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MIT blazes power electronics trail

Posted: 14 Aug 2014 ?? ?Print Version ?Bookmark and Share

Keywords:power? converter? conversion MIT?

Implementing this architecture, the prototype LED driver achieves a power factor (a measure of the waveform quality of the line currents) up around the rarely achieved EPA Energy Star recommendations for LED drivers. The driver also provides a power density five to 10 times that of current commercial systems.

Improved power density, in turn, allows minimising the volume of the inductors and capacitors, which normally are the largest component in such a power supply, so the prototype is much smalleranother major research goal.

"If you can make that LED driver smaller, you can open up a lot more area for heat transfer, which makes the whole system run better," Perreault points out. "Additionally, all things being equal, making it smaller and more integrated ultimately makes it cheaper, which will help these expensive products."

The power conversion technologies developed in the Perreault lab are key ingredients for the world's smallest laptop power adapter supply, created by the MIT spinoff company FINsix. Shipping this fall, FINsix's 65W Dart adapter weighs two ounces and is little bigger than an ordinary electrical plug. Other start-ups and established companies have also adopted and licensed technologies from his group to create innovative products.

Perreault and colleagues have achieved similar success in applying high-frequency switching techniques to greatly enhance the efficiency of radio-frequency power amplifiers. This work has led to the MIT spinoff company Eta Devices, co-founded by Perreault and former MIT associate professor Joel Dawson, which is commercially developing the technology to reduce power consumption for cellular base stations and handsets.

DC distribution in server farms

Some of the approaches used to achieve miniaturisation can be adapted instead to achieve ultra high efficiencies that also bring major paybacks for many applications in DC/DC power conversion, with computer server farms providing some examples.

As cloud-computing services mushroom, server farms are being built and operated on an immense scale worldwide, with more than 8 million servers sold annually, according to market research firm IDC, and with server farms consuming well in excess of 1 per cent of overall electrical energy usage globally.

The energy delivery in state-of-the-art server farms from grid to computation presently incurs substantial loss. Reducing power consumption through higher-efficiency power electronics will chop down electrical bills for servers, storage and communications systems, and for the air conditioning they require.

Many server-farm operators are moving towards DC distribution of power, either at high voltages or low voltages, because of the opportunity to eliminate some conversion stages, Perreault said.

Power distribution in server farms typically begins with three-phase AC, goes through uninterruptible power supplies to battery storage, is converted again to three-phase AC, then converted to DC, then stepped down to final DC loads. An alternative architecture that begins with 380V DC upfront can be more efficient, he explains.

This setup calls for very high efficiency DC/DC power converters, and Perreault's group has worked on sub-systems at several levels, including some that convert from 380V down to 12V, and others in the telecom voltage range of 48V.

These converters employ "soft-switching" techniques that are targeted at very high efficiencies of 97 per cent and above by trying to minimise the energy loss in every transition. The so-called resonant soft-switched converters explored in the Power Electronics Research Group are further architected to operate efficiently under different ranges of voltage and powerlike a bicycle that can shift gears to match its local terrain.

"If systems only had to operate at one voltage, or one power level, it would be relatively straightforward to get very high efficiency and density," Perreault explains. "But when either the voltage or power vary over a very wide range, it suddenly becomes very tricky to do that. We've developed a number of techniques aimed at maintaining high efficiency under these conditions."


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