Page - 92 - in Emerging Technologies for Electric and Hybrid Vehicles

Energies 2016,9, 86 onabattery swapstationhas received increasingattentionduring recent years [37–39]. However, batteryswapstationshavetheproblemof the lackofunifiedbatterystandards forvariousEVs.As willbediscussedin thenextsubsection, themajorityofpapers in the literature tackle transportation problemsusingEVswith charging stations. Nevertheless, there is an emergingnumber ofworks consideringbatteryswapstations. 3.2. RechargingStationLocation Asmentionedbefore, oneof themain issues to be addressed regarding theEVs success is to determine the location of recharging stations. Therefore, it is important to developmethods that allowminimizing thecostsofdevelopinganalternative infrastructure. This“station locationproblem” canbeconsideredaspecific caseofFacilityLocationProblem(FLP).Thekeyquestions commonly faced by facility planners include: (i) the number of facilities; (ii) the locations of these facilities; and(iii) thetypesof facilities (intermsofsize,productvarietyandotherdesignaspects).Most location models focusoneitherminimizingtheaveragecostof travel (themedianproblem)orminimizingthe maximumcostof travel (thecenterproblem). In theparticularcaseofoptimally locatingrecharging stations, several locationmodels havebeenproposed. Thesemodels canbedivided in twomain groups,node-basedandflow-based,dependingontheirassumptionsof refuelingdemandtype[40]. Thep-medianmodel isawell-knownnode-basedmodel thathasbeenused inmanyarticles to locate conventionalgasolineoralternative-fuelvehicles refuelingstations [41].However, since thedemand forvehicles isgenerally intheformoftrafficflowthatpassesbytherefuelingfacilities[42], themajority ofpapers in the literaturearebasedonflow-basedmodels. Specifically, the locationsof recharging stations forEVs,whichpresentssomepeculiaritiesdueto their limiteddrivingrange, isusually tacked usingflow-basedmodels. Thus,Hodgson [42]providedabasic theoretical framework fordealing with theproblemof locatingstations.However, thisapproachdependsontheassumptionthat, ifone station issitedonanodeofapath, thenall therelatedtrafficflowswillbecaptured.Unfortunately, thisassumptioncannotbeapplied toalternative fuelvehicles since thesehavea limitedrangeand needamulti-stopsystemtoextendtheirdrivingdistanceandcarryout long-distance journeys. Inorder toachieve themulti-stopsneededfor long-distance travel,KubyandLim[43]proposed aflowrefueling locationmodel (FRLM).Theobjectiveof theFRLMis tomaximize thecaptureof the trafficflowsoneachpath ifacombinationofstationssitedonthepathscanbesuccessfullyusedto refuelvehicles, so that theycancomplete their trips. Thismodelneeds tobesolved in twostages. The first stage is tofindfeasiblecombinationsofcandidate locationsofstations torefuel theflowsoneach path,andthesecondstage iswhenthesecombinationsareusedas inputs to themodel todetermine thestation locations.Dueto the time-consumingprocessofgeneratingcombinations infirst stage,Lim andKuby[44]providedsomeheuristicalgorithmstosolve largerscaleproblems.CaparandKuby[45] developedanewapproachtosolve theflowrefueling locationprobleminonestage. Three locating logicswereusedtocheckwhetherapathcouldberefueledbythesitedrefuelingstations. Thefirst is if there isno stationbuilt at theorigin then there shouldbeat least one stationbuiltwithinhalf thevehicle rangeto theoriginnode, so that it canbereachablebyhalfa tankof fuelorhalfabattery charge. Thesecondis if there isastationbuiltata location, thenthenextbuilt facilityshouldbewithin thevehicle range,otherwise thevehiclecannot reachthenextstation. The third is if thevehicle range isgreater thanorequal to twotimes thepath length, thenasinglestationatanypointcanrefuel the entirepath. However, these logics areavailableonlywhen thevehiclehas regained its full fuel or charge level (formaximumrange)aftereachperiodofrefuelingat thestations,e.g.,via fuel-tankor batteryexchange,whichmakes thenewerapproachdifficult toapplywithregardtomultiple types ofstationswithdifferent refuelingorrechargingefficiencies. Inaddition, thisapproachcannotsolve thecapacitated locationproblem,wherebyeachstationhasa limitednumberofdemandstohandle. Basically, suchmodelsdonotconsider the factorsof refuelingorrechargingefficiencyandtime,and are limitedto the locationofasinglekindofstationforperformingthebatteryexchange(orvery fast refueling) torefill thevehicles. 92