Control and simulation of doubly fed induction generator for variable speed wind turbine systems based on an integrated finite element approach

Transcription

1 Control and iulation of doubly fed induction generator for variable peed wind turbine yte baed on an integrated finite eleent approach Qiong-zhong Chen*, Michel Defourny #, Olivier Brül* * Univerity of iège, Departent of Aeropace and Mechanical Engineering (TAS) Chein de Chevreuil (B52/3), 4000 iège, Belgiu Eail: qz.chen@ulg.ac.be, o.brul@ulg.ac.be # SAMTECH Headquarter, iège cience park, Rue de Chaeur-Ardennai 8, 403 iège (Angleur), Belgiu Eail: ichel.defourny@atech.co Abtract: Regarding renewable energy and environentfriendly iue, wind energy nowaday ha becoe the fatet-growing energy ource in the world, and thu attract a lot of reearch interet in the wind turbine generation yte. A doubly fed induction generator (DFIG) i ued for variable peed operation in a wind turbine yte to extract ore power. Following a yteatic approach, thi paper invetigate on the odelling and iulation of wind turbine generating yte uing the flexible ultibody iulation oftware SAMCEF/MECANO []. The objective of thi work i to analyze the control-generator-tructure interaction in a wind turbine yte. Firtly, an extenion of the finite eleent ethod i integrated into the flexible ultibody dynaic olver, and thu extend the olver to repreent echatronic yte in a trongly-coupled way. Secondly, DFIG and the control yte are odularly odeled for the wind turbine package. Control of DFIG for grid ynchronization and power optiization are elaborated in detail, and the ethod are validated through a 2MW DFIG wind turbine prototype odel. At the end, a yteatic yte odel of wind turbine tructure connected with the DFIG generating yte i preented, which provide the dynaic analyi for the whole yte in an overall range. Keyword: DFIG, wind turbine, control, trongly-coupled finite eleent approach Introduction A one of the ot proiing renewable energy ource, wind power ha ubtantially increaed for the pat decade and i evaluated a the bet choice to fill the electricity generation gap according to the publihed finding by the International Energy Agency (IEA) in A wind turbine yte i ued to convert wind energy into electrical energy. For a given turbine blade airfoil, the power extracted fro an air trea depend on the wind peed, the air denity and alo the turbine rotating peed. Since wind cannot be controlled, turbine rotating peed i then controlled for optiizing wind power extraction. Therefore, a variable-peed wind turbine i of higher energy efficiency than fixed-peed wind turbine. Beide, variable peed operation can reduce echanical tre on turbine tructure and i claied to be better for acoutic noie reduction [2]. Variable-peed wind turbine are typically baed on a doubly-fed induction generator (DFIG), which can operate over a lip range of /-30% and thu enable the turbine to extract the axiu power fro the wind with variable operating peed. One iportant advantage of DFIG in the application of wind turbine, epecially large-power wind turbine, i that only a lip power, typically 20-30% of the total power, ha to be handled by the bidirectional rotor converter. Conequently, both the power rating requireent and loe can be highly reduced. For the control of a wind-turbine-driven DFIG, different trategie like direct torque control (DTC) and variable tructure control (VSC) have been propoed over the lat decade [3]. However, one coon way i to ue vector control on the bai of d,q-tranforation with tator-flux orientation or tator-voltage orientation (alo referred to a grid-voltage or grid-flux orientation) [4]. Typically, two way can be ued for vector control chee. One i by ean of integral-proportional (IP) regulator and the other i by proportional-integral (PI) regulator. The difficulty then lie in the configuration and the deterination of the coefficient of the regulator. Since a wind turbine yte i a hybrid yte featuring not only echanical tructure, but alo aerodynaic, control yte and the coupling interaction in-between. Coputer-aided tool

