Energy Systems Research Laboratory, FIU

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EnergyLinkIntegrationofAlternativeEnergySystemstothePowerGrid

Prof.OsamaMohammedbLecturegivenby

AhmedMohamed

Energy Systems Research Laboratory, FIU

Lectures8&9ForEEL‐6273:ComputerModelingofPowerSystems

FridaySept21,2012,5:00‐7:15PM(withnobreak)SeeReferencesHandout

PresentationObjectives

Part I is to give a general introduction andPartIistogiveageneralintroductionandknowledgeaboutthetopic.

PartIIistohelptheaudiencelearnaboutissuesbeingconsideredbyresearchersallaroundthe


globe,anddobrainstormingaboutpossiblefutureresearches.

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PARTI:Introduction,DistributedGeneration,Microgrids,ArchitecturesandControl.


Alternative sources of energy

Fossil fuel based Renewable based

Alternative Energy Sources

Fossil fuel-based Renewable-based Diesel Gas hydrogen from reforming

hydrocarbons

Solar Wind Hydro Tidal geothermal energy hydrogen produced

f bl


Note: For an energy source to be considered renewable, the recovery cycle of the source must be considered. For example, a sugarcane plantation used for the production of alcohol has a recovery cycle of one year. In comparison, fossil fuels can take millions of years to recover.

from renewable sources

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DistributedGenerationDefinition Distributedgeneration(DG)istheapplicationofsmallgeneratorsfrom10to10,000

kWscatteredthroughoutapowersystemandeitherinteractingwiththegridorprovidingpowertoisolatedsites.

Dispersedgenerationissometimesusedasaninterchangeableterm,butitshouldbeused for very small generation units in the range 1 to 100kW sized to serveusedforverysmallgenerationunits,intherange1to100kW,sizedtoserveindividualhouseholdsorsmallbusinesses.

HouseholdandruralusersareconcernedwiththedeploymentofDGbecauseoftheoverwhelminginvestmentsrequiredtoconnecttoadistantgrid.

Fortheseusers,DGismoreeconomicalthanthecentralstationsystemplusassociatedtransmissionanddistributionexpansion.

Because of cost and reliability industrial and commercial institutions may decide to


Becauseofcostandreliability,industrialandcommercialinstitutionsmaydecidetoinstallDGasamatchwiththeelectricutilitysystem.

Thiscanhappenwhentheparticularapplicationisofveryhighreliabilityandhighcostorverylowreliabilityandlowcost.

Thebenefits ofDGinclude:Modularity,efficiency,lowornoemissions,securityandloadmanagement.

DistributedGenerationImplementation Themovetowardon‐sitedistributedpowergenerationhasbeenaccelerated

becauseofderegulationandrestructuringoftheutilityindustryandthefeasibilityofalternativeenergysources.

DGtechnologiescanimprovepowerquality,boostsystemreliability,reduceenergycosts, and defray utility capital investment.costs,anddefrayutilitycapitalinvestment.

Fourmajorissues aretypicallyrelatedtoDG:

hardwareandcontrol

effectonthegrid

interconnectionstandards

economicevaluation

Theintegrationofrenewablesourcesofenergyposesachallenge becausetheiroutput is intermittent and variable and must be stored for use when there is


outputisintermittentandvariable andmustbestoredforusewhenthereisdemand.

Ifonlyonerenewableenergysourceisconsidered,theelectricpowersystemissimple.Thesourcecanbeconnectedtoastoragesystemtodeliverelectricityforstand‐aloneuseorinterconnectedwiththegrid.However,ifmultiplerenewableenergysourcesareused,theelectricpowersystemcanberathercomplex,andamicrogridwillbeformed.

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DistributedGenerationEconomics TheoverallU.S.electricitysystemisonlyabout30%efficient[i.e.,thereisanaverage

inputoffourunitsofenergy(coal,nuclear,naturalgas,oroil)todeliveroneunitofelectricity].

DGhasthepotentialofbeinglesscostly,moreefficient,andmorereliable.Mostexistingpowerplants,centralordistributed,deliverelectricitytousersitesatanoverallfuel‐to‐electricityefficiencyintherange28to32%.Thisrepresentsalossofaround70%oftheprimaryenergyprovidedtothegenerator.

Toreduceenergyloss,itisnecessarytoincreasethefuel‐to‐electricityefficiencyofthegenerationplantortousethewasteheat.TheuseofwasteheatinDGclose totheuserincreasesfurthertheoverallefficiencyforspaceheatingorindustrialprocesses.

