Actually, I have a big doubt regarding the inputs of fuzzy logic controller (FLC), since I am new in this area. Most of the example that I found used error and derivative of error as the inputs for FLC. But, it is possible if I use error and integral of error as inputs of my FLC? Actually, I have a highly non-linear process to control.
Thanks..
DEAR HANY
HERE I ATTACH SLIDES THAT WILL HELP
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The error and change in error information are used to get an idea regarding how far the actual output of plant is from its expected or desired value (error) and is it moving towards the set point or away from the set point (this information is obtained through change of error).
For example you are driving a car with target speed of 80 km/hour, you accelerate it and exceed beyond 80 km/h , then you realize that you have overshooted so you reduce the pressure on the accelerator pedal, the speed comes down to 80 km/h and then you maintains there.
In this process you come across 85 km/h point twice, once when you were moving away the set point and again when you are moving towards the set point. In both the cases error is 5 km/h but change in error is different. In this case error information alone is not sufficient to determine the control action. That's why change in error information along with error are used to obtain precise control action.
Dear Hani
You can use the output of (error and derivative of error - fuzzy PD) and integral of error as inputs of your FLC.
Best regards
Dear Hani
You can but it is not advisable as you know that the primary aim of the fuzzy controller is to minimize the error between the reference input and the actual output, so using integral as one of the input to the fuzzy will tends to add up the error. you can employed Fuzzy PD +I technique but remember the integrator does not go to fuzzy but external to fuzzy and added with help of summer before going to the plant.
Dear Hani,
I agree the answer given by Mr. Lukman. However, some fuzzy controllers use also the rate of the error rate, PDD.
Thank you very much for all the suggestions. I really appreciate it. Actually, I tried to use fuzzy logic to control my plant (non-linear), but the Integral absolute error (IAE) that I got was much higher (37) than IAE when I implemented PID (14). This really make me worry, due to my research objective is to prove the efficiency of FLC compared to PID. Maybe I should try Mr Lukman's suggestion. But, if I use Fuzzy PD+I technique, can I still refer it as FLC?
I suggest to call multi-closed-loop control, or enhanced Fuzzy PD control
Thank you very much Prof Rami. I really appreciate your advice.
Thank you..
Salam Cik Hani,
From your post on May 5th, it seemed that the Fuzzy PD+I control as suggested by Mr. Lukman, has not been implemented. Naturally, I'll assume that the higher IAE value (37) you obtained was due to improper implementation of the Fuzzy PI controller. Since the approach you used to design the Fuzzy PI controller was not mentioned, we are unable to provide appropriate comment to your design methodology.
When first designing a fuzzy PI controller, there are a few methods you can use to emulate a PI controller that inherits its linear characteristics. As stated by Mr. Lukman, the integral of error cannot be used directly as the input to the fuzzy logic system as this will cause the error to build up in a nonlinear fashion that could potentially leads to instability (when it accumulates a large amount of error too fast without saturation).
~ Design of a Fuzzy PI Controller ~
Although the integral of error cannot be used, it is still possible to develop a Fuzzy PI controller. Here are 4 general steps to designing the controller:
For more information, please refer to “Fuzzy Controller Design – Theory and Applications,” by Zdenko Kovacic and Stjepan Bogdan.
DEAR HANY
WHEN THE ORDER OF THE SYSTEM IS HIGH
YOU NEED TO RECALCULATE THE ORDER OF
EVERY SYSTEM INTO THE MOST HIGHLY IS
SECOND ORDER
AND THE COMBINED THE ORDER
BY MULTIPLY SYSTEM ORDER
IS POSSIBLE FOR THE
ERROR PARAMETER SYSTEM TO WORK
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yes, it depends on the system identification you have done, but it very possible!
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