Control of Photovoltaic System with A DC-DC BoostConverter Fed
DSTATCOM Using IcosF AlgorithmV. Kamatchi Kannan1* and N.
Rengarajan21Department of Electrical and Electronics Engineering,
K.S.R College of Engineering, K.S.R. Kalvi Nagar,Tiruchengode,
Tamilnadu, India2K.S.R. College of Engineering, K.S.R. Kalvi
Nagar,Tiruchengode, Tamilnadu, IndiaAbstractInthispaper,
athree-phasethree-wireDistributionSTATicCOMpensator (DSTATCOM)which
is fed by Photovoltaic (PV) array or battery operated DC-DC boost
converter is proposedforreactivepower compensation, sourcecurrent
harmonicreductionandloadcompensationinthedistributionsystem.TheproposedDSTATCOMconsistsofathree-legVoltageSourceConverter(VSC)withadcbuscapacitor.
ThePVarrayorbatteryoperatedboost converterisproposedtomaintain the
dc link voltage of the dc bus capacitor for continuous compensation
for the load.
Thispaperpresentstoevaluatetheperformancecomparisonoftwocontrol
strategiesforextractingthereference currents to control the
proposed DSTATCOM. The two control methods are SynchronousReference
Frame (SRF) theory and IcosF algorithm. The switching of VSC will
occur by comparingthe source current with the reference current
using Hysteresis based Pulse Width Modulation (PWM)current
controller. The performance of the DSTATCOMis validated using
MATLABsoftware with
itssimulinkandPowerSystemBlockset(PSB)toolboxes.Thesimulationresultsforthetwocontrolmethods
are compared to validate the superior performance of the
IcosFalgorithm. By comparing, thesource current THD is reduced to
acceptable level 5% of IEEE-519-1992 in IcosF method.Key
Words:DistributionSTATicCOMpensator, PhotoVoltaicArray, Boost
Converter, VoltageSourceConverter,
IcosFControllingAlgorithm1.IntroductionElectricityisaconvenientform
ofenergy for
light-ning,heating,coolingandalsoproducesmotivepowerfor number of
applications. Hence, the annual consump-tion of electricity has
been increasing rapidly throughoutthe world. Thus, the increased
usage of electricity in themodern day world challenges the economic
co-operationsof a power system with a greater focus on power
quality[1,2].Manyresearchershavefocusedonrenewableen-ergysource
basedpower qualityimprovement inthepower distributionsystem[3-5].
Power qualityhascaused a great concern to electric utilities with
the grow-ing use of electronic and computing equipment such as
per-sonalcomputers,uninterruptiblepowersupplies,printers,etc.andothernonlinearloadssuchas
fluorescentlight-ing, adjustable speed drives, heating and lighting
controletc.
Thesenonlinearloadsofpowerelectronicdevicescreatemajorpowerprobleminthedistributionsystemwhich
tends to power quality problem. The various
powerelectronicbaseddevicescalledcustompower
devicesusedtomitigatethepowerqualityproblemshavebeenproposedintheliteraturesurvey[6,7].
Amongthese,DSTATCOM is the most effective device
[8,9].TheDistributionSTATicCOMpensator(DSTAT-COM)isoneoftheshuntconnectedcustompowerde-vice
which injects current through the interface inductorat the Point of
Common Coupling (PCC) to mitigate theJournal of Applied Science and
Engineering, Vol. 16, No. 1, pp. 89-98 (2013) 89*Corresponding
author. E-mail: [email protected] qualityproblems. The
different topologies ofDSTATCOMare reported in the literature such
as a 4-legVSC(VoltageSourceConverter),
threesinglephaseVSC,3-legVSCwithsplitcapacitorDSTATCOM[10,11]. The
proposedDSTATCOMconsists of
three-legVSCwithadcbuscapacitor.TheoperationofVSCissupportedbyadcbuscapacitorwithproperdcvoltageacross
it. For controllingDSTATCOM, andhence togenerate the reference
currents there are number of con-trollers reported in the
literature survey such as instanta-neousreactivepowertheory,
adaptiveneural network,power balance theory, synchronous reference
frame the-oryandIcosFcontrollingalgorithm[4,12-19]. Inthispaper,
the IcosF controlling algorithm is compared withSynchronous
Reference Frame (SRF) theory to validatethe effectiveness of the
IcosFmethod. After tracking thereference currents with the help of
these controllers andbycomparingitwithsourcecurrents,
theswitchingofVSCwill occurandhencecancel out
thedisturbancescausedbythenonlinearloads.
