Impedance Modeling and Stability Analysis of Grid-Forming Static Var Generator for Renewable Energy Power Plants
Zhao Lixuan, Chen Xin, Zhang Donghui
Jiangsu Key Laboratory of New Energy Generation and Power Conversion College of Automation Engineering Nanjing University of Aeronautics and Astronautics Nanjing 211106
Abstract：To enhance grid-connected system voltage support and oscillation suppression capability, new energy power plants are equipped with static var generator (SVG) as a reactive power compensation device. Under the background of widespread deployment of reactive power compensation devices in new energy power stations, grid-forming (GFM) SVG demonstrate superior grid adaptability compared to traditional grid-following (GFL) SVG and synchronous condenser (SC), owing to their self-synchronizing characteristics, second-level dynamic response, and transient support capability. However, current research on the impact of GFM SVG on the stability of new energy power plants is still at an exploratory stage. In particular, the impedance modeling of GFM SVG and the analysis of its influence mechanisms on the stability of new energy power plants still require further in-depth studies. To address the aforementioned issues, this paper establishes the impedance characteristic model of GFM SVG and constructs the aggregated impedance of wind farms after GFM SVG integration. It compares the frequency characteristics between grid-forming and grid-following SVGs, and conducts a quantitative analysis of the influence mechanisms of GFM SVG’s key control parameters on the stability of new energy power plants. First, a multi-harmonic linearization modeling approach is adopted to derive harmonic small-signal mathematical expressions introduced by the power circuit and control loops of GFM SVG. Based on this, the sequence impedance model of GFM SVG is established. Furthermore, a detailed comparative analysis of impedance characteristics between GFM SVG and GFL SVG is conducted. The analytical results demonstrate that the grid-forming control significantly enhances the amplitude of SVG impedance characteristics in both low-frequency and high-frequency ranges. Additionally, grid-forming control improves the negative damping characteristics in sub/super-synchronous frequency bands of impedance, thereby reducing the risk of grid-connected oscillation. To quantitatively evaluate the impact of GFM SVG on wind farm stability, this study employs an impedance aggregation method to establish an aggregated impedance model of a wind farm with transmission lines and transformers after GFM SVG integration, using a wind farm in the Hami region as a case study. A comparative analysis is conducted on the aggregated impedance models of wind farms integrated with GFM SVG, GFL SVG, and SCs under three different grid connection scenarios, the stability analysis results demonstrate that: The integration of GFM SVG into wind farms can effectively narrow the negative damping region of the aggregated wind farm impedance while avoiding the introduction of additional impedance crossover points, thereby enhancing the grid-connected stability of new energy power plants. Building on this foundation, the study conducts an in-depth analysis of the impact mechanisms of grid-forming SVG’s key control parameters (including the DC voltage frequency modulation coefficient, reactive voltage inertia coefficient, and virtual impedance) on the aggregated impedance of SVG-integrated wind farms and their grid-connected stability. Furthermore, the stability boundaries for the DC voltage frequency modulation coefficient and reactive voltage inertia coefficient in wind farm grid-connected systems are established quantitatively, proposing systematic parameter optimization methodologies. Finally, the impact of transmission line parameters on grid-connected system stability is analyzed. Short-circuit ratio improvement percentage (α ) is defined to quantify the improvement in the adaptability of the weak grid after integrating different reactive power compensation devices into new energy power plants. Compared to GFL SVG, wind farms integrated with GFM SVG exhibit significantly enhanced weak grid adaptability and damping effects comparable to synchronous condensers.
赵力轩, 陈新, 张东辉. 面向新能源场站的构网型静止无功发生器阻抗建模及稳定性分析[J]. 电工技术学报, 2026, 41(3): 849-864.
Zhao Lixuan, Chen Xin, Zhang Donghui. Impedance Modeling and Stability Analysis of Grid-Forming Static Var Generator for Renewable Energy Power Plants. Transactions of China Electrotechnical Society, 2026, 41(3): 849-864.
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