Transient Stability Analysis and Optimal Control Strategy of Grid-Forming Converters Based on Circular Current Limiter

Abstract

To limit transient current overshoot in grid-forming (GFM) converters caused by grid voltage sags, a variety of current limiting strategies, including priority-based limiter and circular current limiter (CCL) are employed. Existing research predominantly focuses on the transient stability analysis of priority-based limiting strategies. In this paper, an equivalent model and transient analysis method for GFM converters utilizing CCL is proposed, in which the CCL strategy is equivalent to a resistor inserted in series within the control loop. Based on this model, transient stability analysis under current saturation conditions is further conducted by constructing power-angle curves. An optimal control strategy is proposed to enhance the system’s transient stability by modifying the power references and incorporating an anti-windup loop for the integrator. Finally, simulation results verify the effectiveness of the proposed transient stability analysis method and the optimized control strategy.