Re: Problem in OCST

[A S Hodel]

There weere some cell array/list structure problems in the OCST for which I recently 
submitted fixes; they should be in the CVS sources shortly if not already.

However, your real problem below is in the command
tf2sys([1,0,1],[1 0])
Octave will only accept transfer functions that have a realizable state-space
implementation.  The above system has one more zero than pole, and so
cannot be converted to state space form.

I understand that MATLAB will permit non-proper transfer functions, since
many systems (e.g., the op-amp differentiation circuit) can be approximated
at low frequencies as differentiators.  However, the omitted poles for such
an approximation will have an impact on the root-locus of a system, so the
results need to be handled carefully.

For the time being, you'll need to put in an approximation to a derivative,

s "=" s/(tau*s + 1)  where tau is very small.

On Feb 16, 2004, at 1:48 AM, ผศ.ดร.ศุภชัย วรพจน์พิศุทธิ์ wrote:

> Hello,
>
> I plan to use Octave in my control theory classroom. However, I found some
> strange problems while trying to simulate DC motor with PI controller.
> Function bode() does not work even it should be. Now, I am using Octave
> 2.1.50a on Win2k downloaded from octave.sf.net. May someone please explain
> how to solve this problem?
>
> Thank you in advance
> Supachai
>
> > > motor = tf2sys([4500],[1 361.2 0]);
> > > PI = tf2sys([1 0.1],[1 0]);
> > > G = sysmult(motor,PI);
> warning: in
> /opt/octave/share/octave/2.1.50/m/control/system/__sysgroupn__.m near line
> 44, column 9:
>
> > > > warning ("sysgroup: %s name(%d) = %s name(%d) = %s", kind, ii, kind,
> jj, st1);
>
>
> warning: sysgroup: state name(1) = state name(3) = x_1
> warning: sysgroup:     changed state name 3 to x_1_3
> > > bode(G)
> error: number of columns must match (2 != 1)
> error: evaluating assignment expression near line 97, column 7
> error: evaluating if command near line 71, column 3
> error: called from `sysgroup' in file
> `/opt/octave/share/octave/2.1.50/m/control/system/sysgroup.m'
> error: evaluating assignment expression near line 96, column 9
> error: evaluating if command near line 65, column 3
> error: called from `sysmult' in file
> `/opt/octave/share/octave/2.1.50/m/control/system/sysmult.m'
> error: evaluating assignment expression near line 146, column 11
> error: evaluating while command near line 95, column 3
> error: called from `zp2ss' in file
> `/opt/octave/share/octave/2.1.50/m/control/system/zp2ss.m'
> error: evaluating if command near line 109, column 5
> error: evaluating if command near line 107, column 3
> error: called from `sysupdate' in file
> `/opt/octave/share/octave/2.1.50/m/control/system/sysupdate.m'
> error: evaluating assignment expression near line 153, column 9
> error: evaluating if command near line 152, column 3
> error: called from `sysgetsignals' in file
> `/opt/octave/share/octave/2.1.50/m/control/system/sysgetsignals.m'
> error: called from `bode' in file
> `/opt/octave/share/octave/2.1.50/m/control/base/bode.m'
> > >
>
>
>
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A. S. Hodel, Associate Professor, Dept. ECE, 200 Broun Hall, Auburn University, AL, 36849-5201
334 844 1854 http://www.eng.auburn.edu/users/hodelas address@hidden