After months of excitement and speculation, the results of the Google Little Box Challenge were recently revealed, and Chrysalix portfolio company GaN Systems was proud to learn that their gallium nitride power transistors were used in the winning design. The $1 Million prize, awarded by Google and the IEEE, went to Belgium’s CE+T’s Red Electrical Devils, for designing, building and demonstrating an inverter with the highest power density and smallest volume.
Why did Google launch a power electronics contest and award $1,000,000? Because the world’s unrelenting demand for more power is unsustainable without using fewer materials to manufacture and less energy to operate our electronic devices. And why inverters? Because inverters, which convert direct current (DC) from solar panels or batteries into the alternating current (AC) that is used to power homes, businesses, motors and cars, are a large user of materials and energy. As the organizers of The Little Box Challenge said to the engineers of the world, “Figure out how to shrink an inverter down to something smaller than a small laptop (a reduction of > 10X in volume) and smaller than everyone else, and you’ll win a million dollars (and help revolutionize electricity for the next century).”
The result was a great vindication for GaN – used by the vast majority of the entrants – and demonstrating that indeed a new generation of power transistors was needed to address future power conversion requirements.
The key goal of the challenge was to reach a power density in excess of 50 W/cubic inch in a volume of under 40 cubic inches. The competition was launched in Fall 2014, and while Google didn’t define the technologies to be employed, it was suggested that wide bandgap semiconductors would be the technology best able to meet the criteria.
All of the silicon carbide and gallium nitride companies were invited to make their products and information available to contestants and were listed on the Little Box website. This timing coincided with GAN Systems first parts becoming available in distribution, and as such the company’s GS66508P became the part of choice for many entrants, and a vast majority of the finalists used these parts. Over the next year Google registered over 2000 entrants for the contest. In October 2015, 18 finalists were selected and invited to Denver to submit their units for testing at the National Renewable Energy Laboratory (NREL) in Golden, Colorado.
Representatives of the supporting companies were also invited, and I was there to witness the proceedings. It was one of the most stimulating and enjoyable days I’ve had in a long time! The enthusiasm of the entrants and the level of innovation was truly amazing. There were thousands of hours of dedicated work behind every Little Box – some right up until the very last minute – and the ingenuity shown just astounding – in the topologies, magnetics, cooling and packaging as well as the semiconductors. I’m sure every design has moved the bar in ways we’ll see come to fruition in next generation production devices.
Each of the 18 boxes were left at the NREL for the next few months to undergo final testing. This testing was designed to simulate the rigors of a real-world solar inverter installation. The Google team reported that the first step was to verify that the inverters met all critical safety-related specifications and then to simply turn the inverters on and see if they functioned. Next, was a three-hour procedure to operate the inverters at a number of different operating points and to verify that key specifications were met throughout the test period. After these challenges, the field of 18 finalists was narrowed to the remaining inverters that would proceed to the third round.
Those final inverters were subjected to a 100-hour simulation of real-life conditions, including a direct-current source of electricity that emulated a solar power system, with rapid ramp-ups and ramp-downs in power typical of an intermittently cloudy day, as well as a realistic, changing load typical of a residence that the inverter needed to supply. Each inverter had to meet most of the same specifications required of commercially-available inverters. In the end, only three entries survived the testing and GaN Systems parts powered two of these. The winning inverter design from CE+T produced a power density of 143 W/cubic inch in 14 cubic inches, outperforming the Little Box Challenge power density goal by nearly a factor of 3, which, according to Google, “is 10 times more compact than commercially available inverters.”
The testing demonstrated several key factors about the benefits of GaN technology in inverter design. The winning inverter performed better on measurements of electromagnetic compliance, demonstrating that with the clean rise/fall performance of GaN Systems parts and their small GaNPX package, Electro-Magnetic Interference (EMI) is improved, contrary to early industry fears about gallium nitride’s performance in this regard. Contributing to the reliability of the winning entry was the fact the GaN junction temperature did not exceed 60 °C with an ambient temperature of 30 °C at 2 kW load, demonstrating the excellence of CE+T’s thermal design and the extraordinary efficiency of GaN switches.
Central to the team’s success were the GS66508P gallium nitride power transistors from GaN Systems, the leading manufacturer of GaN power devices. Commenting on the role that GaN transistors played in their design, team member Olivier Bomboir, VP of Product Management and New Business at CE+T Power, explained, “The use of GaN technology enabled our team to reach a power density of ~145 W/in³ for the 2 kVA inverter designed for this project. The reduced gate drive and switching losses of GaN Systems’ GS66508P were critical to our thermal and power density goals. Additionally, we were highly impressed at how reliably the devices performed over the months of rigorous, real-world testing by the NREL team.”
GaN Systems’ CEO Jim Witham, said, “We congratulate the winners for their ground-breaking accomplishment, and are very excited that GaN Systems’ products played a key role in helping the Red Electrical Devils win The Little Box Challenge. This achievement further confirms our belief that gallium nitride semiconductors will be instrumental in helping power design engineers respond to the ever increasing need to develop more efficient power conversion solutions. This technology clearly paves the way toward more powerful, compact and efficient inverter designs.”
Gallium nitride power switching devices are becoming a major factor in the constant quest for greater efficiency in power conversion. Roughly 10% of all the electricity generated around the world is lost as heat through inefficient power conversion. This waste can be reduced to around 1% through the use of GaN Systems proprietary and very high efficiency power conversion semiconductors, providing much higher performance at equal or lower cost.
Since the announcement of the contest and the initial availability of the winning devices, GaN Systems has gone on to expand its family of power switches. Based on its proprietary “Island Technology”, which allows for far greater power capabilities than traditional semiconductor layouts, the company has devices in both 100 and 650 Volt ranges that can switch over 100 Amps. These GaN transistors are now being used in power conversion systems for consumer, industrial and automotive applications, demonstrating dramatic improvements in size, cost and efficiency over previous silicon based solutions.