1,721,125 research outputs found
À propos de l'adjudant général Frossard
No full textRufer Alfred. À propos de l'adjudant général Frossard. In: Annales historiques de la Révolution française, n°186, 1966. pp. 554-555
Robespierre vu par un officier autrichien
No full textRufer Alfred. Robespierre vu par un officier autrichien. In: Annales historiques de la Révolution française, n°176, 1964. pp. 216-219
Robespierre vu par un officier autrichien
No full textRufer Alfred. Robespierre vu par un officier autrichien. In: Annales historiques de la Révolution française, n°176, 1964. pp. 216-219
Rufer (Alfred), Friedens-und Völkerbundsprobleme aus der Zeit der Helvetik. (Problèmes de la paix et de la Société des Nations au temps de la République Helvétique). 1925
No full textBourdon Jean. Rufer (Alfred), Friedens-und Völkerbundsprobleme aus der Zeit der Helvetik. (Problèmes de la paix et de la Société des Nations au temps de la République Helvétique). 1925. In: Revue d'histoire moderne, tome 4 N°20,1929. p. 157
Rufer (Alfred), Friedens-und Völkerbundsprobleme aus der Zeit der Helvetik. (Problèmes de la paix et de la Société des Nations au temps de la République Helvétique). 1925
No full textBourdon Jean. Rufer (Alfred), Friedens-und Völkerbundsprobleme aus der Zeit der Helvetik. (Problèmes de la paix et de la Société des Nations au temps de la République Helvétique). 1925. In: Revue d'histoire moderne, tome 4 N°20,1929. p. 157
Dead time and non-linearities compensation for CHB multi-level converters with integrated ESS feeding EV’s ultra-fast charging stations
No full textThis paper deals with a compensation technique for non-linear behaviour of single phase modular multi-level power converter, feeding electric vehicle fast charging station with split integrated energy storage system. The proposed method calculates the voltage compensation on the basis of the error between the reference and the real currents. It allows highly improving the harmonic content of the grid current in steadystate conditions within a single period of fundamental.LE
Modélisation physique d'un transistor de puissance IGBT : traînée en tension à l'enclenchement
No full textThe IGBT transistor, associating the conduction advantages of the bipolar transistor and the switching advantages of the MOSFET transistor, is widely used in medium and high power applications with an operating voltage of 1.2kV to 4.5kV. New topologies, reducing the losses in the semi-conductor devices, are often proposed and have to be validated through a simulation tool. The finite element method (FEM) simulators accurately analyse losses in components, but the associated simulation time is so long that they cannot be used for complex topologies in power electronics. An equivalent transistor macromodel, correctly and quickly predicting currents and voltages on the element is needed. This thesis proposes an IGBT transistor model based on semiconductor physics and validated through a comparison with finite element simulator results. The model yields very good results regardless of transistor load and operating point. Base conduction is modelled using a novel equivalent charge approach. This results in a relatively simple macromodel with a good representation of the static and dynamic phenomena. The solving method of the Poisson equation has been revisited to fit recent changes of the internal structure of IGBT transistors. All approximations have been validated through fi- nite element analysis using an appropriate simulation set. The approximation of the internal MOSFET, even though based on existing models, takes into account the specificities of the IGBT transistor structure. It shows the degenerated properties of the internal MOSFET compared to the properties of a standard MOSFET, regardless of the operating point. Using intermediate potentials within the semiconductor structure allows a separate analysis of the different voltage contributions. A complete IGBT transistor macromodel has been developed and tested in different power electronics structures. Good results were obtained in all the tested structures with the proposed IGBT transistor macromodel. Parameter extraction can easily be automated using a mathematical tool such as Matlab and only requires few measurements on the device. The obtained results can then be quickly adapted to an other IGBT device.LE
Modélisation et réglage d'un entraînement à haute performance par un moteur réluctant
No full textUsually, each phase of the direct reluctance motor is fed separately by its own inverter producing a squarewave phase current depending on the rotor position. In the present work, a star-connection of the three stator phases is used and the direct reluctance motor is fed by a three-phase switched inverter. The space phasor theory shows that three-phase sinewave currents can produce a constant electromagnetic torque. In this case, the rotating reference frame rotates at half of the rotor speed and in the opposite direction. This command strategy allows to reduce the stator deformation due to the electromagnetic radial force which is very high in this type of motor and which is mainly responsible for the acoustic noise. The electromagnetic torque control is realised by a sliding mode control of the three phase currents. In the rotating reference frame, it is possible to show that the eight commutation states of the switched inverter are placed around an ellipse in the complex plane of the derivatives of the space phasor of the phase current. A study of this ellipse has allowed to determine the maximal torque as a function of the speed for a given continuous voltage. It is important to insure that the torque reference will never exceed this limitation in order to avoid a pullout phenomenon, highly