High Efficiency Double-Fed Induction Generator Applied to Wind Power Generator Technical Analyses

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Enegy and Powe Engineeing, 011, 3, 53-61 doi:10.436/epe.011.3303 Publihed Online July 011 (http://www.scirp.

1 Enegy and Powe Engineeing, 011, 3, doi:10.436/epe Publihed Online July 011 ( High Efficiency Double-Fed Induction Geneato Applied to Wind Powe Geneato Technical Analye Abtact Deng-Chen Sue Pacific Enginee & Contucto, Ltd., Taipei, China Received Decembe 3, 010; evied Januay 30, 011; accepted Febuay 8, 011 High efficiency Double-Fed Induction Geneato applie new powe electonic technology, and utilize vecto contol to fix the magnetic diection of the tato to the vetical axi. Adjuting the input cuent of oto via an invete can epaately contol the co axi and vetical axi cuent of eal powe and eactive powe of a geneato. Taditionally, otating peed affect fequency and the output i untable. Thi tudy concentate on high efficiency Double-Fed Induction Geneato and Taditional Geneato fom mathematic model to deive and contol the chaacteitic imulation and compaion than get an output of high efficiency Double-Fed Indutial Geneato. Thi tudy utilize the imulation oftwae MATLAB/Simulink to imulate the epone chaacteitic of vecto contol of a Double-Fed Indutial Geneato. The opeating and contol function ae bette than thoe of a taditional geneato. Keywod: Double-Fed Induction Geneato, Cut-in Speed, Puhove Toque, Stall Regulato, Pitch Regulato, Invete 1. Intoduction Taiwan i an iland; with mot of it enegy impoted. Becaue of the hotage of an indigenou enegy upply in Taiwan, the intenational enegy maket ha a tong effect on the local economy. Utilizing foil fuel may caue global waming and tempeatue vaiation. The Intenational Kyoto meeting equeted to deceae the foil fuel conumption and minimize the CO emiion to contol the global waming effect. Theefoe, Ameican and Euopean countie ae concentating on the tudy of enewable ouce of enegy, uch a wind powe, ola enegy, ocean tide, hyo powe bioma, etc., wheein the wind ha a ignificant poibility of poducing electic powe. The Taiwanee Govenment ha et up Souce of enewable enegy policy to inceae the clean enegy conumption and pomote the enewable ouce of enegy. Thi table incentive policy ceate the enewable ouce of enegy fom the uounding envionment. It uppot elative indutial development and pomote the enewable ouce of enegy fo all application. Wind come fom the effect of ola and eath otation. It caue aiflow with kinetic enegy. It i called wind powe. Humanity ha utilized wind-poweed device, uch a ailboat, wind-poweed wate wheel, windmill, etc. In the late nineteenth centuy, a windpoweed machine wa connected with a geneato to poduce powe. Wind powe become a main application fo wind enegy [1]. On Taiwan, the annual notheat monoon poduce tong wind along the coat, mountain and emote iland aea. Accoding to a ecent invetigation, ove 000 km of land aea ha an annual aveage wind peed highe than 5 m/. Wind enegy ha an excellent potential and the minimum ecoveable wind enegy i etimated at aound 1000 MW. Taiwan ha abundant wind enegy. Cuently, the Peng-Hu Chung Tun Powe Station and Taiwan Fomoa Platic Mai-Liao Powe Station have intalled wind-poweed geneato, which have opeated uccefully. Howeve, Taiwan ha a limited expeience and few tudie have been made on wind powe. Thi tudy concentate on the analyi and compaion of output chaacteitic fo high efficiency Double-Fed Induction Geneato and Taditional Geneato.. Wind Powe Efficiency Rotation of the eath and ola adiation induce tempea- Copyight 011 SciRe.

