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Re: sys variables for control theory


From: A S Hodel
Subject: Re: sys variables for control theory
Date: Thu, 6 Nov 2003 10:05:15 -0600

The reason behind octave's restriction is to ensure the ability to convert between rational polynomial representations (tf, zp) and state-space representations. That is, a PID in the form described is not physically realizable, that is, the transfer function
is not proper.   A hardware (or software)
implementation requires an extra pole with very fast settling time (relative to open loop
poles and closed loop design poles).

Before investing effort to allow the non-proper transfer functions in octave's toolbox, it would be worthwhile for you to consider and correspond with the list on what capabilities this would provide and how it should interact with the rest of the toolbox. This is not merely a change to an interface routine, but it's a package design approach that's being changed. I think it would involve a lot more than just changing tf2sys.

On Wednesday, November 5, 2003, at 10:56 PM, Doug Stewart wrote:

These thoughts are for those that use octive for control theory and design. I was trying to model a PID controller and use it in a closed loop negative feed back loop. The PID numerator is a quadratic equation and the denominator is first order. Thus the numerator is of higher order than the denominator. Octave's tf2sys.m does not like this but > Matlab's tf.m thinks it is OK. I understand that you can't do a step or bode etc.
on this PID, but I should be able to use it in sysmult.m to form up Gs.
Then use this with feedback to get the closed loop system, and then use step etc.

I think we should take the checking out of tf2sys and let it make any shape of transfer function.

Any comments?????

I will do the work if there is no real objections.

Doug Stewart



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A. S. Hodel, Assoc. Prof, Dept. Elect & Comp Eng, Auburn University, AL 36849-5201
(334) 844-1854 200 Broun Hall address@hidden
Auburn web page: http://www.eng.auburn.edu/~scotte
Personal web page: http://homepage.mac.com/hodelas



-------------------------------------------------------------
Octave is freely available under the terms of the GNU GPL.

Octave's home on the web:  http://www.octave.org
How to fund new projects:  http://www.octave.org/funding.html
Subscription information:  http://www.octave.org/archive.html
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