PID vs FLC - thoughts and references

David - Brubaker (brubaker@cup.portal.com)
Thu, 16 May 1996 15:47:46 +0200


On 960510, Steven Collins wrote:

> I'm looking for references on "PID vs FLC" in real industrial control
> applications (Not the inverted pendulum type stuff!)

Steven,

You may be disappointed. PID control is a specific structure that,
through selection of three gains, provides excellent control of first and
second order linear systems. A fuzzy rulebased approach ("FLC") is a
more or less general structure with many more degrees of freedom that
allows a designer to succeed wonderfully or fail horribly controlling
anything from first order linear systems to high order, deeply non-
linear systems. Therefore, any comparison between a PID and FLC is
not a comparison of the relative merit of two controller types, but the
comparison of how well a designer applies a well-documented,
straightforward "cookbook" specific technique (PID) with how well
she/he applies an as yet not well understood, very general technique
(FLC). That is, the exercise will be far less a comparison of techniques
and far more a comparison of designers.

Also, because three gains will tune a PID system, the design process
involved is easy to describe. Designing a fuzzy rulebased system
involves input selection, membership function definition, rule
definition, and (in actual designs, although these are often included in
membership function scaling) setting loop gains. It is therefore quite
difficult to generate a detailed write-up of the "how's and why's"
involved in a fuzzy rulebased controller design.

Given these caveats, try looking through any of (in no particular
order):

"Fuzzy Logic & NeuroFuzzy Applications Explained", by Constantin
von Altrock, Prentice Hall, 1995, ISBN 0-13-368465-2

"Industrial Applications of Fuzzy Logic and Intelligent Systems", edited
by John Yen, Reza Langari, and Lotfi Zadeh, IEEE Press, 1995, ISBN
0-7803-1048-9

"Fuzzy Logic and Control", edited by Mohammad Jamshidi, Nader
Vadiee, and Timothy Ross, Prentice Hall, 1993, ISBN 0-13-334251-4

"Fuzzy Control Systems", edited by Abraham Kandel and Gideon
Langholz, CRC Press, 1994, ISBN 0-8493-4496-4

"Industrial Applications of Fuzzy Control", edited by Michio Sugeno,
North-Holland, 1985, ISBN 0 444 87829 7

Good luck,

David Brubaker

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David I. Brubaker, Ph.D.
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