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Papers by Dominique Bonvin

Computers & Chemical Engineering, 2003

The main bottleneck in using optimization in industry is the way uncertainty is handled, which fo... more The main bottleneck in using optimization in industry is the way uncertainty is handled, which forms the subject of this series of two papers. The first part dealt with the characteriza- tion of the nominal solution and proposed an approach to separate the constraint-seeking and the compromise-seeking components of the inputs. This second part reviews various strategies for optimization

Proceedings of the 48h IEEE Conference on Decision and Control (CDC) held jointly with 2009 28th Chinese Control Conference, 2009

Solid Oxide Fuel Cells (SOFC) are energy conversion devices that produce electrical energy by the... more Solid Oxide Fuel Cells (SOFC) are energy conversion devices that produce electrical energy by the reaction of a fuel with an oxidant. Although SOFC have become credible alternatives to non-renewable energy sources, efforts are still needed to extend their applicability to a broader scope of applications such as domestic appliances. SOFC are typically operated continuously and are characterized by the presence of stringent operating constraints. For instance, violating the constraint on the cell potential can severely damage the cells. Hence, control and optimization are required to improve cost effectiveness, while respecting operational constraints. Among the numerous control strategies available in the literature, Model Predictive Control (MPC) is an excellent candidate because it can handle constraints explicitly. Furthermore, the control inputs are obtained via the solution of a model-based optimization problem. Only the first moves of the resulting input profiles are applied to...

This paper considers the maximisation of conversion by manipulating the input flowrate for an exo... more This paper considers the maximisation of conversion by manipulating the input flowrate for an exothermic second-order esterification reaction (propionic anhydride + 2-butanol) performed in a semi-batch reactor. Safety considerations impose bounds on the heat release rate in normal operation and on the maximum attainable temperature in the case of cooling failure. The optimal input flowrate is calculated on-line using a

The identification of reliable reaction and mass-transfer rates is important for building first-p... more The identification of reliable reaction and mass-transfer rates is important for building first-principles models of gas-liquid reaction systems. The identification of these rates involves the determination of a model structure (reaction stoichiometry, rate expressions for the reactions and mass transfers) and of the corresponding parameters. The identification of these rate expressions from measured concentrations is a challenging task because of the direct coupling between the reactions and the transfer of reactants and products between the two phases. The identification task can be performed globally in one step by choosing the model structure and estimating the model parameters via the comparison of model predictions and measured data. The approach is termed simultaneous identification since all reactions and mass transfers are identified simultaneously. The procedure needs to be repeated for all candidate model structures. Hence, the simultaneous identification can be computati...

Identification of kinetic models and estimation of reaction and mass-transfer parameters can be p... more Identification of kinetic models and estimation of reaction and mass-transfer parameters can be performed using the extent-based identification method, whereby each chemical/physical process is handled separately. This method is used here to analyze gas-liquid systems under unsteady-state mass transfer. Such a situation is common in the case of diffusion-controlled reactions and is modeled by the film theory, that is, transferring species accumulate in a liquid film. In both the gas and liquid bulks, mass-balance relations describe the species dynamics as ordinary differential equations (ODE) and serve as boundary conditions for the film. On the other hand, the dynamic accumulation in the film is described by Fick’s second law. The resulting partial differential equation (PDE) system is solved by discretization and rearrangement in ODEs. The estimation of diffusion coefficients follows a two-steps procedure. First, the extents of mass transfer are computed from measurements in the t...

The identification of kinetic models is an important step for the monitoring, control and optimiz... more The identification of kinetic models is an important step for the monitoring, control and optimization of industrial processes. This is particularly the case for highly competitive business sectors such as chemical and pharmaceutical industries, where the current trend of changing markets and strong competition leads to a reduction in the process development costs. Moreover, the PAT initiative of the FDA advocates a better understanding and control of manufacturing processes by the use of modern instrumental technologies and innovative software solutions. Reaction systems can be represented by first-principles kinetic models that describe the time evolution of states – numbers of moles, temperature, volume, pressure – by means of conservation and constitutive equations of differential and algebraic nature. These models are designed to include all kinetic phenomena, whether physical or chemical, involved in the reaction systems. Generally, such kinetic phenomena include the dynamic e...

A control synthesis procedure for discrete-time systems with parameter (structured) perturbations... more A control synthesis procedure for discrete-time systems with parameter (structured) perturbations is given. Two cases of parameter bounds are treated: interval bounds and ellipsoidal bounds. Such bounds can be obtained using various identification algorithms. A frequency domain criterion for robust stability is used that handles both cases. The method also allows an estimation of a finite set of critical plants. Based on these further improvements can be made by applying a multimodel design method.