Theabilitytoavoidtransmissionlossesandmakeeffectiveuseofwasteheatmakeson‐sitecogenerationorcombinedheatandpower(CHP)systems70to80%efficient.

Industrial,commercial,andresidentialDGsystemscanbetailoredforefficiencyi t b i f l h t h b ti hill d i t


improvementbyusing,forexample,heatexchangers,absorptionchillers,ordesiccantdehumidificationtoreachoverallfuel‐to‐usefulenergyefficienciesofmorethan80%.

Forexample,Capstonemanufacturesa60‐kWmicroturbine thatuseswasteheattoheatwater.Thissystemhasanenergyefficiencyoffueltousefulenergythatapproaches90%.

Theuseofwasteheatthroughcogenerationorcombinedcooling,heating,andpowerimpliesanintegratedenergysystemthatdeliversbothelectricityandusefulheatfromanenergysource.

Microgrid

• Amicrogrid canbedefinedasaclusterofloadsandDGunitsthatoperatesoastoimprovethereliabilityandqualityofthepowersysteminacontrolledmanner.

• Forconsumers,microgrids canprovidepowerandheatinareliable way.

• Forthedistributionnetwork,microgrids aredispatchablecellsthatcanrespondautonomouslyorfromsignalsfromthepowersystemoperator.


• Informationtechnologyachievements,alongwithnewDGsystemswithintelligentcontrollers,willallowsystemoperatorsandmicrogrid operatorstointeractinanoptimalmanner.

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YourTurn!

ShareyourknowledgeaboutDGs and Microgridswith the rest of the class


DGsandMicrogridswiththerestoftheclassin3minutes!

PRINCIPLESOFPOWERGENERATIONFORINJECTIONINTOTHEGRID

• Whenapplyingelectricalenergyconversiontechnologytorenewableenergysystems,twoclassesofelectricalsystemsmustbeconsidered:stationaryandrotatory.

• Thestationarytypeusuallyprovidesdirectcurrent.Photovoltaicarraysandfuelcellsarethemainrenewableenergysourcesinthisgroup.

• Therotatorytypeusuallyprovidesalternatingcurrent.Induction,synchronous,andpermanent‐magnetgeneratorsarethemaindriversforhydropower,wind,and


g y p , ,gasturbineenergysources.

• Dcmachinesaretherotatorytypebutarenotusuallyemployedbecauseoftheirhighcost,bulkysize,andmaintenanceneeds.

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PowerConversionTechnologies

• Powerelectronicsistheenablingtechnologythatallowstheconversionofenergyandinjectionofpowerfromrenewableenergysourcestothegrid.

• Ifonlyphotovoltaicandfuelcellsystemsareused,adc‐linkbusmightbeusedtoaggregatethem.Acpowercanbeintegratedthroughdc–acconversion


• Ifonlyhydroorwindpowerisused,avariable‐frequencyacvoltagecontrolmustbeaggregatedintoanaclinkthroughanac–acconversionsystem.

(inverter)systems.

FossilFuel‐BasedEnergyIntegration

• Alternativeenergysourcessuchasdieselandgascanalsobeintegratedwithrenewables.

• They have a consistent and constant fuel supply and the• Theyhaveaconsistentandconstantfuelsupply,andthedecisiontoscheduletheiroperationisbasedmoreonstraightforwardeconomicreasonsthananyothers.

• Dieselgenerators,whicharecommerciallyavailablewithsynchronousgeneratorsthatsupply60Hz,anddirectinterconnectionwiththegrid,aretypicallyeasiertoimplement.

G i t bi t f tl i l t d ith


• Gasmicroturbines aremostfrequentlyimplementedwithapowerelectronicinverter–basedtechnology.

• Whenintegratingandmixingallthosesources,amicrogridhastobebasedonadc,aclinkorahigh‐frequencyaclink(HFAC).

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PowerFlowDirections• Thestationarygroupofrenewableenergysourcesdoesnotabsorb

power;theenergyflowsuniquelyoutwardtotheload.• Ontheotherhand,therotatorygroupofrenewableenergysources

requirebidirectionalpowerflow,eithertorotateinmotoringmode(fori b ki t t ) t b b ti (fpumping,braking,orstartup)ortoabsorbreactivepower(for

inductiongeneratorsandtransformers).• Thestoragesystemscanalsobestationary(e.g.,batteries,super‐

capacitors,andmagneticcoils)orrotatory(generators,flywheels,andpumpinghydro).Therefore,ageneralizedconceptofpowerelectronicsisbroadlyneededforrenewableenergysystemstoembracesuchcategories.

