DOC

Study on control strategy of CAN bus network based on event triggered mode

By Tim Kennedy,2014-02-18 23:46
6 views 0
Study on control strategy of CAN bus network based on event triggered modeof,on,CAN,bus,based,event,mode,Study,BUS,MODE

    Study on control strategy of CAN bus network based on event triggered mode HIGHTECHNOLOGYLETFERSIVo1.16No.11Mar.2010IPP.8589

    doi:10.3772/j.issn.10066748.2010.01.016

    StudyoncontrolstrategyofCANbusnetworkbasedon

    eventtriggeredmode?

    LinCheng(林程),ZhouHui~,SunFengchun,NanJinmi

    (NationalEngineeringLabor'at.ryforElectricVehicles,BeijingInstituteofTechnology,Beijing100081,P.R.China)

    Abstract

    In0rdert0reducetheloadrateofCANbusandimprovethereal

    timepeffomaanceofcontrolsys

    tem,CANbuscontrolsystemofapureelectricvehicleisstudied.Cotmnunieationmessagesofeachnode

    areoptimizedandredefinedbysortingthemessageintothreetypes:eontroImessage,statusmessageand

    alaman1essage.EventtriggeredmodeisaddedtothecommunicationwayofCANbus,andthecommuni-

    cati0ncontrolstrategyofthevehicleismade.ItisprovedthatCANbusloadrateofcontrolsystemisre.

    ducedafter0ptimization,andthereal

    timeperformanceofcommunicationisimprovedeffectively.

    Keywords:eleetrievehicle,systemoptimization,eventtriggered,CANbus,controlstrategy"

    0Introduction

    Inordertomeetpeople'sincreasingrequirementto

    automobileperformance,moreandmoreeontmlmodules

    areintegratedtothecontrolnetworksofvehicle,andthe infl0m1ationtransmittedonthenetworkincreasessharply. Especiallyfornewener~vehicle?,2J,

    alargenmaberof

    batterydataaddstheloadofCANbusnetwork,andinflu

    encestherea1.timeperformanceanddependabilityofcon

    trolsystemseriously,.Inordertosolvethisproblem,peo

    plehaveproposedmanysolutions.Forexample,network sectionwasincreasedaceoMingtotheinteractiveinforma

    tion,new.typebuswithhigherspeedwasadopted.Inthis paperoptimizationofthecommunicationtypeofcontrol svstemiscarriedoutundertheconditionofnotchanging hardware,andmeetingcommunicationrequestbutnotin

    creasingnetworkload.

    1CANbuscommunicationnetwork

    CANbusutilizesnondestructivearbitrationmecha

    nismwhenmessagesconflict,andthenodehaving higherprioritywil1gainarbitrationtosendmessages.But ifthereisamessagewith1owerprioritysendingonthe bus.thehigherprioritymessagesmustbewmtmguntil thelowerprioritvmessagesfinishtransmission.There

    sDonsetimeisdefinedasthetimeofmessagefromsending nodesendingouttoreceivingnodecorrectlyreceivingit? Theworstresponsetime

    edasE24]:

    ofmessagescanbeealculat

    ?,

    []+hvphp(m)

    (1)

    B:max{C)(2)

    whereBisblockingtime,whichisthelongesttimethat message-mmaybeblockedbythelowerprioritymes sages.Inordertoimprovethereal?timeperformanceof contmlsystem,thevalueofBmustbereduced.There- abtimerequirementofthelowerprioritymessagesisnot high.andtheydonotparticipateinanyvehiclecontro1. Fig.1Topologicalstmctm'echartofcommunicationnetwork Fig.1isatopologicalstructurechartofcommunlca. tionnetworkofonepureeleetrievehicle.T|lisnetworkis ahigh.speednetworksection,andthebaudrateis 250kbps.Tl1ereare4nodesinthenetworkincludingvehi

    clecontrolunit,motoreontrolunit,automatictransnus sioncontrollerandbattery,managementsystem.Allnodes adopttimetriggeredmodetocommunicate,namelythe nodesendsamessageatflfixedinterva1.

    ileseveralnodeswanttosendmessagesatacer tainmoment,eachmessagecarriesonthecompetitionof righttouseCANbusaccordingtothedefinedpriority. Themessagewithhigherpriorityissentfirst.Thistrigger modeisfeasiblewhentherehasnotmanymessages.Once theamountofmessageincreasesrapidly,itwillinevitably ?SupportedbvtheNati0nalnighTechnology'ResearchandDevelopm

    entProgrammeofChina(No.2008AA1|At46)

    ?Towhomcorrespondeneeshouldbeaddressed.E-mail:zhouhuibit@yahoo.con.eiq

    ReeeivedonSept.1,2009

    86HIGHTECHN0LoGYI.ET1ERSIVl01.16No.1IMar.2ol0 maketheCANbusrunningunderhighloadrate.Because ofthecompetitionofghttouseCANbus,theresponse timeofmessageisdelayedandthedependabilityofthe

controlsystemisreduced.Inordertoimprovethereal

    timeperformanceofCANbuscommunicationsystemand thesafetyofvehicle.itisnecessarytooptimizetl1evehi. clecontrolsystem.

