Sliding mode controlled bioreactor using a time-varying sliding surface

Bioreactor processes based on substrate concentration have both highly non-linear behaviour and parameter uncertainties mostly bounded with physical and biological constraints, which make them a subject area of sliding mode control. This work deals with sliding mode control of a fermentation process in a continuous stirred bioreactor. A new sliding surface is defined using angular information as a function of time that provides adjustable continuous movement of the sliding surface. Computer simulations are presented to show the effectiveness and efficiency of the proposed method and to make a quantitative comparison with the conventional sliding mode controller having a constant sliding surface. The excess amount of substrate concentration in the mixture causes undesired by-product information. Therefore, the substrate concentration should not stay above its desired value for a long time. It is shown in the simulations that the performance of the proposed method, especially in regard to the settling time of the substrate concentration and reaching time, is improved. It is also shown that different system state trajectories could be obtained with the proposed method by adjusting the defined parameters of the angular information.