IEEE Spectrum July, 2017 - 40

highly variable, two-way flow of electricity between, say,
a microgrid and the main grid. What's more, these smart
transformers can be modular, making them easy to transport and install. And they can be significantly smaller than
an equivalent conventional transformer-with as little as
about half the weight and a third the volume.
In the near term, SSTs could be a boon for disaster-recovery
efforts in places with damaged electrical infrastructure and
for settings such as naval vessels, where volume and weight
are at a premium. Further in the future, they
could redefine the electrical grid, creating distribution systems capable of accommodating
a great influx of renewable and stored energy,
dramatically improving stability and energy
efficiency in the process.

jul 2017

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Alternating-current networks rely on voltages in the hundreds of thousands of volts to
transmit power over long distances. But as
the current gets closer to its loads, the voltage needs to come down again. Thus transformers are used
throughout the grid, to step up the electricity exiting a power
plant to a high voltage so that it can be transmitted with great
efficiency, and to step it down at the distribution end, to the
levels appropriate to power factories, businesses, and homes.
Although the transformer has been improved many times
over the years, it is essentially a 19th-century technology,
one that takes advantage of simple principles of electromagnetism. In the most basic version, two coils are wound
around a magnetic core. Because the alternating current
going through one coil of wire-the primary-varies with
time, it produces a magnetic field in the core that also var-

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It would be hard to overstate the importance of transformers in our electrical networks. They're literally everywhere:
on poles and pads, in substations and on private property, on
the ground and under it. There are probably dozens in your
neighborhood alone. It's hard to imagine a world without
them. But my colleagues and I are doing just that.
In the distribution system, transformers typically take
medium, or "primary," voltages measured in the thousands
of volts and convert them to secondary voltages-such as 120,
240, or 480 volts-that can be safely delivered
to homes and businesses all over the world.
It's an approach that's been used since before
alternating current won the war of currents
in 1892. It is difficult to name another electrotechnology that has survived as long.
Nevertheless, it is time to start thinking
beyond the conventional transformer. For
one thing, transformers are bulky. They're
often cooled with oil, which can leak and is
difficult to dispose of safely. Crucially, transformers are passive, one-way tools. They aren't designed to
adjust to rapidly changing loads. This shortcoming will fast
become intolerable as distributed power sources such as
wind turbines, solar panels, and electric-vehicle batteries
feed more and more energy to the grid.
Happily enough, research into a new kind of technology-
one that could address all of these limitations-has been
making significant strides. Thanks to recent advances in
power electronics, we can now contemplate building smart,
efficient "solid-state transformers," or SSTs. They promise
to handle tasks that are difficult if not impossible for a conventional transformer to accomplish, such as managing the

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Table of Contents for the Digital Edition of IEEE Spectrum July, 2017