2 provide a way to reduce cot and iprove efficiency in the deign of wind turbine yte. While pecializing on the echanical tructure and the otion, ot coercial finite eleent ethod (FEM) baed wind turbine oftware can be extended to repreent non-echanical yte by ipleenting a uer-eleent in a weakly-coupled way, which ean that pecific olver are ued for control yte and echanical ubyte repectively, and data are exchanged only at particular counication tie [5]. However, ince the dynaic of the actuator or generator are continuou in tie, weakly-coupled approache could lead to large nuerical error if the tie tep are not et all enough. Thi ethod ight be quite intricate in application, and oetie even unreliable. On thi account, the developent of an integrated flexible ultibody dynaic olver baed on a trongly-coupled ethod would be iportant for achieving better reliability and efficiency. Aong the wind turbine oftware, Sacef for Wind Turbine (S4WT) i baed on the flexible ultibody dynaic olver Sacef/Mecano []. Funded by the Walloon governent, Satech and the Univerity of iège are jointly engaged to develop and iprove the wind-tubine oftware package S4WT under the project Dynawind. The general ai i to develop a coputer-aided tool for cutoization, fatprototyping and optial deign of wind turbine yte baed on the dynaic iulation of the overall yte. Sacef/Mecano offer everal option to include control yte and other non-echanical yte in a nuerical odel. For intance, it i poible to link a D decribing a control algorith or to ue a co-iulation interface with Matlab/Siulink. The proble i then olved according to a weakly coupled trategy. Beide the weakly-coupled approache, functionalitie to decribe the control yte according to the block diagra language have newly been integrated into the flexible ultibody dynaic olver, and thu extend the olver to repreent echatronic yte in a trongly-coupled way [6]. The work preented in thi paper i a contribution by Dynawind. It feature the odelling and control of wind turbine DFIG yte baed on a trongly coupled finite eleent approach. The reaining ection of the paper are organized into three ain part. In the firt part, dynaic odelling of DFIG and it control trategie for variable peed operation are elaborated in detail. The econd part decribe the trongly-coupled iulation approach and the odularly odelling ethod of DFIG control yte on Sacef. Syteatic exaple are given in the lat part for the validation of the odel, the control trategie and the trongly-coupled iulation approach, and alo for the analyi of the control-generator-tructure interaction. 2 Dynaic odel of DFIG For deriving decoupled vector control law for a DFIG, d-q tranforation i ued to ap the 3-phae tator and rotor winding into two orthogonal fictitiou coil with the tator-flux-oriented reference frae. A generalized 5 th order atheatic odel i ued for the odelling of DFIG. For power yte tudie, it i a coon way to ue a per-unit repreentation [7], where the quantitie are expreed a fraction of the bae value. Aue that the tator current i poitive when flowing fro the grid to the achine, then the voltage expreion can be repreented a follow: d v d = R id ψ q ψd ω d v q = R i q ψ d ψq ω d v = R i ψ ψ d v = R i ψ ψ dr r dr l qr dr ω qr r qr l dr qr ω, () where the following notation i ued: v: voltage; i: current; ψ: flux linkage; R, R r : tator and rotor reitance; ω : ynchronou angular peed in electrical eaureent; l : rotor lip; the ubcript d and q repreent the d- and q-axi tator coponent repectively, dr and qr, the d- and q-axi rotor coponent repectively; the upercript "-", a hereinafter defined, indicate per-unit repreentation. The flux linkage equation are: ψ = i i ψ = i i ψ = i i ψ = i i d d dr q q qr dr r dr d qr r qr q, (2) where repreent the tator inductance, r i the rotor inductance and i the utual inductance between the tator and the rotor. The electroagnetic torque expreion can be derived a: Te = ψdiq ψqid. (3) The active and reactive power at the tator and rotor are repectively: P = V i V i, Q = V i V i P = V i V i, Q = V i V i d d q q q d d q r dr dr qr qr r qr dr dr qr, (4)

