IEEE Electrification Magazine - September 2013 - 41

Microgrids could be clustered at distribution levels to
enhance the economics and the reliability of small DGs
such as microturbines and wind-generation turbines as
well as DGs with power electronic (PE) interfaces such as
photovoltaic (PV) arrays and fuel cells. PE interfaces are fast,
enabling full control of transients by introducing virtual
inertia implemented through control loops known as
droops. The implementation of droops would enable adjustments in frequency and voltage, which are in proportion to
real and reactive power at converter terminals. Microgrids
use small generators with low or no i-nertia, which are
mostly equipped with PE interfaces in resistive networks,
whereas the utility grid includes large synchronous
machines with high inertias and an inductive network.
The microgrid control architectures are offered in gridconnected and island modes. Microgrids use two control
architectures: multiagent system control and hierarchical
control. The multiagent control system provides generation unit autonomy, reduces large data manipulation, and
increases the control system reliability; however, the
implementation would require a more complicated control infrastructure, which is not recommended for industrial applications. The hierarchical control of microgrids
includes primary-, secondary-, and tertiary-level operations. The primary control would share the load among
DER units using droops while eliminating circulating currents. The secondary control would eliminate steady-state
errors imposed by primary control. The tertiary control
would ensure the economical and secure operation of the
microgrid and manage the microgrid's energy imports/
exports with the utility grid. The hierarchical control of
microgrids would minimize operation costs and increase
the microgrid reliability and enhance the dynamic performance of a highly nonlinear system through various control strategies. The hierarchical control of islanded
microgrids would use existing DERs for regulating the system frequency in different time spans. In addition, using
microgrids would reduce communication requirements
among local DER units.
In this article, we discuss microgrid objectives and
present options for microgrid operations and their monitoring and control in the context of a functional system
at the Illinois Institute of Technology (IIT) in Chicago.
The microgrid represents a multitier hierarchical control of self-sustaining energy infrastructure with islanding and resynchronization, self-healing, and demand
response capabilities. The intelligent high-reliability distribution system (HRDS) at IIT is equipped with phasor
measurement units (PMUs) for real-time monitoring,
nondispatchable renewable energy production, as well
as conventional and dispatchable energy resources.

Status of a Typical Distribution Network
at a University Campus
IIT is located approximately 2.5 mi south of downtown
Chicago, bounded by 35th Street on the south, Michigan

Avenue on the east, 29th/30th Street on the north, and the
Metra Rock Island train line on the west. Starting with the
campus substations, IIT owns, manages, and operates its
underground electricity distribution system. A cross-tie
feeder between the substations allows for the seamless
operation of the microgrid in the case of a utility grid failure in the shared feeder or one of the individual feeders in
the North or the South Substation. The on-site generation
can also feed the northern part of the campus through the
cross-tie between the North and the South Substations.
In the decade preceding the implementation of the IIT
microgrid, the university experienced several outages
within the campus infrastructure and the utility feeders,
which resulted in partial or complete loss of loads in
buildings and research facilities. Several campus buildings
lost power, including laboratories, resulting in the loss of
experimental data and subjects. The substantial annual
loss of revenue as a result of the outages included the
replacement costs of damaged equipment due to
-undervoltage or -unbalanced voltages (campus facilities as
well as laboratories), the personnel and administrative
costs of restoring and sustaining research and educational
experiments, and the cost and aggravation associated
with disrupted academic classes and laboratories and any
other major campus events such as open houses and conferences that were interrupted by the outages.
The IIT microgrid, funded mostly by a grant from the
U.S. Department of Energy, empowers the campus consumers with the objective of establishing a microgrid that
is economically viable, environmentally friendly, fuel efficient, robust, and resilient with a self-healing capability.
The IIT microgrid enhances its operation reliability by
applying a real-time reconfiguration of power distribution
assets, real-time islanding of critical loads, and real-time
optimization of power supply resources.

Objectives for Establishing a Microgrid
The IIT microgrid is powered by a master controller, which
offers the opportunity to eliminate costly outages and
power disturbances, supply the hourly campus load profile, reduce daily peak loads, and mitigate greenhouse gas
production. The distribution system topology consists of
several loops, which provide redundant electricity supply
to the end consumers. The IIT microgrid would specifically:
xx
demonstrate the higher reliability introduced by the
microgrid system at IIT
xx
demonstrate the economics of microgrid operations
xx
allow for a decrease of 50% of the grid electricity load
xx
create a permanent 20% decrease in the peak load
from the 2007 level
xx
defer a planned substation through load reduction
xx
offer a distributed system design that can be replicated in urban communities.
The criteria for achieving these objectives are short-term
reliability and economical operation. Figure 1 shows the
microgrid elements, functions, and control tasks -associated

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Table of Contents for the Digital Edition of IEEE Electrification Magazine - September 2013