Research On Adaptive Damping Strategies And Analysis Of Sub-synchronous Oscillation For DFIG Based Wind Farm

With the aggravation of the energy crisis and increasingly prominent environmental problems,wind power generation has become the most effective solution among the various methods of renewable energy generation and it has been developed rapidly.Especially,since the double fed induction generator(DFIG)has the adjustable speed and power decoupling ability,it has been rapidly developed and become one of the current wind turbine units.However,there are great differences in structure and control between the DFIG wind turbine and conventional units.Thus,great attention has been paid to large-scale wind power integration.Specifically,the impact of large-scale wind power integration on power system small signal stability is a high research priority.Regarding the issue above,an improved adaptive damping control strategy is proposed to damp sub-synchronous oscillation for DFIG based wind farm.This thesis consists of five chapters.In chapter 1,the introduction about current situation of wind power system and definition and classification of Subsynchronous Resonance(SSR)has been presented.And then the analysis methods and vulnerability of the SSR in different types of wind turbine and the installation effects and causes in DFIG wind farm have been mentioned.In chapter 2,a system model which a DFIG-based wind farm is connected to an IEEE first benchmark model has been established.And the system model consists of two aspects,one is steam generator models,the other is DFIG wind farm.The DFIG's modeling including wind turbine model,drive train model,pitch control model,DFIG dynamic electromagnetic models,as well as the decoupled control of DFIG using traditional PI controller based control of RSC and GSC has been presented.Chapter 3 analysis power system integrated with the DFIG based wind farm,and an ancillary damping control strategy is investigated in order to describe a supplementary control structure of the wind turbine.This control loop includes RSC and feedforward compensator.Besides,the performances of synchronous generator(SG)rotational speed variations at different DFIG operating modes(synchronous,subsynchronous,supers-synchronous)are simulated under different control strategies.In addition,two possible SSRs in DFIG wind farms including induction generator effect(IGE),torsional interactions(TI),are briefly explained,and impacts of some wind farms parameters on these SSRs are investigated based on PSCAD/EMTDC software.In chapter 4,simple adaptive control strategy is proposed to evaluate the convergence performance and damp network subsynchronous oscillations under different control strategies.First,the model reference adaptive control(MRAC)is described based on MIT rule adaptive control strategy.And then the adjustment mechanism is designed evaluating the convergence of the simple adaptive control by simulating active/reactive power of the DFIG under Almost Strictly Positive Real(ASPR)control system.And the gain-scheduling adaptive(GSA)control strategy is proposed to reduce the effects of Subsynchronous Resonance under different wind speeds.Chapter 5 contains conclusion of the thesis.The simulation results show using this controller will help the wind turbines to have a positive contribution in network subsynchronous oscillations damping at different wind speeds and system operating modes.The achievement of this thesis is helpful to promote the safe and stable operation of the power system integrated with DFIG based wind farm,especial for the damping control strategies for SSR.