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

The invention discloses a photovoltaic power generation system and a fault protection method and device thereof, a combiner box and an inverter, and relates to the technical field of photovoltaic power generation. The method comprises the following steps: when a plurality of power conversion units have common positive or common negative power conversion units and protection switch units corresponding to the common positive or common negative power conversion units share protection switches when the protection switch units are connected with corresponding photovoltaic string units, if the photovoltaic power generation system is detected to have a fault, the protection switch units are connected with the corresponding photovoltaic string units; if yes, the plurality of protection switch units are partially disconnected or completely disconnected, so that at most two photovoltaic group strings in the corresponding photovoltaic group string units are connected in parallel, and when the protection switch units cor