ThePhotoVoltaic(PV)moduleorbatteryoperatedboostconverterisproposedto
maintain the dc bus capacitorvoltageof the VSC forproviding
continuous reactive power compensation, sourcecurrent
harmonicreductionandloadcompensationth-roughout the day. The
proposed system is simulated un-der MATLAB environmentusingSIMULINK
andsim-powersystem tool boxes.2.SystemConfigurationFigure 1 shows
the circuit diagramof the
three-phasethree-wiresystemwhichisusedtofeedthenonlinearload
continuously. The nature of the nonlinear load is tocause
distortion in the current. After connecting the non-linear load,
suddenly there will be a distortion in the dis-tributionsystem. In
order to eliminate these distortions,thecontrol
ofDSTATCOMisachievedbyusingSRFtheoryandIcosFalgorithm.TheDSTATCOMconsistsofsixInsulatedGateBipolarTransistor(IGBT)withantiparallel
diodebasedthree-legVSCconnectedinshuntwith thedc bus capacitor. The
PV module or bat-tery withtheDC-DC boostconverteris
connectedwiththedcbus capacitor, whichis
usedtogiveadesiredvoltageacrossthecapacitorforcontinuouscompensa-tion.
According to the gate pulse given, the switching ofVSCwill occur
whichinjects a currents at the PCC90 V. Kamatchi Kannan and N.
RengarajanFigure 1. Circuit diagram of proposed DSTATCOM.through
the interface inductor Lr.3.PhotovoltaicModulePhotovoltaic (PV) is
one of the major power sources,becoming more affordable and
reliable than utilities [20,21]. Photovoltaic is the method of
converting solar radia-tionintodirect current
electricitywhichgenerates anelectricpower by
usingsemiconductorsthatexhibitthephotovoltaic effect. PV module is
a connected assemblyof photovoltaiccells. Hence, it will be
connectedin pa-rallel toproducehighcurrent
andinseriestoproducehighvoltage. Then,
separatediodesandcapacitorsareconnected to avoid the reverse
currents. Figure 2 showsthe equivalent circuit of a PVcell. It
consists of a currentsource in parallel with a diode which
represents the non-linear impedance of the pn junction and also a
small se-riesandahighparallelintrinsicresistance. Theoutputcurrent
of the solar cell can be represented as(1)where, I =Output current
of solar cell, Iph=Photo-current, Isat = Saturation current of the
diode (10-4A), q=Electroncharge(1.610-19C), V=Voltageontheload,
Rs=Seriesintrinsicresistance, Rp=Parallelin-trinsic resistance, k =
Boltzmans constant (1.38 10-23J/K), T = Cell temperature (K), A=
Ideality factor.To model the PV module in
MATLAB-SIMULINK,theparameters areobtainedfrom SHANSHAN
ULICAUL-175Dphotovoltaic module[22]. Thesolar irradi-ance (G) and
temperature (T) were taken as standard
testconditionswhichare1000Watt/m2and25Crespec-tively.The proposed
DSTATCOM has three operating mo-des. They are (i) Day time excess
power mode, (ii) Daytime mode, (iii) Night time mode.i. Day time
excess power modeThePV
arrayoutputdrivestheboostconverterfedDSTATCOMforcompensatingthesourceaswellasitcharges
the 35V battery.ii. Day time modeTo provide continuous
compensation, if the PV out-put voltage is equal to the boost
converter input, the PVarray drives the boost converter so as to
step-up the vol-tageandmatchthedclinkrequirementoftheDSTAT-COM. The
battery is not charged in this mode.iii. Night time modeDuring the
night time the PV array output is absent,thebatterysupplies
theboost converter for providingcompensation at the night
time.4.ControlofDC Capacitor
VoltagewithBoostConverterBoostconverteralsocalledashighefficiencystep-upconverter
whichhasanoutput DCvoltagegreaterthan its input DC voltage. It
consists of two semiconduc-torswitchesandonestorageelement[23,24].
