Research On Transmission Line Modeling And Resonance Suppression Strategy Of Distributed Generation System

In the distributed generation system,when the distribution capacitance of the transmission line is large and cannot be ignored,the system will have two kinds of oscillations: the input current oscillation caused by the interaction between the output impedance of the inverter and the line impedance;the background harmonic voltage oscillation caused by the distributed capacitance and inductance..These two resonance phenomena increase the harmonic content in the system,and the power quality decreases,which affects the stability of the system.Therefore,in the context of new energy generation,this paper studies the causes and suppression methods of the grid-connected current and background harmonic voltage oscillation caused by transmission lines.In order to analyze the current resonance problem caused by the interaction between the inverter and the transmission line impedance,this paper proposes a transmission line linearization model suitable for analyzing the grid-connected system.First,by comparing the fitting accuracy,the Padé fitting method is selected.Secondly,after observing the characteristics of the actual impedance model of the transmission line,the relationship between the fitting order and the line length is studied,and the basic principle of fitting is given.Then consider the skin effect and introduce a de-peaking factor to make the linearization model more accurate.Finally,the effectiveness of the fitted model was verified in the simulation analysis of the grid-connected system.Aiming at the problem of oscillation amplification of background harmonic voltage on the transmission line,the theoretical analysis of the propagation law of background harmonic voltage on the transmission line is carried out firstly,and the change of the position of the voltage standing wave node when the reactive load at the end of the line changes is emphasized.Based on the variation of the endless function and the nodal,this paper proposes a node shifter(Node Shifter,N-Ser)that can realize the harmonic voltage shift on the transmission line by controlling the corresponding subharmonic non-functional quantity.Device.By changing the reactive power of the corresponding subharmonic consumption,the node shifter moves the node of the harmonic voltage standing wave without consuming the active power and affecting the fundamental wave energy,so that the node position matches the transmission line position,thereby realizing Harmonic oscillation suppression on the transmission line.Finally,based on the lumped parameter model of transmission line,the transmission line model of ?-shaped circuit cascade is built,and the linearization model method is verified based on the model.At the same time,the node phase shifter platform based on DSPTMS28335 control is built,which verifies the correctness and effectiveness of the scheme.