A Flexible Four‐Switch Buck–Boost Converter With an Integrated Planar Litz Inductor and Nanocrystalline Magnetic Sheets

ABSTRACT

Flexible and conformal electronic systems require dc–dc converters that combine high efficiency, low profile and flexibility. However, in high‐frequency flexible converters, magnetic components usually dominate thickness, stiffness and loss and the coupled tradeoff among switching frequency, magnetic design and system efficiency remains insufficiently explored. This article presents a flexible four‐switch buck–boost converter featuring an integrated planar Litz inductor and nanocrystalline magnetic sheets. A single‐inductor four‐switch buck–boost topology is adopted to reduce magnetic‐component count and facilitate planar realisation. To improve high‐frequency performance under thickness and flexibility constraints, a dual‐layer interleaved planar Litz winding is developed to suppress AC winding loss, while flexible nanocrystalline powder‐composite magnetic sheets are introduced to enhance inductance and guide magnetic flux. In addition, a frequency‐oriented design method is established by treating switching frequency as the key optimisation variable and a system‐level loss model is developed to jointly optimise the magnetic structure and operating point. A hardware prototype is fabricated and evaluated at 30 V input, 15 V output and 102 W buck operation. Experimental results show that the integrated magnetic structure increases the inductance from 4.6 to 5.95 µH and the prototype achieves a peak efficiency of 92.91% at 300 kHz, validating the proposed design strategy.