Technical paper: How we designed our Google Little Box Challenge-type micro inverter

Olivier Bomboir was invited to present CE+T Power’s technical paper on micro inverters at Intelec 2016, in Austin (Texas, USA).

Robert Eyben and Olivier Bomboir at Google & IEEE Little Box Challenge award ceremony

Robert Eyben and Olivier Bomboir at Google & IEEE Little Box Challenge award ceremony

Abstract – Inverters currently designed for home use are typically only the size of a picnic basket, yet considered too large for their target environment. A size reduction would make them more attractive for domestic solar power applications, as well as for bringing power to remote areas of the world lacking distributed electricity. This project’s key goal was to reach an inverter power density above 50 W/cubic inch (3 W/cm3) in a volume of under 40 cubic inches – a feat which had never been previously achieved using current inverter technology based on a 4 IGBT H-bridge configuration.

Existing commercial products that meet telecom and industrial requirements achieve 98% peak efficiency with a power density of 17 W/cubic inch (1 W/cm3). Increasing the power density to reach a level close to 150 W/cubic inch (10 W/cm3) remains challenging because it is not easy to further improve the efficiency of such H-bridge topology.

Introducing GaN switches is insufficient to reduce the inverter volume. Accordingly, several H-bridge topologies have been evaluated, with the aim of operating the inverter output in ZVS mode at high frequency and reducing inductor size. GaN drivers with improved dV/dt tolerance were not yet available on the market, so new circuits based on existing dV/dt immunity had to be designed to sustain such conditions. New thermal approaches have been simulated and optimized to reduce heatsink sizes, where MLCC capacitors have been assembled in an innovative design to cool the overall system. GaN Systems’ GS66508P GaN power MOSFETs’ reduced gate drive and switching losses were critical to thermal and power density goals. A specific EMC emission has been applied to the common mode filter to minimize noise levels.

Keywords—Micro Inverter; ZVS; GaN; HEMT; High Efficiency

Here is his presentation: