Seite - 54 - in Emerging Technologies for Electric and Hybrid Vehicles

Energies 2017,10, 1217 gridsandoffersavastarrayofadvantages tooffer reliablepowersupplyandadvancedcontrol. Insuchasystem, themuchcovetedcoordinatedcharging iseasilyachievableas interactionwith thegridsystembecomesverymuchconvenientevenfromtheuserend.The interactionofEVs andsmartgridcanfacilitateopportunities likeV2Gandbetter integrationofrenewableenergy. In fact,EVisonetheeightpriorities listedtocreateanefficientsmartgrid [117]. • V2G:V2Gorvehicle togrid is amethodwhere theEVcanprovidepower to thegrid. In this system, thevehiclesactas loadswhentheyaredrawingenergy,andthencanbecomedynamic energystoragesby feedingback theenergy to thegrid. Incoordinatedcharging, theEVloads are applied in the valley points of the load curve, in V2G; EVs can act as power sources to provideduringpeakhours.V2Gisrealizablewith thesmartgridsystem.Bymakinguseof the functionalitiesof smartgrid,EVscanbeusedasdynamic loadsordynamicstoragesystems. The powerflowin this systemcanbeunidirectionalorbidirectional. Theunidirectional systemis analogous to thecoordinatedchargingscheme, thevehiclesarechargedwhenthe load is low,but the timetocharge thevehicles isdecidedautomaticallybythesystem.Vehiclesusing this scheme cansimplybepluggedinanytimeandputthere; thesystemwillchooseasuitabletimeandcharge it. Smartmetersarerequiredforenablingthissystem.Withadrivervariablechargingscheme, the peakpowerdemandcanbereducedby56%[117]. Sortommeetal., foundthissystemparticularly attractiveas it requiredlittleupgradationof theexisting infrastructure; creatingacommunication systemin-betweenthegridandtheEVsisall that isneeded[146]. Thebidirectionalsystemallows vehicles toprovidepowerbacktothegrid. Inthisscenario,vehiclesusingthisschemewill supply energy to thegrid fromtheir storagewhen it is required. Thismethodhas several appealing aspects.Withever increasing integrationofrenewableenergysources (RES) to thegrid,energy storagesarebecomingessential toovercometheir intermittency,but thestorageshaveaveryhigh price. EVshaveenergystorages,andinmanycases, theyarenotusedfora longtime. Example for thispoint canbe thecars in theparking lotsof anofficeblock,where theystayunused till theofficehour isover,orvehicles thatareusedinaspecific timeof theyear, likeabeachbuggy. Studiesalsorevealedthat,vehiclesstayparked95%of the time[117]. Thesepotential storages canbeusedwhenthere isexcessgenerationor lowdemandandwhentheenergy isneeded, it is takenback to thegrid. Thevehicleowners canalsoget economicallybeneficialbyselling this energy to thegrid. In [147],Clement-Nynsetal., concluded thata combinationofPHEVscan provebeneficial todistributedgenerationsourcesbyprovidingstorage for theexcessgeneration, andreleasingthat to thegrid later. Bidirectionalcharging,however,needschargerscapableof providingpowerflowinbothdirections. It alsoneeds smartmeters tokeep trackof theunits consumedandsold,andadvancedmeteringarchitecture (AMI) to learnabout theunit charges in real time toget actual cost associatedwith the chargingordischargingat the exact timeof theday. TheAMIsystemcanshift54%of thedemandtooff-peakperiods,andcanreducepeak consumptionby36%[117]. Thebidirectional system, in fact, canprovide12.3%moreannual revenuethantheunidirectionalone. But takingthemeteringandprotectionssystemsrequired in thebidirectionalmethod, this revenue isnullifiedandindicates theunidirectional systemis morepractical. Frequent charginganddischarging causedbybidirectional charging canalso reducebattery lifeandincreaseenergylosses fromtheconversionprocesses [81,117]. InaV2G scenario,operatorswithavehiclefleetare likely toreduce theircostofoperationby26.5%[117]. Anotherconcept isproducedusingthesmartgridandtheEVs, calledvirtualpowerplant (VPP), whereaclusterofvehicles isconsideredasapowerplantanddealt likeone in thesystem.VPP architectureandcontrol is showninFigure62. Table26showsthecharacteristicsofunidirectional andbidirectionalV2G. 54