1 Introduction
This project is an automated control system designed for a city's water supply system. The goal is to optimize water allocation by controlling the water level in the water plant's reservoir and the pressure at the water outlet. The city's water supply dispatching system mainly consists of two parts: a water source intake and collection system and a constant-pressure water supply system at the water plant. The water source intake and collection system primarily comprises local water supply well groups. Each well group has a centralized control room, and each well has its own control room. The centralized control room houses a centralized control system for starting and stopping the pumps in that group, coordinating and controlling the water intake of each well pump and the external water supply of the variable frequency pumps. The constant-pressure water supply system at the water plant mainly consists of a central control room, high and low voltage power distribution systems, a reservoir, and secondary pump stations. The secondary pump stations directly supply water to the city. The central control room serves as a remote monitoring station, enabling remote centralized management and coordination of the well groups to ensure optimal reservoir water level and optimal outlet pressure. The central control room is the core of the entire dispatching system.
This project uses Siemens S7200 and S7300 PLCs to design the monitoring system, and SimaticWinCC as the host computer monitoring system software. The system integrates advanced equipment such as network communication, fieldbus, PLC controller, industrial computer, and microwave communication, as well as many advanced technologies such as automatic control and remote monitoring, fully demonstrating the application of modern information technology and automation technology in urban water supply systems.
2. Control System Composition
The water supply system is designed as a whole, consisting of four parts: a single well unit at the local station, a well group system at the local station, a central control station, and a central control system.
2.1 On-site single-well control system
The local station single-well control system uses an S7-222 PLC, while the local station well group control system uses an S7-314 PLC. The two are connected via a PROFIBUS fieldbus and exchange information within a predetermined information cycle. The local station single-well control system receives control signals from the well group's local centralized control station (S7-314), completes data acquisition for the entire single-well system, and enables manual, local centralized, and remote control of the motors. It connects to the upper-level central control system via a CP340 communication processor and an FC-201 wireless data transmission radio to complete data acquisition and transmission for the entire well group's local central control station.
The PLC software program for the local well group mainly consists of communication processing programs with lower-level units (each individual well), communication processing programs with higher-level units, local centralized control programs for starting and stopping well group pumps, and local remote control programs for starting and stopping well group pumps.
2.2 Second Pump Station Control System
The second pumping station system is responsible for directly supplying water to the city. The PLC in the second pumping station uses a Siemens S7-314 programmable controller, which is connected to the host computer via a Profibus fieldbus. It is the core of the control cabinet in the pumping station, receiving control signals from the host computer to control the frequency converter speed regulation, and realizing the logical control of signals such as motor start, stop, and reset; it collects and converts signals such as pressure, flow, water level, current, and speed and sends them back to the host computer; it receives valve opening control signals from the host computer to optimize water supply; and it provides overcurrent and overvoltage protection for motors and other equipment.
2.3 Upper-level central control station
As the centralized control center for all individual wells on site, it is responsible for the centralized storage and management of information such as liquid level, pressure, voltage, current, and operating status of each well pump. Simultaneously, as the centralized control center, it is also responsible for the remote centralized start-stop control of all individual well pumps on site. Furthermore, the upper-level central control station PLC is responsible for real-time data exchange with the central control room monitoring center. The upper-level central control station PLC remotely and automatically starts and stops well pumps based on the water level in the water plant's storage tank, and starts and stops the on-site pumps according to control commands from the central control room monitoring center. On the other hand, it uses a cyclical, rotating method to collect real-time data from each individual well. The central control station PLC communicates with the lower-level well group PLCs via wireless data transmission radio. The program mainly completes functions such as pressure detection, soft start-stop of the water supply pumps, and frequency detection and control.
2.4 Central Control Room Control System
The start-up and shutdown of all single-well pumps at the water source and the variable-frequency constant-pressure water supply of the water plant's pumps are controlled by the central control system in the main control room, enabling rational scheduling, management, and monitoring of the entire system. The central control unit in the main control room uses a WINCC industrial computer with a PROFIBUS-DP network card (CP5611) interface as the master station. It is connected to the S7-314 in the second pump house and the S7-314 in the well group center via the PROFIBUS fieldbus. Through the S7-314 in the second pump house, information such as inverter status, valve status, pressure, flow rate, and water level is collected in each information cycle, and the valves are controlled to coordinate the start-up, shutdown, and speed control of each pump, achieving optimization. This forms a multi-level remote distributed control system. The main functions of the central control system in the main control room are: real-time data acquisition, data analysis and processing, control and adjustment functions, screen display, remote communication, human-machine interface, and safety verification. The monitoring screen displays the operational status of all pumping stations at the water source, the water supply process, etc., with one screen showing one view. Furthermore, the data collected by the system can be displayed in real-time on the corresponding dynamic screens. Each screen has a screen switching control button, allowing for convenient screen switching and various operations.
The entire system employs PID control for multiple basic control loops, such as water pressure, valve opening, and pump frequency, across various control system units. Furthermore, intelligent scheduling algorithms, including fuzzy control, are used on the host computer to ensure stable and efficient urban water supply. All master and slave stations communicate via a standard PROFIBUS-DP bus, forming a multi-level remote distributed control system and guaranteeing communication quality.
3. Conclusion
This paper integrates intelligent control, computer, network information and fieldbus technology. Based on the current status of the water supply network, and through detailed analysis of control strategies and fieldbus technology, a remote regional network intelligent monitoring and dispatching system was designed and established.
This system was put into operation in July 2004. Currently, the system operates stably and reliably, stabilizing water pressure and reducing the frequency of water supply network maintenance. After long-term use, feedback indicates that the automatic adjustment effect is basically consistent with the adjustment settings of an experienced engineer. Combined with the practical experience of operators, the automatic control has achieved remarkable results.
