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

fuzzysimulink

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.

Best Answer

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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