Transient Stability Analysis of Islanded Microgrid With Parallel Grid-Forming Converters Considering Current Limitation

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Abstract
To protect grid-forming (GFM) converters from overcurrent damage, current-limiting strategies are typically employed. However, such strategies may compromise the safe and stable operation of islanded microgrids during load restoration. To address this issue, this paper investigates the transient stability of an islanded microgrid with two parallel GFMs and analyzes the evolution of the GFMs’ dynamic behavior after a constant-impedance load is connected. First, a transient mathematical model of the system is developed considering current limiting. Then, since the output power of GFMs varies with their operating modes, significantly affecting the system’s transient stability, a method is proposed to determine both the mode-switching conditions and the final operating mode of each GFM solely within the first swing. On this basis, a hybrid approach combining numerical integration and the equal-area criterion is employed to accurately evaluate the transient stability. Furthermore, the proposed framework is applied to parameter tuning and short-circuit fault analysis in islanded microgrids. Finally, the effectiveness of the proposed method is validated through simulation results.
Funding Information
  • National Key Research and Development Program of China (2022YFB2402900)

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