Research On Several Key Technologies Of Three-Phase Photovoltaic Power System

With the energy shortage and environment pollution caused by the combustion of the fossil fuels, the use of renewable energy is playing a more and more important role in solving the problems of global energy and environmental pollution. Solar energy as an important part of the renewable energy, and photovoltaic power generation has been the main way of developing and utilizing solar energy, so vigorously developing the research of photovoltaic grid connected power system is of great theoretical research value and engineering practical significance. In this paper, three key technologies of two stage grid-connected PV system is studied, maximum power tracking methods, grid-connected control strategy and low voltage ride through control strategy are included.The main work of this paper:(1) In this paper, the engineering mathematical model of PV battery is established considering the fact in the engineering, and the output characteristics of the model are simulated. Several conventional maximum power tracking methods are analyzed and compared. Finally, the method of perturbation and observation is applied to track the maximum power point of the photovoltaic cell. The tracking results of PO method are verified in the Matlab/Simulink simulation platform.(2) Grid-connected control strategy is one of the key technologies of photovoltaic power generation system. In this paper, the topology of the three-phase photovoltaic inverter based on LC filter is analyzed, and the mathematical model of the inverter in the dqO coordinate system is established. In order to improve the grid-connected power, the parameters of LC filter are designed. Double loop PI control is applied to control grid-connected inverter after the current control methods is analyzed and compared. The grid-connected control strategy, photovoltaic cell model and the MPPT method above is combined to build a three phase photovoltaic grid-connected power generation system, the feasibility of these methods are proved by Simulink simulation.(3) The importance of low voltage ride through (LVRT) of PV system is introduced briefly in this paper, and a LVRT control strategy based on the Multi Index Nonlinear Control (MINC) is proposed to provide a solution to the problem of LVRT, which caused by the symmetrical drop of grid voltage. Simulation results show that the DC voltage fluctuation of inverter can be suppressed effectively, the inverter can also transfer corresponding amount of reactive power to grid to support voltage recovery according to the depth of voltage dip, after the fault of grid is cleared, the PV system can realize the unity power factor running quickly.