I only have acces to historical data recorded over the course of a few years. However the data is of a closedloop proces that has already been tuned with PID. The values of P, I and D are known.
How can I determine the openloop transferfunction usign only this data?
A Closed-loop Control System, also known as a feedback control system is a control system which uses the concept of an open loop system as its forward path but has one or more feedback loops (hence its name) or paths between its output and its input. The reference to “feedback”, simply means that some portion of the output is returned “back” to the input to form part of the systems excitation.
A Closed-loop Control System, also known as a feedback control system is a control system which uses the concept of an open loop system as its forward path but has one or more feedback loops (hence its name) or paths between its output and its input. The reference to “feedback”, simply means that some portion of the output is returned “back” to the input to form part of the systems excitation.
For more details we have:
https://www.tutorialspoint.com/control_systems/control_systems_quick_guide.htm
Best regards
Dear Gil Cf
The closed-loop transfer function is the fraction of out-put Laplace to in-put Laplace. You may assume there is one G block in feed-forward path of the open-loop system.
C/R(open-loop)=G.
For this open-loop system, the closed-loop transfer function would be:
C/R(closed-loop)=G/(1+GH).
And therefore:
[C/R(closed-loop)]^(-1)=(1+GH)/G=(1/G)+H.
G=C/R(open-loop)={[C/R(closed-loop)]^(-1)-H}^(-1).
You should know your sensor dynamics as H.
But if there is unitary feedback, then H=1, and you may get:
G=C/R(open-loop)={[C/R(closed-loop)]^(-1)-1}^(-1).
You have C/R as a data, hence you could get C/R as in Laplace domain, using Bode-plot.
Harald Kirchsteiger
Having looked into your suggested topics. I found some valuable information.
A follow up question: how can I use Matlab's system identification toolbox to help me?
I found some research of the university of Delft (CLOSID) and another research by the university of Alberta (CLsysID). They seemed to have developed an extention for matlab to aide in closed loop system identification. However, those systems aren't available to me.
thanks in advance.
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