Research On Three-Phase Photovoltaic Grid-Connected System Based On Two-Switch Buck-Boost

With the depletion of traditional fossil fuels and the gradual aggravation of environmental pollution,the energy problem has attracted worldwide attention.Developing and using green and clean new energy has become the only way for human development.Solar energy has become a research hotspot in the field of new energy because of its easy access,pollution-free and abundant reserves.Photovoltaic power generation is the main form of using solar energy to convert solar energy into easy-to-use electricity.In this paper,the main technology of two-stage three-phase photovoltaic grid-connected power generation system is studied,aiming at achieving efficient and stable grid-connected power generation under wide voltage output of photovoltaic array.The generation principle of photovoltaic cells is analyzed,and a model of Engineering photovoltaic cells is built under Matlab/Simulink.The simulation characteristics of photovoltaic cells in different environments are analyzed.The disturbance observation method and conductance increment method commonly used in MPPT algorithm are analyzed and studied.The MPPT algorithm based on fuzzy control is emphatically studied and designed.Simulink simulation is used to compare the three algorithms to verify the superiority of fuzzy control.Aiming at the wide output voltage characteristic of photovoltaic array changing with environment,the two-switch Buck-Boost converter with the advantages of boost-and-drop function,input-output homopolarity and low voltage stress of switching transistor is studied.A circuit parameter design method is provided for the synchronous mode of the converter.Open-loop simulation under Simulink verifies the correctness of the design method,and the change is also discussed.The closed-loop system of the converter is designed,and the closed-loop simulation model is built to simulate the wide voltage output of the photovoltaic array.The closed-loop results show that the converter achieves smooth switching of step-up and step-down modes,and can effectively improve the power transmission ratio.It can be used as the front-stage DC converter of two-stage photovoltaic power generation under wide output voltage of the photovoltaic array.The grid-connected inverter are deeply studied,and the mathematical model of the three-phase grid-connected inverter in two-phase rotating coordinates is deduced.On this basis,the decoupling control of the inverter is carried out,and the simulation model of the three-phase grid-connected inverter based on SVPWM control technology is built.A three-phase photovoltaic grid-connected power generation system model based on two-switch Buck-Boost is built under Simulink.Combined with the actual engineering background,the parameters of the project are extracted and simulated in the whole model.The simulation results show that the system can run steadily under wide voltage output of the photovoltaic array.The MPPT algorithm can track accurately.The two-switch Buck-Boost converter switches the boost and buck modes,and the THD meets the standard.The unit power factor is effectively connected to the grid,which verifies the feasibility of the overall topology and strategy.