基于plc变频调速恒压供水系统设计大学学位论文.doc

基于PLC变频调速恒压供水系统设计华北科技学院毕业设计PAGEIIPAGEI摘要根据城市居民用水标准为前提和小型自来水厂的供水要求，自行设计了基于PLC变频调速恒压供水系统。恒压供水系统是指用户端在任何时候，不管用水量的大小，总能保证管网中的水压恒的基本定。变频调速恒压供水系统利用PLC、变频器、压力变送器和水泵机组组成闭环控制系统，采用了PLC进行逻辑控制，变频器对水泵机组的调速。本系统是用3台水泵电机的变频循环运行方式，变频器和PLC作为系统控制的核心部件，时刻跟踪压力变送器检测到的管网压力和给定压力的偏差变化，经PLC内部进行PID运算，通过PLC控制变频和工频的切换，自动控制水泵的投入台数和控制变频器的输出频率，进而改变水泵电机的转速来改变供水量，最终保持管网压力稳定在设定值附近。本系统是采用变频器实现对三相水泵电机的软启动和变频调速，运行切换采用“先启先停”的原则，避免了水泵的长时间运行而造成电机的损坏和减少寿命，还增加了液位变送器的实时监控水泵进水源防止水泵的空抽而损坏水泵电机和报警系统是反应系统是否运行正常，水泵电机是否过载、变频器是否异常。关键词：PLC、变频调速、恒压供水系统、压力变送器、液位变送器ABSTRACTThispaperisbasedonresidentialwaterstandardsforwatersupplyrequirementsofthepremiseandwaterworks,todesignaPLC-basedfrequencycontrolwatersupplysystem.WaterSupplySystemmeansthesizeoftheclientatanytime,regardlessofwateruse,alwaysensurethatthewaterpressureconstantinthepipenetworkintheset.FrequencycontrolwatersupplysystemusesPLC,inverter,pressuretransmitter,andthepumpunittoformaclosedloopcontrolsystemusingPLClogiccontrol,theinverterspeedcontrolofpumpunits.Thissystemistheconversioncycleoperationmodeofthewaterpumpmotor,inverterandPLCasthecorecomponentofthesystemcontrolkeepstrackofpressuretransmitterdetectedthepipenetworkpressureandagivenpressurechangeinerror,thePIDbythePLCinternaloperationbythePLCtocontroltheswitchingofthevariablefrequencyandpowerfrequency,automaticcontrolofpumpinputthenumberofunitsandcontrolofinverteroutputfrequency,andthuschangethespeedofthepumpmotortochangethesupplyquantity,andultimatelytomaintainthestabilityofthepipenetworkpressurenearthesetvalue.Thissystemusestheconvertertoachievesoft-startandfrequencycontrolthree-phasewaterpumpmotorrunswitchusingtheprincipleof"firstinitialfirststop"toavoidthelong-runningofthepumpandcausedamageandreducethelifeofthemotor,butalsoincreaseareal-timemonitoringoftheleveltransmitterpumpintotheemptypumpingofwatertopreventpumpdamagetothepumpmotorandalarmsystemistheresponsesystemisfunctioningproperly,whetherthepumpmotoroverload,theinverterisabnormal.Keywords:PLC,FrequencyControl,WaterSupplySystem,pressuretrans