Mitigation of Circulating Currents in Parallel Foil Windings for Medium Frequency Transformers

Abstract

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Design Trade-Off Analysis of Dry-Type Medium Frequency Transformers with Parallel Foil Windings

“…while 𝑣 𝑐 is the total volume of the core, and the specified material properties used in (7) are given in Table . 2.…”

“…However, the circulating currents between asymmetrical parallel-wound foil winding can cause multiple times higher loss inside the windings. In [7], we investigated the presence of circulating currents in parallelwound MFTs. The study showed high ratio of phase and S. Pourkeivannour, M. Curti, and E. A. Lomonova are with Eindhoven Technical University, Electrical Engineering Department, Eindhoven, the Netherlands (e-mail: s.pourkeivannour@ieee.org).…”

“…Drofenik is with ABB Corporate Research Center, Baden, Switzerland. The circuit topology for parallel-wound foil MFTs [7] Thus in this study we address the advantages and the challenges of utilizing parallel foil windings in the design of MFTs. In addition, the choice of conducting material is evaluated by hiring copper and aluminium foil conductors.…”

“…Fig.1a) The structure of a modular ISOP SST, b) The circuit topology for parallel-wound foil MFTs[7] …”

Hybrid Foil-Litz Windings for Highly Efficient and Compact Medium-Frequency Transformers

“…The price for these advantages is the use of more complex and therefore more expensive conductors and core materials to keep the frequencyinduced losses in an acceptable range. In this respect, the conductor choice is constrained among foil or litz wire, e.g., [11]- [14]: litz wire is disfavored by the reduced filling factor, the limited availability and the elevated cost, whereas foil conductor exhibits additional ohmic losses due to the so-called "current crowding" or edge effect, caused by the deformation of the magnetic field due to the insulation clearance to the core [15]. Foil windings exhibit a uniform voltage distribution in the case of steepfronted PWM voltages [16], which is advantageous for MV SST applications; however, the electric field hotspots at the foil winding corners limit the insulation rating [17].…”