EPE Association: EPE 2020 - LS3b: Magnetics

EPE 2020 - LS3b: Magnetics
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2020 ECCE Europe - Conference > EPE 2020 - Topic 01: Devices, Packaging and System Integration > EPE 2020 - LS3b: Magnetics

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   Compact Core Loss Model Based on an Effective Frequency for Arbitrary Core Excitations Including DC-Bias
By Erika STENGLEIN [View]
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Abstract: To predict core losses for arbitrary excitations, the quasi-static energy losses depending on the swing and the DC-bias of the magnetic flux density are multiplied by an effective frequency. Measurement results for various shapes of the magnetic flux density (e.g. sinusoidal and triangular waveforms) with and without DC-bias verify this compact model.

   Enabling foil windings of medium-frequency transformers for high currents
By Thomas GRADINGER [View]
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Abstract: In foil windings of medium-frequency transformers rated for several hundred Ampères and operating at ten or several tens of kHz, parallel connection of foils is necessary to provide sufficient conductor cross-section. In this case, careful winding design is required to keep circulating currents among the foils under control. Such currents were investigated by means of an analytical model, a 2-d finite-element model, and measurements on a reduced-scale transformer for the case of two parallel connected foils. Simulations and measurements yield a consistent picture and show the potential of high extra losses in foil windings with unmitigated circulating currents. In particular, spiral windings of many turns may incur a circulating current that exceeds the useful net current by far if the inductance of the foil connections is small. Practically, it can be expected that the inductance of the foil connections leads to a noticeable reduction of the circulating current. This reduction, however, is not sufficient to bring the AC losses down to acceptable levels, such that it is recommended to transpose the foils between series-connected winding portions. Transposition largely cancels out the axial magnetic flux in the radial gaps between the parallel connected foils. The effectiveness of transposition in balancing the foil currents at frequencies up to 40 kHz is shown both theoretically and experimentally for aluminum foils of 0.2 mm thickness. With proper transposition, the extra AC losses due to circulating currents between foils can be reduced to practically negligible levels.

   Homogenization of Current Distribution in Parallel Connection of Interleaved Winding Layers of High-Frequency Transformers by Optimizing Distance between Windin
By Ryo MURATA [View]
[Download]

Abstract: The windings of high-frequency high-current transformers are required to reduce the proximity effect loss. Therefore, the Litz wire in parallel connection of interleaved winding layers is usually used as the winding of transformers. However, this can cause unbalanced AC current distribution, hindering effective reduction of the copper loss. This paper solves this problem by optimizing the distance between the winding layers based on the analytical principle called the extremum co-energy principle. The transformers used in the experiment to verify this method consists of three parallel-connected primary winding and two parallel-connected secondary winding, PQ core, thin polypropylene sheets for adjusting the distance between the winding layers. As a result, the copper loss can be recused by homogenizing the AC current distribution, and the effectiveness of this method has been clarified by experiments.

   Leakage Inductance Modelling of Transformers: Accurate and Fast Models to Scale the Leakage Inductance Per Unit Length
By Richard SCHLESINGER [View]
[Download]

Abstract: Fast and accurate transformer leakage inductance models are crucial for optimisation-based design of galvanically isolated converters. Analytical models are rapidly executable and therefore specially suitable for such optimisations. These analytical leakage inductance models typically consist of two steps: First, acquire the leakage inductance per unit length and second, scale this value with a suitable length. In this paper, the term leakage length is introduced for the scaling length. It is shown that the leakage length depends on the magnetic energy distribution and the most influential factors are determined. Furthermore, two accurate and fast leakage length models for E-core and U-core transformers with concentric windings are proposed: The Empirically Corrected Axial Flux (ECAF) model is based on a compact modification of the known axial flux formula. The cut line (CL) model pursues a semi-analytical approach and achieves high accuracy at the cost of higher computational effort. The models are verified with more than 6000 FEM simulations and the error of both models is significantly lower than the error of the known axial flux formula.

