PID self Tuner

hi guys,

i have got an error message when i connecte the model to the PID tuner trying to linearize the model but i got a message (The plant model in the PID loop linearizes to zero, and therefore cannot be used in PID controller design. This problem occurs when one or more blocks in the PID loop have zero gain or the feedback loop is not physically closed),

it was working fine nut after i modify the abit of my model as i will show you below it doesnt work any more:

i am sure the problem is here because if i delet the first line command it will work fine, and i want to use these commands

if c>1 c=1; end if c<0 c=0; end

 if c<0.5
     y =0.8*(30^(-c/0.5))*(u1-u2);
 elseif c>0.5
       y =0.15*30^(c/0.5-2)*(u3-u2);
 else
     y=0;
 end

so please help

if its not clear please let me know i will try to explain more

thanks

Answer 1

[Arkadiy Turevskiy]

PID Tuner works by linearizing your nonlinear Simulink model. If the model linearizes to zero, the PID Tuner would give you the message you saw.

As you have already determined yourself, the linearization issue results from this MATLAB Function block that behaves differently depending on the value of some parameter you have in your model.

What you can do is specify the linearization behavior for this block that would make sense by using this functionality.

HTH.

Arkadiy