Transient Stability Analysis and Enhancement of Current-Limited Reverse-Droop Grid-Forming Inverters

In distribution networks with a high resistance-to-reactance (R/X) ratio, grid-forming (GFM) inverters can adopt reverse droop control (P-V, Q-f) to achieve the decoupling of active and reactive power. When grid voltage sags trigger the overcurrent protection of the inverter, the interaction between the circular current limiter and the embedded virtual impedance leads to highly complex nonlinear large-signal dynamics. Reverse droop control drives the system power angle via reactive power, which renders the conventional transient stability analysis method based on the P-δ curve invalid, making it difficult to analyze the transient stability of converters based on reverse droop control. To address these issues, this paper first establishes an equivalent circuit model of a GFM inverter considering the circular current limiter and virtual impedance. Second, a transient stability analysis method based on the Q-δ curve is proposed, and the conditions for the existence of the system’s transient equilibrium point (TEP) and the influence of virtual impedance parameters on it are analytically derived. Subsequently, a parameter tuning strategy based on Bayesian optimization (BO) is proposed. Finally, simulation results verify the accuracy of the proposed theory.