The grid-connected photovoltaic power generation system can convert the DC power output by the solar cell array into AC power with the same amplitude, frequency and phase as the grid voltage, and realizes the connection with the grid and transmits electricity to the grid. The flexibility of this power generation system lies in that when the sunshine is strong, the photovoltaic power generation system supplies the AC load with excess electric energy while feeding the power grid; and when the sunshine is insufficient, that is, the solar cell array cannot provide enough electric energy for the load, It can also obtain electrical energy from the grid to supply power to the load