Maximum Power Point Tracking Method And Grid Connected Control In Photovoltaic Power Generation System

Photovoltaic power generation technology is one of the effective ways to solve the serious problem of global energy shortage.Therefore,vigorously developing photovoltaic power generation technology is an inevitable trend.But the variability of the external environment will have a great impact on the output power and grid connected control of photovoltaic cells.Therefore,photovoltaic power generation system is taken as the research object in this paper,aiming at the Maximum Power Point Tracking control and Grid-connected control of photovoltaic power generation system.The main parts of this paper are as follows:(1)On the basis of a more systematic exposition of the background of the research,the main research of this paper is divided into two parts: the maximum power tracking(Maximum Power Point Tracking,MPPT)and the grid connected control.(2)Based on the analysis of the principle of photovoltaic generation,the mathematical model of photovoltaic cell is deduced,and a general model of photovoltaic cell engineering is established in Simulink.Through the simulation of the photovoltaic cell model,the illumination effect and the temperature effect of the photovoltaic cells are obtained.By analyzing the MPPT control principle of the photovoltaic cells and the principle of the conversion between the input internal resistance and the external load of the photovoltaic power generation system,an independent photovoltaic generation system is built in the Simulink.In the light of uniform illumination,the P-U characteristic curve of photovoltaic cell output shows a single peak characteristic.The three MPPT control methods,such as P&O,INC and SMC,are theoretically analyzed and simulated respectively.The simulation results show that the MPPT control method based on SMC control method can effectively improve the dynamic response speed and stability of the system.(3)Aiming at the problem of multi peak of photovoltaic array under partial shadow condition,the principle of multimodal generation is analyzed,and the function of bypass diode is analyzed concretely.In view of the inherent shortcomings of the PSO algorithm applied to MPPT control under local shadow,this paper adopts the basic PSO algorithm,the PSO algorithm which increases the contraction factor and the PSO algorithm based on SA to carry out MPPT control,and give the flow of the design method.The simulation results show thatcompared with the basic PSO algorithm and the PSO algorithm which increases the contraction factor,the proposed SA based PSO algorithm not only preserves the advantages of the basic PSO algorithm,but also has fast convergence speed and high precision.It can accurately track the MPP of the photovoltaic generation system under the local shadow condition and stabilize it.(4)In the grid system of three-phase photovoltaic power generation,the mathematical model of the loop voltage in the three-phase static voltage of the photovoltaic power generation system is converted to the mathematical model under the rotating coordinate system(d,q)through coordinate transformation and dq decoupling control.The three-phase PV grid connected system is set up in Simulink,and the vector control method based on the voltage orientation of the power grid is used as the control strategy of the three-phase photovoltaic grid connected inverter.The simulation results show that the grid current and voltage can meet the requirements of grid connection under the circumstances of light mutation.