MAHESH CHANAGOND et al.
Citation: 10.2348/ijset05150539
ISSN (O): 2348-4098
ISSN (P): 2395-4752
IMPLEMENTATIONOFSTATCOMONDFIGBASEDWINDFORM
MAHESHCHANAGOND1,PLASINDIAS2
1Master’sScholar,IndustrialElectronicsEngineering,VTUniversity,INDIA.E‐mail:Mahesh.chanagond123@gmail.com
2AssistantProfessor,KLSVDRITHaliyal,KARANATAKA.E‐mail:plasin_dias@yahoo.com
ABSTRACT
The Doubly Fed Induction Generator (DFIG) based wind farm into the power grid has become a major concern for power
systemengineerstoday.Voltagestability&RegulatedisakeyfactortomaintainDFIG‐basedwindfarminserviceduringthe
gridfault.IstudytheimplementationofSTATCOMtoovercomethevoltagestability&regulationissueforDFIGbasedwind
farm connected to a distribution network. The study includes the implementation of a static synchronous compensator
(STATCOM) as a dynamic reactive power compensator at the point of common coupling to maintain stable voltage by
protecting DFIG‐based wind farm interconnected to a distribution system from going off line during and after the
disturbances. The developed system is simulated in MATLAB the results show that the STATCOM improves the transient
voltagestabilityandthereforehelpsthewindturbinegeneratorsystemtoremaininserviceduringgridfaults.
1. INTRODUCTION
DUEtotheincreasingconcernaboutCO2emissiongasses,
renewable energy systems and especially wind energy
generation have attractedgreat interestsin recent years.
Huge no of wind farms have been installed or planned
around the world and the power generation of the wind
turbinesareincreasing.Typicallyallmostallwindfarms,
wind turbines based on the doubly fed induction
generator(DFIG)technology.DFIGisbasicallyastandard
rotor‐wounded induction machine in which stator is
directlyconnectedtothegridsystem,andtheconnection
oftherotortothegridisviaaback‐to‐backpulsewidth
modulation(PWM)convertor.
The rotor converter consists of rotor‐side converter
(RSC)andagrid‐sideconverter(GSC)connectedback‐to‐
back by a dc‐link capacitor. Under any fault conditions,
blocking the RSC of the DFIG is widely used strategy in
order to protect the RSC from over current in the rotor
circuit. In the case of a weak power network and during
the grid fault, the grid side converter (GSC) cannot be
providesufficientreactivepowerandvoltagesupportdue
toitssmallpowercapability,atthisconditionthevoltage
to be instability. In this case, system, immediately
disconnect the wind turbines from the grid to prevent
such a fault and reconnect them when those fault to be
rectified. With the rapid increase in the wind power in
powersystems,trippingofmanywindturbinesinalarge
wind farm during grid faults the system voltage to be
instability.
Manyresearchesandstudieshavebeendoneinorderto
maintain DFIG‐based wind farm in service during grid
disturbances, dynamic reactive power compensation
using FACTS devices has been widely investigated as a
significantsolutiontoachieveuninterruptedoperationof
a wind farm used with DFIGs during grid faults. Static
synchronous compensator (STATCOM) and static var
compensator (SVC) are the two options available to
provide
controlled
dynamic
reactive
power
International Journal of Science, Engineering and Technology- www.ijset.in
compensation. This Paper presents a complete study of
the STATCOM application to improve the stability and
performance of DFIG‐based wind farm connected to a
distribution system during transient disturbances. The
developed system is simulated in MATLAB to verify the
concludedresults.
2. STATCOM
StaticSynchronousCompensator(STATCOM)isaFlexible
ACTransmissionSystem(FACTS)devicethatiscapableof
injecting & absorbing reactive power. Usually, the
STATCOM is applied to voltage support goals. It consists
of a Voltage Source converter (VSC), energy storage
device, coupling transformer connected in shunt to the
distributionnetworkthroughacouplingtransformer.The
VSC converts the AC to DC voltage across the storage
deviceintoasetofthree‐phaseacoutputvoltages.Itcan
continuously inject or absorb reactive power by varying
theamplitudeoftheconvertervoltagewithrespecttothe
line bus voltage, so that a controlled current flows
throughthetiereactancebetweentheSTATCOMandthe
distributionnetwork.