2 54 D.-C. SUE tue diffeence at the eath uface caue ai ciculation. Aiflow in the hoizontal diection poduce wind. The wind velocity ha the following unit: m/, km/h, mph knot (nautical mile/h), with the elationhip a 1 m 3.6 km h.4 mph 1.94 knot In addition, the Beaufot cale can be ued to identify the wind tength. The wind tength ha 0 up to 17 gade (wind velocity fom 0.3 m/ to 61. m/). Wind peue (F) i poduced fom aiflow that i diectly popotional to the cube (pe fomula) of it velocity. 1 F C AU (kw) (1) P whee A : co-ectional aea of wind team (m ) : ai denity (1.5 kg/m 3 ) C P : wind powe coefficient U : wind velocity (m/) The kinetic of wind peue i called wind powe (P), which i wind peue (F) poduced wok pe unit time, 1 3 P C AU () P Fo tall egulato, C P i a function and i a atio of the velocity at wind tip of egulato v. wind velocity, i.e. V and i the oto adiu of wind machine, (ad/) i angle velocity, Figue 1 i the CP - cuve of vaiou angle. The powe poduced by a wind machine i diectly popotional to it co-ectional aea, and the cube of the wind velocity [-4]. Theefoe, the wind machine location i the key facto of powe poduction and powe geneating cot. The wind machine opeating at a pe-et ange of wind velocitie ha to enue the geneato opeate at ated peed. Mean mut be povided to hutdown the geneato opeating to potect the equipment if the wind veloc- ity become exceive. But, the theoetical kinetic enegy of the wind can only be patially utilized conideing the oveall efficiency of machine; only a pat of wind powe can be actually utilized. 3. Chaacteitic of Wind Machine The kinetic enegy of the moving ai (wind) otate the blade of the wind machine. The blade convet the wind enegy to mechanical enegy, which in tun, i conveted to electical enegy by the geneato. The powe output of wind machine i affected by wind velocity, machine efficiency, blade deign, blade pitch, co-ectional aea, etc. [1,]. The wind machine type can be categoized into hoizontal haft and vetical haft depend on hape and otating haft. The vetical haft machine ha a highe axial etadation facto, lowe otating peed, lowe efficiency and equie moe blade mateial, making it unuitable fo powe geneating ue. The hoizontal haft machine can be categoized a facing upwind o downwind. The upwind machine ue a ea udde (mall machine) o univeal mechanim to ene the wind diection and poition the blade to poduce maximum powe. The downwind type ue the cone hape to minimize of the oto to follow wind diection o the blade ae facing the downwind ide. Becaue the wind act on the uppoting tuctue of the wind machine and then on the blade, the eulting peiodic fatigue loading affect the machine opeating life. In geneal, hoizontal haft wind machine ae the upwind type, i.e., blade ae facing the wind. Figue how hoizontal haft wind machine type. The blade election ignificantly affect the otating peed and powe output of machine. Cuently, the majo blade type i thee-blade type. The thee-blade ha le loading vaiation moe table opeation, deceaed fatigue loading, inceaed blade opeating life compaed to two blade and ingle blade unit. In additional, the Figue 1. C P -λ cuve of vaiou angle. (a) Figue. Hoizontal haft wind machine type. (a) Upwide; (b) Downwind. (b) Copyight 011 SciRe.

3 D.-C. SUE 55 opeation of thee-blade i mooth and comfotable of viion, the two-blade unit have an untable otation and ingle blade unit ae unbalance and uncomfotable. Theefoe, the hoizontal thee-blade ae elected fo the cuent tudy of wind machine. Accodingly, the hoizontal haft, upwind and thee-blade wind machine ae evaluated a the bet appoach fo an opeating wind machine [1]. The powe output i elated to wind velocity o wind peed. When the wind peed matche the cut-in peed, the wind machine begin to poduce powe. Fom cut-in peed to the ated peed, the wind machine powe output i diectly popotional to the cube of the wind velocity. Fom the ated peed to cut-out peed, the powe output emain at ated powe. When the cut-out peed exceeded, the wind machine i hut down without powe output to avoid any damage. The blade mut be featheed to have no ignificant otational velocity. Figue 3 how wind velocity and powe output of Veta V Type Wind Powe Geneato at ated powe 660 kw, the cut-in peed, ated peed, and cut-out peed ae 4, 15 and 5 m/ epectively. To maintain the ated powe output fo wind machine and without damaging the geabox and/o geneato, the powe output of the wind machine ha to be contolled. Contol i epaated into a tall egulato and a pitch egulato to contol the amount of wind enegy being abobed and tanfeed to poduce powe [1,]. Table 1 i the compaion of tall egulato and pitch egulato. 4. Taditional Wind Machine Output Chaacteitic Cuently, the majo type of wind-poweed geneato ae pemanent magnet geneato, ynchonou geneato, induction geneato, and high efficiency double-fed geneato [,5]. The theoy and output chaacteitic of the diffeent type of wind-poweed geneato ae explained a follow: 4.1. Pemanent Magnet Geneato The oto of the geneato i made of pemanently magnetic mateial and the oto haft i iven by the blade of the unit. When the otating blade ive the magnetic oto, a otating magnetic field that inteact with the multiple winding of the tato. Thee otating line of magnetic foce induce an altenating voltage in the winding. The altenating cuent induction voltage i EA K (3) whee K : electical coefficient of the geneato Figue 3. Wind velocity and powe output of veta V type wind powe geneato. Table 1. Compaion of tall egulato and pitch egulato. Item Stall Regulato Pitch Regulato Output Chaacteitic Contant Speed Contol Vaiable Speed Contol Stat Wind Velocity Safety Stuctue Ha mall ange of output chaacteitic cuve Can meet contol equiement Can t meet Ha lage ange of output chaacteitic cuve Ha difficulty at high wind peed Ha bette powe quality and lowe tanmiion load compae to tall egulato Highe wind velocity Lowe wind velocity Need beake ytem to potect ove peed Stuctue and maintenance ae eaie Without ove peed poblem Stuctue and maintenance moe complicated Cot Lowe cot Highe cot : oto magnetic flux (Wb) : angle velocity of oto peed (ad/ec) Becaue the otating magnetic field i fixed and the oto otating peed vaie with wind velocity, the output voltage and fequency ae vaiable and cannot povide a table powe upply. The poduced powe mut be un though a ectifie and an invete to be compatible with a 60 Hz powe ytem. Due to the mall capacity and highe cot pe kilowatt of output, thi type i not uitable fo commecial application. It i only uitable fo emote aea without a gid powe upply. 4.. Synchonou Geneato A ynchonou geneato opeate at the ynchonou Copyight 011 SciRe.

