Analysis of variable frequency speed regulation co

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Analysis of variable frequency speed regulation constant pressure water supply system based on PLC

with the increasing automation of aluminum processing industry, the control requirements of aluminum processing production process on water supply system are becoming higher and higher. For example, in the process of air cushion continuous stranding heat treatment, if the pressure of production water is unstable, resulting in the fluctuation of water flow, it will affect the quality of aluminum strip quenching products. If the flow fluctuation is too large, the quenching products will be scrapped. When the water supply pressure is insufficient, the cooling effect of the cooler and plate heat exchanger of the equipment will be affected, which does not meet the requirements of the production process. In serious cases, it may cause the heat dissipation capacity of the equipment and damage the equipment

therefore, the constant pressure water supply with variable frequency speed regulation controlled by programmable controller is adopted in the aluminum processing and production equipment, which lays a foundation for the process control of the production of high-end aerospace aluminum strip products. The programmable controller is used as the core control component, the VVVF frequency converter is used to control the speed of the water pump, and the pressure fluctuation of the water supply is quickly adjusted according to the water consumption of the equipment process, so as to achieve the h of constant pressure water supply, and improve the working stability of the production process

1 the hardware of the system is set up in terms of automobile board.

the hardware of the variable frequency speed regulation constant pressure water supply system is shown in Figure 1, which is mainly composed of Ximen S7-200, abb ACS400 frequency converter, contactor, pressure sensor, water pump and other parts. The control core unit is Ximen S7-200, which is internally equipped with PID control algorithm. According to the set water supply pressure signal and the feedback signal of the pressure sensor installed on the pipeline, it is analyzed, calculated and compared to obtain the pipeline pressure deviation and the change rate of the deviation. After the PID calculation inside the PLC, the PLC outputs the signal controlling the motor speed to the VVVF frequency converter through PROFIBUS communication for adjustment. L the running speed of the water pump motor and the running quantity of the water pump are analyzed. According to the pressure and flow, the number of water pumps put into operation is controlled, and the starting and stopping of the motor and the switching control of frequency conversion and power frequency are completed. Make the working pressure of water for production equipment stable

three 132 kW water pumps are used in the circulating water pump station for parallel operation, and each - 'pump in Guangzhou] factory] is equipped with a stop question, which is convenient for maintenance and use. The pressure sensor installed on the outlet pipe detects the pressure of the factory cooling water, converts the pressure signal into an electrical signal of 4 ~ 20 mA through the pressure transmitter, and inputs it to the analog input module of S7-200PLC. The controller performs proportional integral derivative (PID) calculation according to the required pressure setting value and the actual detected pressure value, and sends the control signal to the frequency converter through the Profibus network to adjust the speed of the pump motor. At the beginning of startup, a water pump accelerates stably under the control of the frequency converter. When the output frequency of the frequency converter reaches 50 Hz and the motor speed reaches the maximum, and the pressure of the outlet pipe still does not reach the set pressure, the programmable controller sends a control signal to automatically switch the first water pump to power frequency operation, and the frequency converter starts the second water pump. If the pressure still does not reach, the following winch is put into the third water pump. When the water consumption of external production equipment decreases, the water pressure in the circulating pipeline will increase, and the pressure sensor will detect and send it to PLC to automatically reduce the output frequency of the frequency converter or reduce the running number of water pumps through calculation

according to the head and flow characteristics of the pump, water refers to the rotation speed and head of the pump of furniture materials in different environments. Moreover, Asahi Huacheng plastics (Changshu) Co., Ltd., which settled in Changshu new materials industrial park this time, when the operating speed of the pump is lower than the fixed value, the output head (pressure) of the pump will become very small. Therefore, it is necessary to set the minimum operating frequency of the frequency converter so that the water pump can output sufficient pressure and protect the motor. Generally, the minimum output frequency of the frequency converter is set to L5 Hz. 2 system program design

PLC system program, mainly including the pressure control program of water pressure and the motor switching program in turn, including the necessary programs such as water pipe leakage, blockage, motor overcurrent protection, etc

the pressure control program of water pressure is mainly to control the water pressure in the circulating water supply pipeline to ensure that the pipeline pressure is consistent with the process set pressure. By installing the pressure sensor at the end of the circulating cooling water pipe for detection and measurement, the pressure signal is transformed into an instrument signal of 4 ~ 20 mA through the pressure transmitter, which is sent to the S7-200 analog quantity module of Ximen for analog-to-digital conversion, and the digital quantity signal of pipeline pressure is obtained, Compared with the pressure setting value input through the upper computer, the CPU performs proportional integral differential PID operation, obtains the control value and sends it to the frequency converter through PROFIBUS communication. The frequency converter controls the speed of the water pump motor, adjusts the output pressure of the water pump, and ensures the stability of the pressure of the circulating cooling water pipe; When the water flow of the production equipment increases and exceeds the water supply of a single pump, the input of the water pump is controlled by PLC. According to the flow and pressure, PLC controls the input and removal of the working water pump and the rated frequency control of the frequency converter on the water pump motor to ensure the stability of the pipeline pressure. When the production water load changes, the output of the frequency converter also changes, and then automatically adjust the speed of the pump motor, forming a closed-loop control system based on the constant set pressure

the switching procedure of water pump motor is mainly to control the operation mode of each water pump motor in the pump station, change the circulating operation of the water pump according to the "fixed" law, and convert the working pump and the variable-frequency pump to avoid the long-term operation of the same water pump and the long-term idleness of the other water pump, so as to ensure that each water pump in the circulating water pump station has the same operation time, and avoid the corrosion and non operation of the standby pump due to long-term idleness. In addition, in the upper computer, through the programming of Win CC, the running time of each water pump is automatically counted, which is convenient for the maintenance of the equipment

3 key points of frequency converter parameter setting

(1) set the start and stop of the frequency converter to use the external signal

(2) set the setting of frequency converter as analog input

(3) set 4 ~ 20 mA to 0 ~ 50 Hz of inverter

Jinan new era Gold Testing Instrument Co., Ltd. specializes in the production of hydraulic universal testing machine, electronic universal testing machine, impact testing machine and other experimental equipment (4) define the relay output of the frequency converter, that is, when the output frequency of the frequency converter reaches 50Hz, or when the frequency drops to l0hz, send a signal to the PLC

(5) set the acceleration and deceleration time of the frequency converter

4 Conclusion

in the circulating water pump station of Guangxi Nannan aluminum processing Co., Ltd., the frequency conversion speed regulation and constant pressure control mode based on programmable control is adopted, which provides a strong guarantee for the stability and accuracy of the aluminum processing and production process. The actual operation shows that after the system is put into operation, the operating pressure of the production water system is stable, the adjustment speed is fast, and the control accuracy is high, creating good benefits for the enterprise production

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