Solving nonlinear circuits with pulsed excitation by multirate partial differential equations

In this paper the concept of Multirate Partial Differential Equations (MPDEs) is applied to obtain an efficient solution for nonlinear low-frequency electrical circuits with pulsed excitation. The MPDEs are solved by a Galerkin approach and a conventional time discretization. Nonlinearities are efficiently accounted for by neglecting the high-frequency components (ripples) of the state variables and using only their envelope for the evaluation. It is shown that the impact of this approximation on the solution becomes increasingly negligible for rising frequency and leads to significant performance gains.Comment: 4 pages, 7 figures, approved for publication in IEEE Transactions on Magnetic

Efficient simulation of DC-DC switch-mode power converters by multirate partial differential equations

In this paper, Multirate Partial Differential Equations (MPDEs) are used for the efficient simulation of problems with 2-level pulsed excitations as they often occur in power electronics, e.g., DC-DC switch-mode converters. The differential equations describing the problem are reformulated as MPDEs which are solved by a Galerkin approach and time discretization. For the solution expansion two types of basis functions are proposed, namely classical Finite Element (FE) nodal functions and the recently introduced excitation-specific pulse width modulation (PWM) basis functions. The new method is applied to the example of a buck converter. Convergence, accuracy of the solution and computational efficiency of the method are numerically analyzed

Multiscale Finite Element Modeling of Nonlinear Magnetoquasistatic Problems Using Magnetic Induction Conforming Formulations

In this paper we develop magnetic induction conforming multiscale formulations for magnetoquasistatic problems involving periodic materials. The formulations are derived using the periodic homogenization theory and applied within a heterogeneous multiscale approach. Therefore the fine-scale problem is replaced by a macroscale problem defined on a coarse mesh that covers the entire domain and many mesoscale problems defined on finely-meshed small areas around some points of interest of the macroscale mesh (e.g. numerical quadrature points). The exchange of information between these macro and meso problems is thoroughly explained in this paper. For the sake of validation, we consider a two-dimensional geometry of an idealized periodic soft magnetic composite.Comment: Paper accepted for publication in the SIAM MMS journa

A Knowledge-Based Analysis of Interlaminar Faults for Condition Monitoring of Magnetic Cores With Predominant Focus on Axial Offset Between the Fault Points

Condition monitoring and fault diagnosis of electromagnetic devices is a normal practice to prevent unpredicted downtime and catastrophic failure. In this sense, interlaminar faults (ILFs) detection or fault diagnosis in the magnetic cores is a key objective. This article aims to present advanced experimental measurements and numerical analysis to study the influence of ILFs on soft magnetic properties of magnetic cores with grain-oriented electrical steels (GOES). The predominant focus of these studies and associated analysis is ILFs with axial offset between the short-circuit points. To carry out the experimental measurements, the stacks of four standard Epstein size strips of GOES were assembled. Each stack was subjected to minor ILF with axial offset from 0 to 200 mm. The test samples were magnetized under controlled sinusoidal induction at a frequency of 50 Hz and peak inductions of 1.1–1.7 T. The impacts of each fault scenario on soft magnetic properties of the test samples were investigated by monitoring and interpreting the dynamic hysteresis loops (DHLs). In favor of supporting the practical measurements, accurate time-domain finite element (FE) models were also undertaken to reproduce the DHLs and to visualize distribution of interlaminar eddy currents and power loss caused by ILFs

Commentaire de : " Transformation thermodynamics: cloaking and concentrating heat flux " - Opt. Express 20, 8207 (mars 2012).

Optics Express a publié en mars 2012 un article concernant la transposition au domaine de la thermique (équation de la chaleur) du principe de la cape d'invisibilité optique. Les auteurs y présentent en particulier la théorie bidimensionnelle d'un métamatériau en forme de disque, aux propriétés thermiques remarquables en conduction pure (équation de la chaleur), dont ils proposent ensuite une réalisation approchée, formée de dix couches d'isolant thermique séparées par dix couches de conducteurs de conductivités thermiques décroissant avec le rayon. Nous donnons ici les résultats d'une expérience numérique complémentaire, consistant à comparer le comportement thermique de la réalisation proposée de ce métamatériau à celui d'une configuration tout à fait banale à deux couches. Cette expérience montre clairement que les auteurs sont allés trop loin dans l'interprétation pratique de leurs résultats théoriques. En particulier, et conformément aux résultats habituels de la thermodynamique, la réalisation approchée qu'ils proposent pour leur matériau théorique (tout comme plus généralement toute autre réalisation, aussi soignée soit-elle), ne permet en aucun cas de protéger un objet de la chaleur mieux que ne le fait un simple isolant d'épaisseur équivalente. L'isolation qu'ils obtiennent est même moins bonne, ce qui enlève tout intérêt pratique à leur travail, qui contient par ailleurs d'autres erreurs

