Impedance Modeling And Stability Analsyis Of DFIG-based Wind Farm With A SVG

With the development of wind power permeability,access of static var generator and complexity of grid conditions,operation stability of DFIG-based wind farm is becoming more and more serious,these factors also make the stability analysis of wind farm harder.Impedance analysis method has clear physical meaning and simple criterion,which makes it suitable for analyze wind farm stability.This thesis focuses on the research of DFIG-based wind farm with a SVG,both frequency domain modeling and time domain simulated verification is applied to carry out the stability analysis of the object.The main research contents are as follows:(1)Since the existing impedance model of SVG does not consider the influence of power control loop,this thesis establishes SVG impedance model that takes ac voltage loop into accounts.First,SVG model with ac voltage loop is established,impedance of outer power loop,inner current loop and PLL is deduced;Next,simulation model of SVG connected to grid is built based on MATLAB/Simulink platform,the correctness of SVG impedance model is verified through frequency scanning.Finally,the impedance characteristic of SVG working on different pattern and their influence on DFIG-based wind farm stability is studied.(2)Since the existing DFIG impedance model cannot clearly explains how every module of DFIG contributes to whole impedance characteristic,this thesis establishes DFIG impedance model suitable for stability analysis.First,DFIG model consists of induction generator,rotor/grid side converter and PLL is established.Next,simulation model of DFIG connected to grid is built based on MATLAB/Simulink platform,the correctness of DFIG impedance model is verified through frequency scanning.Finally,the impedance characteristic and stability of DFIG and its modules is studied,the conclusions are verified on simulation.(3)Since SVG is not included in stability analysis of DFIG-based wind farm in recent researches,this thesis establishes impedance model of DFIG-based wind farm with a SVG.First,impedance model of DFIG-based wind farm with a SVG is established.Next,the influence of different SCR and series compensation degree on DFIG-based wind farm is analyzed.Finally,the impedance characteristic and stability of DFIG-based wind farm when SVG accesses on constant reactive power mode or constant voltage mode is studied,the conclusions are verified on simulation.Above work has significant meaning on completing the impedance modeling method and its application on wind farm analysis as well as enhance the stability of DFIG-based wind farm.The thesis also provides insights on improving stability of DFIG-based wind farm on impedance analysis method.