1.Overview

The control system of the frequency conversion pressure stabilized water supply equipment adjusts the output frequency after calculating by the built-in PID regulator of the frequency converter to realize the constant pressure water supply of the pipe network. The frequency over-limit signal of the frequency inverter (generally can be used as the pipe network pressure limit signal) can be timely notified to the PLC for the frequency conversion pump logic switch. To prevent the phenomenon of water hammer, the start and stop of the pump will be linked to its outlet valve.

2.Implementation plans

Usually in the same road water supply system, set up many common pumps, when the water supply is large, many pumps are fully open, the water supply hours open one or two. In the frequency conversion for constant pressure water supply equipment, two ways are used: one frequency inverter for all the pumps and each pump with one frequency inverter. According to the pressure feedback signal, the output frequency of the frequency inverter is automatically adjusted through PID operation to change the motor speed, and finally achieve the purpose of constant pressure of the pipe network. It is a closed loop, relatively simple but high cost.

According to the feedback principle: in order to maintain a physical quantity unchanged or basically unchanged, we should compare the physical quantity with the constant value to form a closed-loop system. If we want to keep the water pressure constant, we have to introduce the water pressure feedback value compared with the given value, thus forming a closed-loop system. However, the controlled system is characterized by nonlinear and large inertial system. Now the combination of control and PID uses fuzzy control to speed up the response, and PID is used to maintain the static accuracy. This algorithm is available by PLC and intelligent instrument, and the switch between the power frequency and frequency conversion of PLC programming. Practice has proved that using this method is feasible, and the cost is not high. Frequency frequency voltage water supply equipment to maintain the pressure of the water supply network, according to the feedback theorem, the pressure transmitter installed as the feedback element, due to the water supply system length, pipe diameter, the pipe network pressure is slow, so the system is a big lag system, not easy to directly use PID regulator control, and using the PLC control to realize the regulation of the control system.