Transient stability analysis and optimal control strategy of grid-forming converters based on circular current limiter

Abstract

To limit transient current overshoot in gridforming (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 antiwindup loop for the integrator. Finally, simulation results verify the effectiveness of the proposed transient stability analysis method and the optimized control strategy.