Wind energy conversion system with full-scale power converter and squirrel cage induction generator

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1 Internatonal Journal of Physal Senes Vol. 7(46), pp , 9 Deember, 1 Avalable onlne at DOI: /IJPS1.46 ISSN Aadem Journals Full Length Researh Paper Wnd energy onverson system wth full-sale power onverter and squrrel age nduton generator Bouazz Béhr 1, Baha Faouz 1 * and Monef Gasm 1 Unversty of Tuns, ESSTT, 5 Av Taha Hussen, B. P. 56, Montfleury 18, Tuns, Tunse. Natonal Insttute of Appled Senes and Tehnology (INSAT) Centre Urban Nord, B. P. 676, 18 Tuns Cedex, Tunse. Aepted June, 1 Ths paper desrbes a modelng and ontrol of a varable speed squrrel-age nduton generator wth bak to bak power eletrons onverters used n varable speed wnd energy onverson system. The power eletrons s omposed of the generator sde onverter (GSC) ouplng to the grd onneted onverter (GCC) together va DC bus apator. The generator sde onverter (GSC) s ontrolled by dret torque ontrol (DTC). The ontrol objetves of the generator sde onverter (GSC) are to optmze the energy apture from the wnd turbne and supply the magnet flux to the squrrel age nduton generator (SCIG). The GCC onverter delverng the energy from the mahne sde to the utlty grd regulated the DC lnk voltage and the power flows to the grd. The bas dea of P-Q ontrol method used s based on voltage vetor orented ontrol and deouplng n the d-q axs referene frame. The omplete ontrol system has been developed; analyzed and valdated by Matlab smulaton. The two operatng modes of GCC onverter and the performane under atve and reatve power varatons are also presented. The low voltage rde-through (LVRT) performanes of the varable speed wnd turbne (VSWT) s tested, when the grd voltage has dropped to a very low value. Smulaton results onfrmed the effetveness of the proposed ontrol strateges and ther apablty under dfferent ase study. Key words: Varable speed wnd turbne, onverter ontrol, power qualty, bak to bak onverters, vetor orented ontrol. INTRODUCTION Global warmng s aeleratng due to the effets of lmate hange, and nvestments are nreasng n new alternatve power soures to replae exstng fossl fuels. Among the new and renewable energy soures, wnd energy s the lean energy and t rapd growth for the eletrty produton (Haejoon et al., 1). There are dfferent onfguratons of wnd turbne system. The use of squrrel-age nduton generators (SCIG) for dret grd-onneton wnd energy onverson systems (WECS) s well establshed. Wth the last advanes n power eletrons, the use of varable-speed SCIG wth a double stage AC/DC/AC power onverson has beome qute attratve (Watthan and Bunlung, 11; Shahab et al., 11), n both low power and very hgh power levels, nreased energy produton at low wnd and elmnaton *Correspondng author. E-mal: Faouz.Baha@esstt.rnu.tn. of the extaton apator bank. The varable speed wnd turbne s replang onstant speed wnd turbne (CSWT) types to ontrol rotaton speed and mprove effeny wth respet to the wnd veloty. The wnd veloty s not onstant, and there s a rotaton speed for a gven wnd veloty for whh the WT output s maxmum (Whe et al., 1). Thus, t s neessary to operate the WT at varable speeds to hange the rotaton speed aordng to the wnd veloty. The double-fed asynhronous generator and the permanent-magnet synhronous generators, whh are used for varable speed generaton, are not dretly onneted to the grd; an eletron power onverter s nstalled between the generator and the grd. Reently, generators that use a SCIG for fxed speed generaton have been upgraded to the varable speed generaton type that an generate power for the entre seton, as wth PMSG, by addng a full-sale power onverter wth the same apaty as the generator

