Work

Unbalanced-Flux Concept for High Power Density Magnetics and Review of the MHz LLC Transformers

Year: 2025

Type: article

Abstract: High-power-density magnetics are often designed through the MHz-frequency approach, but this method is constrained by excessive core losses, which restrict operation to very low magnetic flux density B, typically lower than 70 mT. Since magnetic power scales with the square of B, this fundamentally limits achievable power density. In practice, the average power density of state-of-the-art MHz magnetic designs remains around 70 W/cm³, far below the requirements of emerging applications. To overcome these limitations, we propose the unbalanced-flux concept, a new magnetic architecture that replaces the traditional balancedflux design paradigm. This approach reduces core loss by approximately 70%, enabling operation at substantially higher B. As a result, the concept achieves a threefold increase in power density compared to MHz-based designs. The approach is experimentally validated in a 1 kW, 380 V/48 V LLC transformer prototype. With natural air cooling, the transformer delivers 750 W at a record 224 W/cm³. With a heatsink, it achieves 190 W/cm³ at 1 kW, with a peak efficiency of 94.6%. These results demonstrate that unbalanced-flux magnetics provide a scalable pathway beyond the MHz, low-B limitations toward the next generation of ultra-high-power-density magnetic components.

Source: IEEE Open Journal of the Industrial Electronics Society

DOI: 10.1109/ojies.2025.3609214

Authors: Sobhi Barg, Adane Hailu, Souhaib Barg, Kent Bertilsson

Institutions: Université Centrale de Tunis, Mid Sweden University

Language: English

Topic: Advanced DC-DC Converters

Subfield: Electrical and Electronic Engineering

Field: Engineering

Domain: Physical Sciences

SDGs: Affordable and clean energy, Industry, innovation and infrastructure

Open Access status: gold

Estimated APC paid: $2,075