High-power-density, GaN-based Interleaved Buck dc-dc Converter for 1 kW Brick Modules with 99 Percent Efficiency
The 48V intermediate bus converter (IBC) is widely used in telecom, wireless, and aerospace applications. With increasing demand in power by the load, there is a need for higher-power converters with high power densities and high efficiencies. The use of gallium nitride (GaN) de-vices allows the converter to run at higher switching frequencies with lower loss. At higher switching frequencies, the magnetics are smaller; if planar magnetics are used, the power density and efficiency can be increased. Fig. 1 shows the proposed topology for the 48 V IBC, a two-stage multi-phase buck converter followed by an LLC-DCX. The buck converter provides regulation, and the LLC-DCX provides isolation for the two-stage converter. The buck converter regulates a variable input of 40 V-60 V to 36 V at the bus at 1 kW. By using an interleaved buck converter, the conduction and switching losses can be de-creased. The overall two-stage converter needs to have both high efficiency and power density, so the area of the buck converter is limited to 30x35x7 mm. Based upon the footprint limitations and preliminary size of the inductor, the most optimal topology for the buck converter is a four-phase interleaved buck converter with two separate coupled inductors. The efficiency and power density of the buck converter will be determined by the design of the coupled inductor. Fig. 2 shows the result of the optimization process for the magnetic design. By starting with the footprint and inductance, all of the losses for the entire buck converter can be calculated. The estimated efficiency versus the power density can be plotted, and then a design point can be chosen. A prototype buck converter has been built and tested, and is shown to achieve 98.5 % efficiency. The two-stage converter has also been assembled and tested. The two-stage converter was able to achieve 96 % efficiency with a power density of 680 W/in3, which is higher than the current state-of-the-art two-stage 48 V IBC.