Photovoltaic power generation system and method

A photovoltaic power generation system, comprising

• an insulation resistance detection apparatus,
• 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 breaking apparatus, an input end of the DC-DC converter is connected to a corresponding photovoltaic unit, an output end of the DC-DC converter is connected to an input end of the inverter, 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 converter into an alternating current;
• the insulation resistance detection apparatus and the controller are configured to:
• when a value of the insulation resistance to ground of the photovoltaic power generation system is less than a preset resistance range, detect an insulation fault in the photovoltaic power generation system, and sequentially control breaking apparatuses on the at least two direct current branch circuits to be disconnected.

A method for diagnosing an insulation fault of a photovoltaic power generation system, wherein the photovoltaic power generation system comprises an inverter and at least two direct current branch circuits, each direct current branch circuit comprises a DC-DC converter and a leakage current detection apparatus, an input end of the DC-DC converter is connected to a corresponding photovoltaic unit, and an output end of the DC-DC converter is connected to an input end of the inverter, and the method comprises, for each of the at least two direct current branch circuits:

• controlling the DC-DC converter of a respective direct current branch circuit to perform direct current to direct current conversion on a direct current that is output by the corresponding photovoltaic unit of the respective direct current branch circuit;
• transmitting the converted direct current to the inverter of the respective direct current branch circuit;
• controlling the inverter to invert the direct current transmitted by the DC-DC converter into an alternating current;
• receiving a leakage current that is of the respective direct current branch circuit on which the leakage current detection apparatus is located and that is detected by the leakage current detection apparatus;
• and,
• when the photovoltaic power generation system runs and a value of a leakage current of the particular direct current branch circuit exceeds a preset range,
• detecting an insulation fault on the particular direct current branch circuit, comprising identifying that the leakage current of the particular direct current branch circuit exceeds the preset range and identifying that a cause of a deviation of the leakage current of the particular direct current branch circuit from the preset range is the insulation fault.