畢業(yè)設(shè)計（論文）-基于VB60實現(xiàn)S7-200PLC對多臺異步電動機的控制

中國礦業(yè)大學(xué)本科生畢業(yè)設(shè)計姓名：XXX學(xué)號：XXXXXXX學(xué)院：信息與電氣工程學(xué)院專業(yè)：電氣工程與自動化設(shè)計題目：基于VB6.0實現(xiàn)S7-200PLC對多臺異步電動機的控制專題：指導(dǎo)教師：XXX職稱：副教授2021年6月徐州中國礦業(yè)大學(xué)畢業(yè)設(shè)計任務(wù)書學(xué)院信電學(xué)院專業(yè)年級電氣工程與自動化05-5學(xué)生姓名XXX任務(wù)下達日期：2021年2月16日畢業(yè)設(shè)計日期：2021年2月16日至2021年6月20日畢業(yè)設(shè)計題目：基于VB6.0實現(xiàn)S7-200PLC對多臺異步電動機的控制畢業(yè)設(shè)計專題題目：畢業(yè)設(shè)計主要內(nèi)容和要求：〔1〕掌握異步電動機的工作原理和控制方法；〔2〕掌握PLC工作原理、工作過程及其使用；〔3〕掌握V4.0STEP7MicroWINSP3以及VB6.0編程軟件的使用；〔4〕完成VB6.0編程實現(xiàn)PC與PLC的通信；〔5〕完成與控制系統(tǒng)配套的模擬實驗；〔6〕完成與畢業(yè)設(shè)計內(nèi)容有關(guān)的英文翻譯〔近三年的文獻〕，不少于3000字；院長簽字：指導(dǎo)教師簽字：

摘要隨著現(xiàn)代工業(yè)的飛速開展，PLC以其高可靠性、配置靈活和完善的功能，在電氣控制中占有越來越重要的地位。PLC與上位機的結(jié)合，并通過VB6.0傳送數(shù)據(jù)所構(gòu)成的計算機監(jiān)控系統(tǒng)，對于近距離傳輸數(shù)據(jù)的現(xiàn)場控制來說是一種性價比很高的解決方案，充分的利用PLC的抗干擾性能和PC機強大的圖形顯示，浮點運算的特點。本文正是為了適應(yīng)社會這一需求而設(shè)計的。本設(shè)計利用VB6.0提供的通信控件MSComm結(jié)合PLC中的通信功能進行編程，實現(xiàn)上位機〔PC〕與下位機〔PLC〕之間在自由口通信協(xié)議下數(shù)據(jù)信息的雙向傳輸，到達高效、精確的控制異步電動機的啟動與停止，點動控制、全壓啟動、星/三角啟動、四臺電機的順序啟動逆序停止以及監(jiān)控電機的狀態(tài)，完成了相應(yīng)的軟件、硬件模擬實驗，在電腦上點擊相應(yīng)的按鈕，PLC上的指示燈相應(yīng)的點亮與熄滅，很好地解決了工程應(yīng)用中的一些實際問題。本設(shè)計詳細論述了異步電動機的工作原理、控制方法、VB6.0的高級編程〔通信〕、以及西門子公司提供的S7-200PLC〔CPU224型〕工作原理、通信編程及異步電動機控制的各種梯形圖、指令表。本設(shè)計以在VB6.0環(huán)境下，實現(xiàn)PLC與計算機通信，有效的控制異步電動機，從而滿足用戶的需要。關(guān)鍵詞：S7-200PLC；VB6.0；自由口通信模式；MSCommABSTRACTAlongwithmodernindustryswiftdevelopment,PLCbyitsredundantreliability,dispositionnimbleandperfectfunction,holdsmoreandmoreimportantstatusintheelectriccontrol. PLCandthesuperiormachineunion,andthecomputersupervisorysystemwhichconstitutesthroughtheVB6.0transmissiondata,regardingtheshortdistancetransmissiondata'sscenecontrolisonekindofperformance-to-priceratioveryhighsolution,thefullusePLCresistancetointerferenceandPCmachineformidablegraphicaldisplay,floatingpointcalculation'scharacteristic.Thisarticleispreciselytoadaptsocialthisdemandtodesign.ThispapersusestheCommunicationcontrolMSCommwhichprovidedbyVB6.0unifyingthecommunicationlanguageinPLCfortheprogramming,realizesTwo-waydatatransmissionbetweenHostcomputer(PC)andthenext-bitmachine(PLC)undercommunicationprotocolofthefreeport,achieveshighlyeffectiveandexactpurposeincontrollingasynchronousmotor'sstartandthestop,step-movecontrol，full-voltagestarting,star-deltastarting,fourmotors'orderedstartingandreversestop,andalsothemotor'sstatemonitoring.moreover,ihavefinishedthepracticalexperimentonthehardwareandsoftware.intheexperiment,clickthebuttonsonthePCscreen,theIndicatorsonPLCwillturnonandoffbythesetorder.aswellasmonitorselectricalmachinery'scondition,hassolvedsomeactualproblemsinprojectapplicationwell.Eachkindoftrapezoidalchartwhich,theinstructionlistthisarticleelaboratedasynchronousmotor'sprincipleofwork,thecontrolmethod,theVB6.0high-levelprogrammingindetail(correspondence),aswellasSiemensprovidesS7-200PLCwhich(CPU224)theprincipleofwork,thecorrespondenceprogrammingandtheasynchronousmotorcontrols.ThispapersrealizesPLCandthecomputer’correspondencebaseVB6.0,effectivelycontrolasynchronousmotor,thussatisfiestheneedoftheusers.Keywords:S7-200PLC；VB6.0；freemouthcorrespondencepattern；MSComm目錄1緒論 表3PLC結(jié)構(gòu)配置可用的已用的直接輸入(%I)328直接輸出(%Q)169模擬輸入(%AI)87模擬輸出(%AQ)86存儲器(M)540V.軟件描述PLC程序是依據(jù)輸入設(shè)備的邏輯要求，程序與其說是表達數(shù)字計算法那么不假設(shè)說主要是表達了邏輯性。許多編制的程序是直接工作在“開或關(guān)〞兩種狀態(tài)，并且它們這種交替的形式分別是與“真或假〞〔邏輯形式〕和“1或0”掃描程序，處理梯形行各種邏輯運算來決定輸出狀態(tài)。最新的輸出狀態(tài)保存到固定存儲區(qū)〔輸出映像區(qū)Q〕。輸出數(shù)據(jù)保存在存儲器中，然后在本次程序掃描的最后設(shè)置或是重置輸出設(shè)備。對于給定的PLC，完整的掃描一次所用的時間或是掃描時間是0.18ms/k(1000步)，最大的程序容量是1000步。擴展系統(tǒng)由主機通過232總線連接PLC組成。主機給程序文檔編輯，保存，打印和程序執(zhí)行監(jiān)控提供了軟件環(huán)境。PLC執(zhí)行程序的過程包括：編輯員畫出源梯形程序，將源程序轉(zhuǎn)變成二進制命令形式，這樣它可以在PLC的微處理器中執(zhí)行并通過連續(xù)傳輸端口從PC中下載到PLC系統(tǒng)。當(dāng)PLC系統(tǒng)處于對機器的實時控制時，PLC系統(tǒng)是在線的且監(jiān)控所有數(shù)據(jù)確保正確的運行。表5PLC模塊和I/O設(shè)定主板模塊1模塊2模塊3模塊4模塊5模擬量輸入模塊數(shù)字量輸入模塊模擬量輸出模塊數(shù)字量輸出模塊1、CPU1、速度反應(yīng)信號1、啟動按鈕信號1、速度反應(yīng)信號〔顯示〕1、繼電器12、電源2、負載電流反應(yīng)信號2、停止按鈕信號2、負載電流反應(yīng)信號〔顯示〕2啟動燈〔運行〕3、定子電流信號3、跳閘按鈕信號3、負載轉(zhuǎn)矩信號〔顯示〕3、繼電器24、速度設(shè)定值信號4、前向開關(guān)信號4、逆變器參考頻率4、停止燈5、控制增益信號5、后向開關(guān)信號5、負載繼電器5、繼電器36、控制時間常數(shù)6、跳閘按鈕信號6、定子繼電器6、跳閘燈7、逆變器模擬端口7、24VDC7、逆變器數(shù)字端口8、24VDC8、24VDC9、24VDCA.PLC速度控制軟件在圖4中，給出了速度控制軟件的流程圖。軟件調(diào)整速度監(jiān)視定速度控制而不管轉(zhuǎn)矩變化。逆變器這會兒在做電機的電源的同時也受到PLC軟件的控制。如果沒有PLC和反應(yīng)控制環(huán)，逆變器也不可能控制電機恒定速度運行。操作員通過控制面板設(shè)定速度和選擇電機向前或是向后的旋轉(zhuǎn)方向。通過按下手動按鈕，電機開始旋轉(zhuǎn)。如果停止按鈕被按下，那么電機停下。如表5所示，對應(yīng)的輸入信號接入到數(shù)字輸入模塊，輸出信號送到數(shù)字輸出模塊。模擬輸入模塊接受定子電流傳感器的跳閘信號Is，測速發(fā)電機的速度反應(yīng)信號，和控制面板的信號。這樣，PLC可以獲得電機被要求的速度和的實際速度。操作員要求的速度和電機實際速度的差值給出了誤差信號。如果誤差信號不是0，而是正或是負，然后，PLC根據(jù)CPU的運算減少或增加逆變器的V/F，因此，電機速度是修正的。控制器采用比例積分型〔PI〕〔如，誤差信號通過增益放大，積分，加給要求的速度〕。最后，控制信號送給數(shù)字輸出模塊，并且連接逆變器的數(shù)字輸入去控制變化量。在開始的時候，操作員通過控制面板上的旋轉(zhuǎn)變阻器改變增益〔增益調(diào)節(jié)〕，模擬輸入模塊接受它的電壓降作為控制增益信號〔0-10V〕。要求的速度是通過改變旋轉(zhuǎn)變阻器得到的，AIM獲取這個信號。它的值送到AOM，并在控制面板上顯示〔設(shè)定速度顯示〕，控制面板上另一個是顯示通過速度反應(yīng)信號計算出的電機實際速度。第三個顯示的是通過負載電流信號計算出來的負載轉(zhuǎn)矩〔Nm〕。它他們對應(yīng)的信號輸出給AOM。掃描循環(huán)掃描循環(huán)控制模式掃描輸入存儲輸入停止模式梯形圖執(zhí)行:速度控制軟件保護軟件關(guān)閉/重啟電機軟件數(shù)據(jù)更新圖3.主程序流程圖NYNY讀入輸入：前向/后向信號定子電流IS啟動信號速度反應(yīng)信號速度設(shè)定信號nsp停止信號計算速度錯誤信號IF錯誤=0修正V/F更新逆變器 圖4速度軟件流程圖B.監(jiān)測和保護軟件圖5給出了軟件流程圖.在電機運行中，不能通過改變開關(guān)位置來改變旋轉(zhuǎn)方向。只有按下停止按鈕才可改變旋轉(zhuǎn)方向。在軟件中編制以下程序,使電機在啟動和帶載運行情況下進行過載電流保護。I〕在DIM中輸入前向后向信號。II〕在AIM中輸入速度設(shè)定值n,負載電流，定子電流，和速度反應(yīng)信號。III〕在無載情況1.0A,如果速度設(shè)定值小于20%,或n<300r/min,電機不會啟動。