• Static systems appear as a dc input converted to a dc or ac output and


• Staticsystemsappearasadcinputconvertedtoadcoracoutputandunidirectionalpowerflow(nomovingparts,lowtimeconstant,silent,novibrations,minimallypolluting,andlowpoweruptonow).

• Therotatingsystemsappearasanacinputconvertedtoadcoracoutputandbidirectionalpowerflow(angularspeed,noise,mechanicalinertia,weightandvolume,andinrush).

ACandDCConversionNeeds

• Storagesystemsarenecessarilybidirectionalsystemswithrequirements of ac and dcrequirementsofacanddcconversion(dependingontheapplication).Thevoltagegeneratedbyvariable‐speedwindpowergenerators,PVgenerators,andfuelcellscannotbedirectlyconnectedwiththegrid.


• Therefore,powerelectronicstechnologyplaysavitalroleinmatchingthecharacteristicsofthedispersedgenerationunitsandtherequirementsofgridconnection,includingfrequency,voltage,activeandreactivepowercontrols,andharmonicminimization.

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PowerConvertersforPowerInjectionintotheGrid• Apowerelectronicconverterusesamatrixofpowersemiconductorswitchestoenableittoconvertsourcesofstationaryelectricpowerintorotatingelectricalpower,andviceversa,athighefficiency.

• Avoltagesourceisdriventomaintainaprescribedvoltageacrossitsterminals,irrespectiveofthemagnitudeorpolarityofthecurrentflowingthroughthesource.Theprescribedvoltagemaybeconstantdc,sinusoidalac,orapulsetrain.

• Acurrentsourcemaintainsaprescribedcurrentflowingthroughitsterminals,irrespectiveofthemagnitudeorpolarityofthevoltageappliedacrosstheseterminals.Again,theprescribedcurrentmaybeconstantdc,sinusoidalac,orapulsetrain.Currentsourceinverters(CSIs)haveseveraladvantagesovervariable‐voltageinvertersbecausetheycanoperateunderawideinputvoltagerangeandaboostconverterstagemaynotberequired.

• Theyprovideprotectionagainstshortcircuitsintheoutputstageandcaneasilyhandletemporaryoverratingsituationssuchaswindgustsorfaultyturbines.Inaddition,CSIshaverelativelysimplecontrolcircuitsandgoodefficiency.

• As disadvantages CSIs produce torque pulsations at low speed cannot handle undersized


• Asdisadvantages,CSIsproducetorquepulsationsatlowspeed,cannothandleundersizedmotors,andarelargeandheavy.Thephase‐controlledbridgerectifierCSIislessnoisythanitschopper‐controlledcounterpart,lossesaresmaller,anditdoesnotneedhigh‐speedswitchingdevices,butitcannotoperateefficientlyfromdirectdcvoltage.Thechopper‐controlledCSIcanoperatefrombatteriesandproducesmorenoiseasaresultofitsneedforhighspeedswitchingdevices.Withtheadventoffast,high‐powercontrolleddevices,VSinvertershavebecomepopular,butmuchR&Disneededbeforetheyareappliedtoveryhighpowersystems.

Z‐sourceconvertersystem

• Theimpedance‐source(Z‐source)powerconverter,isdesignedtoovercomethecharacteristicsassociatedwiththeconventionalV‐sourceandI‐sourceconverters.AZ‐sourceinvertercanproduceanydesiredvoltageregardlessofitsinputvoltage,whichgreatlyreducessystemcomplexity,cost,size,andpowerloss.

• AuniqueLCnetworkinthedclink,makingitpossibleforbuckandboostoperation.


Eventhoughsuchtopologyhasgainedattentioninthepastfewyears(withsomeinterestingfeaturessuchasapplicationtoalmostalltheconversioncircuits:dc‐to‐acinversion,ac‐to‐acconversion,anddc‐to‐dcconversion).

• AZ‐sourceconverterhasmorepassivecomponentsinthelink,andaneconomicalbreakthroughanalysismustbecarriedoutforhigh‐powerapplications.

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YourTurnAgain!

ShareyourknowledgeaboutPower Electronic Converter Applicationswith


PowerElectronicConverterApplicationswiththerestoftheclassin3minutes!

PowerFlow• Decouplingactiveandreactivepowerflowisacommonpracticeinloadflow

studies.Thevariationofactivepowerisstronglycoupledwithpowerangleandfrequencyvariation,whereasreactivepowerisstronglycoupledwithvoltageamplitude.

