Study Of Three Phase Grid-connected Photovoltaic Power Generation System

With the problems of energy shortage and environmental pollution have become more and more prominent, solar energy, as one kind of important renewable energy, receives widespread attention. Grid-connected photovoltaic system is the inevitable trend of large-scale use of solar energy. Grid-connected inverter is the main equipment between PV array and grid, so studies of its main circuit topology and control strategy have important practical significance.First of all, a survey is made on the development of photovoltaic power generation at home and abroad, as well as the major ways of connection between photovoltaic power generation and grid. Research state of output current control of grid-connected inverter is also summarized.Secondly, the paper analyses the topology structure and control strategy of grid-connected photovoltaic power system. In the thesis, the principle of the system is analyzed, maximum power point tracking (MPPT) control of photovoltaic arrays and output control of grid-connected inverter are also studied. After in-depth studies of perturbation and observation method and sliding mode control, which respectively implement MPPT control of photovoltaic arrays and real-time output control of grid-connected inverter, provements are made to them. For the perturbation and observation method, variable step size is adopted. For the sliding mode control, its index reaching law is improved.Based on the detailed theoretical studies above, the paper designs a 25kWp grid-connected photovoltaic power system. In the design, IGBT devices with better performance are used as the switch components of the main circuit, and advanced floating-point DSP is used as the chip of control circuit. These devices, along with the improved perturbation and observation method and sliding mode control method, provide a solid technology and material foundation for setting up the system.Then, to improve the correctness of the theoretical methods which are proposed above, simulations are performed by MATLAB software. Simulation results show that the improved perturbation and observation method can well implement the MPPT control of photovoltaic arrays, improved sliding mode control also can carry out the fast, stable and high precision control of grid-connected inverter.Thought studies on the theory and implementation techniques related to the grid-connected photovoltaic power system, the paper puts forward new and effective methods and its realization in the field of MPPT control of photovoltaic arrays and output control of grid-connected inverter. These work do well to solve the theoretical and technical problems of grid-connected photovoltaic power system, and provide a good theoretical support for promoting the development of photovoltaic power generation.