IEEE Electrification Magazine - June 2017 - 45

Keating Nanogrid controller, which
communicates via ZigBee radio
Measure Bus
with LED light fixtures for adjusting
Voltage Magnitude
the brightness. Once the set points
are received by the fixture module,
the corresponding microcontroller
Lower than
Nominal
produces a pulse width modulation
No
Yes
Voltage?
signal to adjust the output voltage
Yes
No
Battery
Battery Charge:
of the buck-boost converter for
Discharge
Bulk Stage
adjusting the illumination. In addition, the IIT Microgrid controller can
Battery Charge:
Lower than
send supervisory control signals to
Absorption Stage
Low-Level
the Keating Nanogrid controller for
Voltage?
Lower than
guiding the control of LED lights.
Battery Charge:
Yes
Recharging
Float
Stage
The light fixtures are controlled
Voltage?
Request Power
individually because they respond to
from External Sources
No
supervisory control commands issued by the Keating Nanogrid conFigure 19. Battery-control logics.
troller. For example, lighting can be
dimmed strategically when the Keating Nanogrid suffers a power shortage. Furthermore, LED fixtures can be
Low-Level
Nominal Recharging
Absorption
Float
virtually divided into several control
Voltage
Voltage
Voltage
Voltage
Voltage
groups by the Keating Nanogrid controller for enhancing lighting effi44 Vdc
48 Vdc
54 Vdc
49 Vdc
50 Vdc
ciency, which is a great advantage for
a multipurpose gymnasium. For
Charge
Discharge
example, the main court can host
both basketball and volleyball games,
Figure 20. The battery-control parameters in the dc subsystem.
which may require different levels of
brightness when group settings take
power generated by PV arrays back to the IIT Microgrid to
effect in facilitating lighting control for designated events.
improve the microgrid-wide operational efficiency.
Operational Characteristics of the Keating Nanogrid
Figures 22 and 23 present the representative field-testing
The operation of the Keating Nanogrid is aimed at magnifying
results on a summer day. Figure 22 reveals the stochastic
the value of solar energy with the help of installed PV arrays
power output of PV arrays, which lasts from 7 a.m. to 9 p.m.
and batteries. The installed PV system capacity is 173.5 kW,
and peaks at around 2 p.m. As shown in Figure 23, batteries
and batteries can store as much as 330.4 kWh energy, whereas
manage to accommodate the fluctuations of PV power outthe maximum amount of the building loads is approximately
put so that power exchanges between the Keating
150 kW. Thus, the Keating Nanogrid can stand alone without
Nanogrid and the IIT Microgrid are always maintained at
requesting power from the IIT Microgrid in many cases. At certhe schedule level. In particular, the Keating Nanogrid functain hours, the Keating Nanogrid can even feed the excess
tions as an island between 11 a.m. and 1 p.m., and between

dc Bus

ZigBee
Transmitter
Group
or Individual
Settings

Supervisory
IIT Microgrid Control Signal Keating Nanogrid
Controller
Controller

ZigBee
Receiver

Microcontroller

Voltage Input
PWM
Control Signal

LED
Driver

LED
High-Bay

PWM
Input

LED Light Fixture

Figure 21. The LED lighting-control scheme.

IEEE Electrific ation Magazine / j une 2 0 1 7

Table of Contents for the Digital Edition of IEEE Electrification Magazine - June 2017