Research And Simulation Of 20kW Two-stage Grid-connected Photovoltaic Inverter System

With the development of social economy and science and technology,the heavy consumption of traditional energy and the problem of environmental pollution and shortage of resources have become increasingly prominent,forcing people to continuously seek clean and renewable energy,so new energy has become a hot research topic.Compared with the traditional fossil fuels,the new energy has the advantages of small pollution,renewable,large storage,etc.However,because of its low energy density and dispersed characteristics,the new energy is unsuitable for the traditional large-scale centralized power generation and long-distance power transmission.At this point distributed generation highlights its advantages.In order to further improve the performance of distributed photovoltaic grid-connected system,a novel MPPT control method based on two-stage photovoltaic grid-connected system and synchronous detection technology of inverter are studied in the thesis.Firstly,the principle of photovoltaic cell is introduced,and its characteristics are described by mathematical expression,and the commonly used mathematical model is given.Several methods of MPPT used in routine analysis are analyzed,and the implementation methods and analysis of their advantages and disadvantages are given.Combined with the research content,an improved MPPT implementation method is proposed,and its improvement ideas and implementation methods are studied.Secondly,the mathematical model of the front-end interleaved parallel Boost converter and the synchronous rotating coordinate system of the three-phase full-bridge inverter are established.According to the mathematical model,the design method of double closed-loop control system of front-end DC/DC converter is studied firstly,and then the back-end inverter control system is analyzed and designed according to the characteristics of model I and model II.Nextly,the synchronization detection technology based on complex-coefficient filter is studied,and the principle of the application of complex-coefficient filter in synchronization detection technology to eliminate the influence of unbalanced power grid on system synchronization detection is analyzed.Finally,the main circuit parameters design and control parameters tuning of front-end DC/DC converter and three-phase full bridge inverter are studied.The improved MPPT method,the principle of multi-complex filter and the whole two-stage photovoltaic system are verified by simulation.The rationality and effectiveness of the MPPT control method,inverter synchronous detection technology and system control are verified by simulation.