基于PLC变频调速恒压供水系统设计毕业设计论文.docVIP

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 PAGE II PAGE I 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 ABSTRACT This paper is based on residential water standards for water supply requirements of the premise and waterworks, to design a PLC-based frequency control water supply system. Water Supply System means the size of the client at any time, regardless of water use, always ensure that the water pressure constant in the pipe network in the set. Frequency control water supply system uses PLC, inverter, pressure transmitter, and the pump unit to form a closed loop control system using PLC logic control, the inverter speed control of pump units. This system is the conversion cycle operation mode of the water pump motor, inverter and PLC as the core component of the system control keeps track of pressure transmitter detected the pipe network pressure and a given pressure change in error, the PID by the PLC internal operation by the PLC to control the switching of the variable frequency and power frequency, automatic control of pump input the number of units and control of inverter output frequency, and thus change the speed of the pump motor to change the supply quantity, and ultimately to maintain the stability of the pipe network pressure near the set value. This system uses the converter to achieve soft-start and frequency control three-phase water pump motor run switch using the principle of first initial first stop to avoid the long-running of the pump and cause damage and reduce the life of the motor, but also increase a real-time monitoring