3 where P repreent the tator active power, Q i the tator reactive power, P r i the rotor active power and Q r i the rotor reactive power. 3 Control of DFIG Wind turbine Gear box SWr DFIG RSC AC/ DC SW GSC DC/ AC Tranforer SWg Grid Figure : A cheatic configuration of a DFIG wind turbine Grid ynchronization and power control are two control ode of a DFIG in a turbine yte. For a better undertanding of the control proce, it i worth briefly tating the working proce of the wind turbine yte. A cheatic configuration of a DFIG wind turbine i hown in Fig.. In the beginning fro tandtill, the DFIG i diconnected fro the grid. Wind peed i eaured by an aneoeter. Once it reache the cut-in value, the brake i releaed and the rotor blade are driven by the pitch regulation echani fro the feathering poition to a pre-optiized angle. The echanical torque created by the aerodynaic lift fro the blade drive the haft to rotate. At the ae oent, the witch SWg i on, and the dc-link voltage in the bidirectional converter i oon charged. When the rotating peed of the wind turbine reache a certain value (e.g % of the rated peed), SWr i turned on and the oft grid ynchronization proce tart. For variable-peed wind turbine, grid ynchronization i poible at any operational peed. Uually, grid ynchronization proce take le than one econd [8]. Once thi proce i accoplihed, SW i turned on and the tator of the DFIG i connected to the grid, and then the power control ode, which coprie active power optiization and reactive power control, tart. Active power control i for tracking a predefined power-peed characteritic profile and reactive power control i to control the power factor at the grid terinal. DFIG i controlled via the converter on the rotor. The grid ide converter (GSC) i controlled to aintain a contant dc-link voltage and to guarantee the operation of the converter with unity power factor, i.e., zero reactive power [9]. The rotor ide converter (RSC) i controlled for both grid ynchronization and power optiization. To oe degree, RSC can be conidered a a current-controlled voltage ource. Baed on d,q-tranforation with the tator-flux oriented reference frae, control on the d,q-axi rotor current can be decoupled for active and reactive power. Conidering that the tator reitance i coparatively very all, the grid flux orientation align with the tator flux orientation without any ignificant error [4]. On thi account, both the tator-flux-oriented reference and the grid-voltage-oriented reference can be ued for vector control. 3. Grid ynchronization Grid ynchronization control i to regulate the voltage, frequency and phae angle at the tator terinal to be the ae a thoe of the grid before connection. Uing the grid-voltage oriented reference frae, the ynchronization requireent can be forulated a: vd = 0 p.u. v q = v grid = p.u., (5) where v grid repreent the grid voltage aligned with the quadrature axi. Given that the tator i open, the tator current equal zero. Subtitute the flux linkage forulation (2) into equation (), then the tator voltage expreion can be rewritten a: d v = i i d v q = i dr iqr ω d qr dr ω. (6) Cobine equation (5) and (6), and coponent of rotor current in teady tate hould be a: vd i dr= = i qr= 0. (7) Conequently, thee are the reference input to the current controller for grid ynchronization. Since RSC i conidered a a current-controlled voltage ource, rotor voltage expreion can be rewritten a follow by ubtituting equation (2) into () and leaving out the tator current ter: d v = R i i i d v = R i i i r dr r dr l r qr dr ω r qr r qr l r dr qr ω. (8) Then the tranfer function between the rotor current and the rotor voltage can be written in ter of the coplex variable a: i ( ) dr ( ) iqr Gr ( ) = = v ( ) v ( ) R ( / ω ) =. (9) dr qr r r

4 idrref FF ter C dr () % i% l r qr i V dr l r qr DFIG G r () idr α α α R C = G =, (0) r r dr ( ) r ( ) ω where α i a IMC deign paraeter. In the cae of a firt-order yte, α i et to be the deired bandwih of the cloed-loop yte. The relationhip between the bandwih and the rie tie i α =ln9/t rie, where t rie repreent the rie tie [4]. Figure 2: Control bock of q-axi rotor current for grid ynchronization Take the d-axi rotor current control for intance. The control block i hown a Fig. 2, where C dr () repreent a PI controller. The paraeter of the PI controller can be derived by the internal odel control (IMC) ethod a: The ter l r i qr can be conidered a a diturbance. A diturbance etiation i exploited a a feed-forward ter for copenation, a hown in the red box in Fig. 