Research On Photovoltaic Grid-Connected System With Power Quality Adjustment

Energy shortage and environmental pollution problems are becoming more and more serious.In order to solve this difficult problem,various countries have increased their efforts to develop clean energy sources that are easily accessible and pollution-free.The excellent solution of photovoltaic power generation has become a key research field for scientists.However,the photovoltaic system will adversely affect the power quality of the power grid with changes in external conditions such as temperature and light.As a large number of non-linear loads are connected to the end of the power grid,the application of power electronic devices is becoming more and more extensive,and the harmonic content and reactive power content in the power grid are greatly improved.Although a large number of active filters can solve the power quality problem,they are not economical because the active filters are too expensive.In response to the above problems,this dissertation adds the power quality adjustment function to the photovoltaic grid-connected system.The specific work is as follows:First,a mathematical model of photovoltaic cells commonly used in engineering is built,and the output characteristics are studied.On this basis,the conductance increment method is improved,and the research on the key technologies of the previous stage of the two-stage photovoltaic grid-connected system is completed;The topological structure and working principle of photovoltaic grid-connected system with power quality adjustment are introduced and analyzed,and the mathematical model of this system is constructed;Aiming at the long response time of traditional voltage outer loop control and the insufficient DC voltage stability,a voltage outer loop based on power feedforward is designed,and a new command current synthesis method is designed;The characteristics of proportional-integral control,quasi-PR changed from Proportional Resonant,and Proportional Complex Integral are analyzed in detail,and the advantages of multiple PCI methods for the research goals of this dissertation are demonstrated.Finally,the simulation and experimental verification of the photovoltaic grid-connected system with power quality adjustment were carried out.MATLAB/Simulink software was used for simulation to verify the effect of the new variable step size conductance increment method.The system uses proportional integral control,multiple quasi-proportional resonance control,and multiple proportional complex integral control.The simulation results show that the system perfectly achieves the purpose of combining power quality control with photovoltaic grid-connected functions.On this basis,an experimental platform was built,hardware circuits were designed,and comparative analysis of power quality control capabilities was conducted.This is to demonstrate the feasibility and correctness of the system designed in this dissertation...