IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 49, NO. 3, MAY/JUNE 2013 1119

Simulation Comparisons and Implementation ofInduction Generator Wind Power Systems

Yu Zou, Malik E. Elbuluk, Senior Member, IEEE, and Yilmaz Sozer, Member, IEEE

AbstractThis paper describes the performance comparison ofa wind power systems based on two different induction generatorsas well as the experimental demonstration of a wind turbinesimulator for the maximum power extraction. The two inductionmachines studied for the comparison are the squirrel-cage induc-tion generator (SCIG) and the doubly fed induction generator(DFIG). The techniques of direct grid integration, independentpower control, and the droop phenomenon of distribution line arestudied and compared between the SCIG and DFIG systems. Bothsystems are modeled in Matlab/Simulink environment, and theoperation is tested for the wind turbine maximum power extrac-tion algorithm results. Based on the simulated wind turbine pa-rameters, a commercial induction motor drive was programmedto emulate the wind turbine and is coupled to the experimentalgenerator systems. The turbine experimental results matched wellwith the theoretical turbine operation.

Index TermsDoubly fed induction machines, field-orientedcontrol, maximum power tracking, wind power system.

I. INTRODUCTION

THE INCREASING emphasis on renewable wind energyhas given rise to augmented attention on more reliable andadvantageous electrical generator systems. Induction generatorsystems have been widely used and studied in wind powersystem because of their advantages over synchronous genera-tors, such as smaller size, lower cost, and lower requirementof maintenance [1], [2]. The straightforward power conversiontechnique using squirrel-cage induction generator (SCIG) iswidely accepted in fixed-speed applications with less emphasison the high efficiency and control of power flow. However, suchdirect connection with grid would allow the speed to vary in avery narrow range and thus limit the wind turbine utilizationand power output. Another major problem with SCIG powersystem is the source of reactive power; that is, an externalreactive power compensator is required to hold the distributionline voltage and prevent the whole system from overload. On

Manuscript received December 23, 2010; revised June 14, 2011 andDecember 19, 2011; accepted August 22, 2012. Date of publicationMarch 22, 2013; date of current version May 15, 2013. Paper 2010-IACC-547.R2, presented at the 2010 Industry Applications Society Annual Meeting,Houston, TX, USA, October 37, and approved for publication in the IEEETRANSACTIONS ON INDUSTRY APPLICATIONS by the Industrial Automationand Control Committee of the IEEE Industry Applications Society.

Y. Zou was with the Department of Electrical and Computer Engineering,The University of Akron, Akron, OH 44325-3904 USA. He is now with theDepartment of Electrical and Computer Engineering, Saginaw Valley StateUniversity, University Center, MI 48710 USA (e-mail: yz31@zips.uakron.edu).

M. E. Elbuluk and Y. Sozer are with the Department of Electrical andComputer Engineering, The University of Akron, Akron, OH 44325-3904 USA(e-mail: melbuluk@uakron.edu; ys@uakron.edu).

Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/TIA.2013.2253531

the other hand, the doubly fed induction generator (DFIG) withvariable-speed ability has higher energy capture efficiency andimproved power quality and thus has attracted more attentions.With the advent of power electronic techniques, a back-to-backconverter, which consists of two bidirectional converters and adc link, acts as an optimal operation tracking interface betweengenerator and grid [3][5]. Field-oriented control (FOC) isapplied to both rotor- and stator-side converters to achievedesirable control on voltage and power [6], [7]. Generally,the FOC has been presented based on DFIG mathematicalequations only. However, a three-phase choke is commonlyused to couple the stator-side converter into the grid. Therefore,this paper proposes the FOC schemes of stator-side converterinvolving the choke, and it turns out that both stator- and rotor-side converter voltages consist of a current regulation part anda cross-coupling part.

First, this paper presents an experimental setup to emulatethe wind turbine operation in torque control mode and thusto obtain a power operation curve for optimal power control.Second, the modeling and simulation of SCIG and DFIG windsystems are studied. Comparison between SCIG without static-var compensator (STATCOM) and SCIG with STATCOM aswell as DFIG system clearly indicates difference in resulteddistribution line voltage.

