Research On Three-phase Grid Connected Inverter Of Photovoltaic Power Generation

At present, fossil energy is the main structure in the world, but it is the non-renewable resources, the large number of consumption will lead to the depletion of energy, and cause zoology environment are serious destructed. Solar energy is a kind of renewable resources, and it is clean, environmental protection in all alternative energy. So, it is an important form of photovoltaic energy generation that convert the energy of sunlight into electric energy. Now, the PV grid-connected is the main application in the world PV system. Wherein, photovoltaic maximum power point tracking (MPPT) control and grid-connected inverter current control are two key parts in the grid-connected systems. In this thesis, the studies around this two aspects to study, the main contents are as follows:Frist,Analyze several circuit topology about photovoltaic power generation three-phase grid inverter system used commonly, and compares their advantages and disadvantages. On the basis of this article may determine the research three-phase grid inverter topological structure-two levels of photovoltaic grid inverter. Among them, the ideal choice relatively about Boost booster transform circuit is the former stage DC-DC converter, after DC-AC inverter usually adopts the whole bridge inverter circuits, and analyze the working principle of the circuit.Second,Introduce the work principle of photovoltaic cells and its basic characteristics. Analyze several methods commonly used about MPPT, such as Incremental Conductance (INC), Constant Voltage Tracking and Perturbation and Observation method. Put forward a kind of improved MPPT algorithm about hysteresis comparison disturbance observation method that step size change. In order to check the efficiency and accuracy of the method, use MATLAB/Simulink software to simulate. From the simulation results conclude that use the variable step long hysteresis comparison disturbance observation method can tracking the maximum power point fast, and avoid the oscillation phenomena appeared in the Perturbation and Observation method effectively, and improve the photovoltaic system of power generation efficiency.Last,Compare the inverter current control strategy used commonly, and analyze the three-phase grid inverter mathematical model in different coordinate, and establish the SVPWM control strategy that the paper using. If base on the basic principle to carry on formula deduction and calculation, it will increase the difficulty of the controller design. So, by the optimization algorithm, make the inverter realize digital control. The results show that the algorithm to realize the grid control requirements, improve the dynamic response of the system performance, make the utilization rate of DC voltage almost up to100%.