• ThesetwoequationsshowthatforagivengridvoltageVs andinductanceLs,therealpowerisPs andthatthereactivepowerQs canberegulatedbythemagnitudeof V and power angle δ


ofVi andpowerangleδ.• ThereferenceforrealpowerP* andreactivepowerQ* canbeobtainedbysetting

thefollowingreferencepowerangledandinverteracterminalvoltageVi*

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INTEGRATIONOFMULTIPLERENEWABLEENERGYSOURCES

• The figure shows multiple renewable energy sources forming a microgrid,


TypesofEnergyLinkIntegration—DCLink

Advantages:

1.Synchronismisnotrequired.2.Therearelowerdistributionandtransmissionlossesthanwithac‐link.3.Ithashighreliabilitybecauseofparallelsources.4.Althoughtheterminalneedsofadclinkaremorecomplex,thedctransmissioninfrastructureperkilometerissimplerandcheaperthaninaclinks.5.Long‐distancetransmission(forhigh‐voltagelinks)ispossible,whichenablesintegrationofoffshorewindturbinesandother energies with inland networks

Disadvantages:

1.Theneedforcarefulcompatibilityofvoltagelevelstoavoidcurrentrecirculationbetweentheinputsources.2.Theneedforrobustforcedcommutationcapabilitiesincircuitsathighpowerlevels.3 C i ith th l t d


otherenergieswithinlandnetworks.6.Theconvertersrequiredareeasilyavailable.7.Single‐wiredconnectionsallowbalancedterminalacsystems.

3.Corrosionconcernswiththeelectrodes.4.Alargenumberofcomponentsandcontrols.5.Morecomplexgalvanicisolation.6.Highercostsofterminalequipment.7.Difficultieswithmultiterminalormulti‐voltage‐leveloperationfortransmissionanddistribution.

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ACLink Integration

Advantages:

1.Utilityregulationandmaintenanceoftheoperationalvoltage,whichmakesiteasiertoinjectpowerintothegrid.2.Thepossibility,insomecases,ofeliminatingtheelectronicconverters(e.g.,byusingsynchronousgeneratorsorinductiongeneratorsthatestablishtheirownoperatingpoint).3.Easymulti‐voltageandmulti‐terminalmatching.4.Easygalvanicisolation.5.Well‐establishedscaleeconomyforconsumers and existing utilities

Disadvantages:

1.Theneedforrigoroussynchronism,voltage‐levelmatching,andcorrectphasesequencebetweensourcesduringinterconnectionaswellasduringoperation.2.Leakageinductancesandcapacitancesinaddition to the skin and proximity effects that


consumersandexistingutilities. additiontotheskinandproximityeffectsthatcauselossesinlongdistributions.3.Electromagneticcompatibilityconcerns.4.Thepossibilityofcurrentrecirculationbetweensources.5.Theneedforpowerfactorandharmonicdistortioncorrection.6.Reducedlimitsfortransmissionanddistribution.

HFACLink IntegrationAdvantages:

1.Theharmonicsareofhigherordersandareeasilyfilteredout.2.Fluorescentlightingwillexperienceimprovementbecause,withhigherfrequency,theluminousefficiencyisimproved,flickerisreduced,anddimmingisaccomplisheddirectly.Theballastinductanceisreduced

i ll h f i h diproportionallytothefrequency,withacorrespondingreductioninsizeandweight.3.High‐frequencyinductionmotorscanbeusedforcompressors,high‐pressurepumps,high‐speedapplications,andturbines.Acfrequencychangersbasedonmatrixconverterscanbeusedtosoftstarthigh‐frequencyinductionmotors.Asafeoperatingareaisnotarestrictionforsoftswitching,andthereforemodernpowerelectronicdeviceswillbeadvantageous.4.Harmonicripplecurrentinelectricmachineswill

Disadvantages:

1.Thehighcostoftransformers.2.Thelargenumberofdevices(becauseoftheuseofbipolaracswitches).3.Verycomplexcontrol.4. The dependence on future advances of power


decrease,improvingefficiency.5.High‐frequencypowertransformers,harmonicfiltersforbatteries,andotherpassivecircuitcomponentsbecomesmaller.6.Auxiliarypowersupplyunitsareeasilyavailablebytappingtheaclink.Theywouldbesmallerwithhigherefficiencies.7.Batterieshavebeenthetraditionalenergystoragesource,butinHFACmicrogrids,dynamicstorageisanalternative.

