Analysis, Design, and Evaluation of AVCS for Heavy

Analysis,Design,andEvaluationofAVCSforHeavy-DutyVehiclesDraftFinalReportDianaYanakievIoannisKanellakopoulosUCLAElectricalEngineeringLosAngeles,CA90095-1594MOU124PATHResearchReportThisworkwasperformedaspartoftheCaliforniaPATHProgramoftheUniversityofCalifornia,incooperationwiththeStateofCaliforniaBusiness,Transportation,andHousingAgency,DepartmentofTransportation;andtheUnitedStatesDepartmentofTransportation,FederalHighwayAdministration.Thecontentsofthisreportreecttheviewsoftheauthorswhoareresponsibleforthefactsandtheaccuracyofthedatapresentedherein.ThecontentsdonotnecessarilyreecttheocialviewsorpoliciesoftheStateofCalifornia.Thisreportdoesnotconstituteastandard,specication,orregulation.June1996iiAnalysis,Design,andEvaluationofAVCSforHeavy-DutyVehicles|DraftFinalReportDianaYanakievandIoannisKanellakopoulosJune1996AbstractInthelongitudinalcontrolproblemforautomatedheavy-dutyvehicles,animportantcontrolobjectiveisstringstability,whichensuresthaterrorsdecreaseastheypropagateupstreamtheplatoon.Itiswellknownthatwhenvehiclesoperateautonomously,stringstabilitycanbeachievedbyusingspeed-dependentspacingwithconstanttimeheadway;however,thisresultsinlargesteady-stateintervehiclespacings,hencedecreasedtracthroughput.Thisdisadvantageisevenmorepronouncedinheavy-dutyvehicles,whichrequirelargertimeheadwaysduetotheirlowactuation-to-weightratio.Inthisreportwedeveloptwonewnonlinearspacingpolicies,variabletimeheadwayandvariableseparationerrorgain,whichallbuteliminatethisundesirablesideeect.Therstpolicysignicantlyreducesthetransienterrorsandallowsustousemuchsmallerspacingsinautonomousplatoonoperation,whilethesecondoneresultsinsmootherandmorerobustlongitudinalcontrol.Furthermore,thetwocanbecombinedtoyieldevenbetterrobustness,asisshownthroughourqualitativeanalysis.KeywordsAdaptiveCruiseControlAdvancedVehicleControlSystemsAutomatedHighwaySystemsControlAutonomousIntelligentCruiseControlBusesCommercialVehicleOperationsControlAlgorithmsControlSystemsIntelligentVehicleHighwaySystemsLongitudinalControlPublicTransitSpeedControlTruckingVehicleFollowerControliiiivExecutiveSummaryThelongitudinalcontroldesignforplatoonsofautomatedvehicleshastoguaranteethede-siredperformancenotonlyforeachindividualvehicle,butalsoforthewholeformation.Akeypropertyisstringstability,whichensuresthaterrorsdecreaseastheypropagateup-streamtheplatoon.Thefactthatstringstabilitycannotbeachievedforplatoonswithconstantintervehiclespacingunderautonomousoperationhasbeenknownformorethantwentyyears(Garrardetal.1978,Shladover1978).Stringstabilitycanbeguaranteediftheleadvehicleistransmittingitsvelocity(Shladover1978)orvelocityandacceleration(Sheik-holeslamandDesoer1990)toallothervehiclesintheplatoon.Thisapproachyieldsstableplatoonswithsmallintervehiclespacingsatthecostofintroducingandmaintainingcontin-uousintervehiclecommunicationwithhighreliabilityandsmalldelays.Stringstabilitycanalsoberecoveredinautonomousoperationifaspeed-dependentspacingpolicyisadopted,whichincorporatesaxedtimeheadwayterminadditiontotheconstantdistance(ChienandIoannou1992,Garrardetal.1978).Thisapproachavoidsthecommunicationoverhead,butresultsinlargerspacingsbetweenadjacentvehiclesandthusinlongerplatoons,therebyyieldingsmallerincreasesintracthroughput.Thisproblemismuchmoreseriousinthecaseofcommercialheavyvehicle(CHV)pla-toons,primarilyduetotheirlowactuation-to-weightratio:thelevelsofaccelerationanddecelerationachievablebyCHVsarealmostanorderofmagnitudelowerthanforpassengercars.Aswewillseeinsection3,thismakesstringstabilityamuchmoreelusivegoalforCHVs;intheabsenceofintervehiclecommunication,thexedtimeheadwaynecessaryforstringstabilityissignicantlylarger,hencethereductionintracthroughputismuchmorepronounced.Thisnecessitatesthedesignofnewlongitudinalcontrolalgorithms,whicharethefocusofthisreport:wedesignseveralnewspacingpoliciesandcontrolschemeswhichusenonlinearitytoendowthevehiclesintheplatoonwitha\groupconscienceandocca-sionallyevensacricetheindividualperformanceofsomevehiclesinordertoimprovetheperformanceofthewholeplatoon.Insection3wehavefocusedondesigninglongitudinalschemeswhichimproveplatoonperformanceandcontrolsmoothnessduringautonomousoperation,i.e.,intheabsenceofintervehiclecommunication.Weproposetwonewnonlinearspacingpolicieswhichachievethisgoal.First,weintroducethenotionofvariabletimeheadway,i.e.,aheadwaywhich,insteadofbeingconstantvarieswiththerelativespeedbetweenadjacentvehicles.Theeectofintroducingthevariabletimeheadwayhisquitedramatic,asseeninourresultsfromthesimulationofaten-truckplatoon.Theyrevealanimpressivereductionoferrorsandaconsiderablysmoothercontrolactivitywithoutanyincreaseinsteady-stateintervehiclespacing.Another\upgradeistheintroductionofavariableseparationerrorgaink.Ourvsimulationresultsillustratethattheuseofvariableinsteadofconstantkyieldssignicantlyimprovedplatoonperformance:itmakesthecontroleortnoticeablysmootherandallbuteliminatesamplicationoferrosastheypropagateupstreamtheplatoon.TheproposedformofthisnonlinearspacingpolicyissuitableforCHVssinceitalleviatestheeectof