The paper is organized as follows. The wind turbine ismodeled and simulated using the turbine emulator, and an ex-pression of optimal output power versus rotor speed is proposedin Section II. In Section III, the SCIG wind power system is es-tablished based on wind turbine system described in Section II.In addition, the DFIG is introduced by mathematical modelin Section IV, indicating the relationship of voltage, flux, andtorque. At last, steady-state and dynamic experiment/simulationresults are presented and discussed in Section V.

II. WIND TURBINEWind energy is extracted through wind turbine blades and

then transferred by the gearbox and rotor hub to the mechanicalenergy in the shaft, which drives the generator to convert themechanical energy to electrical energy. The turbine model isbased on the output power characteristics, expressed as [3], [8]

Pm =Cp(, ) 12Av3w (1a)

=Rblader

vw(1b)

where Pm is the mechanical output power in watts, whichdepends on power performance coefficient Cp, air density ,turbine swept area A, and wind speed vw. (1/2) Av3w is equal

0093-9994/$31.00 2013 IEEE

1120 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 49, NO. 3, MAY/JUNE 2013

Fig. 1. Schematics of turbine blade from different views.

Fig. 2. Cp curve for the turbine model.

to the kinetic energy contained in the wind at a particular speedvw. The performance coefficient Cp(, ), which depends ontip speed ratio and blade pitch angle , determines how muchof the wind kinetic energy can be captured by the wind turbinesystem. A nonlinear model describes Cp(, ) as [8]

Cp(, ) = c1(c2 c3 c42 c5)ec6 (2)where c1 = 0.5, c2 = 116/i, c3 = 0.4, c4 = 0, c5 = 5, c6 =21/i, and

1

i=

1

+ 0.08 0.035

3 + 1(3)

where Rblade and r are the blade radius and angular frequencyof rotational turbine as depicted in Fig. 1. The Cp curvefor this particular turbine model at different is shown inFig. 2 where it is illustrated that, to achieve maximum Cp,one has = 0 and = 8. The blade with fixed geometrywill have fixed Cp characteristics, as described in (2) and(3). Therefore, to track the optimal output power, the curve ofPmr is the map to follow.

In order to experimentally investigate the operation of windturbine, a wind turbine emulator system is built to operate intorque control mode, using (1a)

T =P

r=

1

2R3bladev

2w

Cp

=1

2R3bladev

2wCm (4)

where Cm is the torque performance coefficient. It is dependenton r, vw, and . Thus, based on turbine Cp model and

Fig. 3. Cm curve for the turbine emulator.

Fig. 4. Wind turbine emulator system.

by assuming = 0, the Cm curve is given in Fig. 3. Atany particular vw, one could obtain different torque and, thus,power output by varying rotor speed. The system configurationis shown in Fig. 4, where the r is fed back to the controller forcalculating Cm and, then, torque command.

III. SCIG WIND POWER SYSTEM

Fig. 5 shows the schematics of the SCIG system including thewind turbine, pitch control, and reactive power compensator.The entire system includes three stages for delivering the en-ergy from wind turbine to the power grid. The first one is windfarm stage which handles with low voltage Vwt, the secondis distribution stage which has medium voltage Vdis, and thethird is grid transmission stage which has high voltage Vgrid.The three-phase transformers take care of the interface betweenstages [9]. As mentioned, nominal power PnSCIG is consideredas active power reference to regulate the pitch angle while Vdisand Idis denote the distribution line-to-line voltage and phasecurrent, and they are monitored to favor the reactive powercompensation for distribution line. This fairly straightforwardtechnique was first used since it is simple and has ruggedconstruction, reliable operation, and low cost. However, thefixed-speed essential and potential voltage instability problemsseverely limit the operations of wind turbine [1], [3].

Since SCIG is of fixed-speed generator, for a particular windspeed, the output active power is fixed as well. Thus, with theincrease of wind speed, so does the output power until thenominal power is reached. The wind speed at this moment

ZOU et al.: COMPARISONS AND IMPLEMENTATION OF INDUCTION GENERATOR WIND POWER SYSTEMS 1121

Fig. 5. SCIG wind power system topology.

Fig. 6. Pitch angle control.

is called nominal wind speed. Beyond this speed, the pitchangle system will prevent the output power from exceeding thenominal value. That is, when the wind speed is below nominalvalue, the power capture can vary with the change of windspeed; and when the wind speed is above nominal value, thepitch angle control system will limit the generated power bychanging the pitch angle. In such way, the output power willbe stabilized at nominal value where the wind speed is alwaysabove nominal speed. The pitch angle is determined by an open-loop control of regulated output active power and by that shownin Fig. 6. Due to the huge size of blade and, thus, inertia, pitchangle has to change in a slow rate and a reasonable range. Itis also worthy to notice that, without reactive power source, inSection V, the SCIG system tends to lead to a voltage droopin distribution line which will cause overload problem. In thesimulation section, the comparison between SCIG system withand without STATCOM is conducted.

IV. DFIG WIND POWER SYSTEM

Traditionally, the dynamic slip control is employed to fulfillthe variable-speed operation in wind turbine system, in whichthe rotor windings are connected to variable resistor and con-trol the slip by the varied resistance [3], [10]. This type ofsystem can achieve limited variations of generator speed, butexternal reactive power source is still necessary. Consequently,to completely remove the reactive power compensation and tocontrol both active and reactive power independently, DFIGwind power system is one of most popular methods in windenergy applications [1], [3], [7]. This paper reproduces DFIGmodel first of all and then concentrates on the controllingschemes of power converters, in which the active and reactivepower are controlled independently. In particular, the stator-sideconverter control involving an RL series choke is proposed.

Both controlling of rotor- and stator-side converter voltages endup with a current regulation part and a cross-coupling part.

The wind turbine driving DFIG wind power system consistsof a wound-rotor induction generator and an ac/dc/ac insulatedgate bipolar transistor (IGBT)-based pulsewidth-modulated(PWM) converter (back-to-back converter with capacitor dclink), as shown in Fig. 7. In this configuration, the back-to-backconverter consists of two parts: the stator-/grid-side converterand the rotor-side converter. Both are voltage source convertersusing IGBTs, while a capacitor between two converters acts as adc voltage source. The generator stator windings are connecteddirectly to grid (with fixed voltage and frequency of grid) whilethe rotor winding is fed by rotor-side converter through sliprings and brushes, at variable frequency.

The control system is divided into two partsstator-sideconverter control system and rotor-side converter control sys-tem. An equivalent circuit of DFIG is depicted in Fig. 8, and therelation equations for voltage V , current I , flux , and torqueTe involve [4], [11], [12] are:

Vds =RsIds sqs + ddsdt

Vqs =RsIqs + sds +dqsdt

(5)

Vdr =RrIdr ssqr + ddrdt

Vqr =RrIqr + ssdr +dqrdt

(6)ds =LsIds + LmIdr

qs =LsIqs + LmIqr (7)dr =LrIdr + LmIds

qr =LrIqr + LmIqs (8)Te =

3

2np(dsIqs qsIds) (9)

where Ls = Lls + Lm; Lr = Llr + Lm; ss = s r rep-resents the difference between synchronous speed and rotorspeed; subscripts r, s, d, and q denote the rotor, stator, d-axis,and q-axis components, respectively; Te is electromagnetictorque; and Lm, np, and J are generator mutual inductance, thenumber of pole pairs, and the inertia coefficient, respectively.

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Fig. 7. Wind turbinedoubly fed induction generator system configuration.

Fig. 8. Equivalent circuit of DFIG. (a) d-axis model. (b) q-axis model.

A. Rotor-Side Converter Control

If the derivative parts in (5) are neglected, one can obtainstator flux as

ds =(Vqs RsIqs)/sqs =(Vds RsIds)/(s)

s =

2ds +2qs. (10)

Because of being directly connected to the grid, the statorvoltage shares constant magnitude and frequency of the grid.One could make the d-axis align with stator voltage vector; it istrue that Vs = Vds and Vqs = 0, thus s = qs and ds = 0,which is of stator-voltage-oriented vector control scheme, as

Fig. 9. Stator voltage FOC reference frame.

depicted in Fig. 9. According to (7)(9), the rotor-side converterreference current is derived as

Idr_ref = 2LsTe3npLms

(11)

where

Pe_ref =Popt Ploss = TerPloss =RsI

2s +RrI

2r +RcI

2sc + F

2r (12)

where Isc, Rc, and F are stator-side converter current, chokeresistance, and friction factor, respectively. Popt, Pe_ref , and

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Fig. 10. Rotor-side converter control scheme.

