OP Oscillating?

[ayub.i....@gmail.com]

Hi, 

Hopefully this is the right place to ask this question. 

I was wondering if it is usually normal for the OP to oscillate? Please see the figure below. This is through a simulation, and I been following the PI Controller information on apmonitor.com. Any advice that would help me decrease the oscillation would be much appreciated.

Thanks,

[John Hedengren]

Great question Ayub. There is a tradeoff between performance and controller aggressiveness. That response wouldn't be good if the actuator could wear out from overuse such as a valve. Here is an example of improving PID performance with modeling and optimization: https://youtu.be/0LiNb_MEXmQ

Moura Oliveira, P.B., Hedengren, J.D., Pires, E.J.S., Swarm-Based design of Proportional Integral and Derivative Controllers using a Compromise Cost Function: An Arduino Temperature Laboratory Case Study, Special Issue: Algorithms for PID Controller, Algorithms, 13(12), 315, DOI: 10.3390/a13120315, 2020. Article

Taysom, S., Hedengren, J.D., Sorensen, C., A Comparison of Model Predictive Control and PID Temperature Control in Friction Stir Welding, Journal of Manufacturing Processes, 29, pp. 232-241, 2017, doi: 10.1016/j.jmapro.2017.07.015. Article

Park, J., Patterson, C., Kelly, J., Hedengren, J.D., Closed-Loop PID Re-Tuning in a Digital Twin By Re-Playing Past Setpoint and Load Disturbance Data, AIChE Spring Meeting, New Orleans, LA, April 2019. Abstract

Many other researchers and practitioners have come up with suggestions for tuning PID controllers. There are ITAE and IMC approaches in the control course: https://apmonitor.com/pdc

John Hedengren

Associate Professor

Department of Chemical Engineering

Brigham Young University

BYU PRISM https://apm.byu.edu

Gekko: https://machinelearning.byu.edu

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Subject: [APM] OP Oscillating?

 

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[Ayub Lakhani]

Hi Dr. Hedengren,

Thanks for the resources, but I am still a little confused. I am simulating one heater as mentioned here, where I used the simplified IMC tuning method (deadtime = 0) as mentioned here. I figured using the moderate tuning method would minimize the oscillation, unless it is okay that the actuator (the heater) oscillates? Maybe I can try a more conservative tuning or try ITAE tuning to see if that is a better option than the moderate IMC tuning?

Ayub Lakhani

To view this discussion on the web visit https://groups.google.com/d/msgid/apmonitor/BYAPR08MB4600FFA32F9FBB46E66F6C0CEE309%40BYAPR08MB4600.namprd08.prod.outlook.com.

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Very Respectfully,

SPC Lakhani, Ayub

Phone: 7148755098

Email: ayub.i....@gmail.com

[John Hedengren]

Ayub,

Try using a derivative filter or else no derivative term (D=0) as with a PI controller: https://apmonitor.com/pdc/index.php/Main/ProportionalIntegralControl The derivative term can amplify measurement noise and it can create a chattering OP.

-John Hedengren

To view this discussion on the web visit https://groups.google.com/d/msgid/apmonitor/CAG%2B7%2BxZETSe6GNaz_k2OWKR0fnd6GkqgOSFBj6LvRp-TA%3DNs6g%40mail.gmail.com.

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Best regards,

John Hedengren

GEKKO Optimization Suite

https://machinelearning.byu.edu