IEEE Electrification Magazine - September 2013 - 44

May 2013. Here, the wind turbine unit would spin when the
wind speed is higher than 10 mi/h (4.47 m/s).

Battery Storage
The IIT microgrid is equipped with a 500-kWh battery
storage system (including ten 50-kWh battery cells)
with 250-kW power capacity, which is connected to
Loop 1. -Figure 9 shows a stack of the flow battery and
the battery inverter, which can regulate the real and
reactive power output.

HRDS Switches
Figure 3. The full-scale model of the natural-gas turbine at IIT.

Figure 4. The solar panel in IIT's charging station.

uses a Viryd wind turbine unit. The wind turbine features
continuous -variable transmission (CVT) technology, which
provides automatic and continuous variable ratio change
that maintains stable rotor speed for the generator as wind
speed changes. This would enable the generator to maintain high efficiency at all wind speeds. The CVT can also
precisely slow the rotor in high wind speed, curtailing the
excess wind power. Figure 7 shows the structure of the
CVT-based wind turbine unit. The role of the variable gear
ratio is to regulate the power output close to the rated value
when the wind speed is within the acceptable range. The
cut-in and cut-off wind speeds for this turbine are 4.5 and
25 m/s, respectively, and the turbine has an 8-m diameter
and 50-m2 sweep area. Figure 8 shows the hourly power
output and the wind speed for the wind turbine unit on 20

VPV, IPV

Vdc

Angle Magnitude
Control Control
ang
mag
PWM

Meters and PMUs

The IIT microgrid is equipped with building meters and
PMUs, which report building electricity consumptions to
the master controller. The master controller will receive an
energy consumption update every 15 min. The load data
recorded on 17 July 2012 at the McCormick Tribune Campus
Center (MTCC) at the IIT microgrid are shown in F
- igure 12.
Approximately 30% of building consumptions at IIT are
shiftable loads, which can be served when the electricity
price is lower. The IIT microgrid is equipped with 12 PMUs
that monitor and record the real and reactive generation
and consumption in real time and provide the information
on instantaneous voltage and current of DER units (including the magnitude and phase angle)
at a sampling rate of one signal per
cycle to the master controller.
-Figure 13 shows a PMU installed at
the North Substation. Figure 14
Qout
shows the real and reactive power of
critical loads and DER units, which
are calculated by master controller
ac Filter
based on the instantaneous values.

Capacitor
Figure 5. The equivalent circuit and power output characteristics of a solar PV cell.

I E E E E l e c t r i f i c atio n Magaz ine / september 2013

Microgrid

MPPT

The HRDS at IIT uses underground closed-loop faultclearing Vista switchgear with SEL-351 directional overcurrent protection relays. The fault isolation takes place in
a quarter of a cycle by automatic breakers. The communication via fiber-optic cables facilitates the coordination
between Vista switches. F
- igure 10 shows the underground
installation of a HRDS switch at IIT. In HRDS, at least two
simultaneous failures in the cable segments feeding a
building from both paths will lead to a -complete outage in
the building. As the chances of two coincident failures is
far less than single failures in cables feeding, the interruption indices of the buildings are improved significantly by
the installation of HRDS. F
- igure 11 shows a loop configuration in distribution system at IIT. Here, in Loop 1, any cable
failure between Vista switches 1C and 1D will be cleared,
and the Stuart and Life Sciences Buildings fed by the
switches will not face any interruptions.

Building Controllers
Building controllers facilitate the
building consumption manage-

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