Three-phase Non-isolated Buck-boost Grid-Connected Inverter Reserch

Non-isolated photovoltaic inverters do not contain isolation transformers and have the advantages of small size and low cost.Therefore,they will become one of the research hotspots of photovoltaic inverters in recent years.First of all,in the non-isolated photovoltaic power generation system,there is a direct electrical connection between the photovoltaic module and the power grid,and a loop is formed between the parasitic capacitance,the photovoltaic power generation system and the power grid,so leakage current is generated.Leakage current will increase grid-connected current harmonics and system losses,as well as damage to power equipment and the ecological environment.In addition,the solar power generation system is susceptible to external environmental factors such as temperature and light intensity,and the output voltage of the photovoltaic panel may fluctuate.The uncertainty and randomness of output have high requirements on the stability of the inverter,and the inverter is required to have a buck-boost capability.Based on the three-phase CSI7 inverter,an improved three-phase non-isolated Buck-Boost connected-grid inverter is proposed.The inverter has a simple structure and can realize the buck-boost inversion while suppressing leakage current.Firstly,the working principle of the inverter is analyzed,and the common mode voltage and inverter gain expression are derived.The common mode voltage is constant by SPWM modulation,which suppresses the generation of leakage current.Secondly,the mathematical model of the inverter is established,and its buck-boost capability is analyzed.The mathematical equation about the modulation ratio between the DC-side input voltage and the AC-side output phase voltage fundamental amplitude is derived.On this basis,the double current closed-loop structure of direct current control is designed and verified by simulation.Based on theoretical analysis and simulation verification,this paper builds a three-phase non-isolated Buck-Boost inverter experimental platform and verifies the correctness and feasibility of the theoretical analysis through experiments.