based on Switched System Theory

The electrical distance between the wind power collection sending end grid and the main grid is relatively long, lacking synchronous power supply support. In this weak grid-connected wind power system, a new type of voltage oscillation phenomenon caused by repeated low voltage ride through (LVRT) of the wind turbine has been observed, threatening the safe and stable operation of power systems. Its dynamic evolution mechanisms and stability analysis approaches need to be studied urgently. Therefore, this paper introduces the switched system theory for dynamic modeling, mechanism explanation, and stability analysis of the repeated LVRT process. Firstly, considering the external connected impedance and internal control dynamics, a novel wind turbine grid-side converter (WT-GSC) switched system model is established, which can characterize the evolution dynamic and mechanism of the voltage oscillation. Then, the common Lyapunov function based sufficient stability criterion and stability index are proposed for stability analysis and assessment of the WT-GSC switched system. Moreover, to improve the system stability, the Sobol' global sensitivity analysis method is adopted to select the dominant parameters, which can be furtherly optimized through the particle swarm optimization (PSO) algorithm. Finally, simulations performed on a modified IEEE 39-bus test system verify the effectiveness of the proposed dynamic modeling and stability analysis methods.