With the integration of large-scale photovoltaic power stations into power grids, the traditional strategy of the backup automatic switch is affected. When a grid fault occurs, due to the existence of photovoltaic power sources, the busbar voltage at the fault point cannot meet the ‘no voltage’ criterion, and the traditional strategy cannot operate correctly. In order to improve new energy utilization and ensure normal input of the backup power supply without disconnecting photovoltaic power sources, a new backup automatic switch scheme based on distributed buffer resistors is proposed. Firstly, the influence of the mismatch between photovoltaic output and load power on the grid-connected point voltage is analyzed. Secondly, distributed buffer resistor branches are connected in parallel at both ends of the DC capacitor in each photovoltaic power generation unit, using buffer resistors to suppress the power imbalance formed in the islanded state after the main power supply is disconnected (before the backup automatic switch operates), realizing safe and fast operation of the backup automatic switch. Finally, MATLAB/Simulink is used to simulate and verify the scenario of extreme mismatch between photovoltaic and load power, and the inrush current can be limited to 1.5 times rated current, which meets the relevant specifications and verifies the feasibility and effectiveness of the proposed new backup automatic switch scheme.