轨道侧光伏电力融入城郊高架城市轨道交通牵引电力系统研究

AppliedEnergy260(2020)114177

Contentslistsavailableat

ScienceDirect

AppliedEnergy

journalhomepage:

/locate/apenergy

Studyoftracksidephotovoltaicpowerintegrationintothetractionpowersystemofsuburbanelevatedurbanrailtransitline

XiaojunShen,HongyangWei,LiWei⁎

DepartmentofElectricalEngineering,TongjiUniversity,Shanghai200092,China

HIGHLIGHTS

.

•TracksidePVpowerintegratedintothetractionpowersystemofurbanrailtransit(URT)isstudied

.

•TracksidePVinstallationinsuburbanelevatedURTLineiseconomicallyfeasibleinShanghai

.

•ADCsidePVintegrationschemeandenergymanagementstrategyhasbeensuggested

.

•SimulationmodelsbasedonthecharacteristicsofURTpowersystemandmovingtrainsaredeveloped

.

•ChallengesandfuturedirectivesforDCsidePVintegrationinURTsystemareoutlined

ARTICLEINFO

ABSTRACT

Keywords:

Urbanrailtransit

DCtractionpowersystemTracksidePV

DCsidePVpowerintegrationEnergystorage

Thetracksideofsuburbanelevatedurbanrailtransit(URT)lineisapotentialplatformforplacingPhotovoltaic(PV)panels.ThispaperhasmadeacomprehensivestudyoftracksidePVpowerintegrationintothedirectcurrent(DC)tractionpowersupplysystemofURT.WiththeelevatedsectionofMetroLine11insuburbanShanghaiasanexample,thepotentialPVinstallationcapacityhasbeenevaluated.BasedontheuniquefeatureoftheDCtractionpowersupplysystem,aDCsidePVintegrationschemeandcontrolstrategyhasbeenpro-posed.ThesimulationmodelsbasedontheelectricalcharacteristicsofURTpowersystemandthemovingtrainhavebeenespeciallydevelopedasaneffectivetooltoperformthescenarioanalysisofdifferentPVintegrationschemes,andanenergysavingparameter“k”hasbeenproposedtoevaluatetheenergysavingeffect.Itcon-cludesthatDCsidePVintegrationcanhelptocompensatethetractionvoltageandreducethecatenarytrans-missionlossinthetractionstageoftrains,therebyithasahigherenergysavingrate.EvenbetterperformancecanbeachievedwithbothPVandenergystoragesystem(ESS)integratedintotheDCtractionpowersystem.Theenergysavingresultcanachievetheeffectof“1+1>2”,whichmeansthetotalamountofenergysavingsisevenlargerthanthesumofPVorESSworkingalone.Moreover,thetractionpowerqualityandsafetywillalsobeimproved.

1.Introduction

URThasbecomethepreferredsolutiontosolvetrafficcongestioninlargeandmedium-sizedcitiesinChinabecauseofbeingfast,safe,punctual,andhavingalargepassengercapacity

[1,2]

.However,itisalsoahugeenergyconsumer.InShanghai,theannualenergycon-sumptionofURTismorethan1.9billionkWh.Theenergyconservationproblemisbecomingincreasinglyprominent

[3]

.

Asakindofrenewableenergy,PVpowergenerationhasnopollu-tionandnonoise,anditisconvenientandflexibletoinstall

[4]

,whichhasbeenwidelyusedinmanyfields

[5,6]

.AnumberofstudieshavebeencarriedoutonPVplants

[7]

,PVgridconnectionsystemsand

controlstrategy

[8,9]

.ItisveryattractivetoinstallPVpanelsinURTsystem.ThefuturedevelopmentofURTurgentlyneedstheintroductionofthisgreen,sustainableandlow-carbontechnology.TherehavebeenalreadysomedemonstrativeprojectsinURT.Singaporehasinstalled1MWofPVsystemontheroofofmetrodepots,whichcanreducecarbonemissionsby500tonsperyear.TheBelgianRailwayCompanyhasbuilta3KMlongPVtunnelwithapowercapacityof3MW.IndianRailwaysinstalledPVmodulesontheroofoftrainstoprovideventi-lation,lighting,andairconditioning

[10]

.Japan’sJRRailwayCom-panyinstalleda453KWPVunitontheroofoftheTokyoplatform,whichisexpectedtogenerate340MWhofelectricityperyearandre-ducecarbonemissionsby101tons

[11]

.ShanghaiShentongMetro

⁎Correspondingauthor.