2 694 Int. J. Phys. S. W nd turbne S C I G G S C G C C GrdUtlty Gearbox Measurement Grd Flter d ab d ab PthControl r MPPT T em GSC Control GCC Control Measurement Fgure 1. Varable speed squrrel-age nduton generator wnd turbne. (Bouazz et al., 1). A varable speed WT wth SCIG an perform varable speed generaton at lower ost ompared to PMSG, and solve the problem of the narrow generaton area used n exstng fxed speed generaton. Thus, varable speed WTs are eonomally mportant. In order to keep power qualty under lmts proposed by standards, t s neessary to nlude ths n ontrol objetves. There are several tehnal ssues arsng from the omplexty of ontrol operaton. Ths paper fouses on a ontrol methodology for mprovng the defeny of the CSWT. The defeny an be mproved by the bak to bak onverter s omposed of two voltage soure onverters onneted together va a d-bus apator. Frst onverter stays between the SCIG and the DC bus apator alled GSC. The funton of the GSC s to produe the mahne flux for the SCIG and to optmum the energy apture from the wnd. The seond onverter stays between the DC bus apator and the grd alled GCC. The funton of ths onverter s to regulate the DC-bus voltage and atve and reatve powers flows. It has two operatng modes: retfyng mode and nvertng mode. When the d-bus voltage s redued, the GCC operated n retfyng mode and to harge the apator to regulate the d-bus voltage. When there s energy from the wnd, the DC-bus voltage nreases and the GCC operates n nvertng mode to supply the energy from the DC bus to the utlty grd and regulate the DC lnk voltage and the powers flows. MODEL OF SQUIRREL-CAGE INDUCTION GENERATOR WIND TURBINE A detaled model of the wnd turbne s llustrated n Fgure 1. The omponents of the wnd turbne nlude a three bladed rotor wth orrespondng pth ontroller, a mehanal gearbox, a SCIG wth a full-sale bak-to-bak onverter, DC lnk apator and a lne flter and onverter ontrollers. The mehanal torque of the wnd turbne s onverted to eletral power at the stator of the SCIG. The varable speed operaton of the wnd turbne s possble by usng a onverter, whh an be obtaned by ontrollng the eletromagnet toque. The grd onneted onverter s onneted to the external power network through a flter, and s the maxmum output power whle mantanng the voltage of the DC lnk wthn the allowable range. Modelng of the wnd turbne The mehanal part of the wnd turbne onssts of a rotor blade, a pth ontrol and a gearbox. The mehanal power an be expressed as: P r m = Av C p( l, b) (1) The output mehanal torque an be alulated from the followng equatons: T r m = Av CT ( l, b) () C p ( l, b) CT ( l, b) = () l In ths paper, the frst order model s used to desrbe the dynam of the wnd turbne and s wrtten by d J T T w r = m - e (4) The eletral torque at the optmum operatng speed s gven by: e e opt r T = T = K w (5) Substtutng (5) nto (4), then dwr J = Tm - K opt wr (6) Where, C p presents the wnd turbne power onverson effeny. It s a funton of the tp speed rato, as well as the blade pth

