Toolbox features

[Aleksei]

This is the topic to turn to if you seek to use a particular feature of the toolbox and run into problems.

[Marco]

Hi,

if I want run a time-domain identification of a fractional order system, can I use a parametric form of the FOTF object (1° parameter of the function FID) ? If it is possible I don’t understand how I can do it.

I try to explain better my request: I have input, output, time vectors for my system in the structure FIDATA. Now I would obtain the identification of system’s parameters that are unknown. The only information that I have is the structure of the transfer function of my system (in particular is in the form K*(s^alfa)/(s^alfa+p) where K(static gain), alfa(order of system) and p(pole) are the system’s parameters). How can I solve this problem?

Thank you

Marco

[Aleksei]

Hello,

Thank you for contacting the FOMCON support forum! You may supply the FOTF object as
fotf('s^alpha','s^alpha+p')
However, both parameters alpha and p must have particular numerical values. The general structure of the model will be retained.

[Marco]

Thank you for the quick response!

A clarification: how I can introduce the static gain K inside the model? in  your answer there is no trace of it and also in the examples the static gain doesn’t appear never.

Thank you.

Marco

[Aleksei]

At this point, the static gain cannot be explicitly set in the model structure.

[Marco]

Hi,

I have a question about the toolbox.

If I have input and output vectors in time domain of a unknown fractional system, is there a function that plot the bode diagrams of this experimental data? And a function to estimate the transfer function?

Thank you

Marco

[Aleksei]

You may estimate the fractional-order transfer function by first creating a fidata() data structure from your y, u, and t vectors, containing output, input, and time instance values, respectively. Next, you could use either the graphical interface fotfid (more convenient) or the fid() function.

It should also be possible, depending on the input/output time series data, to arrive at the frequency-domain representation of the system characteristics, but at the moment there are no tools in FOMCON that would do the conversion for you.

[muralidhar]

Dear alekesi
Im muralidhar,im trying to write a code for the Gui models based function.it still getting errors.if you dont mind please send one example coding regarding fpid_optim function,that related to fpid_optim.fig. thank you

[Aleksei]

You may use the guide tool, integrated into MATLAB, to make modifications to the GUI’s. Since FOMCON code is freely accessible, you can study the existing code.

[Pritesh]

Hi,
I have taken undamped system given below.
ss=tf(1,[1 0 16])
fss=fotf(ss)

Now, when I am plotting step of step(ss) and step(fss).

I am getting different very different plots.

Any reason for the same?

Code:
ss=tf(1,[1 0 16])
fss=fotf(ss)
step(ss)
step(fss)

Thanks in Advance for Nice Toolbox…

[Aleksei]

Hi.

This is indeed a valid concern. Roughly speaking, the difference is due to some constraints of the current implementation of the Grünwald-Letnikov algorithm, which is a fixed-step method. For instance, try lowering simulation step size choosing a time range of about 10-20 seconds—you can easily do this in fotf_gui, i.e. compare results with t=[0:0.01:10] and t=[0:0.001:10]. You will see that the damping ratio of the fractional-order system obtained from the undamped integer-order one will decrease with computation step size.

I will look into this problem soon.

[lili]

pleas can help me

[Aleksei]

Kindly elaborate.

[RAJESH]

i interested on read your thesis related to fractional order controller

[Smita]

Hi,
Could you please tell me which version of FOMCON toolbox is latest?
0.41-beta or 0.42-beta…?

Thanks
Smita

[Author]

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