Mitigation of Power Quality Issues Due to High Penetration of Renewable Energy Sources in

41 Pages·2017·2.97 MB·English

energies
Review
Mitigation of Power Quality Issues Due to High
Penetration of Renewable Energy Sources in Electric
Grid Systems Using Three-Phase APF/STATCOM
Technologies: A Review
WajahatUllahKhanTareen1,2,*,MuhammadAamir3,SaadMekhilef1 ID,MutsuoNakaoka1,
MehdiSeyedmahmoudian4 ID,BenHoran5 ID,MudasirAhmedMemon1 ID
andNaumanAnwarBaig2
1 PowerElectronicsandRenewableEnergyResearchLaboratory(PEARL),Departmentof
ElectricalEngineering,UniversityofMalaya,KualaLumpur50603,Malaysia;[email protected](S.M.);
[email protected](M.N.);[email protected](M.A.M.)
2 DepartmentofElectricalEngineering,InternationalIslamicUniversity,Islamabad44000,Pakistan;
[email protected]
3 DepartmentofElectricalEngineering,BahriaUniversity,Islamabad44000,Pakistan;
[email protected]
4 SchoolofSoftwareandElectricalEngineering,SwinburneUniversityofTechnology,VIC3122,Australia;
[email protected]
5 SchoolofEngineering,DeakinUniversity,WaurnPonds,VIC3216,Australia;[email protected]
* Correspondence:[email protected]@gmail.com;Tel.:[phone]
(cid:1)(cid:2)(cid:3)(cid:1)(cid:4)(cid:5)(cid:6)(cid:7)(cid:8)(cid:1)
(cid:1)(cid:2)(cid:3)(cid:4)(cid:5)(cid:6)(cid:7)
Received:20April2018;Accepted:23May2018;Published:7June2018
Abstract: This study summarizes an analytical review on the comparison of three-phase static
compensator(STATCOM)andactivepowerfilter(APF)invertertopologiesandtheircontrolschemes
usingindustrialstandardsandadvancedhigh-powerconfigurations. Transformerlessandreduced
switchcounttopologiesaretheleadingtechnologiesinpowerelectronicsthataimtoreducesystem
costandoffertheadditionalbenefitsofsmallvolumetricsize,lightweightandcompactstructure,
andhighreliability. Adetailedcomparisonofthetopologies,controlstrategiesandimplementation
structuresofgrid-connectedhigh-powerconvertersispresented. However,reducingthenumber
ofpowersemiconductordevices,sensors,andcontrolcircuitsrequirescomplexcontrolstrategies.
Thisstudyfocusesondifferenttopologicaldevices,namely,passivefilters,shuntandhybridfilters,
andSTATCOMs,whicharetypicallyusedforpowerqualityimprovement. Additionally,appropriate
control schemes, such as sinusoidal pulse width modulation (SPWM) and space vector PWM
techniques, are selected. According to recent developments in shunt APF/STATCOM inverters,
simulationandexperimentalresultsprovetheeffectivenessofAPF/STATCOMsystemsforharmonic
mitigationbasedonthedefinedlimitinIEEE-519.
Keywords:FACTSdevices;activepowerfilter;staticcompensator;controlstrategies;grid-connectedconverter;
SPWM;SVM
1. Introduction
Electricityisanindicationofcomfortablelife,andthedemandforthisenergysourceisincreasing.
Developmentinpowerindustriesincreasesthenumberoflinearandnonlinearloadsineachsystem.
In nonlinear load conditions, many solid-state switching converters draw reactive power and
current harmonics from the AC grid. These nonlinear loads generate harmonics, which produce
disturbanceanddirectlyinfluencehumanlife. Nowadays,eachpieceofequipment,powersystem,
Energies2018,11,1491;doi:10.3390/en11061491 www.mdpi.com/journal/energies
Energies2018,11,1491 2of41
andservice,suchasfurnaces,computerpowersupplies,communicationsystems,renewableenergy
systems,electricalpowergenerations,andhigh-voltagesystems,requiresacontinuouspowersupply.
Researchersanddifferentpowercompaniesarecontinuouslyexploringsolutionstopowerquality
problems[1],suchasharmonics,systemimbalance,loadbalancing,excessneutralcurrent,andpower
systemgridintrusions. Evidently,theincreasingdemandfornonlinearloadsproducesharmonics
in the power system, thereby resulting in poor power quality. Flexible AC transmission system
(FACTS)devices,suchasstaticcompensators(STATCOMs)andactivepowerfilters(APFs),arethe
mostdominanttechnologiesavailableforindustrialandcommercialpurposesandaredeemedthe
solutiontothispowerqualityproblem[2–4].
