Opening the box: Survey of high power density inverter techniques from the little box challenge

The Little Box Challenge (LBC) was a competition sponsored by Google and the IEEE Power Electronics Society in 2014-2015, where participants were challenged to design a high power-density single-phase 2 kVA inverter. This paper surveys the designs from eight different participating teams, including academic grant awardees, finalists, and the winners. Inverter topologies, power decoupling circuits, and thermal management strategies are overviewed for each team. Wide bandgap switches were heavily utilized in both the inverter and power decoupling circuits, particularly GaN switches. Most teams utilized a full-bridge inverter with some variations and the most common power decoupling strategy was the use of a synchronous buck converter and a power buffering capacitor. One team used a multi-level inverter approach and a number of teams proposed innovative power decoupling topologies. Heat sinks and active cooling systems, many of which were custom made, were crucial for teams to stay within the 50 °C case temperature limit. The resulting power density of the surveyed teams ranged from 55.8 to 216 W/in3, all of which exceed the 50 W/in3 LBC requirement. This paper surveys the approaches for various teams, shares experimental results from the Taiwan Tech team, and highlights some innovations from the teams that participated in the LBC.