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ConstantPressureWaterSupplySystemBasedplcAbstract:Basedonesimpleanalysisofthemethodsforwatersupplyuseddomesticallyandabroad,thispaperdiscussestheprincipleandsystem’sstructureofautomaticwatersupplysystembyusingfrequencyconversionspeedregulationindetail.Thenthesystem’sadvantagesarediscussedandsomekeyproblemsthatshouldbepayattentiontodesigningarepresented.Keyword:Frequencyconversionspeedregulation;watersupplywithstablepressure:PIDregulator.1、ForewordAtpresent,supplywaterinresidentialareaandlifeoftheskyscraperofourcountrygenerallyadoptthewaycommonfrequently.Ithasheavyenergyconsumption,highnoise,andtherehasagreatdealofquestionsinthesourceofwater,suchassecondarypollutionetc.Anditisakindofcomparativelyidealmodetoadjustthewatersupplydevicecontrolledrapidlywithfrequencyconversion.Enteringthemiddleandlaterperiodsofthe1990s,asthespeedtechnologyoffrequencyconversionachievesmoredevelopmentbecomesperfect,thewayofthefull-automaticconstantpressurethatbasedonthistechnologysuppliedwaterhasalreadybeenwidelyusedinthedevelopedcountry,andisbecomingriper.Inrecentyears,authorshasmadesomerealworkonrapidlytothetransformationinfrequencyconversionsupplywaterdesignandconstructionofcontrolsystem,haveaccumulatedsomeexperience,andhasformedtheviewonsomequestions.Thereasonwhytheenergy-conservingprinciplefrequencyconversionofthewaterpumpsystemofspeedadjustmentbecomespopularized,ismainlybecausethatithasabetterenergy-conservingresult.Topumpsystemoffrequencyconversion,thewaterpumpafteradjustingthespeedhasfunctionalrelationofthefollowing:Q1/Q2=n1/n2(1)H1/H2=(n1/n2)2(2)ofthetype.Q1,Q2representstheflowbeforeandafterthespeedforthewaterpumprespectively;N1,n2representstherotationalspeedbeforeandafterthespeedforthewaterpumprespectively;H1,H2representstheliftbeforeandafterthespeedforthewaterpumprespectively.Accordingtheabove:H1/H2=(f1/f2)2.Namelyrealliftofawaterpumpispowerthesquareoffrequencyindirectradio.Thereforechangingthepowersupplyfrequencyoftheelectricalmachineryofwaterpumpthroughthefrequencyconvertercancontrolsupportingwaterpressurestrengthofthewaterpump.2constantpressuresasFig.1showssupplywateroftheautomaticallycontrolledfrequencyconversionwater-supplysystemprincipleblockdiagram.P1isthegivepressurevalue,p2fortheactualpressurevaluehadexaminedfromthepipelineofthepressuresensor,PIDregulatorpassestheerroroperationofthetwovalue,andthroughcontrollingthefrequencyoutputofthefrequencyconverter,thusmakethepressureofthepipelineremainthroughoutonestablishingvaluep1.Thissystemcanmeasureusers'instantaneouswaterpressureadjustautomatically,regulatetheamountofquantityofsupplyingwaterandoperationconditionsoftheelectricalmachineryinviewoftheabove.Canaccordingtogivewaterpressurestrengthtosetforandcontrolpressurevaluewhichneeded,maketheequipmentintheconstantpressurestateallthetime,canknowfromloadcharacteristicofelectricalmachineryaxlepoweranditsthethirdpowerofindirectradiorotationalspeedofelectricalmachinerymixed,thatisp1/p2=(n1/n2)3.Forexample,asthefrequencyconverteroutputfrequencyfor35Hz(establishas50Hzatmost),thatistosaythattheactualrotationalspeedis70%o'clockofspecifiedrotationalspeed,thepowerconsumptionofthegovernoris0.73=0.343,accountforspecified35%.Thatistosay,thewaterpumpisalwaysinconstantpressureandturntheworkingstateofmatchingthewayintotheflow,isitisitkeeptoexceedtodispelandbacksetcurrenthaveworkloss.ConstantspeedtransferwithfrequencyconversionspeedaxlepowerchangecurveasFig.2shows,relativelycanknow,itisthemostobviousthatfrequencyconversionadjuststheenergy-conservingresultofspeedway.2、CaseanalysesConstantpressureisitregulateflowofwatertothepurposetouptoconstantpressurethroughsuitingwellrapidlyinfrequencyconversiontosupplywater,thegoalthatitcontrolsfinallyisthewaterpressure.Controllingthetargethasnon-linear,laggingcharacteristics.ThequalityofPIDregulatorperformance,hasdeterminedthequalityofthewater-supplysystemtoagreatextentWhenthesystemisduringthecourseofstartingandstopping,orthepressureestablishingvaluechangesbyalargemargin,becausethereisaverygreatdeviationwithinshorttime,nomatterthecontrolalgorithmofPIDregulatoradoptstheincrementtypeorthepositiontype,itstotalmarkonewillfetchthecistern,waterpumpgroupandcomplementthefittingstoformrelevantly.Thecoreofthissystemisthatfrequencyconversionadjuststhespeedswitchboard,itmonitorsthepressureofthepipenetworkinrealtimethroughthepressuresensor,andchangeintotheelectricsignalandofferthefrequencyconvertertomakeoperation,throughthecontrollingcommonlyoffrequencyconverter,programmablecontrollerPLCandrelayarray,adjustthesystemofsupplyingwaterrapidlyafterformingperfectfull-automaticfrequencyconversion.Frequencyconverterisvariousinkinds,forinstancethetypes,suchasMitsubishi,Fuji,threeKenyaandABB,etc.Generallyoftenselectthepumps,special-purposeseriesofairblowerforuse.WhethertakeMitsubishiFR-A140Easanexample,itexceptgeneralfunctionhadofbrand,therearethefollowingcharacteristics:TheinsideadoptstheintellectualpowermoduleofIPM,itislowesttomakethenoiseoftheelectricalmachinerytoreduce;Frequencyconverter,andwork-frequencypowercanisitswit