Inthepast,harmonicgridproblemsweresolvedusingpassivefilter(PF)devices[5].Thesefilters,
togetherwithlow-costsolutionsforpowerqualityissues,areconsideredtheinitialstageofdevelopment
in mitigating current harmonics [6,7]. APFs are considered the second stage of development and
an effective solution to overcome the limitation of PFs. However, the size, cost, and rating of APFs
are considerably increased by the increasing demand for power system capacity [8,9]. To overcome
theissuesofshuntAPFs,athirdstageofdevelopmentconsistsofhybridpowerfilter(HPF)devices,
which comprise hybrid combinations of PFs with shunt APFs [10]. Furthermore, HPF technology
is evaluated in the fourth stage of development as a unified power quality conditioner (UPQC) [11].
Previousresearch[12,13]onpowerqualityimprovementhasledtoimportantdevelopmentsinFACTS
devices,namely,thestaticvolt-amperereactive(VAR)compensator(SVC),dynamicvoltagerestorer(DVR),
anddistributionSTATCOM(DSTATCOM)[14–16].Suchimprovementscompensateforthemitigation
problemsrelatedtopowerquality,includingpoorloadpowerfactor,loadharmonics,imbalancedload
conditions,andDCoffsetinloads.
Many shunt APFs are impractical for use for high-power-rating components.
Therefore, transformerless and reduced switch count topologies are the leading technologies in
power electronics that aim to reduce system cost and concurrently provide such benefits as small
volumetricsize,lightweight,remarkablycompactstructure,andhighreliability.ModernAPFtopologies
are rapidly replacing the standard ones because of their effective performance, efficient response,
andfavorablecostandsizeattributes.Nevertheless,reducingthenumberofpowersemiconductordevices,
powerconversioncircuits,sensors,andcontrolcircuitsrequirescomplicatedcontrolstrategies[17,18].
Despitetheimportanceofdecreasingthenumberofpowercomponents,nostudyfocuseson
reducedswitchcounttopologiesandcomplexcontrolstrategiesinshuntAPFsandSTATCOMs[19].
The present study focuses on the comprehensive review of advanced reduced switch count
topologies,specificallySAPFsandSTATCOMs,controlschemesforreconfigurablevoltage-fed-type
inverters (VSIs). The control structures and possibilities of implementing grid-connected power
convertersindifferentreferenceframesarediscussedandcompared. Furthermore,theoverviewof
thecompletecontrolschemesandenhancedcontrolstrategies,includingthemostappropriatecontrol
strategies, such as sinusoidal pulse width modulation (PWM) and space vector PWM techniques,
arepresented. ComparisonsandcharacteristicsofoperatingreducedswitchandlegcountVSIsare
concludedaccordingtoawell-surveyedliteraturesummary.Finally,asummaryandrecommendations
forfutureresearcharehighlighted.
2. HarmonicsandInternationalStandards
Theamountorpenetrationofharmonicshadpreviouslybeenlargelyincreasing,therebyaffecting
theperformanceandefficiencyofthesystem[20]. Harmonicsaregeneratedinthesystembecause
of non-linear or critical loads. Harmonics exist in a power grid or power distribution network in
theformofseriesandparallelresonancesgeneratedbyharmoniccurrentloads,whichincreasethe
sourcevoltageandcurrenttotalharmonicdistortion. However,moderntechnologiesinpowerquality
improvementmitigatecurrent,voltage,activeandreactivepower,voltagezero-crossing,andother
issues,suchasharmonics,voltagesagsandswells,notchesandflickers,spikesandglitches,andvoltage
imbalance[21].
Energies 2018, 11, x FOR PEER REVIEW 3 of 41
Energies2018,11,1491 3of41
other issues, such as harmonics, voltage sags and swells, notches and flickers, spikes and glitches,
and voltage imbalance [21].
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PFsaregenerallycoupledwithathyristor-controlledreactortoimproveharmonicmitigationand
reactivecurrentcomponentcompensation. Someofthekeypracticallimitationsareasfollows:
Energies2018,11,1491 4of41
- PFsrequireaseparatefilterforeachharmoniccurrent,andtheirfilteringrangeislimited.
- PFsallowonlyonecomponent(eitheraharmonicorafundamentalcurrentcomponent)topass
atatime.
- Largeamountsofharmoniccurrentsaturateoroverloadthefilterandcauseseriesresonancewith
theACsource,therebyresultinginexcessiveharmonicflowintothePFs.
- PFsamplifysource-sideharmoniccontentsbecauseoftheimpedanceinthesourceofparallel
andseriesnegativeresonancesbetweenthegridandthefilter[29].
