The dual closed-loop function of three-phase photovoltaic grid-connected inverter is to improve the steady-state and dynamic performance of photovoltaic power generation system. The output signal of double closed-loop inner-loop current controller in three-phase photovoltaic grid-connected inverter is used as the input signal of outer-loop voltage controller. Through the interaction of inner-loop control and outer-loop control, the output current and voltage of inverter can meet the requirements of power grid stably and accurately. Therefore, the function of double closed loop in three-phase photovoltaic grid-connected inverter is to improve the steady and dynamic performance of photovoltaic power generation system.