Doctorandus/a PhD student

Name: Carlos A. Valdivieso


KU Leuven

Promotor / Supervisor

Supervisors: Ruth V. Sabariego & Gérard Meunier

Samenvatting van het onderzoek / Summary of Research

Introduction / Objective
This thesis focuses on the development of mathematical models to calculate electromagnetic fields in foil and stranded windings. It aims at devising finite-element formulations that consider the whole stack/bundle of conductors as a periodic homogenizable structure. By doing so, affordable simulations with sufficient accuracy are intended as the research outcome; since traditional finite-element models remain too computationally expensive to be practical software tools.

Research Methodology
The proposed models are established upon the well-known Maxwell’s equations. In such models, the eddy-current and parasitic capacitive effects are estimated without the explicit representation of each winding turn in the geometry/mesh. Between the magnetic and electric fields, the strong coupling is neglected to allow a separate estimation of the eddy- current (resistive and inductive) effects and the capacitive effects. The full wave models accounting for the wave propagation are out of the scope of this thesis. Homogenized formulations are developed to treat the following cases:
1. Eddy-current effects in foil windings
2. Eddy-current effects in stranded windings
3. Capacitive effects in stranded windings

Results & Conclusions
It is possible to accurately estimate the eddy-current and capacitive effects with homogenized finite-element models. Their accuracy depends on different factors e.g., the frequency of operation. By way of validation, the results of all homogenized models are compared to those obtained by accurate but expensive reference finite-element models wherein all turns are explicitly discretized.
Figures (a) and (b) show a zoom of traditional finite-element meshes for foil and stranded windings, respectively; whereas Figure (c) presents the homogenized counterpart. A comparison of the Joule losses vs time between reference “r.” and homogenized “h.” models is shown in Figures (d) and (e). Figure (d) concerns a 20-turn foil winding inductor excited at 200 Hz, 2 kHz and 20 kHz; while Figure (e) pertains to a 128-turn stranded inductor where the homogenized losses are further divided into the skin and proximity effects contributions.

Afbeelding a, b & c

Afbeelding dAfbeelding e