Photovoltaic grid-connected system fault protection method and device based on harmonic injection

The invention relates to the technical field of low-inertia system protection and control, and discloses a photovoltaic grid-connected system fault protection method and device based on harmonic injection. According to the method, when a fault occurs in a photovoltaic grid-connected system, a fault current limiting control strategy is adopted, and the magnitude of a fault current is limited by adjusting an output voltage; injecting a harmonic signal into the photovoltaic grid-connected system on the basis of the three-phase voltage by adopting a harmonic injection control strategy; respectively obtaining a fault equivalent circuit of the photovoltaic grid-connected system before and after harmonic signal injection, and solving a fault distance from a protection measuring point to a fault point; and determining the exit time of the protection measuring point according to the fault distance, and processing the fault of the photovoltaic grid-connected system. According to the method, the harmonic signals with ch