Research On Suppressing Strategies Of Subsynchronous Oscillation With Grid-integration Of DFIG-based Wind Farms Via Series Compensated Lines

There are regional differences between wind farms and load centers in China,and long-distance transmission will be inevitable.Series compensation technology can effectively solve the long-distance transmission of wind power,but it will also cause sub-synchronous oscillation accidents.Therefore,this topic mainly focuses on the mechanism analysis of sub-synchronous oscillation caused by series compensation of doubly-fed wind farms and the establishment of corresponding vibration suppression strategies.Firstly,in order to study the sub-synchronous oscillation mechanism of series compensation grid-connected system of doubly-fed wind farm,the mathematical model of series compensation grid-connected system of doubly-fed wind farm is established,including wind turbine model,transmission chain shafting model,doubly-fed induction generator model and series compensation transmission line model.The control strategies of rotor side and grid side of doubly-fed induction generator are analyzed,and the control strategies of doubly-fed induction generator at Matlab/Simulink are Based on the simulation platform,a series compensation grid-connected system model of doubly-fed wind farm is established,which is suitable for the study of sub-synchronous oscillation.Secondly,the generation mechanism of sub-synchronous oscillation is analyzed,and based on the equivalent resistance of rotor side and the closed-loop transfer function of rotor current of doubly fed wind turbines,series compensation degrees,wind speed and internal current loop of rotor side converter are deduced as the factors affecting sub-synchronous oscillation.The specific effects of series compensation degrees,wind speed and internal current loop control parameters of rotor side converter on sub-synchronous oscillation are analyzed by time domain simulation method.Finally,based on the mechanism of sub-synchronous oscillation,the suppression strategies of sub-synchronous oscillation based on virtual resistance and sub-synchronous current extraction are established.The effectiveness of these two strategies is verified by time domain simulation and spectrum analysis.