IEEE Power Electronics Magazine - December 2022 - 101

used a full-bridge rectifier in the
secondary one now had a converter
that could process power in either
direction (bidirectional conversion).
This led to the dual active bridge
(DAB) converter that is very popular
today in renewable energy systems.
The DAB provides a great way
to move power from a system bus,
like the outputs of an array of solar
cells, to charge a battery. When
needed that same converter, processing
power in the opposite direction,
can be used to transfer power
from the battery to the system bus.
Again we see that new devices
opened the floodgates to new developments
in switch mode power circuits
and topologies. But what next?
The MOSFET and IGBT came
into their own in the mid to late
1980s-over 30 years ago. Since
then there have been no fundamental
advances in power switch technology.
Yes, there has been steady
improvement in all major measures
of performance. Yes, new materials
like GaN and SiC have come into the
mainstream but these are still basically
high performance three terminal
switches. What comes next?
There are some new materials
being investigated, like gallium
oxide, that offer the promise of very
high voltage switches. These, if they
become commercially viable, will be
very valuable in high voltage and
high power applications like solid
state transformers for the utility
grid, large motor drives for the electrification
of transportation like all
electric ships, and perhaps even in
all electric aircraft. But these devices
are still fundamentally three terminal
switches that are unidirectional
in voltage blocking ability.
But there is one new device on the
horizon that could once again enable
significant advancements in power
electronics-the truly integrated and
monolithic bidirectional switch.
A bidirectional switch can block
voltage in either direction and conduct
current in either direction. Bidirectional
switches made up of multiple
devices have been around for
decades. One uses four diodes in a
bridge configuration with the center
of the diode bridge spanned by a transistor.
This configuration was originally
used by bipolar transistors.
Other configurations of diodes and
unidirectional switches are known
that create bidirectional switches.
Many of these have the disadvantage
of requiring two independent gate
drives. A more popular bidirectional
switch is made with two n-channel
MOSFETs. First the source terminals
of the two MOSFETs are connected.
Then the two gate terminals are connected.
The drains then form the
power terminals of the bidirectional
switch and the device is controlled by
a floating gate drive connected
between the device's gate and source
terminals. A big disadvantage of all
of these multidevice bidirectional
switches is that the current must
flow through at least two, and sometimes
three, devices. This leads to a
lot of extra power loss.
A truly integrated bidirectional
switch with only one junction or
channel in the current flow path
would be the first really new solid
state switching device in decades.
While some of the applications in
ac-ac power conversion are obvious,
most interesting will be the
nonobvious applications that power
electronics engineers discover.
Looking at the history of power
electronics we see that it was devices
that fundamentally enabled the
advancement of power electronics.
But the two major waves of solid
state switch development in the late
1950s and late 1970s were followed
by intense periods of circuit and
topology development.
Yet this is not the complete story.
Alongside the development of devices
and circuits there have also been
remarkable advances in power electronics
packaging. Today, there are
two major workshops, the Power
Supply on a Chip (PSOC) and the
International Workshop on Integrated
Power Packaging (IWIPP) that
showcase the latest research and
developments. Some of these packaging
advancements are the result
of advances in mater ials and
manufacturing techniques. Some
are enabled by the very high efficiency
of today's converters that
greatly reduce the need to dissipate
waste heat. No matter the enabler of
these packaging advances the
results, ranging from integrated
converter on top processor chips to
the incredible power conversion
density of Vicor's VI-Chips, are
astounding. I will leave it to an
expert in the field of packaging to
tell that tale.
Power electronics has come a
long, long way since the first solid
state switches were introduced. The
devices led the way but the circuit,
controls, and packaging engineers
were quick to make use of new and
improved devices. The journey has
been amazing and I do believe that
we are experiencing a " golden age "
of power electronics. I also believe
that power electronics, with its ability
to make the world a better place
through the greater availability of
energy to the world at lower and
lower environmental impact will
offer rewarding careers for many,
many years to come.
About the Author
Robert V. White (bob.white@ieee.
org) has more than 40 years of industry
experience as a power electronics
engineer. He has worked in product
design, systems and applications
engineering, technical marketing,
and technology development. He has
been an active volunteer with the
IEEE Power Electronics Society,
serving several years on the Administrative
Committee, two terms as the
Technical Vice President, and as the
Chapter Chair. He received the
B.S.E.E. degree from the Massachusetts
Institute of Technology and the
M.S.E.E. degree from the Worcester
Polytechnic Institute. He is currently
pursuing the Ph.D. degree in power
electronics with the University of
Colorado, Boulder, CO, USA. Presently,
he is the Chief Engineer of
Embedded Power Labs, Highlands
Ranch, CO, USA, a power electronics
consulting company. He is a Life Fellow
of the IEEE.
December 2022 z IEEE POWER ELECTRONICS MAGAZINE 101
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