3 Mehanal power (W) The power oeffent The torque oeffent Béhr et al. 695 Table 1. Parameters of the performane power oeffent (a) (b) Pth angle (deg) Tp speed rato Pth angle (deg) 5 4 Tp speed rato () x Pth angle (deg) Tp speed rato Fgure. Charatersts of the wnd turbne. (a) Power oeffent. (b) Torque oeffent. () Mehanal power. angle n a pth ontrolled wnd turbne. The parameter s defned as the rato of the tp speed of the turbne blades to wnd speed, and s gven by: v R w t r l = = K (7) gear v p v The power oeffent s a funton of tp speed rato and blade pth angle and an be approxmated by substtutng () nto 8: x x 5, C p 1 4 exp 6 Where 1 8 x = l + b - b (8) The oeffent 1-8 depends on the wnd turbnes. To obtan orret Cp urve for turbne used n ths paper 1-8 are proposed as shown n Table 1. The haratersts of the wnd turbne, for dfferent values of the pth angle are llustrated n Fgure. Fgure ndates that there s one spef tp speed rato at whh the turbne s most effent. Normally, a varable speed wnd turbne follows the optmal power oeffent to apture the maxmum power up to the rated speed by varyng the rotor speed to keep the system at optmal tp speed rato. Then, t operates at the rated power wth power ontrol durng hgh wnd speed by atve ontrol of the blade pth angle. Pth ontrol The pth angle ontroller wth the wnd turbne s used to lmt the output power at the termnal of the nduton generator when the wnd speed s over the rated speed. When wnd speed exeeds ts nomnal value, the speed of aerodynam rotor and power produed

4 696 Int. J. Phys. S. 1 + ref - s max mn onverter s summarzed by the expressons below: Vd gk gk d j j j= 1 dgk L + R = - u + (V d - d ) å (1) Fgure. Pth angle ontroller. d d j gk k= j= 1 dv C = - å d (14) by the turbne nrease. Ths s unwanted phenomenon, whh s provdng to damage of the wnd turbne. The pth ontrol an be used to avod ths apparton. The speed of the rotor for stronger wnds an be lmted and kept onstant at the rated value by hangng the pth angle of the blades. The prnple of ths method llustrated by Fgure s explaned on wnd turbne desgned for nomnal wnd speed equal to 1 m/s. Squrrel-age nduton generator model (SCIG) The eletr part of the wnd turbne largely onssts of a SCIG and a full-sale bak-to-bak onverter. The SCIG was represented by the followng equatons: Wth Lm Lm Lr Ls s = s s, s = 1 -, r =, t r =, t s = LsLr Lr Rr Rs l L m Bak-to- bak onverter model The mathematal model of a bak-to-bak onverter an be obtaned from desrptons of the relatonshp between the supply, onverter voltages and lne urrents n Conorda referene frame. The remanng eletral parts of the system are generator sde onverter (GSC) and the grd onneted onverter (GCC). The generator sde onverter (GSC) s dental n desgn to the GCC onverter. The stator voltage omponents of the nduton mahne n Conorda referental frame are gven by: = a (1) va d = b (11) vb d ( ) ( ) ìï da w 1 = - + a - w b - l a + l b + v a s t s t r t rls ls ls db w 1 1 = - w a - + b - l a + l b + vb ï s t s t r ls t rls ls í (9) dl a = - Rsa + va dl b ï = - Rsb + vb ïî d = ( b da + a db ) (1) As a result, the full model of the grd, apator and GCC (9) RL flter on the grd onneted onverter The GCC onverter s onneted to the grd through a RL flter. Aordng to the statonary referene frame an be expressed the eletral model: L d u R L L d u R L f = - f + wg f f = - f - wg f BACK-to-BACK CONVERTER CONTROLLER DESIGN (15) The bak to bak onverter ontrol module onssts of a generatorsde onverter ontroller, a grd onneted onverter ontroller, and a d-lnk ontroller. Here, P and Q are the referenes of the g g atve and reatve power njeted to the grd. The atve power referene P s determned by the losed- loop of the d-lnk voltage. The reatve power referene Q g an be followng the requrements of the grd management serve. It an satsfy the unty power fator (UPF) operaton of the GCC onverter by tng Q g to zero. Generator sde onverter ontroller Fgure 4 shows a blok dagram of the generator-sde onverter ontroller module that onssts of dret torque