The invention discloses a
variable structure control method of a grid-connected
photovoltaic system, used for controlling a two-stage circuit structure or a single-stage circuit structure. The method comprises the following steps of respectively determining each
control point value, comprising V1-V6 and Vr1-Vr4, wherein a reference
voltage value of a
direct current bus is Vref, and an actual output
voltage value of a photovoltaic battery array is VPV; and concretely controlling according to the following conditions: firstly, when the VPV of the photovoltaic battery array is
ranging from V1 to V5, the grid-connected
photovoltaic system works under the two-stage circuit structure and a two-stage
control mode, and the set Vref of the reference
voltage of the
direct current bus is relevant to the size and the variation direction of the VPV; secondly, when the VPV of the photovoltaic battery array is
ranging from V4 to V6, the grid-connected
photovoltaic system works under the single-stage circuit structure and a single-stage
control mode; and thirdly, when the VPV of the photovoltaic battery array is
ranging from V4 to V5, the grid-connected photovoltaic
system works under a
hysteresis control mode. Through the method, the working
voltage range is enlarged, and the
equipment use efficiency is remarkably improved.