- The design parameters of PFs in an AC system depend on the system operating frequency,
whichchangesarounditsnominalvalueaccordingtovariableloadconditions.
- PFsonlyeliminatefrequenciestowhichtheyaretuned,thusresultinginlimitedcompensation,
largesize,andtuningissues.
3.2. ShuntAPFs
APFswereintroducedandinvestigatedasasolutiontothelimitationsofPFs. AnAPFconsistsof
an active switching device and passive-energy storage devices, such as inductors and capacitors,
which provide superior compensation characteristics, including voltage and current harmonics,
voltageimbalancecompensationforutilities, andcurrentimbalancecompensationforconsumers.
APFsmitigatereactivepower,neutralcurrent,changinglineimpedance,frequencyvariation,voltage
notch,suddenvoltagedistortion,transientdisturbance,andvoltagebalanceandimprovethepower
factorofvoltageandcurrentinmedium-powersystems[30].
Different APF topologies and control methodologies have been proposed and progressively
investigatedasaperceivedsolutiontocriticalissuesinhigh-powerloadapplications[31,32]. APFsare
classifiedintomanycategoriesinaccordancetosubsequentmeasures. ThecircuitstructureofanAPF
commonlyincludesavoltage-sourcePWMinverterwithaDC-linkcapacitor. Evidently,current-source
APFsaresuperiorintermsofcompensatingcurrentdynamics. However,voltage-sourceAPFsperform
betterthancurrent-sourceAPFsintermsoffilterlossesandPWMcarrierharmonicreduction. Table1
showsthesurveyresultsforshuntandseriesAPFs[11].
Table1.Comparisonofactivepowerfilters(APFs)inpowerqualityimprovementtechniques.
Category ShuntAPF SeriesAPF
Connectionwithsystem Parallelwithdistributionsystem Connectedinserieswithdistributionsystem
Action Currentsource Voltagesource
Voltageratedatfullloadrating
Currentratedatfullloadrating
Currentratingcomprisespartially
Filterrating Voltageratingispartiallycompensated
harmonicandpartlyreactive
voltagecomponent
currentcomponents
Mitigationofvoltageharmonics,sag,andswells
Harmonicloadcurrentfiltering
Mitigationofcurrentharmonics
Functioning Compensationforreactivecurrent
Compensationofreactivecurrent
Mitigationofcurrentunbalance
Mitigationofcurrentunbalances
Sourceimpedanceexertsnoeffect
Characteristics Sourceandloadimpedanceexertnoeffecton
oncompensationforcurrent
ofcompensation compensationforvoltagesourceloads.
sourceloads.
Injectedcurrentmaycauseexcess
Alow-impedanceparallelbranch(forimprovementof
Application currentwhenappliedtoavoltage
powerfactor)whenworkingwithcurrentsourceload
sourceload.
Nonlinear/inductivecurrent
Nonlinear/capacitivevoltagesourceloadsor
Loadconsidered sourceloadsorharmonics
harmonicscontainingvoltagesourceloads
containingcurrentsourceloads
ThebasiccompensationprincipleofshuntAPFsiseliminatingthecurrentharmonicsgeneratedby
criticalloads. Generally,APFsareinstalledinashuntpositionnearthenonlinearloadtocompensate
Energies 2018, 11, x FOR PEER REVIEW 5 of 41
Energies2018,11,1491 5of41
The basic compensation principle of shunt APFs is eliminating the current harmonics generated
by critical loads. Generally, APFs are installed in a shunt position near the nonlinear load to
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dsienpuicstoeiddainl, Fasig duerpei2ct[e2d8 ]i.n Figure 2 [28].

Figure 2. Basic compensation principle of the SAPF.
Figure2.BasiccompensationprincipleoftheSAPF.
3.3. STATCOM
3.3. STATCOM
FACTS devices are increasingly required in modern transmission systems for high-power
FACTS devices are increasingly required in modern transmission systems for high-power
transfers [34]. Two types of FACTS devices, namely, SVCs and STATCOMs [35], can restore active
transfers[34]. TwotypesofFACTSdevices,namely,SVCsandSTATCOMs[35],canrestoreactive
power current and dynamic reactive power compensation [36]. These devices consist of the modular
powercurrentanddynamicreactivepowercompensation[36]. Thesedevicesconsistofthemodular
unit of the voltage source converter (VSC) equipped with insulated-gate bipolar transistors (IGBTs)
unitofthevoltagesourceconverter(VSC)equippedwithinsulated-gatebipolartransistors(IGBTs)
for rapid switching and controlling using the PWM scheme. A STATCOM is a shunt device that is
forrapidswitchingandcontrollingusingthePWMscheme. ASTATCOMisashuntdevicethatis
connected with PCC to provide voltage support and active and reactive power, increase transient
connected with PCC to provide voltage support and active and reactive power, increase transient
stability and improve damping. A brief detailed classification of the FACTS devices is shown in
stability and improve damping. A brief detailed classification of the FACTS devices is shown in
Figure 3 [37,38].