ontrol (DTC). It s well known that the bas onept of DTC based drves s to ontrol both stator flux and eletromagnet torque smultaneously. In the onventonal DTC approah ntated by Takahash, these referene values are ensured by dret seleton of a sutable voltage vetor. In Fgure 4, the generator eletromagnet torque referene s obtaned by the MPPT ontrol method proposed. The MPPT trakng The power of the turbne s optmzed by an MPPT algorthm. The ontrol onssts of varyng the speed of the turbne n order to reman the rato of the tp speed at around ts optmum value. The power oeffent of the turbne s equal to ts maxmum value. In these ondtons the maxmum power s gven by: max = opt r (16) P K w Wth K opt.5 C pmax R poptk gear g

5 Béhr et al. 697 SCIG a b GSC PWM d C o r a b d 1 d d d 1 d d Transformaton d Swthng Table N d T H H T s s V s V s H H T MPPT t s s s s V R s s s s s T p( ) em s s s s ref T em T em Fgure 4. Shemat dagram of the generator sde onverter GSC ontroller. Grd onneted onverter ontroller Fgure 5 llustrates the proposed grd onneted onverter ontroller module onsstng of vetor orented ontrol (VOC). The am of the GCC onverter s to regulate the d-lnk voltage and mantan the balane between the d-lnk power and powers suppled to the grd. Ths s done by ontrollng the urrent axs omponent of the lne sde. The atve and reatve power gven by: Pg = ( u + u ) Qg = ( u - u ) (17) The bas prnple of the vetor orented ontrol method s to ontrol the nstantaneous atve and reatve grd urrents and, onsequently, the atve and reatve power, by separate ontrollers. The grd voltages and urrents are frst sensed. By means of the phase loked loop (PLL), the grd angle and frequeny an be deteted n order to synhronze the voltage output of the grd onneted onverter wth grd. The demanded amount of power s frst estmated from the utlty grd at the desred power fator, n onsequene, the s values of urrents n a synhronous referene frame synhronzed wth grd voltage are alulated. Consequently, the urrent ontrollers are tryng to brng the atual urrents to ts referenes. So far s how the ontroller ould be onstruted. When we mpose values of atve and reatve powers, we an determne the urrent referenes: = = ( u Pg + uq g ) ( u + u ) ( upg - uqg ) ( u + u ) (18) Wth the assumpton of zero reatve power ommand, the urrent ommand equatons an be smplfed suh that: = = P u g (19) Ths paper employs the method of voltage deouplng ontrol. Sne we have the voltage ross ouplng terms between the d-q axs s ompensated by u = v - wl g u = v + wl g Substtutng () n (15), then ()

6 698 Int. J. Phys. S. P g s et DC voltage Control d I g d q Current ontroller I g d q s et u g d q dq ab s et u g ab PWM d 1 GC C PWM Refereneurrents alulaton Q g U g d q dq ab s PLL U g ab R f L f I g ab Grd Fgure 5. Control box dagram s of the proposed VOC GCC onverter. s e t PI v Lg u Lg 1 1 Rf 1 s s e t PI v Lg u Lg 1 1 Rf 1 s Current ontroller loops Grd onneted model Fgure 6. Deouplng between the d and q axes. L d v R L d v R f = - f f = - f (1) The voltage termnals are ndependent from the ross ouplng term. They an be ontrolled separately for d-q axs. The grd onneted onverter and the regulaton urrent loops an be desrbed by the dagram blo of Fgure 6. The power of the DC sde s gven by: P d = VdId () The -value of the atve power s determned by: g d C P = P - P (4) DC-lnk model and proposed ontroller The apator n the d-lnk voltage s an energy storage deve. In desrbng the transt of the output power of the GSC to the grd. Fgure 7 shows the d-lnk model wth ts ontroller. The power stoked n the apator C d P = V I () RESULTS AND DISCUSSION Operatng mode of the GCC In Fgure 8 present the smulaton results of the bdretonal PWM onverter wth a proposed vetor orented ontrol (VOC) strategy and deouplng ontrol of d-q urrent omponent. It has two operatng modes:

