Search

Invited Poster; International audience; Bulk MgB2 superconductors have a promising potential as trapped field magnets, and have a number of attractive properties, such as being rare-earth-free and a low density. However, these superconducting materials have magneto-thermal instabilities visible through flux jumps. These flux jumps occur during conventional magnetization measurements, even at low sweep rates below 10 T/min. In this paper, we investigated the influence of different additions on the flux jumps during Pulsed Field Magnetization (PFM) of MgB2 bulk samples obtained by spark plasma sintering (SPS). PFM experiments are carried out on MgB2 pellets (20 mm diameter and 3.5 mm height) cooled down to an initial temperature of 10 K, 15 K and 20 K. Finally, we discuss the potential of the additions to the MgB2 material in order to avoid flux jumps and increase the resulting trapped field capabilities.

International audience

International audience; This article presents an essential step for identifying and locating faults encountered on rotating electrical machines. It is based on the use of a surface acoustic wave (SAW) vibration sensor. It ensures the capture of mechanical vibrations by a contactless and totally passive process. For the best determination of the resonance frequency, three processing methods are implemented: fast Fourier transform (FFT), discrete wavelet transform (DWT) and the empirical modal decomposition (EMD).

International audience; Multi-terminal DC network (MTDC) offers great potential for long distance huge power delivery with multi-direction power transmission capability. However, the key obstacle in a realization of MTDC is the lack of existing commercial protection device can withstand the DC fault that rises rapidly and surge tenfold within several milliseconds over the whole system. The new technology called Superconducting Fault Current Limiter (SFCL) could bring a solution to the main bottleneck of the MTDC networks. In this work, a novel approach of an accurate model of resistive type SFCL in series with proactive hybrid DC circuit breaker is proposed to protect five terminal MTDC network. The system tested under the worst DC fault scenario. The numerical analysis carried out using (EMTP-RV) software, and the simulation results show how effectively SFCL can reduces the fault current and increases the breaking capability. Not only that, but increases the system stability also.

Poster; International audience; In the design phase of the inductor required for the magnetization of High Temperature Superconductor (HTS) bulks, modeling and simulation are necessary for the design of this inductor. In this paper we have developed an analytical model to calculate the inductance for a coil of a ferromagnetic circuit with gap including a superconducting pellet. This model is based on the determination of the magnetic vector potential from solving the Laplace’s and Poisson’s equations in different regions of interest, using the separation of variables method in which the Cartesian coordinates are used. The boundary and continuity conditions between regions are considered to determine the global solution. This analytical resolution is carried out using a computation code developed under MATLAB. The results obtained are compared with those obtained by a numerical simulation based on the finite element method implemented under COMSOL. A remarkable concordance is observed between both approaches.

International audience

To face the intensive use of natural gas and other fossil fuels to generate hydrogen, water electrolysis based on renewable energy sources (RES) seems to be a viable solution. Due to their fast response times, and high efficiency, proton exchange membrane electrolyzer (PEM EL) is the most suitable technology for long-term energy storage, combined with RES. Like fuel cells, the development of fit DC-DC converters is mandatory to interface the EL to the DC grid. Given that PEM EL operating voltages are quite low and to meet requirements in terms of output current ripples, new emerging interleaved DC-DC converter topologies seem to be the best candidates. In this work, a three-level interleaved DC-DC buck converter has been chosen to supply a PEM EL from a DC grid. Therefore, the main objective of this paper is to develop a suitable control strategy of this interleaved topology connected to a PEM EL emulator. To design the control strategy, investigations have been carried out on energy efficiency, hydrogen flow rate, and specific energy consumption. The obtained experimental results validate the performance of the converter in protecting the PEM EL during transient operations while guaranteeing correct specific energy consumption.

We would like to thank A. Wiederhold, X. L. Zeng (Saarland University, Germany), C. Chang, T. Hauet (IJL Nancy, France) for assistance during the measurements.; International audience; We compare the temperature and field dependence of the critical current densities of high-Tc superconductor materials intended for various bulk applications like trapped-field magnets. This comprises bulk samples of YBa2Cu3Ox (YBCO), MgB2 and iron-based materials, including also various versions of the YBCO compound like melt-textured ones, infiltration-growth processed ones, and YBCO foams. Critical current densities and flux pinning forces were obtained from magnetization loops measured using Quantum Design SQUID and PPMS systems with applied magnetic fields of up to ±9 T. The obtained data are compared to each other with respect of the optimal cooling temperature possible using modern cryocoolers. Furthermore, we plot the temperature dependencies of the critical current densities versus the normalized temperature t = T /Tc. This enables a direct judgement of the performance of the material in the trapped field applications.

In this paper we present an electromagnetic model to compute translational motion eddy current in a conductive plate of an induction heater. The movement of the plate in a dc magnetic field created by a PM inductor generates induced currents that are at the origin of a heating power by Joule effect. The magnetic field expressions due to the PMs is obtained by solving the three dimensional Maxwell equations by the method of separation of variables, using a magnetic scalar potential formulation and a magnetic field strength formulation. The motional eddy currents are computed and the finite length extremity effects are taken into account using the image’s method. The proposed model takes into account the reaction field due to induced currents. The obtained results are close to those obtained from the 3D FE simulations and experiments.

