A Dynamic Equivalent Method for PMSG Based Wind Farms Under Asymmetrical Faults

In this paper, a three-machine equivalent method applicable to asymmetrical faults is proposed considering the operating wind speed and fault severity. Firstly, direct-driven permanent magnet synchronous generator wind turbines (PMSGs) are clustered based on their different active power response characteristics considering the wind speed, the fault severity, and the negative sequence control strategy. Further, single-machine equivalent methods are proposed for each cluster of PMSGs. In particular, for the PMSGs with ramp recovery characteristics, a single-machine equivalent model with multi-segmented slope recovery is proposed, which can more accurately reflect the characteristics of the wind farm during the fault recovery. Moreover, an iterative simulation method is proposed to obtain the required clustering indicators before the actual occurrence of faults. Therefore, the proposed equivalent method can be used to analyze any anticipated contingency. Eventually, the effectiveness of the proposed method is verified on a modified IEEE 39-bus system.Comment: 13 pages, 20 figure

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

The significant electrical distance between wind power collection points and the main grid poses challenges for weak grid-connected wind power systems. A new type of voltage oscillation phenomenon induced by repeated low voltage ride-through (LVRT) of the wind turbine has been observed, threatening the safe and stable operation of such power systems. Therefore, exploring dynamic evolution mechanisms and developing stability analysis approaches for this phenomenon have become pressing imperatives. This paper introduces switched system theory for dynamic modeling, mechanism elucidation, and stability analysis of the repeated LVRT process. Firstly, considering the external connection impedance and internal control dynamics, a novel wind turbine grid-side converter (WT-GSC) switched system model is established to quantitatively characterize the evolution dynamic and mechanism of the voltage oscillation. Subsequently, a sufficient stability criterion and index grounded in the common Lyapunov function are proposed for stability analysis and assessment of the WT-GSC switched system. Moreover, to enhance the system stability, the Sobol' global sensitivity analysis method is adopted to identify dominant parameters, which can be further optimized via the particle swarm optimization (PSO) algorithm. Finally, simulations conducted on a modified IEEE 39-bus test system verify the effectiveness of the proposed dynamic modeling and stability analysis methods.Comment: 10 pages, 10 figure