Figure3[37,38].
At the distribution level, STATCOM devices are operated as an active filter to achieve harmonic
Atthedistributionlevel,STATCOMdevicesareoperatedasanactivefiltertoachieveharmonic
filtering, power factor correction, neutral current compensation, and load balancing [39]. APFs are an
filtering,powerfactorcorrection,neutralcurrentcompensation,andloadbalancing[39]. APFsare
advanced technology that offers faster dynamic response, smaller size, lower system cost, and higher
anadvancedtechnologythatoffersfasterdynamicresponse,smallersize,lowersystemcost,andhigher
performance under low-voltage oscillations than SVC devices. Energy storage devices improve
performance under low-voltage oscillations than SVC devices. Energy storage devices improve
power quality and provide rapid controllable transient response to the bus voltage by injecting or
powerqualityandproviderapidcontrollabletransientresponsetothebusvoltagebyinjectingor
absorbing the corresponding amount of reactive power into or from the system. Such devices
absorbingthecorrespondingamountofreactivepowerintoorfromthesystem. Suchdevicesmaintain
maintain the minimum values of amplitude, phase, and frequency to control voltage flickers during
the minimum values of amplitude, phase, and frequency to control voltage flickers during fault
fault events. In addition, the inconsistent flow of reactive power between the supply power grid and
events. Inaddition,theinconsistentflowofreactivepowerbetweenthesupplypowergridandthe
the loads is prevented [40]. Table 2 presents the best available solution for the specific compensation
loads is prevented [40]. Table 2 presents the best available solution for the specific compensation
challenges [41–43].
challenges[41–43].
Energies2018,11,1491 6of41
Energies 2018, 11, x FOR PEER REVIEW 6 of 41
Conventional FACTS-Devices
(switched) (fast, static)
Voltage Source
R, L, C, Transformer Thyristor-Valve
Converter (VLC)
Static Synchronous
Shunt Switched Shunt Static Var
Compensator
Devices Compensation (L, C) Compensation (SVC)
(STATCOM)
TCR - Thyristor Controlled Reactor
Shunt Capacitive Compensation
TSR - Thyristor Switched Reactor
Shunt Inductive Compensation
TSC - Thyristor Switched Capacitor
MSC -Mechanically Switched Capacitor
Static Synchronous
Series Switched Series Thyristor Controlled Series
Series Compensator
Devices Compensation (L, C) Compensator (TCSC)
(SSSC)
TCSR - Thyristor Controlled Series Reactor
TSSC - Thyristor Switched Series Capacitor
TSC - Thyristor Switched Capacitor
Series Capacitors
Unified/Interline Power
Shunt and Series Phase Shifting Dynamic Flow
Flow Controller
Devices Transformer Controller (DFC)
(UPFC/IPFC)
STATCOM + SSSC coupled via a common DC voltage link.
Shunt and Series HVDC Back to Back HVDC VSC Back to Back
Devices (HVDC B2B) (HVDC-VSC B2B)

Figure 3. Overview of the major FACTS devices.
Figure3.OverviewofthemajorFACTSdevices.
The following sections discuss the high penetration of renewable energy sources in the electrical
power grid system for reactive power compensation and harmonic mitigation problems.
Thefollowingsectionsdiscussthehighpenetrationofrenewableenergysourcesintheelectrical
powergridsystemforreactivepowercompensationandharmonicmitigationproblems.
