Method for calculating short-circuit current peaks in grid-connected photovoltaic systems with positive-negative sequence decoupling control

Research on the fault transient process and short-circuit current peaks of renewable energy sources (RES) such as photovoltaic (PV) and wind power provides critical insights for equipment selection and protection settings. However, most existing methods for calculating short-circuit current peaks are only applicable to inverter-based models using sequence component coupling control. In practical grids, single-phase grounding faults—common in real-world scenarios—cause voltage imbalance, leading to double-frequency power fluctuations due to negative-sequence voltage. According to grid codes, inverters should inject negative-sequence reactive currents during asymmetric faults to mitigate voltage unbalance. Positive-negative sequence decoupling control not only enhances stability under asymmetric faults but also improves dynamic response. This paper first establishes a PV power model with positive-negative sequence decoupling control, analyzes its fault transient characteristics, and proposes a transient short-circuit current calculation model during faults. By investigating the damping ratio, a practical expression for the short-circuit current peak under decoupled control is derived. Simulations validate the theoretical feasibility and accuracy.