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Re: Not able to add delay to transfer function
From: |
Sergei Steshenko |
Subject: |
Re: Not able to add delay to transfer function |
Date: |
Thu, 30 Jul 2020 01:14:41 +0300 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 |
On 29/07/2020 22:53, shall689 wrote:
Hello Torsten,
That seems to work.
I also tried (1+s*tau)/(1-s*tau), but the step response gave me the error:
"open_gl_renderer: data values greater than float capacity error"
(1+s*tau)/(1-s*tau) was mentioned on page 2 of this document:
http://users.ece.utexas.edu/~buckman/H3.pdf
Thanks,
Stephen
--
Sent from: https://octave.1599824.n4.nabble.com/Octave-General-f1599825.html
I do not understand why you are trying to add something to your transfer
function (delay in this case). IIRC, in the beginning you stated you had
frequency response of your system. I asked whether the response was
complex (as in complex numbers) or just magnitude - I don't remember
getting a reply; I asked the question to better understand the task at hand.
If you have complex frequency response, you probably don't even need the
corresponding transfer function. This is because having the response and
the PID parameters you can have the resulting complex frequency response
which can be converted by 'ifft' into the resulting impulse response,
which also means it can be converted into step response (probably the
step response of most interest).
Anyway, having complex frequency response you can try to obtain rational
polynomial (i.e. either B(s)/A(s) or B(z)/A(z)) using 'invfreqs' or
'invfreqz' functions respectively. I believe what I'm writing is
methodologically correct, though from practice I know that for "funky"
frequency responses obtaining the resulting rational polynomial is very
tricky, i.e. small polynomial orders are not sufficient, and high
polynomial orders give convergence problems - do not fit the input
complex frequency response well.
If you only have magnitude response, you still need to obtain complex
frequency response - otherwise you can't build the corrected systems. Is
this the case and are you trying to add delay to the magnitude response
? If that's the case, I do not think your methodology is correct. Not
that you don't need delay - quite the opposite. But for minimum phase
systems magnitude response and phase response are tightly related - see
https://en.wikipedia.org/wiki/Kramers%E2%80%93Kronig_relations#Magnitude_(gain)%E2%80%93phase_relation
,
https://en.wikipedia.org/wiki/Minimum_phase#Relationship_of_magnitude_response_to_phase_response
. So, you really need to know complete true phase response of your system.
Anyway, I'm just a curious observer ...
--Sergei.