Figure3shows the circuit diagramof a boost converter. When
theswitch is closed, the inductor gets charged by the PV
orbatteryandstores the energy. The diode blocks thecurrent flowing,
so that the load current remains constantwhich is being supplied
due to the discharging of the ca-pacitor. When the switch is open
the diode conducts andthe energy stored in the inductor discharges
and chargesthecapacitor. Therefore, theloadcurrent remainscon-stant
throughout the operation.Theoutput voltageof theboost converter
canbewritten asControl of Photovoltaic System with A DC-DC Boost
Converter Fed DSTATCOM Using IcosF Algorithm 91Figure 2. Equivalent
circuit of a PV cell. Figure 3. Circuit diagram of a boost
converter.(2)Theboost converterwhichisusedtomaintaintheoutput
voltage constant for all the conditions of
tempera-tureandvariationsinsolarirradiance.Theinputtotheboostconverteris35V
andtheboostedoutputvoltagewillbe670V.Theswitchingfrequencyischosento25KHz.
Theinductanceusedintheboost converter is0.0191
mH.5.SynchronousReferenceFrameTheoryThe block diagram of
Synchronous Reference
Frame(SRF)theory[4]isshowninFigure4.Fromthisalgo-rithm,thereferencesourcecurrentisgeneratedtocon-trol
the proposed DSTATCOM. The load currents, PCCvoltages and dc bus
voltage are sensed as a feedback sig-nal. The load currents from
the a-b-c frame are first con-verted to a-b-0 frame and then to
d-q-0 frame. The equa-tion used for conversion is given
below(3)Theinput tothefirst PIcontroller
istheerrorbe-tweenthereferencedcbusvoltage(
)*Vdcandthesenseddcbusvoltage(Vdc)ofDSTATCOM. Thelosscompo-nent of
the current (iloss) is the output of the PI controller.iloss(n) =
iloss(n-1) + Kpd(Vde(n) Vde(n-1)) + Kidvde(n)(4)where,
KpdandKidaretheproportional andintegralgains of the dc bus voltage
PI controller. Therefore thereference source current is(5)The
actual and reference PCC voltage are fed to
an-otherPIcontrollerforregulatingthePCCvoltage.Thereferencequadraturecurrent
iqristheoutput ofthePIcontroller. This iqr is added to the dc
component of iq.iqr(n) = iqr(n-1) + Kpq(Vte(n) Vte(n-1)) +
Kiqvte(n)(6)where, KpqandKiqaretheproportional
andintegralgainsofthePCCvoltagePIcontroller.Thegeneratedreference
quadrature axis current is(7)Therefore the resultant d-q-0current
are againcon-vertedbacktothereferencesourcecurrent
usingre-verseparktransformation. APWMcontrollerisusedfor
generatingthegatepulsetotheDSTATCOMbyusing the reference and sensed
source current.6.Proposed ICOSF AlgorithmThe block diagram of IcosF
controlling algorithm
isshowninFigure5isusedtoextractthereferencecur-rents[25].Thesourcecurrents(isa,isbandisc),theloadcurrents
(iLa, iLb and iLc), the ac terminal voltages (va,
vb,vc)andthedcbusvoltage(Vdc)aresensed. TheIcosFcontrolling
algorithm is used to generate only the activecomponent of the load
currents i.e. IcosF (where I = am-plitudeoffundamental loadcurrent
andF=displace-ment angle of load current). Hence by combining the
in-phaseandquadraturecomponent,thereferencecurrentcan be
generated.Thethree-phasenonlinear loadcurrent canbeex-pressed as92
V. Kamatchi Kannan and N. RengarajanFigure 4. Control algorithm for
SRF.(8)(9)(10)where,IL(abc)nandF(abc)n=amplitudeandphaseangleof
nthharmonic current in a, b and c phases, IL(abc) = loadcurrent in
