Enhanced Dynamic Set-point Weighting Design for Two-Input-Two-Output (TITO) Unstable Processes

Abstract

Abstract Control of unstable systems with time delays usually result in overshoots in the closed loop responses. The intricacy involved in multivariable unstable processes further makes the problem more challenging. In industry, set-point weighting is one of the recommended methods to minimize the overshoot. However, design of the set-point weighting parameters determines the percentage of minimization of the overshoot. In this paper, a method is proposed to design the set-point weighting parameters for unstable multivariable processes which is relatively simple and also reduces the overshoot. Weighting is considered for both proportional (β) and derivative (γ) terms in the PID control law. In the closed loop relation for set-point tracking, the coefficients of ‘s’ and ‘s3’ both in the numerator and denominator are made equal in order to find dynamically β and γ. The obtained expressions for β and γ are simple and dynamically depends on the controller parameters and are applied to TITO systems in present work. Decouplers are used in TITO systems mainly to reduce the interaction between the loops so that they can be viewed as independent loops. Decoupler design suggested by (Hazarika and Chidambaram [1] has been used in this work and two TITO unstable processes with time delays are illustrated here. Comparison with the reported methods available in literature verifies that the proposed method gives improved closed loop performance.