Ploss are desired optimal output active power, reference activepower, and system power loss. Combining (10)(12), the activepower is used as command inputs to determine current refer-ence Idr_ref . Meanwhile, the output reactive power is the statorreactive output power since the stator-side converters reactivepower is set to be zero. Then, one has

Qo =Qs +Qsc = Qs = Im [(Vds + jVqs)(Ids + jIqs)]

= VdsIqs = Vds 1Ls

(s LmIqr). (13)

Thus, the regulation of reactive power can lead to Iqr_ref , andthen, the rotor-side converter voltage signals V 1dr and V 1qr arederived by the regulation of currents. In addition, the feedfor-ward coupling parts V 2dr and V 2qr are derived based on (6) and(8), as

V 2dr =RrIdr ss(LrIqr + LmIqs)V 2qr =RrIqr + ss(LrIdr + LmIds) (14)

where the superscripts 1 and 2 denote the current regulationpart and cross-coupling part, respectively. At last, rotor-sideconverter voltage signals in dq-axes are expressed as

Vdrc =Vdr = V1dr + V

2dr

Vqrc =Vqr = V1qr + V

2qr (15)

where subscript rc denotes the rotor-side converter. After theconversion of dq abc, the rotor-side converter voltage Vabc_rccan be obtained. Fig. 10 exhibits the control scheme for theaforementioned procedure.

B. Stator-Side Converter Control

Concerning the use of three-phase series RL choke betweenstator- and stator-side converter, a cross-coupling model isrequired to derive the voltage signal of stator-side converter, asdescribed in Fig. 11

Vdsc =Vds VdchVqsc =Vqs Vqch (16)

where the subscripts sc and ch denote the variables of stator-side converter and choke. The coupling part of voltage signalsV 2dch and V 2qch is expressed as

V 2dch =RcIdsc sLcIqsc

Fig. 11. Equivalent circuit of stator-side-converter choke. (a) d-axis model.(b) q-axis model.

V 2qch =RcIqsc + sLcIdsc. (17)

Moreover, V 1dch and V 1qch are determined by the regulation ofcurrents Idsc and Iqsc in which the current reference Iqsc_ref isgiven directly while Idsc_ref is determined by the regulation ofdc-link voltage Vdc. Thus, above all, the stator-side convertervoltage signals Vdsc and Vqsc are obtained as follows anddepicted in Fig. 12:

Vdsc =Vds V 1dch V 2dchVqsc =Vqs V 1qch V 2qch. (18)

V. EXPERIMENTAL AND SIMULATION RESULTS

A. Wind Turbine and Operation Curves

The experimental wind turbine emulator system is shownin Fig. 13, where a 3-hp induction motor, driven by ABBASC550 was operated in torque-control mode to simulate aturbine. The wind turbine model is programmed into the DSP-based control card from microchip. The controller takes thewind turbine parameters and operating conditions from the user.Moreover, the controller measures the generator speed and thenproduces the torque command to the induction machine drive.A generator system is coupled to the induction motor to be ableto apply variable loading conditions.

For a given wind speed of vw = 13 m/s, the Tr char-acteristics are simulated by implementing different operationpoints on the curve. By varying generator load, the rotor speedand Cm are varied according to (1)(4), and the torque iscalculated in DSP and fed to generator. It is shown in Fig. 14that the operation points of the experimental system matchthose derived from theoretical calculations. These experimental

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Fig. 12. Stator-side converter control scheme.

Fig. 13. Experimental setup for wind turbine emulator.

Fig. 14. Experimental turbine operation torque results (solid line refers totheoretical result; spots refer to experimental results).

TABLE IWIND TURBINE EXPERIMENTAL SYSTEM PARAMETERS (vw = 13 m/s)

results are listed in Table I. Figs. 15(a) and (b) and 16(a) and(b) show the speeds, torques, armature currents, and inductionmotor phase currents for steady-state operation points A and B

Fig. 15. Operation point A of Fig. 14. (a) (Lower trace) Torque. (Middle trace)Speed. (Upper trace) Armature current using 1/50 probe. (b) Phase currents ofinduction motor10 mV/A.

