Magnetic material comparisons for high-current gapped and gapless foil wound inductors in high frequency dc-dc converters

Abstract

The inductor often drives the dc-dc converter size. Thus, the inductor optimization process is required for the most effective design. The paper presents inductor analysis only. The material properties are essential for the design size. In this paper, various magnetic materials are analysed and investigated for use in a practical design. The investigation is concerned with the magnetic material selection for a dc-dc power inductor in the medium (20 kHz) to high (150 kHz) frequency range. The materials under investigation are iron-based amorphous metal, silicon steel, nanocrystalline, ferrite, and gap-less powder materials. A lumped parameter algorithm is derived which includes such effects as the foil ac copper loss effects, the gap core loss, and the cooling path. The algorithm is implemented in EXCEL and generates material comparisons over a range of frequencies, ripple ratios, cooling paths. The results show that the core power loss limited inductor tends to be oversized while the minimum size is achieved for the design which is at the sweet-spot where the size is driven by the core power loss, winding power loss and core saturation limit. A 1.25 kW half-bridge dc-dc converter is built in order to proof the algorithm feasibility at the interest frequency range.