Analysis, Optimization and Control of Grid-Interfaced Matrix-Based Isolated AC-DC Converters

295 Pages·2022·14.692 MB·English

by  Jaydeep Saha

Springer Theses
Recognizing Outstanding Ph.D. Research
Jaydeep Saha
Analysis,
Optimization
and Control
of Grid-Interfaced
Matrix-Based Isolated
AC-DC Converters
Springer Theses
Recognizing Outstanding Ph.D. Research
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Jaydeep Saha
Analysis, Optimization
and Control
of Grid-Interfaced
Matrix-Based Isolated
AC-DC Converters
Doctoral Thesis accepted by
National University of Singapore, Singapore, Singapore
Author Supervisor
Dr.JaydeepSaha Assoc.Prof.SanjibKumarPanda
ResearchFellow,DepartmentofElectrical DirectorofPowerandEnergyGroup,
andComputerEngineering DepartmentofElectricalandComputer
NationalUniversityofSingapore Engineering
Singapore,Singapore NationalUniversityofSingapore
Singapore,Singapore
ISSN 2190-5053 ISSN 2190-5061 (electronic)
SpringerTheses
ISBN 978-981-19-4901-2 ISBN 978-981-19-4902-9 (eBook)
https://doi.org/10.1007/978-981-19-4902-9
©TheEditor(s)(ifapplicable)andTheAuthor(s),underexclusivelicensetoSpringerNature
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TomybelovedWife,Pratirupa
Supervisor’s Foreword
Itisagreatpleasuretowriteaforewordtothisbookoninterestingandinnovative
modulation,controlanddesigntechniquesforgrid-connectedisolatedsingle-stage
AC-DCconversion.
Startingwiththeinstallationofthefirstdistributionsystemstowardstheendof
the 19th century, the electrical power system has undergone a variety of changes.
However, the 21st-century power grid has been undergoing a plethora of changes,
mainlyfuelledbythecommitmentsmadebyanumberofgovernmentsaroundthe
worldtocombatclimatechange.Theemergenceofsmartgridisreversingtheorga-
nizationalapproachofthepowergridfromatop-downtoabottom-upapproach,with
renewable-baseddistributedgenerationbecomingacommonplace.Thoughahuge
AC-based generation-transmission-distribution power network is in place, there is
increasing penetration of DC power (mainly in the power distribution grid) due to
proliferationofDCsources(e.g.solarphotovoltaic,fuelcells),batteryenergystorage
systemsandDCloads(e.g.electronics,electricvehicles,smartlightingsolutions).
Thus, AC-DC and DC-AC conversions would be a necessity for the foreseeable
future. Power electronics is becoming a more common technology in the power
grid, ranging from integration of renewables, battery, electric vehicles and so on.
Theapplicationofgrid-connectedpowerelectronicshasitsnuancesandchallenges
whichneedstobecarefullyinvestigated,buttheopportunitiesandpossibilitiesare
magnanimous.
Powertransformerspresentinthepowersystemtodayoperateatthedesignated
linefrequency(50HzforSingaporeand60HzforUSA)andareveryrobustsolutions,
buthavelimitedfunctionalities,whichmaynotbesufficientforalltherequirements
ofthefuturegrid.Forexample,whenitcomestointegrationofrenewablesorbattery
energystorageorrenewable-richmicrogridswiththeutilitygrid,apartfromgalvanic
isolation,anAC-DCconversionsolutionisnecessary.Thus,thereisnochoicebutto
resorttopowerelectronicstechnology.Aboutadecadeago,powerelectronicrein-
forcementoftransformerswouldbecriticizedasitwouldaffecttheefficiencyand
powerqualityoftheequipment.Buttoday,thewide-bandgap(WBG)semiconductor
deviceswithhighbandwidthofswitchingfrequencyandhighpowerhandlingcapa-
bilities have helped to eliminate many bottlenecks with respect to grid-connected
vii
viii Supervisor’sForeword
powerconversion.Thishasnotonlymadepower-electronics-reinforcedsmarttrans-
formersareality,butalsohelpedtonurturethegrowthofconceptslikesolid-state
transformer,whichnestsahigh-/medium-frequencytransformerandthusprovides
acompactisolatedpowerconversionsolutionthatcanmeettheexpectationsofthe
modernsmartgrid.
