Research On Variable Frequency Constant Pressure Water Supply System Based On PLC Control

Along with the development of economy and society,water supply system has become an indispensable part in people's daily production and living. In the circumstance of the relative energy shortage and the background of the national advocacy of energy conservation,the high energy efficiency and high reliability has become an inevitable trend, so the water supply system in the constant pressure frequency conversion has become the one of the most valuable and meaningful research topic.This topic,which is based on full understanding of the water supply system works and the water demand in some area, is designed by a constant pressure water supply and remote monitoring system which is constituted by Siemens SIMATIC S7-300PLC,MM430inverter, pressure sensors, pumping unit, the host computer and other major equipment.The system uses advanced PID closed-loop control algorithm, compares the acquisition of water supply pipe network water pressure and the actual pressure settings, the inverter comes with PID regulator can adjust the amount which is given based on the deviation between the two amounts, in order to regulate the inverter's frequency, so it can adjust the motor speed to ensure a constant water pressure.The system has functions like remote manual control system, on-site manual control, automatic variable frequency and automatic power frequency,etc.It also has remote monitoring systems for the real-time display of the water supply status and alarm information.This paper expounds the basic characteristics and operating point of the water supply system, indicates the energy efficiency of variable frequency control water supply;it analyzes the water status and conversion in the way of multiple pumps water supply to explain the rationality of the use of multiple pumps in parallel water supply program; it gives PID control parameter and adjustment process to explain the convenience of using the inverters own PID function to achieve the closed-loop control; it analyses the process in the pump motor variable frequency and power frequency operation mode switch and make a change of control of the electrical design and the design control procedures of PLC; it analyses the communication protocol between the host machine, HMI and PLC to complete the communication settings between them;At last it configurates the monitor screen of the host computer and the PLC,simulates fault alarm by WinCC remote monitoring of the water supply system. In this way it achieve the effect to further improve and modify the control parameters of the system by configurating simulation screen. The final results show that the system is constant pressure water supply system with high reliability and energy efficiency.