Three-level inverter, control method, and system

A method for controlling a three-level inverter, wherein the three-level inverter comprises a plurality of controllable switch components comprising a first switch component, a second switch component, a third switch component, a fourth switch component, a fifth switch component, and a sixth switch component, wherein each of the controllable switch components comprises a parallel connected junction capacitor and an anti-parallel connected diode, a first terminal of the first switch component is connected to a positive direct current bus, a second terminal of the fourth switch component is connected to a negative direct current bus, a second terminal of the first switch component is connected to a first terminal of the second switch component and a first terminal of the fifth switch component, a first terminal of the fourth switch component is connected to a second terminals of the third switch component and a second terminal of the sixth switch component, a second terminal of the second switch component and a first terminal of the third switch component are connected to a direct current bus midpoint, and a second terminal of the fifth switch component and a first terminal of the sixth switch component are connected together to form a bridge arm terminal, and the method comprises:

• in a positive half cycle, controlling the third switch component to be conducted after the first switch component is conducted, and controlling the third switch component to be disconnected before the first switch component is conducted next time;
• and
• in a negative half cycle, controlling the second switch component to be conducted after the fourth switch component is conducted, and controlling the second switch component to be disconnected before the fourth switch component is conducted next time.

A photovoltaic power generation system, comprising a three-level inverter and a photovoltaic unit, wherein

• the photovoltaic unit comprises a plurality of photovoltaic modules, and an output terminal of the photovoltaic unit is connected to an input terminal of the three-level inverter;
• and
• the photovoltaic unit is configured to:
• convert light energy into a direct current and transmit the direct current to the three-level inverter comprising a plurality of controllable switch components comprising a first switch component, a second switch component, a third switch component, and a fourth switch component, wherein each of the controllable switch components comprises a parallel connected junction capacitor and an anti-parallel connected diode, a first terminal of the first switch component is connected to a positive direct current bus, a second terminal of the fourth switch component is connected to a negative direct current bus, a second terminal of the first switch component is connected to a first terminal of the second switch component, a first terminal of the fourth switch component is connected to second terminal of the third switch component, a second terminal of the second switch component and a first terminal of the third switch component are connected to a direct current bus midpoint;
• and further comprising a controller, wherein the controller controls working states of the controllable switch components by sending control signals;
• and
• the controller is configured to:
• in a positive half cycle, control the third switch component to be conducted after the first switch component is conducted, and control the third switch component to be disconnected before the first switch component is conducted next time;
• and
• in a negative half cycle, control the second switch component to be conducted after the fourth switch component is conducted, and control the second switch component to be disconnected before the fourth switch component is conducted next time.