Optimal control of fed-batch fermenters S. Valentinotti† C. Cannizzaro‡ M.Rhiel‡ U. Holmberg† U. ... more Optimal control of fed-batch fermenters S. Valentinotti† C. Cannizzaro‡ M.Rhiel‡ U. Holmberg† U. von Stockar‡ D. Bonvin† †Institut d’Automatique, EPFL, 1015 Lausanne, Switzerland ‡Institut de Genie Chimique, EPFL, 1015 Lausanne, Switzerland Fermentors are often run in a fed-batch manner to avoid the formation of overflow metabolites. At a high growth rate, the most efficient metabolic pathway(s) of certain microorganisms become saturated resulting in overflow metabolite production. These byproducts are undesirable since their accumulation in the reactor may be inhibitory and the productivity of biomass and growth-associated products is reduced. The ideal way to run such fed-batch fermentation is to grow the cells in the reactor at the critical growth rate, i.e., the point at which overflow metabolite production begins. However, since this value changes from run to run, or even during a given fermentation, its identification is not trivial. A simple way to overcome this difficulty is to main...

Proceedings of 1995 American Control Conference - ACC'95, 1995

ABSTRACT

This paper deals with the real-time optimization of uncertain plants and proposes an approach bas... more This paper deals with the real-time optimization of uncertain plants and proposes an approach based on surrogate models to reach the plant optimum when the plant cost gradient is imperfectly known. It is shown that, for processes with only box constraints, the optimum is reached upon convergence if the multiplicative gradient uncertainty lies within some bounded interval. For the case of general constraints, conditions are derived that guarantee plant feasibility and, in principle, allow enforcing cost decrease at each iteration.

Lower and upper bounds for a given function are important in many mathematical and engineering co... more Lower and upper bounds for a given function are important in many mathematical and engineering contexts, where they often serve as a base for both analysis and application. In this short paper, we derive piecewise linear and quadratic bounds that are stated in terms of the Lipschitz constants of the function and the Lipschitz constants of its partial derivatives, and serve to bound the function's evolution over a compact set. While the results follow from basic mathematical principles and are certainly not new, we present them as they are, from our experience, very difficult to find explicitly either in the literature or in most analysis textbooks.

The material presented in this document is intended as a comprehensive, implementation-oriented s... more The material presented in this document is intended as a comprehensive, implementation-oriented supplement to the experimental optimization framework presented in a companion document. The issues of physical degradation, unknown Lipschitz constants, measurement/estimation noise, gradient estimation, sufficient excitation, and the handling of soft constraints and/or a numerical cost function are all addressed, and a robust, implementable version of the sufficient conditions for feasible-side global convergence is proposed.

Computers & Chemical Engineering, 2003

The main bottleneck in using optimization in industry is the way uncertainty is handled, which fo... more The main bottleneck in using optimization in industry is the way uncertainty is handled, which forms the subject of this series of two papers. The first part dealt with the characteriza- tion of the nominal solution and proposed an approach to separate the constraint-seeking and the compromise-seeking components of the inputs. This second part reviews various strategies for optimization

Proceedings of the 48h IEEE Conference on Decision and Control (CDC) held jointly with 2009 28th Chinese Control Conference, 2009

Solid Oxide Fuel Cells (SOFC) are energy conversion devices that produce electrical energy by the... more Solid Oxide Fuel Cells (SOFC) are energy conversion devices that produce electrical energy by the reaction of a fuel with an oxidant. Although SOFC have become credible alternatives to non-renewable energy sources, efforts are still needed to extend their applicability to a broader scope of applications such as domestic appliances. SOFC are typically operated continuously and are characterized by the presence of stringent operating constraints. For instance, violating the constraint on the cell potential can severely damage the cells. Hence, control and optimization are required to improve cost effectiveness, while respecting operational constraints. Among the numerous control strategies available in the literature, Model Predictive Control (MPC) is an excellent candidate because it can handle constraints explicitly. Furthermore, the control inputs are obtained via the solution of a model-based optimization problem. Only the first moves of the resulting input profiles are applied to...

This paper considers the maximisation of conversion by manipulating the input flowrate for an exo... more This paper considers the maximisation of conversion by manipulating the input flowrate for an exothermic second-order esterification reaction (propionic anhydride + 2-butanol) performed in a semi-batch reactor. Safety considerations impose bounds on the heat release rate in normal operation and on the maximum attainable temperature in the case of cooling failure. The optimal input flowrate is calculated on-line using a

The identification of reliable reaction and mass-transfer rates is important for building first-p... more The identification of reliable reaction and mass-transfer rates is important for building first-principles models of gas-liquid reaction systems. The identification of these rates involves the determination of a model structure (reaction stoichiometry, rate expressions for the reactions and mass transfers) and of the corresponding parameters. The identification of these rate expressions from measured concentrations is a challenging task because of the direct coupling between the reactions and the transfer of reactants and products between the two phases. The identification task can be performed globally in one step by choosing the model structure and estimating the model parameters via the comparison of model predictions and measured data. The approach is termed simultaneous identification since all reactions and mass transfers are identified simultaneously. The procedure needs to be repeated for all candidate model structures. Hence, the simultaneous identification can be computati...

