Decoupling control of a multiple-input, multiple-output process: Case studies of multi-tank system and distillation column

Multiple Input-Multiple Output (MIMO) systems are very common in process industries, but can be difficult to control. A phenomenon called coupling occurs in a MIMO system when the controller output from one loop acts as disturbance to other control loops. This thesis studies a solution to coupling by introducing a decoupler to a Proportional Integral Differential (PID) control system. A decoupler is a feed-forward controller added to the traditional feedback loop to cancel out loop disturbance. The effect of a decoupler on the performance of control system was explored by comparing (1) the time it takes to achieve control and (2) the combined error incurred during the control process. In this study, a simulation software, LoopPro is used to model and control two systems; multi-tank system and distillation column. Step test data were used to identify process model and a tuning procedure based on Internal Model Control is illustrated. The extent of loop interaction was also analyzed from the Relative Gain Matrix.