International audience; This paper deals with a high frequency model of inorganic insulated coils used to build high temperature (HT°) machine. The HT° wire has a nickel layer protecting the copper against oxidation and a thin inorganic coating with reduces insulation properties. Therefore, the coils must be designed with a special care for getting a good distribution of turn-to-turn voltage during the fast transients excited by a steep voltage increment of the PWM inverter. A specific coil structure is proposed and a high frequency (HF) equivalent circuit able to compute the turn-to-turn voltages during transients. A finite element based method for determining magnetic couplings between turns, is proposed.

International audience; Bulk High Temperature Superconductors (HTS) can be magnetized and act as permanent magnet much stronger than conventional ones as NdFeB. The design of the inductor is a key point to perform the desired magnetization of the HTS bulk. In this paper, we focus on modeling a Pulsed Field Magnetization (PFM) process of an HTS bulk using a coil powered with a magnetizer. The built model is a 2D axisymmetric problem, based on the H formulation and coupled with electrical equations though the magnetic flux seen by the magnetizing coil. The calculation of this magnetic flux in the H formulation is not trivial and was validated using magnetic vector potential formulation on a coil in the air. Assuming different operating conditions, the bulk HTS is then modeled using four different properties corresponding to air, perfect diamagnetic, copper and HTS. It was shown that simulating a PFM process could lead to different value of peak current and applied magnetic field to the bulk HTS, depending on the critical current density of the bulk, for example. These variations are in the range of the air and diamagnetic cases. Therefore, the proposed method should be used in order to predict a realistic trapped magnetic field in the HTS bulk by taking into account its reaction seen by the coil during the PFM process.

International audience; Cyber-physical system representation is one of the current challenges in Modeling and Simulation. In fact, multi-domain modeling requires new approaches to rigorously deal with it. Co-simulation, one of the approaches, lets modelers use several M&S tools in collaboration. The challenge is to find a way to enable co-simulation use for non-IT experts while being aware of assumptions and limitations involved. This paper deals with co-simulation basic principles teaching through practice. we propose an iterative and modular co-simulation process supported by a DSL-based environment for the MECSYCO co-simulation platform. Through a thermal use case, we are able to introduce co-simulation in a 4 hours tutorial destined to our students. Efficient energy management is one of this century challenges. The current trend to deal with it is to build cyber-physical system (CPS) [Kleissl and Agarwal, 2010]. CPS are physical systems monitored and supervised by one or several computers through a communication networks [Ra-jkumar et al., 2010]. Smart-grids are examples of CPS where the energy network is coupled with a communication network to enable remote monitoring and control. The Modeling and Simulation (M&S) of such systems is one of the current challenges in M&S due to the inter-disciplinary issues they raise. It requests the development of new methods which deal with multi-domain by integrating each expert point of view in the same rigorous and efficient M&S activity. Co-simulation [Gomes et al., 2018] is a way to achieve it.

National audience

Silicon carbide (SiC) MOSFET features low on-resistance per area even at high temperatures compared to a silicon (Si) counterpart with the same voltage rating. However, SiC MOSFET exhibits a unique behavior over operating temperatures due to the presence of interface trap charges. The effect of temperature on the on-resistance of SiC MOSFET has been studied through experimental measurements at difference temperatures from - 30 °C to 150 °C. The results show that high contribution of channel resistance is the critical factor to determine the behavior of SiC MOSFET with temperature.

Purpose The purpose of this paper is to develop a rapid and realistic modelling approach for the design and characterization of high temperature superconducting (HTS) coils and windings carrying DC currents. Indeed, the strong dependence of the electromagnetic properties of such materials on the magnetic field makes the design and characterization of HTS systems a delicate operation where local quantities have to be evaluated. Design/methodology/approach A volume integral modelling approach has been developed taking into account the electric nonlinearity of the HTS material which is represented by power law. The variations of the characteristic quantities of the HTS (critical current density and power law exponent) with the magnetic flux density are also taken into account by using Kim’s law. The volume integral modelling allows to model only the active parts of the system and thus to overcome the difficulties linked to the multiscale dimensions. Findings The model has been tested in a case study in which simulation results were compared to measurements and to finite element analysis. A good agreement was found which validates the model as a rapid and efficient tool for HTS coils and windings design and modelling. Practical implications HTS coils are important elements of emerging superconducting devices which require a high level of reliability, such as generators or motors. The proposed approach is interesting to speed up the design and optimization procedures of such systems. Originality/value Advanced structures of the basic elements have been used in the volume integral modelling, which results in a considerable gain in computation time and in memory-space saving while keeping a high level of precision and realism of the modelling, which has been verified experimentally.

International audience; The present paper focuses on the effect of reduced hydrogen stoichiometry on the dynamic behavior of a PEMFC directly hybridized with SC or non-hybridized, using the European standard cycling protocol (FC-DLC) for transport applications. Two gas stoichiometry factors have been considered, at 1.2 and 1.1. Whereas direct hybridization of a single cell enables to reduce the hydrogen overconsumption from 28 % to 20 % at hydrogen stoichiometry of 1.2, the overconsumption was further reduced to 10 % by reducing the stoichiometry to 1.1. The durability of a single fuel cell has been investigated by comparing the long-term cycling operation depending on the hydrogen stoichiometric conditions, for both hybridized and non-hybridized fuel cell. The non-hybridized fuel cell, at hydrogen stoichiometry of 1.2, was operated for 687 h (end of life), whereas the non-hybridized fuel cell at 1.1, could not be operated due to the sudden, excessive voltage drop in the high current density period of the cycle. On the contrary, the hybridized fuel cell was successfully submitted to cycling for more than 1000 h at both conditions of hydrogen stoichiometry. The GDL appears to be responsible for the failure of non-hybridized fuel cell performance, whereas no particular degradation was evidenced with hybridized configurations. Finally, the technique has been successfully applied to a three-cell stack, with very comparable voltage profiles of the individual cells over the cycling protocol.

International audience; In control of electric machines, removing the current sensors from the electric powertrains has a great importance owing to saving on manufacturing and maintenance costs. This paper addresses the Model-Free-Controller (MFC) as a current sensor-less controller that do the control task for a Permanent-Magnet-Synchronism-Machine (PMSM) without using neither sensor nor estimator for stator current. As this controller is model free, it doesn't require any information about parameters. MFC tries to control the drive system just with measuring the rotor speed and dc bus voltage. Simulation study has been done to show the MFC's robustness under ideal and parametric error condition.

International audience; In the present work, an easily implementable method to reduce CPU time for some 3D FEM problems is presented. A translational displacement between two parts on both sides of a planar airgap is taken into account with a change of coordinates in the airgap region along the z-axis. To achieve this, formulation and post processing are slightly adapted. In this digest, the proposed method is applied to an academic problem. Results are compared to a usual method. Time saving, ease of implementation and precision on prelimary results are really encouraging with a strong reduction of CPU time keeping a low relative deviation. The method could be easily applied to any configurations with planar airgap as MAGLEV, axial motor or levitation device.

International audience

International audience; This paper presents an exact analytical subdomain model of dual-stator consequent-pole permanent-magnet (DSCPPM) machines accounting for tooth-tips, which can accurately predict the armature reaction field distribution in DSCPPM machines. In the proposed subdomain model, the field domain is composed of four types of sub-regions, viz. magnets, outer/inner air gaps, slots and slot openings. The analytical expressions of vector potential in each sub-region are determined by boundary and interface conditions. In comparison to the analytically predicted results, the corresponding flux density field distributions computed by finite element (FE) method are analyzed, which confirms the excellent accuracy of the developed subdomain model.

International audience; In this paper, a so-called OPTimized Pulse Width Modulation (OPT-PWM) strategy with a minimal number of commutations for a multilevel converter (MC) is proposed. The principle is based on the reduction of the number of switch commutations by removing the unnecessary ones for each voltage level transition. The OPT-PWM strategy is applied to a five-level H-Bridge Neutral Point Clamped (HB-5L-NPC) inverter. A specific block based on a state machine is added to conventional modulation techniques to perform the transitions from a given voltage level to another one via the best trajectory with a minimal number of commutations. The principle of this additional block can be applied to any modulation technique. In this paper, the proposed strategy is validated first by simulation and then through experimental tests.

