Systemintroduction
DCSusuallyadoptsahierarchicalstructure,eachleveliscomposedofseveralsubsystems,andeachsubsystemachievesanumberofspecificfinitegoals,formingapyramidstructure.
ReliabilityisthelifeofthedevelopmentofDCS.TherearethreemainmeasurestoensurethehighreliabilityofDCS:First,widelyusehigh-reliabilityhardwareequipmentandproductiontechnology;Second,widelyuseredundanttechnology;Itistoextensivelyrealizesystemfault-toleranttechnology,faultself-diagnosisandautomaticprocessingtechnologyinsoftwaredesign.TheMTBFofmostoftoday'sdistributedcontrolsystemscanreachtensofthousandsorevenhundredsofthousandsofhours.
Developmenttrend
Inrecentyears,therehavebeenmanynewdevelopmentsintheDCS-relatedfield,mainlyinthefollowingaspects.
(1)Thefunctionofthesystemisdevelopinginanopendirection.ThestructureoftraditionalDCSisclosed,anditisdifficulttobecompatiblebetweenDCSofdifferentmanufacturers.TheopenDCSwillgiveusersgreaterautonomyinsystemintegration,anduserscanchooseequipmentfromdifferentmanufacturersandsoftwareresourcestoconnecttothecontrolsystemaccordingtoactualneedstoachievethebestsystemintegration.ThisincludesnotonlytheintegrationofDCSandDCS,butalsothebroadintegrationofDCSandPLC,FCSandvariouscontrolequipmentandsoftwareresources.
(2)Instrumenttechnologyisdevelopingtowardsdigital,intelligentandnetworkeddirection.Theintelligentandnetworkeddevelopmentofindustrialcontrolequipmentcanpromotethefurtherdecentralizationanddownwardmovementofprocesscontrolfunctions,realizing"fulldigital"and"fulldecentralized"controlinthetruesense.Inaddition,becausethesesmartmetershavehighaccuracy,goodrepeatability,highreliability,andfeaturetwo-waycommunicationandself-diagnosisfunctions,theinstallation,useandmaintenanceofthesystemaremoreconvenient.
(3)Industrialcontrolsoftwareisdevelopinginthedirectionofadvancedcontrol.Extensiveapplicationofvariousadvancedcontrolandoptimizationtechnologiesisthemosteffective,directandvaluabledevelopmentdirectionfordiggingandimprovingthecomprehensiveperformanceofDCS,includingthedevelopmentandindustrializationofadvancedcontrol,processoptimization,informationintegration,systemintegrationandothersoftwareapplication.Inthefuture,industrialcontrolsoftwarewillalsocontinuetodevelopinthedirectionofstandardization,networking,intelligenceandopenness.
(4)ThesystemarchitecturedevelopstowardsFCS.Fromapurelytechnicalpointofview,therearethreewaystointegratefieldbusintoDCSatthisstage:①IntegrationoffieldbusontheI/ObusoftheDCSsystem-throughafieldbusinterfacecardhungontheI/ObusoftheDCS,makingTheinformationfromthefieldbusseenbytheDCScontrollerisjustlikecomingfromatraditionalDCSdevicecard.Forexample,theDeltaVsystemlaunchedbyFisher-Rosemountusesthisintegratedsolution.②TheintegrationoffieldbusinthenetworklayeroftheDCSsystemistointegratethefieldbussystemonthehigher-levelnetworkoftheDCS.ThisintegrationmethoddoesnotrequirechangestotheDCScontrolstationandhaslittleimpactontheoriginalsystem.Forexample,Smar's302seriesfieldbusproductscanintegrateitsfieldbusfunctionsattheDCSsystemnetworklayer.③ThefieldbusisintegratedwiththeDCSsysteminparallelthroughthegateway-thefieldbusandDCScanalsobeintegratedinparallelthroughthegatewaybridge.Forexample,thefieldbussystemofSUPCONusestheHARTprotocolbridgetoconnectthesystemoperatingstationandthefieldinstrument,soastorealizethecommunicationfunctionbetweenthefieldbusequipmentmanagementsystemoperatingstationandtheHARTprotocolfieldinstrument.
