Design of constant pressure water supply system by using virtual instrument fuzzy control technology

Urban water supply has always been a major problem in the process of urban development. At present, the shortage of urban energy has increasingly restricted the overall development of the city. The traditional pump set water supply system not only makes the water pressure unstable, but also wastes a lot of water. Energy, the power consumption of factories has risen sharply, and energy conservation and environmental protection have become the theme of this era. In order to maximize energy utilization, engineers have designed various control methods for water supply systems, but most of them require a lot of equipment investment and complex programming, and self-optimization of control methods cannot be achieved. Based on the traditional control method, this paper applies the virtual instrument fuzzy control technology to realize constant pressure water supply. The method is simple in programming design, beautiful in operation interface, and reliable in control, which ensures the stability of water supply pressure, saves energy, and also reduces energy consumption. It provides an interface for the network management of urban water supply in the future. 1 Introduction to virtual instrument control

1.1 Virtual Instruments

The so-called virtual instrument is a computer instrument system in which the virtual panel is designed and defined by the user on a hardware platform with a general computer as the core, and the measurement and control functions are realized by software. The user operates the virtual panel with the mouse or keyboard, just like using a special measuring and controlling instrument. The essence of the virtual instrument is to use the Display function of the computer monitor to simulate the traditional control panel, express the output results in various forms, use the powerful software functions of the computer to realize the operation, analysis, processing and storage of the data, and use the I/O interface device to complete the operation. Signal acquisition, measurement and control. A computer is a measurement and control system.

1.2 Virtual Instrument Fuzzy Controller

The fuzzy logic toolbox of virtual instruments is used to design rule-based fuzzy controllers, and the main application fields are industrial process control and expert systems. It consists of 4 subVIs:

(1) Design VI of fuzzy logic controller. It provides a friendly human-computer interaction interface, consisting of a fuzzy membership function editor, a fuzzy rule library editor and an input and output performance test.

(2) Load the fuzzy controller VI. It loads all fuzzy controller parameters stored in a file with the extension FC into the Fuzzy Controller VI.

(3) Fuzzy controller VI. It can add the designed fuzzy controller to the block diagram program of Labview as a functional module.

(4) Test the fuzzy controller VI. It is used to test the basic performance of the fuzzy controller. The function of the fuzzification unit is to convert the precise quantity on the real number universe into the fuzzy quantity that the fuzzy logic system can handle, that is, the degree of membership. Using Labview’s fuzzy logic toolbox, you can not only design fuzzy controllers under a friendly graphical interface, but also use Labview’s various function libraries, especially to connect with hardware such as data acquisition equipment, to quickly build the required control system , to carry out the actual simulation and application of the fuzzy controller.

2. The principle of fuzzy control of urban water supply

2.1 Principles of urban water supply

The whole control system consists of 4 pumps, and a frequency converter switches to control the start, stop and speed regulation of the pumps. Through programming, the pumps work according to certain process requirements. During the working process, the four pumps are started in sequence according to the change of water pressure. The principle to follow is to start first and stop first, as shown in Figure 1.

  Design of constant pressure water supply system by using virtual instrument fuzzy control technology

2.2 The principle of constant pressure water supply control

When the system starts to work, first set the water pressure value, and then start the system. The system first starts the M1 water pump, the speed of the M1 water pump begins to increase, and the water pressure of the water pipe gradually increases. The pressure detector detects the pressure of the water pipe and transmits it to the computer in real time. The computer judges the user’s water consumption through real-time calculation. When the set value is reached, the system judges that the water consumption is large, so the M1 pump is changed from frequency conversion control to ordinary power frequency control to realize full power start, and then the M2 water pump is started by frequency conversion, the speed of the pump increases, and the water pressure is further increased. Until the current water pressure value reaches the set value, according to the above principle, when the water consumption increases, the pumps will be turned on in turn. On the contrary, when the water consumption decreases and the frequency conversion reduces the speed of the water pump to the lower limit, the sequence of opening will be followed. Turn off the water pump to stabilize the pressure at the set value and realize constant pressure water supply. The entire control process is dynamic and self-adjusting, without human control.

3. Application examples

3.1 The hardware composition of the control system

The fuzzy control system based on virtual instrument is composed of a PXI bus computer, PXI6259 analog acquisition card, signal conditioning, Siemens frequency converter and water pump. The whole control is realized through Labview8.2 programming on the computer.

3.2 Labview software control interface design

The process of developing control system using Labview programming language can be divided into two steps: (1) developing instrument panel, data report, board driver, data analysis program, etc.; (2) generating instrument panel and corresponding data analysis management function according to user requirements virtual instrument. The fuzzy control system based on virtual instrument is shown in Figure 2.


3.3 Design of Fuzzy Controller Based on Labview Programming

Taking the error e of the water pressure given value SV and the actual water pressure measurement value PV and the change rate ec of e as the input of the controller, after fuzzification, it is converted into a description in fuzzy language, and the fuzzy control law is used to judge the control value. The real value, then this value is collected through the PXI6259 template to control the inverter, and then control the speed of the water pump.The system takes five fuzzy sets to describe the water pressure error e, the error rate of change ec and the control variable u. The fuzzy sets on the domain {-4, 4) are as follows[NL,NB,NM,NS,0,PS,PM,PB,PL].

Run the fuzzy logic controller design VI in the Labview environment, and set the input and output variable language values ​​and the corresponding membership functions through the membership function editor. To enhance the robustness of the controller, the triangular membership function is selected. Run FCT in the Labview environment, open the FuzzyLog-icControlDesign module, and design parameters such as input and output variables and the membership function shape of each language variable through FuzzySetEditor with an interactive interface. The membership functions of the three variables e, ec and u are triangles, and the universe of discourse is discrete as[-4,-3,-2-1,0,1,2,3,4]At level 9, the design and modification of various parameters can be carried out intuitively and conveniently through the Labview fuzzy set editor. Through the interactive graphical programming environment provided by Labview and its fuzzy logic toolkit, the design of basic fuzzy controllers can be carried out conveniently and efficiently.

The whole control is simple and practical, the interface is simple and intuitive, easy to operate, and the saved data is regularly analyzed to optimize system parameters and maximize energy use. The entire design can meet the requirements of the actual urban water supply system, while maximizing energy savings.

4 Conclusion

After the virtual instrument fuzzy control constant pressure water supply system is put into operation, after more than one year of operation, its energy saving effect is obvious. , with a frequency conversion can meet the user’s requirements. At the same time, the data collected by the system is continuously analyzed and optimized. Compared with the traditional control system, this set of control system saves electricity by 30% to 35% on average, which greatly improves the electricity saving rate.

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