International audience

International audience

International audience; The iron-based superconductors display interesting superconducting properties for applications, such as their reasonably high superconducting transition temperature Tc, very high upper critical fields Hc2, and relatively small anisotropy [1]. Among them, FeSe superconductor shows exceptional characteristics: Tc above 100 K with monolayer FeSe [2] or 27 K under pressure [3], modification of the properties by adding Te, a very rich phase diagram. It also allows an easy and cheap production of superconducting material and they are rare-earth free. Furthermore, superconducting properties are closely related with the presence of defect and one way to enhance or decrease those properties is to use irradiation process. Few experimentations where already done on single crystal FeSe [4]-[9], but not on polycrystalline FeSe, which is most relevant for applications like, e.g., supermagnets. This project is being carried out in this context. By means of two experimental campaigns, our objective is to add point-like defects (electron irradiation with SIRIUS facility) and columnar tracks (heavy-ion irradiation with GANIL facility). Magnetization loops and critical current densities of FeSe samples after electron irradiation will be compared to the reference one. Some analysis will be done regarding a possible phase transition of the characterized samples.References:[1]A. Gurevich, “Iron-based superconductors at high magnetic fields,” Rep. Prog. Phys., vol. 74, no. 12, p. 124501, Dec. 2011.[2]J.-F. Ge et al., “Superconductivity above 100 K in single-layer FeSe films on doped SrTiO 3,” Nat. Mater., vol. 14, no. 3, pp. 285–289, Mar. 2015.[3]Y. Mizuguchi, F. Tomioka, S. Tsuda, T. Yamaguchi, and Y. Takano, “Superconductivity at 27K in tetrago-nal FeSe under high pressure,” Appl. Phys. Lett., vol. 93, no. 15, p. 152505, Oct. 2008.[4]F. Massee et al., “Imaging atomic-scale effects of high-energy ion irradiation on superconductivity and vortex pinning in Fe(Se,Te),” Sci. Adv., vol. 1, no. 4, p. e1500033, May 2015.[5]Y. Sun, A. Park, S. Pyon, T. Tamegai, T. Kambara, and A. Ichinose, “Effects of heavy-ion irradiation on FeSe,” Phys. Rev. B, vol. 95, no. 10, Mar. 2017.[6]A. E. Kar’kin, T. Wolf, A. N. Vasil’ev, O. S. Volkova, and B. N. Goshchitskii, “Effect of neutron irradiation on the properties of the FeSe compound in the superconducting and normal states,” Phys. Met. Metallogr., vol. 113, no. 5, pp. 455–459, May 2012.[7]Y. Sun et al., “Enhancement of critical current density and mechanism of vortex pinning in H + -irradiated FeSe single crystal,” Appl. Phys. Express, vol. 8, no. 11, p. 113102, Nov. 2015.[8]S. Teknowijoyo et al., “Enhancement of superconducting transition temperature by pointlike disorder and anisotropic energy gap in FeSe single crystals,” Phys. Rev. B, vol. 94, no. 6, Aug. 2016.[9]D. Ahmad et al., “Effect of proton irradiation on the fluctuation-induced magnetoconductivity of FeSe 1− x Te x thin films,” New J. Phys., vol. 19, no. 9, p. 093004, Sep. 2017.

This paper proposes a new Unified Switch Fault Diagnosis (UFD) approach for two-stage non-isolated DC-DC converters used in energy harvesting applications. The proposed UFD is compared with a switch fault diagnosis consisting of two separate fault detection algorithms, working in parallel for each converter. The proposed UFD is simpler than the two parallel fault diagnosis methods in realization. Moreover, it can detect both types of switch failures, open circuit and short circuit switch faults. It can also be used for any two-stage non-isolated DC-DC converters based on two single switch converters, no matter the converter circuits in each stage. Some selected simulation and Hardware-in-the-Loop (HIL) experimentation results confirm the validity and efficiency of the proposed UFD. Also, the proposed UFD is applied successfully for fault-tolerant operation of a buck/buck&ndash, boost two-stage converter with synchronous control and a redundant switch.

International audience; The FeSe compound is the simplest high-temperature superconductor (HTSc) possible, and relatively cheap, not containing any rare-earth material. Although the transition temperature, Tc, is just below 10 K, the upper critical fields are comparable with other HTSc. Preparing FeSe using solid-state sintering yields samples exhibiting strong ferromagnetic hysteresis loops (MHLs), and the superconducting contribution is only visible after subtracting MHLs from above Tc. Due to the complicated phase diagram, the samples are a mixture of several phases, the superconducting beta-FeSe, and the non-superconducting delta-FeSe and gamma-FeSe. Furthermore, antiferromagnetic Fe7Se8 and ferromagnetic alpha-Fe may be contained, depending directly on the Se loss during the sintering process. Here, we show MHLs measured up to ±7 T and determine the magnetic characteristics, together with the amount of superconductivity determined from M(T ) measurements. We also performed a thorough analysis of the microstructures in order to establish a relation between microstructure and the resulting sample properties.

International audience; This article is focused on the development of an energy management algorithm applied to a multi-stack fuel cell (FC) system for DC microgrid applications. To guarantee the performance of the FC stacks, the current ripple is reduced by employing multiphase interleaved boost converters. A proposed advanced control technique of the multi-stack with multiphase converters for the proton exchange membrane (PEM) FCs is estimated based on a differential flatness approach, in which it can track the power demand in real-time. Furthermore, the differential flatness based-control can ensure the balance of the DC bus voltage of the DC microgrid when load disturbance occurs. The flatness-based energy management strategy is based on both inner current loops (control of the multi-stack PEMFC through their multiphase interleaved boost converters) and outer voltage loop (DC bus voltage regulation). Compared to classic PI controllers mainly based on the linearization of the system to obtain the transfer function (making complex its application), the flatness-based theory leans on time-domain making it easier its use for various applications while ensuring good performances. To validate the proposed control structure, an FC converter system (5 kW) is realized and validated in the laboratory. For hydrogen production, the methanol FC system has consisted of a reformer engine that changes water mixed methanol liquid into hydrogen to supply FC stacks (ME(2)Power Fuel Cell System: 50 V, 5 kW). The proposed control algorithm is tested experimentally by using a dSPACE controller board platform. Simulation and test bench results authenticate the excellent performance during load cycles in DC microgrid.