DCShasalwaysfocusedoncontrol,andituses"dispersion"asitskeyword.However,moderndevelopmentfocusesmoreonthecomprehensivemanagementofsystem-wideinformation.Inthefuture,"comprehensive"willbecomeitskeyword.Itwilldeveloptowardstherealizationofintegratedautomationofcontrolsystems,operatingsystems,planningsystems,andmanagementsystems,andimplementreal-timecontrolfromthelowestlevel.Optimizedcontrolrisestoproductionscheduling,businessmanagement,andeventhehighestlevelofstrategicdecision-making,formingaflexibleandhighlyautomatedintegratedmanagementandcontrolsystem.
HardwareArchitecture
InspectingthehierarchyofDCS,DCSlevelandcontrolmanagementlevelarethetwomostbasicpartsofDCS.
Theprocesscontrollevelspecificallyrealizesthedecentralizedcontrolfunctionsofsignalinput,transformation,calculationandoutput.IndifferentDCS,thecontroldevicesoftheprocesscontrollevelaredifferent,suchasprocesscontrolunit,fieldcontrolstation,processinterfaceunit,etc.,buttheirstructureisroughlythesameandcanbecollectivelyreferredtoasfieldcontrolunitFCU.Theprocessmanagementleveliscomposedofanengineerstation,anoperatorstation,andamanagementcomputer.Itcompletesthecentralizedmonitoringandmanagementoftheprocesscontrollevelandisusuallycalledanoperationstation.ThehardwareandsoftwareoftheDCSaredesignedaccordingtothemodularstructure,sothedevelopmentoftheDCSisactuallytocombinethevariousbasicmodulesprovidedbythesystemintoasystemaccordingtoactualneeds.Thisprocessiscalledtheconfigurationofthesystem.
(1)Fieldcontrolunit
Thefieldcontrolunitisgenerallyfarawayfromthecontrolcenterandinstallednearthesite.Itshighlymodularstructurecanbeconfiguredaccordingtotheneedsofprocessmonitoringandcontrol.Processcontrolunitsranginginsizefromafewmonitoringpointstohundredsofmonitoringpoints.
Thestructureofthefieldcontrolunitiscomposedofmanyplug-ins(orcards)withscatteredfunctionsinstalledintheplug-inboxaccordingtoacertainlogicalorphysicalsequence.EachfieldcontrolunitanditscontrolmanagementlevelThebusconnectionisusedtorealizeinformationexchange.
Thehardwareconfigurationoftheon-sitecontrolunitneedstocompletethefollowing:
Theconfigurationoftheplug-inisbasedontherequirementsofthesystemandthecontrolscale.Configurethehostplug-in(CPUplug-in),powerplug-in,andI/Oplug-in,Communicationplug-insandotherhardwaredevices;
HardwareredundancyconfigurationRedundantconfigurationofkeyequipmentisanimportantmeanstoimprovethereliabilityofDCS.DCScanusuallyperformhostplug-in,powerplug-in,communicationplug-inandnetwork,AllkeyI/Oplug-inscanbeconfiguredredundantly.
HardwareinstallationDifferentDCS,fortheinstallationofvariousplug-insintheplug-inbox,therewillbecorrespondingregulationsinlogicalorphysicalorder.Inaddition,thefieldcontrolunitisusuallydividedintotwotypes:basictypeandextendedtype.Theso-calledbasictypemeansthatvariousplug-insareinstalledinaplug-inbox,butmoreoften,anexpandablestructureisrequired,thatis,afieldcontrolunitalsoincludesSeveraldigitalinput/outputexpansionunitsareconnectedtoeachotherbyabus.
Inessence,thestructureandconfigurationrequirementsofthefieldcontrolunitareconsistentwiththehardwareconfigurationofthemodularPLC.
(2)Operationstation
Operationstationisusedtodisplayandrecordtheprocessdatafromeachcontrolunit,anditistheoperationinterfacefortheinteractionofhumanandproductionprocessinformation.Typicaloperatingstationsincludehostsystems,displaydevices,keyboardinputdevices,informationstoragedevicesandprintoutputdevices,etc.,whichmainlyimplementpowerfuldisplayfunctions(suchasanalogparameterdisplay,systemstatusdisplay,multiplescreendisplay,etc.),alarmfunctions,Operationfunction,reportprintingfunction,configurationandprogrammingfunction,etc.
