Study On Control Techniques In PV Generation Syetem

Nowadays, on account of the problems of environmental pollution and exhaustion of energy sources become worse, the solar energy application has been a hot spot that most countries compete against each other to develop. Photovoltaic(PV) systems are paid more attention to among its various application.However,as the output characteristic of photovoltaic cells is non-linear,and be easily influenced by the outer environment, how to make the use of solar energy more effective has become a difficult problem in this area. Solar array Maximum Power Point Tracking (MPPT) control and photovoltaic grid-connected inverter control are the two core part of PV grid connected system. This paper tries to study photovoltaic system with the target of maximizing the efficiency of solar energy, and both the theoretical and experimental research of controller of photovoltaic system has been done. In this thesis, the main contents are as following:Firstly, this paper systemically summarizes the research background, and then subject of solar photovoltaic power generation technology, and a brief introduction of this topic research status and research significance. Then introduces the principle of photovoltaic system and basic composition,which determines the main research contents.Secondly, introduces the operational principle and performance characteristic of PV cells, and describes the equivalent circuit and mathematical model dentally, and sunshine intensity, junction battery temperature and series resistance of photovoltaic cells effects on output characteristics are analyzed. Based on the operational theory and mathematical model, a dynamic model for photovoltaic array, which can simulate the characteristics corresponding to different ambient temperatures, solar radiations and photovoltaic array's parameters, is proposed. This dynamic simulation model solved the limitation for only specific photovoltaic array model is presented. And it summarizes the current power tracking control algorithm.Thirdly,this paper introduces several traditional Maximum Power Point Tracking (MPPT) control algorithms. By comprising these control algorithms, the respective advantages and disadvantages have been found, and summarize the Maximum Power Point Tracking control algorithm at home and abroad. Researched the implementation strategy of Maximum Power Point Tracking control, and building simulation model of system modules. Based on this, a modified Perturbation and Observation Algorithm is introduced, Simulation and experimental result demonstrate that the proposed method can effectively reduce the tracking power loss and have good performance in both dynamic response and steady-state.Finally,Established mathematical model which is based on the SPWM voltage/current type, and grid-connected inverter control.Designed parameters of PI control, analysis of control system error.This paper focus on single-phase grid-connected system which can work on not only the Photovoltaic grid-connected system but also the Photovoltaic independent system,the control method of virtual value outer loop and instantaneous value inner loop,which can eliminate the static error, as well as make the output wave well. At the same time gave structure diagram to meet the independence and the grid two modes of operation of the output filter control.