Online Variable Topology-Type Photovoltaic Grid-Connected Inverter

In photovoltaic (PV) grid-connected generation system, the key focus is how to expand the generation range of the PV array and enhance the total efficiency of the system. This paper originally derived expressions of the total loss and grid current total harmonics distortions of cascaded inverter and H-bridge inverter under the conditions of variable output voltage and power of the PV array. It is proved that, compared with the H-bridge inverter, the operation range of the cascaded inverter is wider, whereas the total loss is larger. Furthermore, a novel online variable topology-type grid-connected inverter is proposed. A bidirectional power switch is introduced into the conventional cascaded inverter to connect the negative terminals of the PV arrays. When the output voltages of the PV arrays are lower, the proposed inverter works under cascaded inverter mode to obtain wider generation range. When the output voltages of the PV arrays are higher, the proposed inverter is transformed into equivalent H-bridge inverter mode to reduce the total loss. Thus, wider generation range and higher efficiency are both implemented. Specific demonstration of the proposed inverter based on five-level cascaded inverter is presented. The detailed experimental results verify the accuracy and feasibility of the theoretical analysis and the proposed inverter topology.