Inaddition,theDCSoperationstationisdividedintooperatorstationandengineerstation.Fromtheperspectiveofsystemfunctions,theformermainlyrealizesgeneralproductionoperationsandmonitoringtasks,andhasfunctionssuchasdatacollectionandprocessing,monitoringscreendisplay,faultdiagnosisandalarms.Inadditiontothegeneralfunctionsoftheoperatorstation,thelattershouldalsohavefunctionssuchassystemconfigurationandcontroltargetmodification.Fromtheperspectiveofhardwareequipment,theengineerstationandoperatorstationofmostsystemsarecombined,andonlyoneengineerkeyboardisusedtodistinguishthem.
Softwaresystem
ThesoftwaresystemofDCScanusuallyprovideuserswithquiteawealthoffunctionalsoftwaremodulesandfunctionalsoftwarepackages.ControlengineersusetheconfigurationsoftwareprovidedbyDCStocombinevariousfunctionsThesoftwareperformsappropriate"assemblyandconnection"(ieconfiguration)togeneratevariousapplicationsoftwarethatmeettherequirementsofthecontrolsystem.
Softwaresystem
Thesoftwareofthefieldcontrolunitmainlyincludessoftwaremodulessuchasdatainspectioncenteredonreal-timedatabase,controlalgorithm,controloutputandnetworkcommunication.
Thereal-timedatabaseplaystheroleofthecentrallink,wheredataisshared,andeachexecutioncodeexchangesdatawithit,whichisusedtostorethedatacollectedon-site,controloutput,andintermediateresultsandcontrolofsomecalculations.Informationaboutthestructureofthealgorithm.Thedatainspectionmoduleisusedtorealizethecollectionoffielddataandfaultsignals,andrealizethenecessaryauxiliaryfunctionssuchasdigitalfiltering,unitconversion,andcompensationcalculation.ThecontrolfunctionofDCSisgeneratedthroughconfiguration.Differentsystemsrequiredifferentcontrolalgorithmmodules.Thefollowingmodulesareusuallyinvolved:arithmeticoperationmodule,logicoperationmodule,PIDcontrolmodule,variantPIDmodule,manualautomaticswitchingmodule,Non-linearprocessingmodule,actuatorcontrolmodule,etc.Thecontroloutputmodulemainlyrealizestheoutputofthecontrolsignaltodealwiththefault.
Softwaresystem
TheoperationstationinDCSisusedtocompletethetasksofsystemdevelopment,generation,testingandoperation,whichrequiresthesupportofcorrespondingsystemsoftware,whichincludestheoperatingsystem,Programminglanguageandvarioustoolsoftware,etc.AcompletesetofDCS,theapplicationsoftwarerunningontheoperatingstationshouldbeabletoachievethefollowingfunctions:real-timedatabase,networkmanagement,historicaldatabasemanagement,graphmanagement,historicaldatatrendmanagement,detaileddatabasedisplayandmodification,recordreportgenerationandprinting,Man-machineinterfacecontrol,controlloopadjustment,parameterlist,serialcommunicationandvariousconfigurations,etc.
Configuration
ThedevelopmentprocessofDCSismainlytheprocessofusingsystemconfigurationsoftwaretogeneratevariousapplicationsoftwareaccordingtotheactualneedsofthecontrolsystem.Configurationsoftwarefunctionsincludebasicconfigurationconfigurationandapplicationsoftwareconfiguration.Thebasicconfigurationconfigurationistogivethesystemconfigurationinformation,suchasthenumberofvariousstationsinthesystem,theirindexmarks,themaximumnumberofpointsofeachcontrolstation,theshortestexecutioncycleandmemorycapacity.Theconfigurationoftheapplicationsoftwareincludesrelativelyrichcontent,mainlyincludingthefollowingaspects.
