MLPE photovoltaic system and method for photovoltaic string control in MLPE photovoltaic system

A module level power electronics (MLPE) photovoltaic system comprising a control unit, at least one inverter and at least two photovoltaic strings, wherein:

• a direct-current bus of the inverter is connected in parallel with the at least two photovoltaic strings;
• each of the at least two photovoltaic strings comprises at least one photovoltaic branch, an output end of each photovoltaic branch is connected in series between two poles of an output end of a photovoltaic string where the photovoltaic branch is located;
• the photovoltaic branch comprises a MLPE device and at least one photovoltaic module connected with an input end of the MLPE device;
• and
• the control unit communicates with each MLPE device and is configured for:
• detecting an output current of each photovoltaic string in the MLPE photovoltaic system;
• determining whether the MLPE photovoltaic system has unbalanced string currents;
• and
• if it is determined that the MLPE photovoltaic system has unbalanced string currents, controlling, for photovoltaic strings connected in parallel to a same inverter in the MLPE photovoltaic system, a voltage of a photovoltaic string with a larger output current to be reduced, or controlling a voltage of a photovoltaic string with a smaller output current to be increased, to reduce a backflow current to a preset range, wherein the backflow current is a current that is generated by the photovoltaic string with the larger output current and flows into the photovoltaic string with the smaller output current,
• wherein the inverter samples the output current of each photovoltaic string separately.