International audience; In this paper, four fuel economy strategies using power tracking control of the fuel cell boost converter and fuel cell optimization through the control of the fueling regulators were analyzed. The performance and safe operation in conditions of load disturbances and variations of renewable energy were considered. A benchmark strategy was used as a well-known strategy, which was based on the static feed-forward control of the fueling regulators. One of the four strategies is new and was based on switching the optimization reference to air and fuel regulators based on a threshold of the required power from the fuel cell system. The advantages of using the power tracking control and the optimization based on two variables instead of one are highlighted in sizing the battery capacity and its lifetime, and obtaining fuel economy respectively. The percentages of fuel economy for the analyzed strategies compared to the reference strategy are between 2.83% and 4.36%, and between 7.69% and 12.94%, in the case of a dynamic load cycle with an average of 5 kW and 2.5 kW, respectively

DC microgrid applications include electric vehicle systems, shipboard power systems, and More Electric Aircraft (MEA), which produce power at a low voltage level. Rapid developments in hydrogen fuel cell (FC) energy have extended the applications of multi-phase parallel interleaved step-up converters in stabilizing DC bus voltage. The cascade architecture of power converters in DC microgrids may lead to large oscillation and even risks of instability given that the load converters considered as loads feature constant power load (CPL) characteristics. In this article, the output DC bus voltage stabilization and the current sharing of a multi-phase parallel interleaved FC boost converter is presented. The extended Port-Hamiltonian (pH) form has been proposed with the robust controller by adding an integrator action based on the Lyapunov-Energy function, named &ldquo, Adaptive Hamiltonian PI controller&rdquo, The stability and robustness of the designed controller have been estimated by using Mathematica and Matlab/Simulink environments and successfully authenticated by performing experimental results in the laboratory. The results have been obtained using a 2.5 kW prototype FC converter (by two-phase parallel interleaved boost converters) with a dSPACE MicroLabBox platform. The FC main source system is based on a fuel reformer engine that transforms fuel methanol and water into hydrogen gas H2 to a polymer electrolyte membrane FC stack (50 V, 2.5 kW).

In electrolyzers, Faraday’s efficiency is a relevant parameter to assess the amount of hydrogen generated according to the input energy and energy efficiency. Faraday’s efficiency expresses the faradaic losses due to the gas crossover current. The thickness of the membrane and operating conditions (i.e., temperature, gas pressure) may affect the Faraday’s efficiency. The developed models in the literature are mainly focused on alkaline electrolyzers and based on the current and temperature change. However, the modeling of the effect of gas pressure on Faraday’s efficiency remains a major concern. In proton exchange membrane (PEM) electrolyzers, the thickness of the used membranes is very thin, enabling decreasing ohmic losses and the membrane to operate at high pressure because of its high mechanical resistance. Nowadays, high-pressure hydrogen production is mandatory to make its storage easier and to avoid the use of an external compressor. However, when increasing the hydrogen pressure, the hydrogen crossover currents rise, particularly at low current densities. Therefore, faradaic losses due to the hydrogen crossover increase. In this article, experiments are performed on a commercial PEM electrolyzer to investigate Faraday’s efficiency based on the current and hydrogen pressure change. The obtained results have allowed modeling the effects of Faraday’s efficiency by a simple empirical model valid for the studied PEM electrolyzer stack. The comparison between the experiments and the model shows very good accuracy in replicating Faraday’s efficiency.

Breaking the DC fault in HVDC grid is the greatest challenge for DC grid protection system. Although there are many scientific researches investigating the high voltage DC breakers, yet, there is still always a trade-off between the interruption time and the breaking capability. Therefore, combining between the superconducting fault current limiter (SFCL) technology with a fast DC circuit breaker could bring a solution to this limitation. In this work, an accurate model of resistive-type SFCL (r-SFCL) considering the electro-thermal behaviour, is proposed to be placed in series with ABB proactive hybrid DC circuit breaker (PHCB). To test the viability of the system, a pole-to-pole DC fault scenario was imposed in a HVDC grid. The numerical analysis was undertaken with (EMTP-RV®) software, while the simulation results show how effectively the SFCL can reduce the fault current below the maximum breaking capability. Also, it is concluded that there is a positive interaction between the r-SFCL and PHCB.

The main objective of this paper is to develop a dynamic emulator of a proton exchange membrane (PEM) electrolyzer (EL) through an equivalent electrical model. Experimental investigations have highlighted the capacitive effect of EL when subjecting to dynamic current profiles, which so far has not been reported in the literature. Thanks to a thorough experimental study, the electrical domain of a PEM EL composed of 3 cells has been modeled under dynamic operating conditions. The dynamic emulator is based on an equivalent electrical scheme that takes into consideration the dynamic behavior of the EL in cases of sudden variation in the supply current. The model parameters were identified for a suitable current interval to consider them as constant and then tested with experimental data. The obtained results through the developed dynamic emulator have demonstrated its ability to accurately replicate the dynamic behavior of a PEM EL.

