IEEE Power & Energy Magazine - May/June 2021 - 86

electrical and safety codes, standards for physical construction, product safety rules that include functionality operating points, and state and local regulations and mandates.
Further, the interrelationships of the requirements vary
significantly from country to country, state to state, city
to city, and, often, utility to utility. Smart grid technologies
and microgrids use communication, such as power line carriers, wireless systems, the Internet, and, recently, optical fiber,
in newer and larger installations. Methods to improve control
and monitoring functions when connected to EPSs are continuously being improved and implemented. It is noted that
the communications ensuring that all systems are compatible can have beneficial and detrimental impacts on protection. Many monitoring and measurement systems and devices
depend heavily on wireless communications, communication
methods, and protocols. The wide use of new communication
technologies is covered by numerous standards, but communications for direct applications to protect microgrids and interconnected EPSs are in various and early development stages.
A simplified block diagram depicting the interconnection
of a generic microgrid connected at a point of interconnection
is shown in Figure 2. It is based on the requirements provided
in the standard specifying the functions of microgrid controllers, IEEE 2030.7. It is provided as an example of power

flows and communications. Communications are often hardwired, but implementations now use more wireless connections, which have improving quality and security. Optical fiber
is a desirable but more expensive communication media that
provides inherent security and speed. The diagram shows that
interoperability requirements are becoming more complex,
and device compatibility is a new challenge to incorporating
secure communications to optimize one or more microgrids.
The aggregator shown in the figure can be used for a single
microgrid that employs wireless and hardwired communications, and it can be used to gather the information provided by
many microgrids. Its output can be used to provide improved
protection and optimize the value of the combination of
microgrids. Incorporating it provides an advantage in that
components within a microgrid can be modularized without
sacrificing the protection functionalities and interoperability
with the utility distribution system.
Control categories associated with the interconnection of
microgrid networks to an area EPS are provided in Figure 3.
The device-level functions deliver control in microseconds
to seconds. They are considered the primary control of a
microgrid. The local area and microgrid supervisory control functions act in seconds to days and can be taken as
the secondary control. The grid-interactive control functions

Microgrid Components
Hardwired
Communications

Electrical Production
and Distribution
Network

Energy
Management
System

Power Flow

Aggregator
Analyzer
Optimizer

Rotating
Generation
(Dispatchable)

Point of
Interconnection
Intelligent
Breaker

Breaker
Control Module
Microgrid Controller and
Control System
(Centralized or Distributed)

Renewable and
Combined Heat and
Power Resources
(Curtailable)

Electrical and
Thermal Energy
Storage
(Dispatchable)

Reports Direction and
Magnitude of Power Flow

* All Components and Subsystems Can Be Accessed With Wireless Communications
Represents Component Subsystems That May Be Modularized

Controllable
Loads
(Dispatchable)

figure 2. A conceptual virtual system for microgrids and DERs that can be used in a mesh network.
86

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IEEE Power & Energy Magazine - May/June 2021

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