A Novel Hybrid Magnetic Core Structure for Planar Medium-Frequency Transformer

This letter proposes a novel planar hybrid magnetic core structure to address the significant eddy current loss issue of nanocrystalline (NC) laminated core in medium-frequency and high-frequency transformers. The proposed approach mitigates eddy current losses caused by flux components perpendicular to the nanocrystalline cores by introducing ferrite cores that redirect these flux components. The hybrid core structure was validated with a planar transformer with rectangular coils subjected to PWM-wave excitation from 200V-600V and 20–200 kHz. Compared with the NC-only design, the hybrid core structure demonstrates a 26.7% loss reduction under 600 V/20 kHz excitation, along with improved uniformity in flux density and temperature distribution. This approach is also validated over a wide frequency range (20–200 kHz) at a fixed voltage amplitude of 200 V, where the loss reduction increases with frequency, reaching 47.8% at 200 kHz. Moreover, the proposed hybrid structure also demonstrated its effectiveness in a planar transformer with Double-D (DD) coils at 200 V, achieving more than 50% core-loss reduction in the 50–200 kHz range compared with the NC-only design.