This work presents a miniaturised 1 kW three-phase LLC resonant converter for aircraft, converting 270 V DC to 28 V within a half-brick and targeting over 20 kW/L. Three stacked half-bridges divide device stress and gain by three, while a wye-delta transformer adds a √3 step-down, so most voltage reduction is achieved topologically rather than by extreme turns ratios. With GaN devices, planar three-phase magnetics and synchronous rectification, the prototype operates at 1.0–1.4 MHz, achieves 96.5% peak efficiency, and exhibits low input/output ripple that cuts required capacitance. The paper outlines FHA-based design and iterative optimisation of Lr, Cr and Lμ, balanced three-column magnetics for planar cores, and layout-driven losses. Two hardware prototypes validate feasibility; the GaN rectifier version shows improved thermal headroom. The approach addresses MEA constraints on isolation, EMI and volume, and charts a path to 20 kW/L modules.