a, b and c phases6.1In-PhaseComponentofReferenceSourceCurrentsThe
amplitude of active power component of funda-mental load currents
are given as(11)(12)(13)Hence, theamplitudeof activepower component
offundamentalloadcurrentisextractedatzerocrossingof the unit
template in-phase with PCC voltages.For a balancedsource current,
the magnitude of ac-tive component of reference current can be
given as(14)where, Ismd = output of the dc bus voltage PI
controller.TheerrorindcbusvoltageofVSCatnthsamplinginstant is given
as(15)where, Vdcr(n) = reference dc bus voltage, Vdc(n) = senseddc
bus voltage.Theoutput ofthePIcontroller formaintainingdcbus
voltageof theVSCat thenthsamplinginstant isgiven
as(16)where,KpdandKid=Proportionalandintegralgainofthedcbusvoltage,Vdce(n)andVdce(n-1)=Voltageerrorsin
nthand (n-1)thinstant.The amplitude of the three-phase voltage is
given as,(17)The unit vector in phase with va, vband vcare derived
as(18)In-phasecomponent of referencesourcecurrents areestimated
as(19)6.2QuadratureComponentofReferenceSourceCurrentsTheunitvectors(wa,wbandwc)inquadraturewith(va,vbandvc)canbecalculatedusingthein-phaseunitvectors
(ua, ub and uc) given as(20)Control of Photovoltaic System with A
DC-DC Boost Converter Fed DSTATCOM Using IcosF Algorithm 93Figure
5. Block diagram of IcosF
algorithm.(21)(22)Theamplitudeofreactivepowercomponentoffunda-mental
load currents are given as(23)(24)(25)Thus, theamplitudeof
reactivepower component
offundamentalloadcurrentisextractedatzerocrossingof the unit
template in-phase of PCC voltages.For balanced source currents, the
magnitude of reactivecomponent of reference currents can be given
as(26)where,Ismq=outputoftheacterminalvoltagePIcon-troller.The
error in amplitude of ac terminal voltage at nthsam-pling instant
is given as(27)where, Vtr(n)=reference ac terminal voltage,
Vt(n)=three-phase ac terminal voltage.The output of the PI
controller for maintaining the am-plitude of ac terminal voltage at
the nthsampling instantis given
as(28)where,KpaandKia=proportionalandintegralgainoftheacterminalvoltage,Vde(n)andVde(n-1)=voltageer-rors
in nthand (n-1)thinstant.The quadrature component of reference
source currentsare estimated
as(29)6.3ReferenceSourceCurrentsThereferencesourcecurrentscanbeextractedbythesumofin-phaseandquadraturecomponentsofthereference
source currents and it is given as(30)(31)(32)Thus, these reference
source currents ( , )* * *i i isa sb scandare compared with the
source currents (isa, isb and isc) inhysteresis based PWM current
controllerfor generatinggate signals for IGBT switches in
DSTATCOM.7.Simulation Resultsand DiscussionTheanalysis of PVor
batteryinterfacedtoboostconverter operated DSTATCOM for a
three-phase three-wiresystemhas
beendoneusingMATLABsoftwareusingSIMULINKandPowerSystemBlockset
(PSB)toolboxes. The power system simulation parameters
con-sideredforsimulationisshowninAppendix. Thepro-posedDSTATCOM is
connectedin shuntwith the non-linear load. Firstly, the polluted
source current waveformcreated by nonlinear load is shown in Figure
6(a). The in-jected current waveformfor IcosFalgorithmis shown
inFigure6(b). Thematlabsimulationhasbeendonefor94 V. Kamatchi
Kannan and N. RengarajanFigure 6.
