The Grid Type Photovoltaic Inverter System Based On Improved MPPT Research

As the dwindling of fossil energy, as well as the environmental pollution caused by the burning of fossil fuels, the development and utilization of new clean energy is increasingly brought to the attention of the human.The solar energy, as the most promising source of energy, is in developing by all the country. Among them, the photovoltaic power generation technology, as one of the most important form of solar energy development, has the advantages of simple structure, easy construction, its technique get unprecedented development. The paper, based on grid type photovoltaic inverter system,has done a system research of this technology.In this paper, the structure of the grid type photovoltaic inverter system has been made a brief introduction, according to the size of the system,it is divided to two main type distributed and centralized,and the system is mainly composed of photoelectric conversion of photovoltaic array, the boost chopper circuit,realizing the function of MPPT,the inverter circuit,realizing the voltage inverter,the filter circuit realizing the cutting out of the harmonic filter.Firstly,starting from the working principle of the solar cell,analysis output characteristics of solar cells and photovoltaic arrays, solar cells and photovoltaic arrays’s mode are established by mathematical methods, and through the simulation in Matlab/Simulink, make a result of output characteristic curve,base on the outside light intensity and temperature changes.Secondly,a brief introduction of different inverter circuit has been carried on, this paper selects the single-phase two-stage inverter circuit as the research object without transformer, respectively, to the former level,BOOST circuit, the second level, full bridge inverter circuit, the end level,LCL passive filter circuit,is analyzed and design the parameter, building up the topological structure of the photovoltaic inverter system.Thirdly, in order to realize from the PV array output power to the grid control, we need to choose a reasonable control strategy to control the PV inverter, with the photovoltaic inverter control system,this paper first explain the MPPT control principle and introduces the conventional MPPT control strategy, and then choose the single current loop grid-connection control strategy, establish simulation model in Matlab/Simulink. Due to the MPPT control decisive role in the photovoltaic power generation systems, the paper focuses on the MPPT control, through the simulation, analysis the conventional MPPT control strategy, points out the problems existing in the conventional MPPT control strategies.Lastly,in view of the problems existing in the conventional MPPT control, this paper puts forward a kind of strategy based on the sliding mode variable structure control method by variable index reaching law, through the comparison with conventional MPPT control analysis, it can track the maximum power point faster, and its stability is also better, less susceptible to interference, and also suitable for the situation of local shadow,this strategy has high practical value.