Topology Derivation Method of Buck-Boost Common-Ground Nonisolated Inverters Based on Graph Theory

Non-isolated inverters are widely applied in photovoltaic (PV) power generation systems due to their advantages of high-power density, high efficiency, and low cost. However, the non-isolated inverters have common-mode leakage current (CMLC), which endangers personal safety. In addition, the output voltage of the PV cell is relatively low, a buck-boost inverter is required to meet the requirement of the load or grid connection. Since non-isolated buck-boost dual-grounded inverters can eliminate the CMLC completely and have the buck-boost capability, they have gained extensive attention in PV power generation systems. Nevertheless, there is no topology derivation theory for the buck-boost dual-grounded non-isolated inverters. Therefore, a topology derivation method for buck boost dual-grounded non-isolated inverters based on graph theory is proposed. The proposed derivation method is illustrated in detail. Topologies with four switches are taken as an example to illustrate the derivation method. Operating principles of two topologies are illustrated. Simulation results for the two topologies verify the theoretical analysis. Furthermore, one of the proposed topologies is validated through experimental results. Finally, comparison among different buck-boost common-ground inverters is given.