Thebookisdedicatedtowardsinvestigationanddevelopmentofhigh-efficiency,
high power-density AC-DC converters for medium-voltage AC (MVAC) and low-
voltage AC (LVAC) grid-connected applications. Firstly, a qualitative analysis
of the grid-connected MVAC-LVDC conversion reveals the merits of cascaded
modular conversions, and a further quantitative analysis of the submodule possi-
bilities for cascaded modular conversion shows superiority of the single-stage
front-end half-bridge matrix-based dual-active-bridge (FE-HB MB-DAB) AC-DC
submoduletopology.Secondly,anelaboratediscussionontheanalysisofmodula-
tion, optimal design methodology and soft-switching strategy for the FE-HB MB-
DAB is presented, with experimentally obtained efficiency (η) of 96.6%, power
density(ρ)of2.49kW/L,unity-power-factoroperationandnearfull-cycleZVSof
allSiC-MOSFETsoverawideloadrange(12–100%).Thisdemonstratesasignif-
icantimprovementovertheperformanceoftheconventionaltwo-stageconversion
strategy.Thirdly,amachine-learning(ML)-aidedη-ρoptimalsolid-statetransformer
(SST) design framework is proposed and experimentally validated. Subsequently,
the issue of power routing imbalance in single-stage MVAC-LVDC converters is
studied,andamitigatingpowerbalancecontrolsolutionisproposedandexperimen-
tally validated. Lastly, the single-stage three-phase isolated LVAC-LVDC conver-
sion strategies for LV grid-connected applications are investigated, which exhibit
that DAB-type conversion (experimental η = 96.35%, ρ = 2.4 kW/L and LVAC
sidecurrentTHDof4.1%)demonstratessuperiorperformancethannon-DAB-type
conversion(experimentalη=93.6%,ρ=2.1kW/LandLVACsidecurrentTHDof
5.6%).Hence,thisbookextensivelycoverstheory,analysis,designandcontrolofa
newgenerationofisolatedAC-DCconversionforgrid-connectedapplications,with
adequateexperimentalverification.
Accordingtome,thisbookwillbebeneficialforprofessionalsbothattheindustry
and academia. Industry professionals will get to familiarize with the need-of-the-
hourresearchthrusttowardsdesignandcontrolofgrid-connectedpowerelectronic
converter,whereastheresearchcommunitywouldgetatasteofthenewdirectionto
explorethepossibilitiesofML-assistedoptimalpowerconverterdesign,modulation
andcontroltechniquesthatcanpotentiallyimprovepowerconverterperformance.I
amsurethatthebookwouldappearfascinatingtoallthepeoplewhoare,inanyway,
associatedwiththepowerelectronicsdomain.Thisworkhasthepotentialtoopenup
newavenuesfortechnologyadoptionintheemergingareasoffast-chargingofelectric
vehicles,greendatacentres,energy-controlcentreofrenewable-richmicrogrids,etc.
Singapore Assoc.Prof.SanjibKumarPanda
May2022
Summary
Thetraditionalfossil-fuel-basedpowersystem(withunidirectionalelectricalpower
andinformationflowalongthethreesegmentsofgeneration,transmissionanddistri-
bution)isexperiencingaparadigmshiftduetoincreasingpenetrationofrenewable
energysources,asaresultofrisingenvironmentalconcernsanddwindlingexpense
ofrenewableenergyharvestinginfrastructure.Asaresult,thepowersystemisgetting
revampedtowardsthesmartgridconcept,wheremicrogrids/nanogrids(consistingof
distributedenergyresources,storageandactive/passiveloads)areexpectedtoform
thefunctionalblocks.Thecentralizedutility-gridconceptanditsenormousinfras-
tructure would still be existing with the distribution system getting modernized in
thecomingfewdecades.Powerelectronicsisalreadyavisibletechnologyintoday’s
gridwithapplicationssuchasFACTS,HVDCtransmission,powerelectronics-based
circuitbreakers,inverters,convertersforintegratingrenewableenergysources,etc.
Thepowerelectronicstechnologyisexpectedtodominatethepowersystemofthe
future due to the necessity of continuous controllability and enhanced smart func-
tionalitiesatthepointofinterconnectionofthemicrogrids/nanogridswiththeutility
gridandduetotheproliferationofotherpowerelectronicsdependentapplications
likebatteryenergystorageintegration,vehicle-to-grid,electricvehiclefastcharging,
etc.AdedicatedoverviewofthevariousMVgrid-connectedisolatedMVAC-LVDC
conversionstrategiesisdiscussedtoestablishthemeritsofcascadedmodularmulti-
level conversion strategy for MV grid-connected applications. Simultaneously, a
focused discussion on the solid-state transformer (SST) technology (a MV grid-
connected application with medium-frequency isolation) is provided to show its
relevance and applicability for MVAC-LVDC conversion, which reveals the need
forhigh-powerdensitySSTarchitectureswithcomparableefficiencyandcostwith
respecttocontemporaryline-frequencytransformer(LFT)-basedsolutions.Abrief
overviewoftheLVgrid-connectedLVAC-LVDCconversionstrategiesispresented
whichshowstheneedformoreresearcheffortstowardsthedevelopmentofsingle-
stagethree-phaseLVAC-LVDCconverterswithenhancedefficiency,powerdensity
andreliability.
