Research And Design Of High-power Three-phase Photovoltaic Grid-connected Inverter

With the outbreak of the energy crisis and environmental problems,there is an urgent need for renewable energy that can replace traditional sources.As the core equipment of solar photovoltaic power generation,photovoltaic grid-connected inverter has always been the key content of academic research.In this paper,three-phase photovoltaic grid-connected inverter as the research object,mainly on its topology structure,mathematical model,control strategy and other issues are studied.On the basis of summarizing the control technology of three-phase photovoltaic grid-connected inverter,this paper compares the advantages and disadvantages of several topologies of grid-connected inverter,adopting the isolated two-stage LCL three-phase photovoltaic grid-connected inverter with the boost circuit in the front stage and the full-bridge inverter circuit in the latter stage.According to the determined three-phase photovoltaic grid-connected inverter,the principle is described,and its mathematical model under three-phase stationary coordinate system,two-phase stationary coordinate system and two-phase rotational coordinate system is deduced.Aiming at the problem that the proportional integral control can not realize the zero steady state error tracking of AC quantity,the quasiproportional resonant control is introduced,a composite controller with quasi-proportional resonant + integral is studied to realize the control of grid-connected current,and the capacitance current feedback method is used to suppress the resonance of LCL photovoltaic grid-connected inverter,and finally,this paper constructs a three-ring control system based on the composite controller with DC bus voltage control ring as outer ring and grid-connected current and capacitance current as inner ring,analyzes the stability of the system,discusses the design of the controller,and realizes the quality control of the inverter output grid-connected current waveform.The hardware and software design of three-phase photovoltaic grid-connected inverter is carried out.The simulation model of three-phase photovoltaic grid-connected inverter under several controllers is established,and the grid-connected current spectrum diagram and grid-connected current waveform diagram are obtained,and the simulation results are analyzed and compared,which shows that the harmonic distortion rate under the composite controller with quasi-proportional resonance + integral is lower than that of other controllers,and the control effect is better.The experiment of small power prototype is carried out,and the validity of the analysis and design is verified by analyzing the experimental waveform of small power.