3.3.1. Multilevel PV-STATCOM Applications in Grid-Connected Systems
3.3.1. MultTilheev ecloPnVv-eSnTtiAonTaCl OtMwoA- papnldic atthiorenes-lienveGl riidn-vCerotnern eccotendfigSuyrsatteiomnss are not suitable for
photovoltaic (PV) applications in high-power-rating systems [44,45]. Many configurations are
Theconventionaltwo-andthree-levelinverterconfigurationsarenotsuitableforphotovoltaic(PV)
inefficient in harvesting maximum power, have a low utilization factor, and require a large AC filter
applicaatt itohnes oinutphuigt hf-opr ohwigehr -rpaotwinegr sqyusatleitmy. sA[4 g4r,4id5-]c.oMnnaenctyedc osnofilagr uPrVat ipoonwsearr ecoinndeiftfiiocnieinngt iinnvheartrevre sting
maximcounmvepntoiownearll,yh raevqeuiarelso wa turatnilsifzoarmtioern ffoarc tgoarlv,aannidc irseoqlautiioren atol amrgatechA tChefi gltreidr avtoltthaegeosu wtpituht tfhoer high
powerinqvueratleirt yo.utAputg. rTidhe-c coonnnceepctt eodf sPoVl-aSrTAPTVCOpoMw seyrstceomnsd iist iroenquinirgedi ntvo erretgeurlactoe nrveaeln atinodn arelalyctirveeq uires
atranspfoowrmere trhfrooruggha ltvhaen ciocnivsoerltaetri oanndto mmitaigtacthe tthhee glirmiditavtioolntas goefs cwonivthentthioenianl vPeVrt einrvoeurtteprsu t[.46T]h. eThceo ncept
cascaded H-bridge (CHB) inverter in multilevel PV-STATCOMs is an advanced configuration for
ofPV-STATCOMsystemsisrequiredtoregulaterealandreactivepowerthroughtheconverterand

mitigate the limitations of conventional PV inverters [46]. The cascaded H-bridge (CHB) inverter
in multilevel PV-STATCOMs is an advanced configuration for high-solar-power applications and
Energies2018,11,1491 7of41
has isolated input DC sources and no additional DC power source requirement for STATCOM
devices[47,48].
Table2.Comparisonoftheadvancedtechnologysolutionforthereactivepowercompensationchallenges.
SVCPLUS Synchronous
Technology MSC(DN)/MSR SVC HybridSTATCOM
(STATCOM) Condenser
Provisionof
short-circuit
Fastdynamic Fastdynamic Fastdynamic power,inertia,
Compensationof compensationand compensationand compensationand dynamic
Application
predictableload voltagerecovery voltagerecovery voltagerecovery compensation,
duringfaults duringfaults duringfaults andvoltage
recovery
duringfaults
Continuous
Switching Limitedswitchingonly Unlimitedswitching Unlimitedswitching Unlimitedswitching
operation
V/I Good Superiorunder Superiorunder Good
Noresponse
characteristic overvoltageperformance voltageperformance voltageperformance overloadcapability
AdjustablebyMSC Adjustableby Symmetricaloutput: Unsymmetricaloutput: Adjustableby
Controlrange
andMSRranges branchranges Adjustablerange Adjustablerange generatorsize
Inbuiltredundancyin
Inbuiltredundancyin Inbuiltredundancy Depending
Redundancy Noinbuiltredundancy powermodulesandin
thyristorvalves inpowermodules onsolution
thyristorvalves
TCRissourceof Harmonically Harmonically
Susceptible Notsusceptible
Harmonics harmonics—AC self-compensated—no self-compensated—no
toharmonics toharmonics
filtersrequired filtersrequired filtersrequired
2–5cycles,depending
Responsetime 2–3cycles 1.5–2cycles 1.5–2cycles seconds
onbreaker
Operation Verylow,depending Low,primarilyvisual Verylow,primarily Verylow,primarily Low,inspection
andmaintenance onbreaker inspection visualinspection visualinspection every3–4years
Lossesat0
0.3%oftheratedoutput 0.15%oftherated 0.15%oftherated ~1%oftherated
MVAR 0%
power outputpower outputpower outputpower
outputpower
Availability >99% >99% >99% >99% >98%
Inthestudyof[49], aPVinverteroperatedasaSTATCOMfortheoptimaluseofthesystem,
provided active power during daytime, when solar energy is available, and provided reactive
powerwhenirradiationwaslow. Similarly,inseveralstudies,PVinvertersoperatedasSTATCOMs
duringdaytimetoprovidethereactivepowercompensationinadistributionutilitynetwork[50,51].
However,theperformanceofthesystemdependsontheratedcapacityoftheinverter,theconstant
DC-linkvoltage,andthemaximumpowerpoint(MPP)instanttimetrackinginthedistributionutility
network[52]. Inthestudyof[53],aPV-STATCOMwasadoptedwithactivepowerfilteringagainst
powerqualityissuesinthePVsystem,suchastransientvoltages,voltageflickering,andharmonics.
Therefore,aPV-activefilter-STATCOMisdesignedforharmonicmitigationandcontinuousregulation
ofreactivepowerforgridapplications.
