Research On Control Strategy Of LCL Inverter Of Photovoltaic Grid-connected System

With the rapid development of economy,energy resources,as a national strategy for the development of national economy and the progress of the society has a significant effect,however,the energy shortage and the environment pollution of fossil fuel combustion caused problems caused the extensive concern of various countries.In order to reduce environmental pollution,the world began to focus on the development of new energy technology.With its unique advantages,solar energy is regarded as an important energy source by every country in the world.In order to improve the utilization efficiency of solar energy and the quality of grid-connected current,scholars from all over the world began to study the photovoltaic power generation technology,which made the photovoltaic power generation technology flourish.In this paper,a two-stage grid-connected photovoltaic system is selected as the research object,and the two key technologies of DC bus voltage control and grid-connected current tracking control in the post-stage inverter module are mainly studied.Firstly,this paper introduces the front and back structures of the two-stage photovoltaic grid-connected system.In the pre-structure,the model of the photovoltaic cell is established in this paper,and the output characteristic curves of the photovoltaic cell under different external conditions are obtained through simulation.In the post-stage structure,this paper mainly introduces the selection of inverter and the establishment of the mathematical model of the selected inverter.Secondly,this paper introduces the control method of DC bus voltage in the post-stage control module of inverter,and proposes a Tracking Differentiator(TD)based PI control method for the traditional Proportion-Integral(PI)control method with low response speed and large overshot.This paper also introduces the nature and principle of TD,and verifies the suppression effect of TD on noise through simulation.Then the PI control method based on TD is applied to the control of DC bus voltage,and the control effect of the traditional PI control method and the PI control method based on TD on DC bus voltage is analyzed through simulation.The simulation results show that the PI control method based on TD has a better control effect on the DC bus voltage,reduces the overshoot of the system,and has a simple structure,which is easy to implement in engineering.Finally,in view of the problem that the grid-connected current of the later-stage LCL type grid-connected inverter is easy to produce Disturbance,this paper puts forward the grid-connected current Control method based on Active Disturbance Rejection Control(ADRC),and analyzes the advantages and disadvantages of the classical PID Control and the composition and principle of ADRC,decouple the mathematical model of the LCL type photovoltaic grid-connected inverter,and establish the simulation model of the grid-connected current Control method based on ADRC.The ADRC controller is designed to test this paper,the grid current control effect,based on the MATLAB/Simulink of grid current control method based on ADRC and PI control method are compared,and the simulation shows the grid current control method based on ADRC for harmonic disturbance suppression effect is better,and achieve no overshoot tracking,and does not need to add additional sensors.