contious time model - linear analysis toolbox

I've been using the linear analysis toolbox quite a bit lately for generating linear models within simulink. >> Tools / control design / linear analysis..

For some reason the models generated are generally discrete. I appreciate that their are a few functions for shifting between discrete and continuous time however is their a way of defining the output when generating the linear model? There doesn't appear to be any obvious options within the GUI. Generally I get a discrete model but now and again the toolbox spits out the desired continuous time model..

Cheers,

Jamie

Answer 1

[Arkadiy Turevskiy]

Linear Analysis Tool is part of Simulink Control Design.

Here is an excerpt from the doc:

By default, the software chooses the slowest sample time of the multirate model. If the default sampling time is not appropriate, specify a different linearization sample time and repeat.

So the sampling time of the resulting linear model depends on the model you are linearizing. If that model has discrete-time components, than the tool (with default options) will return a discrete-time model.

If you want a continuous-time model, specify "Sample Time" value in "Options" to be 0, as described in the section of the doc linked to above.

Regarding your comment that generated code does not tend to run: could you provide an example of that?

Thanks.

Arkadiy

[Jamie]

Thanks for your response.

I had quite a large model and unbeknownst to me I had been cropping and introducing a discrete time block while giving it a 'tweaking'. Took me a few weeks to spot it - by chance as it happens..

With regards the generated code - When using the snapshot tool (Tools / control design / Operating point snapshots.. ) the program terminates on the following error;

'undefined function 'plus' for input arguments of type 'opcond.OperatingPoint'.

The error appears to relate to a call to findop, the source of which I have been unable to determine.

Best,

Jamie

[Arkadiy Turevskiy]

Hi Jamie,

Is there any way you could provide your model and the code that creates an error. The best way would be to submit a help request:

http://www.mathworks.com/support/service_requests/contact_support.do

or you can send them to me directly.

Thanks.

Arkadiy