1.Overview
The PID regulator in the frequency inverter is used to calculate and adjust its output frequency, so as to achieve the purpose of constant pressure water supply to the pipe network. The frequency of the inverter output exceeds the limit (usually can be regarded as the limit voltage of the entire pipe network), which can make the PLC get timely prompt when the variable frequency pump is logically switched. In order to avoid the phenomenon of water hammer, the start and stop of the pump should be connected to its exhaust valve.
2. Implementation plans
Under normal circumstances, in the same road water supply system, there are a number of commonly used pumps, in the case of large water supply, multiple pumps are opened at the same time, and only one to two pumps are supplied. In the variable frequency speed regulation of constant pressure water supply device, two ways are adopted: one frequency inverter for all pumps and one frequency inverter for each pump. On this basis, PID operation is used to automatically adjust the output frequency of the inverter and change the speed of the motor, so as to realize the function of constant pressure of the pipe network. This is a closed loop, relatively simple, but expensive.
According to the feedback principle, in order to keep a physical quantity constant or basically constant, it is necessary to compare this physical quantity with a fixed value, thus forming a closed loop. If the water pressure is to remain constant, the water pressure feedback value compared to the given value must be introduced, thus forming a closed-loop system.
However, the control system is a large inertia, nonlinear system. The current combination of control and PID uses fuzzy control to speed up response and PID to maintain static accuracy.
This method can be realized by PLC and intelligent instrument, and can also be programmed by PLC to realize the switch between power frequency and frequency conversion. Practical application shows that the method is feasible and the cost is low.
Frequency and voltage water supply device in the water supply network to maintain the pressure, according to the feedback principle, the pressure transmitter used as a feedback element, because the length of the water supply system, pipe diameter, pipe network pressure are relatively slow, therefore, this system is a system with a large lag, can not simply use PID regulator for control, but use PLC to adjust.