(a)Sourcecurrentwithoutcompensation, (b)In-jected current with
IcosF
algorithm.twodifferentcontrollingmethods.Thecontrollingme-thods are
synchronous reference frame theory and IcosFalgorithm.
Thecompensatedsourcecurrent
waveformforSRFtheoryandIcosFalgorithmareshowninFig-ures7(a)&(b).From
Figure7,thesourcecurrentwithIcosF algorithm is made pure sinusoidal
when comparewith source current with SRF theory. The simulation
re-sultsofPhaseA currentforwithoutDSTATCOM,withSRF theory based
DSTATCOMand IcosF basedDSTATCOMareshowninFigure8. Whennonlinearload
is connected continuously to the power system, theTotal
HarmonicDistortion(THD) of about 23.98%ispresentedin the system.
This THD is reducedto
5.38%whenSRFtheoryisusedtogeneratethefiringpulse.Similarly, when
IcosF is employed, then the THD is fur-ther reducedto1.22%.
Thereforeafter compensation,source current THD is reduced to
acceptable level 5%
ofIEEE-519-1992standard.ThusprovestheefficiencyofIcosFbasedDSTATCOM.
The THDcomparisonforSRFandIcosFmethodsisshowninTable1. Therealpower
andreactivepower waveformsfor
IcosFcon-trollerareshowninFigures9and10.Thetransientre-sponse of
the boost converter is shown in Figure 11.8.ConclusionThe
simulation of the Photovoltaic (PV) array or bat-tery operated
DC-DC boost converter fed three-leg VSCbasedDSTATCOMhas
beencarriedout for reactivepower compensation, source harmonic
reduction and loadcurrent compensationinthe distribution system.
Theboost
converterisusedtostepupthevoltagesoastomatchthedclinkvoltageof
thethree-legVSCbasedDSTATCOM for continuous compensation. The
DSTAT-COMwascontrolledbySRFtheoryandIcosFalgo-Control of
Photovoltaic System with A DC-DC Boost Converter Fed DSTATCOM Using
IcosF Algorithm 95Figure 7. Source current waveform(a) SRF theory,
(b) IcosFalgorithm.Figure 8. Current harmonics and its
THDwaveformfor with-out and with controlling algorithms.Table 1.
Comparison of THD values of DSTATCOMAfter compensationTHD in
allthree phasesBeforecompensationSRF theoryIcosF algorithmPhase A
23.98 5.38 1.22Phase B 23.98 5.65 1.14Phase C 23.98 5.82 1.19rithm.
When comparing SRF theory with IcosF method,the IcosFmethod is
foundeffectivebecausethe sourcecurrent THDis reduced below the
(IEEE-519-1992) per-missiblelimit of5%.
TheMATLABsoftwarewithitssimulinkandPowerSystemBlockset
(PSB)toolboxeshas been used to validate the proposed
system.AppendixAC line voltage: 415 V, 50
HzNon-linearload:ThreephasebridgerectifierwithR=20WAC inductor: 2.5
mHDC bus capacitance of DSTATCOM, Cdc: 7000 mFDC bus voltage of
DSTATCOM: 670 VDC voltage PI controller: Kpd = 0.1, Kid = 196 V.
Kamatchi Kannan and N. RengarajanFigure 9. Real power waveform (a)
Source, (b) Injected, (c)load for IcosF controller.Figure 10.
Reactive power waveform (a) Source, (b) Injected,(c) Load for IcosF
controller.Figure 11. Transient response of boost converter
voltage.PCC voltage PI controller: Kpq = 0.1, Kiq =
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Rengarajan
