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Research On Sub-synchronous Oscillation(SSO) In A Wind Farm Integrated Power System

Posted on:2019-01-04Degree:MasterType:Thesis
Country:ChinaCandidate:L WangFull Text:PDF
GTID:2382330563991397Subject:Electrical engineering
Abstract/Summary:PDF Full Text Request
In China,large-scale development and utilization of wind energy has become an integral part of national energy strategy.However,Wind farms are frequently located in remote areas,far from the bulk of electric power users,and require long transmission lines to connect to the grid.Series capacitive compensation of doubly-fed induction generator(DFIG)based wind farm is an economical way to increase the power transfer capability of the transmission line connecting the wind farm to the grid.However,a factor hindering the extensive use of series capacitive compensation is the potential risk of sub-synchronous oscillation(SSO).This oscillatory phenomenon may cause severe damage in the wind farm,if not prevented.With controlled power electronic converters are increasingly being used in power systems,a controlled power electronic converter can cause instabilities when interacting with other dynamic subsystems in a power system.The main work includes the following three parts:A small-signal model and PSCAD/EMTDC simulation model of single machine infinite bus system composed of DFIG and series compensation are built,and the SSO characteristics of a DFIG-based wind farm connected to series compensated transmission system are researched by using eigenvalue analysis and time-domain simulation.Analysis and simulation results show that the wind speed,the proportional parameter of the inner loop of the rotor-side converter and series compensation degree exert a significant effect on the sub-synchronous oscillation characteristics of the system.A method that can mitigate sub-synchronous oscillation in the wind farm by emulating a virtual series resistance on the rotor is proposed.The equivalent circuit model of DFIG is obtain,taking into account the structure of inner current control loop in RSC and virtual resistance controller.Both the eigenvalue analysis and time-domain simulation have validated the effectiveness of this damping method.Input admittance expressions for a voltage-source converter(VSC)are derived.Using impedance and admittance matrices the closed-loop stability analysis of the converter-grid interaction are researched.The expressions for the elements of the VSC input-admittance matrices,in which the current control loop,the direct-voltage control loops,and the phase-locked loop(PLL)used for synchronization are modeled.The main benefit of the method lies in its generality: any grid impedance-symmetric or unsymmetric-can be modeled,while a modification of the VSC control system simply implies finding another input-admittance matrix.
Keywords/Search Tags:doubly-fed induction generator (DFIG), wind farm, series compensation, subsynchronous oscillation (SSO), eigenvalue analysis, virtual resistance, input admittance
PDF Full Text Request
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