Fuzzy Logic Tuning 3

[controlnovice]

Anyone have information on tuning fuzzy logic?

I've been to some classes that explain fuzzy logic, and I can understand that. But none of those classes talk about tuning fuzzy logic. I found a good paper on the internet from the Technical University of Denmark, but it states to insert a PID controller first.

Is there any information out there that would help me tune a fuzzy logic controller that is already installed and appears to not be functioning or would benefit with better tuning parameters?

The FLC I am looking at has tuning parameters for error, change in error and change in output. I can probably figure out the error and change in error parameters. It's the change in output that I'm having problems with.

 

[jsummerfield]

I have not used fuzzy logic for tuning but it is an available algorithm with some control systems. I think that there is a dead-band "don't care" area where no control action exists; like gap action. Control action exists above and below the dead-band area.

John

 

[sabap]

Check this article from University of Honk Kong's website. You can download it easily.

Fuzzy PID Controllers
for Industrial Applications
G. Ron Chen
Lecture for EE 6452
City University of Hong Kong

 

[controlnovice]

Sabap,

Thanks for the source, but I couldn't find anything of that title, or any articles that were of help.

Can you provide a direct link?

 

[sabap]

Check this:

http://www.iau.dtu.dk/~jj/pubs/fpid.pdf

This article is on tuning of Fuzzy PID controllers. The other one, you can get through email.

 

[frankeng9]

controlnovice,

You have stumbled into a vast area of engineering. The tuning of real-time, closed-loop controllers can be as much art as science. You are doing the right thing in asking for help before trying the “tweak-and-see” method of achieving stable, crisp control. In actuality, Fuzzy Logic controllers are a variation of PID control. To enhance your basic understanding of real-time control systems and the associated tuning of controllers, you might want to focus on PID control first. By gaining an understanding of how PID control works in the real world and how the tuning of the controller via the gain variables works, you will be in good shape to deal with the tuning aspects of Fuzzy Logic. Several organizations offer lots of material on PID control and PID/Fuzzy Logic tuning. You might want to explore the Instrument Society of America (

http://www.isa.org)

for starters.

 

[controlnovice]

Very well written frank. Thanks for the response.

I am very familiar with PID control and tuning. I understand the parameters of PID tuning and understand how each of them affect the control.

I understand the two input parameters of Fuzzy logic (FLC), although I have not had to tune a FLC yet in real-time. I have been to classes at ISA and have read numerous articles about FLC, but still do not feel comfortable with how to tune the output parameter of FLC. I don't know if its the same for all FLC, but the FLC we are using have a parameter for the output, and I just can't find information on exactly how it affects the control. I can always do the 'tweak and see' method, but I would like to know what the output parameter is doing before I 'just do it'.

 

[xnuke]

You can simulate your FLC with a software package and then adjust the parameters to see what effect they have on the mapping. I use MATLAB with the fuzzy logic toolbox for this purpose.

xnuke

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[ipupkin]

frankeng9,

Fuzzy Logic controllers are not simply a variation of PID control. A PID controller is linear, a Fuzzy controller can be "very" non-linear.

But, of course, a common method of tuning a Fuzzy controller is tuning it to obtain a response similar to PID.