4 56 D.-C. SUE otating peed of an altenating cuent ytem to which it i connected. A ynchonou geneato equie diect cuent to be upplied to the oto winding via lipping to poduce the oto magnetic flux. The pime move (wind) ive the geneato oto foming a otating magnetic field that induce a voltage in the tato winding of the unit. The winding of the tato ae aanged o that a thee-phae voltage i poduced. Inteaction of otating magnetic field of ynchonize otation, which induct a thee-blade voltage. The induction voltage of altenating cuent i EA K (4) whee K : electical coefficiency of geneato : oto magnetic flux (Wb) yn : angula velocity of oto otating at ynchonou peed yn πf (ad/ec) f : tato fequency, f nm P 10 n m : oto ynchonize peed (pm) P : numbe of oto pole Output powe (neglecting tato eitance) i P out yn 3VE T A in δ (5) X whee, V T : voltage aco geneato teminal (volt) X : ynchonou eactance ( ) δ : phae angle diffeence between EA and VT (degee). In geneal, the lage powe upply ytem need to ue two et o moe ynchonou geneato to combine into ytem fo upply powe. It ha the advantage of inceaed ytem efficiency, deceaed pae capacity, eae of unit maintenance, inceaed powe upply eliability and meeting optimal dipatch, etc. Figue 4 how output powe and toque angle fo aied pole and cylinical oto of ynchonou geneato. Synchonou geneato applie to wind-poweed unit when the otating blade diectly ive the oto without any geabox, avoiding the noie and wea of mehing ive gea. When the actual wind peed exceed the deign wind peed and the unit i opeating at full load, a pitch contol ytem i intalled to adjut the blade angle to educe the powe extacted fom the wind. Pitch contol limit oto peed and powe output to eliminate oveload/ovepeed damage. The ynchonou geneato i ame a the pemanent magnet geneato. The output voltage and fequency vaie with the wind velocity. The wind machine nomally otate at 0-30 pm compaed to the maximum ynchonou peed of 3600 pm fo a 60 Hz gid ytem. Figue 4. Output powe chaacteitic of ynchonou geneato. In ode to make the wind machine output compatible with the 60 Hz gid, the machine output mut pa though a ectifie to become a DC and then though an invete to match the ytem fequency befoe being tepped-up via a tanfome to feed into the powe gid Induction Geneato The thee-phae induction geneato ue magnetic induction theoy to tanfe the electical enegy in the fom of magnetic flux fom tato to oto, without any wie connection. Powe fom an extenal ouce enegize the tato, cauing the oto to tun, jut like an induction moto. The otating peed of the oto i lightly lowe than the otating magnetic flux in the tato. Thi type geneato i alo called an aynchonou machine. When the oto peed of an induction geneato exceed the peed otating magnetic field in the tato, and the oto diection i conitent with otating magnetic field, the oto will tend to pull the tato field fate. Thi action caue a evee toque in the otating diection, thu cauing the induction geneato to opeate a a geneato at the fequency and voltage of the initial powe upply to the tato. In a popely deigned machine, the magnetic link between the oto and tato i tong enough to pevent the oto going into ove peed, egadle of the enegy input fom the blade. The definition of otating diffeence atio fo an induction geneato i nyn nm 100% (6) n yn whee, n yn : ynchonou peed of magnetic field (pm) n : oto peed of oto (pm) m Copyight 011 SciRe.

