A time-domain homogenization technique for lamination stacks in dual finite element formulations

AbstractA time-domain homogenization technique is developed to take the eddy currents in lamination stacks into account with dual 3-D magnetodynamic b- and h-conform finite element formulations. The lamination stack is considered as a source region carrying predefined current density and magnetic flux density distributions describing the eddy currents and skin effect in each lamination. These distributions are related and are approximated with sub-basis functions. The stacked laminations are then converted into continuums with which terms are associated for considering the eddy current loops produced by parallel fluxes, through the homogenization of the sub-basis function contributions

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

Evaluation of a Quasi Coaxial Printed Circuit Board Transformer

Abstract: Minimization of leakage inductance of a transformer is very often one of the main focus points during the design because of the adverse effects it may have on some power electronics circuit topologies. There are however applications in which the leakage inductance may be used as a circuit element, in which case it should be predictable and easily realizable. Coaxial transformers are known for the ease with which the leakage inductance may be predicted but obtaining these values repetitively is still a problem because of the manner of manufacture. This work investigates the possibility of utilizing printed circuit board (PCB) technology to manufacture coaxial transformers and to increase the accuracy with which the desired leakage inductance may be obtained. Finite element methods (FEM) as well as experimental results are used to support the proposed ideas. A planar transformer is also analyzed in the same way to accentuate the design advantages offered by the proposed quasi-coaxial transformer

Numerical simulation of the magnetization of high-temperature superconductors: 3D finite element method using a single time-step iteration

We make progress towards a 3D finite-element model for the magnetization of a high temperature superconductor (HTS): We suggest a method that takes into account demagnetisation effects and flux creep, while it neglects the effects associated with currents that are not perpendicular to the local magnetic induction. We consider samples that are subjected to a uniform magnetic field varying linearly with time. Their magnetization is calculated by means of a weak formulation in the magnetostatic approximation of the Maxwell equations (A-phi formulation). An implicit method is used for the temporal resolution (Backward Euler scheme) and is solved in the open source solver GetDP. Picard iterations are used to deal with the power law conductivity of HTS. The finite element formulation is validated for an HTS tube with large pinning strength through the comparison with results obtained with other well-established methods. We show that carrying the calculations with a single time-step (as opposed to many small time-steps) produce results with excellent accuracy in a drastically reduced simulation time. The numerical method is extended to the study of the trapped magnetization of cylinders that are drilled with different arrays of columnar holes arranged parallel to the cylinder axis

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

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

A Perturbation Finite Element Technique for Modeling Electrostatic MEMS

Projet ARC (Convention 03/08-298, “Modélisation, Simulation Multiphysique et Optimisation de Problèmes Couplés - Application aux Micro-Systèmes Électromécaniques (MEMS)”

Remake of a Magento web store content management system into system for employees\u27 attendance tracking

Diplomska naloga obsega predelavo Magento sistema za upravljanje vsebin spletne trgovine v sistem za evidenco dela zaposlenih. V prvem delu diplomskega dela so najprej predstavljeni razlogi za izbor Magento sistema, prikazane pa so tudi nekatere ze obstojece spletne resitve za evidenco dela zaposlenih. Sledi predstavitev Magento sistema, oziroma princip delovanja njegove MVC arhitekture. Nato sledi opis orodij, s katerimi je izdelan Magento sistem, ter opis orodij, ki smo jih dodali za ucinkovitejse in uporabniku prijaznejse delovanje nasega sistema za evidenco dela. V drugem delu je opisan postopek izdelave, ki se zacne s postopkom redukcije Magento sistema, v bolj splosen sistem za razvoj spletnih aplika- cij. S pomocjo primera implementacije glavnega modula, ki sluzi sistemu za evidenco dela zaposlenih, prikazemo razvoj modulov v Magento sistemu in predstavimo tudi primer razsiritve obstojece funkcionalnosti Magento sis- tema. Sledi se opis vseh ostalih funckionalnosti, ki smo jih implementirali za sistem za evidenco dela, ter opis izdelave dizajna, ki poskusa slediti najno- vejsim trendom pri razvoju spletnih aplikacij. V zadnjem delu pa so predstavljeni cilji nadaljnega razvoja aplikacije, kjer nekateri temeljijo na ze obstojecih funkcionalnostih Magento sistema.This thesis comprises a rework of the Magento e-commerce content manage- ment system into an employee attendance tracking system. In the rst part of the thesis the reasons for selecting Magento system are presented and also some already existing web solutions for employee attendance tracking are shown. Next is the presentation of the Magento system, that is, principles of its MVC architecture. After that follows the description of the tools on which Magento is based upon and some of the tools we used to make our employee attendance tracking software better. The second part describes the development process, which starts with the reduction of the Magento system, to a more general system for web based application development. With the help of the implementation process of our main module, which serves the purpose of the employee attendance tracking system, we describe the module development process in Magento system and present an example of extending a core functionality. Next, the presentation of the remaining functionalities implemented for our employee attendance tracking system follows, and the description of the design, which attempts to follow the newest trends in web application development. In the last part we present the goals of the future development of the application, where some of them are based on already existing functionalities of the Magento system

Progressive Models of Current Sources for the Magnetic Vector Potential Finite Element Formulation

peer reviewedProgressive refinements of the current sources for the magnetic vector potential finite element formulation are done with a subproblem method. The sources are first considered via perfect magnetomotive force or Biot-Savart models up to their volume finite element models, from statics to dynamics. Conversions of the common volume sources to surface sources are first done to lighten the computational resources. Accuracy improvements are then efficiently obtained for local currents and fields, and global quantities, i.e. inductances, resistances, Joule losses and forces

Perturbation Finite Element Method for Efficient Copper Losses Calculation in Switched Reluctance Machines

Copper losses dissipated in the windings of electric machines are the sum of classical ohmic dc losses and additional ac eddy current losses. In fact, the level of eddy current losses is strongly correlated with the manner of disposition of coil conductors in machine slots. Then, to improve the efficiency in electric machines, the selection of an optimal winding configuration becomes substantial. Since eddy current losses derive from the strong electromagnetic coupling between current density and time-dependent magnetic field, which cannot be solved easily, numerical analyses, such as particularly the one using the finite element (FE) method, are often used. As for the FE modeling, it can employ moving band technique to perform the rotor motion and Newton-Raphson iterations to deal with the nonlinear behavior of magnetic circuits. It leads then to a substantial computational time that hinders any process of conception or optimization of winding geometries. To overcome this issue, a 2-D FE model reduction based on the perturbation method is proposed. It starts from one approximate FE solution of a simplified complete machine modeling to find fast but accurate solutions in slots subdomains when any variation of geometrical or physical data occurs. It allows adapting nonconforming meshes and provides clear advantages in repetitive analyses when we search the optimized winding configuration for a given number of turns. © 1965-2012 IEEE