Probing Control : Analysis and Design with Application to Fed-Batch Bioreactors

In most control problems the objective is to control the output at a desired value in spite of disturbances. In some cases, the best setpoint is not known a priori and it should be found online to optimize the process performance. This thesis examines a probing strategy that can be applied for this class of problems. The focus is on the application of the technique to the control of feed supply in fed-batch fermentations of the bacterium Escherichia coli. The thesis is divided into three parts. In the first part, the convergence properties of the probing algorithm are examined. The analysis is limited to processes modeled by a linear time-invariant dynamic in series with a static nonlinearity. Stability and performance analysis taking into account the process dynamic is performed. Tuning guidelines that help the user for the design are also derived. The second part presents a novel cultivation technique based on the probing approach. The fermentation technique combines the advantages of probing control and temperature-limited fed-batch technique. The feeding strategy is well adapted for prolonged operation at the maximum oxygen transfer capacity of the reactor. The efficiency of the method is demonstrated by simulations and experimental results. The strategy leads to a high biomass and it limits the degradation of the recombinant protein activity in the late production phase. In the third part, the probing feeding strategy is evaluated in industrial-scale bioreactors. Based on experimental results the influence of scale and complex medium is discussed. It is shown that the flexibility and robustness of the technique makes it a useful tool for process development

Analysis of a Probing Control Strategy

In this paper we analyse an extremum controller based on a pulse technique. The idea is to superimpose probing pulses to the control signal and use the size of the pulse response in the output for feedback. The probing control strategy has been used with success for the control of the substrate feeding in E. coli cultivations. The stability analysis is done here for systems of Hammerstein type with a piecewise affine nonlinearity. Stability regions of the closed-loop system are derived by solving suitable linear matrix inequalities. Some robustness results with respect to uncertainty in the plant are also given

A modified probing feeding strategy: control aspects

The paper presents a fermentation technique, which combines the advantages of the probing feeding strategy and the temperature limited fed-batch technique. The early phase of the cultivation is run under glucose limited conditions by using the original probing technique. When the maximum oxygen transfer capacity of the reactor is reached, the temperature is decreased to lower the oxygen demand. A slight glucose excess, achieved by downwards probing pulses, guarantees that thetemperature is the only limiting factor. To achieve a good control of the dissolved oxygena mid-ranging controller manipulating the stirrer speed and the temperature is used. A model describing the temperature influence on the cellmetabolism is derived to facilitate the controller design. The feeding strategy is illustrated by an experiment

L’expérimentation animale dans la Fabrica (1543) d’André Vésale

En 1543, André Vésale publiait son grand ouvrage, De humani corporis fabrica libri septem, chez Oporinus à Bâle, consacré à la description et à l’explication du corps humain. On a souvent retenu de cette œuvre les critiques contre Galien et surtout contre ses successeurs qui avaient transféré à l’homme les caractéristiques observées chez l’animal, mais on a longtemps négligé le fait que la pensée de Vésale était encore en grande partie et en toute logique soumise aux paradigmes et aux notions..

Anti-windup in mid-ranging control

The implementation of anti-windup methods in mid-rangingcontrol needs further attention. It is demonstrated how use of standard anti-windup schemes may give unnecessary performance degradation during saturation. The problem isillustrated for two separate systems, control of oxygen concentration in a bio-reactor and temperature controlof a cooling system. In the paper, guidelines are derived for how to design the standard anti-windup scheme to recover performance. As an alternative a modified anti-windup scheme for mid-ranging control is presented that minimizes the performance degradation during saturation

Les techniques actuelles d’etude de l’anatomie de la substance blanche du systeme nerveux central

L’étude des fibres de la substance blanche de l’encéphale demeure complexe. Pour ce faire plusieurs méthodes ont été utilisées pour mieux comprendre la disposition de la micro anatomie de ces fibres. La technique de dissection des fibres ex vivo fût la première technique .Elle a ensuite été abandonnée au profit du microtome et de l’histologie du fait des difficultés pratiques engendrées. C’est à partir de 1956 qu’elle a connu un regain d’intérêt avec son amélioration par Josef Klingler. A partir des années 2000 alors que la technique continue d’être améliorée, une autre technique de dissection in vivo est mise au point. Les méthodes de d’étude de la substance blanche de l’encéphale se résument à la dissection selon la technique de Klingler et la tractographie réalisée par l’IRM en tenseur de diffusion

Microanatomy of the trigeminal cavum: Meckel's cave

The anatomy of the trigeminal cavum also known as Meckel's cave is still poorly understood despite the number of various descriptions available in the literature. The new concept of parasellar compartment means that Meckel's cave and the cavernous sinus constitute a unique entity. We sought to understand anatomic organization of the trigeminal cavum through dissection of 5 previously frozen, formalin-fixed human heads under operating microscope and to gain further knowledge about pathological processes developed in this intracranial region. Meckel’s cave appeared as an invaginated fingered-glove structure tightly attached to the lateral wall of the cavernous sinus and is located in the ventro-lateral quadrant delineated by petro-clinoid folds. The trigeminal porus was observed to be located halfway between the back of the dorsum sellae and the porus of the internal auditory meatus. The trigeminal nerve is the main constituent of Meckel’s cave. The microanatomy of Meckel’s cave is described and the trigeminal cavum can be involved in pathological processes such tumors, meningiomas and trigeminal neuralgia.Keywords: Microanatomy, parasellar compartment, trigeminal cavum, cavernous sinu

Start-up Optimization of a Combined Cycle Power Plant

In the electricity market of today, with increasing demand for electricity production on short notice, the combined cycle power plant stands high regarding fast start-ups and efficiency. In this paper it has been shown how the dynamic start-up procedure of a combined cycle power plant can be optimized using JModelica. org, proposing a way to minimize the start-up time while maximizing the power production during start-up. The physical models have been developed in Modelica, adapted to suit optimization purposes and extended to optimization problems. Constraints keeping the lifetime consumption of critically stressed components under control are limiting factors. The plant models have been successfully optimized to full load

Start-up Optimization of a Combined Cycle Power Plant

In the electricity market of today, with increasing demand for electricity production on short notice, the combined cycle power plant stands high regarding fast start-ups and efficiency. In this paper it has been shown how the dynamic start-up procedure of a combined cycle power plant can be optimized using JModelica. org, proposing a way to minimize the start-up time while maximizing the power production during start-up. The physical models have been developed in Modelica, adapted to suit optimization purposes and extended to optimization problems. Constraints keeping the lifetime consumption of critically stressed components under control are limiting factors. The plant models have been successfully optimized to full load

Models of a post-combustion absorption unit for simulation, optimization and non-linear model predictive control schemes

An increasing demand on load flexibility in power supply networks is the motivation to look at flexible, and possibly optimal control systems for power plants with carbon capture units. Minimizing the energy demand for carbon dioxide removal under these circumstances reduces the cost disadvantage of carbon capture compared to conventional production. In this work a dynamic model in Modelica of a chemical absorption process run with an aqueous monoethanolamine (MEA) is developed, and used for solving optimal control problems. Starting from a rather detailed dynamic model of the process, model reduction is performed based on physical insight. The reduced model computes distinctly faster, shows similar transient behavior and reflects trends for optimal steady-state operations reported in the literature. The detailed model has been developed in Dymola, and the reduced model is used in JModelica.org, a platform supporting non-linear dynamic optimization. First results are shown on the dynamic optimization of the desorption column, the main cause of energy usage in the process