7 Béhr et al PI C PC - + P g d P d Fgure 7. DC-lnk voltage modelng and proposed ontroller. Fgure 8. Smulaton results usng VOC ontrol durng operatng mode of GCC onverter. (a) AC urrent and voltage. (b) AC voltage and GCC onverter voltage. () DC-bus voltage. retfyng mode and nvertng mode. It an be seen from Fgure 8, that the proposed ontrol strategy of dret power ontrol ensures smooth ontrol of atve and reatve power and regulaton of d-bus voltage. The nverson of the power and onfrm the desred power transfer. The response of the a lne urrent and a voltage orrespondng of two operatng modes s presented n Fgures 8 and shows the desred power flows between the DC-sde to AC-sde. Note that, the DC- bus voltage follows ts referene wth a very low rpple. onverter to grd at.5 s and then baked to at.54 s, whle the reatve power s stepped from 1 kvar (ndutve) to 1 kvar (apatve) at.5 s and baked to 1 kvar at.54s. The transent response of both atve and reatve powers for the proposed ontrol sheme s wthn a few mllseonds, whereas the dynam response of the proposed VOC ontrol s largely dependent on the PI parameters of urrents ontroller loops. Fgure 9 shows also learly that the ontrol strategy has aheved muh mproved performane wth well-smoothed atve/reatve powers and a urrents. Power steps performane n GCC Fgure 9 shows the system response durng varous atve and reatve power steps for the proposed ontrol strategy of the GCC onverter. The atve power s stepped from to kw and exported from the Turbulent wnd speed Ths seton evaluates the overall operaton of the varable speed squrrel age nduton generator by smulaton results. The of the proposed ontrol strateges from Fgure 1 llustrates the evoluton of the

8 61 Int. J. Phys. S. (A) (B) Fgure 9. System responses durng varous atve and reatve power steps (A) Invertng mode (B) Retfyng mode; (a) atve power (kw). (b) reatve power (kvar). () three-phase AC urrents. Fgure 1. Smulaton behavor of the Varable speed squrrel-age nduton generator wnd turbne n a turbulent wnd speed.

9 Lne to lne voltage Béhr et al % 9% 7% Lower value of voltage band Tme when a fault ours Tme (m) Fgure 11. Voltage profle aordng to the requrements for LVRT apablty of synhronous generators (Daunghom et al., 1). man eletral and mehanal varables under turbulent wnd speed. Wnd profle s presented n Fgure 1. It an be observed that the wnd s osllatng around the mean wnd speed. The losed-loop VSWT manages to hange ts rotatonal speed, n order to optmum the energy apture from the wnd turbne, aordng to mposed energy relablty. Ths ontrol objetve s aomplshed, as t an be seen on the temporal evoluton of the power oeffent and of the pth ontrol. The same onluson an be drawn from the evoluton of the aerodynam power, pth angle and from the power oeffent varaton versus the wnd speed. The pth ontrol objetve has been aomplshed. When the wnd speed s over the rated speed, the aerodynam power s lmted on the value. The ontrol strateges objetves have been aheved, as t an be seen on the temporal evoluton of the three phase a urrents, the DC-lnk voltage and the powers flow to the grd. Note that, the DC bus voltage s mantaned around ts referene and the snusodal waveform of urrent njeted to the grd s establshed. The eletral and mehanal varables whle a turbulent wnd speed of 1 m/s wll be nfluened by the dsturbane and therefore osllatng