E-mailaddress:

weili@

(L.Wei).

/10.1016/j.apenergy.2019.114177

Received16April2019;Receivedinrevisedform7November2019;Accepted13November20190306-2619/©2019ElsevierLtd.Allrightsreserved.

2

X.Shen,etal.AppliedEnergy260(2020)114177

CompanyalsostartedconstructionofPVrooffor6.8MWvehicleseg-ment

[12]

.ThosedemonstrativecasesshowthatPVaccesstorailtransitcanachievedirectenergyconsumptionandutilizationoftheterminal,whichnotonlyreducestheoperatingcost,butalsoeffectivelyreducesthepowertransmissionloss,therebyachievingthegoalofgreenlowcarbondevelopmentofURT.Therefore,itisofgreatvaluetostudytheapplicationofPVpowerinURTsystem.

TheintegrationmodeofPVisdeterminedbythecharacteristicofURTpowersupplysystem.TherearetwopossiblePVintegrationmodes:AC(alternativecurrent)sideaccessandDCsideaccess.TheACsideaccessmodeeitherinvertsthePVpowerintothelowvoltagesystem,orfeedsitbacktothepowergrid.TheDCsideaccessmodeconvertsPVpowerintoDCtractionpowersystemandprovidestractionpowertothetraindirectly.

Currently,theACsidePVaccessmode,whichiseasiertoimple-ment,isadoptedbymostoftheabovedemonstrativeprojectsandat-tractsmoreattentionofresearchers.Jinetal.

[13]

expoundedthefeasibilityandenergyefficiencyofPVpowergenerationsysteminURTsystem,andproposedtouselowvoltagesideaccessinelevatedstationstoprovideaprospectforchangingtheenergysupplymodeofURT.AccordingtothecharacteristicsofURTandtheadvantagesofPVsystem,Wangetal.

[14]

putforwardtheapplicationschemeofPVintegrationintheelevatedstation,depotparkinglotandelevatedsection.Pankovitsetal.

[15]

proposeatopologyofPVintegrationintotheURTsystem,whileMengetal.

[16]

proposedtocombineESSwithPVpowergenerationtoachievefulluseofPVenergy.§engöretal.

[17]

proposedarailwaystationenergymanagementsystemmodelcom-posedofPVandESS,indicatingthefuturedevelopmenttrendofURT.Beyhanetal.studiedthefeasibilityofusingPVpowerfortheinteriorlightingoftheurbanrailvehicles

[18]

.

Interestingly,thevoltagegeneratedbyPVpanels,generallyaround600–800VDC,matchescoincidentlywiththeDCtractionvoltage.ItmeansthatthePVpowercouldbeintegrateddirectlyintotheDCtractionpowersystemwithlesspowerlossthroughasimpleDC/DCpowerconverter.Moreover,theDCsidePVaccessmodecanalsoworkwithESSwhichwillnotonlyreduceenergytransmissionloss,butalsohelptostabilizethetractionnetworkvoltage.Nevertheless,therearefewstudiesonDCsideaccessmode.Hayashiyaetal.

[19]

studiedthefeasibilityofusingsmartgridtechnologyforrailtransitpowersupplysystems,andpointedoutthatDCsideaccessmodecanreduceenergyconsumptionandtransmissionloss,butonlythroughestimation.Cic-carellietal.

[20]

exploredthefeasibilityofconnectingPVandsuper-capacitorESStoDCtractionsystems,andanalyzedthePVcost.Sayedetal.

