构网型并网逆变器在不对称短路故障下的暂态稳定性分析

Compared with traditional grid-following grid-connected inverters (GFL-GCIs), grid-forming grid-connected inverters (GFM-GCIs) can provide voltage and frequency support to the grid, effectively improving the stability of power electronic-based new power systems, and have received widespread attention in recent years. However, when the grid experiences an asymmetrical short circuit fault, the GFM-GCI system may face transient instability issues, which have been less studied. In this paper, the GFM-GCI system under an asymmetrical short circuit fault is studied, and the conventional droop control is improved by proposing a new reactive power droop control structure. This structure allows the system to accurately control the positive and negative sequence reactive currents during low voltage ride-through, ensuring compliance with grid regulations. Based on this, a double-loop control structure model for the positive and negative sequence voltage and current of the GFM-GCI system under an asymmetrical short circuit fault condition is established. The composite sequence network of the system under the asymmetrical short circuit fault condition is obtained using the symmetrical component method, and the positive and negative sequence phase angle characteristic curves are further analyzed. The influence of system parameters on the transient synchronous stability of the positive and negative sequence systems is quantitatively analyzed using the equal area method. Finally, the correctness of the theoretical analysis is verified through simulations and semi-physical experimental platforms.