Studies On Characteristic And Suppressing Strategies Of Subsynchronous Oscillation With DFIG-based Wind Farms

With the increase of unit capacity of wind turbine and wind farm scale, theinteraction effect between large-scale wind farms and the grid gradually increased,especially with the implementation of the Wind&Fire baling transporting modes andplanning long-distance and high-point series compensation degree of networktransmission systems, large capacity wind farms and network operation may exacerbatethe risk of subsynchronous oscillations(SSO) of the accident, in order to explore themechanism of the SSO system and improve the ability to network security and stabilitywhen wind farms connected to the grid, therefore, focusing on gird-connected doublyfed induction generator(DFIG) based wind farm, this dissertation intends to analysis thesubsynchronous oscillation characteristics and suppression strategies.This dissertation mainly includes the following parts:①Concerning the wind turbine drive train, the doubly-fed generator, dynamicmodels and control strategy of DFIG, and synchronous generator and other small-signalmodel,a detailed mathematical model for small signal stability analysis withDFIG-based wind farms was established, in addition, building the simulation modelsand control strategies on DigSILENT/PowerFactory platform to lay the foundation forfurther research sub-synchronous oscillation characteristics.②In order to research the impact of DFIG-based wind farms interconnected topower grid on subsynchronous oscillation of turbogenerator, By utilizing modal analysismethod, the changes of the system subsynchronous oscillation modes in a IEEE firstbenchmark power system with and without DFIG-based wind farms are investigated.Respectively, the presented models and modal analysis are demonstrated by comparisonwith the time-domain simulation results in DigSILENT/PowerFactory platform. Finally,regarding for the different conditions of wind speed and reactive power of the windfarms, the variation of subsynchronous oscillation mode was discussed.③In order to improve the control capability of large-capacity wind farmsdepressing power system SSO, the mechanism of DFIG-based wind farms for dampingSSO and an ancillary damping control strategy are investigated. By introducing thetransfer functions between turbo-generator speed and wind farms output active/reactivepower, the expression of the DFIG-based wind farms active/reactive power for thedamping ratio and damping effects on the power system was derived, and the condition of the positive damping was obtained.④In order to design the additional damping control strategies to achieve the goalof providing effective damping in the whole sub-synchronous frequency band,according to the obtained phase angle range of the transfer functions betweenturbo-generator speed and wind farms output active/reactive power, by utilizing theturbo-generator speed signal and the optimization of the phase compensation parametersof the PID controller, the additional damping control strategies based on theactive/reactive power loop of DFIG was proposed respectively, dynamic performancesof additional damping control were simulated by using the active/reactive power loopand compared to the non damping strategy scenario.The research achievements have great significance in the analysis of SSO and toensure the stability of the power system. Further more, it can provide theoreticalreferences and decision supports for suppressing the subsynchronous oscillation of windpower systems.