EPE 2020 - LS3b: Magnetics
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2020 ECCE Europe - Conference > EPE 2020 - Topic 01: Devices, Packaging and System Integration > EPE 2020 - LS3b: Magnetics
	[return to parent folder]

	Compact Core Loss Model Based on an Effective Frequency for Arbitrary Core Excitations Including DC-Bias By Erika STENGLEIN	[View] [Download]
Abstract: To predict core losses for arbitrary excitations, the quasi-static energy losses depending on the swing and the DC-bias of the magnetic flux density are multiplied by an effective frequency. Measurement results for various shapes of the magnetic flux density (e.g. sinusoidal and triangular waveforms) with and without DC-bias verify this compact model.

	Enabling foil windings of medium-frequency transformers for high currents By Thomas GRADINGER	[View] [Download]
Abstract: In foil windings of medium-frequency transformers rated for several hundred Ampères and operating at ten or several tens of kHz, parallel connection of foils is necessary to provide sufficient conductor cross-section. In this case, careful winding design is required to keep circulating currents among the foils under control. Such currents were investigated by means of an analytical model, a 2-d finite-element model, and measurements on a reduced-scale transformer for the case of two parallel connected foils. Simulations and measurements yield a consistent picture and show the potential of high extra losses in foil windings with unmitigated circulating currents. In particular, spiral windings of many turns may incur a circulating current that exceeds the useful net current by far if the inductance of the foil connections is small. Practically, it can be expected that the inductance of the foil connections leads to a noticeable reduction of the circulating current. This reduction, however, is not sufficient to bring the AC losses down to acceptable levels, such that it is recommended to transpose the foils between series-connected winding portions. Transposition largely cancels out the axial magnetic flux in the radial gaps between the parallel connected foils. The effectiveness of transposition in balancing the foil currents at frequencies up to 40 kHz is shown both theoretically and experimentally for aluminum foils of 0.2 mm thickness. With proper transposition, the extra AC losses due to circulating currents between foils can be reduced to practically negligible levels.

	Homogenization of Current Distribution in Parallel Connection of Interleaved Winding Layers of High-Frequency Transformers by Optimizing Distance between Windin By Ryo MURATA	[View] [Download]
Abstract: The windings of high-frequency high-current transformers are required to reduce the proximity effect loss. Therefore, the Litz wire in parallel connection of interleaved winding layers is usually used as the winding of transformers. However, this can cause unbalanced AC current distribution, hindering effective reduction of the copper loss. This paper solves this problem by optimizing the distance between the winding layers based on the analytical principle called the extremum co-energy principle. The transformers used in the experiment to verify this method consists of three parallel-connected primary winding and two parallel-connected secondary winding, PQ core, thin polypropylene sheets for adjusting the distance between the winding layers. As a result, the copper loss can be recused by homogenizing the AC current distribution, and the effectiveness of this method has been clarified by experiments.

	Leakage Inductance Modelling of Transformers: Accurate and Fast Models to Scale the Leakage Inductance Per Unit Length By Richard SCHLESINGER	[View] [Download]
Abstract: Fast and accurate transformer leakage inductance models are crucial for optimisation-based design of galvanically isolated converters. Analytical models are rapidly executable and therefore specially suitable for such optimisations. These analytical leakage inductance models typically consist of two steps: First, acquire the leakage inductance per unit length and second, scale this value with a suitable length. In this paper, the term leakage length is introduced for the scaling length. It is shown that the leakage length depends on the magnetic energy distribution and the most influential factors are determined. Furthermore, two accurate and fast leakage length models for E-core and U-core transformers with concentric windings are proposed: The Empirically Corrected Axial Flux (ECAF) model is based on a compact modification of the known axial flux formula. The cut line (CL) model pursues a semi-analytical approach and achieves high accuracy at the cost of higher computational effort. The models are verified with more than 6000 FEM simulations and the error of both models is significantly lower than the error of the known axial flux formula.