2. However, it i alo poible to introduce an "active daping" factor to the control loop, o that the diturbance can be daped with the ae tie contant a the control dynaic [4]. ω ref C Tω () T eref C it () i qrref C viqr () v qr ω i qr Qref C iq () i drref C vidr () vdr DFIG i dr Figure 3: Decoupled peed (active power) and reactive power control of DFIG 3.2 Active power optiization control A entioned before, DFIG i controlled according to a predefined power-peed characteritic profile to optiize the wind power extraction. Thu, the active power optiization control i actually the peed control. According to decoupled d-q axi apping, d- and q-axi rotor current coponent are controlled for reactive and active power repectively. Cacaded PI or IP controller are ued, and the IMC or pole placeent ethod i ued repectively to derive the paraeter of the controller. Active power control coprie 3 cacaded loop: q-axi rotor current control, torque control and peed control, while the reactive power control coprie reactive power and d-axi rotor current control. A cheatic diagra of the decoupled peed (active power) and reactive power control i hown in Fig. 3, where the controller are either IP or PI regulator except for the torque control part. Conidering that torque i difficult to be eaured, it i ot often controlled in an open-loop anner [4] Current control To derive decoupled rotor current control law, everal condition hould be noted beforehand. Fro equation (), ψ and ψ approxiately equal vq and d vd repectively in teady tate. Thu, ψ d v q = p.u. ψ q v d = 0 p.u. q. () Then, according to d,q-axi tator flux linkage forulation in equation (2): Denote ( ), i i i i d dr q qr X = r 2. (2), and ubtitute the rotor flux linkage equation (2) and the tator-rotor current equation (2) into the rotor voltage equation (), then, where X d v = R i i E qr r qr qr qr ω Eqr = l X idr, (3) can be treated a a diturbance. Thu, the tranfer function between the

5 rotor current and the rotor voltage i: G viqr Iqr ( ) ( ) = = Vqr ( ) X Rr ω. (4) Siilar to that of the grid ynchronization proce, the paraeter of the PI controller can be derived by the IMC ethod a: α α X α R C = G =. (5) r viqr ( ) qr ( ) ω Torque control Torque can be expreed in the for of controllable q-axi rotor current by ubtituting equation (-2) into (3): T i e = qr. (6) The tranfer function between the q-axi rotor current and the torque then becoe iqr ( ) CiT ( ) = =, (7) T ( ) which i ued for the open-loop torque control Speed control e The inertia of the rotating wind turbine yte i very high. However, copared to the turbine itelf and the generator rotor, the inertia of the haft i negligibly all [0]. Fro the generator rotor point of view and neglecting the haft inertia, the echanical balance equation can then be derived a []: TT JT dωr Te = J g 2 ηn ηn, (8) where T T i the turbine torque created by the aerodynaic lift on the blade; T e i the generator electroagnetic torque, id. et., the reiting torque; J g i the inertia of the generator rotor itelf; J T i the inertia of the turbine; n i the gearbox reduction ratio; η i the energy traniion efficiency; ω r i the rotating peed of the generator rotor in echanical eaureent. Norally, the wind turbine i a lot heavier than the generator, and J T /ηn 2 i larger than the generator rotor inertia [0]. Denote the equivalent inertia and the input torque by J and T repectively, the above equation can be rewritten a: d =, (9) ωr T Te J Since the torque to peed loop i a pure integral eleent, an IP regulator i ued for the peed control to derive a econd-order for for the cloed-loop yte, a hown in Fig. 4. Conidering that current dynaic are uch fater than peed dynaic, the electroagnetic torque T e can be expreed a T eref. ω ref K i / T eref K p T /(J) Figure 4: Control block of the peed The tranfer function of the cloed loop yte turn to be a tandard econd-order for a: ω ( ) K /J = ω K /J K /J r i 2 ref ( ) ( p ) i ω r. (20) The paraeter of the controller are then tuned through pole placeent. Denote the daping factor and the natural frequency of the econd order yte by ζ d and ω nd repectively, and the paraeter of the IP controller can then be given by: K p= 2ζ dωnd J 2 K i= ωnd J. (2) There are oe approxiation ethod on