Transient Fault Current Calculation Method for the PV Grid-Connected System Considering Dynamic Response of PLL

The transient fault characteristics of photovoltaic (PV) grid-connected systems are highly dependent on the dynamic response of control links. The phase-locked loop (PLL) in the inverter control system plays an important role, and its dynamic output response will affect the PV transient fault characteristics. The existing method for PLL dynamic response calculation is based on the small-signal simplified model, and requires to previously measure the fault steady-state voltage phase at the point of common coupling (PCC). This limitation leads to inaccurate calculation and prevents the method from being applied in practical engineering. Here, to accurately describe the PV transient fault characteristics, an accurate model for calculating the PLL dynamic response independent of the fault steady-state voltage is established, and the model is further linearized to improve its computation efficiency. On this basis, a PV transient fault current calculation method that considers the PLL dynamic response is proposed. Compared with the existing method, the proposed method can more accurately calculate the dynamic response of the PLL and the fault transient characteristics of PV power source. Finally, simulation cases based on PSCAD/EMTDC are carried out to verify the accuracy of the proposed method and its superiority compared with the existing method.