[21]

proposedaDC/DCconvertertopologyofthePVsystemconnectedtotheDCside,butdidnotmakeanin-depthstudyonthePVpowerconsumptionstrategy.Inaddition,Greenetal.

[22]

andthemutationchangecharity10:10areworkingtogetheronthetopologyandcontrolmodeofdirectaccesstothetractionpowersupplysystemusingPVpanelalongbothsidesofthetrack.Sofar,therehasnotbeenanyrelatedreportonDCsideaccessdemonstrativeproject.

ThereareseveralinstallationalternativesofPVpanelinURTwhichcanbethetrainroof,parkinglot,depotroof,soundbarrier,theelevatedplatformroofandthetwosidesofelevatedline.Inthispaper,withelevatedMetroLine11insuburbanShanghaiasanexample,wefocusonthefeasibilityofPVinstallationalongthetracksideofsuburbanelevatedlineastheprobabilityofthisareabeingshadedbytallbuildingsislessthanthatindowntownarea.Basedonthecharacter-isticsofURTpowersupplysystem,acomprehensivestudyismadeofPVintegrationintotheDCtractionpowersystemintermsofpotentialPVinstallationcapacity,possiblePVaccesspoints,energysavingrateandpowerqualityimprovement.Thenoveltyofthispaperissum-marizedasfollows:

(i)FeasibilityandinstallationpotentialoftracksidePVinstallationinsuburbanelevatedlinehasbeenevaluatedwithShanghaiMetroLine11asanexample.

(ii)BasedontheuniqueelectricalcharacteristicsofURTpowersupplysystem,simulationmodelsofURTpowersystemandthemovingtrainhavebeenespeciallydevelopedasaneffectivetooltoperformthescenarioanalysisofdifferentPVintegrationschemes.

(iii)ADCsidePVintegrationschemeandenergymanagementstrategyhasbeenproposed.ScenarioanalysishasbeenperformedtoassesstheenergysavingcharacteristicsofDCsidePVintegration.Anenergysavingrateparameter‘k’hasbeenproposedtoevaluatetheenergysavingeffect.

(iv)ComparativeanalysishasbeenmadeonACandDCsidePVin-tegrationintermsofenergysavingeffect,powersupplyqualityandsafety,andweconcludethatDCsidePVintegrationhasmoreadvantageintermsofenergysavingrateandpowerqualityim-provement.

Thepaperisstructuredasfollows:

Section2

ismainlyaboutthetechnicalandeconomicanalysisofthefeasibilityoftracksidePVin-tegrationbasedonthedataofShanghaiURTLine11.

Section3

dis-cussestheuniquecharacteristicsofURTpowersystem,andabriefDCsidePVintegrationschemeandenergymanagementstrategyhasbeenproposedaccordingly.In

Section4

,theenergysavingeffectanalysisofDCsidePVintegrationhasbeenperformedbasedonsimulation.

Section5

isacomparativeanalysisofACandDCsidePVintegrationintermsofenergysavingeffect,powersupplyqualityandsafety.Thenin

Section6

,thechallengesandfutureopportunitiesaresummarizedandfinally

Section7

summarizesthisresearch.

2.FeasibilityoftracksidePVinstallationinsuburbanelevatedURTline

2.1.PotentialcapacityoftracksidePVinstallation

Inthepasttwodecades,URThasdevelopedrapidlyinChina.AsofApril2019,38citieshaveopenedsubways.Amongthem,ShanghaiMetrohasamileageof705km,rankingthefirstintheworld.ItisnoteworthythattheURTlinesusuallyhavelong,elevatedsectionsinthesuburbsofChina’sbigcities.Thetracksidealongtheelevatedsections,whichisfreeoftheshadingoftallbuildings,canbeusedforPVinstallation.

Inwhatfollows,weuseShanghaiMetroLine11asanexampleandanalysethepotentialofthetracksidePVcapacity,anditisaquitere-presentativemetrolineinChina’sbigcities,whichisfeaturedbythelongelevatedsuburbansection.ShanghaiMetroLine11hasanoper-atingmileageofabout82km,startingattheDisneyStationinsoutheastShanghai,crossingthecitycentre,andendingatHuaqiaoStationinnorthwestShanghai.Thecitycentresectionrunsunderground,andthesuburbansectioniselevated.Thereare14elevatedstationsinall,withalengthofapproximately22.5km.ThepossibletracksidePVin-stallationspacecanbetheareabetweenthetrackandthesidebarrier,asshownin

Fig.1

.

ShanghaiislocatedattheforefrontoftheYangtzeRiverDeltainChina,withthecoordinatesof31o14′northlatitudeand121o29′eastlongitude.Ithasanannualsunshineof1665.3handanannualaveragedailyradiationof12317.8kJ/m2

[23,24]

.AccordingtothestudyofZangetal.

[25]

,theyearlyoptimumtiltangleofsolarpanelinShanghaiisα=24.2°.ThespacewhichcanbeusedforplacingthePVpanelforLine11is1.60mwide,andthustheinstallableareaisap-proximately39,500m2forasingleline.SinceURThasuplinkanddownlinklines,thetotalavailableareaisabout79,000m2.Supposetheeffectivepossibleareais80%andtheefficiencyofPVmodulesis15%,thePVcapacitycouldbearound9.48MWp,andtheannualpowergenerationisabout11,840,000kWh.

Table1

showsthedataoftheelevatedsuburbansectionsofURTinShanghaiandBeijingbyDecember2018.Mostofthelineshavelongsuburbanelevatedsections,whicharesuitableforPVinstallation.ItcanbeseenthatsuburbanURTlinesprovideanewplatformfordistributed

3

X.Shen,etal.

Fig.1.PVInstallationdiagramononetracksideofelevatedURTline(a)Thetrackofelevatedline(b)PossiblePVinstallationlocationonthetrackside.

Table1

DataofsomeelevatedsuburbanlinesinShanghaiandBeijing.

City

LineNo.

Length

Numberofelevatedstations

Shanghai

Line5

30km

18

Line8

12Km

4

Line9

12km

4

Line16

50km

10

Line17

17km

6

Beijing

Line5

9km

7

Line13

40km

15

PVpowergenerationsystemandhasgreatapplicationpotentials.

2.2.Returnofinvestment(ROI)oftracksidePVinstallation

ROIisanotherkeyissuetoconsiderinthefeasibilitystudyoftracksidePVinstallationinURTsystem.Theon-gridpriceofPVpowergenerationsetbytheNationalDevelopmentandReformCommissionofChinais1yuan/kWhinShanghai,andtheyearlyrevenuegeneratedbythePVsystemis11,840,000yuanaccordingly.WiththecurrentcostofroofPVinChinabeingabout10,000yuan/kW,theone-timeinvestmentoftracksidePVsysteminthesuburbansectionofLine11willbe94,800,000yuanandtheROIwillbeabout8years.WiththePVcostgettingdownandthepowergenerationefficiencyenhanced

[26]

,thetimecostfortheROIwillbeevenless.AccordingtoJinyueYanetal,

AppliedEnergy260(2020)114177

Citypower

AC110kV

\

Mainsubstation

AC35(33)kV

Step-downsubstation

Tractionsubstation

DC1500V

AC400V

/

+

Train

—-Rail

Fig.2.ThediagramofURTpowersupplystructure.

thesubsidy-freePVelectricitypricecanbeevenachievedinChinawiththedevelopmentofPVtechnology

[27]

.ThetracksidePVinstallationwhichtakesfulladvantageoftheidlespaceoneithersideoftheele-vatedtrackisverypromising.ItwillbringhugeeconomicandsocialbenefitsforacitylikeShanghai.

3.PVpowerintegrationintotheDCtractionpowersystem

3.1.PossiblePVaccesspointsinURTpowersystem

InChina,theinputoftheURTpowersupplysystemisACpowergrid,andtheoutputisDCtractionpowersystem(750Vor1500V)andAClowvoltagesystem(400V).TheDCtractionpowersystemprovidestractionpowertothetrainbyconverting35kVACinputinto750Vor1500VDCoutput;theAClowvoltagesystemprovideslighting,ven-tilationandairconditioningpowertostationsbytransforming35kVACinputinto400VACoutput.

Fig.2

illustratesoneofthetypicalstructuresofURTpowersupplysystem.Theinputisa35kVACvoltagesourcetransformedfromthe110kVACcitypowergrid.TheoutputofURTpowersupplysystemisthe400VACsystemtransformedthroughthestep-downsubstationand1500VDCtractionpowersystemconvertedbythetractionsubstation.

AccordingtothefeatureofURTpowersupplysystem,thepossiblegridconnectionpointsforPVpoweraccessisshownin

Fig.3

.TheACsideaccesspointcanbe35kVor400VACbusandDCsideaccesspointisthe1500VDCbus.

TheACsidePVaccessmodecanberealizedthroughagrid-con-nectedinvertertoensurethattheoutputpowermeetsthevoltageandfrequencyrequirementsoftheACbus

[28,29]

.TheenergymanagementstrategyofACsideaccessisrelativelysimpleandcanrefertotheex-istingresearchfindingsinrelatedfields

[30,31]

.ThedisadvantageofACsideaccessisthatitalwaysneedsaninvertertoensuretheproper

AC110kVGridAC33/35kVAC400V

(1)(2)

transformersACload

transformer

itransformer(3)DCload

DC750/1500V

Fig.3.ThepossiblegridconnectionpointsforPVpoweraccess.

4

X.Shen,etal.AppliedEnergy260(2020)114177

integrationofPVpowerintotheACbus,whichwillintroduceharmonicpollutiontotheoriginalsystemandincreasetheoperationcost.Moreover,ifPVpowerisintegratedintothe35kVACbusandsentbacktotheurbangrid,thebidirectionalpowerflowbetweenthegridandtheURTpowersystemwillcausevoltagefluctuationandincreasetheriskofshort-circuit,whichwillnotonlyaffectthenormaldeploymentofthepowersector,butalsoposesasafetyhazardtotheoperationofrailvehicles

[32]

.

Asmentionedin

Section1

,theDCsidePVaccessmodecanfeedthePVpowerdirectlyintotheDCtractionpowersystemthroughasimpleDC/DCconverter,whichismoreefficientcomparedwithACsideac-cess.SincethePVpowerwillnotbesentbacktotheupperlevelACsystembutabsorbedbythetrains,thepowerqualityandharmonicpollutionissuesarenotsodominant

[33]

.AnotheruniqueadvantageisthattheDCsideaccessmodecanhelptostabilizethevoltagefluctua-tionoftractionpowersystemcausedbythefrequentlyswitchingop-erationmodeofthetrain.Inthefollowingpart,basedonthechar-acteristicsofDCtractionpowersystem,theDCsidePVaccessschemeandenergymanagementstrategyarefullydiscussed.

3.2.CharacteristicsofDCtractionpowersystem

TheDCtractionpowersystemofURTisatime-varyinginteractivesystem.Theuniquefeatureischaracterizedbyitsload—themovingtrain.Thepowerdeliveredtothetrainismainlysuppliedbythetwonearbytractionpowerstations.Whenthetrainismoving,theim-pedancebetweenthetractionpowersubstationandthetrainisalsochanging,andthevoltagedropinthecatenarycannotbeneglected.Meanwhile,thetrainfrequentlyswitchestheworkingmodefromac-celerating,coastingtobraking,whichwillcauseseriousvoltagefluc-tuation.