IV〕負載增加0.4NM(額定轉(zhuǎn)矩的40%),1.3A,速度設(shè)定值低于40%或n<600r/min,那么電機不會啟動。V〕如果負載增加1.0NM(額定轉(zhuǎn)矩),1.5A并且如果轉(zhuǎn)速設(shè)定值超過100%或n1500r/min,電機進入停機程序。VI〕在所有其他情況下,電機進入速度控制模式，速度控制軟件如A局部描述的執(zhí)行。速度控制模式切斷電機程序讀入輸入：▽前向/后向信號▽負載電流信號IL▽啟動信號▽定子電流信號IS▽速度設(shè)定信號▽速度反應(yīng)信號不啟動電機速度控制模式速度控制模式Y(jié)YYYYYIFns＜300啟動電機IFns＜600IFnsp＞1500IFIS＞1.5AIFIS速度控制模式切斷電機程序讀入輸入：▽前向/后向信號▽負載電流信號IL▽啟動信號▽定子電流信號IS▽速度設(shè)定信號▽速度反應(yīng)信號不啟動電機速度控制模式速度控制模式Y(jié)YYYYYIFns＜300啟動電機IFns＜600IFnsp＞1500IFIS＞1.5AIFIS＞1.3ANIFIS＜1.0A轉(zhuǎn)子方向鎖定NNNNN圖5監(jiān)視和保護軟件流程圖關(guān)機和重啟電機軟件在圖6給出了軟件流程圖。在過載情況下，電機停機,跳閘燈(黃)亮.操作員必須釋放熱繼電器,然后通過按下跳閘或停止按鈕關(guān)掉跳閘燈。熱繼電器設(shè)定為電機額定電流值1.5A。這樣電機可以重新啟動。操作員可以按下停止按鈕來停止電機:顯示的實際速度變?yōu)榱?,啟動燈(綠)關(guān)閉，停止燈(紅)閉合且持續(xù)亮3S。電機停止后和驅(qū)動系統(tǒng)重啟前負載馬上卸下。即使啟動按鈕已經(jīng)按下,電機在停止后,3秒鐘之內(nèi)不能啟動。讀入輸入：停止信號讀入輸入：停止信號負載電流IL定子電流ISIFIS＞1.5AY合上跳閘燈翻開三相自動開關(guān)將速度顯示置位為0翻開啟動燈〔綠〕合上停止燈〔紅〕翻開負載自動開關(guān)等待3秒種斷開跳閘燈〔黃〕翻開熱繼電器啟動電機監(jiān)視和保護模式N速度控制模式圖6.電機停止/重啟流程圖英文原文DesignandImplementationofPLC-BasedMonitoringControlSystemforInductionMotorMariaG.Ioannides,SeniorMember,IEEEAbstract—Theimplementationofamonitoringandcontrolsystemfortheinductionmotorbasedonprogrammablelogiccontroller(PLC)technologyisdescribed.Also,theimplementationofthehardwareandsoftwareforspeedcontrolandprotectionwiththeresultsobtainedfromtestsoninductionmotorperformanceisprovided.ThePLCcorrelatestheoperationalparameterstothespeedrequestedbytheuserandmonitorsthesystemduringnormaloperationandundertripconditions.TestsoftheinductionmotorsystemdrivenbyinverterandcontrolledbyPLCproveahigheraccuracyinspeedregulationascomparedtoaconventionalVfcontrolsystem.TheefficiencyofPLCcontrolisincreasedathighspeedsupto95%ofthesynchronousspeed.Thus,PLCprovesthemselvesasaveryversatileandeffectivetoolinindustrialcontrolofelectricdrives.IndexTerms—Computer-controlledsystems,computerizedmonitoring,electricdrives,inductionmotors,motioncontrol,programmablelogiccontrollers(PLCs),variable-frequencydrives,voltagecontrol.I.INTRODUCTIONSincetechnologyformotioncontrolofelectricdrivesbecameavailable,theuseofprogrammablelogiccontrollers(PLCs)withpowerelectronicsinelectricmachinesapplicationshasbeenintroducedinthemanufacturingautomation[1],[2].Thisuseoffersadvantagessuchaslowervoltagedropwhenturnedonandtheabilitytocontrolmotorsandotherequipmentwithavirtuallyunitypowerfactor[3].ManyfactoriesusePLCsinautomationprocessestodiminishproductioncostandtoincreasequalityandreliability[4]–[9].Otherapplicationsincludemachinetoolswithimprovedprecisioncomputerizednumericalcontrol(CNC)duetotheuseofPLCs[10].Toobtainaccurateindustrialelectricdrivesystems,itisnecessarytousePLCsinterfacedwithpowerconverters,personalcomputers,andotherelectricequipment[11]–[13].Nevertheless,thismakestheequipmentmoresophisticated,complex,andexpensive[14],[15].FewpaperswerepublishedconcerningdcmachinescontrolledbyPLCs.Theyreportboththeimplementationofthefuzzymethodforspeedcontrolofadcmotor/generatorsetusingaPLCtochangethearmaturevoltage[16],andtheincorporationofanadaptivecontrollerbasedontheself-tuningregulatortechnologyintoanexistingindustrialPLC[17].Also,othertypesofmachineswereinterfacedwithPLCs.Thereby,anindustrialPLCwasusedforcontrollingsteppermotorsinafive-axisrotorposition,directionandspeed,reducingthenumberofcircuitcomponents,loweringthecost,andenhancingreliability[18].Forswitchedreluctancemotorsasapossiblealternativetoadjustablespeedacanddcdrives,asinglechiplogiccontrollerforcontrollingtorqueandspeedusesaPLCtoimplementthedigitallogiccoupledwithapowercontroller[19].OtherreportedapplicationconcernsalinearinductionmotorforpassengerelevatorswithaPLCachievingthecontrolofthedrivesystemandthedataacquisition[20].Tomonitorpowerqualityandidentifythedisturbancesthatdisruptproductionofanelectricplant,twoPLCswereusedtodeterminethesensitivityoftheequipment[21].OnlyfewpaperswerepublishedinthefieldofinductionmotorswithPLCs.Apowerfactorcontrollerforathree-phaseinductionmotorutilizesPLCtoimprovethepowerfactorandtokeepitsvoltagetofrequencyratioconstantunderthewholecontrolconditions[3].Thevectorcontrolintegratedcircuitusesacomplexprogrammablelogicdevice(CPLD)andintegerarithmeticforthevoltageorcurrentregulationofthree-phasepulse-widthmodulation(PWM)inverters[22].Manyapplicationsofinductionmotorsrequirebesidesthemotorcontrolfunctionality,thehandlingofseveralspecificanaloganddigitalI/Osignals,homesignals,tripsignals,On/off/reversecommands.Insuchcases,acontrolunitinvolvingaPLCmustbeaddedtothesystemstructure.ThispaperpresentsaPLC-basedmonitoringandcontrolsystemforathree-phaseinductionmotor.Itdescribesthedesignandimplementationoftheconfiguredhardwareandsoftware.Thetestresultsobtainedoninductionmotorperformanceshowimprovedefficiencyandincreasedaccuracyinvariable-loadconstant-speed-controlledoperation.Thus,thePLCcorrelatesandcontrolstheoperationalparameterstothespeedsetpointrequestedbytheuserandmonitorstheinductionmotorsystemduringnormaloperationandundertripconditions.II.PLCASSYSTEMCONTROLLERAPLCisamicroprocessor-basedcontrolsystem,designedforautomationprocessesinindustrialenvironments.Itusesaprogrammablememoryfortheinternalstorageofuser-orientatedinstructionsforimplementingspecificfunctionssuchasarithmetic,counting,logic,sequencing,andtiming[23],[24].APLCcanbeprogrammedtosense,activate,andcontrolindustrialequipmentand,therefore,incorporatesanumberofI/Opoints,whichallowelectricalsignalstobeinterfaced.InputdevicesandoutputdevicesoftheareconnectedtothePLCandthecontrolprogramisenteredintothePLCmemory.Inourapplication,itcontrolsthroughanaloganddigitalinputsandoutputsthevaryingload-constantspeedoperationofaninductionmotor.Also,thePLCcontinuouslymonitorstheinputsandactivatestheoutputsaccordingtothecontrolprogram.ThisPLCsystemisofmodulartypecomposedofspecifichardwarebuildingblocks(modules),whichplugdirectlyintoaproprietarybus:acentralprocessorunit(CPU),apowersupplyunit,input-outputmodulesI/O,andaprogramterminal.Suchamodularapproachhastheadvantagethattheinitialconfigurationcanbeexpandedforotherfutureapplicationssuchasmultimachinesystemsorcomputerlinking.III.CONTROLSYSTEMOFINDUCTIONMOTORInFig.2,theblockdiagramoftheexperimentalsystemisillustrated.Thefollowingconfigurationscanbeobtainedfromthissetup.a)Aclosed-loopcontrolsystemforconstantspeedoperation,configuredwithspeedfeedbackandloadcurrentfeedback.Theinductionmotordrivesavariableload,isfedbyaninverter,andthePLCcontrolstheinverterV/Foutput.b)Anopen-loopcontrolsystemforvariablespeedoperation.TheinductionmotordrivesavariableloadandisfedbyaninverterinconstantV/Fcontrolmode.ThePLCisinactivated.c)Thestandardvariablespeedoperation.Theinductionmotordrivesavariableloadandisfedbyaconstantvoltage-constantfrequencystandardthree-phasesupply.Theopen-loopconfigurationb)canbeobtainedfromtheclosed-loopconfigurationa)byremovingthespeedandloadfeedback.Ontheotherhand,operationc)resultsiftheentirecontrolsystemisbypassed.IV.HARDWAREDESCRIPTIONThecontrolsystemisimplementedandtestedforawoundrotorinductionmotor,havingthetechnicalspecificationsgiveninTableI.Theinductionmotordrivesadcgenerator,whichsuppliesavariableload.Thethree-phasepowersupplyisconnectedtoathree-phasemainswitchandthentoathree-phasethermaloverloadrelay,whichprovidesprotectionagainstcurrentoverloads.Therelayoutputisconnectedtotherectifier,whichrectifiesthethree-phasevoltageandgivesadcinputtotheinsulatedgatebipolartransistor(IGBT)inverter.Itstechnicalspecifications[25]aresummarizedinTableII.TheIGBTinverterconvertsthedcvoltageinputtothree-phasevoltageoutput,whichissuppliedtothestatoroftheinductionmotor.Ontheotherhand,theinverterisinterfacedtothePLC-basedcontroller.ThiscontrollerisimplementedonaPLCmodularsystem[5],[26]–[28].ThePLCarchitecturereferstoitsinternalhardwareandsoftware.Asamicroprocessor-basedsystem,thePLCsystemhardwareisdesignedandbuiltupwiththefollowingmodules[29]–[37]:?centralprocessorunit(CPU);?discreteoutputmodule(DOM);?discreteinputmodule(DIM);?analogoutputsmodule(AOM)?analoginputsmodule(AIM)?powersupply.OtherdetailsofthePLCconfigurationareshowninTablesIIIandIV.Aspeedsensorisusedforthespeedfeedback,acurrentsensorisusedfortheloadcurrentfeedback,andasecondcurrentsensorisconnectedtothestatorcircuits[32].Thus,thetwofeedbackloopsoftheclosed-loopsystemaresetupbyusingtheloadcurrentsensor,thespeedsensor,andtheAIM.Atachogenerator(permanentmagnetdcmotor)isusedforspeedsensing.Theinductionmachinedrivesitsshaftmechanicallyandanoutputvoltageisproduced,themagnitudeofwhichisproportionaltothespeedofrotation.Polaritydependsonthedirectionofrotation.ThevoltagesignalfromthetachogeneratormustmatchthespecifiedvoltagerangeoftheAIM(0–5Vdcand200-kinternalresistance).OtherPLCexternalcontrolcircuitsaredesignedusingalow-voltagesupplyof24Vdc.Forthemanualcontrol,theschemeisequippedwithstart,stop,andtrippushbuttons,aswellaswithaforwardandbackwarddirectionselectorswitch.AsshowninFig.2,allofthedescribedcomponents:amainswitch,anautomaticthree-phaseswitch,anautomaticsinglephaseswitch,athree-phasethermaloverloadrelay,aloadautomaticswitch,signallamps(forward,backward,start,stop,trip),pushbuttons(start,stop,trip),aselectorswitch(fortheforward/backwarddirectionofrotation),aspeedselector,againselector,aswellasthePLCmodulesandtherectifier-inverterareinstalledinacontrolpanel.TheprogramisdownloadedintothePLCfromapersonalcomputerPCandanRS232serialinterface.V.SOFTWAREDESCRIPTIONPLC’sprogrammingisbasedonthelogicdemandsofinputdevicesandtheprogramsimplementedarepredominantlylogicalratherthannumericalcomputationalalgorithms.Mostoftheprogrammedoperationsworkonastraightforwardtwo-state“onoroff〞basisandthesealternatepossibilitiescorrespondto“trueorfalse〞(logicalform)and“1or0”(binaryform),respectively.Thus,PLCsofferaflexibleprogrammablealternativetoelectricalcircuitrelay-basedcontrolsystemsbuiltusinganalogdevices.Theprogrammingmethodusedistheladderdiagrammethod.ThePLCsystemprovidesadesignenvironmentintheformofsoftwaretoolsrunningonahostcomputerterminalwhichallowsladderdiagramstobedeveloped,verified,tested,anddiagnosed.First,thehigh-levelprogramiswritteninladderdiagrams,[33],[34].Then,theladderdiagramisconvertedintobinaryinstructioncodessothattheycanbestoredinrandom-accessmemory(RAM)orerasableprogrammableread-onlymemory(EPROM).EachsuccessiveinstructionisdecodedandexecutedbytheCPU.ThefunctionoftheCPUistocontroltheoperationofmemoryandI/Odevicesandtoprocessdataaccordingtotheprogram.EachinputandoutputconnectionpointonaPLChasanaddressusedtoidentifytheI/Obit.Themethodforthedirectrepresentationofdataassociatedwiththeinputs,outputs,andmemoryisbasedonthefactthatthePLCmemoryisorganizedintothreeregions:inputimagememory(I),outputimagememory(Q),andinternalmemory(M).Anymemorylocationisreferenceddirectlyusing%I,%Q,and%M(TableIII).ThePLCprogramusesacyclicscaninthemainprogramloopsuchthatperiodicchecksaremadetotheinputvariables(Fig.3).Theprogramloopstartsbyscanningtheinputstothesystemandstoringtheirstatesinfixedmemorylocations(inputimagememoryI).Theladderprogramisthenexecutedrung-by-rung.Scanningtheprogramandsolvingthelogicofthevariousladderrungsdeterminetheoutputstates.Theupdatedoutputstatesarestoredinfixedmemorylocations(outputimagememoryQ).TheoutputvaluesheldinmemoryarethenusedtosetandresetthephysicaloutputsofthePLCsimultaneouslyattheendoftheprogramscan.ForthegivenPLC,thetimetakentocompleteonecycleorthescantimeis0,18ms/K(for1000steps)andwithamaximumprogramcapacityof1000steps.Thedevelopmentsystemcomprisesahostcomputer(PC)connectedviaanRS232porttothetargetPLC.Thehostcomputerprovidesthesoftwareenvironmenttoperformfileediting,storage,printing,andprogramoperationmonitoring.TheprocessofdevelopingtheprogramtorunonthePLCconsistsof:usinganeditortodrawthesourceladderprogram,convertingthesourceprogramtobinaryobjectcodewhichwillrunonthePLC’smicroprocessoranddownloadingtheobjectcodefromthePCtothePLCsystemviatheserialcommunicationport.ThePLCsystemisonlinewhenitisinactivecontrolofthemachineandmonitorsanydatatocheckforcorrectoperation.PLCSpeedControlSoftwareInFig.4,theflowchartofthespeedcontrolsoftwareisillustrated.Thesoftwareregulatesthespeedandmonitorstheconstantspeedcontrolregardlessoftorquevariation.Theinverterbeingthepowersupplyforthemotorexecutesthiswhile,atthesametime,itiscontrolledbyPLC’ssoftware.TheinverteralonecannotkeepthespeedconstantwithoutthecontrolloopwithfeedbackandPLC.Fromthecontrolpanel,theoperatorselectsthespeedsetpointandtheforward/backwarddirectionofrotation.Then,bypushingthemanualstartpushbutton,thentherotationstops.ThecorrespondinginputsignalsareinterfacedtotheDIMandtheoutputsignalstotheDOMasshowninTableIV.TheAIMreceivesthetripsignalISfromthestatorcurrentsensor,thespeedfeedbacksignalfromthetachogenerator,andthesignalfromthecontrolpanel.Inthisway,thePLCreadstherequestedspeedandtheactualspeedofthemotor.Thedifferencebetweentherequestedspeedbytheoperatorandtheactualspeedofthemotorgivestheerrorsignal.Iftheerrorsignalisnotzero,butpositiveornegative,thenthePLCaccordingtothecomputationscarriedoutbytheCPUdecreasesorincreasestheV/Foftheinverterand,asaresult,thespeedofthemotoriscorrected.Theimplementedcontrolisofproportionalandintegral(PI)type(i.e.,theerrorsignalismultipliedbygainKP,integrated,andaddedtotherequestedspeed).Asaresult,thecontrolsignalissenttotheDOMandconnectedtothedigitalinputoftheinvertertocontrolV/Fvariations.Atthebeginning,theoperatorselectsthegainKPbyusingarotaryresistormountedonthecontrolpanel(gainadjust)andtheAIMreceivesitsvoltagedropascontrollergainsignal(0–10V).Therequestedspeedisselectedusingarotaryresistorandt