Why does the output of my System Identification Toolbox model IDMODEL not match the output of the IDDATA object when I transfer these models into Simulink?

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MathWorks Support Team 2011-6-20

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I am creating a IDDATA object "z" and I am estimating an IDMODEL "m" using the System Identfication Toolbox. When I use the COMPARE function as follows,

compare(z,m)

I get a good fit. However, when I export these models into Simulink and try to see the results on a Scope, I find that the output of the model does not match the output of the IDDATA object. I am not sure why Simulink is giving the wrong result.

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Answer 1

MathWorks Support Team 2011-6-20

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This change has been incorporated into the documentation in Release 2011a (R2011a). For previous releases, read below for any additional information:

When transferring the estimated model to Simulink, it is not reasonable to expect that the model output would match the experimental data output, unless the correct initial states are specified. See the attached article for a description of this requirement and how to fulfill it. Basically, an estimate of the initial states must be obtained and inserted into the model block. This estimate may be obtained by using the function PE on the simulation data object.

See the attached model and MATLAB file for an example.