Fig.4

isaschematicdiagramthetypicalspeedprofileofthemetrotrainbetweentwostationsandthecorrespondingcatenaryvoltagefluctuationunderdifferentworkingmodesofthetrain.Thespeedprofileofthemetrotrainispredefinedbythemetrotraintimetable.‘U0’istheratedcatenaryvoltagewithoutmovingtrain,whichisusuallyaround1500V.ForaDC1500VURTtractionpowersystem,theworkingvoltagefluctuationrangesfrom1000Vto1800V.

Therearethreetypicaloperationstagesforthetrainrunningbe-tweentwostations:stage‘1’istheaccelerationstage,stage‘2’isthecoastingstage,andstage‘3’isthebrakingstage.Instage‘1’,thetrainisaccelerating,andthepowerdemandisincreasing.Themaximumpowerofasingletraincanreachupto4MWorevenhigher,andthecurrenttransmittedthroughthecatenarycanreach3000Aorevenhigher,whichwillcausesignificantcatenaryvoltagedropatthepantograph.In

Fig.4.Typicalspeedprofileoftrainandthecorrespondingcatenaryvoltagefluctuation.

stage‘2’,thetrainiscoasting,andthepowerdemandismuchlesscomparedwithstage‘1’.Inthisstage,thepowerismainlyconsumedbytheconstantlowpowerloadsuchasairconditionandventilationsystem.Therefore,thecurrenttransmittedthroughthecatenarywillbemuchsmallerandthevoltagefluctuationismuchlessaccordingly.Instage‘3’,thetrainisbraking.ItwillfirstregeneratethebrakingenergytothenearbyacceleratingtrainsthroughtheDCcatenaryresultinginthecatenaryvoltagerise.Iftheregenerativevoltageexceedsthethreshold,generallysetas1780V,theon-boardresistorwillbetrig-geredtoconsumetheextrabrakingenergy.

Usually,thebakingenergyofthetrainisabout40%ofthetractiveenergy.However,intheactualworkingscenarioofURT,thebrakingenergycannotbefullyutilizedthroughregenerativebrakingbecausethenearbytrainsmaynotworkinaccelerationmodeorhaveenoughcapacitytoabsorbthebrakingenergy.

3.3.PVaccessschemeandenergymanagementstrategyinDCtraction

powersystem

WiththepurposeofefficientuseofbrakingenergyandsmoothingthevoltagefluctuationofDCtractionpowersystem,aDCsidePVac-cessschemewithESSisproposed,asshownin

Fig.5

.ThePViscon-nectedtotheDCbusandtheESSviaasingleinput,dual-outputDC/DCconverter.TheESSisconnectedtotheDCbusthroughabidirectionalDC/DCconverterwhichenablesdoubledirectionpowerflow.

BasedontheabovePVaccessscheme,abriefDCsideenergyab-sorptionandutilizationconceptisdeveloped,asshownin

Fig.6

.

Inthemorningandeveningpeakhours,theirradiationintensityisweak.Therearemoretrainsinoperationwithalargerpassengerflowvolume.Thetrainisinaheavyloadstate,andthereisagreatdemandforpowerinthetractionstage,whichwillcausealargedropinthecatenaryvoltage.ThePVpowergenerationduringthisperiod,how-ever,isinadequate.Ontheonehand,thesmallPVpowergenerationhaslittlevoltagecompensationeffectinthisperiodoftime,andontheotherhand,thereexistspowerlossinthetransmissionprocess.Therefore,duringthepeakhoursofoperation,thePVpowergenerationsystemdoesnotsupplypowertothecatenarydirectly,butstoresenergyinthestoragesystemtochargetheenergystoragedevice.Thedeviceprovidesstablepowertothegridthroughthestoredenergyinthestoragesystem,whichcompensatesthecatenaryvoltageinatimelymannerandthusensuresthesecurityofthetractionnetwork.Theen-ergymanagementstrategyinmorningandeveningpeakhoursisshownin

Fig.6

(a).

