Non-linear control of continuous bioreactors

Control of bioreactors has achieved importance in the recent years. This ma y be due to the fact that they ape difficult to control which may be attrib uted to its nonlinear dynamic behavior. The model parameters of the bioreac tor also vary in an unpredictable manner. The complexity of the biochemical processes inhibits the accurate modeling and also the lack of suitable sen sors make the process state difficult to characterize. Considerable emphasi s has been placed on the control of fed-batch fermenters because of their p revalence in industries. However, when production of biomass is to be optim ized, continuous operation is desirable. Several procedures are available f or the nonlinear control of processes, viz., differential geometric approac h, internal model control approach, reference synthesis technique, predicti ve control design, etc., but the major disadvantage of these approaches is the computational time required to perform the prediction optimization. In this study, a nonlinear controller based on a polynomial discrete time mode l (NARMAX) is evaluated for its performance on a fermentor. It can be shown that a nonlinear self-tuning controller based on NARMAX model can be exten ded to the control of fermenters. The response is smooth for both load and setpoint changes even when process parameters are assumed to be zero and un certainty in parameters are present and in the presence of controller const raints. The control action can be made more or less robust by changing the design parameters appropriately. Therefore, nonlinear self-tuning controlle r is suitable for control of industrial processes.