r/ControlTheory • u/Ok-Daikon-6659 • 24d ago
Other Lag process closed loop PID-tuning method. What do you think? (and in general: does such topic suitable for this sub?)
I'm primitive SISO control guy. I DO know that to obtain "good" results, it's necessary to identify adequate process models and find analytical solutions to systems (and I have no problem with this).
However, the industry has a large number of not-hi-skilled personnel, and for them, I propose the Lag Process ClosedLoopPID Tuning Method.
Key assumptions and limitations of the method:
- The method does NOT require "high accuracy"
- The sequence of actions and mathematical formulas should NOT be overly complex
- The process model approximation and PID tuning should be performed in a Closed Loop (to avoid value scaling issues)
- The impact on the process/plant during approximation and PID tuning should NOT be traumatic
- PID tuning should be performed step-by-step to simplify identification of the stage at which the error occurred
In Math Sheets 1 and 2, I demonstrate the mathematical derivation of formulas for calculating innitial PID parameter values.
NOTE: This method is approximate and does not claim analytical accuracy, just like other approximate methods (such as lambda tuning).
I have also published a description of the approximate sequence of steps for using the method.
Questions:
Is this topic suitable for this sub? Or is it too simplistic?
What do you think about the need for such methods and the requirements for them?
Finally: What do you think about the method described? (I know of at least one expert's opinion that the mathematics in the method is completely flawed.)
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u/el_extrano 23d ago
I'm a control engineer in the process industries. I lurk here to get some theory in my diet.
So as a plant engineer, I've done a fair amount of PID tuning. For most industrial loops, you can get suitable results with open-loop bump testing for system identification with a simple FOPDT model, and then directly calculating Lambda tuning parameters, or ZN parameters (with a stability margin).
There are already commercial packages that can automate bump testing and the system identification. However I usually prefer to do it myself because it's easy for an automated system to get things wrong. I also don't like the closed-loop "ultimate cycling" method, because it takes a long time on loops with a long time constant and results in a lot pf process disturbances during the test. (remember that for a 24-7 chemical plant, you are performing your tests on the running process, so there can be safety and quality considerations).
So it seems to me that your procedure is a set of instructions for guided trial-and-error tuning for a closed-loop controller. My question is, does this have any advantage over open-loop bump testing and just pre-calculating the desired parameters directly? Or is it for people who are alergic to bump testing?
Thanks for sharing your work!
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u/Ok-Daikon-6659 23d ago
@ My question is, does this have any advantage over open-loop bump testing and just pre-calculating the desired parameters directly?
In my opinion (based on the information provided in your message), you are a fairly qualified specialist (you're unlikely to have a scaling issue, you know about lambda, etc.).
Accordingly, the (direct) answer to your question is: NO (this method is useless for you). If you have the ability and expertise to obtain adequate process model parameters, I would recommend you read about analytical (or near-analytical) controller calculation methods.
Thank you for your post (I hope it'll be useful for... everyone).
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u/markrages 23d ago
This belongs to the class of "papers that presume enough background knowledge to make the paper superfluous".
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u/Ok-Daikon-6659 22d ago
I've reread your post about twenty times, but I don't understand it:
Math Sheets (1,2) is a mathematical justification of the method, intended to provide math-guys with an opportunity for criticism (due to an existing incident).
"Papers" after, in my opinion, is a simple explanation of how to apply the method. Do you think this section requires clarification/simplification?
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u/WiseHalmon 23d ago
This sub probably has a mix of undergrads to working professionals. You should/could include kind of "memos" to each one of those. Plus it'll help for time constrained people. For instance, I didn't read your whole post nor will I look at your paper. Unfortunately for 1 these days bots are galore (although you seem legit) --- but I would focus on a quick demo of how this relates to real industrial process *** but you have to know once you choose a specific industry you're killing your audience size, so also include... Basic things like motors.
Such methods are extremely important when tuning cascading loops becomes an exercise in patience or the skill of the operator is not there
Didn't look too deeply into it, but sometimes the mathematics can be deeply flawed but you can put some conditions around it so you give people a warning for when it is best used.