unwanted in the speed control. Despite the fact that the resolver inside the casing of the direct reluctance motor produces a small periodic error, it is accurate enough for the position measurement and to produce the three current references. However, the derivative of the position measurement provides a speed evaluation with such a ripple that the speed control cannot be outstanding. So, for the speed measurement, an additional laser rotary encoder is used. The experimental study in the steady-state mode of the speed control shows the presence of an electromagnetic torque ripple. This is a residual ripple caused by the dissimilarity between the stator poles teeth-shapes and the magnetic saturation effect. Although this torque ripple is rather low compared with the usual command strategy, two methods are proposed in order to compensate it. The first method is based on the use of a correction factor depending on the tooth angle. First, in steady-state conditions, the correction factor is stored off-line in a table. Then it is used in-line as a feedforward disturbance compensation. The second method of reducing the residual torque ripple consists in implementing an observer of variable disturbance. This is a disturbance observer able to determine the frequency content of the torque ripple. For instance, in order to observe the continuous component, the fundamental wave as well as the harmonics 2, 3, and 6, the observer must have ten poles. The main difficulty to deal with such an observer is the fact that each pole moves quickly as a function of the motor speed. So, in order to guarantee the observer stability over a large range of speed, the poles are located dynamically regarding to the motor speed by the way of a discontinuous adaptation of the feedforward coefficients. The theoretical study and the numerical simulation have allowed to formulate some criteria about the way of locating the poles. Experimental results confirm the efficiency of the observer of variable disturbance in order to reduce the electromagnetic torque ripple.LE
Multiphysical Characterization of Medium-Frequency Power Electronic Transformers
Get PDFEurope is currently making a great effort in order to improve the sustainability and reduce the environmental impact of its energy and transportation systems. A key role on these initiatives is played by efficient generation systems, like cogeneration, and clean or renewable energies, like wind or solar energy, as well as, by efficient and improved transportation technologies. In the evolution of these energy and transport systems, the development of Power Electronic Converters with greater functionality, higher reliability, higher efficiency, lower cost, and more sophisticated control will be essential. The main goal of future Power Electronic Converters will be to increase power density, reduce cost and improve reliability. This way, volume, weight and material reduction as well as reliability will gain the future market. A great contribution of these goals will be made by new high-power semiconductor devices, which permit the extension of the frequency range of power converters, and consequently the reduction of magnetic components. A good example of one of these systems are medium-frequency power conversion systems, also known as Power Electronic Transformers, which are able to convert electric power as convectional transformers but with increased features: volume and weight reduction, power transfer and quality control etc. The present work introduces a complete characterization of a medium-frequency power transformer, suitable for efficient Power Electronic conversion systems. The motivation of the present work stems out from the need to evaluate the constraints of conventional transformer characterization and design methodologies. The proposed expressions are able to successfully address the problematic related to non-sinusoidal waveforms, typical of medium-frequency power transformers. Moreover, a design methodology for the optimal design of medium-frequency power transformers is introduced. The characterization, as well as the design methodology, are verified by means of finite element simulations and measurement results.LE
Semi-rotary and Linear Actuators for Compressed Air Energy Storage and Energy Efficient Pneumatic Applications
No full textThis text explains the use of compressed air for energy storage and efficient pneumatic applications. Chapters cover the elementary physical and engineering principles related to compressed air, including compression and expansion characteristics, adiabatic, polytropic, and isothermal phenomena, and energy content within a given volume. The author also discusses the advantages and drawbacks of pneumatic technology and presents innovative ways to increase the energy efficiency of pneumatic actuators. A key highlight of the book is the introduction of a method to enhance efficiency by incorporating expansion work alongside constant pressure displacement. The author presents an analysis of various cylinder assemblies where energy efficiency is notably improved compared to conventional pneumatic actuators. The book serves as a primary reference for mechanical engineering students and as a handbook for engineers designing efficient pneumatic devices. Key features: - Fundamental and advanced information about actuators and their pneumatic applications - Focus on energy efficiency testing - Systematic chapter order for effective learning progression, with a working example to support comprehension - References for further reading - Appendices providing additional insights and resources Readership: Mechanical engineering students and engineers working on pneumatics.PH-ST
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