Table Of ContentAPOWERQUALITYSOLUTIONWITHLOWINVERTERRATINGS
BY
RAY-SHYANGLAI
ADISSERTATIONPRESENTEDTOTHEGRADUATESCHOOL
OFTHEUNIVERSITYOFFLORIDAINPARTIALFULFILLMENT
OFTHEREQUIREMENTSFORTHEDEGREEOF
DOCTOROFPHILOSOPHY
UNIVERSITYOFFLORIDA
1996
Inmemoryofmymother
&
TomywifeShwu-Yuann
and
mydaughterKaren
ACKNOWLEDGMENTS
Iwouldliketoexpressmydeepestappreciationtothechairmanofmycommittee,
Dr.KhaiD.T.Ngo,forhisguidance,encouragement,patience,and,notlessimportant,
financialsupportforaslowlearnerlikeme.Ireceivedmymaster'sdegreeunderDr.
Ngo'ssupervision,too,sixyearsago.Ihavelearnedalotfromhimovertheseyears,andit
hasgreatlyreshaped my life'spath. I also want to thankDr. Dennis P. Carroll,Dr.
AlexanderDomijan,Dr.KennethK.O,andDr.LocVu-Quocfortheirparticipationonmy
committee.
MyspecialthanksgotoDr.Domijanforprovidingmetheequipmenttofinishmy
experimentandMr.TariqAslamBuchhforcarryingtheextraheavyequipmentwithme.1
must thank Dr. Vu-Quoc for helping me cut the magnetic core in preparing the
experiment.
Therewillbealwaysawoundborneinmymindthatmymotherpassedaway
whileIcouldnotstaywithherinherlastminutes,especiallyasithappenedonlyfourdays
afterIhadvisitedherandreturnedtoUF.Therewouldnothavebeenanychanceof
advancedstudyformewithoutherlife-longsacrifice.
ThereisnowordtodescribemygratitudetowardmywifeShwu-Yuannforher
supportandtolerance,especiallyasshegavemethepleasureofbeingababygirl'sfather
notlongago.
iii
TABLEOFCONTENTS
pages
ACKNOWLEDGMENTS
iii
ABSTRACT vi
CHAPTERS
1 INTRODUCTION 1
2 CONCEPTSANDEXISTINGSOLUTIONSOFHARMONIC
ELIMINATIONANDACTIVEFILTERING 12
2.1 ActiveFilterinSerieswithPowerLineandShuntPassiveFilter 15
2.2 ActiveFilterinSerieswithShuntPassiveFilter 16
2.3 ActiveFiltersinSerieswithPowerLineandinSerieswith
ShuntPassiveFilter 20
3 OPERATIONSOFPULSE-WIDTH-MODULATEDINVERTERS 28
3.1 IntroductiontoPowerElectronicConverters 28
3.2 OperationsofFull-BridgeInverter 32
3.3 OperationsofThree-PhaseVoltage-FedInverter 42
3.4 OperationsofThree-PhaseCurrent-FedInverter 52
4 THEPROPOSEDLOW-RATINGSPOWERQUALITYSOLUTION 81
4.1 ACurrent-FedInverterastheActiveFilter 82
4.2 AVoltage-FedInverterastheActiveFilter 98
4.3 LossMechanismsandPowerRatingsoftheActive/PassiveHybrid
Filters 101
4.4TotalHarmonicDistortionErrorsDuetotheOpen-LoopControl 108
5 EXPERIMENTALRESULTSOFATESTSYSTEM 132
6 SUMMARYANDCONCLUSION 159
iv
APPENDICES
A PSPICE®FILES 161
B MATLAB®SCRIPTFILESANDOUTPUTS 188
REFERENCES 201
BIOGRAPHICALSKETCH 207
V
AbstractofDissertationPresentedtotheGraduateSchool
oftheUniversityofFloridainPartialFulfillmentofthe
RequirementsfortheDegreeofDoctorofPhilosophy
APOWERQUALITYSOLUTIONWITHLOWINVERTERRATINGS
By
Ray-ShyangLai
December1996
Chairman:KhaiD.T.Ngo
MajorDepartment:ElectricalandComputerEngineering
The feasibility of a three-phase current-fed inverter for active filtering of
distributionsystemharmonicswasinvestigatedsincemostofthepublishedworksinthis
fieldhaveemployedvoltage-fedinverters.
Thestudyshowedthatthevoltage-fedhybridfiltergenerallyhaslessconduction
lossesthanthecurrent-fedonenomatterwhattypesofpassivefiltersareemployed.From
thelossstandpoint,thecurrent-fedinverterissuitablefortheroleofactivefilteronly
when it is in series with a parallel-resonantpassive filter tuned at the fundamental
frequency,insteadofthepopularcompoundseries-resonantfilterstunedat5th,7th,and
Uthharmonics.Thefunctionoftheparallel-resonantfilter,insertedinbetweenthepoint
ofcommoncouplingandtheoutputcapacitorofthecurrent-fedinverter,istopreventhigh
fundamentalcurrentfromcirculatingintheinvertercircuitry.Thepower(VA)ratingsof
thesemiconductorcomponentsandpowerlossesoftheinverterthereforearereduced.
vi
Thestudyalsorevealedthat,incontrasttothevoltage-fedinverter-basedhybrid
filter,whichrequiresboththeloadvoltageandthelinecurrenttobesensedandfunctions
correctlyonlyunderclosed-loopfeedbackcontrol,thecurrent-fedinverter-basedhybrid
filtercanperformactivefilteringsimplybyscalingthefundamentalremovedloadcurrent
tobethedutyratiofortheinverter.
