Application Of Frequency Conversion Technology In The Constant Pressure Water Supply System

In order to solve the problem that the management of water-supply operation is still backward and the phenomenon of water resources wasting is exceedingly serious, this paper introduce some advanced technologies such as computer, frequency transformer, programmable logical controller (PLC) and so on into water-supply network, the constant pressure water supply system is devised to achieve the variable-frequency speed control by making use of the electric controlling system composed of S7-200PLC, MM440 frequency transformer, miniature circuit breaker, AC contactor, thermal relay, DC power supply, miniature electro-magnetic relay, sorts of indicator lights and host command devices.By researching principle of the constant pressure water supply, the relevant equipments are selected and the composition structure of the constant pressure water supply system is designed. According to the control requirement, water pump set is composed of four water pumps, this four water pumps are successively switched operating conditions between variable frequency and power frequency, this a procedure that the water is cycled in sequence among the four pumps is accomplished to fulfill the water supply.This paper specifies the circuit of the system hardware and the programming thought, according to the relationship between the circuit of frequency transformer and the water pressure of the pipe network, main circuit and control loop are designed and the relevant flowchart and principle diagram are given.By analyzing the controlled object, the self-tuning of PID parameters and selections of sampling period and control period are achieved. By using the iterative algorithm, the inner PID instruction system of CPU module of PLC can be applied to S7-200, it meets the design requirements.The system software is designed by using the modular design method and the system software is real time monitored by using the configuration software, these can ensure safety operation for the system. In Chapter VI, the debugging process of system is described in detail, according to analyzing the picture of the real-time monitoring and the curve of operation of the constant pressure water supply system and based on results, the improvement scheme is put forward.