IEEE Electrification Magazine - March 2016 - 21

The resilience of
the power system is
inevitably dependent
not just on reducing
the number of
outages but also
on how the grid
will respond to
such events.

process, critical load centers such as
University continued to supply a
military bases, hospitals, and univernumber of loads, including a hospital,
sities must be given precedence. As
for two days, while the surrounding
illustrated in Figure 4, conventionally,
grids were without power.
the restoration process initiates from
If a microgrid is damaged during a
the transmission level and proceeds
major storm, the microgrid uses its
toward the distribution level. In this
master controller to perform local
context, load restoration would be
self-healing quickly and salvage as
done as the last step in a process that
much load as possible to turn the
may take days to be completed.
lights back on. The restoration will
What's more, the limited operating
also be initiated from the transmismargins of centralized power systems
sion side and advanced toward the
exacerbate the restoration process,
distribution grid. Indeed, the whole
which can delay the restoration of
restoration procedure would be percertain loads. Such challenges have
formed simultaneously, a downward
highlighted the weaknesses of cenprocess from the transmission grid,
tralized electric power system restotogether with an upward process
ration and operation in critical situations and shed light
from the distribution level (see Figure 5).
on the merits of using microgrids for enhancing the power
Microgrid Implementation
grid resilience. The unique characteristics of microgrids,
As microgrids are deployed worldwide, myriad of new
which make them suitable for expediting the power grid
challenges and opportunities have emerged. However,
restoration, are listed as follows:
xx
Operation flexibility: In the event of any natural disaswriting a general prescription for implementing all
ters, the microgrid master controller would optimize
microgrid projects across the world seems impractical.
the status of upstream and downstream grids as it
Indeed, it is difficult to generalize such projects because of
switches between the grid-connected and island
their relatively unique and local characteristics. The only
modes. It also determines the optimal level of power
certainty is that most utilities in both developed and
transacted with the upstream
grid, the optimal schedule of
local resources, and the adaptive
settings for protection devices.
Moreover, grid reconfiguration
could be done if necessary.
Microgrid Master
xx
Self-supply: When the supply of
Controller
power to a microgrid is interrupted due to an upstream grid
fault, microgrid customers are
Upstream
Grid
supplied with a wide variety of
energy sources, often renewable
ones, along with energy storage
Point of
Communication
devices. Particularly, this feature
Common
Network
would considerably facilitate the
Coupling
load restoration process.
Accordingly, the master controller
can island the microgrid when the
storm hits, and the microgrid, which
can be restored quickly, can supply
critical loads such as hospitals and
military bases using local generation and storage facilities. As a realEnergy Aggregators Conventional Electric Vehicle Renewable
world example, on 11 March 2011,
Distributed
Storage
Parking Lot
Distributed
when a 9.0-magnitude earthquake
Generation
Generation
devastated the northeast coast of
Japan and led to one of the deadliest
tsunamis the world has ever seen,
Sendai microgrid at Tohoku Fukushi Figure 3. An overview of a typical microgrid.
!

IEEE Electrific ation Magazine / March 2 0 1 6

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