Thomas Ewald


Last Name

Ewald

First Name

Thomas

ORCID

0000-0002-0147-967X

Organisational unit

03889 - Biela, Jürgen / Biela, Jürgen

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2021 - 202616
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Publications1 - 10 of 16
  • High-Frequency Inductors using an Air Gap Fringing Shield: Cost-effective Design without Litz Wire
    Item type: Conference Paper
    Ewald, Thomas; Jeong, Min; Taha, Yildiz; et al. (2025)
    PCIM Conference 2025 - International Exhibition and Conference for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management
    In converter systems with inductors carrying a current waveform with non-negligible high-frequency components, increased HF losses occur. In case of gapped inductors, this increase is mainly due to the impact of the magnetic fringing field emanating from the air gap. Recently, a conductive shield to reduce these losses has been proposed. While losses in the shield itself occur, the HF winding losses are reduced significantly. This article compares the concept based on a conductive shield in various application scenarios with conventional inductor designs. The designs are compared regarding overall losses, temperature rise, volume & weight, and costs.
  • Modelling of the Hotspot Temperature in Gapped Single Layer Inductor Windings Using a Conductor Homogenisation Technique
    Item type: Conference Paper
    Ewald, Thomas; Elmiger, Lukas; Korthauer, Bastian; et al. (2025)
    PCIM Conference 2025 - International Exhibition and Conference for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management
    In gapped inductors, which are often operated at high frequencies, the magnetic fringing field emanating from the air gap induces local eddy currents in the windings. Macroscopically, this leads to significantly increased overall winding losses of the component. Microscopically, the local eddy current losses also lead to a locally increased loss density in the conductors, which leads to a thermal hotspot in the conductors in close vicinity to the air gap. This article explores this currently unexplored phenomenon in terms of measurements, analytical modelling and FEA analyses. In order to enable faster 3D FEA analyses, this article presents an analytical method to homogenise the circular conductors, that is capable of reducing the computational cost of intensive 3D FEA eddy current simulations by over 90 %.
  • Analytical Time Domain Eddy Current Loss Model for Simple 2D Conductor Geometries and Arbitrary Exciting Waveforms
    Item type: Journal Article
    Ewald, Thomas; Biela, Jürgen (2026)
    IEEE Transactions on Magnetics
    This article addresses the limitations of conventional frequency domain eddy current models for loss modeling under non-sinusoidal excitation and especially under a priori unknown and arbitrary exciting waveforms. A novel approach is presented, deriving a time domain eddy current loss model that provides a general solution for arbitrary exciting waveforms and closed-form analytical solutions for certain simple conductor geometries (e.g., round and rectangular). The model separates the spatial and temporal dependencies of the eddy currents, enabling the analysis of transient phenomena and visualisation of dynamic current redistribution. An efficient cumulative integration algorithm is presented for the computation of the time dependency. This makes the method particularly well suited for power electronics, where it can be applied to compute time domain phenomena in the conductors of inductor or transformer windings, either for analysing specific effects or in circuit simulations. Here, the cumulative step-wise algorithm enables very high computational efficiency. The proposed methodology offers a powerful tool for understanding and predicting eddy current behavior with potential extensions to core loss modeling.
  • Analytical winding loss and inductance models for gapped inductors with Litz or solid wires
    Item type: Journal Article
    Ewald, Thomas; Biela, Jürgen (2022)
    IEEE Transactions on Power Electronics
  • Frequency-dependent inductance and winding loss model for gapped foil inductors
    Item type: Journal Article
    Ewald, Thomas; Biela, Jürgen (2022)
    IEEE Transactions on Power Electronics
    For comprehensively optimizing high-frequency foil wound inductors, the calculation of the increased inductance and the additional eddy current losses due to a two-dimensional fringing field caused by air gaps in the center leg is mandatory. This paper proposes an analytical model to accurately calculate the inductance and the additional eddy current losses in gapped inductors with foil windings. The analytical field expressions are combined into closed form conduction loss and inductance formulas and are verified by measurements. The frequency dependency of the inductance due to the shielding effect of the foil conductors is discussed.
  • Modelling Framework Architecture for Converter Optimisation and Virtual Component Prototyping
    Item type: Conference Paper
