Re: Not able to add delay to transfer function

[Sergei Steshenko]

On 03/08/2020 10:11, shall689 wrote:
> Hello Sergei and GoPro,
>
> I was able to compute the actual transfer function, so I won't need to
> convert the frequency response to the transfer function right now.
>
> Also, I came to the conclusion I didn't actually need a delay.  I needed a
> ZOH hold.  I was able to get it by doing the following (using info Torsten
> gave me):
> s = tf('s')
> [num,den] = padecoef(1/20000,1) % 1st order pade
> sys  = tf(num,den)
> zoh = (1-sys)/s
>
> Also, I was able to get the same thing from slide 14 of
> http://ecee.colorado.edu/~ecen5807/course_material/sampled/
>
> Stephen
>
>
>
> --
> Sent from: https://octave.1599824.n4.nabble.com/Octave-General-f1599825.html
Now that you have your transfer function, if not yet you better test its 
accuracy. By that I mean measure the transfer function magnitude and 
phase responses and compare them to the actual system measured data 
(using which you approximated the transfer function) and make sure that 
the differences are small enough - I'd say no more than 1db in magnitude 
and no more than 5 degrees in phase.

Having done that you might consider changing the tool. I suggest to 
switch to a SPICE-type simulator with convenient GUI. I myself LTSpice a 
lot under Linux under 'wine'.

LTSpice has arbitrary behavior voltage and current sources, and they can 
utilize Laplace transform - on that read in e.g. 
http://ltwiki.org/?title=B_sources_%28complete_reference%29 . So you can 
code your system transfer function and the rest should be trivial. If I 
understand correctly, PID controller in terms of electronics is Ri -> C 
-> Rd circuit with possibly an amplifier, with Ri being mostly 
responsible for integration, and Rd being mostly responsible for 
differentiation (this is a very simplified explanation).

So all in all you'll have to draw a very simple circuit in LTSpice 
circuit editor and you will be able to easily simulate it and easily 
play with PID controller parameters. LTSpice has very nice graphs/waves 
display, so you'll have easy access to all intermediate points of your 
system model.

--Sergei.