Convertisseur DC/DC 3kW pour photovoltaïque: diplôme 2015

L’objectif du projet est de développer un système électronique permettant de tester différentes topologies de convertisseurs DC/DC de 3kW

Control of the Toycopter Using a Flat Approximation

International audienceThis paper considers a helicopter-like setup called the Toycopter. Its particularities reside first in the fact that the toycopter motion is constrained to remain on a sphere and second in the use of a variable rotational speed of the propellers to vary the propeller thrust. A complete model using Lagrangian mechanics is derived. The Toycopter is shown to be nondifferentially flat. Nevertheless, by neglecting specific cross-couplings, a differentially flat approximation can be generated and used for controller design, provided the controller gains do not exceed certain bounds that are given explicitly. The achieved performance is better than with standard linear controllers, especially during large displacements that induce strong nonlinear gyroscopical forces. The results are illustrated both in simulation and experimentally on the setup

La responsabilité sociale de l’entreprise à l’aune des restructurations : une étude de cas dans l’industrie des machines suisses

Le contexte contemporain, marqué par la globalisation de l’économie, coïncide avec un affaiblissement des modes traditionnels de régulation du marché du travail. Que ce soit par présomption d’impuissance ou par conviction, nombreux sont ceux qui s’en remettent au sens de la responsabilité des acteurs entrepreneuriaux. Dans la droite ligne du concept de « responsabilité sociale des entreprises », l’entreprise est alors considérée comme la mieux placée pour relever les défis écologiques et sociaux. Ce papier vise à tester l’impact effectif de ces discours appelant à la responsabilité sociale des entreprises dans le cas du processus de restructuration de l’usine Tornos dans le Jura suisse. La première partie rappelle le contexte légal helvétique et les ressources qu’il fournit, tandis que la deuxième analyse la manière dont ces instruments ont été mobilisés par les syndicats et les représentants des salariés dans le cas Tornos. La conclusion tire les principaux enseignements de cette étude de cas.The contemporary context of economic globalisation coincides with a weakening of the traditional top-down modes of regulating the labour market. Be it because of a presumed powerlessness or through genuine conviction, it is believed that corporate social responsibility (CSR) may be a valid substitute to the conventional regulatory mechanisms. In line with such a view, the firm is considered as adequately equipped in order to take up ecological and social challenges. This paper analyses the actual impact of such CSR rhetorics in restructuring processes. It is based on the case study of a Swiss company from the metalworking sector, Tornos. Part 1 lists the legal and conventional resources available in Switzerland, while part 2 analyses how these tools were mobilised by trade unions and workers’representatives in the case of Tornos. The conclusion summarises the main lessons with regard to the impact and relevance of CSR in the Swiss context

Quotient method for controlling the acrobot

This paper describes a two-sweep control design method to stabilize the acrobot, an input-affine under-actuated system, at the upper equilibrium point. In the forward sweep, the system is successively reduced, one dimension at a time, until a two-dimensional system is obtained. At each step of the reduction process, a quotient is taken along one-dimensional integral manifolds of the input vector field. This decomposes the current manifold into classes of equivalence that constitute a quotient manifold of reduced dimension. The input to a given step becomes the representative of the previous-step equivalence class, and a new input vector field can be defined on the tangent of the quotient manifold. The representatives remain undefined throughout the forward sweep. During the backward sweep, the controller is designed recursively, starting with the two- dimensional system. At each step of the recursion, a well-chosen representative of the equivalence class ahead of the current level of recursion is chosen, so as to guarantee stability of the current step. Therefore, this stabilizes the global system once the backward sweep is complete. Although stability can only be guaranteed locally around the upper equilibrium point, the domain of attraction can be enlarged to include the lower equilibrium point, thereby allowing a swing-up implementation. As a result, the controller does not require switching, which is illustrated in simulation. The controller has four tuning parameters, which helps shape the closed-loop behavior

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A quotient method for designing nonlinear controllers

An algorithmic method is proposed to design stabilizing control laws for a class of nonlinear systems that comprises single-input feedback-linearizable systems and a particular set of single-input non feedback-linearizable systems. The method proceeds iteratively and consists of two stages; it converts the system into cascade form and reduces the dimension at every step by creating quotient manifold in the forward stage, while it constructs the feedback law iteratively in the backward stage. The paper shows that the construction of these quotient manifolds is well defined for feedback-linearizable system and, furthermore, it can also be applied to a class of non feedback-linearizable systems

Avoiding Feedback-Linearization Singularity Using a Quotient Method -- The Field-Controlled DC Motor Case

Feedback linearization requires a unique feedback law and a unique diffeomorphism to bring a system to Brunovsk´y normal form. Unfortunately, singularities might arise both in the feedback law and in the diffeomorphism. This paper demonstrates the ability of a quotient method to avoid or mitigate the singularities that typically arise with feedback linearization. The quotient method does it by relaxing the conditions on diffeomorphism, which can be achieved since there is an additional degree of freedom at each step of the iterative procedure. This freedom in choosing quotients and the resulting advantage are demonstrated for a field-controlled DC motor. Using a Lyapunov function, the domain of attraction of the control law obtained with the quotient method is proved to be larger than the domain of attraction of a control law obtained using feedback linearization

Numerical algorithm for feedback linearizable systems

A numerical algorithm that achieves asymptotic stability for feedback linearizable systems is presented. The nonlinear systems can be represented in various forms that include differential equations, simulated physical models or lookup tables. The proposed algorithm is based on a quotient method and proceeds iteratively. At each step, the dynamic system is desensitized with respect to the current input vector field. Control is obtained by tracking a desired value along the input vector field at each step. The numerical algorithm uses the direction on the tangent manifold at a given point and its variation around that point. This enables the algorithm to produce control values simply using a simulator of the nonlinear system

Are soil carbon credits empty promises? Shortcomings of current soil carbon quantification methodologies and improvement avenues

As the consequences of climate change are looming large, agricultural soil carbon credits have emerged as an increasingly advocated lever to incentivize the reduction of greenhouse gas emissions and promote carbon storing farming practices. These credits are exchanged on self-regulated voluntary carbon markets, each of them using distinct protocols to assess the changes in soil carbon stocks and convert them into carbon credits. Although serious discrepancies between protocols have already been noted regarding general carbon credit accounting principles, an in-depth evaluation of how changes in soil organic carbon stocks are calculated is still lacking. In this context, the primary objective of our study was to investigate how changes in soil organic carbon stock are estimated by the major carbon credit protocols worldwide. We evaluated the requirements of each protocol regarding the estimation of the initial SOC stock as well as the modelling and/or measurement of changes in stock with time. We found that existing protocols vary greatly in their scientific rigour. We showed in particular that some protocols do not require in situ soil analyses to estimate initial soil carbon stocks but rely on regional values, leading them to potentially overestimate these stocks by up to 2.5 times. Our study also found that the protocols relying on models require different farming practices and different levels of information for each practice to estimate SOC stock changes. The protocols relying, at least partly, on soil sampling also displayed different requirements for the sampling design, sampling tools, SOC analysis methods and SOC stock calculation methods. On this basis, we suggest reforms designed to improve and standardize the quantification of carbon stock changes in soils and to improve the reliability of soil carbon credits