Table Of ContentPOWER ELECTRONIC
CONVERTERS FOR
MICROGRIDS
POWER ELECTRONIC
CONVERTERS FOR
MICROGRIDS
SuleimanM.Sharkh
UniversityofSouthampton,UnitedKingdom
MohammadA.Abusara
UniversityofExeter,UnitedKingdom
GeorgiosI.Orfanoudakis
UniversityofSouthampton,UnitedKingdom
BabarHussain
PakistanInstituteofEngineeringandAppliedSciences,Pakistan
Thiseditionfirstpublished2014
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1 2014
Contents
AbouttheAuthors xi
Preface xiii
Acknowledgments xv
1 Introduction 1
1.1 ModesofOperationofMicrogridConverters 2
1.1.1 GridConnectionMode 2
1.1.2 Stand-AloneMode 3
1.1.3 BatteryChargingMode 3
1.2 ConverterTopologies 4
1.3 ModulationStrategies 6
1.4 ControlandSystemIssues 7
1.5 FutureChallengesandSolutions 9
References 10
2 ConverterTopologies 13
2.1 Topologies 13
2.1.1 TheTwo-LevelConverter 13
2.1.2 TheNPCConverter 14
2.1.3 TheCHBConverter 15
2.2 PulseWidthModulationStrategies 16
2.2.1 Carrier-BasedStrategies 17
2.2.2 SVMStrategies 22
2.3 Modeling 27
References 28
3 DC-LinkCapacitorCurrentandSizinginNPCand
CHBInverters 29
3.1 Introduction 29
3.2 InverterDC-LinkCapacitorSizing 30
3.3 AnalyticalDerivationofDC-LinkCapacitorCurrentRMSExpressions 32
vi Contents
3.3.1 NPCInverter 33
3.3.2 CHBInverter 36
3.4 AnalyticalDerivationofDC-LinkCapacitorCurrentHarmonics 37
3.4.1 NPCInverter 38
3.4.2 CHBInverter 39
3.5 NumericalDerivationofDC-LinkCapacitorCurrentRMSValueand
VoltageRippleAmplitude 41
3.6 SimulationResults 42
3.7 Discussion 45
3.7.1 ComparisonofCapacitorSizeforthe
NPCandCHBInverters 45
3.7.2 ComparisonofPresentedMethodsforAnalyzingDC-Link
CapacitorCurrent 46
3.7.3 ExtensiontoHigher-LevelInverters 48
3.8 Conclusion 48
References 48
4 LossComparisonofTwo-andThree-LevelInverterTopologies 51
4.1 Introduction 51
4.2 SelectionofIGBT-DiodeModules 53
4.3 SwitchingLosses 54
4.3.1 SwitchingLossesintheTwo-LevelInverters 54
4.3.2 SwitchingLossesintheNPCInverter 57
4.3.3 SwitchingLossesintheCHBInverter 58
4.4 ConductionLosses 58
4.4.1 ConductionLossesintheTwo-LevelInverter 60
4.4.2 ConductionLossesintheNPCInverter 61
4.4.3 ConductionLossesintheCHBInverter 63
4.5 DC-LinkCapacitorRMSCurrent 65
4.6 Results 69
4.7 Conclusion 70
References 71
5 MinimizationofLow-FrequencyNeutral-PointVoltage
OscillationsinNPCConverters 73
5.1 Introduction 73
5.2 NPCConverterModulationStrategies 74
5.3 MinimumNPRippleAchievablebyNVStrategies 77
5.3.1 LocallyAveragedNPCurrent 78
5.3.2 EffectofSwitchingConstraints 79
5.3.3 Zero-RippleRegion 81
5.3.4 ALowerBoundaryfortheNPVoltageRipple 81
5.4 ProposedBand-NVStrategies 83
Contents vii
5.4.1 CriterionUsedbyConventionalNVStrategies 83
5.4.2 ProposedCriterion 84
5.4.3 RegionsofOperation 85
5.4.4 Algorithm 88
5.4.5 SwitchingSequences–ConversiontoBand-NV 90
5.5 PerformanceofBand-NVStrategies 91
5.5.1 NPVoltageRipple 91
5.5.2 EffectiveSwitchingFrequency–OutputVoltageHarmonic
Distortion 93
5.6 SimulationofBand-NVStrategies 94
5.7 HybridModulationStrategies 100
5.7.1 ProposedHybridStrategies 101
5.7.2 SimulationResults 102
5.8 Conclusions 106
References 107
6 DigitalControlofaThree-PhaseTwo-LevelGrid-Connected
Inverter 109
6.1 Introduction 109
6.2 ControlStrategy 112
6.3 DigitalSamplingStrategy 113
6.4 EffectofTimeDelayonStability 115
