IEEE Systems, Man and Cybernetics Magazine - July 2021 - 14

Table 1. The agents of the proposed SDEN.
Cyberelement
Client
Buffer
Physical Entity
Flexible load
Cache
Source
Router
Server
PV: photovoltaic
Short-term storage
Long-term storage
Aggregated production mainly from distributed generation
Computer or embedded system
Computer(s) orchestrating the SDEN
Examples
EVs, dishwasher, sauna, space heating
Batteries, heat pumps
Synthetic fuel
Solar PV forming a virtual power plant
Smart meter or home energy management system
Software in cloud server
material, informational, and decision-making processes
[13]. Typically, cyberphysical systems are based on relatively
autonomous (but interdependent) entities that can
act within the system boundaries. These entities are
referred to as agents and are often defined via a dedicated
software platform [31]. The SDEN proposed in this article
is such a platform, in which cyber (software-defined)
agents are designed in accordance with their specific physical
functions. The cyberphysical relationships among the
agents are determined by PEM, which enables the agents
to produce, consume, allocate, and store energy packets.
Table 1 presents the nomenclature employed in this study;
it is clearly inspired by the conventional naming of computer
network elements and Internet peer-to-peer applications
[32] as well as wireless communication resource
allocation methods [33]. The agents as well as their interrelated
operations are explained in detail in the section " The
Virtual Microgrid as a Cyberphysical System. "
Client
Router
Request
Request
Accepted
Accepted
Ack
Ack
Delivery
Ack
Figure 3. A handshake example: a client requests
a service that is accepted by the server and then
delivered using the energy available in a given buffer.
Ack: acknowledge.
14 IEEE SYSTEMS, MAN, & CYBERNETICS MAGAZINE July 2021
Server
Buffer
To coordinate their actions, the SDEN agents need to
communicate to either request a service or reply to a
service request as well as schedule actions related to
energy delivery or storage. This communication is
defined in the cyberdomain based on the following
generic types of messages:
◆ Request: Clients send a message to their respective
energy server detailing the service they require, which
includes, for example, how many energy packets they
need, how these packets need to be allocated over time,
and the deadline for the service to be accomplished.
◆ Acceptance/rejection: After receiving a request, the
server assesses the current and future states of the
energy inventory to make a decision, which is then
communicated to the respective client with a yes or no
message. In the case of a yes message, the client will
wait for the delivery/schedule messages. In the case of
a no message, the server sends a message that will
enable the client to plan its new request.
◆ Delivery/storage: The energy server dynamically
updates the schedules of energy packet delivery and
storage based on the accepted services and production
forecasts. Following the plan, the server sends messages
to the clients or storage units, indicating that they
need to be ready to receive their packets.
◆ Acknowledgment: Clients and servers may also send
acknowledgment messages about the delivery of energy
packets, in a sense similar to TCP/Internet protocol.
◆ Emergency: Some clients may also have the chance to
send messages requesting urgency in the service. For
example, a change of plans related to EV usage may
require urgent messages to be sent to request charging.
Such messages should be rare.
Figure 3 illustrates a typical message exchange under the
proposed PEM protocol. This communication among the
software agents ultimately determines the cyberphysical
system dynamics. In the following sections, we present the
details of how this generic protocol can be used to build the
proposed virtual microgrid and, more importantly, achieve
efficient management of microgrid resources.
IEEE Systems, Man and Cybernetics Magazine - July 2021

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