Intheoff-peakhoursduringtheday,theirradiationintensityisusuallystrong.Whenthetractionnetworkvoltageisrelativelylow(correspondingtotheequivalenttractionofthevehicle),thePVmod-ulestransmitpowertothegriddirectlythroughtheDC/DCconverter.Asitdoesnotpassthroughtheenergystoragedevice,theenergylossisreduced.Whenthetractionnetworkvoltageisrelativelyhigh(corre-spondingtotheequivalentregenerativebrakingofthevehicle),thePVsystemchargestheenergystoragedevice,whichthenreleasestheen-ergywhenthetractionnetworkvoltagedropstoacertainvalueto

ESS

DC/DCConverter

DC

DC

DC

DC

PV

Bidirectional

DC/DCConvertor

Traction

Substation

Train1

Tractioncatenary

Trainn

Rail

Fig.5.ADCsidePVaccessschemewithESS.

X.Shen,etal.

Fig.6.SchematicdiagramofDCsideenergymanagementstrategy.(a)PowerflowwhenPVout<PVmin(b)PowerflowwhenPVout>PVmin.

achievebetterenergyefficiency.Inanyoftheabovestagesoratnight,theESSinalsoinvolvedinbrakingenergyrecovery.Theenergyman-agementstrategyintheoff-peakhoursisshownin

Fig.6

(b).

Theenergyabsorptionandutilizationstrategycanbesummarizedasfollows:whentheoutputPVpowerislowerthantheminimumsetthresholdPVmin,itwillbeusedforchargingESS;whentheoutputPVpowerishigherthantheminimumsetthresholdPVmin,andiftheca-tenaryvoltageUnet<Umin(thesetminimumcatenaryvoltagethreshold),bothPVandESSwillsupplypowertothecatenarytofillthevoltagevalleycausedbythetractionofthetrain.IfUnet>Umax(thesetmaximumcatenaryvoltagethreshold),ESSwillabsorbthepowergeneratedbyPVandregenerativebrakingofthetraintoshavethevoltagepeak.IfUmin<Unet<Umax,thePVpowerwillbedelivereddirectlytothecatenarywhichwillhelptoreducetheenergycon-sumptionfromtractionpowerstation.

4.DiscussiononenergysavingeffectofPVpowerintegrationinto

DCtractionpowersystem

4.1.Energysavingrateparameter‘k’

Inordertoevaluatetheenergysavingeffectunderdifferentenergymanagementstrategies,hereweintroduceaparameter‘k’torepresentenergysavingrate.Itcanbecalculatedbythefollowingexpression:

k=

W0−W1

Wpv(1)

whereW0denotestheoriginalenergyconsumptionofthetractionpowersystemofURTwithoutPVintegration,W1denotesthatwithPVintegration,andWpvistheenergygeneratedbythePVsystem.TheenergyconsumptionofthetractionpowersystemofURTiscalculatedbasedonthepowerflowofthetractionpowerstation.Byintroducingthisparameter,wecanhaveaclearjudgementoftheenergysavingeffectunderdifferentPVenergymanagementstrategies.Apparently,thelargerthevalueofk,thebettertheenergysavingeffectachieved.

Inwhatfollows,theenergysavingeffectwithPVintegrationunderdifferentenergymanagementstrategieswillbestudiedthrough

AppliedEnergy260(2020)114177

Table2

Theparametersusedinsimulation.

Tractionsubstationspacing

3km

Tractiondistance(FromItoII)

1.4km

Unitimpedanceofcatenary

34.36e−6O/m

Unitimpedanceofrail

39.5e−6O/m

Systemno-loadvoltage

1500V

Ratedcapacityoftractionstation

8.8MVA

Equivalentinternalresistanceoftractionsubstation

0.05O

Ratedpoweroftrain

4MVA

Maximumtractionspeed

80km/h

Tractionacceleration

0.9m/s2

Brakingdeceleration

–1.0m/s2

theoreticalanalysisandsimulation,andweuseparameter‘k’asanindicatortoevaluatetheenergysavingeffect.

4.2.Energysavinganalysisunderdifferentscenarios

Basedont