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Topics: Control pump via VFD use external PID control on AC Drives
#1
Start by
Munzir Adnan
02-17-2014 10:23 PM

Control pump via VFD use external PID control

I want to control a motor (pump) speed via vfd in such a way that when temperature of the water increases the pump speed also increased and when temperature of the water decreases the speed of the motor (pump) also decreased ..... can we used external PID control with a VFD OR use a VFD having a PID control option and then tune up that PID control ?

It has to implement to maintain the temperature of water to a certain range

To control the cooling system as i stated above , what things / parameter should i calculate and measure first ?

i have ABB ACS 550 VFD which has a in built PID function , so how to tune up its PID ?
Do i need of a sensor i.e Pt 100 and a current signal converter for this setup ?
02-18-2014 12:36 AM
Top #2
sumesh p k
02-18-2014 12:36 AM
Hai munzir,
Most of the vfds are comes with built in PID settings, Use a temperature sensor as the analog input, Which we want to connect in For control the speed of motor, . Parameters are motor name plate specifications and P,I And D values for the PID.
If you have any more doubts just replay to me.........
02-18-2014 03:31 AM
Top #3
Muralidhar Ekambaram
02-18-2014 03:31 AM
How ever with PT100 I do agree you do require signal conditioner unless and until the VFD you are employing does have a inbuilt signal conditioner. Please check thru the capabilities of the drive expected to be employed.
02-18-2014 05:46 AM
Top #4
sumesh p k
02-18-2014 05:46 AM
Yes Muralidhar sir, i mean analog signal need to connect for vary the speed, like 4 -20 ma corresponding to temperature.
02-18-2014 08:09 AM
Top #5
Abhinav Sharma
02-18-2014 08:09 AM
First measure the temperature using RTD or thermocouple. Use a transmitter to convert the signal into a standard 4-20 mA signal. Use this 4-20 mA signal as an input to the PID of your VVF. The output of the PID should be the speed command for the VVF. Now you have to tune the PID slightly so that you can get the desired change in speed for the desired change in temperature
02-18-2014 10:24 AM
Top #6
Richard (Dick) Caro
02-18-2014 10:24 AM
As Sharma suggests, bring the temperature measurement to the drive using its 4-20mA input port. You will need some ABB software called DriveWindow Light 2 that connects to the drive via its EIA 232 serial port. You may need a USB to serial port converter to do this if your PC does not have a serial port. I have not used this software before, but it should allow you to set up the built-in PID function block as a temperature controller and to scale the 4-20mA input over the temperature range you need.
02-18-2014 01:15 PM
Top #7
Munzir Adnan
02-18-2014 01:15 PM
Sumesh p K :

What would be the P , I & D values for this process ?

thanks
02-18-2014 03:32 PM
Top #8
Munzir Adnan
02-18-2014 03:32 PM
Abhinav Sharma :

To tune the PID slightly so that i could get the desired change in speed for the desired change in temperature , what parameters should i change slightly ?

And also clarify me is it trial and error base procedure ?

Thanks awfully
02-18-2014 06:16 PM
Top #9
Nitin Kakkar
02-18-2014 06:16 PM
There're software tools available for PID tuning but I dare say it's a trial error to some extent. You need to tune following parameters: Kp(propotional gain) and Ti(Integral time). As a guideline you may follow the procedure below:
1. Give a step change of eg 5% to the setpoint and observe the actual value if it reacts too slow then increase Kp or vice-versa.
2. With Kp alone error between setpoint and actual will never be zero, if it's too slow to remove the offset, then decrease Ti or other way round.

Make few step response to make sure tuning is good. While making tuning keep the process as much stable as possible.

Please note PID tuning is pretty subjective thing, if you will google you can find handful of articles explaining it.

Hope this helps.
02-18-2014 08:25 PM
Top #10
Munzir Adnan
02-18-2014 08:25 PM
Nitin Kakkar :

Would you mention those handy articles here ?

thanks indeed
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