evaluating the relationhip between the ettling tie t d and ζ d and ω nd. In a particular ituation of an over-daped yte, ω nd 5.8/t d [3]. Once the deired dynaic repone i evaluated, the IP controller paraeter can then be tuned accordingly. et' recall that the ynchronization proce i very fat, uually le than 00, and once it i accoplihed, right after the power control proce tart. Conidering that the inertia of a wind turbine i very high, the peed i alot contant during the ynchronization. Therefore, the initial value of the integral ter of the IP controller can be accordingly et a ω t K p /K i, where ω t tand for the predefined initial peed of the ynchronization. 3.3 Reactive power control A entioned above, the converter GSC i controlled to operate with unity power factor. Thi ean that the traniion of reactive power between DFIG and the grid i only through the tator [9]. The reactive power at the grid terinal i then equal to the tator reactive power: Q = Q = v i v i, (22) q d d q ikewie, ubtitute equation (5) and (2) into (22) and the expreion can be derived in the for of controllable d-axi rotor current a:

6 Then, Q = ( i dr ) i dr= ( Q ). (23). (24) Particularly, when the deired tator reactive power i zero, then i =. (25) dr The current control in the reactive control loop i iilar to that of the peed (active power) control loop, and will not be reiterated here. 4 Strongly coupled approach and odelling ethod on Sacef 4. Strongly coupled approach A coupled echatronic proble can be odularly decopoed into a echanical yte and a control yte. The echanical yte can be odelled uing the finite eleent flexible ultibody forali, and the control yte i uually decribed uing block diagra language. To olve the coupled proble, nuerical tie integration ethod have to be applied for both ubyte. In the cae of a weak coupling approach, repective integration olver are ued for the ubyte accordingly. The coupling of the ubyte then iplie the coupling of the different olver, o that tability and convergence propertie can be affected [5]. For the cae of a trongly-coupled approach, only one optiized olver i applied to both ubyte o that the required order of accuracy and tability can be eaily enured for the iulation of a echatronic yte. In flexible ultibody dynaic, the Newark faily of iplicit olver have been applied extenively. To extend the olver to repreent a echatronic yte, an extended generalized-α ethod i propoed in reference [6]. Baed on that, an integrated olver ha newly been developed into Sacef for the iulation of flexible ultibody tructure coupled with non-echanical ubyte. The forulation relie on a odular block diagra decription of the control yte, which i now available on Sacef. y ( q, q&, q&&, λ ) Mechani Control yte Figure 5: Scheatic diagra of the coupling in a echatronic yte Baed on the finite eleent ethod for the echanical part and on the block diagra language for the control part, a echatronic yte can be decribed a hown in Fig. 5, where q i the vector of echanical coordinate, λ i the vector of agrange ultiplier related with the kineatic contraint and y i the vector of control output. The dynaic can be repreented by the following coupled equation: Mq && Φ ( λ Φ) g(q,q, & ) y 0 T a q k p t = kφ(q) = 0 x& f (q,q,q,λ, & && x, y, t) = 0 y h(q,q,q,λ, & && x, y, t) = 0, (26) where the firt two equation are the equation of otion of the echanical ubyte and the lat two equation are the tate pace equation of the control ubyte. a i the output localization atrix, the ter a y repreent the generalized force exerted by the actuator and generator on the echanical yte, x i the vector of control tate variable and the other ybol are coonly known and can be referred to [6]. The trongly coupled echanical and tate equation are obtained by nuerical aebly and their tie-doain iulation i baed on an extenion of the generalized-α ethod. A detailed decription of the tie integration algorith can be found in [6]. 4.2 Modular odelling of DFIG control yte on Sacef With the integration of the new trongly-coupled olver, the DFIG control yte were odelled for S4WT. The yte i decopoed into ubyte and odularized. Decopoition i baed on the analyi of the function of each coponent. All odel, including the generator itelf and the controller, are aied at general-purpoe ue. Extra node are introduced to repreent the tate and output variable fro the generating control yte, which i iilar to the way for the tructure yte. A tangent atrix can then be derived for the Newton iteration, with difference in the coefficient for tate variable and tructural node. 5 Siulation and validation In thi ection, two iulation exaple will be preented for validating the odel of the DFIG control yte and alo the trongly-coupled olver. A 2MW DFIG prototype odel i ued for the iulation analyi. The paraeter of the DFIG are lited a follow [7]:

