Control method and system for three-phase grid-connected inverter, and three-phase grid-connected inverter

A system for controlling a three-phase grid-connected inverter, wherein the system is applied to a three-phase three-leg grid-connected inverter comprising a filter capacitor, wherein one terminal of the filter capacitor is connected to an output inductor of a corresponding bridge leg, and the other terminal of the filter capacitor is connected to a negative electrode of a direct current input bus;

• and the system comprises:
• a cycle dividing module configured to divide a power grid cycle into a plurality of equal intervals, wherein in each of the plurality of equal intervals, two inductor currents are in a same direction, and a third inductor current is in a direction opposite to the direction of the two inductor currents;
• and
• an alternately controlling module configured to control, in an interval of the power grid cycle, the two inductor currents in the same direction under a discontinuous inductor current mode, to control fundamental wave components of the two inductor currents in the same direction to be sine waves in the power grid cycle, wherein phases of the two inductor currents in the same direction are shifted based on a power factor demand, to generate a phase difference between each of the two inductor currents in the same direction as well as the third inductor current and a power grid voltage in the power grid cycle.