5 D.-C. SUE 57 Figue 5 follow Kichhoff voltage law, the voltage loop equation fo ingle-phae effective cicuit of an induction geneato i V R jx XmIS jxmi (7) R (8) 0 jx mi j X X m I In Equation (7) and (8), only the magnetic eactance, jx m, i conideed and the flux banch eitance of the coe, R c, i neglected. The conveion powe and toque of an induction geneato ae epeented a 1 Pconv 3I R (9) P conv ind (10) m Figue 6 how the toque-peed chaacteitic cuve of induction geneato with diffeing oto eitance value. The poduced powe i diectly popotional to the toque applied to the tato by the blade and thu oto, but if the input toque developed by the wind on the blade, i lage than puhove toque, the induction geneato will ove peed. Theefoe, when applied to a wind-poweed geneato an adequate beake, oto eitance contol, blade pitch contol o imila device to pevent high wind peed and/o exceive toque fom inducing ove peed of the blade and oto [1]. The induction geneato oto i without a magnetic field cicuit, to change the magnetic field to contol the output voltage and i not elf-exciting. The equied eactive powe fo excitation need i upplied by a connection fom an extenal capacito o fom gid ytem. The excitation powe contol the voltage at the geneato teminal, which upply the powe to gid ytem [5]. The advantage of induction geneato ae tuctual implification; exciting field ytem i not equied, unneceay to ynchonize opeation, eay fo opeation and maintenance. When induction geneato deive powe fom wind, the elf-exciting type i ued. A capacito i intalled aco the teminal to povide the equied eactive powe fo tatup and impove the powe facto duing opeation Compaion Synchonou Geneato and Induction Geneato The tato contuction i identical fo a ynchonou geneato and an induction geneato. The majo diffeence i oto deign and contuction. The winding of oto of a ynchonou geneato need to have diect cuent (DC) fo excitation to poduce the oto magnetic field but the dampe winding of the oto of the induction geneato need to be hot-cicuited to poduce oto magnetic field. Table how the compaion of ynchonou and induction geneato. Figue 5. Effective cicuit of a ingle phae of an induction geneato. Table. Pefomance compaion of ynchonou and induction geneato. Item Synchonou Geneato Induction Geneato Stato tuctue Roto tuctue Speed Reactive powe compenation End voltage contol Thee-phae winding Ha evidenced and contolled pole oto winding need to connect to DC ouce Opeating at ynchonize peed Not needed Caue exciting ytem contol Thee-phae winding Ha cage oto, winding doen t need to connect DC Opeating at ove-ynchonou peed Fom ytem o connect to capacito Can t contol Convete device Needed Not needed Figue 6. Toque-peed chaacteitic cuve of an induction geneato with diffeent oto eitance value. Maintenance Complicate and difficult Simple and eay Cot Expenive Cheap Copyight 011 SciRe.

6 58 D.-C. SUE 5. High Efficiency Double-Fed Induction Geneato The diadvantage and limitation of the elf-exciting induction geneato include the difficulty to adjut the output voltage and fequency, the need to be opeated at ove-ynchonou peed, the mall ange of output powe, etc. Cuently, new development in the winding of the induction geneato and vecto contol theoy a applied to contolling the oto input voltage and fequency can modulate the powe input and output chaacteitic of the geneato oto. With the advantage of opeating in an aubynchonou peed ange, output can exceed ated powe; cloe contol of output voltage and fequency i obtained. Figue 7 how a double-fed induction geneato tuctue [] Model of Double-Fed Induction Geneato Afte tanfomation and d-q tanfomation of a theephae dynamic model fo a double-fed induction geneato [3,4], the equation of dynamic model can be witten a: d d Vd R Id q (11) d q Vq R Iq d d V R I q (1) d q Vq R Iq m e J f M e qi diq L whee Figue 7. Stuctue of double-fed induction geneato. : angle peed of oto,ad ec d LI d MI q LI q MIq (13) MId L I q MIq L Iq Due to geneato opeating at teady condition, theefoe, with futhe analyi, the tem d can be ne glected, allowing the voltage of tato and oto to be e-witten a: V R I L I MI d d q q V R I L I MI q q d V R I L I MI q q V R I L I MI q q d 5.. Related Equation of Vecto Contol (14) The output of double-fed induction geneato i connected to powe ytem; theefoe, the voltage of haft end i equal to the voltage of ytem. The vecto contol theoy i to fix magnetic diection of tato to the vetical axi. d and q 0 M (15) e diq L The magnetic toque i only elated with oto cuent of co-axi. Neglect wie eitance of tato, R the voltage of tato end and voltage of vetical axi-co axi fo double-fed induction geneato can be witten a: d n Vn ; n a, b, c (16) Vd 0 and Vq V Ue vetical axi-co axi a efeence bae, ewite the voltage, cuent and magnetic of tato end, a follow: Vd 0 (17) Vq V d d LI d MI q LI q MIq 0 (18) MId L I MI L I I q q q 1 MI L M Iq Iq L d (19) Copyight 011 SciRe.