International audience

A buck-based, isolated, high-voltage-ratio DC/DC converter that allows supplying a proton exchange membrane (PEM) electrolyzer from a micro-wind energy conversion system ( μ WECS) has been recently presented. It exhibits low ripple at the switching frequency on the output voltage and current and represents an attractive solution for low-cost hydrogen production. In this paper, a more accurate mathematical model of such a converter is derived and discussed. Then, a model-based robust controller is designed in the frequency domain using the Internal Model Control structure and in the context of H 2 ∕ H ∞ optimal control. The controller satisfies the condition of robust stability and behavior, i.e., it guarantees stability and the desired behavior in the presence of parametric variations and unmodeled dynamics. In particular, the robustness in the presence of variations of DC-link voltage and buck input inductance is verified from the theoretical point of view. The validation of the controller is performed by integrating it into a detailed switching model of the DC/DC converter, which is implemented on a widely used circuit-oriented simulator. Good results are obtained in terms of dynamic and steady-state behavior, even in the presence of the above variations. A comparison is also carried out with the results obtained using an integral controller designed on the basis of the above mathematical model. Such a comparison shows the superiority of the robust controller over the integral controller in all the operating conditions, especially when the DC-link voltage is subject to significant variations and is affected by a non-negligible low-frequency ripple due to the presence of the diode rectifier at the output of the μ WECS.

Developed in the nineties, lithium batteries have colonized our environment in less than thirty years and they keep spreading faster and faster. Powerful, efficient, light and compact, this technology remains hazardous. In order to limit the danger and slow the aging of lithium cells, most of such batteries embed a management system. The latter needs to access some internal states, which are not directly measurable. This thesis intends to estimate these variables using a nonlinear observer, which is based on an electrochemical model. The behavior of the battery is driven by the transportation phenomenon of its main electrochemical species. We therefore built a finite dimensional electrochemical model of these adapted to estimation. It relies on the spatial discretization of the partial differential equations, which describe these transportation phenomena. It also formulates some assumptions, such as the fact that an electrode globally behaves like a single particle of its active material. The obtained state space model has affine dynamics and a nonlinear output. Among the existing observers for such systems that we are aware of, none can be applied directly to the developed model. Hence, we developed new ones whose stability is guaranteed provided a linear matrix inequality holds, which is used to construct the observation gain. We then confront these observers to experimental data acquired on commercialized batteries. The obtained results are encouraging and the observer seems to be a fair compromise between physical meaning and numerical complexity, En 30 ans, les batteries Li-ion ont littéralement colonisé notre environnement depuis et leur déploiement s’accélère. Puissante, efficace, légère et compacte, cette technologie présente des problèmes de sécurité. C’est pourquoi la plupart de ces batteries sont équipées de systèmes de gestion. Ils nécessitent l’accès à certains états internes qui ne sont pas tous mesurables. Cette thèse se propose d’estimer les variables en question à l’aide d’observateurs non-linéaires. Un observateur permet d’estimer des états inaccessibles à la mesure, à partir des mesures disponibles et d’un modèle mathématique des dynamiques mises en jeu. Les transports électrochimiques à l’œuvre dans les batteries sont responsables de leur comportement. Nous en proposons un modèle électrochimique adapté à l’observation. Celui-ci repose sur la discrétisation spatiale des équations aux dérivées partielles décrivant ces phénomènes et sur une série d’hypothèses. Présenté comme un système sous forme de représentation d’état, les dynamiques sont affines et l’équation de sortie est non-linéaire. Parmi les observateurs de systèmes à sortie non-linéaire dont nous avons connaissance, aucun ne peut s’appliquer directement au modèle proposé. Nous en avons donc développé de nouveaux dont la stabilité est garantie lorsqu’une inégalité matricielle est satisfaite. Nous avons ensuite confronté ces observateurs à des données expérimentales d’éléments commercialisés. Le comportement de l’observateur est encourageant et semble être un bon compromis entre sens physique et complexité numérique

