A Control Strategy for Enhancing the Transient Stability of SOP System Based on Virtual Capacitors

Soft open points (SOPs) offer real-time power flows control, the rapid self-healing of faults, and the balance of feeder load, which are widely applied in the distribution networks (DNs). However, distribution networks based on SOP often suffer from large signal disturbances such as grid voltage dips (GVDs) during operation, and their stability needs to be further improved to ensure the safe and stable operation of the SOP system. This article proposes a stable control strategy based on virtual capacitors and verifies the effectiveness of this method through theoretical analysis using mixed potential theory (MPT). Firstly, the virtual capacitor control strategy proposed in this article that can enhance the stability of SOP systems is stated. Secondly, a nonlinear average model of SOP was established, and based on MPT, the large signal stability criteria (LSSC) for the SOP system using virtual capacitor control strategy were derived. Based on this criterion, the impact of DC side capacitance on system stability was analyzed, and the effectiveness of virtual capacitance strategy to enhance the system's stable operation capability was verified. Finally, the correctness of the obtained criteria and the feasibility and effectiveness of the virtual capacitor strategy were verified through Matlab/Simulink time-domain simulation.