6.5 CapacitorCurrentObserver 116
6.6 DesignofFeedbackControllers 119
6.7 SimulationResults 121
6.8 ExperimentalResults 123
6.9 Conclusions 127
References 128
7 DesignandControlofaGrid-ConnectedInterleavedInverter 131
7.1 Introduction 131
7.2 RippleCancellation 135
7.3 HardwareDesign 137
7.3.1 HardwareDesignGuidelines 138
7.3.2 ApplicationoftheDesignGuidelines 145
7.4 ControllerStructure 146
7.5 SystemAnalysis 149
7.5.1 EffectofPassiveDampingandGridImpedance 151
7.5.2 EffectofComputationalTimeDelay 151
7.5.3 GridDisturbanceRejection 154
7.6 ControllerDesign 154
7.7 SimulationandPracticalResults 158
7.8 Conclusions 167
viii Contents
References 167
8 RepetitiveCurrentControlofanInterleavedGrid-Connected
Inverter 171
8.1 Introduction 171
8.2 ProposedControllerandSystemModeling 172
8.3 SystemAnalysisandControllerDesign 175
8.4 SimulationResults 178
8.5 ExperimentalResults 179
8.6 Conclusions 182
References 182
9 LineInteractiveUPS 185
9.1 Introduction 185
9.2 SystemOverview 188
9.3 CoreController 192
9.3.1 VirtualImpedanceandGridHarmonicsRejection 193
9.4 PowerFlowController 195
9.4.1 DroopingControlEquations 195
9.4.2 SmallSignalAnalysis 196
9.4.3 StabilityAnalysisandDroopingCoefficientsSelection 200
9.5 DCLinkVoltageController 206
9.6 ExperimentalResults 209
9.7 Conclusions 217
References 218
10 MicrogridProtection 221
10.1 Introduction 221
10.2 KeyProtectionChallenges 221
10.2.1 FaultCurrentLevelModification 221
10.2.2 DeviceDiscrimination 223
10.2.3 ReductioninReachofImpedanceRelays 223
10.2.4 BidirectionalityandVoltageProfileChange 224
10.2.5 SympatheticTripping 224
10.2.6 Islanding 224
10.2.7 EffectonFeederReclosure 224
10.3 PossibleSolutionstoKeyProtectionChallenges 225
10.3.1 PossibleSolutionstoKeyProtectionChallengesforan
IslandedMicrogridHavingIIDGUnits 225
10.4 CaseStudy 229
10.4.1 FaultLevelModification 231
10.4.2 BlindingofProtection 232
10.4.3 SympatheticTripping 233
Contents ix
10.4.4 ReductioninReachofDistanceRelay 233
10.4.5 Discussion 234
10.5 Conclusions 235
References 236
11 AnAdaptiveRelayingSchemeforFuseSaving 239
11.1 Introduction 239
11.1.1 PreventiveSolutionsProposedintheLiterature 240
11.1.2 RemedialSolutionsProposedintheLiterature 241
11.1.3 ContributionsoftheChapter 242
11.2 CaseStudy 242
11.3 SimulationResultsandDiscussion 245
11.4 FuseSavingStrategy 247
11.4.1 OptionsandConsiderationsfortheSelectionof
I ofthe50Element 249
pickup
11.4.2 AdaptiveAlgorithm 251
11.5 HowReclosingWillBeApplied 252
11.6 Observations 255
11.7 Conclusions 257
References 257
AppendixA SVMfortheNPCConverter–
MATLAB®-SimulinkModels 261
A.1 CalculationofDutyCyclesforNearestSpaceVectors 261
A.2 SymmetricModulationStrategy 262
A.3 MATLAB®-SimulinkModels 263
References 279
AppendixB DC-LinkCapacitorCurrentNumericalCalculation 281
Index 285
About the Authors
Suleiman M. Sharkh obtained his BEng and PhD
degrees in Electrical Engineering from the University
of Southampton in 1990 and 1994, respectively. He is
currently the Head of the Electro-Mechanical Research
Group at the University of Southampton. He is also the
Managing Director of HiT Systems Ltd, and a visit-
ing Professor at the Beijing Institute of Technology and
BeijingJiaotongUniversity.