At system voltage is a decrease, the STATCOM inject
reactive power (STATCOM capacitive). At system voltage
is increases; it absorbs reactive power (STATCOM
inductive) .The VSC uses forced commutated power
electronic devices (GTOs, IGBTs or IGCTs) to synthesize
itsterminalvoltagefromaDCvoltagesource.Equivalent
circuitdiagramofSTATCOMshowninfig1
539
MAHESH CHANAGOND et al.
Citation: 10.2348/ijset05150539
ISSN (O): 2348-4098
ISSN (P): 2395-4752
windings. Mechanical power applied at the generator
shaft by the prime mover is thus converted to electrical
power that is available at the stator windings. In
conventional induction generators, the relationship
betweenthefrequenciesoftheacvoltagesinducedacross
thestatorwindingsofthegeneratorandtherotorspeed.
Figure1
The same operating principles can be apply in a doubly‐
fed induction generator. The only difference is that the
following the magnetic field created in the rotor is not
static(asitiscreatedusingthree‐phaseaccurrentinstead
ofdccurrent),butratherrotatesataspeedproportional
tothefrequencyoftheaccurrentsfedintothegenerator
rotor windings. This means that the rotating magnetic
field passing through the generator stator windings not
onlyrotatesduetotherotationofthegeneratorrotor,but
also due to the rotational effect produced by the ac
currents fed into the generator rotor windings equation.
Therefore, in a doubly‐fed induction generator, both the
rotation speed of the rotor and the frequency of the ac
currentsfedintotherotorwindingsdeterminethespeed
of the rotating magnetic field passing through the stator
windings, and thus, the frequency of the alternating
voltage induced across the stator windings. Taking into
account the principles of operation of doubly‐fed
induction generators, it can thus be determined that,
when the magnetic field at the rotor rotates in the same
direction as the generator rotor, the rotor speed and the
speedoftherotormagneticfieldaddup.
4. DOUBLY‐FEDINDUCTIONGENERATORSUSED
INWINDTURBINES
Figure2
In this IGBT based STATCOM model is used. The overall
schemeoftheSTATCOMcircuitisshowninFig.1andthe
controlsystemblockdiagramisshowninFig2
The real andreactive power injected bythe STATCOM is
givenbyfollowingequations.
WhereδistheangleofV1withrespectofV2.Insteady
stateoperation,thevoltageV2generatedbytheVSCisin
phase with V1 (δ=0), so that only reactive power is
flowing(P=0).IfV2islowerthanV1,QisflowingfromV1
to V2 (STATCOM is absorbing reactive power). On the
reverse,ifV2ishigherthanV1,QisflowingfromV2toV1
(STATCOM is generating reactive power). The amount of
reactivepowerisgivenbythefollowingequation
3. DOUBLYFEDINDUCTIONGENERATOR
In conventional three‐phase synchronous generator,
whenanexternalsourceofmechanicalpowermakesthe
rotor of the generator rotate, the static magnetic field
createdwhenthedccurrentfedintothegeneratorrotor
windingrotatesatthesamespeedastherotor.Atthis,a
continually changing magnetic flux passes through the
stator windings as the rotor magnetic field rotates,
inducing the alternating voltage across the stator
International Journal of Science, Engineering and Technology- www.ijset.in
Mostdoubly‐fedinductiongeneratorareusedinindustry
due to generate electrical power in large (power‐utility
scale) wind turbines. This is primarily due to the many
advantages doubly‐fed induction generators over other
typesofgeneratorsinapplicationswherethemechanical
powerprovidedbytheprimemoverdrivingthegenerator
varies greatly. To better understand the advantages of
using doubly‐fed induction generators to generate
electricalpowerinwindturbines.
Large‐size wind turbines are basically divided into two
types which are fixed‐speed wind turbines and Variable‐
speedwindturbines.