Fig. 16. Operating point B on Fig. 4 (a) (1) Torque. (2) Speed. (3) Armaturecurrent1/50 probe. (b) Phase currents of induction motor10 mV/A).

of Fig. 14. The torque and speed quantities are presented inper unit (p.u.) as base turbine torque being 41 N m and baseturbine speed being 553.8 r/min, which leads to 0.457-p.u.torque and 0.7-p.u. speed for point A. Similarly, the torqueand speed are 0.96 and 1.157 p.u., respectively, for point B.The experimental power results are scaled into p.u. by basepower of 1116.8 W. The results are plotted in Fig. 17, indicatingan optimal power operation point at C, where the power ismaximum for this particular wind speed.

The other optimal power operation points for different windspeeds are emulated in the same way so that the optimal powercurve can be applied as a reference to the generator controller.In this paper, for different wind speeds and fixed = 0, thePmr curve is presented in Fig. 18 for wind speeds rangingfrom 6 to 14 m/s. By connecting the maximum points of allcurves, the relationship between maximum output power andthe rotor speed can be proposed as

Popt = 0.55723r 0.50812r + 0.4792r 0.1449 (19)

which is reference for optimal active power control.

ZOU et al.: COMPARISONS AND IMPLEMENTATION OF INDUCTION GENERATOR WIND POWER SYSTEMS 1125

Fig. 17. Experimental turbine operation power results (solid line refers totheoretical result; spots refer to experimental results).

Fig. 18. Pmr curve for the turbine model.TABLE II

SCIG-BASED WIND POWER SYSTEM PARAMETERS

B. SCIG

A traditional SCIG wind power system is developed inMatlab/Simulink, and the related system data used are givenin Table II.

In order to investigate the system performances, a ramp windspeed vw is assumed that varies from t = 10 s to t = 16 s and,then, it remains constant to the end of simulation t = 40 s.Fig. 19(a)(e) shows the dynamic variations and steady statesof pitch angle , generator speed r, produced active power P ,and consumed reactive power Q. First, the fluctuation in the

Fig. 19. Simulation results for SCIG system: (a) Wind speed vw; (b) generatorspeed r ; (c) active power P ; (d) reactive power Q; (e) pitch angle .

results during t = 0 to 2.5 s is due to the initial conditions.In the simulation, the initial speed of generator is set at slips = 0.01p.u. with respect to synchronous speed and, then, re-sponse to the wind speed input disturbance. Other initial valuesfor power and voltages are zero. The steady-state results forvw = 8 m/s indicate the operation points r = 1.0015p.u. andP = 0.29 MW on Fig. 18. Since it is lower than nominal valueof 0.855 MW, pitch angle control is not working. After t = 10 s,with the increase of vw, so do the r and P until t = 13 s whenvw exceeds the nominal value (11 m/s). This is because thepitch control is triggered to limit the increase of output powerP and Q as shown in Fig. 19(b)(d). In this way, the pitchcontrol effectively limits the output P around the nominal valueof 0.855 MW and settles a new pitch angle at roughly t = 17 s.This nominal operation point can also be observed in Fig. 18(vw = 11 m/s;P = 0.855 MW;r = 1.005 p.u).

It is noted that the rotor speed can only vary in very smallscope around 1 p.u. (fixed-speed system) and, thus, impossibleto achieve optimal active power output. Thus, the active poweroutputs at vw = 8 m/s and 11 m/s in SCIG are 0.29 and0.855 MW which are lower than those in later DFIG system.Also, without independent control ability, SCIG system con-sumes reactive power of 0.41 Mvar in the steady state, whichwill lead to line voltage droop. To provide necessary reactivepower, a STATCOM is added on the distribution line to inves-tigate the improvement. As in Fig. 20, distribution line voltagecan drop by approximately 0.055 p.u. in SCIG system withoutSTATCOM, which will be a potential induction of overload insystem. In contrast, SCIG system with STATCOM can holddistribution voltage to 0.99 p.u. and favorable to grid systemstability. The compensated reactive power from STATCOM isshown in Fig. 21 and is equal to 0.3 Mvar in the steady state,a little bit less than the real consumed value in Fig. 19(d).Although STATCOM provides impressive help on constantdistribution line voltage, the DFIG presents better result anddoes not need the help from STATCOM, as shown in Fig. 20.

1126 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 49, NO. 3, MAY/JUNE 2013

Fig. 20. Distribution voltages for SCIG system with/without STATCOM andDFIG system.

