On Fractional Order Predictive PI Controller Design for a MIMO Reactive Distillation Process

Abstract

Abstract In this paper, fractional-order predictive PID control scheme is applied in composition control of boiling fractions of a reactive distillation plant set up for the esterification reaction between acetic acid and ethanol. The controller shares similar structural features with Model-based Predictive Controller (MPC) as many attractive benefits of Dynamic Matrix Control (DMC) are retained such as constraint handling capability. However, it optimizes a different objective function formulated to achieve a more robust control action. These robust properties make it attractive to multivariable process control applications. Process’s state space model is assumed to be available and the model is augmented for prediction of future outputs. Thereafter, a structured cost function is defined which retains the design objective of fractional-order predictive PI controller. Optimisation of this cost function results in realising a near-optimal MIMO controller with reduced input control efforts. Simulation studies using Giwa’s reactive distillation column demonstrates better control performance over dynamic matrix control of the same system. It also rejects disturbances, both measured and unknown disturbances, better than Dynamic Matrix Control system under similar conditions. A major contribution of this paper is the development of a MIMO fractional order predictive PI controller for multivariable process control applications such as composition control of a reactive distillation column.