Developed in the nineties, lithium batteries have colonized our environment in less than thirty years and they keep spreading faster and faster. Powerful, efficient, light and compact, this technology remains hazardous. In order to limit the danger and slow the aging of lithium cells, most of such batteries embed a management system. The latter needs to access some internal states, which are not directly measurable. This thesis intends to estimate these variables using a nonlinear observer, which is based on an electrochemical model. The behavior of the battery is driven by the transportation phenomenon of its main electrochemical species. We therefore built a finite dimensional electrochemical model of these adapted to estimation. It relies on the spatial discretization of the partial differential equations, which describe these transportation phenomena. It also formulates some assumptions, such as the fact that an electrode globally behaves like a single particle of its active material. The obtained state space model has affine dynamics and a nonlinear output. Among the existing observers for such systems that we are aware of, none can be applied directly to the developed model. Hence, we developed new ones whose stability is guaranteed provided a linear matrix inequality holds, which is used to construct the observation gain. We then confront these observers to experimental data acquired on commercialized batteries. The obtained results are encouraging and the observer seems to be a fair compromise between physical meaning and numerical complexity; En 30 ans, les batteries Li-ion ont littéralement colonisé notre environnement depuis et leur déploiement s’accélère. Puissante, efficace, légère et compacte, cette technologie présente des problèmes de sécurité. C’est pourquoi la plupart de ces batteries sont équipées de systèmes de gestion. Ils nécessitent l’accès à certains états internes qui ne sont pas tous mesurables. Cette thèse se propose d’estimer les variables en question à l’aide d’observateurs non-linéaires. Un observateur permet d’estimer des états inaccessibles à la mesure, à partir des mesures disponibles et d’un modèle mathématique des dynamiques mises en jeu. Les transports électrochimiques à l’œuvre dans les batteries sont responsables de leur comportement. Nous en proposons un modèle électrochimique adapté à l’observation. Celui-ci repose sur la discrétisation spatiale des équations aux dérivées partielles décrivant ces phénomènes et sur une série d’hypothèses. Présenté comme un système sous forme de représentation d’état, les dynamiques sont affines et l’équation de sortie est non-linéaire. Parmi les observateurs de systèmes à sortie non-linéaire dont nous avons connaissance, aucun ne peut s’appliquer directement au modèle proposé. Nous en avons donc développé de nouveaux dont la stabilité est garantie lorsqu’une inégalité matricielle est satisfaite. Nous avons ensuite confronté ces observateurs à des données expérimentales d’éléments commercialisés. Le comportement de l’observateur est encourageant et semble être un bon compromis entre sens physique et complexité numérique

International audience

A superconductor can induce currents when exposed to a variation of an external magnetic field, created for example by a pulsed current flowing through a coil. As these induced currents circulate indefinitely, a trapped magnetic field is generated, which is the remaining magnetic field produced by the superconductor alone when the applied magnetic field has disappeared. This process is called Pulse Field Magnetization (PFM). In this article, we are interested in the modeling of the PFM of an array of several High Temperature Superconducting (HTS) pellets. A 3D model has been developed, based on the Finite Element Method (FEM), and coupled with an external electrical circuit. In this model, A and H formulations are coupled using appropriate boundary conditions to take advantage of each other in specific regions. The presented results are the current density during the magnetization process and the trapped magnetic field trapped in the HTS. These results highlight the need to model such a problem in 3D., Un supraconducteur peut induire des courants lorsqu’il est soumis à une variation de champ magnétique extérieur, créé par exemple par une impulsion courant circulant dans une bobine. Ces courants induits circulant indéfiniment, il en résulte un champ magnétique piégé, qui est le champ magnétique restant produit par le seul supraconducteur quand le champ magnétique appliqué a disparu. Ce procédé est appelé aimantation par un Champ Magnétique Pulsé (CMP). Dans cet article, nous nous sommes intéressés à la modélisation de l’aimantation par CMP d’un arrangement de plusieurs pastilles Supraconductrices à Haute Température Critique (SHTC). Nous avons développé un modèle de calcul 3D basé sur la Méthode des Eléments Finis (MEF) couplé avec un circuit électrique externe. Dans ce modèle, les formulations en A et H sont couplées à l’aide de conditions aux frontières appropriées afin de tirer avantages de chacune d’elles dans des régions spécifiques. Les résultats présentés sont la densité de courant durant le procédé d’aimantation et le champ magnétique piégé dans les SHTC. Ces résultats mettent en évidence la nécessité de modéliser un tel problème en 3D.

International audience; In the more electric aircraft context, dc distribution systems have a time-varying structure due to the flexible distributed loads and complex operation conditions. This feature poses challenges for system stability and increases the difficulty of the stability analysis. Besides, the risk of instability may be increased under constant power load condition due to the negative incremental impedance characteristic. To this end, this article proposes an improved interconnection and damping assignment passivity-based control scheme. Particularly, an adaptive interconnection matrix is developed to establish the internal links in port-controlled Hamiltonian models and to generate the unique control law. The damping assignment technique is addressed to tune the dynamic characteristic. In order to meet the load requirements of different voltage levels, the design procedures were given for determining the control law in both boost converter and buck converter cases. The simulation and experimental results are performed to demonstrate the validity of the proposed control approach.

This paper deals with hydrogen production via water electrolysis, which is considered the most attractive and promising solution. Specifically, the use of renewable energy sources, such as wind electric power generators, is hypothesized for supplying the electrolyzer, aiming to strongly reduce the environmental impact. In particular, micro-wind energy conversion systems (μWECSs) are attractive for their low cost and easy installation. In order to interface the μWECS and the electrolyzer, suitable power conditioning systems such as step-down DC-DC converters are mandatory. However, due to the requested high conversion ratio between the DC bus grid, i.e. the output of a three-phase diode rectifier connected to the output of the electric generator, and the rated supply voltage of the electrolyzer, the classic buck converter alone is not suitable. Therefore, a converter is proposed and designed, consisting of a buck converter, a full-bridge IGBT converter, a single-phase transformer, and a diode bridge rectifier; LC filters are also included between buck and full-bridge converters, and at the output of the diode bridge rectifier with the aim of reducing the ripple on currents and voltages. The components of the described physical system from the output of the three-phase rectifier up to the electrolyzer are then modeled assuming the transformer as ideal, and the model is employed for designing a PI-type controller. Experimental results are provided in order to demonstrate the effectiveness of the developed converter and its control for these applications.

