Capacity Allocation Strategy for Grid-Forming Converters Based on Transient Voltage Stability

With the increasing proportion of renewable energy generation, the power system exhibits “dual-high” characteristics, leading to prominent transient voltage stability issues in weak grids. In renewable energy stations, grid-following converters (GFL) are highly dependent on phase-locked loops (PLL), making them prone to synchronization instability and control instability under transient low-voltage conditions. To address this challenge, this paper proposes a capacity allocation strategy for grid-forming converters (GFM) in weak grids to enhance PLL transient voltage stability. First, the differences in transient voltage response characteristics between GFL and GFM are analyzed. Then, the mechanism of PLL transient instability in GFL is thoroughly revealed, and the critical voltage threshold for ensuring PLL synchronization is derived. With the goal of minimizing the number of GFM configurations, voltage constraints are incorporated, and a GFM capacity allocation method is designed based on the voltage control coefficient. The strategy synergizes GFM’s voltage source support capability during the initial transient phase (elevating the voltage nadir) and GFL’s rapid reactive power response advantage during the stable phase, enabling renewable energy stations to achieve active and fast transient voltage support. Through MATLAB/Simulink simulations, the optimized GFM ratio effectively maintains transient stability, providing a practical solution for the large-scale and reliable integration of renewable energy.