El Análisis cualitativo de datos con ATLAS.ti

Este artículo presenta las características, el procedimiento y la utilidad práctica del análisis de datos cualitativos en el proceso de investigación. Se trata de una tarea enormemente compleja para «dar sentido» a datos muy ricos y densos de significados en los estudios de carácter cualitativo. El trabajo describe cómo aplicar una herramienta informática, el ATLAS.ti, a este procedimiento analítico para su mayor sistematicidad, así como la mejor explotación y optimización de los resultados obtenidos. Se opta por un enfoque metodológico y con valor orientativo sobre el desarrollo autónomo de las tareas comunes del análisis de datos, como son la codificación y la categorización, la construcción de redes semánticas para la generación teórica, y la obtención de resultados parciales para plasmar en los informes de investigación

Finite element models for studying the capacitive behaviour of wound components

peer reviewedFinite element models of increasing accuracy are proposed for the study of the capacitive behaviour of wound magnetic components. Simple models, which are based on the classical assumption of a decoupling between electric and magnetic fields, are first described. Formulations which enable such a coupling are then presented. The models are tested on various coreless inductors, made of round conductors or copper sheets. The results are discussed and compared with experimental data measured with an impedance analyzer

Existence results for the A−φ−B\mathbf{A}-\varphi-\mathbf{B} magnetodynamic formulation of the Maxwell system with skin and proximity effects

International audienceThe $\mathbf{A}-\varphi-\mathbf{B}$ magnetodynamic Maxwell system given in its potential and space-time formulation is a popular model considered in the engineering community. It allows to model some phenomena such as eddy current losses in multiple turn winding. Indeed, in some cases, they can significantly alter the performance of the devices, and consequently can no more be neglegted. It turns out that this model is not yet analytically studied, therefore we here consider its well-posedness. First, the existence of strong solutions with the help of the theory of Showalter on degenerated parabolic problems is established. Second, using energy estimates, existence and uniqueness of the weak solution of the $\mathbf{A}-\varphi-\mathbf{B}$ system is deduced

Subproblem h-Conform Formulation for Accurate Thin Shell Models Between Conducting and Nonconducting Regions

peer reviewedA subproblem method (SPM) with h-formulation is developed for correcting the inaccuracies near edges and corners that arise from using thin shell (TS) models to replace thin volume regions by surfaces. The developed surface-to-volume correction problem is defined as a step of multiple SPs, with inductors and magnetic or conducting regions, some of them being thin. The TS model assumes that the fields in the thin regions are approximated by a priori 1-D analytical distributions along the shell thickness (C. Geuzaine et al., “Dual formulations for the modeling of thin electromagnetic shells using edge elements,” IEEE Trans. Magn., vol. 36, no. 4, pp. 799–802, 2000). Their interior is not meshed and ratherextracted from the studied domain, which is reduced to a zero-thickness double layer with interface conditions (ICs) linked to 1-D analytical distributions that however neglect end and curvature effects. This leads to inaccuracies near edges and corners that increase with the thickness. To cope with these difficulties, the authors have recently proposed a SPM based on the h-formulation for a thin region located between non-conducting regions (Vuong Q. Dang et al., “Subproblem Approach for Thin Shell Dual Finite Element Formulations”, IEEE Trans. Magn., vol. 48, no. 2, pp. 407–410, 2012). The magnetic field h is herein defined in nonconducting regions by means of a magnetic scalar potential , i.e. h = -grad{\phi} , with discontinuities of through the TS. In this paper, the SPM is extended to account for thin regions located between conducting regions or between conducting and nonconducting regions, in the general case of multiply connected regions. In these regions, the potential is not defined anymore on both sides of the TS and the problem has to be expressed in terms of the discontinuities of h, possibly involving on one side only, to be strongly defined via an IC through the TS. In the proposed SP strategy, a reduced problem with only inductors is first solved on a simplified mesh without thin and volume regions. Its solution gives surface sources (SSs) as ICs for added TS regions, and volume sources (VSs) for possible added volume regions. The TS solution is further improved by a volume correction via SSs and VSs that overcome the TS assumptions, respectively suppressing the TS model and adding the volume model. Each SP has its own separate mesh, which increases the computational efficiency. Details on the proposed method will be given in the extended paper, with practical applications