Study on the Effect of Control Switching Delay on New Energy Inverter Fault Overcurrent

In the event of a grid fault, the new energy grid-connected control system will switch from the steady-state operation mode to the low-voltage ride-through (LVRT) mode once the low-voltage detection module detects that the voltage has fallen below a threshold value. However, a delay in low-voltage (LV) detection may cause transient overcurrent issues, which have not received sufficient attention in existing research. To address this issue, this paper takes the three-phase short-circuit fault of a photovoltaic (PV) feeder line as an example, analyzes the influence of varying voltage sag depths on LV detection time, and reveals the impact of voltage sags on the peak fault current, considering the control switching delay. The findings indicate that the larger the voltage sags are, the shorter the LV detection delay tends to be. Additionally, the peak fault current does not necessarily occur in the scenario with the most severe voltage sags and may exhibit an asymmetric distribution trend, with a middle extreme value. The validity of the conclusions is verified through model construction on the PSCAD/EMTDC simulation platform and the power system dynamic simulation platform.