# Fractional Control Basic

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Viewing 15 posts - 16 through 30 (of 36 total)
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• #1031
Pritesh Shah
Guest

Hi,

I want to use stepinfo for fractional order system.

It is giving error.

Could you please give one example?

Thanking You,

#1033
Aleksei
Keymaster

You may use stepinfo() on an approximated system. This function is not yet available for fotf systems.

#1035
Pritesh Shah
Guest

Regarding FInding Norm 2.
———————

Dear Alekesi,

I want to find norm 2 of fractional order controller.

G2=fotf(tf([0.5 -0.1 0.01],[1 2 1 0]))
Fractional-order transfer function:
0.5s^{2}-0.1s+0.01
——————
s^{3}+2s^{2}+s
norm(G2)
Error::
Attempt to reference field of non-structure array.

Error in fotf/freqresp (line 14)
a = G.a;

Error in fotf/norm>@(x)freqresp(x,G).*freqresp(-x,G) (line 25)
f = @(x)freqresp(x, G).*freqresp(-x,G);

fx = FUN(x);

[fx,too_close] = f(x);

Error in fotf/norm (line 27)
n = quadgk(f, -dx*1i, dx*1i) / (2*pi*1i);
—————————————————–

Also, if you can help me out to explain important of norm 2, it will be useful to me.

Thanking You,

#1039
Aleksei
Keymaster

This is a bug. Consider the following patch: https://fomcon.net/forums/topic/preliminary-releases-and-patches/#post-1037
Towards your second request, see the following PDF: http://www.abo.fi/~htoivone/courses/robust/rob2.pdf

#1089
syed naeem haider
Guest

Hi,

i am trying to use fractional integrator in simulink with physical model,, but the problem i am facing is that physical ball and beam system is attached with pc and matlab version used in that system is Matlab2008a ,,,, so when i load fomcon toolbox i do not get ant fractional blocks in simulink library of fomcon… ” FOTF_gui ” is working fine ….. in matlab ,,, but i cannot use fractional blocks in simulink…..

is there any way possible to use fractional integrator in simulink model by using fractional transfer function from work space to simulink…..

or any way to make fractional transfer function in simulink without blocks …..

#1093
Aleksei
Keymaster
#1102
pritesh shah
Guest

Hi Aleksei,

Hope you are fine. Once again, thanks for nice toolbox.

I have some basic

1. If order of fractional parameters between, 1 to 2, than what is the effect on stability?

2. If more then 2, than what is the effect on stability?

There is some concept q*pi/2, but I am not able to understand properly.

#1107
Nitish Katal
Guest

Dear Sir,

I’ve been using the FOMCON toolbox and its working great.

I have some issue regarding the check of stability of the Fractional Order System;

Say I’ve a FO plant G and a FO PID Controller, how can I check for the stability of this system directly,

Like is the system is STABLE return 1 if NOT-STABLE return 0.

#1110
pritesh shah
Guest

Hi Alekesi,

I want to find out output of system using lsim function.

If it is same time interval (T), then we are able to get correct results.

But, in one of the problem, time interval is not the same. I am getting different answer.

Say example,

G=fotf(‘1′,’s^0.5+1’);
u=ones(1, 1001);
t=0:0.01:10;
y=lsim(G,u,t);
% I will get correct result as time vector has same interval.

% if t has variable time values, I am not getting correct answer.
% U have checked code of lsim, h=t(2)-t(1)

#1112
Aleksei
Keymaster

Dear Nitish,
The function you are looking for is called isstable(). Therefore, just do isstable(feedback(G_PLANT*G_FOPID,1)).

• This reply was modified 8 years, 11 months ago by Aleksei.
#1113
Aleksei
Keymaster

Dear pritesh,
This is a known problem with fixed-step solvers. The suggested method is to decrease step size until the results are the same.

#1114
pritesh shah
Guest

Hi Nitish,

I think, You can make system closed loop transfer function using feedback function.

Check for stability of closed loop system.
Say Example,
G is fO plant, C is FPID.

G=fotf(‘1′,’s^0.5+1’);
C=fracpid(1,1,0.5,1,0.5)
G_C=feedback(G*C,1);
isstable(G_C)

#1191
pritesh
Participant

Dear Alekesi,

I want to define fractional transfer function k/(s+a)^alpha.
where, alpha is fractional order between 0 to 1.

#1196
pritesh
Participant

Dear Alekesi,

Any idea about inverse Laplace of fractional order system?

Y(s)= (k1*s^(lam+mu)+k2*s^lam+k3)/(k1*s^(lam+mu+1)+(1+k2)*s^(lam+1)+T*s^(lam+2)+k3*s);

I want to find out inverse Laplace of Y(s)?

#1197
Aleksei
Keymaster

You may want to check this out: http://www.tuke.sk/petras/foc_laplace.pdf

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