Système hybride

Résumé

Un système hybride est un système dynamique faisant intervenir explicitement et simultanément des comportements continus et discrets. Ces systèmes sont classiquement constitués de processus continus (par exemple, des équations différentielles) interagissant avec ou supervisés par des processus discrets (par exemple automates finis). Ils résultent également de l'organisation hiérarchique des systèmes de contrôle/commande complexes, ou de l'interaction entre des algorithmes discrets de planification et des algorithmes continus de commande. Justification des modèles hybrides Les approches de modélisation en automatique sont fondés sur :

des modèles d’équations différentielles et aux différences (états continu, à temps continu ou discret), modèles fréquentiels pour les systèmes continus ;
des modèles états-transitions et modèles markoviens pour les systèmes événementiels.

Les méthodes d’analyse « classiques » prennent en compte un seul aspect à la fois, l’aspect continu

Source officielle

https://fr.wikipedia.org/wiki/Syst%C3%A8me_hybride

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Hybrid dynamical systems are those with interaction between continuous and discrete dynamics. For the analysis and control of such systems concepts and theories from either the continuous or the discrete domain are typically readapted. In this thesis the ideas from perturbation theory are readapted for approximating a hybrid system using a continuous one. To this purpose, hybrid systems that possess a two-time scale property, i.e. discrete states evolving in a fast time-scale and continuous states in a slow time-scale, are considered. Then, as in singular perturbation or averaging methods, the system is approximated by a slow continuous time system. Since the hybrid nature of the process is removed by averaging, such a procedure is referred to as dehybridization in this thesis. It is seen that fast transitions required for dehybridization correspond to fast switching in all but one of the discrete states (modes). Here, the notion of dominant mode is defined and the maximum time interval spent in the non-dominant modes is considered as the 'small' parameter which determines the quality of approximation. It is shown that in a finite time interval, the solutions of the hybrid model and the continuous averaged one stay 'close' such that the error between them goes to zero as the 'small' parameter goes to zero. To utilize the ideas of dehybridization for control purposes, a cascade control design scheme is proposed, where the inner-loop artificially creates the two-time scale behavior, while the outer-loop exponentially stabilizes the approximate continuous system. It is shown that if the origin is a common equilibrium point for all modes, then for sufficiently small values of the 'small' parameter, exponential stability of the hybrid model can be guaranteed. However, it is shown that if the origin is not an equilibrium point for some modes, then the trajectories of the hybrid model are ultimately bounded, the bound being a function of the 'small' parameter. The analysis approach used here defines the hybrid system as a perturbation of the averaged one and works along the lines of robust stability. The key technical diffierence is that though the norm of the perturbation is not small, the norm of its time integral is small. This thesis was motivated by the stick-slip drive, a friction-based micropositioning setup, which operates in two distinct modes 'stick' and 'slip'. It consists of two masses which stick together when the interfacial force is less than the Coulomb frictional force, and slips otherwise. The proposed methodology is illustrated through simulation and experimental results on the stick-slip drive.

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Design of the heat exchanger network for the SOFC-GT concept

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Within the challenge of sustainability, climate change mitigation and energy supply a promising way of more rational energy conversion is decentralized power generation and the co-production of power and heat. The combination of a solid oxide fuel cell (SOFC) with a gas turbine (GT) in an hybrid system is considered as a promising technology in this context. The process performance is highly influenced by the optimal energy integration satisfying cooling and heating requirements. Therefore, the goal of this project consists in the study of the heat exchange phenomena and of the design of the heat exchanger network.

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Microbial bioelectrochemical cells for hydrogen generation based on irradiated semiconductor photoelectrodes

Fabian Fischer, Ulf Anders Hagfeldt, Michele Morgante, Nikolaos Vlachopoulos

In recent years, one of the most important challenges of the 21st century is to satisfy the ever-increasing world's energy demand. Many efforts are being undertaken to find alternative renewable energy sources, which ideally should outcompete fossil fuel use in all its aspects. In this respect, photo-assisted microbial bioelectrochemical cells (MBECs) in which the reduction of water to hydrogen takes place have been of considerable interest in recent years. Two categories of such systems have been investigated: MBECs with a semiconductor photocathode or photoanode, and hybrid systems, in which an MBEC cell with dark electrodes is coupled to an electrochemical photovoltaic cell. A common denominator of all these systems is the need of microorganisms at the anode, the action of which results in the generation of an electron flow by organic matter oxidation. The aim of this review is to describe the general working principles, with respect to both biochemical and electrochemical aspects, and the performance of various categories of hydrogen-generating photo-assisted MBECs.

IOP PUBLISHING LTD2021

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EPFL2003