The old saying says good things come in small packages. Google and the Institute of Electrical and Electronic Engineers (IEEE) seem to agree having launched the Little Box Challenge, an open competition with a US$1 million first prize to find innovative electronic designs to shrink power inverters down from their current bigger-than-a-bread-box size to something less than the size of a small laptop.

A power inverter is a device that converts the direct current (DC) electricity stored in batteries to alternating current (AC) electricity that most of the electrical devices around our homes consume. In this case, the challenge requires entrants to use 450 volts DC – a common voltage used in multi-battery solar panel or wind turbine systems – and convert it to domestic 240 volt AC capable of supplying 2 kW of power. But size is key, with a power density of at least 50 watts per cubic inch required to make the cut.


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Reducing the size of inverters to something more manageable – at around 40 cubic in (655 cubic cm) – will make them cheaper to manufacture. In this way, the ultimate vision for the competition is to expand the use of solar power in homes, lead to more efficient distributed electrical grids and help bring electricity to remote areas.

However, reading the fine print reveals that any design also offer AC output of a quality that is as good or better than current run-of-the-mill inverters. For example, the AC frequency total harmonic distortion (how well the unit replicates, for example, a standard AC power supply sine wave) of any inverter competing in the challenge needs to be less than 5 percent and have a power factor efficiency (that is the difference between the input power and the output power) greater than 95 percent.

These are figures that stable computer power supplies are expected to achieve and, given that the inverter must be capable of delivering around 2 kW of power, this results in a power density of at least 50 W per cubic inch, which is a very ambitious target indeed.

Other equally difficult challenges include keeping any external surface of the device that can be easily touched – including air vents – at temperatures below 60° C (140° F), which with such tightly-packed components and relatively high wattages will be thermodynamically challenging to say the least. And to make it even more difficult, the competition specifically forbids any external cooling methods, such as water circulation, to be used.

Google believes that the newly available range of wide band gap (WBG) semiconductors, such as Gallium Nitride (GaN) and Silicon Carbide (SiC) will likely be the best type of devices to incorporate in the designs and is actively promoting their use. Google has provided a list of WBG device manufacturers who have web pages describing their technology which will detail how these devices may give contestants an advantage in the competition. The sites will also detail a way of getting hold of some of their semiconductors for use in competition inverters.

If you think that you can design and build an inverter that meets these and other specifications, the deadline for entering the challenge is September 30, 2014, with full technical and testing application details to be supplied by competitors by July 22, 2015.

Up to 18 submissions will be considered for the final stage of testing and the competitors will be required to bring their inverters in person to a testing facility in the US by October 21, 2015. After a raft of assessments conducted in over 100 hours of testing, and as determined by a panel of judges, the individual or team design that best meets the brief will be announced the winner.

Google Research is also making a limited number of awards available to academics in concert with the prize and applications may be made at the Research Google Website.

All going to plan, the grand prize winner is expected to be announced in January, 2016.

Source: Little Box Challenge

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