Research On Active Damping Method For Grid-Connected Inverter With LCL Filter

Two-level three-phase grid-connected inverter with LCL filter is studied in this paper,and the control of ICF(inverter-side current feedback)single current loop is researched and improved to solve the problem of the influence that natural resonance of the LCL filter and digital control delay on the stability of the control system bring.Firstly,the system mathematical modeling of the grid-connected inverter with LCL filter is established and the influence of the digital control delay on the system is analyzed.The mechanism of the grid-side voltage feedforward control on the operating characteristics of the system is studied.Analyzing the relationship between the parameters of the LCL filter and the stability of system,and the influence of the filter parameter changes on the stability of the system is defined.Then the condition of filter parameters under ICF control and GCF(grid-side current feedback)control are studied.On this basis,in order to settle down the problem of the fs/6 oscillation and bandwidth limitation which caused by digital control delay,the current prediction method is introduced into the current feedback channel to eliminate the influence of the digital control delay on the system.The stability of the system is analyzed when the introduces link is carried out,and clearly that the introduction of the prediction link reduced the stability margin of the system at fs/2.Therefore,a virtual high frequency damping method(VHD)is proposed to solve the high frequency oscillation and parameter adaptability problems caused by current prediction,thus improving the stability margin as well as dynamic and static characteristics of the system.In addition,in view of the fact that the low-pass filter(LP)characteristics of the feedback channel are usually ignored in the existing research,which leads to the inconsistency between the research results and the actual situation.This paper introduces the LP link into the system model and further analyzed and found that the introduction of the LP link has changed the frequency interval definition of the ICF control in the existing study.On this basis,the resonant frequency interval controlled by ICF is redefined,and the studied high frequency damping control algorithm is applied to the grid-connected inverter system with LP link for theoretical analysis and parameter adaptation experiments.Finally,the simulation are carried out based on Matlab/Simulink simulation software,and the theoretical analysis is verified one by one.The related hardware circuit was built,and the experimental content was verified by the experimental platform of My Way’s PE-Expert3 as the control core.The theoretical analysis and experimental results were compared and analyzed,which showed that the theoretical analysis,simulation results and experimental results were consistent.The conclusion verified that the validity as well as correctness of the analysis method and control algorithm in this paper.