IEEE Electrification Magazine - June 2016 - 8

VIeWPOInT

Figure 3. MEGs used for data center power. (Photo courtesy of Pos-En.)

center, thus eliminating transformers, switchgear, inverters, and rectifiers throughout the entire data
center infrastructure. Capital
expenditures are reduced by simplifying power system design
through the elimination of ac
e q u i p m e n t a n d re d u c t i o n i n
cooling capacity.

Researchers at the Lawrence
Berkeley National Laboratory have
been investigating efficiency in data
centers since 2004. Poor efficiency of
power distribution brought about the
idea of eliminating some of the power
conversions by using 380 Vdc. Results
of their research were outlined in the
November 2012 issue of IEEE Power &
Energy Magazine, appropriately titled
"Edison Redux: 380 Vdc Brings Reliability and Efficiency to Sustainable
Data Centers." According to the article, replacing legacy power distribution with 380 Vdc was 28% more efficient than with 208 Vac. In addition,
findings estimated up to a 15%
decrease in costs due to elimination
of components and simplification of
the power distribution system. These
findings were peer reviewed and confirmed by the open industry consortium The Green Grid.

Obstacles to dc
There are some key issues keep us
from widely adopting dc as a standard in the United States, and until
these issues are addressed, we cannot expect the dc revolution to take
root. Some of the issues include:
x understanding
x standards
x products.

Lack of dc Knowledge
There is a popular misconception that
dc is more dangerous than ac, despite
countless articles to the contrary.

I E E E E l e c t r i f i cati o n M agaz ine / j un e 2016

(Consider the electric chair widely
believed to be an invention financed
by Edison to prove that ac is more
dangerous.) There is also the misconception that power losses from dc are
greater than those from ac, which is
often true because dc is usually at
such a low voltage, but at the same
voltage dc is always more efficient. In
addition, there is a feeling that dc cannot be used to run long distances
despite ample evidence from longdistance high-voltage dc lines.
In the "war of the currents"
between Tesla and Edison, there was
a very strong argument that ac could
be inexpensively and efficiently
transformed to higher voltages. At
the time, this was the only transformation that allowed for high-voltage
transmission and distribution. But as
groups such as the FREEDM Systems
Center and their industrial partners
develop advanced power electronic
solutions to transform any electricity
to ac or dc using solid-state transformers, this argument becomes less
valid, and all of these elements
devolve into a fear of the unknown.

dc Standards
There are a few standard dc voltages,
such as the 12-V standard in vehicles
or the 5-V standard for universal serial
bus devices, but for higher power,
widely adopted higher standard voltages must be developed. Owing to the
50-V standard for touch safe operations, there is a clean breakpoint at
48 V, and many products already conform to this standard. Additionally,
forklifts and the telecom industry
have settled on this as a standard voltage. Both the European Telecommunications Standards Institute (ETSI) and
the EMerge Alliance have standardized on 380 Vdc and produced guidelines for dc power distribution. These
standards have been in use for several
years. But even if a user wanted one of
the standard dc distribution voltages
in their home, business, or industry,
few engineers could lean on existing
codes and standards to select

Table of Contents for the Digital Edition of IEEE Electrification Magazine - June 2016