Research On Control Strategy Of Three-Phase Grid-Connected Inverter

There are many factors that affect the quality of wind power grid connection,among them,the selection and control methods of inverter is the key factor affecting the quality of grid connection.The selection of topology and the design of control method,which will have important influence on grid-connection efficiency,harmonic content and grid-connected quality,it will definitely influence the safety and reliability of grid-connected system.With the analysis of the inverter topology and traditional control methods,a new direct power control method and a repetitive control method are proposed,and a detailed analysis process is given.First of all,this paper chooses three-phase grid-connected inverter as the object of study,analyzing its topology construction and operating principle,giving its detailed mathematical modeling process;Based on three different filtering forms of L,LC,LCL,The LCL filter is chosen as the grid-connected filter.At the same time,the analysis process of the SVPWM modulation mode is given,its simulation model is given.The control target and the overall control scheme are determined,it will provides the basic theory for the follow-up research.Secondly,the inverter select the direct power control as the control method,analyzing the traditional direct power control using query switch table,its operating principle is explained.The mathematic model is built,the intergrated control scheme of the control method is given.The Simulation model of the strategy is estabilshed,and its simulation results were analyzed.Traditional power control is easy to implement,but there is no fixed switching frequency and power fluctuations and other issues.In this paper,the direct power control method of power prediction is put forward,which working process is analyzed in detail.Second-order Lagrangian interpolation method is used instead of linear interpolation method to provide fixed switching frequency and reduce power error.Building the simulation model of the improved control strategy,analyzing the simulation results of the two different control method.Thirdly,this paper analyzes the principle and implementation process of the traditional repetitive control,giveing the process of mathematical analysis.In the meantime,it analyze the control defect.Based on this,an improved` frequency adaptive repetitive control strategy was proposed,its principle and process are analyzed in detail,and the design process of the improved control method is analyzed,its overall control scheme is given,building the mode of simulation and the result of the simulation is analyzed.At last,the realization and design process of phase-locked loop is expatiated,and its control performance is analyzed in detail.The mathematic modeling process is given and the simulation is verified.Under the conditions of three-phase balanced voltage,the simulation and analysis are given under the condition of not containing harmonic wave and containing harmonic wave.