Adaptive linearizing control of bioreactors

In this communication we shall present developments concerning the synthesis of Single-Input, Single-Output (SISO) and Multi-Input, Multi-Output (MIMO) adaptive linearizing algorithms for the operation of bioreactors. Results will be illustrated for the baker’s yeast fermentation process. The synthesis of these non-linear control laws is performed by employing differential geometry techniques with system linearization by state feedback. The controller design includes a step of order reduction of the process state model. The adaptive feature comes from the on-line estimation of the required process time varying parameters. The adaptive algorithm proposed enforces a desired and pre-set second order convergence dynamics as originally introduced by Oliveira et al. (1). Formulating the estimator on this basis leaves the user with the choice of two simple and intuitive tuning parameters with physical meaning - a damping coefficient and a natural period of oscillation.Instituto de Sistemas e Robótica; Universidade do Porto. Faculdade de Engenharia; Comunidade Europeia, programa HC&M

A new adaptive scheme for the adaptive linearizing control of bioprocesses

This work deals with the development of model-based adaptive control algorithms for bioprocess operation. Non-linear adaptive control laws are proposed for single input single output regulation. Parameters are continuously adapted following a new adaptive scheme which ensures second-order dynamics of the parameter error system. A computational study is presented of the application of this theory to baker’s yeast fermentation. Results put in evidence the efficient performance both of the adaptive scheme and of the related control laws.Instituto de Sistemas e Robótica, Pólo do Porto

Requisitos e realização de uma instalação experimental para estudos de modelização e controlo em processos de fermentação

O presente trabalho descreve a integração de técnicas de controlo automático em processos biotecnológicos. Fazse uma análise dos requisitos específicos que uma instalação experimental (reactor biológico e sistema informático) deve apresentar para estudos de monitorização e controlo. É descrito um sistema de aquisição de dados e controlo por computador para processos de fermentação, com aplicação a um processo de produção de fermento de padeiro à escala laboratorial.This work concerns the integration of automatic control techniques in biotechnological processes. An analysis of the specific requirements of an experimental set up (biological reactor equipment plus hard- and software system) for monitoring and control studies is presented. A data acquisition and computer controlled system is described for fermentation processes, with particular application, in this instance, to baker’s yeast production at laboratory scale

Model-based estimation of reaction rates in stirred tank bioreactors

In this paper an adaptive model-based algorithm is proposed for the on-line estimation of reaction rates in stirred tank bioreactors. The main design condition imposes that the observation errors reflecting the mismatch between the estimated parameters and the 'true' values follow second-order dynamics of convergence. The gain matrices are shown to be functions of the state and of user-defined damping coefficients and natural periods of oscillation for second-order trajectories. The application of the algorithm is illustrated with a simple case-study involving the estimation of the specific reaction rate for a single substrate, single product scheme.Junta Nacional de Investigação Científica e Tecnológica (JNICT)

Stability, dynamics of convergence and tuning of observer-based kinetics estimators

This work discusses issues concerning stability, tuning and dynamics of convergence of observer-based kinetics estimators. The analysis focuses on both continuous and discrete time formulations of the estimation algorithms. Concerning the former, it is shown that, with proper tuning, stability can be guaranteed, while simultaneously imposing a desired quasi-time invariant second order time response for the convergence of estimates to true values. Concerning the latter, an algorithm is presented, based on a forward Euler discretisation, whose error system is shown to be linear time-invariant. Furthermore, stability conditions were derived, which define the stable domain for the discretisation period as function of the tuning parameters. The theory is illustrated with a case-study of Baker’s yeast fermentation. Results clearly confirm the theoretical developments. In particular, results concerning the stability domain for the Euler-based discrete formulation of the estimator are shown to have relevant practical implications

Tuning of observer-based estimators: theory and application to the on-line estimation of kinetic parameters

This paper deals with the tuning of observer-based estimators. Initially, these algorithms were designed for estimating on-line kinetic parameters, like specific growth rates, in bioprocesses, and have proved to be very successful in practical applications. Here a systematic tuning approach that allows a decoupled estimation of each parameter and the assignment of the estimator dynamics independently of the process dynamics is proposed. The presented approach is illustrated on an animal cell culture example in numerical simulation and with real-life data

A study on the convergence of observer-based kinetics estimators in stirred tank bioreactors

This paper is devoted to the tuning problem of the "observer-based kinetics estimator" in stirred tank bioreactors. This algorithm estimates the reaction kinetics from the on-line knowledge of the state variables (either from measurement or by means of state observer), when the yield coefficients are known. The relation between the dynamics of convergence and the tuning procedure is explored. The method proposed imposes a second-order dynamics to the convergence of the estimator. This approach will be shown to compare favourably with a pole placement based technique, in an application to a baker's yeast fed-batch fermentation.Junta Nacional de Investigação Científica e Tecnológica (JNICT) - contract numbers BIC/636/92, BD/224/90-IF, BD/1476/91-RM

Computer-based studies on bioprocess engineering : II - Tools for process operation

In this paper we review recent advances on the practice and theory of process control with particular emphasis to the operation of bioreactors. We present in detail a case-study on the modelling, model-based identification and adaptive control of fed-batch baker's yeast fermentation.Junta Nacional de Investigação Científica e Tecnológica (JNICT) - contract numbers BD/224/90-IF, BD/1476/91-RM.Instituto Nacional de Investigação Científica (INIC)