Scientific direction Development of key enabling technologies
Transfer of knowledge to industry

PhD : selection by topics

Wind turbulence effect on ventilation engineering

Département des Technologies Solaires (LITEN)



Ventilation systems in buildings, whether mechanical by extraction, mechanical by insufflation, natural or hybrid, are subjected to the effects of wind. Depending on the orientation of the outlet / inlet ports, the pressure conditions can substantially change the air change rates. A better understanding of the effects of wind and particularly the up to day neglected turbulence effects would allow a better understanding of the interactions with the ventilation systems and contribute to the development of tools for ventilation engineering (finer dimensioning Ventilation systems and development of hybrid ventilation strategies). The increasing energy performance of buildings, from the first regulations to now, brings ventilation systems to the forefront of equipment for regulating indoor ambiances from both an energy and health point of view. In the present subject, wind turbulence and pressure fluctuations generated inside the building will have to be considered with regard to the envelope leackage (and the dynamics of water diffusion within it), the times delay of ventilation devices and sources of internal pollutants. The identification of the effects contributing to or opposing the air renewal should consider the different balances between the mechanical and natural effects (aerodynamics and thermal) and their dynamics.

Interleaved current source inverters for high power PV converters prototyping

Département des Technologies Solaires (LITEN)



Conventionally, systems for converting electrical energy in the photovoltaic domain are voltage inverter type structures [4] - [7]. In this case, the conversion chain of the photovoltaic energy is composed of two stages: a DC-DC converter followed by a voltage inverter (VSI). These voltage source topologies have short-term disadvantages (link capacitor lifetime problems) [5], [8], [9] and relatively low efficiency (due to a double conversion) [5]. As an alternative solution, the current inverter (CSI) structure can be used. Among the advantages of the CSI structure, can be listed: -A reduction in the number of power components, due to the conversion of energy with a single conversion stage [5] -A longer converter lifetime (compared to conventional structures) due to the suppression of the link capacitor [5], [8], [9] and a voltage in the blocked state seen by the switches lower [11] -Integration of natural short-circuit protection On the other hand, the CSI topology has the following disadvantages: -Relatively high conduction losses due to the series connection of devices (MOSFET + Diode) [4], [6] -Special protection requirements for AC and DC sides [4] For the CSI topology, one possible way to overcome the disadvantage of high switching losses is to use Wide bandgap devices (WBGs). Specifically, SiC semiconductors, because of their higher voltage ranges. The LSPV is currently working on: -The characterization of WBG semiconductors in 1.7kV blocking voltage -The design and building of a 100 kW CSI (using custom modules) -The characterization of the efficiency of the converters by calorimetric methods -The study and building of a high power multi-level CSI converter The subject of the thesis is the logical continuity of this work with an important part relative to the control of the structure, the interleaving of the blocks, the reduction of the size of the input inductor. [1] Jäger-Waldau, A. (2016). PV Status Report 2016. JRC Science for Policy Report (Publications Office of the European Union, 2016). [2] Photovoltaics report. Fraunhofer Institute for Solar Energy Systems-ISE, Freiburg, November 2016. Retieved May 2017. [3] BURGER, Bruno. Power Electronics for Photovoltaics. 2015. [4] Sahan, B., Araujo, S. V., Noding, C., & Zacharias, P. (2011). Comparative evaluation of three-phase current source inverters for grid interfacing of distributed and renewable energy systems. IEEE Transactions on Power Electronics, 26(8), 2304-2318. [5] Bülo, T., Sahan, B., Nöding, C., & Zacharias, P. (2007, September). Comparison of three-phase inverter topologies for grid-connected photovoltaic systems. In Proc. 22nd Eur. Photovolt. Sol. Energy Conf. Exhib., Milan, Italy. [6] Martin, J., Bier, A., Catellani, S., Alves-Rodrigues, L. G., & Barruel, F. (2016, May). A high efficiency 5.3 kW Current Source Inverter (CSI) prototype using 1.2 kV Silicon Carbide (SiC) bi-directional voltage switches in hard switching. In PCIM Europe 2016; Proceedings of (pp. 1-8). VDE. [7] Sahan, B., Vergara, A. N., Henze, N., Engler, A., & Zacharias, P. (2008). A single-stage PV module integrated converter based on a low-power current-source inverter. IEEE Transactions on Industrial Electronics, 55(7), 2602-2609. [8] Wang, H., Liserre, M., & Blaabjerg, F. (2013). Toward reliable power electronics: Challenges, design tools, and opportunities. IEEE Industrial Electronics Magazine, 7(2), 17-26. [9] Yang, S., Bryant, A., Mawby, P., Xiang, D., Ran, L., & Tavner, P. (2011). An industry-based survey of reliability in power electronic converters. IEEE Transactions on Industry Applications, 47(3), 1441-1451. [10] Engler, A., et al. "Design of a 200W 3-phase module integrated PV inverter as part of the European project PV-MIPS." Proceedings of the 21st European Photovoltaic Solar Energy Conference and Exhibition, Dresden, Germany. 2006. [11] Felgemacher, C., Araujo, S. V., Noeding, C., & Zacharias, P. (2016, May). Benefits of increased cosmic radiation robustness of SiC semiconductors in large power-converters. In PCIM Europe 2016; Proceedings of (pp. 1-8). VDE. [12] Rashid, M. H. (2010). Power electronics handbook: devices, circuits and applications. Academic press.

