Is the n4sid model an LTI model?

2012 4 12
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I have a prediction model derived by n4sid.
when I set the variables with setmpcsignals for MPC controller, it is warned "The first input argument of the "setmpcsignals" command must be a non-empty "lti" object".
Isn't an idss model LTI?

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LEI CAO
LEI CAO 2012-4-12
My model is a 5-input-3-output state-space model which can be opened in LTI viewer. And I simulated the MPC controller in MPC tool GUI.
Now I would try with an arbitary distuabance other than step, sine or gaussian specified in MPC tool. But when I use "setmpcsignals" to define the variables, it still gives the alarm...
What could be the possible reason?
LEI CAO
LEI CAO 2012-4-12
I guess the problem is in the matrix K.
The idss model is
x(t+Ts)=Ax(t)+Bu(t)+Ke(t)
y(t)=Cx(t)+Du(t)+e(t)
The matrix D=0, K is not zero.
When I set K=0, the alarm doen't occur any more. But the model is not good enough then.
Is there any mothod to overcome this issue?
Rajiv Singh
Rajiv Singh 2012-10-12
What matlab release are you using? Could you post some reproduction steps? As such, an estimated idss model should be usable in MPC and you should not have to set K to zero.

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LEI CAO
LEI CAO
2012-4-12

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