Sliding mode controlled bioreactor using a time-varying sliding surface

Abstract

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.

Exponential Mapping Function for Nonlinear Control

“…This modified exponential function in its basic form allows for the controller to have strong actuation for small errors. This is related to the sigmoidal functions proposed in [11], [13], and [14], but the exponential mapping is more flexible in the sense that it can also generate a weak actuation for higher errors.…”

“…Another idea [13] was the use of a parabolic function coupled to a shifted sigmoid function to change the linear discontinuous control with the equivalent term computed with a simplified, model-based piecewise function. This nonlinear parabolic sliding surface was:…”

Neural Network-Based State Estimation for a Closed-Loop Control Strategy Applied to a Fed-Batch Bioreactor

“…In the particular case of fed-batch bioreactors, some nonlinear control strategies were developed to improve the process efficiency and the "batch-to-batch" reproducibility [6], as well as to deal with the unavoidable uncertainties typically present in bioprocesses [7].…”

A new adaptive controller for bio-reactors with unknown kinetics and biomass concentration: Guarantees for the boundedness and convergence properties

“…Using the exact linearization and estimation algorithms in [34], a nonlinear adaptive controller was proposed for a fed-batch bioprocess. In [38], the adaptive control for bioreactors is improved through sliding mode control. The gain-scheduling methods and adaptive control are combined in [15] to control the pH of a bioreactor in a fermentation processes.…”