Design of a 75kW Three-Level DC/DC GaN Converter for Automotive Fuel-cell Application

Nowadays, fuel cells represent a promising alternative to replace battery packs for electric vehicles where weight is a concern or where electrical charging is not possible. With respect to a battery pack, built up to 800V, the output voltage of fuel cell stacks is rather low (typically below 200V) and also it is strongly dependent on the load current. Therefore, the integration of a fuel cell in an electrical powertrain needs a DC-DC converter that must exhibit high efficiency and power density. Therefore, this paper presents the design and optimization of a 75 kW, multi-level DC-DC converter leveraging the benefits of the gallium-nitride (GaN) power devices and on the ceramic technology for the capacitors. The paper presents results regarding the GaN device selection with loss analysis, the DC link capacitor sizing and the design of magnetic components. The estimated power density of the converter is 41.7kW/L with a 99.1% overall maximum efficiency.