International audience

A power management strategy for a proton exchange membrane (PEM) electrolyzer connected to a wind turbine conversion system (WTCS) is proposed in this paper. It is based on the characterization of the wind turbine and the electrolyzer as well. With the aim to interface the WCTS and the PEM electrolyzer, a stacked interleaved DC-DC buck converter has been chosen due to its benefits for this application from output current ripple and reliability point of view. This converter is controlled so that it can have a dynamic faster than the wind turbine avoiding overvoltage during transients, which could damage the PEM electrolyzer. In order to assess the performance of the power management strategy, experimental tests have been carried out. The reported results demonstrate the correct behavior of the system during transient operation.

International audience; In light of the low efficiency of photovoltaic (PV) panels and varying environmental conditions, it is necessary to develop methods for maximum power extraction of PV panels in any environmental conditions. Here, a new hybrid method is proposed for maximum power point tracking (MPPT). The fuzzy logic control-based method is very fast and accurate but difficult to implement. In addition, this method depends on PV arrays. The three-point weight method is another MPPT method that does not compromise on the maximum power point under fast transient conditions. The advantages of both methods are utilized in the proposed method. Furthermore, the overall complexity is decreased by simplifying the fuzzy logic part. The three methods were experimentally validated and, in addition, were numerically simulated in Matlab.

In this paper, a procedure is proposed to optimally design a boost converter (including its input filter and its control) for embedded applications, where power density and high efficiency are crucial criteria. The load consists of a constant power load (CPL), which represents the most stringent case in term of stability issues. This optimization problem can be treated as a multi-objective one, which aims to maximize compactness and efficiency of the studied system. In order to find a trade-off between compactness and efficiency, the two objective functions (volume and power losses), a genetic algorithm was implemented to generate the most convenient design solutions (Pareto front). The operating conditions include both steady and fast output power load transients (step-up and step-down). Since CPL transients may lead to large deviations of the output voltage from its nominal value, the control strategy is discussed as well and included in the design procedure. The presence of a differential input filter is likely to interact with the constant power load and cause some instability issues. A constraint function excludes solutions that do not respect the feasibility, the magnetic saturation or the stability constraints.

Invited Poster; International audience; Despite the large magnetic fields that can be generated by High-Temperature Superconducting (HTS) bulks, very few bulk HTS machines have been developed worldwide. To explore the potential of such machines, a 30-kW low speed, radial-gap synchronous generator with an air-cored rotor and a conventional stator with ferromagnetic teeth has been realized by TUMSAT. Each field pole on the rotor is composed of a rectangular array of 15 square GdBaCuO bulks cooled down through a thermosiphon. A trapped magnetic field Bp greater than 3 T is targeted at the top center of each bulks, which means that roughly 6 T must be applied through the pulse field magnetization (PFM). By means of a 3D modeling of the machine's pole, the paper aims to design a coil to magnetize the array of 15 bulks.

Poster; International audience; On the market of NMR spectroscopy, there is a growing interested in compact and high-resolution magnets. This can only achieve by using High Temperature Superconducting bulks magnets such as GdBaCuO. Moreover, bulk HTS magnets exhibit ultra-high stability and offer the possibility to use cryogen free cooling. A way to design NMR magnet is to exploit the magnetic field produced by two face-to-face HTS bulks. Since uniformity required by NMR systems is crucial, dedicated tools are required in order to improve the magnetization process of HTS bulks and also for designing the shim coils efficiently. In this paper, we address the problem of estimation of magnetic field uniformity produce by a HTS bulk magnet by means of spherical harmonics decomposition.

This paper presents the dynamic behavior of an induction machine coupled with a magnetic gear. An analytical modeling for the machine and the gear is first developed. This model is used to predict the transient performance of the machine for a direct-on-line starting.

International audience

National audience

The subject of the paper is a three-dimensional analysis of a coupled fluid-thermal and electromagnetic field in permanent magnet synchronous machine that can work at very high temperatures. To obtain the distribution of the airflow and temperature we employed the coupled fluid-thermal model of the machine. This allowed us to check whether the temperature in sensitive elements does not exceed the permissible limits. The analysis took into account the effect of the color and the smoothness of the machine housing on the temperature distribution in its interior. The influence of design on the temperature distribution and distribution of hot spots was tested. Two topologies are studied considering magnet mounted on the rotor surface or buried in the rotor soft magnetic core. The simulation results were compared with measurements made on a prototype.