In this paper, extensive simulations are performed on the FOPTD Unstable systems having uncertain process model parameters (i.e process gain (Kp), time constant ( τ ) and dead time (t d ), in order to design a robust PI/PID controller with better disturbance rejection and servo response, without compromising the robust performance (Robust stability) of the system. A simple PI/PID controller design and tuning method is described and compared from the point of view of the control system

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... for the First order plus time delay (FOPTD) process. For FOPTD Un-stable systems, the step responses obtained by the proposed method when uncertainty in the process model parameters exist, are compared to the responses obtained by Visioli [3], IMC(Wang/Hang)[5] and Huang-Chen [2] methods. The Proposed controller settings give a robust performance for uncertainty in model parameters. The performance of PID tuning techniques is analyzed and compared on basis of minimization of error and transient response specifications. A theoretical analysis of robustness and stability of the proposed controller is done using Kharitonov's theorem (Barmish) [4] to validate the simulation results obtained using MATLAB/SIMULINK.