    Ewald, Thomas; Krismer, Florian; Biela, Jürgen (2024)
    2024 Energy Conversion Congress & Expo Europe (ECCE Europe)
    Comprehensively optimising electric converter sys tems for a specific application remains a significant challenge, since no unified modelling environment exists that is capa ble of combining the required models effectively for system optimisation. The main problems still existing are a lack of modularity, flexibility, unified interfaces, and expandability of existing architectures, when it comes to combining the existing individual calculation models of a converter system. This article introduces a comprehensive converter modelling framework that implements a converter system as a virtual prototype, allowing for separate and holistic system calculations based on this concept. Moreover, the architecture is modular, enabling the definition and separate optimisation of subunits and individual components. In addition, the framework offers flexibility by enabling its expansion through new converter and component virtual prototypes.
  • Frequency-Dependent Equivalent Circuit Parameter Calculation of Gapped Multiwinding Inductors
    Item type: Conference Paper
    Ewald, Thomas; Schlesinger, Richard; Agner, Jan; et al. (2022)
    2022 International Power Electronics Conference (IPEC-Himeji 2022- ECCE Asia)
    Accurate and fast models of the equivalent circuit elements of gapped multiwinding inductors are essential to design galvanically isolated converters such as the Flyback converter and the LLC-converter. This paper derives equivalent circuit parameters of gapped multiwinding inductors from 2D magnetic field models proposed in this paper. It is shown and quantitatively examined that frequency affects resistance and inductance values of magnetically coupled windings by several effects. Especially eddy currents in windings induced by the air gap field play a significant role besides the well known skin- & proximity effect. The proposed model accurately takes into account all these effects in foil- and round wire conductors. The model is verified with FEM simulations and measurements.
  • Analytical eddy current loss model for foil conductors in gapped cores
    Item type: Conference Paper
    Ewald, Thomas; Biela, Jürgen (2021)
    2021 23rd European Conference on Power Electronics and Applications (EPE'21 ECCE Europe)
    For modelling and optimizing gapped high-frequency inductors, the calculation of eddy current losses in foil windings due to the two-dimensional fringing field caused by air gaps in the core is important. The winding loss models must offer a high accuracy when calculating the 2D field distribution and must be computationally efficient in order to enable several thousand calculations required during the optimization. This article proposes an analytical model based on the magnetic vector potential formulation that can predict the eddy current losses in foil windings due to the fringing field of an arbitrary number of air gaps. The analytical model is combined into a closed-form loss formula and verified by FEA simulations.
  • Analytical model and concept study of an air gap fringing shield to reduce losses in gapped inductors
    Item type: Journal Article
    Ewald, Thomas; Biela, Jürgen (2024)
    IEEE Transactions on Power Electronics
    The impact of the magnetic fringing field emanating from the air gap in gapped inductors on the high-frequency losses has been known for a while. While most research focuses on accurately calculating these losses, attempts to reduce them through suitable measures are rare. This article investigates a concept that uses a fringing field shield to attenuate the fringing field at higher frequencies, thereby reducing losses in the winding. With this approach, losses in the shield itself occur, but the overall winding losses are reduced by 24% for an inductor subjected to a current waveform with a mixed harmonic spectrum and a dominant low-frequency component. The concept is proven using a manufactured prototype.
  • Eddy currents in rectangular conductors: Analytical 2D loss model in the context of magnetic component design
    Item type: Conference Paper
    Ewald, Thomas; Biela, Jürgen (2023)
    2023 25th European Conference on Power Electronics and Applications (EPE'23 ECCE Europe)
    The calculation of high-frequency winding losses caused by eddy currents in solid conductors with circular cross-section has already been discussed sufficiently often. However, there is currently no such treatment for conductors with rectangular cross-section in literature. In this article such a model is presented, which is based on a simplified two-dimensional formulation for the magnetic field inside conductors with rectangular cross-section. Similar to existing circular conductor models, the formulation is linked to an external, magneto-quasi-static field in the core window by means of boundary conditions, which makes it possible to a certain degree to calculate the frequency-dependent eddy current losses.
Publications1 - 10 of 16