Control of Fermentation Processes as Variable Structure Systems

Abstract An essential pending problem in the modeling and control of fermentation processes is the variability of biological systems, expressed as predictable or unpredictable structural alterations in the control plant. Such phenomena, naturally or artificially induced, require flexible alteration of control system structure by proper switching to one or another control strategy. In order to overcome the rigid restriction imposed upon the plant structure by the conventional control approach, we propose here a two-level hierarchical scheme, which provides the control system with a kind of structural adaptability. In the second level of the system, which operates in the structural space of the plant and performs intelligent functions, the current plant structure is recognized as an element of a finite set of structures defined on the base of expert knowledge. In the first level, which works in the state space of the plant, the control strategy relevant to the current plant structure is picked out from a defined pool and the corresponding control action is calculated. This approach has been realized as a real-time software system intended for control of various fermentation processes.