Research On Subsynchronous Oscillation In Doubly Fed Wind Farm

As a kind of clean renewable energy,wind energy has been paid more and more attention from all over the world.Our country develops the wind power generation greatly,the current total installed capacity is the first in the world.However,as the scale of the wind power access system is getting larger and larger,the wind power grid connected to the system has more and more influence on the stability of the system.The wind farm subsynchronous oscillation problem is one of them,In recent years,there are many accidents happened.Therefore,it is of great theoretical and practical significance to study the sub synchronous oscillation of wind farms.In this paper,the subsynchronous oscillation caused by interaction between wind generators in double fed wind farm is mainly studied.Firstly,this paper introduces the current development status of wind power generation,the current mechanism and analysis method of the subsynchronous oscillation in wind farm,and the influence of the related factors.A conclusion is drawn that there are few studies on subsynchronous oscillation in the wind farm.Then,this paper studys the principle and the basic structure of DFIG.Aerodynamics model,induction generator model,two-mass shaft system model,converter and its control system model of DFIG are discussed in detail,and the detailed mathematical model of each part is obtained.In summary,a DFIG model is established for the study of subsynchronous oscillation.Next,it introduces the mathematical principles and basic concepts of eigenvalue analysis,and derives the Linearized model of double fed wind farm grid connected system.On this basis,a eigenvalue analysis method based on open loop mode resonance is proposed,the first is to study the theory of the open loop mode resonance between two DFIGs,and open loop mode resonance index that is used to forecast closed loop model is proposed.Finally,subsynchronous oscillation in double fed wind farm is simulated and analyzed through examples,the influence of the related control parameters,the DFIG output and the number of the DFIG on the subsynchronous oscillation is studied in this paper.It is verified that the eigenvalue analysis method based on the open loop mode resonance is effective.The result shows that,When the open loop subsynchronous modes of DFIGs are close or equal,open loop mode resonance occurs,so that the strong interaction between DFIGs.Under the influence of this strong interaction,the stability of the closed loop mode of DFIG reduces even leads to subsynchronous oscillation of the system.By using the resonant theory of open loop mode,an explanation is provided for the mechanism of "frequency drift"occurring in the wind farm.