[scilab-Users] System Identification with frfit()
Michael J. McCann
mjmccann at iee.org
Tue May 6 13:20:15 CEST 2008
John,
If you know something about the underlying physics of the
system, then that is, in my view (as a control and dynamic systems
person), the place to start.
I suspect that you can get the peak with a second order
under damped-pair of poles, and fake the rest of the drop off or rise
with first order (left half plane) poles and zeros. It might be
easier to build a model up from these basic components (as products
in a transfer function) rather than try to get a mechanical solution
method. However, it's possible you have a non-minimum phase system so
it will be trickier.
Mike.
==============================================
At 10:53 2008-05-06, you wrote:
>Bonjour,
>I have measured the phase and magnitude response of a system and I
>am trying to identify a model for it with frfit(). This works well
>up to about 10Hz but then can be 20dB different in gain, 150degrees
>in phase. Best fit is with order 3 or 4.
>My data is a log frequency sweep from 0.7Hz to 60Hz. It is a little
>noisy (+/- 0.5dB, +/-3deg). The response has a 'peak' in the phase
>between 7 and 20Hz and increasing gain over this region.
>I tried separating the model. First I divided the measured data by
>the modeled response (to extract just the data that does not fit the
>model) and then frfit() to the remaining data. This did not help as
>the fit to the remaining data was just as bad.
>Can anybody suggest how to analyse this system?
>Thanks for any help,
>Regards, John
Dr Michael J. McCann, Date: 2008.05.06 11:18gmt
BSc(Eng), DIC, PhD, CEng, FIEE.
McCann Science.
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