Identification of kinetic models and estimation of reaction and mass-transfer parameters can be p... more Identification of kinetic models and estimation of reaction and mass-transfer parameters can be performed using the extent-based identification method, whereby each chemical/physical process is handled separately. This method is used here to analyze gas-liquid systems under unsteady-state mass transfer. Such a situation is common in the case of diffusion-controlled reactions and is modeled by the film theory, that is, transferring species accumulate in a liquid film. In both the gas and liquid bulks, mass-balance relations describe the species dynamics as ordinary differential equations (ODE) and serve as boundary conditions for the film. On the other hand, the dynamic accumulation in the film is described by Fick’s second law. The resulting partial differential equation (PDE) system is solved by discretization and rearrangement in ODEs. The estimation of diffusion coefficients follows a two-steps procedure. First, the extents of mass transfer are computed from measurements in the t...

The identification of kinetic models is an important step for the monitoring, control and optimiz... more The identification of kinetic models is an important step for the monitoring, control and optimization of industrial processes. This is particularly the case for highly competitive business sectors such as chemical and pharmaceutical industries, where the current trend of changing markets and strong competition leads to a reduction in the process development costs. Moreover, the PAT initiative of the FDA advocates a better understanding and control of manufacturing processes by the use of modern instrumental technologies and innovative software solutions. Reaction systems can be represented by first-principles kinetic models that describe the time evolution of states – numbers of moles, temperature, volume, pressure – by means of conservation and constitutive equations of differential and algebraic nature. These models are designed to include all kinetic phenomena, whether physical or chemical, involved in the reaction systems. Generally, such kinetic phenomena include the dynamic e...

A control synthesis procedure for discrete-time systems with parameter (structured) perturbations... more A control synthesis procedure for discrete-time systems with parameter (structured) perturbations is given. Two cases of parameter bounds are treated: interval bounds and ellipsoidal bounds. Such bounds can be obtained using various identification algorithms. A frequency domain criterion for robust stability is used that handles both cases. The method also allows an estimation of a finite set of critical plants. Based on these further improvements can be made by applying a multimodel design method.

Optimal control of fed-batch fermenters S. Valentinotti† C. Cannizzaro‡ M.Rhiel‡ U. Holmberg† U. ... more Optimal control of fed-batch fermenters S. Valentinotti† C. Cannizzaro‡ M.Rhiel‡ U. Holmberg† U. von Stockar‡ D. Bonvin† †Institut d’Automatique, EPFL, 1015 Lausanne, Switzerland ‡Institut de Genie Chimique, EPFL, 1015 Lausanne, Switzerland Fermentors are often run in a fed-batch manner to avoid the formation of overflow metabolites. At a high growth rate, the most efficient metabolic pathway(s) of certain microorganisms become saturated resulting in overflow metabolite production. These byproducts are undesirable since their accumulation in the reactor may be inhibitory and the productivity of biomass and growth-associated products is reduced. The ideal way to run such fed-batch fermentation is to grow the cells in the reactor at the critical growth rate, i.e., the point at which overflow metabolite production begins. However, since this value changes from run to run, or even during a given fermentation, its identification is not trivial. A simple way to overcome this difficulty is to main...

Proceedings of 1995 American Control Conference - ACC'95, 1995

ABSTRACT

This paper deals with the real-time optimization of uncertain plants and proposes an approach bas... more This paper deals with the real-time optimization of uncertain plants and proposes an approach based on surrogate models to reach the plant optimum when the plant cost gradient is imperfectly known. It is shown that, for processes with only box constraints, the optimum is reached upon convergence if the multiplicative gradient uncertainty lies within some bounded interval. For the case of general constraints, conditions are derived that guarantee plant feasibility and, in principle, allow enforcing cost decrease at each iteration.

Lower and upper bounds for a given function are important in many mathematical and engineering co... more Lower and upper bounds for a given function are important in many mathematical and engineering contexts, where they often serve as a base for both analysis and application. In this short paper, we derive piecewise linear and quadratic bounds that are stated in terms of the Lipschitz constants of the function and the Lipschitz constants of its partial derivatives, and serve to bound the function's evolution over a compact set. While the results follow from basic mathematical principles and are certainly not new, we present them as they are, from our experience, very difficult to find explicitly either in the literature or in most analysis textbooks.

The material presented in this document is intended as a comprehensive, implementation-oriented s... more The material presented in this document is intended as a comprehensive, implementation-oriented supplement to the experimental optimization framework presented in a companion document. The issues of physical degradation, unknown Lipschitz constants, measurement/estimation noise, gradient estimation, sufficient excitation, and the handling of soft constraints and/or a numerical cost function are all addressed, and a robust, implementable version of the sufficient conditions for feasible-side global convergence is proposed.