    2.1,nleoptimizationofmessagecontent

    emessageisdefinedasCAN2.0B.Iftheinfor.

    marionamountofonenodeistoolarge,anextramessage frameshouldbeadded.Forexalnple:thecellnumberof apureelectricvehicleismolethan100basically.Inor. dertomonitorthestateofeachcel1.thevoltageandtem. peratureofeachcellmustbeshown.evoltageofthe lithium-ionbatterychangesintherangeof3.60V4.20V basically.Thevalueabytecanexpressis0255.soeach

    celJneedstwobytesfordefiningvoltage.Becausethere. quirementoftemperatureprecisionisnothigh,andnor

    realtemperatureisunder255.abyteisenoughtomeet thedemands.Eachcellneeds3bytestoexpressneces. saryinformation.Supposingthatapureelectricvehicle uses104cells.soitneeds312bytestodefinebatteryin. formation.Eachmessagecallonlydefine8databytes,so 39messagesareneeded.Eachframeneeds0.416msto finishtransmissionunderthebestsituationonly.Ifsend. ingintervalisdefinedas100ms.theCANbusloadrateis uDt016.224%.

    InordertoreduceeloadrateofCANbusunder

    conditionofnotdecreasinginformation.itisneededtodi

    videcommunicationcontentofeachnodeintothreeparts: controlmessage,statusmessage,andalarmmessage.All informationisdefinedbyoneortwoframesintheoriginal communicationprotocolandsentouttogether.Notalljn.

    formationisnecessarytobesentallthetime.soitis neededtoclassifythecommunicationcontent.Becauseof contmllinginformationcaninfluencetheperformanceof vehicledirectly.controllinginformationneedstobesent inrealtime.estatusinformationisdividedintotwo kinds.Onehasnoeffectonoperationofvehicle.butit needstobesentinrealtimebecausethedriverusedto watchtheinformationonthemeter.Itistimetriggered, suchasspeed,thetotalvoltageandheeleetriccurrent,

    etc.Theotherkindonlyneedstobesentunderacertain condition.suchasallvoltageinformationofcel1.Itison. 1yneededtosendthemaximn/nvalueandtheml'nimum valueofthevoltageasUSUa1.Whenthevoltagesofsome cellsaretoohighortoolow.orwhenevehicleis

    charging.theinformationofalJcellscallbesentinrea1. time.Itcanreducethebusloadandimprovethereal

    timeperformanceofeontrolsystemwhenthebatteryis norma1.111emethodofprocessingthesecondtypeofstate informationissimilartothatofthealarminformation.e nodeisinthesleepstatewhenthereisnotrouble.andis activatedoncetroubletakesplace.Itiseventtriggered. AIInodeinformationisredefinedaccordingtotheabove principle.Table1ismessagesdefinitionbeforeoptimiza? tionandTable2ismessagesdefinitionafteroptimization. Thefirstframeiseventtriggeredandthefollowingframe istimetriggered.

    Table1MotorcontroHermessagedefinitionbeforeoptimized HIGHTECHN0IJ()GY1ITrERS1V01.16No.1{Mar.201087 2.2Optimizationofmessagetriggeredmode

    Inordertomakegoodcontrolstrategyofsending

    message,messagetriggeredmodeneedscorresponding0p? timizationbecauseofthecommunicationprotocol's change.

    Distributionofpriorityisasfollows:Thecontrolin. formationhasthehJlghestpriority,andthesafetyrelevant information'spriorityishigherthanthealarminforma. tion'sprioritybutlowerthanthecontrollinginformation's priority.andthestateinformation'spriorityisthelowest. Table3isIDoftheCANnodebeforeoptimization, andTable4isIDoftheCANnodeafteroptimization. Table3IDdefinitionofcommunicationprotocolbeforeoptimization Table4IDdefinitionofcommunicationprotocolafteroptimization 3Controlstrategyofsendingmessage

    Themessageafteroptimizationisdividedintotwo kinds.Oneistimetriggered,andtheotheriseventtrig? gered.TheloadrateofCANbusislowwhenonlythe firsttypeofmessageistransmittedonthebus,andthe controlsystemcanruninagoodstate.Whenthesecond typeofmessagerequirestobesent,thestateofCANbus becomesverybadbecausetheamountofinformationin

    creasessharply.Thetimeoftransmittingmessageisde

    layedmuchanditinfluencesthewholecommunication DeIf0rmaneeofcontrolsystem.Inordertoensurethatthe performanceofvehiclewi11notbeinflueneedunderany ciremnstance.agoodcontrolstrategymustbemadewhen alJmessagesdemandtobesent.

    Vehiclecontrolunithasthehighestpriorityand managestherightofusingCANbus.Itcancancelsome nodes'usingrightofCANbusinsomespecialsituation, sothatacertaintaskcanbefinishedintheshortesttime

    andthereal--timeperformanceofthevehiclecontrolsys-. terncanbeimproved.

    Thepriori~ofmessagethatiseventtriggeredis higherthanthemessagethatistimetriggered,butitis lowerthanvehiclecontrolunit's.

    Whenthereareonlytimetriggeredmessages,the messagescompetewitheachotherandtheonewithhigh

    estprioritywillgettheusingrightofCANbus. Inordertoimprovethequalityofshiftinggearsand shortencommunicationdelaytime,vehiclecontrolunit willregainothernodes'bususingfightbesidesAMTand motorcontrollerandrequiresthetwonodes'message transmittingintervalbringupfromlOOmsto10mswhen AMTshiftsgears.Afterfinishingshiftinggears,vehicle controlunitwillresumeothernodes'bususingright. Inordertoreducethebusloadrateunderthenormal situation,batterymanagementsystemsendsmaximum voltageandminimumvoltageofsinglecell,maximum temperatureandminimumtemperature,totalvoltageand totalelectriccurrentinrea1.time.Becauset}1eamountof informationofsinglebatteryislarge,itissentinevent triggeredmode.Whentheminimumvoltageislowerthan theminimumregulationvalueorthemaximunlvoltageis higherthanthemaximumregulationvalueandwhenbat- terytemperatureisbeyondtheallowedrange,battery managementsystemCansendtheinformationofthisbat

    terytoCANbus,orwhenvehiclecontrolunitsendsorder tothebatterymanagementsystem,batterymanagement systemcouldsendallbatteries'informationtoCANbus. IfsomenodeneedstosendalarminformationtoCAN

    bus,itmustapplythebususingrightfromvehiclecontrol unitthroughtheotherframeofthisnode.Aftergetting usingrightitcansendalarminformationtothebusfor20 times,thenthisframegetsintoawaitingstateuntilthe troublestatechanges.

    Inordertoexaminewhetherthevehicleinformation isintegral,vehiclecontrolunitcandemandallmessages becomingtimetriggered.

    Timetriggeredmodeandeventtriggeredmodeare integratedthroughoptimizingthecontrolstrategy.Itim

    provestherealtimeperformanceofcommunicationand reducesthebusloadrateeffectively.

    4Thefunctionofcontrolsystembeforeand

    afteroptimization

    TheloadrateofCANbusandthetransmittingtime ofkeycontrolinformationregardedasevaluatingobjects 88HIGHrECHN0IJ()GYLErnRSIVo1.16No.1IMar.201O areusedtoevaluatetheperformanceOfthecontrolsystem beforeandafteroptimization.

    Theloadrateundernormalmodebeforeoptimization canbegotby

    ++++

    +++39×(3)

    l2

    

    ll

    x

    l2

    j

    Theloadrateundernormalmodeafteroptimization

    canbegotby =++

    ++?++++(4

    Theloadratewhenshiftinggearsbeforeoptimization

    eanbegotby =+++×10+++

    ++++

    (5)

    Theloadratewhenshiftinggearsafteroptimization

    Canbegotby :

    Crnc22

    ×10+×10(6)

    TheresultsareshowninFigs.27. 23400236002380024OOO242O02440024600248O02500025200

    (ms)

    Fig.2Theloadrateundernormalmodebeforeoptimization

    6.0

    5.5

    5.0

    4.5

    4.0

    3.5

    3.0

    25

    2O

    1.5

    1.0

    O5

    0

    2180022ooo2220o224002280023ooo2320023400 (ms)

    Fig.3Theloadrateundernormalmodeafteroptimization

    19.5

    .

    185

    :

    18.o:

    2150021700219002210022

    ,

    3O0225002270022900~10023300 (ms)

    Fig.4Theloadrate0fshiftinggearsbeforeoptimization

    6?0

    5.8

    5.6

    5.4

    5.2

    5.0

    4.8

    Z

    4-6

    4-4

    4.2

    4.0

    214002l6002l8o022O002220o2240022600228002300o23200

    (ms)

    Fig.5Theloadrateofshiftinggearsafteroptimization

    l0

    lO.8

Report this document

For any questions or suggestions please email
cust-service@docsford.com