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ONVEYORSWITHSIMPLERBELTPROFILESANDLIMITEDCONVEX/CONCAVESECTIONSTHEYARERELATIVELYSIMPLE,1OWCOST,RELIABLE,MAINTENANCEFREEDEVICESTHATPROVIDEEXCELLENTSOFTSTARTINGRESULTSTOTHEMAJORITYOFBELTCONVEYORSINUSETODAYVARIABLEFILLDRAINCOUPLINGSDRAINABLEFLUIDCOUPLINGSWORKONTHESAMEPRINCIPLEASFIXEDFILLCOUPLINGSTHECOUPLINGSIMPELLERSAREMOUNTEDONTHEACMOTORANDTHERUNNERSONTHEDRIVENREDUCERHIGHSPEEDSHAFTHOUSINGMOUNTEDTOTHEDRIVEBASEENCLOSESTHEWORKINGCIRCUITTHECOUPLINGSROTATINGCASINGCONTAINSBLEEDOFFORIFICESTHATCONTINUALLYALLOWFLUIDTOEXITTHEWORKINGCIRCUITINTOASEPARATEHYDRAULICRESERVOIROILFROMTHERESERVOIRISPUMPEDTHROUGHAHEATEXCHANGERTOASOLENOIDOPERATEDHYDRAULICVALVETHATCONTROLSTHEFILLINGOFTHEFLUIDCOUPLINGTOCONTROLTHESTARTINGTORQUEOFASINGLEDRIVECONVEYORSYSTEM，THEACMOTORCURRENTMUSTBEMONITOREDTOPROVIDEFEEDBACKTOTHESOLENOIDCONTROLVALVEVARIABLEFILLDRAINCOUPLINGSAREUSEDINMEDIUMTOHIGHKWCONVEYORSYSTEMSANDAREAVAILABLEINSIZESUPTOTHOUSANDSOFKWTHEDRIVESCANBEMECHANICALLYCOMPLEXANDDEPENDINGONTHECONTROLPARAMETERSTHESYSTEMCANBEELECTRONICALLYINTRICATETHEDRIVESYSTEMCOSTISMEDIUMTOHIGH,DEPENDINGUPONSIZESPECIFIEDHYDROKINETICSCOOPCONTROLDRIVETHESCOOPCONTROLFLUIDCOUPLINGCONSISTSOFTHETHREESTANDARDFLUIDCOUPLINGCOMPONENTSADRIVENIMPELLER,ADRIVINGRUNNERANDACASINGTHATENCLOSESTHEWORKINGCIRCUITTHECASINGISFITTEDWITHFIXEDORIFICESTHATBLEEDAPREDETERMINEDAMOUNTOFFLUIDINTOARESERVOIRWHENTHESCOOPTUBEISFULLYEXTENDEDINTOTHERESERVOIR,THECOUPLINGISL00PERCENTFILLEDTHESCOOPTUBE,EXTENDINGOUTSIDETHEFLUIDCOUPLING，ISPOSITIONEDUSINGANELECTRICACTUATORTOENGAGETHETUBEFROMTHEFULLYRETRACTEDTOTHEFULLYENGAGEDPOSITIONTHISCONTROLPROVIDESREASONABLYSMOOTHACCELERATIONRATESTOBUTTHECOMPUTERBASEDCONTROLSYSTEMISVERYCOMPLEXSCOOPCONTROLCOUPLINGSAREAPPLIEDONCONVEYORSREQUIRINGSINGLEORMULTIPLEDRIVESFROML50KWTO750KW13VARIABLEFREQUENCYCONTROLVFCVARIABLEFREQUENCYCONTROLISALSOONEOFTHEDIRECTDRIVEMETHODSTHEEMPHASIZINGDISCUSSIONABOUTITHEREISBECAUSETHATITHASSOUNIQUECHARACTERISTICANDSOGOODPERFORMANCECOMPAREDWITHOTHERDRIVINGMETHODSFORBELTCONVEYORVFCDEVICESPROVIDEVARIABLEFREQUENCYANDVOLTAGETOTHEINDUCTIONMOTOR,RESULTINGINANEXCELLENTSTARTINGTORQUEANDACCELERATIONRATEFORBELTCONVEYORDRIVESVFCDRIVESAVAILABLEFROMFRACTIONALTOSEVERALTHOUSANDKW,AREELECTRONICCONTROLLERSTHATRECTIFYACLINEPOWERTODCAND，THROUGHANINVERTER,CONVERTDCBACKTOACWITHFREQUENCYANDVOLTAGECONTRO1VFCDRIVESADOPTVECTORCONTROLORDIRECTTORQUECONTROLDTCTECHNOLOGY，ANDCANADOPTDIFFERENTOPERATINGSPEEDSACCORDINGTODIFFERENTLOADSVFCDRIVESCANMAKESTARTINGORSTALLINGACCORDINGTOANYGIVENSCURVESREALIZINGTHEAUTOMATICTRACKFORSTARTINGORSTALLINGCURVESVFCDRIVESPROVIDEEXCELLENTSPEEDANDTORQUECONTROLFORSTARTINGCONVEYORBELTSANDCANALSOBEDESIGNEDTOPROVIDELOADSHARINGFORMULTIPLEDRIVESEASILYVFCCONTROLLERSAREFREQUENTLYINSTALLEDONLOWERPOWEREDCONVEYORDRIVES，BUTWHENUSEDATTHERANGEOFMEDIUMHIGHVOLTAGEINTHEPASTTHESTRUCTUREOFVFCCONTROLLERSBECOMESVERYCOMPLICATEDDUETOTHELIMITATIONOFVOLTAGERATINGOFPOWERSEMICONDUCTORDEVICES，THECOMBINATIONOFMEDIUMHIGHVOLTAGEDRIVESANDVARIABLESPEEDISOFTENSOLVEDWITHLOWVOLTAGEINVERTERSUSINGSTEPUPTRANSFORMERATTHEOUTPUT，ORWITHMULTIPLELOWVOLTAGEINVERTERSCONNECTEDINSERIESTHREELEVELVOLTAGEFEDPWMCONVERTERSYSTEMSARERECENTLYSHOWINGINCREASINGPOPULARITYFORMULTIMEGAWATTINDUSTRIALDRIVEAPPLICATIONSBECAUSEOFEASYVOLTAGESHARINGBETWEENTHESERIESDEVICESANDIMPROVEDHARMONICQUALITYATTHEOUTPUTCOMPAREDTOTWOLEVELCONVERTERSYSTEMSWITHSIMPLESERIESCONNECTIONOFDEVICESTHISKINDOFVFCSYSTEMWITHTHREE750KW/23KVINVERTERSHASBEENSUCCESSFULLYINSTALLEDINCHENGZHUANGMINEFORONE27KMLONGBELTCONVEYORDRIVINGSYSTEMINFOLLOWINGTHEPRINCIPLEOFTHREELEVELINVERTERWILLBEDISCUSSEDINDETAIL2NEUTRALPOINTCLAMPEDNPCTHREELEVELINVERTERUSINGIGBTSTHREELEVELVOLTAGEFEDINVERTERSHAVERECENTLYBECOMEMOREANDMOREPOPULARFORHIGHERPOWERDRIVEAPPLICATIONSBECAUSEOFTHEIREASYVOLTAGESHARINGFEATURES1OWERDV/DTPERSWITCHINGFOREACHOFTHEDEVICES，ANDSUPERIORHARMONICQUALITYATTHEOUTPUTTHEAVAILABILITYOFHVIGBTSHASLEDTOTHEDESIGNOFANEWRANGEOFMEDIUMHIGHVOLTAGEINVERTERUSINGTHREELEVELNPCTOPOLOGYTHISKINDOFINVERTERCANREALIZEAWHOLERANGEWITHAVOLTAGERATINGFROM23KVTO416KVSERIESCONNECTIONOFHVIGBTMODULESISUSEDINTHE33KVAND416KVDEVICESTHE23KVINVERTERSNEEDONLYONEHVIGBTPERSWITCH2,321POWERSECTIONTOMEETTHEDEMANDSFORMEDIUMVOLTAGEAPPLICATIONSATHREELEVELNEUTRALPOINTCLAMPEDINVERTERREALIZESTHEPOWERSECTIONINCOMPARISONTOATWOLEVELINVERTERTHENPCINVERTEROFFERSTHEBENEFITTHATTHREEVOLTAGELEVELSCANBESUPPLIEDTOTHEOUTPUTTERMINALS，SOFORTHESAMEOUTPUTCURRENTQUALITY，ONLY1/4OFTHESWITCHINGFREQUENCYISNECESSARYMOREOVERTHEVOLTAGERATINGSOFTHESWITCHESINNPCINVERTERTOPOLOGYWILLBEREDUCEDTO1/2ANDTHEADDITIONALTRANSIENTVOLTAGESTRESSONTHEMOTORCANALSOBEREDUCEDTO1/2COMPAREDTOTHATOFATWOLEVELINVERTERTHESWITCHINGSTATESOFATHREELEVELINVERTERARESUMMARIZEDINTABLE1UVANDWDENOTEEACHOFTHETHREEPHASESRESPECTIVELY；PNANDOARETHEDCBUSPOINTSTHEPHASEU，FOREXAMPLE，ISINSTATEPPOSITIVEBUSVOLTAGEWHENTHESWITCHESS1UANDS2UARECLOSED，WHEREASITISINSTATENNEGATIVEBUSVOLTAGEWHENTHESWITCHESS3UANDS4UARECLOSEDATNEUTRALPOINTCLAMPING，THEPHASEISINOSTATEWHENEITHERS2UORS3UCONDUCTSDEPENDINGONPOSITIVEORNEGATIVEPHASECURRENTPOLARITY，RESPECTIVELYFORNEUTRALPOINTVOLTAGEBALANCING，THEAVERAGECURRENTINJECTEDATOSHOULDBEZERO22LINESIDECONVERTERFORSTANDARDAPPLICATIONSAL2PULSEDIODERECTIFIERFEEDSTHEDIVIDEDDCLINKCAPACITORTHISTOPOLOGYINTRODUCESLOWHARMONICSONTHELINESIDEFOREVENHIGHERREQUIREMENTSA24PULSEDIODERECTIFIERCANBEUSEDASANINPUTCONVERTERFORMOREADVANCEDAPPLICATIONSWHEREREGENERATIONCAPABILITYISNECESSARY,ANACTIVEFRONTENDCONVERTERCANREPLACETHEDIODERECTIFIER,USINGTHESAMESTRUCTUREASTHEINVERTER23INVERTERCONTROLMOTORCONTRO1MOTORCONTROLOFINDUCTIONMACHINESISREALIZEDBYUSINGAROTORFLUXORIENTEDVECTORCONTROLLERFIG2SHOWSTHEBLOCKDIAGRAMOFINDIRECTVECTORCONTROLLEDDRIVETHATINCORPORATESBOTHCONSTANTTORQUEANDHIGHSPEEDFIELDWEAKENINGREGIONSWHERETHEPWMMODULATORWASUSEDINTHISFIGURE，THECOMMANDFLUXISGENERATEDASFUNCTIONOFSPEEDTHEFEEDBACKSPEEDISADDEDWITHTHEFEEDFORWARDSLIPCOMMANDSIGNALTHERESULTINGFREQUENCYSIGNALISINTEGRATEDANDTHENTHEUNITVECTORSIGNALSCOSANDSINAREGENERATEDTHEVECTORROTATORGENERATESTHEVOLTAGEANDANGLECOMMANDSFORTHEPWMASSHOWNPWMMODULATORTHEDEMANDEDVOLTAGEVECTORISGENERATEDUSINGANELABORATEPWMMODULATORTHEMODULATOREXTENDSTHECONCEPTSOFSPACEVECTORMODULATIONTOTHETHREELEVELINVERTERTHEOPERATIONCANBEEXPLAINEDBYSTARTINGFROMAREGULARLYSAMPLEDSINETRIANGLECOMPARISONFROMTWOLEVELINVERTERINSTEADOFUSINGONESETOFREFERENCEWAVEFORMSANDONETRIANGLEDEFININGTHESWITCHINGFREQUENCY，THETHREELEVELMODULATORUSESTWOSETSOFREFERENCEWAVEFORMSUR1ANDUR2ANDJUSTONETRIANGLETHUS,EACHSWITCHINGTRANSITIONISUSEDINANOPTIMALWAYSOTHATSEVERALOBJECTIVESAREREACHEDATTHESAMETIMEVERYLOWHARMONICSAREGENERATEDTHESWITCHINGFREQUENCYISLOWANDTHUSSWITCHINGLOSSESAREMINIMIZEDASINATWOLEVELINVERTER,AZEROSEQUENCECOMPONENTCANBEADDEDTOEACHSETOFREFERENCEWAVEFORMSINORDERTOMAXIMIZETHEFUNDAMENTALVOLTAGECOMPONENTASANADDITIONALDEGREEOFFREEDOM，THEPOSITIONOFTHEREFERENCEWAVEFORMSWITHINTHETRIANGLECANBECHANGEDTHISCANBEUSEDFORCURRENTBALANCEINTHETWOHALVESOFTHEDC1INK3TESTINGRESULTSAFTERSUCCESSFULINSTALLATIONOFTHREE750KW/23KVTHREELEVELINVERTERSFORONE27KMLONGBELTCONVEYORDRIVINGSYSTEMINCHENGZHUANGMINETHEPERFORMANCEOFTHEWHOL