Frequency Domain Identification with multiple input amplitudes for SISO system?

Hi,

I have frequency response data for a system which is sensitive to input amplitudes (so magnitude and phase for n amplitudes at k frequencies). I want to use this data to identify the model (or build an analogous model). Yet I am having trouble to make it clear to the System Identification Toolbox, that I only have 1 SISO model, and n responses at different input amplitudes.

I use this document as a reference: Frequency Domain Identification: Estimating Models Using Frequency Domain Data

In this document, the data is imported with the following command:

zfr = AMP.*exp(1i*PHA*pi/180);
Ts = 0.1;
gfr = idfrd(zfr,W,Ts);

How can I add the input amplitude information to this data?

Regards, grub

Answer 1

[Arkadiy Turevskiy]

Frequency-domain data can only be used for estimating linear time-invariant (LTI) models in System Identification Toolbox - models such as transfer functions and state-space models. For LTI models, the amplitude of the output signal is always the amplitude of the input signal times the magnitude of the LTI's model transfer function.

So if you are estimating an LTI model, the amplitude of the input signal is not important - it is the ratio of output amplitude to input amplitude that is needed (as well as the phase).

So you need to convert your data to an FRD object, where at each frequency you have amplitude and phase.

Then follow the example you link to.