7 Bae voltage (line-to-line): V bae = 690 V; Bae power: P bae = 2 MW; Grid frequency: f = 50 Hz; Nuber of pole: n p = 4; Stator reitance: R = p.u.; Rotor reitance : R r = p.u.; Stator eakage inductance: l = p.u.; Rotor leakage inductance: rl = p.u.; Mutual inductance: = p.u.. The inertia of the generator itelf i 00kg 2. However, ince the inertia of the wind turbine yte i barely known, everal etiation ethod are dicued in reference [2]. Uually, the inertia tie contant of a 2MW wind turbine range fro 3.5 to 6. For the per-unit repreentation, here in thi paper, the bae current i defined a I bae =P bae /V bae ; the bae reitance R bae = V bae /I bae = ω bae, where bae i the bae inductance; the bae flux linkage ψ bae =V bae /ω ; the bae peed ω bae =2ω /n p ; and conequently the bae torque T bae =P bae /ω bae. 5. DFIG alone with defined torque input In thi ection, a iple exaple of the DFIG running alone with defined driving torque i tudied. The purpoe of thi iulation exaple i to verify the odel and the control trategie. The DFIG i operating given p.u. driving torque in the very beginning. When the peed reache 0.8p.u. of the bae peed, the ynchronization proce tart. Once thi proce i copleted, then right away tart the peed and reactive power control. Initially, the reference peed i et to be p.u.. Then after 4, it i changed to 0.9p.u., and again, it i changed to.p.u. fro 6. Finally, while aintaining the ae reference peed, the driving torque i raped down to 0.5p.u. fro 8.5 to 9.5. A for the paraeter of the controller, ince the dynaic of the electrical yte i uch fater than the echanical yte, the rie tie for the current control loop i et to 0 (α = 29 for the PI controller), while the ettling tie for the peed control loop i et to (ζ d =, ω nd =5.8 for the IP controller). For the integrated FEM olver, an autoatic tie tep chee i ued for the iulation. Selected iulation reult are hown in Fig. 6. Fig.6(a) how the grid ynchronization proce of the A-phae tator voltage with the A-phae grid voltage. Thi proce take only about 25. A one can ee fro Fig.6(b) and Fig.6(c), the repone for both peed and reactive power control are atifactory. Fro Fig.6(d), it can be eaily derived that peed control i deterined by the control of q-axi rotor current and reactive power control i by the d-axi rotor current, and thu they are decoupled. ynchronization tart ynchronization finihe (a) (b) i qr i dr (c) (d) Figure 6: DFIG alone: (a) Grid ynchronization repone; (b) Speed repone; (c) Stator reactive power; (d) q,d-axi rotor current.

8 Figure 7: A odel of wind turbine generating yte on S4WT ynchronization tart ynchronization finihe Power 8/ / Turbine peed (a) (b) i dr Reactive power i qr Active power (c) (d) Figure 8: Full wind turbine repone: (a) Grid ynchronization proce; (b) Speed repone with different wind peed; (c) Power output; (d) q,d-axi rotor current. 5.2 The integration of the wind turbine tructure odel with the DFIG odel A yteatic odel of a 2MW wind turbine integrated with the DFIG odel i preented in thi ection. The odel on S4WT i hown in Fig. 7. Soe elected paraeter of the turbine yte are a: 4 of blade length, 75 of tower height and 06 of the gearbox ratio. The blade are odeled a elatic bea and the aerodynaic load are coputed uing the blade eleent oentu theory, ee [3] for ore detail about the underlying forulation. The interet here i to analyze the control-generator-tructure interaction in a wind turbine yte. An approxiate inertia tie contant 3.5 i ued for deriving the IP controller paraeter. However, ince it' difficult to be accurate, a higher daping factor could be ued for the econd-order yte of the cloed peed control loop. Given that the inertia of the turbine yte i very large, the ettling tie i et a 2.5. A for the PI controller, the ae paraeter are ued a thoe in the previou