(1)Theconfigurationofthecontrolloop
TheconfigurationofthecontrolloopisessentiallytheuseofvariousbasicfunctionalmodulesprovidedbythesystemtoformavarietyofactualControlSystem.Atpresent,theconfigurationmethodsprovidedbyvariousDCSsaredifferent.Insummary,therearedesignatedcomputingmoduleconnectionmethods,judgmenttablemethods,steprecordingmethods,andsoon.
Theconnectionmethodofthedesignatedcomputingmoduleistocallvariousindependentstandardcomputingmodulesandconnectthemwithlinestoformavarietyofcontrolloops.Finally,thecontrolsoftwareisautomaticallygenerated.Thisisakindofinformationflowandcontrolfunction.Veryintuitiveconfigurationmethod.Thejudgmenttablemethodisapureformoffillingintheform,aslongasyoufillinthecontentoranswerthequestionsonebyoneaccordingtotherequirementsoftheconfigurationform,thismethodisveryconducivetotheuser'sconfigurationoperation.Thestepentrymethodisaprogrammingmethodbasedonlanguageinstructions,withalargedegreeoffreedominprogramming,andvariouscomplexfunctionscanbeachievedthroughsomeskills,buttheconfigurationefficiencyislow.Inaddition,becausethisconfigurationmethodisnotintuitiveenough,itoftenplaceshigherrequirementsonthetechnicallevelandconfigurationexperienceoftheconfigurationengineer.
(2)Real-timedatabasegeneration
Thereal-timedatabaseisthemostbasicinformationresourceofDCS.Thesereal-timedataarestoredandmanagedbythereal-timedatabase.InDCS,therearemanywaystoestablishandmodifyreal-timedatabaserecords.Thecommonlyusedmethodistousegeneraldatabasetoolsoftwaretogeneratedatabasefiles.ThesystemdirectlyusesthisdataformatformanagementorusesacertainmethodtoconvertthegenerateddatafilesintoTheformatrequiredbyDCS.
(3)Generationofindustrialprocesspictures
DCSisacomprehensivecontrolsystem,whichmusthaverichcontrolsystemanddetectionsystempicturedisplayfunctions.Obviously,differentcontrolsystemsneedtodisplaydifferentpictures.Ingeneral,combiningtheoverview,grouping,controlloop,flowchart,alarmandotherscreens,showingvariousmeasurementandcontrolparametersandsystemstatusinappropriateformssuchascharacters,bargraphs,curves,etc.,isabasicofDCSconfigurationRequire.Inaddition,variousvariablecatalogscreens,operationguidancescreens,faultdiagnosisscreens,engineermaintenancescreensandsystemconfigurationscreenscanalsobedisplayedasrequired.
(4)Generationofhistoricaldatabase
AllDCSsupporthistoricaldatastorageandtrenddisplayfunctions.Thehistoricaldatabaseisusuallycompiledbyuserswithoutprogrammingonthescreen.Thetechnologygeneratesadatafilethatdefinesthestructureandscopeofeachhistoricaldatarecord.Thedatainthehistoricaldatabaseisgenerallydividedintogroups,andthedatatypeandsamplingtimeineachgrouparethesame.Whengenerating,definetherelevantinformationofeachdatapoint.
(5)Reportgeneration
ThereportprintingfunctionoftheDCSoperatorstationisalsoconfiguredthroughthereportgenerationpartoftheconfigurationsoftware.DifferentDCShasthereportprintingfunction.Thereisabigdifference.Generallyspeaking,DCSsupportsthefollowingtwotypesofreportprintingfunctions:oneisperiodicreportprinting,andtheotheristriggerreportprinting.Userscangeneratedifferentreportformsaccordingtotheirneedsandpreferences.
Advancedcontroltechnology
ThebiggestfeatureofDCSincontrolisthatitreliesontheflexibleconfigurationofvariouscontrolandcomputingmodules,whichcanrealizediversifiedcontrolstrategiestomeetdifferentconditions.Needtomakeitsimpletoimplementarathertediousandcomplicatedpropositionintheunitcombinationinstrument.Withtherequirementsofhighflexibilityandhighefficiencyputforwardbyenterprises,thecontrolschemebasedonclassiccontroltheorycannolongerbeadapted.Aftertheadvancedcontrolstrategyrepresentedbymultivariablepredictivecontrolisproposedandsuccessfullyapplied,advancedprocesscontrolisaffectedbytheprocess.Thegeneralconcernoftheindustry.Itneedstobeemphasizedthatthewideapplicationofvariousadvancedcontrolandoptimizationtechnologiesisthemosteffective,directandvaluabledevelopmentdirectionfordiggingandimprovingthecomprehensiveperformanceofDCS.
