This paper introduces a variable frequency constant pressure water supply system with AI intelligent controller and frequency converter as its core.
The system consists of four parts: pressure sensor of water supply pipeline, centrifugal pump, frequency converter and AI intelligent controller. By detecting the water supply pressure of the pipeline, the AI intelligent controller drives the frequency converter to control the rotational speed of the main and auxiliary pumps to achieve constant pressure control of the water supply pipeline, which improves the stability of the water supply pressure, avoids the pollution of the water quality of the secondary water tank, and realizes the purpose of saving electricity and water. With the expansion of the enrollment scale in Colleges and universities, the number of students is increasing year by year, which is close to saturation in many colleges and universities. Especially in some schools with a long history of running schools, the old water supply equipment of campus water supply system is aging due to the lack of time to expand and update hardware equipment. Especially in the dormitory areas where water supply is concentrated, the old roof water tank secondary water supply system is still used. The real problem is the dormitory top floor. Secondary water tank cleaning, maintenance and water quality management, lack of effective management, which buried the hidden dangers of drinking water safety, secondary pollution phenomenon. The quality of dormitory water supplied by secondary water tank is deteriorating year by year. Some samples of water supply by water tank are found to be unqualified in turbidity, total bacteria, PH and other indicators. At the same time, the traditional secondary water tank water supply will fluctuate with the change of water consumption in student dormitories, especially in dormitories with high floors. These will directly affect the quality of water supply in student dormitories, and may even affect the health of students. In order to effectively reduce the secondary pollution of water supply in roof water tank and improve the stability of water pressure, the method of introducing frequency converter constant pressure water supply system can be used to solve the problem.
The constant pressure water supply system proposed in this paper is mainly composed of AI intelligent controller, thermostatic element pressure sensor of water supply pipeline, frequency converter and water pump. When the water consumption exceeds the water output of the main pump, the frequency converter controls the water supply of the main pump to maintain pressure. When the water consumption exceeds the water output, the pressure sensor senses the drop of fluid pressure in the pipe. After analysis and calculation, the intelligent controller outputs signals to the frequency converter control at the same time. Two pumps work to increase water supply pressure. The frequency converter controls the operation of the pump and adjusts the number of pumps according to the water consumption, thus greatly improving the stability of water supply, saving electricity and water. At the same time, the water supply system after transformation is completely closed, which can also solve the pollution problem of the traditional secondary water tank water supply.
The water pressure signal detected by the pressure sensor at the outlet of the pipe network is fed back to the AI intelligent controller by the frequency conversion constant pressure water supply system. By comparing with the given value of the pressure built in the controller, the control signal is output to the external control terminal of the frequency converter through the PID operation, and then the speed of the pump motor is controlled by the frequency converter to ensure the water supply demand. Therefore, by controlling the speed of the pump motor, the outlet pressure of the pipeline can be adjusted to meet the user’s water demand and achieve constant pressure control. Through the pipeline pressure sensor installed at the outlet of the pipeline network, the pressure signal is converted into standard electrical signal of 4-20mA, which is fed back to the AI intelligent controller and compared with the built-in given value for PID operation.
The standard electrical signal is output from 4-20mA and converted to 1-5V voltage signal by the converter. The voltage signal output by the controller is divided into two sections according to 0-50% and 50-100%. The main pump converter is equipped with receiving 1-3V voltage signal to output 0-50Hz to the converter, and the secondary pump converter is equipped with receiving 3-5V voltage signal to output 0-50Hz. This kind of system divides the output of a controller into several segments, and the corresponding actuator is controlled by each signal segment. In the case of relatively few users, the controller drives the main pump converter to control the main pump motor. When the user increases the full load of the main pump, the secondary pump converter starts to control the secondary pump motor, thereby increasing the outlet pressure of the pipeline network. Frequency conversion constant pressure water supply system is mainly composed of four parts: AI intelligent controller, fluid conveying equipment, water supply pipeline pressure sensor and frequency converter. The control device of this system adopts AI intelligent controller of Yudian Electric Company, model AI-818A. AI intelligent controller is an artificial intelligence controller designed by Yu Yu electric company. The instrument adopts advanced modular structure to provide various output specifications. As the instrument adopts digital input correction system, its measuring accuracy is as high as 0.
2, making it widely suitable for precise control of variables such as temperature, pressure, flow and liquid level. In terms of communication, the instrument is equipped with an optoelectronic isolation RS485 communication interface with an isolated power supply, which enables the instrument to communicate with other intelligent devices and upper computers. Because centrifugal pumps have the advantages of small volume, large flow rate, easy maintenance and high efficiency, centrifugal pumps are often selected as fluid conveying equipment in constant pressure water supply system. Centrifugal pump is mainly composed of pump body and impeller. The impeller is installed on the rotating shaft driven by the motor. The blade is rotated by the motor drive shaft, and negative pressure is formed at the inlet. The fluid is sucked in and the pump is excluded under the action of centrifugal force. The power of centrifugal pump can be selected according to the National Code for Design of Water Supply and Drainage in Buildings, which defines the pump power = flow * head * density * gravity acceleration. In addition, the working efficiency of the pump is about 70%, and the safety factor of the motor is set. The diffused silicon pressure sensor is the core of the diffused silicon pressure sensor in the constant pressure water supply system. When the pipe pressure acts on the sensor, the Whiston bridge made of diffused silicon loses its balance, resulting in an output voltage proportional to the pressure, which is converted into a standard 4-20mA DC signal through the transmitter. Frequency converter is a device that adjusts the speed of AC motor by changing the frequency of power supply. It is mainly used in three-phase asynchronous motor speed regulation. Frequency conversion speed regulation can reduce the starting current of the motor and realize the speed regulation without pole, so it has the function of frequency conversion and energy saving, and is widely used in the speed regulation system of the fan and pump. According to the technical requirements of water supply and the structure block diagram of frequency conversion constant pressure water supply system, the laying of water supply network and the installation of electrical control equipment are completed, and then the parameters of AI intelligent controller and frequency converter are reasonably set up, including the water supply flow rate, floor height, pump power and pressure transmitter measurement range in dormitory area.
The system adopts the split-range control scheme. The main and secondary converters as the executive part receive the segment control signals from AI intelligent controller respectively, and change the output frequency according to the signal size. The PID parameters of AI intelligent controller are determined by engineering tuning method. Among them, P is the ratio coefficient of speed parameter similar to PID regulator. The larger the value, the stronger the proportional and differential action is, and vice versa; M5 is to keep the integral time of parameter and parameter PID regulation the same; T is the lag time, and the differential time action is the same in PID regulation. The constant pressure water supply system needs no static error control, so PI control is chosen as the control law, P 30-70% and M5 24-180 s.
Frequency conversion constant pressure water supply system based on AI intelligent controller can effectively improve the secondary pollution and fluctuation of water supply pressure existing in traditional secondary water tank water supply. Because the pump motor is controlled by frequency converter, stepless speed regulation is realized, starting current is reduced, water supply stability is greatly improved, power and water saving are saved.