IEEE Power & Energy Magazine - July/August 2017 - 55

and achieve maximum possible revenue streams from PJM
market participation while in the grid-connected mode. The
DERs include generation sources, energy storage, and controllable loads (demand response facilities). All of the power
supply resources (generation and storage) on the GridSTAR
microgrid are inverter-based units that can sustain operation of the microgrid in the islanded mode with the available
DERs. DERs that are currently available on the GridSTAR
microgrid are described next.
Energy Storage

These energy storage facilities are available on the GridSTAR microgrid
✔ The GridSTAR microgrid includes an energy storage
facility that is rated 250 kW (125 kWh); this energy
storage unit (battery) can produce 250 kW for approximately 30 min. This unit has been used to participate
in the PJM frequency regulation market. The energy
storage facility includes batteries, a smart inverter,
and a battery energy management facility (Power
Factor 250) supplied by Princeton Power. This facility will be the primary source of power when the
GridSTAR microgrid is operating in islanded mode
[along with solar (photovoltaic) PV generating units
that are described in the next section]. This unit is
currently under repair. In addition, the PIDC and its
partners may elect to deploy a larger energy storage facility that can sustain critical loads while in
islanded mode.
✔ The ZNE house includes a 10-kWh battery that can
supply the critical loads for an "indefinite" period (assuming average solar resources and the solar PV units
are supplying expected power).
A vehicle-to-grid demonstration program was planned
for the GridSTAR facility. However, energy storage capabilities that may be available in EVs that are being charged
at any given time at one of the three charging stations at
GridSTAR have not been included as available resources for
the microgrid.
Generating Capabilities

The GridSTAR microgrid includes solar PV generating facilities that are mounted on the ZNE roof, the EV
charging station canopy, and the solar training facility.
Maximum output from these generating units is 10 kW.
The GridSTAR complex includes a solar forecasting facility that can develop reasonably accurate short-term forecasts of solar irradiance using continuous measurements
of cloud cover and cloud cover movement. As part of the
project, the team will research using the short-term solar
forecast to improve the management of DERs within the
GridSTAR microgrid.
The GridSTAR microgrid contains renewable resources
with protection systems that are difficult to design for
microgrid operation in islanded mode. Significant research
july/august 2017

activities for this are taking place around the world, including in the IEEE Power & Energy Society Power Systems
Relaying Committee.
Controllable Loads

Another existing DER within the GridSTAR is controllable
loads (also known as demand response) that will enable the
microgrid controller to balance the connected load with the
available power supply to achieve more effective control of
voltage and frequency when operating in islanded mode.
When energy supply resources (i.e., storage and generation)
on the islanded microgrid are limited, the microgrid can use
the controllable load resource to shed load to balance load
and power supply (generation and storage) in the island. It
is also possible to use the controllable load facilities to shed
load automatically during power shortages when operating
in grid-connected mode by using smart inverter schemes
included in these resources.
The following controllable load (demand response) facilities are available on the GridSTAR microgrid:
✔ Buildings 100 and 101 energy management systems:
Buildings 100 and 101 include building energy management systems (BEMS) supplied by Radius Systems. These systems enable TNY in building 100 and
101 to curtail the noncritical heating, ventilation, and
air-conditioning (HVAC) load and lighting load
during power shortages as part of a demand-response
program. This system can reduce the total demand
in each building by up to 50%. The distributed microgrid control system-microgrid automation control
system (DMGCS-MACS) will use Landis and Gyr's
(L&G)'s AMI communication to coordinate these
facilities to achieve better balance between load and
generation, which is especially important when the
microgrid operates in islanded mode.
✔ Noncritical loads in the ZNE house: The ZNE house
includes facilities to automatically disconnect noncritical loads in the house when a power outage occurs.
The DMGCS-MACS will use AMI communication to
perform the load shedding as needed to balance supply and demand on the GridSTAR microgrid.
✔ EV charging curtailment: It is possible to curtail EV
charging on the three EV charging stations at GridSTAR. The microgrid controller system can disable
EV charging altogether on some of these charging stations. In the future, it may be possible to curtail "fast"
(level 2) charging. However, this capability is currently
not available.
✔ Manual load curtailment: If it is necessary to balance load
and generation on the microgrid, the GridSTAR load can
be reduced manually by operating circuit breakers in the
power distribution panels in buildings 100 and 101 and
the chapel. However, this method is relatively slow due to
manual intervention and cannot be used when rapid (immediate) load curtailment is needed.
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