IEEE Electrification Magazine - March 2014 - 17

line transients, reactive power control schemes for multiple inverters, impact of cloud cover on solar PV, use of
dr, and issues surrounding the reverse power flow on
secondary grid networks.
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IEEE Standard 1547.8: draft recommended practice
for establishing methods and procedures that provide supplemental support for implementation strategies for the expanded use of ieee 1547 standards.
the purpose of this guide is to segregate fast-tracked
der projects from those requiring deeper levels of
analysis due to high penetrations of distributed solar
PV. it seeks to make rdeg and other der utility
friendly, with the prime solution
set revolving around advanced
smart inverters. the top topics of
inquiry by ieee are voltage regulation and power quality and
how best to optimize the group
behavior of der sized between
10 and 20 Mw in scale.
this set of ieee 1547 standards was
being reviewed in december 2013 and
will likely undergo further revisions
and enhancements moving forward.
another set of ieee standards that
would accelerate the deployment of
microgrids is the Smart grid interoperability 2030 Series, which represents a draft guide for it, electric
power systems, and end-use loads
and applications. an ieee working group is currently
building on the overall interoperability subjects embodied in ieee Standard 2030. the latter covers the engineering, communications, and it industries' products
designed for the smart grid, including standards for eV
integration (ieee Standard P2030.1) and energy storage
(ieee Standard P2030.2 and ieee Standard P2030.3).

voltage dc networks. among the advantages of dc distribution network infrastructure are:
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eliminated reactive power constraints
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eliminated need to synchronize diverse generation
sources to a single ac grid frequency
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overall higher system efficiency
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ease of interconnection of dc generation sources
(solar, wind, and fuel cells)
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ease of interconnection of electrochemical devices
(flow and other forms of advanced battery systems).
led by companies such as intel, Johnson Controls, and
emerson Network Power, the eMerge alliance is now
advocating for a return to dc systems
in the developed world. these systems would subsequently pave the
way for state-of-the-art dc digital systems in the developing world. even
today, companies like Nextek Power
specialize in dc power distribution
optimization. Nextek Power offers a
direct coupling technology that displaces the need for dc/ac inverters for
microgrids interconnecting to the
larger utility ac grid. in addition, aBB
has been selling high-voltage dc
transmission systems for about five
decades and also offers a variety of
dc-based products relevant to
microgrids.
there is heated debate today
about the advantages and disadvantages of dc. here are
just a few of the myths that need to be debunked,
according to dc advocates, for this class of power distribution equipment to become widely accepted and help
push dc microgrids into the mainstream:
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DC is only 1% or 2% more efficient, so why bother? while
this may be true at low-voltage levels, recent research
by a variety of entities that include intel shows that
medium voltage (380 V dc) is 7-8% more efficient.

Current trends
toward a more
distributed energy
future appear to
make microgrids
an inevitable
augmentation of
today's centralized
grid infrastructure.

The Buzz About dc

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DC requires large conductors and can only be trans-

the world has changed over the past 100 years. while
large centralized power plants will continue to play a role
in providing ac power to the wholesale macrogrid, there is
growing momentum at the distribution level of electric
service to diversify power offerings and pursue dc-ac
hybrid solutions. More and more, the loads served today
by ac power grids are natively dc. in fact, according to
some estimates, approximately 80% of loads in commercial and residential structures are now native dc. given the
enormous political and policy support for inverter-based
native dc power sources such as solar PV, wind, fuel cells,
and energy storage, it makes sense to reduce dc-ac-dc
conversion losses and integrate dc distribution networks
such as microgrids into the power supply infrastructure.
Many of the utility concerns and the subjects described
by the aforementioned ieee standards relating to
microgrids can be mitigated in novel ways by medium-

mitted for a few meters at a reasonable cost. again,
this is true for the majority of systems deployed today
at the −12 V, −24 V, or −48 V level, it does not hold true
at the same 380 V medium voltages now being developed for distribution networks.
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If a network is run off of dc batteries, this eats up all

of the efficiency gained by the dc current. while there
is some validity to this fear, it is equally true that this
may be an appropriate tradeoff for a reliability gain
that can reach 1,000%.
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Arc flash is an unacceptable hazard for dc. again, new
technologies, such as magnetic arc breakers and
switched interlocks, can address these safety
concerns at a relatively modest cost.
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AC is safer because the voltage crosses zero at either

50 or 60 times/s (i.e., 50- or 60-Hz ac grids). this is

IEEE Electrific ation Magazine / MARCH 2 0 1 4

Table of Contents for the Digital Edition of IEEE Electrification Magazine - March 2014