He has 20 years research experience in the field of
electricalandelectromagneticsystems,includingelectric
switches, power electronics, electrical machines, con-
trol systems, and characterization and management of
advancedbatteries.Todatehehaspublishedabout150publications.Hehasobtained
research grant income of about £2M from the Research Councils and industry since
1998.Hehassupervised11PhDstudentstocompletionandiscurrentlysupervising5
PhDstudents.HeisanestablisheddoctoralexternalexaminerintheUKandabroad,
includingEurope,China,andAustralia.Hisresearchhascontributedtothedevelop-
mentofanumberofcommercialproducts,includingrimdrivenmarinethrusters(TSL
Technology Ltd), down-hole submersible motors for drilling and pumping oil wells
(TSLTechnologyLtd),sensorlessbrushlessDCmotorcontrollers(TSLTechnology),
powerelectronicconvertersformicrogrids(BowmanPowerSystemsandTSLTech-
nology), high-speed PM alternators for Rankine cycle and gas microturbine energy
recovery systems (TSL Technology, Bowman Power Systems, and Freepower), and
batterymanagementsystems(ReapSystemsLtd).
HewasthewinnerofTheEngineerEnergyInnovationandTechnologyAwardthat
was presented at the Royal Society London in October 2008 for his work on novel
rimdrivenmarinethrustersandturbinegenerators,whichareproducedcommercially
under licence by TSL Technology Ltd. He was also awarded the Faraday SPARKS
award in 2002. He is a past committee member of the UK Magnetics Society, a
memberoftheIETandaCharteredEngineer.
xii AbouttheAuthors
MohammadA.AbusarareceivedtheBEngdegreefrom
BirzeitUniversity,Palestine,in2000,andthePhDdegree
from the University of Southampton, UK, in 2004, both
in electrical engineering. From 2003 to 2010, he was
with Bowman Power Group, Southampton, UK, respon-
sible for research and development of digital control of
powerelectronicsfordistributedenergyresources,hybrid
vehicles, and machines and drives. He is currently a
SeniorLecturerinRenewableEnergyattheUniversityof
Exeter,UK.
GeorgiosI.OrfanoudakisreceivedhisMEnginElectri-
calEngineeringandComputerSciencefromtheNational
TechnicalUniversityofAthens(NTUA),Greece,in2007,
andhisMScinSustainableEnergyTechnologiesfromthe
UniversityofSouthampton,UK,in2008.Hethenjoined
the Electro-Mechanical Research Group at the Univer-
sity of Southampton and obtained his PhD in 2013. His
research focused on the modulation and DC-link capaci-
torsizingofthree-levelinverters.SinceOctober2012heis
working as a Research Associate in a Knowledge Trans-
fer Partnership (KTP) with the University of Southamp-
ton and TSL technology Ltd., performing R&D work on
inverters for motor drive applications. Dr Orfanoudakis is a member of the IEEE
PowerElectronicsSociety.
BabarHussainreceivedtheBScdegreeinelectricalengi-
neering from the University of Engineering and Tech-
nology, Taxila, Pakistan, in 1995 and the PhD degree in
electrical engineering from the University of Southamp-
ton, Southampton, UK, in 2011. He has more than 10
years experience in the electric power sector. His major
research interests include protection of distribution net-
workswithdistributedgeneration,powerquality,andcon-
trolofgrid-connectedinverters.
