Design of Constant Pressure Water Supply System for a Residential District Based
on PLC
Guofang Gao
College of electrical and information engineering
Chongqing University of Science amp; Technology
Chongqing, China
gaoguofangcq@ 126.com
Abstract—The stability, reliability and economy of water supply system directly affect the normal work and life of the users, and it also reflects the management level of the water supply system. According to the energy saving principle of the frequency conversion and energy saving of water supply system, the design scheme of the automatic control system of the upper computer with PLC as the controller and the frequency converter is presented. From the hardware selection, circuit design, the lower computer control program, the upper computer monitor screen and so on to make a detailed demonstration and design. Through on-line debugging of the constant pressure water supply system, the system has the advantages of strong stability, reliability, operation convenience, good monitoring and so on.
Key-words-constant pressure water supply; frequency conversion; PLC; WINCC
I. Introduction
China has long been in the municipal water supply, high- rise building water supply, industrial production and other aspects of the technology has been relatively backward, industrial automation is low. In the peak period of water supply, water supply is often lower than demand, water pressure is reduced in short supply; and in the low peak period, water supply is often higher than the demand, water pressure increased, this will cause energy waste, and may cause the water pipe burst and water equipment damage. Traditional regulating water supply pressure of the frequent start stop motor control and water tower in secondary water supply regulation way, the former produces a lot of energy to power in the load impact, equipment continuous opening and stopping will influence on the service life of equipment; the latter needs a lot of investment and covers an area of, because it is a secondary water supply, can not guarantee the safety and reliability of the water quality[l],
II. Selection of overall scheme
Frequency conversion speed regulating operation is very stable and reliable, no phenomenon of frequent start mode fbr the soft start, equipment running smoothly, to avoid the electrical and mechanical shock, there is no risk of secondary pollution caused by the water tower. District water supply (pressure pump station) frequency conversion constant pressure water supply system in the 135kW, the
Dengfeng Cao
Chongqing Branch
China Telecom Corporation Limited
Chongqing, China
18908360806@189.cn
requirements of constant pressure water supply system can be adjusted according to the residents water consumption, to achieve energy saving purposes, the system is simple and reliable, good economic. For common constant pressure water supply system, mainly from the relay power distribution and water pump parts of the two parts of the composition.
A. SCM and Frequency Converter Control System
The scheme is simple, and the output voltage is controlled by the feedback signal of the pressure sensor, and the output voltage is calculated by the internal PID of the converter, so as to achieve the purpose of constant pressure. After signal conditioning by the micro-controller A/D port sampling, after the CPU treatment, determine the frequency of the pump frequency or power frequency operation mode[2]. However, the system has the disadvantages of low reliability, operation is not convenient, etc., and its block diagram is shown in figure 1.
Figure 1. Single Chip Microcomputer Control System.
B. DSP Variable Frequency Control System
The pressure sensor detects the pressure of the pipe network, and through the CPU chip A/D port sample processing, the pressure signal acquisition and sampling of the fault by CPU processing, through the calculation of PWM output CPU signal to the IPM power module output adjustable voltage, control the pump speed. At the same time to achieve the IPM power module temperature and current voltage monitoring, the input voltage of the power network is collected by the voltage transformer and the A/D port is sampled and processed[3]. The scheme can achieve high precision control, but the system is too complex, and the design cycle of software and hardware is not suitable fbr the
978-1-4673-7755-3/16/S31.00 ©2016 IEEE
constant pressure frequency conversion water supply system.
lt; START 〉
The block diagram is shown in Figure 2.
Fault Detection
Figure 2. DSP frequency Conversion Control System
Initialization(Manual I nput
Starting Sequence)
〔Fault Handling |
N
water Hnessure Control Signal Sarnplingand PID Caloulauon iUDroubnetrol Subroutine
WINCC Manual Control""] [polling Subroutine |
C. PLC-Converter Control System
The lower computer adopts PLC or other controller, and the output of the converter is controlled by the lower computer, so as to achieve the purpose of the pump speed regulation. Using the PID PLC command to achieve control algorithm, and the use of its programming software PID control panel can easily adjust the PID parameters automatically, thereby reducing the inconvenience of manual adjustment, and can achieve a good effect. WINCC design of the upper computer can achieve real-time data monitoring, manual/automatic mode selection and fault display alarm, in order to achieve the purpose of on-site monitoring and easy operation.
|dutput Control]
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