Inthestudyof[54],aSHAPFbasedonacascadedH-bridgemultilevelinverter(CHB-MLI)was
testedforhigh-powerPVapplicationswithreducedfiltersize,maximizedPVcellpowerextraction,
andimprovedutilizationfactorthroughreactivepowercompensation. Withadvancedlevelcontrols,
thePV-STATCOMsystemcanbeadoptedforactivefilterapplications. Furthermore,PV-STATCOM
invertersimprovethestabilityofvoltage-sensitiveloadsduringgridfaultconditions[55]. Inthestudy
of[56,57],aPV-STATCOMwithoutaDC–DCconverterwastested;reducedswitchcountconfigurations
controlledtheDC-linkvoltagethroughtheoperationofSTATCOM,andthePV-STATCOMsystem
improvedtheutilizationfactorandpowerqualitybycompensatingthereactivepowerreferencein
therangeof0–1P.U.withreducedsystemsizeandcost. Instudy[58]emphasizedthenecessityof
multifunctionPVinvertersanddifferentactiveandpassivecontrolsinresolvingpowerqualityissues.
Furthermore, three different controls, namely, abc, d–q, and alpha–beta controls, were discussed
with a comparison of suitable topologies on the basis of consumer applications [59]. A brief
review of anti-islanding techniques and power quality issues were discussed in the study of [60].
Energies2018,11,1491 8of41
Acomprehensivereviewofpowerquality,stability,andprotectionandthenegativeimpactsofPV
systemsduetovoltageparametercontrolandstaticcompensationtechniquesinthepowerdistribution
gridwerediscussedinthestudiesof[61,62]. Meanwhile,[63]investigatedaCHB-basedinverterand
modularmultilevelconvertersforSTATCOMapplicationsandcomparedreactivepowercontrolsfor
largePVapplications[64].
IndependentDClinksmakeCHB-basedinvertersasuitablecandidateforPVandSTATCOM
applicationsbecauseofthefollowingadvantages: (a)asmallfilterproduceslowTHD;(b)anoutput
transformerisunnecessarybecauseoftheincreasednumberofmodules,whichextendtheoutput
voltage level with low rating; (c) the cost and size of the power components are reduced by the
low-voltage-leveloperation;(d)thecostandsizeofthepowercomponentsandauxiliaryequipmentare
reducedbecausethevoltagelevelsineachmodulearelow. Amodifiedselectiveharmonicelimination
PWM(SHE-PWM)techniquewasdiscussedinthestudyof[65]foratransformerlessSTATCOMthat
wastestedusingtheCHBconfigurationforgridapplications[66,67]. TheindependentDC-linksources
inPV-STATCOMapplicationsreducesystemcost. Therefore,theCHB-MLImultilevelconfiguration
with phase-shifted modulation techniques is suitable for large-scale systems [68]. An advanced
selectiveswappingschemewasadoptedina154-kV21-levelCHBinverter-basedSTATCOMsystem
toreducetheissueofDCripplevoltage[69].
In the study of [70,71], a sinusoidal voltage waveform was achieved using SHE-PWM.
Furthermore,inthestudyof[72],thesensorsattheDC-linkswereeliminatedbyadoptingthecontrol
duetothenonlinearparameteruncertaintiespresentedfortheCHB-MLIinthestudy. Zero-sequence
voltage and negative sequence current schemes were tested under one- and two-line faults for
aCHB-basedSTATCOMtoreduceswitchinglosses[73]. Anotheractivepowerbalancecontrolscheme
was tested to regulate the reactive power for a CHB inverter; the positive- and negative-sequence
controlcomponentsweremonitoredforDC-linkvoltagebalanceunderthebalancedorimbalanced
conditionsofthegridvoltage[74]. Therefore,aPV-STATCOMinverteroperatesontwoAC-source
controllersatthesamefrequencylevel. Thesourceswithhighvoltageamplitudeprovidereactive
powertotheothersources.Inthisstudy,themagnitudeoftheinverteroutputdependsonthereference
reactivepowersignal. Similarly,thesourceswithleadingphaseangleprovideactivepowertothe
othersources. Inconclusion,theSTATCOMcanbeusedtoeliminateharmonicsandcompensatefor
laggingandleadingVAR.
STATCOMdevicesaimtoproviderapidloadvoltageregulationalongthecontrollableexchange
ofreactivepowerinthesystem,aswellasachievepowerqualityimprovement,reactivepowercontrol,
voltage regulation, power swing, and improvement of transmission line capacity during power
systemfaults[75]. However,manyotherpowerconverters,suchasDSTATCOMs[76],UPQCs[77],
and DVRs [78], also eliminate harmonics and imbalance issues in the generation and utilization
of the system [79,80]. A DSTATCOM is a synchronous voltage generator or a static synchronous
compensatorwithacouplingtransformer,aninverter,andanenergystoragedevicesimilartothatof
theconfigurationofaSTATCOM.TheDSTATCOMinjectsorabsorbsuninterruptedcapacitiveand
inductivereactivepowerintoorfromthedistributionsystem[81].
