Study On Interaction Mode Between Wind Farm And The Power Grid By Using Small Signal Analysis Method

As a renewable and sustainable clean energy source,the key technology of wind energy has experienced enormous development.Not only the capacity of the wind turbine generator(WTG)but also that of the wind farm is increasing continuously.At the same time,the abnormal operation events of large sacle grid-connected wind farms are growing continuously,which influences the normonal operation of the wind farm and even results in the off grid of the wind farm or the damage of WTG.Generally,the abnormal operation events are attributed to be resulted from sub-synchronous resonance and low frequency oscillation,but the source of the problem and the interaction principle should be studied further.The paper is aimed to provide theoretical basis for developing effective damping strategies through the research of interaction mode between the wind farm and the power grid.The main contributions of this paper are: after establishing the small signal models of fixed speed induction generator(FSIG),doubly fed induction generator(DFIG)and permanent magnet induction generator(PMSG),finding out all the interation modes and the dominated variables for the three types of WTGs through calculating the eigenvalues and participation factors of the models;through changing the initial values of the small signal models,studying the influence of the output power of WTG on the interaction modes;based on the small signal models of different types of identical two-WTG systems,studying the influence of various combination of initial values on the interaction modes;studying the varying trend of each interaction mode when the WTGs are in parallel operation in both identical wind farm and hybrid wind farm.Firstly,the paper introduces the research state of the interaction between the wind farm and the power grid home and aboad,and also elaborates the exact definition of sub-synchronous interaction(SSI)and low frequency oscillation.Secondly,the small signal models of FSIG,DFIG and three types of PMSGs are established according to the structure of the mainstream WTGs.Based on participation factor analysis,every oscillation frequency is studied in detail and the accurate classication for each oscillation mode is conducted.Simultaneously,the initial value of the small signal models is changed to study its influence on the interaction modes.Then,the small signal model of the identical two-WTG system is deduced and its interaction mode is also studied.In addition,the influence of different combination of the initial values of the two-WTG system on the interaction mode is researched.At last,on the basis of the reaearch of the fundamental wind farm layout principles,the small signal models of identical wind farm and hybrid wind farm are developed respectively to study the development trend of every interaction mode.