Photovoltaic inverter direct current side fault detection and cause positioning method

The invention discloses a photovoltaic inverter direct current side fault detection and cause positioning method, and belongs to the field of fault diagnosis of photovoltaic inverters. The method comprises the steps of sampling voltage and current signals before and after a fault of a photovoltaic inverter; detecting an overvoltage fault or an undervoltage fault on a direct current side by performing threshold judgment on a direct-current voltage; and carrying out front and back stage instantaneous power difference detection and total harmonic distortion rate judgment under an overvoltage fault, similarly, carrying out front and back stage instantaneous power difference detection and direct current direction judgment under an undervoltage fault, and outputting corresponding fault cause results. The method can accurately judge the fault type and cause of the DC side fault of the photovoltaic inverter, and has the advantages of simple implementation, economy, rapidness and the like; external sensors do not need