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 intervals based on zero crossing points of fundamental waves of three inductor currents, wherein in each of the plurality of intervals:
• two of the three inductor currents are in a positive direction, and other inductor current is in a negative direction, or
• one of the three inductor currents is in a positive direction, and other two inductor currents are in a negative direction, wherein a direction in which the inductor current flows from a bridge leg side to an alternating current side of a power grid is the positive direction, and a direction in which the inductor current flows from the alternating current side of the power grid to the bridge leg side is the negative direction;
• and
• a current controlling module configured to control, in an interval of the power grid cycle, the three inductor currents in a discontinuous inductor current mode, so that fundamental components of the three inductor currents to be sine waves.