Fractional-order Modeling and Internal Model Control for Pulp Batch Cooking Process

The pulp batch cooking process, a complicated black box process, is carried out in a sealed digester of high temperature and pressure. Based on the analysis of the batch cooking process mechanism, the nonlinear part of the mechanism model is mathematically approximated by function fitting and numerical approximation. A novel fractional-order model is proposed for solving the problem of model imprecision and system parameters uncertainties in batch cooking process. For the fractional-order system, a fractional-order PID controller is designed, and the internal model control is adopted to simplify the adjustable parameters of the fractional-order controller. Then the controller parameters are tuned by maximum sensitivity and stability margin so that a good robust performance can be achieved under a good dynamic response condition. The simulation results show that the fractional-order internal model control of the batch cooking process is superior to the integer-order control in terms of overshoot, response speed, and robustness.