around ther nomnal value. The osllatons are transent and not onsderable. Low voltage rde-through performanes of the VSWT In ths seton, the performane of the generator when affeted by large faults or small dsturbanes s analyzed. Espeally, the followng effets are nvestgated. The grd ode of most ountres requres wnd generators to stay onneted n the ase of grd faults (Low voltage rdethrough apablty (LVRT) or fault rde through apablty (FRT)) (Daunghom et al., 1). It s of partular mportane to transmsson system operators, that wnd farms stay onneted n ase of faults at major transmsson levels leadng to a voltage depresson n a wde area, whh ould lead to a major loss of wnd generaton f wnd farms were not equpped wth LVRTapablty. Therefore, LVRT-apablty s a defnte requrement for all larger wnd farms (Daunghom et al., 1). The man ssue of varable speed squrrel-age nduton generator wnd turbne s ther ablty to reman n synhronsm durng and after major voltage sags. The followng fault senaros at the system are smulated. Three phase short-rut wth 15 ms learng tme (4% retan voltage), three phase short-rut wth 15 ms learng tme, (6% retan voltage) and three phase shortrut wth 15 ms learng tme, (8% retan voltage). The fault duraton was hosen to be 15 ms, whh represents a worst ase assumpton n the PEA system for frst-zone fault learng tmes. Addtonally a voltage profle (Fgure 11), aordng to the grd onneton ondtons from E.ON (Daunghom et al., 1) for squrrel age nduton generator mahnes, s appled to the system and the generator response n ths study s gven. Smulaton results of a three-phase fault wth 15 ms duraton (8% retan voltage) at nomnal wnd speed ondtons show aordng to Fgure 1. Smulaton results of a three-phase fault wth 15 ms duraton (4 and 6% retan voltage) at nomnal wnd speed ondtons show aordng to Fgure 1. Therefore, varable speed squrrel-age nduton generator wnd turbne provdes reatve power support n ase of grd dsturbanes and to stay onneted to the grd. In addton, the njeted reatve urrent s enough to aomplsh restrtve grd ode requrements smlar to the German operator E.ON Netz.

10 61 Int. J. Phys. S. Fgure 1. Smulaton results of a three-phase fault wth 15 ms duraton (8% retan voltage). Fgure 1. Smulaton results of a three-phase fault wth 15 ms duraton. (A) 4% retan voltage, (B) 6% retan voltage; (a) Grd voltage magntude (pu). (b) GCC onverter voltage magntude (pu). () Atve and reatve power flows to the grd (Kw and kvar). (d) Generator rotor speed (pu). Conluson A ontrol system for a varable speed squrrel age nduton generator drven by the wnd turbne has been presented. A omprehensve ontrol strategy for the wnd generaton system s suggested and developed. Generator sde onverter s ontrolled by dret torque ontrol method and the grd onneted onverter s ontrolled by the vetor orented ontrol method and deouplng ontrol n the d-q axs referene frame. The

11 Béhr et al. 61 power extraton proesses from the wnd to the utlty grd are ooperatve between both onverters. The generator sde s operated forget the eletral energy from the wnd to the DC bus apator and the grd onneted s operated to transfer the power from the apator to the utlty grd. The two operatng modes and the deouplng ontrol mode of the GCC onverter gve the apablty of ndependent ontrol of atve and reatve powers wth bdretonal power fellows. Compared to the tehnologes of varable speed wnd turbnes, varable speed squrrel-age nduton generator wnd turbne has a number of substantal advantages due to ts ther ablty to reman n synhronsm durng and after major voltage sags and the apablty to keep power