Minimisation des inductances propres des condensateurs à film métallisé

In this article, we examine the different factors responsible for the equivalent series inductance in metallized capacitors and we propose structures for capacitors that reduce this inductance. After recalling the structure of metallized capacitors we compare, by experimental measurements, the inductance due to the winding and that one added by the connections. The latter can become preponderant. In order to explain the experimental evolution of the winding impedance vs. frequency, we describe an analytical model which gives the current density in the winding and its impedance. This model enables us to determine the self resonant frequency for different types of capacitors. From where, we can infer the influence of the height of capacitors and their internal and external radius upon performances, It appears that to reduce the equivalent series inductance, it is better to use flat windings and annular windings.Dans cet article nous examinons les différents facteurs responsables de l'inductance équivalente série dans les condensateurs à film métallisé et proposons des géométries de condensateurs qui réduisent cette inductance. Après avoir rappelé la structure des condensateurs à film métallisé, nous comparons, par des mesures expérimentales, l'inductance due au bobinage et l'inductance ajoutée par les connexions. Cette dernière peut devenir prépondérante. Afin d'expliquer l'évolution de l'impédance du bobinage en fonction de la fréquence, nous décrivons un modèle analytique qui donne la densité du courant dans le bobinage et l'impédance de ce dernier. En outre, ce modèle permet de déterminer la fréquence de résonance série de divers types de condensateurs ce qui permet de déduire l'influence de la hauteur des condensateurs et de leurs rayons interne et externe sur les performances. Il apparaît ainsi que, pour diminuer l'inductance équivalente série, il vaut mieux employer des bobinages plats et des bobinages annulaires

Asymmetrical Current Distribution in Metallized Film Capacitors

International audienceThe presence of high frequency currents in the vicinity of metallized capacitors can generate eddy currents in the metallizations, with a possible negative impact on the reliability and lifetime of these components. These phenomena are due to the asymmetrical distribution of the field lines. We present a model derived from the physical relations between the current density, the strength of the magnetic field, the electromotive force in a capacitor winding and its plates, and the conductivity of the different materials. This model also takes into account anisotropy due to the structure of the winding. The results obtained from this model can be compared to the measurements of the electromotive force detected by a loop in the vicinity of a capacitor under operation. Finally, the consequences of nonsymmetrical magnetic field distribution are discussed in the light of the results obtained from the model

Homogénéisation des matériaux constituant les condensateurs bobinés à films métallisés

The structure of metallized capacitors is complex and the sizes of the constituting elements are dissimilar. Consequently, direct computation of fields and current densities is impossible. In this paper, we give some macroscopic properties (impedances, admittances) of the capacitor winding, obtained thanks to an homogeneization method. These properties are helpful to compute the current and heating distribution in capacitors.La structure des condensateurs métallisés est complexe et les tailles des éléments constitutifs sont dissemblables. En conséquence, le calcul direct de champs et de densités de courant est impossible. Dans cet article, nous donnons quelques propriétés macroscopiques (impédances, admittances) du bobinage, obtenues grâce à une méthode d'homogénéisation. Ces propriétés permettent de calculer la répartition des courants et des échauffements dans les condensateurs

Reliability determination of aluminium electrolytic capacitors by the mean of various methods: application to the protection system of the LHC

The lifetime of power electronic components is often calculated from reliability reports, but this method can be discussed. We compare in this article the results of various reliability reports to an accelerated ageing test of component and introduced the load-strength concept. Large aluminium electrolytic capacitors are taken here in example in the context of the protection system of LHC (Large Hadron Collider) in CERN where the level of reliability is essential. We notice important differences of MTBF (Mean Time Between Failure) according to the reliability report used. Accelerating ageing tests carried out prove that a Weibull law is more adapted to determinate failure rates of components. The load-strength concept associated with accelerated ageing tests can be a solution to determine the lifetime of power electronic components

Étude des perturbations conduites et rayonnées dans une cellule de commutation

The principles used in static conversion and the rise of the performances of the new switching devices contribue to increase the level of electromagnetic noises emitted by electronic converters. We have studied the way how these perturbations are created and coupled through their environment in conducted and radiated mode by a switching cell. This one can work in hard switching, zero current or voltage switching modes. We first outline the general problems of electromagnetic pollution and their metrology in converters. Then we describe the experimental environment. We analyse the mechanisms of generation of parasitic signals in a switching cell related to the electrical constraints and its switching mode. The simulated results, issued of the analytical models obtained, are confronted with the experimental ones. Then we show a method to calculate analytically the $E$ and $H$ near fields. It has been confirmed by experimental results. At last, we present, in a synthetic manner, the main results obtained, relative to the switching mode and the electrical constraints, using a new characterizing method. Theses results will allow the designer to incorporate the electromagnetic considerations in the conception of a converter.Les principes de commutation employés en conversion statique, l'évolution des performances statiques et dynamiques des composants, contribuent à faire des dispositifs de conversion statique de puissants générateurs de perturbations conduites et rayonnées. Nous nous sommes attachés à étudier les mécanismes de génération et de couplage des perturbations, tant en mode conduit que rayonné dans des structures à une seule cellule de commutation et fonctionnant selon les trois principaux modes de commutation : commutation forcée, à zéro de courant (ZCS), et à zéro de tension (ZVS). Après la mise en évidence de la problématique de pollution électromagnétique dans les structures et leur métrologie, nous décrivons l'environnement expérimental étudié. Nous analysons ensuite les principaux mécanismes produisant les perturbations au sein d'une cellule de commutation en introduisant un certain nombre de composants parasites. Les modèles sont simulés et confrontés aux résultats expérimentaux. Nous décrivons alors une méthode, validée expérimentalement et permettant de calculer les intensités des champs $E$ et $H$ proches émis. Enfin, nous présentons de façon synthétique les résultats observés selon les régimes de fonctionnement de la cellule de commutation et les contraintes électriques et dynamiques qu'elle subit. Nous avons, pour ce faire, développé une méthode originale de quantification des signaux perturbateurs. Les résultats obtenus doivent permettre d'intégrer les problèmes de pollution électromagnétique au stade de la conception d'un dispositif

Thin wire approximation for PCB modeling of the EMC of power converters

This paper deals with the modeling of Printed Circuit Boards (PCB) for numerical resolution of a power circuits electromagnetic Compatibility (EMC). The well-adapted model for numerical resolution is the thin wire model. Thus, the PCB trace is replaced by N thin wires. Each wire radius is calculated as a function of the PCB dimensions. This model is applied to calculate the radiated electric field from a PCB circuit using the moment method which is well-suited for thin wire modeling. By observing the influence of the electromagnetic field radiated from the circuit, the number of equivalent wires required to have coherent results is established. The study of the current distribution in the wires shows that the thin wire model takes into account both the skin and the proximity effects

Constraints generated by fluorescents lamps on the electrical network

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Study of accelerated aging of supercapacitors for transport applications

International audienceOne important part of the electrical transportation systems is the energy-storage system. This can be based, for example, on supercapacitors. In this paper, we propose to study its behavior under constraints similar to their uses in power and railway-traction systems. We define an adequate measurement protocol for accelerated aging which is applied to supercapacitors according to two accelerated factors: effective current and temperature. We model the supercapacitors for different states of health. The modeling gives a good estimation of the variation of electrical parameters of the supercapacitor at different states. We reveal general indicators of the supercapacitor's aging, and we discuss about its life cycle