Sequence Impedance Modeling of Grid-Forming Converter Considering the Difference of Current Loop Control Domain and Comparative Analysis of Power Grid Applicability
Lan Zheng, Wang Haihui, He Dong, Sun Zhifeng, Chen Liyang
School of Transportation and Electrical Engineering Hunan University of Technology Zhuzhou 412007 China
Abstract：As an indispensable device in the modern power system, the grid-forming converter (GFM) plays a vital role in the power grid with highly permeability. Especially in the context of the continuous increase in the proportion of renewable energy power generation, its support performance for weak power grids has become a hot topic in the research field. The output impedance characteristics of GFM are not only related to its own operational stability, but also directly affect the dynamic response and stability of the entire power grid. Therefore, it is of great significance to study the output impedance characteristics of GFM to improve the overall performance and reliability of the power system. In the current internal loop control strategy, the dq domain proportional-integral (PI) control and the phase domain quasi-proportional-resonant (QPR) control are two widely used methods. The dq domain PI control is known for its simplicity and ease of implementation, while the phase domain QPR control excels in harmonic suppression and dynamic response. However, although these two control strategies have achieved good results in practical applications, their impedance modeling and comparative analysis are relatively insufficient. Especially in the modeling of phase domain impedance, where the complexity and nonlinearity of phase-domain control pose additional challenges to related research. To complement this part of the study, this paper explores in depth the impedance modeling methods of GFM under different control domains. Firstly, we construct the harmonic linearization order impedance model of GFM under PI control and QPR control, respectively. These two models not only consider the fundamental component, but also fully consider the influence of the harmonic component on the impedance characteristics, so as to describe the impedance characteristics of GFM more accurately. By comparing the two models, we find that there are significant differences in the impedance characteristics of GFM under the two control strategies. The impedance characteristics under PI control are relatively stable, but they are easily affected by the strength of the grid and the number of grids. On the other hand, the impedance characteristics under QPR control are more flexible and can better adapt to changes in the grid environment. Furthermore, we use the established model and combine with the Nyquist criterion to analyze the effects of PI control and QPR control on grid connection stability under different grid strengths and grid connection numbers. The analysis results show that the applicability of PI control is relatively weak in the strong power grid environment, because the stability of the power grid itself is strong and the requirements for converters are relatively low. QPR control can better suppress harmonic interference and improve the steady-state performance of the power grid. However, under extremely weak grid conditions, PI control shows stronger applicability. Because the stability of the power grid is weak at this time, the converter needs to have a stronger support capacity. PI control can achieve better support for the power grid by adjusting the parameters. In addition, we also found that both PI control and QPR control showed good stability in multi-GFM grid-connected systems. This is due to the fact that both control strategies have good current regulation and dynamic response speed. Finally, we verify the correctness of the above theoretical analysis through simulation experiments. The simulation results show that the GFM under the two control strategies can maintain stable grid-connected operation under different grid conditions. At the same time, we also find that the simulation results are consistent with the theoretical analysis results, which further verifies the effectiveness and accuracy of the impedance model established in this paper. These research results not only provide a useful theoretical reference for the optimal design and stable operation of GFM, but also provide important technical support for the application of grid-based converters in high-permeability power grids.
兰征, 王海晖, 何东, 孙志峰, 陈立阳. 考虑电流环控制域差异的构网变流器序阻抗建模及电网适用性对比分析[J]. 电工技术学报, 2026, 41(3): 834-848.
Lan Zheng, Wang Haihui, He Dong, Sun Zhifeng, Chen Liyang. Sequence Impedance Modeling of Grid-Forming Converter Considering the Difference of Current Loop Control Domain and Comparative Analysis of Power Grid Applicability. Transactions of China Electrotechnical Society, 2026, 41(3): 834-848.
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2026, Vol. 41 
