A Critique of Little Box Challenge Inverter Designs: Breaking from Traditional Design Tradeoffs

Since the introduction of wide-bandgap (WBG) power semiconductor devices, high power density (PD) inverter design has become an increasingly popular topic in modern research literature. The 2014-2015 Little Box Challenge (LBC) cosponsored by Google and the IEEE sparked even more interest in this area because WBG-based designs aspired to achieve upward of 215-W/in
³
power densities. This article reviews several key topics of importance that are related to realizing such high PD gallium nitride (GaN) WBG-based inverter designs. More specifically, this article includes a comprehensive survey of technologies employed by participating LBC finalists in their efforts to achieve new levels of PD in 400-Vdc to single-phase 240-Vac conversion applications while maintaining tight specifications on dc ripple, ac ripple, and aggressive requirements on efficiency. Both singlephase dc-to-ac conversion and the related active energy buffer circuit topologies used by all LBC finalists are documented and compared. Additionally, a graphical trend line and figure of merit (FOM) are developed that compare PD vis-?-vis efficiency of all proposed solutions. These are used to gain insight into how particular designs were able to achieve relatively higher PD levels and to illustrate how the GaN-based design from the University of Illinois at Urbana-Champaign (UIUC) was able to achieve the highest density power conversion in this competition. Furthermore, enhanced auxiliary devices and techniques used in the CE+T and Virginia Tech (VT) designs are discussed as well.