Photovoltaic power generation system and fault protection method and device thereof, combiner box, and inverter

A fault protection method for a photovoltaic power generation system, the photovoltaic power generation system comprising a plurality of photovoltaic string units, a plurality of protection switch units, and a plurality of power conversion units, each of the plurality of photovoltaic string units comprising at least N photovoltaic strings, and each of the plurality of protection switch units comprising a plurality of protection switches, wherein each of the plurality of protection switch units is adapted to connect one of the plurality of photovoltaic string units to a corresponding one of the plurality of power conversion units to form at least two photovoltaic string branches, each of the at least two photovoltaic string branches being adapted to connect one photovoltaic string or two parallel photovoltaic strings, where N is an integer greater than or equal to 3, the fault protection method comprising:

• disconnecting, when there are co-positive power conversion units or co-negative power conversion units in the plurality of power conversion units and the protection switch units corresponding to the co-positive power conversion units or the co-negative power conversion units share a protection switch when connected to their corresponding photovoltaic string units, part or all of the plurality of protection switch units in response to detecting a fault in the photovoltaic power generation system, such that at most two photovoltaic strings in each of the corresponding photovoltaic string units are connected in parallel,
• wherein when the protection switch units corresponding to the co-positive power conversion units or the co-negative power conversion units are disconnected, their corresponding photovoltaic strings are disconnected separately by at least three protection switches.