Power conversion apparatus

A power conversion apparatus comprising:

• a direct current end,
• a positive direct current bus,
• a negative direct current bus,
• a positive bus capacitor,
• a negative bus capacitor,
• at least three inverter bridge arms,
• a switch unit,
• a controller, and
• filter inductors,
• filter capacitors, and
• alternating current ends that correspond to the at least three inverter bridge arms, wherein
• the direct current end is configured to connect to a photovoltaic module or an energy storage battery, and the alternating current ends corresponding to the at least three inverter bridge arms are configured to connect to a power grid;
• the positive direct current bus and the negative direct current bus are connected to the direct current end, and the positive bus capacitor and the negative bus capacitor are sequentially connected in series between the positive direct current bus and the negative direct current bus;
• a first end and a second end of each of the at least three inverter bridge arms are respectively connected to the positive direct current bus and the negative direct current bus, a third end of each inverter bridge arm is connected to a bus midpoint after sequentially passing through a filter inductor and a filter capacitor that correspond to each inverter bridge arm, and the switch unit, the bus midpoint is a connection point between the positive bus capacitor and the negative bus capacitor, and serial connection points of the filter inductors and the filter capacitors corresponding to the at least three inverter bridge arms are respectively configured to connect the alternating current ends corresponding to the at least three inverter bridge arms;
• and
• the controller is configured to:
• when a voltage of the power grid is less than or equal to a first voltage threshold, control the switch unit to be turned off or impedance of the switch unit to be increased;
• and after the switch unit is turned off or the impedance of the switch unit is increased, control a modulated wave of each inverter bridge arm to be a modulated wave obtained by superimposing a first common-mode modulation signal on an initial modulated wave of each inverter bridge arm, to increase amplitude of the modulated wave of each inverter bridge arm, wherein the initial modulated wave is a modulated wave of each inverter bridge arm during normal operation of the power conversion apparatus.