In fixed‐speed wind turbines, three‐ phase asynchronous
generators are generally used. Because the generator
output is given directly to the grid (local ac power
network),therotationspeedofthegeneratorisfixed,and
so is the rotation speed of the wind turbine rotor. Any
fluctuationinwindspeednaturallycauses,themechanical
poweratthewindturbinerotortovaryand,becausethe
rotationspeedisfixed,thiscausesthetorqueatthewind
turbine rotor to vary accordingly. Whenever a wind less
occurs, the torque at the wind turbine rotor thus
increases significantly while the rotor speed less varies.
Therefore, every less wind stresses the mechanical
components in the wind turbine and causes a sudden
increase in rotor torque, as well as in the power at the
wind turbine generator output. Any fluctuation in the
output power of a wind turbine generator is a source of
instabilityinthepowernetworktowhichitisconnected.
Invariable‐speedwindturbines,therotationspeedofthe
wind turbine rotor is allowed to vary as the wind speed
540
MAHESH CHANAGOND et al.
ISSN (O): 2348-4098
ISSN (P): 2395-4752
Citation: 10.2348/ijset05150539
varies.Thisprecludestheuseofasynchronousgenerators
in such wind turbines as the rotation speed of the
generator is quasi‐constant when its output is given
directly to the grid. The same is true for synchronous
generators which operate at a strictly constant speed
whentieddirectlytothegrid.
Thisiswheredoubly‐fedinductiongeneratorscomeinto
play, as they allow the generator output voltage and
frequencytobemaintainedatconstantvalues,nomatter
thegeneratorrotorspeed.Byadjustingtheamplitudeand
frequency of the ac currents fed into the generator rotor
windings, it is possible to keep the amplitude and
frequency of the voltages produced by the generator
constant, despite variations in the wind turbine rotor
speedcausedbyfluctuationsinwindspeed.Bydoingso,
this also allows operation without sudden torque
variations at the wind turbine rotor, thereby decreasing
thestressimposedonthemechanicalcomponentsofthe
wind turbine and smoothing variations in the amount of
electricalpowerproducedbythegenerator.
Using the same means, it is also possible to adjust the
amount of reactive power exchanged between the
generator and the ac power network. This allows the
powerfactorofthesystemtobecontrolled.Finally,using
a doubly‐fed induction generator in variable‐speed wind
turbinesallowselectricalpowergenerationatlowerwind
speeds than with fixed‐speed wind turbines using an
asynchronousgenerator
5. DFIGBASEDWINDFORM
Wind farm in this consists of Doubly Fed Induction
Generator i.e. DFIG. The DFIG is Wound Rotor Induction
Generatorwiththestatorwindingsdirectlyconnectedto
the constant‐frequency three‐phase grid and the rotor
windingsisfedbytherotorsideconverter(RSC)andthe
grid side converter (GSC) connected back‐to‐back as
shown in the Fig 4.2 . At steady state the RSC
independentlyregulatesstatoractiveandreactivepowers
where as GSC keeps the DC link voltage constant
independent of magnitude and direction of the rotor
power. In this paper the wind farm is represented using
semi power system toolbox in Matlab/Simulink where 6
wind turbines and DFIGs are represented as one
equivalentDFIGdrivenbysingleequivalentwindturbine.
Each individual DFIG wind turbine represents a 1.5MW
windturbinegenerator(WTG)system,Theparametersof
the equivalent wind turbine and DFIG are given in table
4.1.
DFIG stator is connected directly to the grid. So during
grid fault, high current will be induced in the rotor
windings and the protection system will block the RSC.
The grid side converter (GSC) cannot provide sufficient
reactivepowerandvoltagesupportduetoitssmallpower
capability,andtheremightbeariskofvoltageinstability.
As a result, utilities disconnect the DFIG immediately for
its protection. To minimize effects of the grid side
disturbances on DFIG wind farm during and after fault,
reactivepowercompensationisrequiredtoremainDFIG‐
windfarminservicebecauseDFIG‐basedwindfarmcan’t
providesufficientreactivepowerandvoltagesupportdue
toitslimitedpowercapacity.
