Design of Robust PID Controllers for Unstable Processes

The IMC-PID tuning rule has been proposed for the several unstable processes and unstable process with negative zero. The results of the searching of the IMC filter for the PID controller design clearly exhibit that the critically damped filter doesn´t always gives the best response, and it depends upon the category of the process model. The value of damping factor (xi) in IMC filter can be adjusted as the process having different time-delay/time-constant ratio for getting optimum value of integral time. The controller setting gives a robust performance for uncertainty in the process model parameters. The simulation studies show that the proposed design method provides better disturbance rejection when the controller are tuned to have the same degree of robustness by a measure of maximum sensitivity (Ms). The set-point response has been adjusted by using the setpoint filter of as a two degree of freedom controller