There is a literature gap in terms of the quantitative evaluation of the AC-
DCsubmoduletopologiesformodularMVgrid-connectedisolatedMVAC-LVDC
ix
x Summary
conversion.Briefdescriptionsforeachoftheavailablesingle-phaseAC-DCconver-
sion submodules in literature along with other possible submodule topologies are
providedinthisthesis,andacomparativeevaluationisprovidedwhileconsidering
thecriteriaofpowerdensity,efficiency,cost,failurerate,numberofcomponentsand
controlcomplexity.Thiscomparativestudyshowsthemeritsofsingle-stageisolated
AC-DC submodules over the conventional two-stage isolated AC-DC submodules
andrevealsthatthedirectmatrix-baseddual-active-bridge(MB-DAB)submoduleis
themostsuitablesubmoduletopologyforisolatedMVAC-LVDCconversionappli-
cation (based on the considered criteria). Subsequently, the two direct MB-DAB
configurations, i.e. front-end half-bridge (FE-HB) and front-end full-bridge (FE-
FB),arestudiedtorevealtheirmodulationboundaries(whichhasnotbeenanalysed
intheliteratureyet).ThisstudyrevealsthattheFE-HBMB-DABtopologyhasbetter
meritscomparedtotheFE-FBMB-DAB,asitofferstwicethemodulationflexibility
andtwicetheAC-DCstep-downwitha33%reductioninnumberofsemiconductor
devicesandtherequiredcontrolflexibility.
The single-stage single-phase FE-HB MB-DAB topology is relatively nascent,
and its modulation has not been discussed in great detail in the recent literature.
In this thesis, a holistic description and associated formulations of the exhaustive
setofzerocurrentswitching(ZCS)andzerovoltageswitching(ZVS)constrained
modulation modes of the FE-HB MB-DAB converter are presented. The subse-
quent theoretical analysis of the modulation boundaries reveals that there are only
four feasible modulation modes that can form six feasible modulation schemes as
acombinationofvariousfeasiblemodulationmodes.Amultiobjectiveefficiency—
powerdensity(η–ρ)designoptimizationalgorithmisalsopresentedthatresultsin
the η–ρ optimal design limits for the six feasible modulation schemes for various
combinations of component datasets and switching frequencies. A complete SiC-
MOSFET-basedFE-HBMB-DABhardwareprototypeisfabricatedaccordingtothe
componentandoperationalspecificationsofthemultiobjectiveη–ρdesignoptimiza-
tionresultsandtheexperimentallyobtainedη=96.1%andρ=2.49kW/Lillustrate
strongcoherencewiththetheoreticallyobtainedoptimalMB-DABdesign’sresults
(thus validating the theoretical analysis and optimization results). As far as ZVS
soft-switchingstrategiesforSiC-MOSFET-basedMB-DABAC-DCconvertersare
concerned, the proposed methodologies in the literature either suffer from incom-
pleteZVSofSiC-MOSFETsduetomodetransitionorcomputationallyexpensive
optimalmodulationschemebyrestrictingtheswitchingschemetoasinglemodu-
lationmode.AnanalyticalexpressionbasedZVSmodulationstrategyispresented
in this thesis to achieve near full-cycle ZVS turn-on of all the SiC-MOSFETs in
the FE-HB MB-DAB converter over a wide range of loading conditions with the
capabilityofpowerfactorcorrection,whichensureslowcomputationalcomplexity
and direct implementability on a common microprocessor. A PSIM simulation is
developed for a 2.2 kW(pk) MB-DAB converter using component manufacturer’s
PSPICE models to study the working principle of the proposed ZVS modulation
schemebeforehardwareimplementation.Finally,theexperimentalresultsexhibita
conversionefficiencyof96.6%,UPFoperation,ACcurrent’sTHDof2.9%atfull-
load, along with near full-cycle ZVS turn-on of all MOSFETs over a wide range