Transient Fault Current Calculation Method of Photovoltaic Grid-Connected System Considering the Dynamic Response of Phase-Locked Loop

The transient fault characteristics of photovoltaic (PV) grid-connected system depend on the dynamic response of each control link. Phase-locked loop (PLL) plays an important role in PV grid-connected system. The dynamic output response of PLL affects the PV transient fault characteristics through coordinate transformation. Existing calculation method for PLL dynamic response is based on the premise that the voltage phase change at the point of common coupling (PCC) is small and the steady-state phase after the fault can be measured, and the calculation error of transient current is large. To accurately describe the PV transient fault characteristics, this work proposes a calculation method of PV transient fault current by considering the dynamic response of PLL. First, the dynamic characteristics of the current inner loop are analyzed in detail, and the transient fault current of $\boldsymbol{d}-\boldsymbol{q}$ axis is calculated. Second, the accurate calculation model of the dynamic response of PLL is established, and the dynamic output of PLL is obtained. The transient fault current calculation model considering the dynamic response of PLL is finally established. Compared with existing calculation method for transient fault current, the proposed method accurately describes the dynamic response characteristics of PLL and the PV transient current change characteristics. Finally, simulation analysis based on PSCAD/EMTDC verifies the accuracy of the proposed method.