Pump load sharing, PID for pumps
In my project, 4 pumps connected with one common header. I want to maintain the required pressure in that common header. In first cycle P1 is on, Actual pressure is not matched with required pressure P2 is on, if it is not matched then P3 . I have a VFD for speed control. How can i make a load sharing between pumps? explain about this PID control
note: components are AC500 PLC+ VFD+ CP600 HMI
As Flavio recommended, the easiest way is to use Pump Control functions in VFD, they are already prepared for that kind of tasks.
In case you want to realize pump control trough PLC, that means you have to create similar logic in the PLC.
You have to send a speed setpoint from PLC to each VFD, from one PID in the PLC, with process variable = common header, and output 70-100%. You have to take in consideration MIN and MAX permissable setpoint for the pumps (usually min=70 max=100% of nominal speed of the pumps, when they produce something - check with the pump people).
Lets assume only P1 is working, output of the PID is going directly as a setpoint for P1. When the demand increases, PID will increase the setpoint to P1.
When the PID output is nearly 100%, you will need to start P2 also (by additional logic with limit value and hysterezis for example).
After P2 is started, you have to divide PID output by 2 and send it to P1 and P2.
For example P1 and P2 will receive 100-70=30/2=15+70=85% (have to check pump characteristics and ensure approx. the same flow after the transfer from P1 to P1+P2)
That is for me load sharing (otherwise you fix P1 to 100% and start P2 from 70%, but no load sharing here)
In same logic you are going up for P3..., => divide the setpoint by 3. Also down when demands decreases.
For more advanced load sharing, you have to read the current of each pump, and make a correction in speed reference for each pump, in order to equalize the pump's currents too (as you may be know, even the same pumps have a different characteristics, especially when work on the same header).
Of course, this description is like idea only.
You will need to precize it during programming and commissioning.