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Norman
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PID Tune: Plant cannot be linearized. Why?

Asked by Norman
on 18 Jun 2014
Latest activity Commented on by Norman
on 19 Jun 2014
Hello everyone,
I'm using simulink for simulating a cooling system. When I try to use the tune button on the PID it opens the tuning window and say:
Plant cannot be linearized.
Why is this happening?
The PID is doing is job. I've attached files.
Thank you very much for the help,
Norman

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2 Answers

Answer by Arkadiy Turevskiy on 18 Jun 2014
 Accepted Answer

The plant is linearized, but the linearization at t=0 is a gain of zero. Most likely this happens due to initial conditions in the model. You can ask the PID Tuner to linearize the model at a simulation snapshot of say t/2, when everything comes to steady state.
When you do that, the PID Tuner successfully linearizes the model and designs a PID controller.
Here are the snapshots of the steps using R2014a.

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Answer by Norman
on 19 Jun 2014

Thank you very much for your answer, I've got what I have to do, but of I push the Re-linearize Closed Loop command, nothing happens.
I'm also working with the R2014a. Thank you for the support,
Norman

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Try setting simulation time to 3600 instead of t, as you have now. When I tried your model yesterday, somehow using t instead of a number for specifying simulation time was causing PID Tuner some trouble. This is a bug that will be fixed. Meanwhile, just type in 3600 and everything should work.
Now it works fine! Thank you very much!
Norman

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