Intheactualprocesscontrolsystem,thesystembasedonPIDcontroltechnologyaccountsformorethan80%.TheadvantagesanddisadvantagesofthePIDloopapplicationplayadecisiveroleinachievingthestable,efficientandhigh-qualityoperationofthedevice.AllDCSmanufacturershaveTakingthisasapowerfulcompetitiveweighttoseizethemarket,theydevelopedtheirownPIDself-tuningsoftware.Inaddition,accordingtothecontrolfunctionofDCS,basedonthebasicPIDalgorithm,variousimprovedalgorithmscanbedevelopedtomeetthevariousneedsoftheactualindustrialcontrolsite,suchasPIDcontrolwithdeadzone,PIDcontrolwithintegralseparation,anddifferentialfirstPIDcontrol,incompletedifferentialPIDcontrol,PIDcontrolwithlogicselectionfunction,etc.
DifferentfromthetraditionalPIDcontrol,thepredictivecontrolalgorithmbasedonthenon-parametricmodelpredictsthefutureoutputstateofthesystemthroughthepredictivemodel,andusestherollingoptimizationstrategytocalculatethecurrentcontrolleroutput.Accordingtodifferentimplementations,therearevariousalgorithms,suchasinternalmodelcontrol,modelalgorithmcontrol,dynamicmatrixcontrol,andsoon.Atpresent,practicalpredictivecontrolalgorithmshavebeenintroducedintoDCS.Forexample,theIDCOMcontrolalgorithmsoftwarepackagehasbeenwidelyusedinactualindustrialprocessessuchashydrocracking,catalyticcracking,atmosphericdistillation,andcatalyticreformingofnaphtha.Inaddition,thereareHoneywell’sHPC,Yokogawa’sPREDICTROL,YamatakeHoneywell’sKalmanfilter-basedpredictivecontrollerdevelopedintheTDC-3000LCNsystem,andsoon.ThistypeofpredictivecontrollerdoesnotsimplyplacetheKalmanfilterbeforethepreviouspredictivecontroltoperformnoisefiltering,butusestheKalmanfilterasanoptimalstateestimatortoperformoptimalstateestimationandnoisefilteringatthesametime.
Therearemanyadvancedcontrolalgorithms.Atpresent,manydomesticandforeigncontrolsoftwarecompaniesandDCSmanufacturersareracingtodevelopadvancedcontrolandoptimizedcontrolengineeringsoftwarepackages,hopingtoembedadvancedcontrolandoptimizedcontrolstrategiesintheconfigurationsoftware.
Introductiontoitsapplication
Whenalargeamountofon-siteinformationentersthecomputercontrolsystemdirectlyfromthesmartinstrumentorthroughthefieldbus,thereareproblemsinthesharingandinteractionofon-siteinformationbythecomputer'sinternalapplications.Duetothelackofaunifiedconnectionstandard,industrialcontrolsoftwareoftenneedstodevelopdedicateddriversforhardwaredevices.Inthisway,oncethehardwaredeviceisupgraded,thecorrespondingdriverneedstobechanged,whichincreasesthemaintenancecostofthesystem.EventhoughtheSCADAinthecomputerhasanindependentdriver,itisgenerallynotallowedtoaccessthesameequipmentatthesametime,otherwiseitiseasytocausethesystemtocrash.Itcanbeseenthat,asthebottompartoftheentireinformationsystemoftheenterprise,thefieldcontrollayermustbeintegratedwiththeprocessmanagementlayerandthemanagementdecision-makinglayer.Inthisway,thereisalsotheproblemofhowthemonitoringcomputercommunicatesandtransmitsinformationwithothercomputers.Sincecontrolsystemsareoftendedicatedsystemsdevelopedbydifferentmanufacturers,theyhavepoorcompatibilitywitheachotherandlackofeffectivecommunicationinterfaceswithhigh-levelbusinessmanagementsoftware.Therefore,communicationspecificationshavebecomeabottleneckrestrictingthecontrolsystemfrombreakingthrough"informationislands".
