Research On Modeling And Control Strategies Of PV Grid-Connected System

With the rapid development of national economy,the demand for electricity is gradually increasing,not only require adequate supply but also have a higher quality.As some new energies can make up for the shortage of traditional energies,so it has become the main research trend of the future energy development.Due to its reliability and flexibility,microgrid system has attracted the attention of researchers.Because of its pollution-free,renewable,universal and flexible,photovoltaic power generation comes gradually into everyone’s vision.Photovoltaic power generation can work in gridconnected mode or stand-alone mode,grid-connected mode is an important technical support to promote grid-connected photovoltaic power generation,this dissertation is about how to realise the photovoltaic grid-connected operation quickly and effectively.Photovoltaic cells convert solar energy into electricity,constituting the basis of photovoltaic grid-connected power generation.In this dissertation,we established its mathematical model after studying its power generation process,and achieved its voltagecurrent and voltage-power characteristics by Matlab/Simulink.After that,to solve the maximum power tracking problem,variable step-length conductance increment method is used and a state feedback controller is designed based on Boost chopper(Boost Chopper,also known as Boost converter).The simulation results show the effectiveness of proposed algorithm.In this dissertation,the three-phase voltage inverter is applied to the photovoltaic grid-connected system,by analyzing the topology structure and working principle of the inverter,the energy flow between photovoltaic cells and the grid is mapped.Then the topology of whole grid-connected system is designed,and its mathematical model is obtained by analyzing the main circuit.Based on the mathematic model of grid-connected system,this dissertation designs two controllers based on output regulation and backstepping control strategy.Then frequency-reactive power feedback is added to shorten the islanding detection time and the local or global asymptotic stability of the system is achieved.The simulation model of grid-connected system is built in Matlab/Simulink,and the above control strategies and traditional control strategy are simulated and verified,simulation results show that the designed controllers based on output regulation and backstepping can make DC bus voltage reach a stable value quickly,achieve conditions of the grid-connected quickly,which is more superior to traditional control strategy.