9 exaple. The iulation ituation i a follow. The initial wind peed i et to 8/ and the initial turbine peed i to be.rad/ (accordingly 0.74p.u.). The aerodynaic torque drive the turbine to rotate. Grid ynchronization control tart when the generator rotating peed reache 0.8p.u.. After 8, the wind peed change to /. For 8/ of the wind peed, the axiu wind power i aued to be extracted with 0.9p.u. of the rotating peed, while.p.u. i that for a wind peed of /. A wind power-peed characteritic diagra i hown on the botto right of Fig. 8(b). Alo, an autoatic tie tep chee i applied. Selected iulation reult are hown in Fig Concluion Thi paper tudie the odelling and control of DFIG in variable-peed wind turbine yte baed on an integrated, trongly-coupled finite eleent approach. New block diagra functionalitie for the decription of control yte are integrated into Sacef/Mecano ultibody dynaic olver. Thi allow the iulation of echatronic yte in a trongly-coupled way, o that the intricacy and uncertainty of uing a third-party control engineering oftware can be avoided. The DFIG generator and the controller odel are developed in a odular, paraeterized way. They are built to expand the MECANO wind turbine package, and are alo aied at general-purpoe ue baed upon trongly-coupled iulation. Detailed control trategie are preented for grid ynchronization and power optiization. Siulation reult how the validity of the DFIG odel and the trongly-coupled iulation approach. A coprehenive wind turbine yte odel i preented to analyze the coupling effect aong different coponent. Control of the generator will influence both the energy extraction and the echanical tructure life due to the utual coupling. Acknowledgeent Thi reearch work wa carried out under grant nuber (DYNAWIND) fro the Walloon Region (Belgiu) which i gratefully acknowledged. Reference Superregui, A., "Methodology for ooth connection of doubly fed induction generator to the grid", IEEE Tranaction on Energy Converion, 2009, 24, [4]. Peteron, A., Analyi, odeling and control of Doubly-Fed Induction Generator for wind turbine, PhD thei, Chaler Univerity of Technology, Göteborg, Sweden, [5]. Buch, M. and Schweizer, B., "Nuerical Stability and Accuracy of Different Co-Siulation Technique: Analytical Invetigation Baed on a 2-DOF Tet Model", Proceeding of the t Joint International Conference on Multibody yte Dynaic, appeenranta, Finland, May 25-27, 200. [6]. Brül, O. and Golinval, J. C., "The generalized-α ethod in echatronic application", Zeitchrift für angewane atheatik und echanik (ZAMM), 2006, 86, [7]. Ekanayake, J. B., Holdworth,. and Jenkin N., "Coparion of 5th order and 3rd order achine odel for doubly fed induction generator (DFIG) wind turbine", Electric Power Syte Reearch, 2003, 67, [8]. Goez, S. A. and Aenedo, J.. R., "Grid ynchroniation of doubly fed induction generator uing direct torque control", Proceeding of IEEE 28th Annual conference of the Indutrial Electronic Society, Sevilla, Spain, Nov. 5-8, [9]. Hanen, A. D., Sørenen, P., Iov, F. and Blaabjerg, F., "Centralied power control of wind far with doubly fed induction generator", Renewable Energy, 2006, 3, [0]. Rotoen, H. O., Undeland, T. M. and Gjengedal T., "Doubly fed induction generator in a wind turbine", Proceeding of the IEEE/Cigre workhop on wind power and the ipact on power yte, Olo, Norway, Jun. 7-8, []. Cetinkunt, S., Mechatronic, John Wiley & Son, Inc., Hoboken, New Jerey, [2]. Rodriguez, A. G. G., Iproveent of a fixed-peed wind turbine oft-tarter baed on a liding-ode controller, PhD thei, Univerity of Seville, Seville, Spain, [3]. Heege, A., Betran, J. and Radovcic, Y., "Fatigue load coputation of wind turbine gearboxe by coupled finite eleent, ulti-body yte and aerodynaic analyi", Wind Energy, 2007, 0, []. Géradin, M. and Cardona, A., Flexible ultibody dynaic: a finite eleent approach, John Wiley & Son, New York, 200. [2]. Chowdhury, B. H. and Chellapilla, S., "Double-fed induction generator control for variable peed wind power generation", Electric Power Syte Reearch, 2006, 76, [3]. Tapia, G. Santaaria, G. Telleria, M. and