7 D.-C. SUE 59 Deivative fom the above equation, the magnetic field and voltage of oto i M L I L L M L q q L I MV M di M q L L V R I L L I V R I L di L I MV L M q M q q L L (0) (1) The eal powe and eactive powe of the tato of a double-fed induction geneato can be peented a: VM P V I V I I () d d q q q L V V M Q V I V I I (3) q d d q L L Fom the above deivative, the eal powe and eactive powe of tato fo the double-fed induction geneato can be calculated. The cuent of vetical axi and co axi fo oto can be epaately contolled Simulation Analyi If the oftwae MATLAB/Simulink i ued to imulate the vecto contol epone chaacteitic of Double-Fed Induction Geneato, and the above theoetical deivative i olved uing the following imulation paamete with the eult hown on Figue 8 and 9: Figue 8. Simulation of epone eult fo eal powe and eactive powe. Copyight 011 SciRe.

8 60 D.-C. SUE Figue 9. Simulation of epone eult of contol cuent fo oto vetical axi and co axi. R 0.05, R 0.05, M 47.3 mh, L 50 mh, L 50 mh The geneato powe output i 5000 W and peed i 3600 pm. The powe contol etting of Double-Fed Induction Geneato i 5000 W fo eal powe and 00 VAR fo eactive powe, peed i 340 pm ( = 0.05). Fom the above imulation eult, the vecto contol of a high efficiency Double-Fed Induction Geneato and the magnetic field of the tato i fixed on the vetical axi. The eal powe and eactive powe component of the output only elated to the elative tength of the cuent of co axi and the vetical axi of the oto. The geneato can opeate at lowe than ynchonou peed, which doe not limit to opeate at ove the ynchonou peed. At ove ynchonou peed, the tato and oto poduce powe; theefoe, the output i highe than the ated powe and ha an excellent chaacteitic of voltage and fequency adjutment. 6. Concluion Fom the above analyi and becaue uitable wind powe i available in Taiwan, the following concluion ae deived: 1) Ue the vecto contol fo the high efficiency Double-Fed Induction Geneato, to contol the output powe of the wind-poweed geneato. Even if the wind velocity i untable, it can apidly adjut the cuent in the co axi and vetical axi of the oto to contol the atio of eal powe to eactive powe to obtain the deied chaacteitic of the output powe. ) The geneato can be opeated ub-ynchonou peed and output i highe than the ated powe. It ha excellent adjutment chaacteitic fo voltage and fequency. Theefoe, the high efficiency Double-Fed In- Copyight 011 SciRe.

9 D.-C. SUE 61 duction Geneato i an optimal election fo new windpoweed geneato application. 7. Refeence [1] T. Buton, D. Shape, N. Jenkin and E. Boanyi, Wind Enegy Handbook, John Wiley & Son, Inc., Hoboken, 001. doi:10.100/ [] A. Peteon, Analyi, Modeling and Contol of Double-Fed Induction Geneato, PhD Thei, Chalme Univeity of Technology, Gothenbug, 003. [3] L. Zhang and C. Watthanaan, A Matix Convete Excited Double-Fed Induction Machine a a Wind Powe Geneato, 7th Intenational Confeence on Powe Electonic and Vaiable Speed Dive, London, 1-3 Septembe 1998, pp doi: /cp: [4] J. G. Slootweg, H. Polinde and W. L. Kling, Dynamic Modelling of a Wind Tubine with Double Fed Induction Geneato, Powe Engineeing Society Summe Meeting, Vancouve, 011, pp doi: /pess [5] P. Kundu, Powe Sytem Stability and Contol, McGaw-Hill, Inc., New Yok, Copyight 011 SciRe.

7. Inverter operated induction machines

7. Inverter operated induction machines 7. Invete opeated induction machine Souce: Siemen AG, Gemany Dept. of Electical Enegy Conveion Pof. A. Binde 7/1 Invete-fed induction machine Fequency convete (invete) geneate thee-phae voltage ytem with