Extended Language for Real Time Systems Monitoring

Département Ingénierie Logiciels et Systèmes (LIST)

Laboratoire d'Ingénierie dirigée par les modèles pour les Systèmes Embarqués



The Phd Thesis is related to the ARTiMon monitoring tool developed in our Laboratory. The actual version of ARTiMon accepts a temporized linear time temporal logic for the specification of system requirements. The goal of the thesis is to study and implement language extensions and particularly we would like to specify probabilistic properties and have probabilistic verdicts. Other extensions could be explored, like fuzzy logic, regular expressions, automata, and analysis in the frequential domain in order to obtain a rather universal specification language.

Study of biomass mixture reactivity (ash and carbon matrix)

Département Thermique Biomasse et Hydrogène (LITEN)

Laboratoire de Préparation de la Bioressource



The context is the thermochemical valorization of unused biomass waste (agricultural or forestry residues) in energy vectors (combustion, gasification for 2G biofuels). These biomasses have properties (composition and ash content) inducing liquid phases that may or may not be desirable depending on the processes. The objective is to formulate biomass mixtures based on the thermodynamic equilibrium between solid and liquid phases to adapt the proportion of liquid to the needs of the processes. The main lock to check is to obtain a chemical reactivity. Dilution of the existing phases of the resources to be blended will not produce the desired effect. Furthermore, it must be verified that the carbon matrix of the biomass mixture has a gasification / combustion kinetics compatible with the processes. The thesis will focus on the study of the presence of liquid phase in the ashes of biomasses and their mixtures by melting / quenching then characterization SEM-EDX and XRD, the kinetics of chemical reaction of ashes by X-ray diffraction at high temperature, the kinetics of combustion/gasification of the carbon matrix of biomasses and their mixtures in thermobalance by thermogravimetric analysis TGA and study of the grain size of biomasses on chemical reactivity (ash, carbon matrix) The results obtained on the ashes may give rise to a chemical reactivity model and those on the carbon matrix can then be integrated into the kinetic models already developed in the laboratory, which will extend the validity of the latter to biomass mixtures.

Microalga cultivation on acqueous phase based on hydrotermal liquefaction





Hydrothermal liquefaction is a process that converts wet biomass (10-30% solids) into an oil which can then be refined and used as a biofuel. This process is considered one of the most promising route for the production of biofuels from microalgae. Hydrothermal liquefaction also produces gas, a solid called biochar and an aqueous phase resulting from the water contained in the biomass. The gas consists mainly of CO2 that can be recycled in the microalgae culture and used for their growth. Biochar is a solid rich in carbon and can be used as a soil amendment. As for the aqueous phase, it contains large amounts of nutrients (in the form of ammonium and phosphate ions) which have been dissolved during hydrothermal liquefaction and which can be re-used by microalgae for their growth. However this aqueous phase also contains organic molecules potentially toxic for microalgae. The objective of this thesis project is to study the culture of microalgae on this aqueous phase. For that, we will first identify the compounds that would be the most toxic for the growth of microalgae. Then, we will study the tolerance of microalgae to these toxic molecules and the impact of these molecules on growth. These tests will be carried out at different culture scales (from mL to hundreds of liters) and will integrate the hydrothermal liquefaction process into a biorefinery concept where the use of material and energy flows are optimized.

Inverse reinforcement learning of a task performed by a human





Learning from demonstration involves an agent (e.g., a robot) learning a task by watching another agent (e.g., a human) performing the same task. It often uses reinforcement-learning methods to improve the robot's ability to perform a task in new situations (i.e., generalization). These methods involve providing a positive reinforcement (i.e., a reward) when the outputs of the algorithms help achieving the task, but require a human designed reward function. The more the task is complex the more difficult is the reward function to design, but it can be learned from a series of examples with methods called inverse reinforcement learning. The use, jointly or not, of these techniques has shown encouraging results, but which are limited to toy examples and cannot be adapted as such to tasks more representative of the industrial environment. During the thesis, the PhD student will analyze and test state-of-the-art previous works. S/He will then propose a method, combining inverse reinforcement learning to other algorithms (e.g., generative adversarial networks, GAN), so that the robot will understand the task performed by the operator (with as little explanation from the operator as possible), and will generalize enough to make the robot robust to dynamic environments (obstacles, moving objects?). This method should be suited for a "pick and place" task in an industrial environment and ensure a reasonable enough learning period (information a priori, feedback from the operator) for tasks of medium complexity.

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