Research And Application Of Photovoltaic Power Grid-connected Inverter System

With the rapid development of world economy, the using of non-renewable energy is growing rapidly, the energy crisis, environmental degradation has become increasingly serious, it has become the biggest one of all the problems human being facing, in such a severe form, people began to focus on researching and developing renewable and clean energy. Solar energy is most abundant on earth hidden, and it is one of the major alternatives of non-renewable energy resources, the human can use pollution-free energy sources, the development and utilization of solar energy is of great strategic significance, photovoltaic technology is a very important technology in the applications of solar energy, researching and development of solar energy is an inevitable trend, it has become the most popular energy topics.photovoltaic power system control method and inverter topology are mainly researched in this paper. As the high price of photovoltaic cells, while the conversion`s efficiency is relatively low, in order to reduce overall system cost and more efficient using of solar energy,the core of photovoltaic inverter systems conversion efficiency becomes the key, and this conversion efficiency only by improving its control strategy and optimization of topological structures.According to actual situation, double-bipolar system structure without a transformer is used in this paper, main contents is divided into three parts:(1) DC side: The principle of the photovoltaic cells and it`s output characteristics, the establishment of the battery simulation model, using matlab / simulink simulation software to simulate sunlight in different environments and different intensities of solar cell output characteristics. Simulation and actual measurement data are compared to verify the correctness of the model for subsequent simulation of the whole system basis; analysis of a variety of maximum power tracking strategy, the incremental conductance method selected most of this article MPPT strategy, DC -DC link using BOOST boost circuit, the working principle of the circuit is analyzed, the selected model and parameters of various components.(2) AC side: The topology and control strategies of inverter is the focus of this paper, by analyzing the structure of the traditional inverter bridge, there are some defects such as direct connection between upper and lower leg, in order to improve these shortcomings, this paper presents a two BUCK inverter topology structure; By studying to the hysteretic PWM and fixed frequency PWM of inverter, through analysis, the sinusoidal hysteresis loop width of the current control strategy and the three-loop control strategy be suggested in this paper; The study of filter in the AC side is also one of the issues, through a series of mathematical principles analysis, the conventional LC filter is selected and the size of its parameters be choosed.(3) Simulation results and hardware design: Based on the proposed two control strategies, builing a simulation module of the whole system with MATLAB / SIMULINK. Through the results of simulation and experimental ,this inverter system can make the output power factor close to 1. Establishing a 1KW PV grid system and handling all the test data with DSP, and the experimental results show that the adopted control strategy and design approach is feasible and effective, the design of main circuit and control circuit is reasonable.