4.Thedependenceonfutureadvancesofpowerelectroniccomponents.5.Concernsaboutelectromagneticcompatibility.6.Extremelyreducedlimitsandtechnologicalproblemsfortransmissionanddistributionathighfrequencies.

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MicrogridArchitecture

• Inmicrogrids,thereisasinglepointofconnectiontotheutilitycalledthepointofcommoncoupling.p g

• Somefeederscanhavesensitiveloadsthatrequirelocalgeneration.Intentionalislandingfromthegridisprovidedbystaticswitchesthatcanseparatetheminlessthanacycle.

• Whenthemicrogridisconnected,powerfromlocalgenerationcanbedirectedtothe feeder with noncritical loads or be sold to the utility if agreed or allowed by net


thefeederwithnoncriticalloadsorbesoldtotheutilityifagreedorallowedbynetmetering.Inadditiontoallowingbetterefficiency,wasterecovery,andtailoredreliability,amicrogridisdesignedfortherequirementsofendusers,astarkdifferencefromthecentralgenerationparadigm.

• Keytothischaracteristicistherelianceontheflexibilityofadvancedpowerelectronicsthatcontroltheinterfacebetweendistributedresourcesandtheirsurroundingacsystem.

HierarchicalcontrolofDGsystems• Inadditiontothepowerelectronicscontrol,amicrogrid

requiresoperationalcontroltoensureeconomiccommitmentanddispatchwithinenvironmentalandotherconstraints.

• InaDGpowersystem,thereareneedsofcoordinationofcontrollayers.

• Ahierarchicalsystemconsistsofseveraldecision‐makingcomponentsandhasanoverallgoal,whichisdistributedamongitsindividualcomponents.

• Thelevelsofthehierarchyexchangeinformation(usuallyvertically)amongthemselvesinaniterativemode,andasthelevelincreases,thetimehorizonincreases(i.e.,lower‐levelcomponentsormodulesareusuallyfasterthantheir

Hierarchicalconfiguration


higher‐levelcounterparts).

• Inamultilayerhierarchicalstructure,thefirstlayeractsastheregulationordirectcontrollayer.Itisfollowedbyoptimization,adaptation,andselforganizationfunctions.

• Amulti‐echelonstructureconsistsofanumberofsubsystemssituatedinlevelssuchthateachonecancoordinatelower‐levelunitswhileitisitselfcoordinatedbyahigher‐levelunit.

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FirstControlLayer‐‐Actuator

• Themosttime‐demandinglevelofcontrol,thefirstlayer(actuator),isrelatedtotheswitchingofhigh‐power transistors in the power electronicpowertransistorsinthepowerelectronicconverters.

• Thistaskrequireshigh‐speed,real‐timecontrolwithsamplingratesontheorderofmicroseconds.

• Vectorcontrol,spacevector,pulse‐width


modulation,currentregulation,suppressionofharmonics,andpowerelectronicdeviceprotectionarewithinthislayer.

SecondControlLayer‐‐Supervisor

• Asecondlevelofcontrol(supervisor)isrequiredtomanagethesystem;togeneratepowersetpoints to control the power flow among the energypointstocontrolthepowerflowamongtheenergysource,energystorage,andload;tocontroldcoracbusvoltage;andtomonitorfaultysignals.

• TheparticularsignalstobecontrolleddependonthespecificDGtechnology,butsamplingratesonthe order ofmilliseconds are typically required


theorderofmilliseconds aretypicallyrequired.

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ThirdControlLayer‐‐Excecuter

• Thethirdlevelofcontrol(executor)isrelatedtocommunicationstoexternalequipmentandtheoutsideworld,whichprovidesavarietyofremotemonitoringand, p y gcontrol.

• Theexecutorlevelisresponsibleforimplementationofcontrolschemestoproduceasmuchenergyfromthesystemaspossibletorecovertheinstallationcost.

• Policiesrelatedtothecostsoffuel,maintenance,andnegotiation with neighbor sites are implemented in this


negotiation withneighborsitesareimplementedinthislevel.

• Typically,samplingtimesareontheorderofminutes,andhours arerequiredtoimplementsuchpolicies.

GotSomethingtoshare?

ShareyourknowledgeaboutDG controlwith the rest of the class in 3


DGcontrolwiththerestoftheclassin3minutes!

