fuzzy pid cotroller is not converging to a reference point while pid controller converges for the same scenario

Question

Beenish Mazhar 2013-2-1

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I am trying to implement fuzzy pid controller in simulink as uploaded at

http://tinypic.com/view.php?pic=2ag269h&s=6

Fuzzy controller has two inputs, error and derivative of error and 3 outputs Kp, Ki, Kd. Problem is that if I run this program in ode 45 it gets stuck and if I run in ode 4 it gives me wrong output. However for the same state space and same values of Kp, Ki, Kd obtained through fuzzy controller if I make another program not involving fuzzy controller but having only PID controller then I get the perfect converging output. Can anyone please please guide me what is the reason behind this.

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Answer 1

Arkadiy Turevskiy 2013-2-1

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Is Fuzzy Logic Controller always creating just constants for Kp, Ki, and Kd? If not, then the results would be expected to be different from a PID controller with fixed gains.

Another suggestion is not to use a pure derivative block, and instead use implementation of a derivative signal as discussed here.

HTH.

Arkadiy

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Beenish Mazhar 2013-2-3

Sir I think you are suggesting to implement pid in the way as I have uploaded at: http://tinypic.com/view.php?pic=e2io3&s=6 but implementing it in this way simulink gives me error:'Derivative input 1 of 'piddifftry/Transfer Fcn1' at time 0.062867815254137 is Inf or NaN. Stopping simulation. There may be a singularity in the solution. If not, try reducing the step size (either by reducing the fixed step size or by tightening the error tolerances)'. Using a simple pid controller it works absolutely well. How to resolve this.Also fuzzy controller is just creating constants Kp, Ki, and Kd.

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