基于plc的变频恒压供水系统设计本科毕业论文.doc

PAGE PAGE PAGE I 基于PLC的变频恒压供水系统设计 摘要 本文设计了一种由PLC与变频器组成的替代传统水塔供水的变频恒压供水系统。它由一台变频泵、一台工频泵、一台备用泵组成，以PLC作为主控制器，实现系统的启动制动、供水模式选择、水泵电机监测、电机故障报警以及故障电机切换至备用电机等功能。该系统对供水管网压力信号进行实时检测，并根据压力值决定启动电机的台数和电机的运行工况，变频器实现变频工况下水泵电机的无级调速。变频恒压供水系统的可靠运行主要取决于对水压信号的稳定控制，当压力信号控制不稳定时，达不到恒压供水的目的，而且会出现水锤效应，损坏电机和供水管网，所以在该系统中对压力信号采用PID控制，即将采集的管网压力信号由模拟量输入口送入PLC，经PLC自带的PID运算模块进行PID控制，然后由PLC的模拟量输出口送给变频器，作为变频器的输出频率控制信号。PID控制可使水压信号快速稳定在预定值。系统还对水泵电机的转速和电流进行了监控，当电机发生故障时，报警信号灯和蜂鸣器动作，同时故障电机自动切换到备用电机，保证可靠供水。综上所述，本系统具有变频节能、安全可靠、实时优质供水等优点。 关键词：PLC，变频器，恒压供水，PID，电机监控 FREQUENCY CONVERSION CONSTANT PRESSURE WATER SUPPLY SYSTEM DESIGN BASED ON PLC Abstract A kind of constant pressure water supply system is designed in this paper. It was composed of PLC and transducer instead of the traditional water tower supplies water system. The system was constituted of a frequency conversion pump, a power frequency pump and a standby pump. PLC is made as the main controller. It realizes the functions of start-up and braking system, water supply mode selection, monitoring the water pump motor, pump motor breakdown alarm and switch breakdown motor to the standby electric motor and so on. The pressure signal of water supply pipe network is examined in real-time and the pressure value in accordance with the decision of the number of motors to start up and the motors’ operating conditions. The transducer is used for stepless speed regulation of motor. The frequency conversion constant pressure water supply systems reliability service is mainly decided to the stable control of pressure signal. Anticipated purpose cannot be achieved when the control of pressure signal is unstable. Water hammer effect will be generated. Motors and water supply pipe network may be damaged. Therefore, PID control is used in the system for pressure signal. It means that the pressure signal is operated by the PLC built-in PID module, and then output the result to the transducer as the transducer control signal. The PID control enables the pressur