how to Design PID controller for second order untable process

How a PID controller can be designed for a second order SISO process, of the form -a/S^2-b, where a,b>0 .

Answer 1

[Arkadiy Turevskiy]

Not sure if that is what you are looking for, but here is how you could do it in Control System Toolbox:

>>a=1; % change to desired value

>>b=4; % change to desired value

>>s=tf('s');

>>plant=-a/(s^2-b);

>>C=pidtune(plant,'PID'); design pid controller

>>step(feedback(C*plant,1)); plot the step response of the closed-loop system

>>pidtool(plant); % open the GUI for interactive tuning

HTH. Arkadiy

[Harshit Gole]

sir ,

after entering the command

"C=pidtune(plant,'PID');"

it is showing an error

"??? Undefined function or method 'pidtune' for input arguments of type 'tf'."

please guide me.

[Walter Roberson]

pidtune is new as of R2010b

http://www.mathworks.com/help/toolbox/control/rn/bsllzup-1.html