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PARTII:RelatedHotResearchTopics,ExistingState‐of‐the‐ArtSolutions

(PublishedAlreadyintheLiterature),NewResearchIdeas


ControlofPowerConditioningUnitsIntegratingRenewableEnergy—Anexampleproblem

AC‐DCandDC‐DCboostconvertershavetransferfunctionswithhighnon‐linearity. ThetransferfunctionislinearizedaroundanoperatingpointandthePIcontrolleris

basedonthislinearizedversionofthetransferfunction. This limits the stable operating range of the controller a band around a certain value of Thislimitsthestableoperatingrangeofthecontrollerabandaroundacertainvalueof

loadcurrent.

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2

V is the output voltageVg is the input voltageD is the duty cycle (control parameter)R is the output resistanceRL is the inductor internal resistance


The duty cycle to output voltage boost converter’s transfer function is highly nonlinear. It has to be linearized around a limited operating range such as 1, 2 and 3.

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More Need for a Smart Controller

186

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tag

e (V

olts

)

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Vol

tage

(V

olts

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Conventional PI Controller—Less ripple at steady state, BUTpoor transient response

0 0.25 0.5 0.75 1

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Time (sec)

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0 0.25 0.5 0.75 1

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Time (sec)

Conventional PID Controller—More ripple at steady state, BUTgood transient response


0 0.25 0.5 0.75 1

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194

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Time (sec)

Vol

tage (V

olts

) Smart Controller—Lessripple at steady state, and good transient response

ProposedSolutionfromtheLiterature[1] Inordertomaximizetheoperatingrangeofthecontrol

systemandmakethecontrollercapableofhandlingwiderangeofoutputcurrents,theparametersofthePIDcontrollerweretunedatdifferentoperatingranges

Afuzzyagentisthenusedtoautonomouslysettheparametersbasedonthecurrentoperatingpoint.

Ablockdiagramoftheproposedsmartcontroller

ToenhancethetransientresponseoftheconverterbycontrollingthederivativegainofthePIDcontroller

Thetuningprocessaimsatminimizingtherisetime,settlingtime,rippleandsteadystateerroroftheoutputvoltage oftheboostconvertercorrespondingtostepchangesininputvoltageandload.

ts

Energy Systems Research Laboratory, FIU• Conventional PI controller Load step change response (220W-1kW) • Smart PID controller Load step change response (220W-1kW)

Res

ult

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MoreControlIssuesandProposedSolutionsforDiscussion Controllingahybridsourcesystem isnotaneasycontroltask.In[2],Jiangetaldeveloped

adigitallycontrolledfuelcell/batteryhybridsource.Digitaltechnologywasappliedinthe control of power electronics due to many advantages over analog technology such asthecontrolofpowerelectronicsduetomanyadvantagesoveranalogtechnologysuchasprogrammability,lesssusceptibilitytoenvironmentalvariations,andlowpartscount.TheusercansettheFCcurrentlimit,batterycurrentlimit,andbatteryvoltagelimitinthedigitalcontroller.

In[3],theauthorsdevelopedamodifieddroopcontrollertoovercometheproblemsattachedtoparallelingDC‐DCconvertersinstandaloneDCsystems.Circulatingcurrentbetweenconverterswasusedtomodifynominalvoltagessuchthaterrorbetweenthemisreduced.Thisimprovescurrentsharingamongconverters.Theadvantageofthedevelopedalgorithmasclaimedbytheauthorsisthat,equalcurrentsharingisachievedl h l l l


alongwithlow‐voltageregulation. Athighswitchingfrequenciesandpower,theswitchinglossesbecomesignificant.In[4],

theauthorsdescribedanonisolated highstep‐upDC‐DCconvertersusingzerovoltageswitching (ZVS)boostintegrationtechnique(BIT)andtheirlight‐loadfrequencymodulation(LLFM)control.

GotAnyNewIdeas?

DEMAND‐SIDEMANAGEMENT Loadmanagementimpliesmodifyingtheloadprofilebypeak‐loadclipping,valleyfilling,

loadshifting,reducingvoltage(brownout),reducingload,andloadbuilding. Demand‐sidemanagement(DSM)meansmodifyingenergyusetomaximizeenergy

efficiency.Incontrasttosupply‐sidestrategies,whichincreaseorredistributesupplies(bybuildingnewpowerplantsorchangingsystemreconfigurations),thegoalofDSMistosmoothoutthepeaksandvalleysinelectric(orgas)demand.

Itmakesthemostefficientuseofenergyresourcesanddeferstheneedtodevelopnewpowerplants.Thismayentailshiftingenergyusetooff‐peakhours,reducingoverallenergyrequirements,orincreasingdemandforenergyduringoff‐peakhours.