6. EXPERIMENTALSETUP
Figure4
Figure.4showsthesinglelinediagramofthetestsystem
usedforthisstudy.Thegridmodelconsistsofa120kV,
60 Hz, grid supply point, feeding a 25 kV distribution
system through 120/25 kV, 47 MVA step down
transformer, which feeding a 575V system through
25kV/575V,12MVAstepdowntransformer.
Therearetwoloadsinthesystem;oneloadof2MVA,0.9
pf(lag)at30Kmfromtransmissionline,andastaticload
of 500 KW at 575V bus. The 25 kV, 30 Km long line is
representedasnominal‐Πline.TheDFIG‐basedwindfarm
consists of six wind turbines each with 1.5 MW (total 9
MW)whichhaveaprotectionsystemmonitoringvoltage,
current, machine speed and DC link voltage is connected
at 575V bus. The wind speed increases slowly from 8
m/secandreachesthefinalconstantvalueof14m/secat
16sec.Allthetestsherearestudiedaftersystemreaches
steady state i.e. after 16 sec. The GSC in DFIG maintains
the DC link voltage almost constant at 1200 V during
normal operating condition. The STATCOM is shunt
connected at the sending end bus (25kV bus) to provide
dynamiccompensationofreactivepower.Theparameters
ofthesystemcomponentsaregiveninTable4.1
Figure3:ConfigurationofDFIGwindEnergyconversion
systemusingback‐to‐backconverter.
International Journal of Science, Engineering and Technology- www.ijset.in
Table1
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MAHESH CHANAGOND et al.
Citation: 10.2348/ijset05150539
7. SIMULINK MODEL OF
O WITHOU
UT STATCO
OM
LTS
ANDRESUL
ISSN (O): 2348-4098
ISSN (P): 2395-4752
9. APPLICAT
TIONS



Gridsupply
ysystem.
StandaloneePVsystemfforresidentiaalapplication.
UsedinsmaallscaleIndu
ustrialUPS.
10
0. CONCLUSIION
SIMULINKMO
ODELOFWIT
TSTATCOMA
ANDRESULT
TS
Dynamic reacttive power compensatio
on is the most
hnique to inttegrate the DFIG‐based
D
Succcessful tech
wind
farm to the po
ower grid du
uring grid disturbances.
d
This
pap
per has investigated the application of
o a STATCO
OM to
acccomplish uninterrupted o
operation of DFIG‐based wind
farm during fau
ultconditionss. The STATC
COM is conneected
at the point of common cou
upling (PCC) where the DFIG‐
D
g
to proviide a
bassed wind farrm is conneccted to the grid,
volltagesupporttandpreventttheunderv
voltageprotection
fro
omtrippingth
hewindfarm
m.However,w
withoutSTAT
TCOM
theevoltageatP
PCCwillfallbelow0.75pu
u,sothatthe wind
turrbinehastob
betrippedfro
omthepoweernetwork.Ittwas
con
ncluded thatt the STATC
COM producces the requ
uired
reaactivepower tomaintain theWindfarrminserviceeand
pro
oduces a bettter voltage profile independent of wind
speeed variation
n. In additio
on STATCOM
M has a fastt and
sm
mooth response due to tyype of switch
hes used com
mpare
witththeusingo
oftwoanti‐paarallelThyrisstorswithnaatural
com
mmutation in
n case of SV
VC. However, the STATCO
OM is
succh an expenssive applicattion when a large amount of
injeectedreactiv
vepowerisrequiredsuch
haslinetolin
neor
3‐p
phasefault.
RE
EFERENCES
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umar Venayaagamoorthy, and
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oltageinstabiility
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ountofreacttivepowerw
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itrequired
Itwillremov
vesthesag&swell
Itreducesthecomplexity
yofthesystem
m.
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® 7 User’s Gu
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Citation: 10.2348/ijset05150539
ISSN (O): 2348-4098
ISSN (P): 2395-4752
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