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PID Tune: Plant cannot be linearized. Why?

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Norman
Norman on 18 Jun 2014
Commented: Adhip Shukla on 16 Nov 2019
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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Accepted Answer

Arkadiy Turevskiy
Arkadiy Turevskiy on 18 Jun 2014
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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More Answers (1)

Norman
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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Arkadiy Turevskiy
Arkadiy Turevskiy on 19 Jun 2014
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.
Norman
Norman on 19 Jun 2014
Now it works fine! Thank you very much!
Norman
Adhip Shukla
Adhip Shukla on 16 Nov 2019
Hi Arkadiy,
In my model also it is showing the same error and I tried what you have suggested above can you look into my model once and tell me how to tune my PID block.

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