Fig. 21. STATCOM compensated reactive power.

C. DFIGBy using the proposed optimal power curve as well as the

system parameters listed in Table III, the DFIG wind powersystem is simulated. The DFIG system allows the optimal(maximum) output power operation in the absence of reactivepower source. Also, the independent control of active andreactive power is achieved.

In the Matlab/Simulink model, the converter switch fre-quency is set to be 27 times the grid frequency f . To achieveacceptable accuracy, the power circuit and the control circuitmodels are discretized at different time steps. It is worthy tonote that the nominal apparent power and nominal active powerare considered as nominal electrical power and nominal me-chanical power in this wind power system [3], [13]. Simulationand control system parameters are listed in Table IV and arepreloaded into workspace before running the simulation andeasy to be modified in m file.

First of all, the steady-state results of the system areshown in Fig. 22(a)(d), where four wind speed cases vw =7, 9, 10, and 12 m/s to verify the optimal power output trackingare presented. All of them kept the bus voltage at 1200 Vdc,indicating the well operation of stator-side converter, while thereactive power is set to be zero as the input command. In orderto track the optimal active power output, optimal rotor speedsare implemented accordingly. For instance, one could recall in

TABLE IIIDFIG-BASED WIND POWER SYSTEM PARAMETERS

TABLE IVSIMULATION AND CONTROL PARAMETERS

Fig. 18 that, at vw = 7 m/s, the optimal output active poweris 0.17 p.u. with nominal power of 1.5 MW, i.e., 0.255 MW. Alittle bit power droop could be observed from simulation resultswhich are caused by power loss in (12). Meanwhile, the optimalrotor speed is also achieved at 0.75 p.u., same as the value inFig. 18. Similarly, the optimal trackings of output power androtor speed are exhibited in other wind speed cases as well.Therefore, it can be concluded that the system works well tofollow the optimal power control at steady-state operation. It isnoticed that P and Q are vanished during the first cycle (1/60 s)in displayed result because of the calculation time cost.

Second, the system dynamic response to varied wind speedsis investigated. Due to the large H of the system, dynamic vari-ation can last and be observed in a long time period before con-verging to the steady-state values. To shorten such period, H =0.1 s is used in this part of simulation. With stable steady-stateinitial values, three regular types of wind speeds are examinedfor dynamic responses, including step, ramp, and gusty winds.The varied winds and corresponding results for Vdc, r, P , andQ are shown in Figs. 23 and 24, where the system can alwaysreach a new optimal steady state after a few seconds. In theaforementioned results, the reduced inertia constants can onlydecrease the converging time, making the system reach a newsteady state quicker, and it has no effects on steady-state values.

At last, the system dynamic response to a grid disturbance isinvestigated. At vw = 9 m/s, a remote voltage droop in grid isprogrammed from t = 0.09 to 0.29 s. The dynamic responses

ZOU et al.: COMPARISONS AND IMPLEMENTATION OF INDUCTION GENERATOR WIND POWER SYSTEMS 1127

Fig. 22. System responses to different constant wind speeds. (a) DC-link voltage Vdc. (b) Rotor speed r . (c) Active power P . (d) Reactive power Q.

Fig. 23. Wind step response. (a) DC-link voltage Vdc. (b) Rotor speed r .(c) Active power P . (d) Reactive power Q. (e) Wind speed vw .

are presented in Fig. 24. During this process, since the windspeed remains the same, control system effectively makes thesystem recovers in approximate 0.1 s.

D. Comparison Between Two SystemsA summary of SCIG and DFIG systems is presented in

Table V based on research of this paper. The comparison showsthe superiority of DFIG system over SCIG system in terms ofefficiency, controllability, and high-power applications. Also,

Fig. 24. Dynamic responses to grid voltage droop. (a) DC-link voltage Vdc.(b) Rotor speed r . (c) Active power P . (d) Reactive power Q. (e) Grid voltageVgrid.

the higher cost of slip rings and power electronics can becompensated by more power output.

