hello.
I have a closedloop system which is composed of PI controller and
plant. I don't know the model of plant, but I can online get the
closedloop dominant poles.
I want to online tuning PI controller parameters, I don't know how to
tuning controller parameters by closedloop dominant poles.
good luck and thanks!
 hello.
 I have a closedloop system which is composed of PI controller and
 plant. I don't know the model of plant, but I can online get the
 closedloop dominant poles.

 I want to online tuning PI controller parameters, I don't know how to
 tuning controller parameters by closedloop dominant poles.

 good luck and thanks!

You have two unknowns and one known. That isn't enough. Normally one has a
plant model and a desired response and then calculates the controller gains.
BTW, what makes you so sure that the controller needs to be a PI controller
if you don't know the plant model.
Peter Nachtwey
He should have one known for each pole location, which makes one known
point for each plant state plus one for the integrator. If he knows the
PI gains he should, in theory at least, be able to derive the system
polynomial for the closedloop system and from there get to the system
polynomial for the openloop system.
It's terribly round about, though.
Yes, but you are assuming that forest knows that. I am not making
that assumption. He could have told us what the transfer function was
if he knew. How often have you see people use the wrong number of
gains? Too often. Many people people don't understand what you just
said and why it is so.
Any method that you would use to get the pole locations should be able
to give you a more direct measurement of the plant transfer function.
Either ARMA methods (say with a step disturbance input) or frequency
sweep methods (which I prefer, and have detailed both on my website and
in my book*) can give you a plant model, even when you're in
closedloop. Why, then, do you want to mess around with such indirect data?
The article is
http://www.wescottdesign.com/articles/FreqMeas/freq_meas.html .
The book is "Applied Control Theory for Embedded Systems", by me,
published by Elsevier.
http://www.powells.com/partner/30696/s?kw=Wescott+Tim will buy you a
book,
http://www.elsevier.com/wps/find/bookdescription.cws_home/707797/description#description
will get you the publisher's description.
* I would have liked to include a section on determining plant transfer
functions using ARMA methods, but I was running out of time to have the
book published this year  I hope to have an article at some point;
should the book go to a 2nd edition the article will make it's way into
the measurement chapter.
thanks for your good ideas!
I don't know plant model, so I can't design other controller.
Therefore I only use PI controller.
I know closedloop dominant poles. It is equivalent that I get the
reducedorder model of closedloop. I think it's wrong that derived
plant model from reduced closeloop model and controller, so I can't
archive plant model.
This is not a practical problem. I only do a research. So I don't
identify plant model.
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