The AC-controllable VSC can be used as a multifunction STATCOM with modified control
structuretoprovideharmonicelimination,reactivepower,andloadimbalancecompensationunder
nonlinear loads and non-ideal main voltage conditions. The potential applications of STATCOM
devicessuchasAPFs,aretestedforactivepowerfiltering,andreactivepowersuppliesareconsiderably
attractivetodistributionengineers[82]. Table3demonstratesreactivepower-compensatingdevices
againstvariouscontrolparametersthatarerelatedtothesaiddevices[83,84]. Theseparametersare
automaticvoltagecontrol,STATCOM,SVCandthyristor-controlledseriescapacitor.
Energies 2018, 11, x FOR PEER REVIEW 9 of 41
The AC-controllable VSC can be used as a multifunction STATCOM with modified control
structure to provide harmonic elimination, reactive power, and load imbalance compensation under
nonlinear loads and non-ideal main voltage conditions. The potential applications of STATCOM
devices such as APFs, are tested for active power filtering, and reactive power supplies are
considerably attractive to distribution engineers [82]. Table 3 demonstrates reactive
Energies2018,11,1491 9of41
power-compensating devices against various control parameters that are related to the said
devices [83,84]. These parameters are automatic voltage control, STATCOM, SVC and thyristor-
controlleTdab sleer3ie.sC coamppaacriitsoorn. ofcontrolparametersaffectedbyreactivepower-compensatingdevices.
Parameters StaticCapacitors Capacitor&ReactorBank AVC STATCOM SVC TCSC UPFC
Table 3. Comparison of control parameters affected by reactive power-compensating devices.
Reactivepower ** *** ** **** *** ** ****
Parameters Static Capacitors Capacitor & Reactor Bank AVC STATCOM SVC TCSC UPFC
Activepower ** ** * * **
Reactive power ** *** ** **** *** ** ****
Voltagestability ** ** ** **** *** *** ****
Active power ** ** * * **
VVolotlatgaegec osntatbroillity ** ** ** ** ** ** ****** ** **** ** **** * ********
FVlicoklteargceo cnotnrotrlol ** ** * ** ****** ** **** ** ** ********
Flicker control * **** *** ****
Harmonicreduction * ****
Harmonic reduction * ****
Powerflowcontrol *** ****
Power flow control *** ****
OOscsiclillalatitoionnd damamppiningg * * **** ** ** ** ***** * ********
HHigighh nnuummbbeerr ooff ““**””i sisp rperfeerfererdre.d.
3.3.2. Wind Turbine STATCOM (WT-STATCOM) Applications in Grid-Connected Systems
3.3.2. WindTurbineSTATCOM(WT-STATCOM)ApplicationsinGrid-ConnectedSystems
The evolution of power electronic technology has created two generation of FACTS devices in
TheevolutionofpowerelectronictechnologyhascreatedtwogenerationofFACTSdevicesin
wind farms. These devices are classified into two generations, namely, the old thyristor-type and the
windfarms. Thesedevicesareclassifiedintotwogenerations,namely,theoldthyristor-typeandthe
advanced VSC-type [38,85], and are used to mitigate voltage instability, reactive power
advancedVSC-type[38,85],andareusedtomitigatevoltageinstability,reactivepowerproblems[86],
problems [86], and harmonic distortion to improve the power quality of the network [87].
andharmonicdistortiontoimprovethepowerqualityofthenetwork[87].
The thyristor-based FACTS devices in wind farms are SVCs. The main structure of the SVC
The thyristor-based FACTS devices in wind farms are SVCs. The main structure of the SVC
consists of capacitors and inductances that are controlled by thyristors. The STATCOM consists of a
consistsofcapacitorsandinductancesthatarecontrolledbythyristors. TheSTATCOMconsistsof
main component of modular VSC, which is equipped with IGBTs that are controlled by PWM. Figure
a main component of modular VSC, which is equipped with IGBTs that are controlled by PWM.
4 shows the structure of an induction generator-based wind turbine and a STATCOM that is
Figure 4 shows the structure of an induction generator-based wind turbine and a STATCOM that
connected to a grid and a wind turbine terminal [88]. A coupling transformer is installed to provide
is connected to a grid and a wind turbine terminal [88]. A coupling transformer is installed to
galvanic isolation and to control the flow of reactive power during steady- and transient-state
providegalvanicisolationandtocontroltheflowofreactivepowerduringsteady-andtransient-state
conditions [88]. With these modified control strategies, the STATCOMs are superior to other
conditions[88]. Withthesemodifiedcontrolstrategies,theSTATCOMsaresuperiortoothermitigation
mitigation methods, such as SVCs and series-saturated reactors during normal and transient
methods,suchasSVCsandseries-saturatedreactorsduringnormalandtransientconditions[89].
conditions [89].
