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I摘要随着改革开放的不断深入，我国中小城市的城市建设及其经济迅猛发展，人民的生活水平不断提高；同时，城市需水量日益加大，对城市供水系统提出了更高的要求。供水的可靠性、稳定性、经济节能性直接影响到城区的建设和经济的发展，也影响到城区居民的正常工作和生活。本文根据城区供水管网改造工程设计了一套由PLC、变频器、远传压力表、多台水泵机组、计算机等主要设备构成的全自动变频恒压供水及其远程监控系统，具有自动工频/变频恒压运行、可实现远程自动控制和现场手动控制等功能。论文分析了采取变频调速方式实现恒压供水相对于传统的阀门控制恒压供水方式的节能机理。通过对变频器内置PID模块参数的预置，利用远传压力表的水压反馈量，构成闭环系统，根据用水量的变化，采取PID调节方式，在全流量范围内利用变频泵的连续调节和工频泵的分级调节相结合，实现恒压供水且有效节能。论文论述了采用多泵并联供水方案的合理性，分析了多泵供水方式的各种供水状态及转换条件，分析了电机由变频转工频运行方式的切换过程及存在的问题。给出了实现有效状态循环转换控制的电气设计方案和PLC控制程序设计方案。系统有效地解决了传统供水方式中存在的问题，增强了系统的可靠性。并与计算机实现了有机的结合，提升了系统的总体性能。关键词：PLC；变频调速；恒压供水；变频工频切换AbstractWiththecontinuousdeepeningofreformingandopeningup,theconstructionandeconomyofsmallandmedium-sizedcitiesinChinahavedevelopedrapidly.People'slivingstandardshaveimprovedconstantly.Thewatersupplysystemisdemandedmoreascitywaterconsumptionincreasing.Theurbanconstructionandeconomicdevelopmentandalsopeople’sdailyworkandlifeareimpacteddirectlybythereliability,stabilityandtheeconomicalofenergyconservationofthewatersupplysystem.AnautomaticconversionandvoltageconstantWaterSupplyandremotemonitoringsystem,whichconsistofthePLC,theconverter,theremotetransitionpressuregauges,themulti-pumpsunit,thecomputerandsoon.Itisofautomaticline-frequency/conversionfunction,remoteandlocalautomaticcontrol.Inthispaper,themechanismofenergysaving,whichusesspeedgoverningwithinvertortodesignvoltageconstantwatersupplysystem,competingwithtraditionalvalvecontrolledpressureconstantsystem.ClosedloopsystemisbuiltbypresettingtheparameterofthePIDinsideofconvertor,andfeedbackofremotetransitonhydraulicmeter.UsingthestepregulationofconvertorpumpandfrequencypumpinfullrangofflowtoapplyPIDcontrolonthechangeofwaterachievesenergysavingofvoltageconstantwatersupply.Thispaperdiscussesthereasonabilityofwatersupplyschemewithmuchpumpparallelconnection,andanalysestheconversionconditionandthevariousstatesofwatersupplyofthemuchpumpwayofwatersupplyaswellastheswitchprocessandtheproblemofageneratorfromvariablefrequencyoperationmodetoworkfrequencyoperationmode.Inaddition，thecombinationofthesystemandthecomputerisachieved，whichimprovedtheoverallfunctionofthesystem．Keywords：PLC;VariableVelocityVariablefrequency;Constantpressurewater-supply;variablefrequencytoworkingfrequency目录摘要........................................................................................................................IABSTRACT.............................................................................................................II1绪论.....................................................................................................................11.1课题背景及意义................................................................................................11.2变频恒压供水的现况........................................................................................11.3变频恒压供水系统的特点................................................................................32变频恒压供水系统理论分析...............................................................................42.1供水系统的基本特性........................................................................................42.2不同控制方式下的能耗分析与比较................................................................52.3变频恒压控制的理论模型................................................................................62.4供水系统中的水锤效应及消除方法................................................................73供水系统恒压控制与硬件设计...........................................................................83.1异步电动机调速方法及选型............................................................................83.1.1变极调速.........................................................................................................83.1.2变频调速.........................................................................................................93.2供水系统的方案确定......................................................................................103.2.1供水系统的流量类型...................................................................................103.2.2总体设计方案确定........................................................................................103.2.3恒压供水电控系统组成................................................................................123.3控制系统的硬件设计与选型...........................................................................133.3.1主电路设计....................................................................................................133.3.2电气控制电路设计........................................................................................143.3.3系统主要配置的选型....................................................................................163.4PLC的选型.......................................................................................................193.5系统可靠性措施..............................................................................................204PLC控制系统的设计.......................................................................................224.1水泵工频/变频运行状态及转换过程分析.....................................................224.1.1供水状态及其转换....................................................