Design of a sliding mode controller for a biochemical process by using an intermediate output variable

Sliding mode control of a chemical process is considered in this paper. The process is nonlinear and the dynamics is highly involved due to the strong interdependencies between the variables involved. The considered process has two state variables named dimensionless concentration and temperature. The goal is to maintain a desired concentration level by suitably altering the coolant temperature. The design is based on the control of an intermediate variable, which is defined as the fictitious output of the process. If the fictitious output tracks an appropriately scaled command signal, it is guaranteed to observe precise tracking in the time evolution of the concentration. The design is based on the nominal model and tests have been carried out on a highly demanding set of operating conditions. The results have shown that the proposed mechanism successfully drives the dimensionless concentration to its desired level and maintains the temperature bounded. Furthermore, certain degrees of robustness displayed against disturbances and uncertainties is another important merit of the presented control scheme.