Simulationworksconfirmedtheanalysis.Withtheduty-ratiodirectlyderivedfrom
theloadcurrent,thecurrent-fedinverter-basedactivefilteringonaprototypeone-branch
distribution system loaded with a 3kW full-bridge diode rectifier has been done
successfully.Theresultsoftheexperimentareinaccordancewiththeanalysis.Using
3kWasthepowerbaseandselectingthesemiconductordeviceswithappropriateratings
fortheinverters,theinverterlossesare0.82%p.u.forthecurrent-fed/parallel-resonant
filter, 0.08% p.u. for the voltage-fed/parallel-resonant filter, and 2.09% p.u. for the
current-fed/compoundseries-resonantfilterwiththesamecapacitance(150|J.F)ineach
passivefilter.Increasingthecapacitanceincreasestheinverterlossesintheconventional
hybridfilter, butdoes notincrease the inverterlossesin theproposedconfiguration.
However,theVAratingsoftheparallel-resonantpassivefilteraretwicetheratingsofthe
series-resonantfilter,andhighinductancesarerequired.
Insummary,theproposedhybridfilter,consistingofathree-phasecurrent-fed
inverterand aparallel-resonant passive filter tuned atthe fundamental frequency, is
suitableforactivefilteringofdistributionsystemswithlowoveralllossesandlowVA
ratingsoftheinvertercomponents.Thecontrolofthiscurrent-fedcombinationissimpler
thanthecontrolofvariousvoltage-fedcombinations.
vii
CHAPTER
1
INTRODUCTION
Theadvancesinmodemsemiconductordevicesdevelopmenthaveincreasedthe
scopeofapplicationsforvariouselectroniccomponentsanddevices,suchasinHVDC[1,
Chapter10],variable-speedmotordrives[2],andvariouspowerAC-to-DCandDC-to-
ACconverters[3,4].Withtheincreasingapplicablerangesofvoltage,current,andpower,
electroniccomponentsanddeviceshavebecometheessentialsincontrol,regulation,and
powerdeliveryofelectricalpowersystemsnowadays.WithnonlinearV-Icharacteristics
in nature, the growing application ofpower electronic devices increases the power
demandsandpresentsaseriouspowerqualityproblemtopowersystems[5,6,7,8,9,10,
11],especiallyinthedistributionlevel[12,13].
Nonlinearloadscontributetothequalitydeteriorationofapowersourcethrough
the generation ofharmonic and fundamental frequency reactive currents. The load-
generated harmonic currents interact with the finite distribution/transmission line
impedancetoproduceharmonicvoltagesateverybusalongthepowersystem,whichmay
causeserioushazardstothepowersystemandotherpowerusers[1,Chapter10].The
fundamental frequencyreactive current wastes the generatedpower andmaypose a
stabilityproblem[1,Chapters2 and 11] tothecontrolofpowersystems.Thepower
qualitycanbefurtherdeterioratedifthesagsandsurges,causedbyunbalancedthree-
phasecurrents,subsynchronousfrequencycurrents,orlargeloadtransients,arepresented
inthesupplyvoltageprofileofthesystem.
Basedontherequirementthat,ideally,onlyin-phasevoltagesandcurrentsofthe
fundamentalfrequencyshouldexistinthepowersystem,thequalityofapowersource
canbecategorizedas
•correspondingtotalharmonicdistortion(THD,expressedin%ofthefunda-
mentalcomponent)ofloadvoltageandlinecurrent,
•powerfactor,PF,and
•%sagorsurgeoffundamentalvoltageofthepowersource.
Thedefinitionsof%THD,powerfactor,andsag/surgecanbederivedfromFigure1.1.
FromFigure1.1(a),die%THDoflinecurrent isdefinedas
THD. = Vl s-I si
hi
TTTv (1-1)
1 sh
%THD. = 100XTHDj
wherei^iisthefundamentalcomponentofi^,andIjandl^i aretheroot-mean-square
(rms)valuesof andi^i,respectively.Thepowerfactor(PF)ofthepowersystemwitha
nonlinearloadisdefinedas
PF = y^cos(t)
ss
1 (1.2)
cose))
a/i+THD^i
whereVgisthermsvalueoflinevoltage and^isthephaseanglebetween andi^iin
Figure1.1(a).FromEquation(1.2),itisclearthattheharmoniccomponentsofanonlinear
loadcurrentwill yieldalowerpowerfactor,andhencemake thepowersystemless
efficient,comparedtoalinearloadwiththesamefundamentalcurrentandphaseangle
3
betweenthevoltage andcurrent.Figure 1.1 andEquation (1.2) assumethattheline
voltagedoesnotcontainanyharmoniccomponent. Ifthereareharmonicsintheline
voltagespectrum,Equation(1.2)isrewrittenas
PF = -——cos<l)j
ss
(1.3)
= Vl. +THd\:J•a/i+THD^COSCj)^
where V^j is the fundamental rms value ofv^; is the phase angle between the
fundamentalvoltageandcurrent;andTHDyisthetotalharmonicdistortionofVj.When
the loadisnonlinear, the currentharmonics are always accompanied by thevoltage
harmonicsandtheefficiencyofthepowersystemisfurtherreduced.
All major industrial standards impose power quality guidelines on electrical
utilities,users,andelectricalequipmentmanufacturersinordertomaintainanacceptable
powerqualityforallparties[14].Forpowerutilitiesandusers,theresponsibilitiescanbe
simplyclassifiedasfollows:
•tosuppressthe%THDofvoltagesuppliedtousersand
•tostabilizethefundamentalfrequencyvoltage
forthepowerutilities,and
•tosuppressthe%THDofcurrentinjectedintoutilitiesand
•tosustainanacceptablepowerfactor
forthepowerusers.Thesplitoftheresponsibilitieshappensatthepointofcommon
coupling(PCC),asshowninFigure1.2.
