PID Tune: Plant cannot be linearized. Why?

Asked by Norman on 18 Jun 2014

Latest activity Commented on by Norman on 19 Jun 2014

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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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Answer by Arkadiy Turevskiy on 18 Jun 2014

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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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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 on 19 Jun 2014

Now it works fine! Thank you very much!

Norman

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