IEEE Electrification - September 2020 - 95

Control Nodes

We have also
implemented
reduced-order
models of the DERs,
loads, and the
network on the
Typhoon HIL devices
to reduce the
modeling complexity.

The decision-making entities in the
cyber layer are referred to as control
nodes. Depending on the type of
control architecture-centralized,
decentralized, or distributed-the
appropriate control node is utilized.
For the emulation of a centralized
control architecture, the cyber layer
makes use of a single National In--
struments (NI) Compact RIO (cRIO)
9068 as the sole control node (see
Figure 4). The cRIO 9068 controller is
an industrial-grade real-time microcontroller that provides an easy way
to build and actualize the centralized
architecture using the NI LabVIEW
system design software. For implementing a distributed
decision-making architecture, the cyber layer utilizes
multiple Arduino-based hardware devices as control
nodes. These Arduino-based control nodes apply the necessary algorithms and protocols needed to realize the
control architecture.

Communication

between each control node and the
appropriate physical-layer emulator, i.e., a Typhoon HIL device or a
standard computer executing an
OpenDSS simulation.
The control nodes employ the Zigbee
protocol and communicate among
themselves wirelessly via a MaxStream XB24-DMCIT-250 revB XBee
wireless module that is interfaced to
an Arduino Due. To employ the Modbus TCP/IP protocol for establishing
bidirectional communication link
with the lower-level controllers as
well as with the appropriate physicallayer emulator, the control nodes use
the Ethernet shield model W5100 that
is also interfaced with the Arduino Due device. A laboratory prototype of the Arduino Due-based control node is
shown in Figure 5. An overview of the C-HIL testbed
architecture described previously is provided in Figure 6.

Microgrid Control Architectures
This section presents an overview of the centralized and
distributed coordination architectures utilized for
microgrid control. We also provide details on how we use
the testbed to implement the two architectures. We do not
provide details on the decentralized control architecture,
which is a hybrid between the centralized and distributed
architectures; however, we do explain how it can be easily
implemented using the testbed described previously.

To implement the coordination and control tasks effectively, the testbed employs several different bidirectional communication links between the various components. The
Typhoon HIL simulator provides several options for communication with external devices. Out of these options, we
employ the Modbus TCP/IP protocol as it is one of the
industry standards for communication. The cRIO 9068 controller also provides the capabilities to implement Modbus
TCP/IP protocol, allowing us to interface the controller with
the lower-level TI controllers and Typhoon HIL devices. Similar to the Typhon devices and the cRIO controller's communication, the TI MSP-EXP432e401y also makes use of its
Ethernet board to allow the implementation of the Modbus
TCP/IP protocol and setup communication links with the
devices in the testbed. To set up the TCP/IP private network
in the testbed, we utilize an Ethernet switch. This infrastructure provides the capabilities to set up a centralized
Figure 4. An NI cRIO 9068 device.
control architecture in the testbed.
A similar setup is used when
using multiple Arduino-based
control nodes. The control nodes
Xbee Module + Xbee Shield
implement two standard proto(Enables Wireless Communication)
cols to facilitate communication
Ethernet Shield
in this setup:
(Enables
Ethernet
Communication)
1) the Zigbee protocol for peer-topeer wireless communication
Arduino Microcontroller Board
among control nodes
(Enables Implementation of Control
2) the Modbus TCP/IP protocol for
Algorithms)
Ethernet communication be--
tween each control node and
the lower-level controllers and Figure 5. The laboratory-grade control node prototype.

Laboratory-Grade
Control Node

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IEEE Electrification - September 2020

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