qualty under lmts proposed by standards (Appendx; Tables 1, and ). Nomenlature: C p Power oeffent; P, m, The mehanal power; T m, The mehanal torque; T e, The eletral torque; v, Wnd speed; v t, Blade tp speed; l, Tp speed rato; b, Pth angle; K gear, Gearbox rato; A, Area swept by rotor blades; w, The rotatonal speed of the rotor, u, u onverter;, onverter; l, l a D bus voltage. b r d-q axs voltage of grd onneted, d-q axs urrent of grd onneted,, d-q axs flux of nduton mahne;, Gandomkar A, Mahmoud A, Prasteh H, Parastar A, Kahourzade S (11). Improvement of dret torque ontrol n hgh power nduton motors. Int. J. Phys. S. 6(1): Guseppe S, Jan S, Ambra S (). Improvng Voltage Dsturbane Rejeton for Varable-Speed Wnd Turbnes. IEEE Trans. Energy Conv. 17():4-48. Haejoon A, Heesang K, Hongwoo K, Hyungoo K, Seokwoo K, Glsoo J, Byongjun L (1). Modelng and voltage ontrol of varable-speed SCAG-based wnd farm. S. Dret, Renewable Energy 4:8-5. Hu J, Shang L, He Y, Zhu ZQ (11). Dret Atve and Reatve Power Regulaton of Grd-Conneted DC/AC Converters Usng Sldng Mode Control Approah. IEEETrans. Power Eletron. 6(1):1-. Pena R, Cardenas R, Blaso R, Asher G, Clare J (1). A age nduton generator usng bak to bak PWM onverters for varable speed grd onneted wnd energy system. Proeedng n the 7th Conf. IEEE Ind. Eletron. So. : Shahab S, Fatemeh K, Tayebeh K, Zeynab K (11). Maxmum power pont trakng of varable speed wnd energy onverson system. Int. J. Phys. S. 6(): Tomonobu S, Yasutaka O, Yasuak K, Motok T, Atsush Y, Naomtsu U, Toshhsa F (9). Sensor-less maxmum power pont trakng ontrol for wnd generaton system wth squrrel age nduton generator. S. Dret, Renewable Energy 4(4): Vvek A, Rakesh KA, Pravn P, Chetan P (1). Novel Sheme for Rapd Trakng of Maxmum Power Pont n Wnd Energy Generaton Systems. IEEE Trans. Energy. Conv. 5(1):8-6. Watthan S, Bunlung N (11). An mplementaton of feld orented ontrolled SCIG for varable speed wnd turbne. Proedng n 6 th IEEE Conf. Ind. Eletron. Appl. pp Whe M, Chh M, Fsheng CH (1). Fuzzy neural network output maxmzaton ontrol for sensorless wnd energy onverson system. S. Dret, Energy 5(): Yuln Y, Ydong CH, Zhyun J, Wang LI, Weyang W (1). Development of KW Expermental Platform for Wnd Power Generaton System Usng SCIG. Pro. IEEE Int. Symp. Power Eletron. Dstrb. Gener. Syst. pp Zh D, Xu L, Wllams BW (9). Improved dret power ontrol of grdonneted DC/AC onverters. IEEE. Trans. Power Eletron. 4(5): REFERENCES Bouazz B, Baha F, Gasm M (1). A Fuzzy Dret Power Control for a Varable Speed Wnd Turbne. Int. Rev. Aut. Cont (IREACO). 5(1). Chong HNg, Ran L, Jm B (8). Unbalaned grd fault rde through ontrol for a wnd turbne nverter. IEEE Trans. Ind. Appl. 44(): Daunghom K, Premrudeepreehaharn S (11). Fault Rde-Through of Fully Enlosed Squrrel-Cage Induton Generators for Wnd Farms n Thaland. Pro. IEEE Int. Conf. Trans. Dstr. Expos. pp. 1-6.

12 614 Int. J. Phys. S. Appendx Table 1. Induton mahne parameters. Parameter Value Rated power (kw) Mahne rated speed (tr/mn) 1515 Number of pole pars Stator resstane (mohms) 6. Rotor resstane (mohms) 4.8 Stator ndutane (mh) 11.8 Rotor ndutane (mh) 11.6 Magnetzng ndutane (mh) 11.6 Rated frequeny (Hz) 5 Nomnal voltage (V) 4 Table. Wnd turbne parameters. Parameter Value Rated power (kw) Optmal power oeffent.475 Optmal tp speed rato 8.1 Turbne radus (m) 14 Nomnal wnd speed (m/s) 1 Mnmum wnd speed (m/s) 4 Gear box 1: Equvalent moment of nerta (kg.m ) 5 Power ontrol Pth ontrol Table. Interonnetng grd parameters. Parameter Value D-bus voltage (V) 76 D-bus apator (mf) 1 Flter resstane (mohms) 5 Flter ndutane (mh).5