VI. CONCLUSIONThis paper has presented the comparison of the wind turbine

systems using SCIG and DFIG generator systems. With theexperimentally investigated wind turbine model, a SCIG anda DFIG wind power systems are modeled and simulated in

1128 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 49, NO. 3, MAY/JUNE 2013

TABLE VSUMMARY OF SCIG AND DFIG WIND POWER SYSTEMS

Matlab/Simulink. An optimal active-power-versus-rotor-speedrelationship has been proposed for turbine model first, and itfunctions as a lookup table for tracking the maximum outputactive power. The SCIG system presents the need of externalreactive power source to support grid voltage, and it can keepthe output power at the nominal level by pitch control butcannot accordingly change the rotor speed to achieve maximumwind power capture at different wind speeds. In contrast, theDFIG system does not need reactive power compensator tohold distribution line voltage and achieves optimal active powercontrolling. Both voltage control schemes for two convertersconsist of a current regulation part and a cross-coupling part.The turbine emulator system performs well and follows thetheoretical and simulated maximum power extraction points indifferent operating conditions.

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Yu Zou received the B.S. and M.S. degrees in elec-trical engineering from Tianjin University, Tianjin,China, in 2004 and 2007, respectively, and the Ph.D.degree from the Department of Electrical and Com-puter Engineering, The University of Akron, Akron,OH, USA, in 2012.

He is currently an Assistant Professor with theDepartment of Electrical and Computer Engineering,Saginaw Valley State University, University Center,MI, USA. His research interests include power elec-tronics and electric machine controls.

Malik E. Elbuluk (S79SM97) received the B.Sc.degree (with honors) in electrical engineering fromthe University of Khartoum, Khartoum, Sudan, in1976 and the M.S., E.E., and D.Sc. degrees in electri-cal engineering from the Massachusetts Institute ofTechnology, Cambridge, MA, USA, in 1980, 1981,and 1986, respectively.

He is a Professor with The University of Akron,Akron, OH, USA, where he has been since 1989. Hewas with the faculty of the Department of Electricaland Computer Engineering and the Electric Power

Research Center, North Carolina State University, Raleigh, NC, USA, from1986 to 1989. He was a Summer Research Fellow at the NASA Lewis ResearchCenter, Cleveland, OH, USA, from 1991 to 2010. His work at NASA includedalternative energy systems, low-temperature electronics for space missions,modeling and simulation of the Space Station Freedom, power by wire, powerelectronic building blocks, starter/generator for aircraft engines, and sensor-less control of electromechanical actuators for the more electric aircraft. Histeaching and research interests include the areas of power electronics, electricmachines, control systems, fuzzy logic, and neural networks.

Prof. Elbuluk actively publishes and reviews papers for the IEEE Con-ferences and TRANSACTIONS and has organized and chaired a number ofsessions for the IEEE Power Electronics, IEEE Industry Applications, andIEEE Industrial Electronics Societies. He was an Associate Editor for theIEEE TRANSACTIONS ON POWER ELECTRONICS and was the ManufacturingSystems Development and Applications Department Vice-Chair for the IEEETRANSACTIONS ON INDUSTRY APPLICATIONS and also the Vice-Chair andTechnical Program Chair for the Industry Automation and Control Committee.He is a Registered Professional Engineer in the State of Ohio.

Yilmaz Sozer (M04) received the B.S. degree inelectrical engineering from the Middle East Techni-cal University Ankara, Ankara, Turkey, and the M.S.and Ph.D. degrees in electric power engineering fromRensselaer Polytechnic Institute, Troy, NY, USA.His graduate work focused on power electronics andthe development of control algorithms for electricmachines.

Before joining the faculty of the Department ofElectrical and Computer Engineering, The Univer-sity of Akron, Akron, OH, USA, after the comple-

tion of his doctorate degree, he worked with Advanced Energy Conversion,Schenectady, NY, USA. He is currently an Assistant Professor with the De-partment of Electrical and Computer Engineering, The University of Akron,engaged in teaching and research. His research interests are in the areas ofcontrol and modeling of electrical drives, alternative energy systems, designof electric machines, integrated and belt-driven starter/alternator systems, high-power isolated dc/dc converter systems, large industrial static power conversionsystems that interface energy storage, and distributed generation sources withthe electric utility.

Dr. Sozer has been involved in IEEE activities which support power elec-tronics, electric machines, and alternative energy systems. He is serving as anAssociate Editor for the IEEE Industry Applications Society (IAS) Electric Ma-chines Committee and Secretary of the IEEE IAS Sustainable and RenewableEnergy Systems Committee.

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