TheemergenceofOPC(OLEforProcessControl)hasestablishedasetofcommunicationinterfacespecificationsthatmeettherequirementsofindustrialcontrol,sothatthecontrolsoftwarecanefficientlyandstablyperformdataaccessoperationsonhardwaredevices.Informationexchangecanalsobecarriedoutflexiblybetweenthetwo,whichgreatlyimprovestheinteroperabilityandadaptabilityofthecontrolsystem
Fromthesoftwarepointofview,OPCcanberegardedasa"softwarebus"standard.First,itprovidesachannelstandardforreal-timedatatransmissionbetweendifferentapplications(evenbetweenapplicationsondifferentworkstationsconnectedthroughanetwork);secondly,italsodefinesachannelforprocesscontrolneeds.Transmissionandexchangeformat.ThearchitectureoftheOPCstandardisaclient/servermodel,thatis,thesoftwareisdividedintoOPCserverandOPCclient.TheOPCserverprovidesthenecessaryOPCdataaccessstandardinterface;OPCclientsaccessOPCdatathroughthestandardinterface.
SoftwaredevelopedusingOPCstandardsisbasedoncommondataandinterfacestandards,sotheyhavestrongversatility.Thishasverypracticalsignificanceinthefieldofindustrialcontrol.TheOPCservercanbeprovidedbydifferentvendors,anditscodedeterminesthedetailsofhowtheserveraccessesthephysicaldeviceanddataprocessing.ButthesearealltransparenttotheOPCclientprogram,onlyneedtofollowthesamespecificationormethodtoreadthedataintheserver.Similarly,softwarevendorsonlyneedtoaddtheirownsoftwaretotheOPCinterfacetoobtaindatafromtheOPCserverwithoutworryingabouttheunderlyingdetails.ThroughOPCinterface,OPCclientprogramcanconnectwithoneormoredifferentOPCservers.Atthesametime,anOPCservercanalsobeconnectedtomultipleclientprogramstoformamany-to-manyrelationship.AnyproductthatsupportsOPCcanbeseamlesslyintegratedwiththesystem.BecauseOPCtechnologyisbasedonDCOM,clientprogramsandserverscanbedistributedondifferenthoststoformanetworkedmonitoringsystem.
ThedevelopmentandapplicationofOPCtechnology,bothsuppliersandenduserscangethugebenefitsfromit.Firstofall,OPCtechnologyeffectivelyseparateshardwareandapplicationsoftware.Hardwaremanufacturersonlyneedtoprovideasetofsoftwarecomponents,andallOPCclientprogramscanusethesecomponentswithouttheneedtore-developdrivers.Oncethehardwareisupgraded,youonlyneedtomodifytheI/OinterfacepartoftheOPCserverwithoutchangingtheclientprogram.Secondly,aslongastheindustrialcontrolsoftwaredevelopsasetofOPCinterface,itcanuseaunifiedwaytoaccessandoperatetheequipmentofdifferenthardwaremanufacturers.Inthisway,hardwareandsoftwarevendorscanfocusontheircorepartsinsteadofcompatibilityissues.
Forendusers,sincethereisnoneedtoworryaboutinteroperability,thereismoreroomforselectionandreplacementofsoftwareandhardware,sothattheintegrationofheterogeneouscomputersystemswillbecomeverysimple.Userscanfocusonthefunctionsandapplicationsoftheentiresystem,whichalsomeanscostreduction.Inaddition,theuseofOPCcomponentsisalsoveryconvenient,usersonlyneedtoperformsimpleconfiguration.
OPCserveradoptsaunifiedstandardintheunderlyingcontrolsystem,whichrealizestheeffectiveconnectionbetweenapplicationprogramsandfieldequipment,playsanimportantroleasabridge,andalsopromotestheenterprisefieldcontrollayerandproductionprocessmanagementlayer.,Integrationofmanagementdecision-makinglevel.