Generalized optimal 3-degree of freedom parallel cascade control strategy for stable, unstable and integrating chemical processes

Abstract

To control stable, unstable and integrating chemical processes, a new three-degree of freedom (3DOF) decoupled parallel cascade control architecture (PCCA) is proposed. The proposed PCCA assimilates two/three controllers (secondary disturbance rejection controller, stabilizing controller for only unstable/integrating plants and set-point tracking controller). Internal model control approach (IMCA) augmented with integral of squared error (ISE) minimization and robustness considerations are adopted to design both the secondary loop disturbance rejection controller and the outer-loop set-point tracking controller with the satisfactory performance-robustness tradeoff. Maximum sensitivity constraints and Routh-Hurwitz stability criteria are applied to design the proportional-derivative (PD) controller which stabilizes the unstable and integrating primary plant. It is worth mentioning that the suggested decoupled 3DOF PCCA requires tuning of only two/three controller parameters which are less when compared to recently reported strategies. Robust stability of the suggested 3DOF PCCA is studied in the presence of uncertainty. The simulation results epitomize that the suggested methodology imparts pre-eminent enhancement in closed-loop performance (faster setpoint following and disturbance elimination) for both nominal as well as perturbed plants.