IEEE Power & Energy Magazine - January/February 2014 - 73

support and service restoration to the utility. under such
conditions, the operation of the distribution network necessitates enhanced protocols for communication at all levels
of the distribution system to assist distribution management
system (dMs) operators with real-time decisions.
smart distribution systems establish microgrids and apply
smart grid to the establishments for managing 1) dErs and
storage technologies, 2) demand-responsive proactive consumers, and 3) decentralized control of energy resources
and distribution feeders resulting from the formation of
microgrids. Microgrids are often connected to distribution
feeders and offer load and generation control to provide
continuity of supply in the event of utility grid disturbances.
such microgrid control has a hierarchical structure for
enhancing the security, controllability, and flexibility of distribution network operations. Microgrids can be operated in
a grid-connected mode, in which their loads are partially
supplied by the distribution system, or in an island mode, in
which the local generation supplies the entire microgrid load
in case of a major outage at the utility distribution system.
a microgrid has its own energy management system for the
control of its dErs and for devising demand-response strategies. as a result, a microgrid can behave as an active load in
a distribution network that can also be isolated from the rest
of network. By incorporating available microgrids in load
restoration procedures, the distribution utility can improve
its load restoration capability and further enhance distribution system reliability.
in a modern distribution system, microgrids are regarded
as reliable alternatives to more traditional methods of restoring deenergized areas of distribution systems and providing
secure energy resources to local entities until the utility grid
is restored. a decentralized power grid can use microgrids
to isolate a neighborhood in the event of disasters and serve
critical systems and buildings like data centers, hospital

communities, and campuses by utilizing local generation
and storage facilities.
the technologies incorporated in microgrids are developing, and real-world examples have been deployed in various
countries. honeywell's White oaks project in Maryland is
an example of deployed microgrids in the united states; the
microgrid supplied power to local systems during a summer storm in 2012. synergetic thinking is a crucial part of
improving the economics of microgrids and lowering the
cost of energy in general rather than focusing only on electricity. up-front planning for serving customer loads could
increase microgrid energy efficiency to more than 75%.
depending on its capacity, a microgrid can provide ancillary
services such as frequency and voltage support by injecting
power into the grid. the sendai 1-MW microgrid at tohoku
fukushi university in Japan is an example of a university
microgrid. it operated for two days in island mode during
the March 2011 earthquake and tsunami while the surrounding region was without power. their unique characteristics
make microgrids suitable candidates for service restoration
duty in power distribution networks.

Distribution System Service
Restoration Using Microgrids
current operating practices require dEr units to be
promptly disconnected in any disturbances and be reconnected once the distribution system is energized and rated
voltages and frequency have been restored. however, active
management strategies in microgrids could lead to distributed control in island mode, which may not require the
disconnection of microgrid dErs in a major disturbance.
in blackouts, distribution system downtime can be reduced
by providing a fast blackstart of local generation resources
in island operation. a microgrid that has remained fully
functional and lies in the restoration path can be started

Utility Grid
DMS

Microgrid

Tertiary

Secondary

Primary

figure 1. Hierarchical control of a distribution system with multimicrogrids.
january/february 2014

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Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - January/February 2014