Design of a 75 kW Three-Level DC/DC GaN Converter for Fuel Cell Electric Powertrains

Fuel cells are increasingly recognized as a viable alternative to traditional battery packs in electric vehicles, particularly for applications requiring reduced weight and extended range. Despite their advantages, the low and load-dependent output voltage of fuel cell stacks (typically below 200 V) requires high-efficiency boost DC-DC converters to achieve the DC voltage required by the traction inverters, usually in the range 400 V to 800 V. In this context, gallium nitride (GaN) technology enables switching frequencies exceeding 100 kHz, making it a prime candidate for power converters having high power density. This paper presents the design and experimental validation of a 75 kW interleaved multilevel DC–DC boost converter based on GaN power devices, developed to interface fuelcell stacks with 800 V traction inverters. Detailed characterization of the GaN switches is performed via doublepulse testing to properly evaluate the switching losses. This information is used for the thermal design of a liquidcooled heat sink ensuring safe operation below a 150 ∘C junction temperature. Magnetic design includes differential and commonmode inductors finiteelement analysis to meet ripple and powerdensity constraints. The DClink capacitor bank employs PLZT ceramic capacitors to minimize volume and losses. The assembled prototype achieves a volumetric power density of approximately 21 kW/L and a gravimetric density of 15 kW/kg. Dynamic load tests demonstrate a peak efficiency of 98.7% and robust current sharing and capacitor voltage balancing across all operating conditions.