Control method and device for switching off-grid to grid-connected inverter, inverter and system

The invention discloses a control method and device for switching an inverter from an off-grid state to a grid-connected state, an inverter and a system, and belongs to the technical field of electronic power. The method comprises the following steps: in an off-grid operation stage of an inverter, when it is detected that a power grid returns to normal, obtaining a first electrical parameter of the power grid; determining a target droop coefficient according to the first electrical parameter, a second electrical parameter of the inverter at the current moment and a droop coefficient of the inverter for droop control at the current moment; adjusting the droop coefficient of the inverter towards the direction of the target droop coefficient so as to enable the inverter to perform droop control according to the adjusted droop coefficient; determining whether the first electrical parameter and the second electrical parameter meet a grid-connected condition or not, and if yes, controlling the inverter to be switch