DSMstrategiescanbeclassifiedaspeak‐clippingorvalley‐fillingstrategies. Inpeak‐clippingstrategy,acontrollerseekstoreduceenergyconsumptionatthetimeof

peakload.Inprogramstoreducepeakload,theutilityorconsumergenerallyexertscontroloverappliancessuchasairconditionersorwaterheaters.DGsystemssuchasphotovoltaicandsolar–thermalpowersuppliescanplayaroleinclippingpeakdemandifitcoincideswiththeiroutput.


p Invalley‐fillingstrategies,thegoalistobuildupoff‐peakloadstosmoothouttheloadand

improvetheeconomicefficiencyoftheutility. Anexampleofvalleyfillingischargingelectricvehiclesorelectrolyzingwatertoproduce

hydrogenandoxygenatnight,whentheutilityisnotrequiredtogenerateasmuchpowerasduringtheday.Largebatterystoragecanalsobeoperatedatnight,andtheenergystoredcanbeusedforpeakclippingduringtheday.

Economicassessment,includingcharginganddischarginglosses,mustbeaccountedfortovalidatethefeasibilityofthisoption.

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ImplementationofDSM Themostobviousexampleisalow‐priceelectricitytarifftomaintainloadfornuclear

powerandlargecoal‐burningstationsatnight.Thereareseveraloptionsforimplementingnighttimetariffmeasures: Consumermetersareswitchedtodifferentenergy‐flowregistersbyalocalclockora

radiosignal(suchasintheUnitedKingdom,oftennamed‘‘Economy7’’),whichallowsg ( g y )allloadtochangetariff.Consumers’billsshowenergyconsumedateachtariff,andtheyarechargedaccordingly.

Specificloads(e.g.,storageheatersandwater‐tankheaters)areenabledbytimeclocksorripplecontrol(asignal‘‘downthewire’’),asiscommoninAustraliaforwaterheatersandintheUnitedKingdomforspaceheaters.Theseloadsarewiredonaseparatecircuitwithaseparatemeterregister.

Thetechnologyforremoteswitching(ripplecontrol)iswidelyavailable(e.g.,fromLandis+Gyr andSiemens).Therearemanywaystocommunicatesuchcontrol,includingthrough long wave radios mobile telephone networks and signals sent on power lines


throughlong‐waveradios,mobiletelephonenetworks,andsignalssentonpowerlines. Moderndigitalelectronicsofferaccurate,low‐costcommunicationfortariffinformation

ordirectcontrol.Also,moderncommunicationmethodsallowremotemeteringtomeasureandmonitorelectricityconsumptionatshortintervals(e.g.,minutes).AnalysisofsuchinformationallowsrecommendationsforDSMandreducedconsumption.Thecommunicationtechnologiesforremotemeteringaresimilartothoseneededforremoteswitching.

ResearchExamplefromtheLiterature In[5],Ahmedetaldevelopedanenergymanagement

algorithmthataimsmainlyatmanagingtheenergywithinahybridsystemsuchthattheeffectofpulsed(shortduration)loadsonthepowersystemstabilityisminimized.

Moreover,anaverageannualsavingofaround7%isachievedbyshiftingloadstooff‐peakhours.


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MoreProposedDSMAlgorithmsforDiscussion—OptimizationandPHEVs

Solvinganoptimization managementproblemincomplexsmartgridsissubjectedtoresearch.In[6],Logenthiran etalpresentedademandsidemanagementstrategybasedon load shifting technique for demand side management of future smart grids with aonloadshiftingtechniquefordemandsidemanagementoffuturesmartgridswithalargenumberofdevicesofseveraltypes.Theday‐aheadloadshiftingtechniqueproposedinthatpaperwasmathematicallyformulatedasaminimizationproblem.Aheuristic‐basedEvolutionaryAlgorithm(EA)thateasilyadaptsheuristicsintheproblemwasdevelopedforsolvingthisminimizationproblem.

WithexpectedhighpenetrationofPHEVs,researchersinvestigatewaystooptimizetheutilizationoftheirV2Gcapability.In[7],theauthors.Thispaperaimsatinvestigatedthepotentialbenefitsofbatteryelectricvehicles(BEVs)andplug‐inhybridelectricvehicles(PHEVs)asdynamicallyconfigurabledispersedenergystorageactinginavehicle‐to‐b ld (V2B) d V2B h ll bl d b f


building (V2B)operatingmode.V2BisaconceptthatispracticallyviabletodaybeingfarsimplerthanV2G,anditmaybeimplementedona3–5yeartimehorizonwhileV2Gmaytake10–15yearstogainwideracceptance.Basedonthebatterycharacteristics,thebenefitsofusingBEVs/PHEVsasenergystoragefordemandsidemanagement(DSM)andoutagemanagement(OM)arediscussedindetail.

