Optimal control of a fed-batch fermentation process

Abstract

Optimisation of fed-batch fermentation processes usually employs the calculus of variations to determine optimal feed-rate profiles that will maximise a given objective function. This results in a two-point boundary-value problem and because of the nonlinear nature of the processes, the optimal solution usually falls out as an openloop control algorithm. One advantage of this approach is that it does not need measurements of state variables which are often difficult to obtain on-line. Instead it assumes that the state variables are proceeding along known paths a-priori determined by models. However, the disadvantage of such an approach is that the performance will severely deteriorate in the presence of process disturbances or plant-model mismatch. Recently, on-line estimation of state variables has been successfully developed and used in the industry and therefore a method which operates the fedbatch fermentation in a closed-loop control scheme using state feedback is proposed. This is achieved by a two-step method. First, the optimal substrate concentration profile which governs the biochemical reactions in the fermentation process is determined. Then a controller is designed in closed-loop form to track this desired profile. Simulation studies for both primary and secondary metabolite production processes show that better performance is obtained by this closed-loop aptifaaal control method than by the openloop optimal feed rate profile method. This is due to the self-correcting property of the proposed method, which proves to be advantageous when there are disturbances or plant-model mismatch.

Framework for online optimization of recombinant protein expression in high-cell-densityEscherichia coli cultures using GFP-fusion monitoring

“…It assumed that the state variables proceeded along paths predetermined by the model. A disadvantage of this deterministic approach is that the performance will severely deteriorate in the presence of process disturbances or modeling errors (Vanishsriratana et al, 1997). Online estimation of parameter values, however, can make feedback control strategies possible.…”

Modelling and control of fed-batch fermentation processes: towards improved quality and productivity

“…In the literature, the derived optimal control profile is usually implemented in an open-loop sense. Based on the development of on-line estimator of substrate concentration (Zhang et al, 1996), a two-step optimisation scheme has been developed in which the system can be operated under feedback (Vanichsriratana et al, 1997). The method separates the task into determining an optimal substrate concentration profile followed by feedback controller design to track such a profile.…”

“…The method separates the task into determining an optimal substrate concentration profile followed by feedback controller design to track such a profile. A comparison between the two-step method and the open loop optimal feed rate profile approach is given in Vanichsriratana et al, 1996Vanichsriratana et al, , 1997.…”