基于双序动态耦合模型的跟网型逆变器在不对称电网故障下的同步稳定性分析

To deal with asymmetrical grid faults, grid-following inverters are required to output positive- and negative-sequence currents to regulate the voltage at the point of common coupling. Owing to the negative-sequence current injection, the stability mechanism of the dual-sequence synchronizations becomes more complicated under asymmetrical scenarios. In this article, a dual-sequence dynamic coupling model, which takes into account both positive- and negative-sequence current couplings as well as power angle difference, is proposed. Based on this model, not only the existence conditions of positive- and negative-sequence equilibrium points are identified, but also the transient process stability conditions of the operating points are determined, resulting in a complete transient stability judgment foundation during asymmetrical grid faults. It is pointed out that couplings between the positive- and negative-sequence synchronization processes bring about more transient synchronization instability. Simulation and experimental results verify that the proposed synchronization stability analysis based on the dual-sequence dynamic coupling model has higher accuracy for inverters under asymmetrical grid faults compared with the previous methods.