摘要：现有恒压供水一般采用水泵恒速调节或改变传动装置的水泵变速调节方式，工作效率低，故障率高，浪费了大量能源；而采用变频调速的供水系统，具有节能、稳定等优点。研究本课题是为了提高我国泵站的工作效率，从而满足现在城镇和工业用水的基本要求。通过介绍水泵的类型、变频调速的原理、能耗和安全性对恒压供水系统进行分析。

研究设计了三个水泵的工频/变频切换运行。系统硬件需选择正确的PLC、变频器、水泵机组、压力传感器和液位变送器。水泵之间的运行切换采用“先启先停”的原则。通过设置两种供水模式信号作为给定水压，压力传感器将检测的当前水压信号发送到PLC，通过PID运算，达到控制变频器的输出电压和频率的目的。 57703

毕业论文关键词：变频调速，恒压供水，PLC 

Abstract: The existed constant pressure water supply system usually worked in the mode that the pump speed is constant or the mode that the pump speed is adjust by a gearing. This kind of system works with low efficiency and high failure rate, thus wasting a lot of energy. While the water supply system with variable frequency control have the advantages such as energy efficiency, stable, etc.. A control system is studied to improve the efficiency of the pumping, so as to meet the basic water requirements of the town and industry. The type of pumps and the principle of variable frequency control are introduced, then the energy consumption and safety are studied to analysis the water system.

A system with three pumps switching between variable frequency mode and power frequency mode is studied and designed. The proper PLC, VFD, pump set, pressure sensor and liquid level transmitter should be selected. The pumps switch with first initial first stop principle. Two water supply modes are set as the aim pressure, and the signal from the pressure sensor is sent to PLC. The output voltage and frequency of the VFD is controlled by PID operation.

key word：variable frequency control，constant pressure water supply，PLC

目  录

1  课题背景 4

2  恒压供水系统分析 4

2.1  水泵的介绍 4

2.1.1  水泵的工作原理 4

2.2  水泵的调节方式及优缺点分析 5

2.2.1  恒速调节 5

2.2.2  变速调节 5

2.3  变频调速供水系统 6

2.3.1  变频调速原理 6

2.4  系统的能耗分析 9

2.4.1  从水泵管路的流体功率看节能 9

2.4.2  从水泵的工作效率看节能 10

2.5  系统安全性 10

2.5.1  水锤效应 10

2.5.2  水锤效应的产生原因 11

2.5.3  水锤效应的消除 11

2.5.4  延长水泵寿命的其他因素 11

3  系统的硬件设计 12

3.1  系统主要设备的选型 12

3.1.1  PLC及其扩展模块的选型 12

3.1.2  变频器的选型 12

3.2  系统主电路分析及其设计