GotAnyNewIdeas?

IslandingandInterconnectionControl

• Unintentionalislandingisaconcernfortheutilitybecausesourcesconnectedtothesystembutnotcontrolledbytheutilityposeapossibilityofharmtoutilitypersonnel

• Furthermore,specialsynchronizationandvoltage‐levelmatchingmeasureswillhavetobetakenforreconnectionoftheutilitypower.

y yanddamagefromuncontrolledvoltageandfrequencyexcursions.

• Inaddition,utilityequipmentsuchassurgearrestersmaybedamagedbyovervoltages duringashift‐neutralreferenceorresonance.

island


• Islandingcanleadtoasynchronousreclosure,whichcandamageequipment.Itisthereforeimportantthatmicrogrid systemsincorporatemethodstopreventunintentionalislanding.

• However,intentionalislandingmayoccurwhenasecureaggregationofloadsandsourcescapableofoperatinginparallelwith,orto,endusersallowspowerflowonlywithinthemicrogrid orsafelyexportsittotheutilitygrid.

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MoreResearchDirections

Energypricingwiththeexistenceofdistributedgeneration[8].

P i bili d fi i Powersystemprotection,stabilityandreconfigurationwiththeexistenceofdistributedgeneration.

Absenceofinertiainstationaryrenewableenergysources.Stabilityandcontrolproblem![9]

Loaddemand/renewableenergyforecasting.Linearandnon‐linearregression,ANN,Kernelmethods,greymodelsd l h d l d l d


andseveralothermodelsaredeveloped. Securityanalysisofpowersystemswithhighpenetrationofdistributedgeneration.

More…

References1. Ahmed Mohamed; Elshaer, M.; Mohammed, O. , ”Control enhancement of power conditioning units

for high quality PV systems,” Electric Power Systems Research, vol. 90, pp. 30-41, Sept. 2012.2. Zhenhua Jiang; Dougal, R.A.; , "A Compact Digitally Controlled Fuel Cell/Battery Hybrid Power

Source," IEEE Transactions on Industrial Electronics, vol. 53, no. 4, pp. 1094-1104, June 2006.3 A d S F d B G "M difi d d t ll f ll li f d d t i3. Anand, S.; Fernandes, B.G.; , "Modified droop controller for paralleling of dc-dc converters in

standalone dc system," Power Electronics, IET , vol. 5, no. 6, pp. 782-789, July 2012.4. Hyun-Wook Seong; Hyoung-Suk Kim; Ki-Bum Park; Gun-Woo Moon; Myung-Joong Youn; , "High

Step-Up DC-DC Converters Using Zero-Voltage Switching Boost Integration Technique and Light-Load Frequency Modulation Control," IEEE Transactions on Power Electronics, vol. 27, no. 3, pp. 1383-1400, March 2012.

5. Mohamed, A.; Salehi, V.; Mohammed, O.; , "Real-Time Energy Management Algorithm for Mitigation of Pulse Loads in Hybrid Microgrids," IEEE Transactions on Smart Grid, In Press.

6. Logenthiran, T.; Srinivasan, D.; Tan Zong Shun; , "Demand Side Management in Smart Grid Using Heuristic Optimization,“ IEEE Transactions on Smart Grid, vol. 3, no. 3, pp. 1244-1252, Sept. 2012

7 P C D tt P K i M "BEV /PHEV Di d E St f V2B U i th


7. Pang, C.; Dutta, P.; Kezunovic, M.; , "BEVs/PHEVs as Dispersed Energy Storage for V2B Uses in the Smart Grid," Smart Grid, IEEE Transactions on , vol. 3, no. 1, pp. 473-482, March 2012.

8. Pantos, M.; , "Exploitation of Electric-Drive Vehicles in Electricity Markets," IEEE Transactions onPower Systems, vol. 27, no. 2, pp. 682-694, May 2012.

9. Ashabani, S.M.; Mohamed, Y.A.I.; , "A Flexible Control Strategy for Grid-Connected and Islanded Microgrids With Enhanced Stability Using Nonlinear Microgrid Stabilizer," IEEE Transactionson Smart Grid, vol. 3, no. 3, pp. 1291-1301, Sept. 2012.

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Energy Systems Research Laboratory, FIU