A photovoltaic power generation system, comprising an inverter , a controller, and at least two direct current branch circuits, wherein each direct current branch circuit comprises a DC-DC converter and a leakage current detection apparatus , wherein an input end of the DC-DC converter is configured to be connected to a corresponding photovoltaic unit , and an output end of the DC-DC converter connected to an input end of the inverter , wherein the DC-DC converter is configured to: perform direct current-direct current conversion on a direct current that is output by the corresponding photovoltaic unit , and then transmit a converted direct current to the inverter ; the inverter is configured to invert the direct current transmitted by the DC-DC converters into an alternating current; each leakage current detection apparatus is configured to: detect a leakage current of the direct current branch circuit on which the leakage current detection apparatus is located, and send the leakage current to the controller; the controller is configured to: when the photovoltaic power generation system enters a running state, detect that an insulation fault occurs on the respective direct current branch circuit, when a value of a leakage current of a direct current branch circuit of the direct current branch circuits exceeds a preset range; the photovoltaic power generation system characterized in that the controller is further configured to: before the photovoltaic power generation system enters the running state, detect a direct current branch circuit on which an insulation fault occurs, based on values and directions of the detected leakage currents. each direct current branch circuit comprises a DC-DC converter and a leakage current detection apparatus , wherein an input end of the DC-DC converter is configured to be connected to a corresponding photovoltaic unit , and an output end of the DC-DC converter connected to an input end of the inverter , wherein the DC-DC converter is configured to: perform direct current-direct current conversion on a direct current that is output by the corresponding photovoltaic unit , and then transmit a converted direct current to the inverter ; the inverter is configured to invert the direct current transmitted by the DC-DC converters into an alternating current; each leakage current detection apparatus is configured to: detect a leakage current of the direct current branch circuit on which the leakage current detection apparatus is located, and send the leakage current to the controller; the controller is configured to: when the photovoltaic power generation system enters a running state, detect that an insulation fault occurs on the respective direct current branch circuit, when a value of a leakage current of a direct current branch circuit of the direct current branch circuits exceeds a preset range; the photovoltaic power generation system characterized in that the controller is further configured to: before the photovoltaic power generation system enters the running state, detect a direct current branch circuit on which an insulation fault occurs, based on values and directions of the detected leakage currents. <EOS>