IEEE Electrification - December 2020 - 26

specifications are detailed in Table 2. The BDC is fully automated and managed by the Tesla integrated controller,
depicted in Figure 10, which aggregates real-time information from all of the Tesla building blocks, including the
battery pods in each Powerpack battery storage unit, the
inverter modules in the Powerpack inverter, and multiple
sensors. The Tesla integrated controller uses commands
received from the IIT Microgrid and the Crown Hall
nanogrid controllers to optimize the commands sent to
the individual Tesla building blocks.

PV Array Utilizing Microinverters
at the Crown Hall Nanogrid
The PV array located on the roof of Crown Hall includes
230 PV modules, where each PV module is equipped with
a smart grid ready Enphase IQ 6+ Microinverter, as shown
in Figure 11. Each microinverter has a maximum power
point tracking (MPPT) range of 27-37 Vdc and a maximum
output power of 290 volt-amperes. The microinverters

TABLE 1. A list of the Crown Hall nanogrid

components.
Nanogrid
-Components

Design Specifications

PV module

Hanwha Q Cell Q.Peak L-G4.2 360 M

Battery module

Tesla Powerpack-2 battery module

Bidirectional
ac-dc converter

Tesla Powerpack-2 inverter module

dc-dc converter

Schneider Electric Xantrex XW MPPT 80 600

Microinverter

Enphase IQ 6+ microinverter

Islanding relay

Schweitzer Engineering Laboratories
SEL-700G

Transformer

Schneider Electric EX300T3H

have an interconnected data link between them, where
the operation information is aggregated and utilized by
an Envoy PV controller. The use of microinverters in the
proposed configuration offers multiple advantages. First,
it maximizes the individual PV modules for optimizing
the PV system's power and energy output in the Crown
Hall nanogrid. The multiple PV modules in a conventional
configuration would be connected in series to form a PV
string, where multiple PV strings are connected in parallel
and controlled by a single inverter. Under the sting inverter configuration, if one PV module was affected by shade
(for example, a cloud, tree shadow, roof beam, or penthouse shadow), the dc output of that PV module would be
dropped significantly, and the operation point of the
entire PV string and other strings on the same inverter
would be dropped to accommodate the affected PV module. So if a PV string has nine PV modules and four PV
strings per inverter, then the shaded module would only
be running at the MPPT point, and the remaining 35 modules would be operating at a suboptimal point.
By comparison, the proposed microinverter configuration allows each PV module to use its own microinverter,
where the modules are interconnected with the ac bus.
Accordingly, each PV module is operated independently at
its own MPPT point and will be optimized individually for
performance. One shaded PV module is not going to affect
the entire system. Figure 12 depicts the PV modules on
the roof of Crown Hall running at their independent optimal operation points. The second benefit of the proposed
configuration is the enhanced reliability of the nanogrid.
In a conventional configuration, a single PV module failure
will affect the entire PV string. In the proposed microinverter configuration, all of the PV panels are in parallel at
the ac bus, where any single module failure would only
affect the module itself. This configuration has enhanced

TABLE 2. The specifications of the Tesla

Powerpack BDC at the Crown Hall nanogrid.

Figure 9. The individual battery rack with 16 interior battery pods.

I E E E E l e c t r i f i cati o n M agaz ine / DECEMBER 2020

Height, Width, Depth

2,140 mm, 1,254 mm )
1,014 mm

Weight

1,200 kg

Rated output power

300 kW

Nominal ac voltage

480 Vac

Maximum dc input voltage

900 Vdc

Peak efficiency

99%

Total current demand distortion

<3%

Power regulation accuracy

<2%

Total power command response
time

<25 ms

Maximum rise time

<8 ms

Ambient operating temperature

−30 - 50 °C

IEEE Electrification - December 2020

Table of Contents for the Digital Edition of IEEE Electrification - December 2020