VPCC Vgrid Grid
X
L z
s
z
Transformer f
Wind turbine V, Is
VPCC
VSC
Control
system
ISTATCOM
Vdc
C
Capacitor Inductor
STATCOM

FFiigguurree 44.. TThhee ssttrruuccttuurree ooff tthhee WWTT bbaasseedd FFSSIIGG ccoonnnneecctteedd ttoo SSTTAATTCCOOMM..

Anenergystoragesystem(ESS)withSTATCOMprovidesanewrobustdecentralizedcontrol
operation for high-wind-power applications [90]. The controller operates on the linear quadratic
output–feedback method and provides a promising solution for high-wind-power systems [91].
Energies2018,11,1491 10of41
Another robust STATCOM control was presented [92], and it controls the active and reactive
powerandpitchangleofwindturbineinductiongeneratorsforimprovedlow-voltageridethrough
(LVRT)capability. Thelimitationofthiscontrolistheenhancedtorqueproducedinsidetheinduction
machine,whichproducesahighmaximumtorqueandstressesthedrivetrainduringfaultrecovery.
Therefore, an advanced indirect torque control (ITC)-based control is used to limit the maximum
torqueoftheSTATCOMcontroller[93].
Inanotherstudy[94],theSTATCOMandSVCwerecomparedintermsofLVRTdevelopment.
TheSTATCOM,whichis15%cheaperthantheSVC,isthemoreeconomicalsolution. Inconclusion,
SVC devices have limited capabilities at low voltage levels. However, advanced STATCOMs can
maintain reactive power output over a wide range of voltages with a smaller structure and faster
controlresponsethanSVC[94].
Generally, a STATCOM FACTS device is installed for an entire wind farm [86,95], multilevel
fullH-bridgewhereasanSVC-typethyristor-controlledresistor(TCR)deviceisinstalledforasingle
windturbine. Besidesreactivepowerregulation,theseFACTSdevicesprovideisolationandfirewall
protectiontowindturbinesagainsttheeffectsofgriddisturbancesandconnectthewindturbineswith
lowX/Rratioorweakgrids[96]. Astudy[97]thereforeusedahybridelectrolyserandfuelcellsystem
tocontroltheramprateofwindturbinepowerandenhancethevoltagequalityatthePCC.Thesystem
stoppedtheinrushpowerflowsintheelectrolyserandthefuelcellpathbycontrollingthefrequent
start-upandshutdownofthefuelcellstacks,whichareeffectsassociatedwiththegrid-connected
windfarms. STATCOM-basedcontrolmethods[98]areadoptedtoregulategridreactivepowerand
maintainasuitablelevelofvoltagesagonthegridandpreventthewindturbinefromdisconnecting
fromthegridduringfaults. TheunifiedpowerflowcontrollerisoneofthemostadvancedFACTS
devices used in wind applications and consists of two power converters. One converter controls
asaSTATCOMandtheotheroperatesasastaticsynchronousseriescompensatortocontrolpower
flow with the limitation of high cost [99,100]. During grid faults, the reactive power demand can
becompensatedbyanexternaldynamicSTATCOMandanESS[101],suchashybridbattery–super
capacitorenergystorage[102]. TheESSsystemwithSTATCOMprovidesapromisingsolutionfor
windpowersystemapplications[91].
4. StandardClassificationofShuntAPFs
Generally,APFsareclassifiedintotwocategories,namely,DCandACpowerfilters.DC–APFsare
designed with a thyristor configuration for high-power drives [55] and high-voltage DC systems.
An AC–APF configuration consists of active solutions, such as active power quality and line
conditioners and instantaneous reactive power compensators for current and voltage harmonics.
Shunt APFs are classified under three categories, namely, topology-, converter-, and phases-type
configurations. Topology-typefilterscanbedelegatedasshunt,series,andhybridAPFs(HAPFs),
asshowninFigure5.
Converter-typefiltersareclassifiedasVSIandcurrent-fed-typeinverters(CSI).Figure6aillustrates
theconfigurationoftheCSI–APF,abridgestructuretopologythatconsistsofadiodethatisconnectedin
serieswithasemiconductorself-commutatingswitchingdevice(IGBT)[28].Thediodeisusedforreverse
voltageblockingwiththeinterfacingDCenergystorageinductorinthesystem.Thistopologyshowshigh
valuelossesandrequireshigh-valueinstalledACpowercapacitors.Furthermore,thedynamicresponse
timeisslow,andadditionalcomplexcontrolisrequiredtoregulatetheharmoniccurrent.