IEEE Power & Energy Magazine - May/June 2021 - 85

programs; and the crafting of standards for microgrid systems,
applications, and protection. The agency's support helps to
encourage collaboration and, very importantly, as featured in this article, the drafting and upgrading of standards
and codes for system designs and installations. Microgrids
have evolved for more than a decade, with the term advanced
microgrid referring to microgrids compatible with new smart
grid technologies (in particular, two-way communications)
and inverter-based renewable generation and storage (as compared to the past prevalence of generators). The players, advocates, standards, and activities for real and predictive growth
for advanced microgrids that lead to new protection requirements and standards are shown in Figure 1.

Utility and Mandated Requirements
for Microgrids and DERs

Several requirements have been phased in through time
to help encourage the installation of more solar and energy
storage. An important mandate is that new solar and storage installations must use inverters that interact with distribution networks. These inverters are critical components in
microgrid systems, and interconnection rules can be extended
to them. Inverter features include volt/volt-ampere reactive
support functions that provide voltage controls through the
in-phase current and reactive current elements of back-fed
power. The dynamic volt/volt-ampere reactive support and
ride-through capabilities add much needed synthetic inertia
to the distribution system. Synthetic inertia can be analogous
to that provided by mechanical generators when connected to
an EPS. This is an important feature to have when considering protection. Inverter requirements that create challenges
for the protection of loads and EPSs include soft starts that
lessen the impact of extremely variable power back-fed to the
utility, displacement power factor support, and inverter ridethrough to handle EPS disturbances.
In mid-2019, grid-connected inverters were mandated in
California to have an Internet Protocol for communications,
which is a set of standardized rules enabling computers to communicate on a network. Communication capabilities facilitate utility control and aggregation control. Aggregators and
inverters communicating with utilities are to use the new IEEE
2030.5, Standard for Smart Energy Profile Application Protocol, guidelines for communications, monitoring, and control.

This article focuses on standards for design, installation, and
applications. Mandates apply to legislated rules for installations, interconnection and interoperability, performance,
metering, and communications of microgrids in many U.S.
states. Among the first is Rule 21, which governs the California Public Utility Commission's jurisdictional interconnections. Rule 21 is a tariff that describes the interconnection, operating, and metering requirements for generation facilities to be
connected to a utility's distribution system. It sets rules for the
performance, function, metering, and communications of generation and storage facilities. It was originally adopted in 1982
and has undergone three major updates since 2000 to establish
a more standardized analysis and procedures for the intercon- Interconnection of a Microgrid
nection of DERs. Rule 21 is not a protection requirement but The interconnection and interoperability of microgrids and
provides a well-defined procedure for technical screening to DERs with EPSs are guided by national and international
enable " fast-track reviews " as well as a more detailed study standards. They specify electrical functionalities, general
process for larger and more complex interconnections. It continues
Microgrid Growth Players
to evolve through the Smart Inverter
Working Group, which meets reguPrimary
Advocates*
Primary
Advocates*
larly to develop recommendations
* U.S. Departments of Energy and Defense
* U.S. Department of Homeland Security
for advanced inverter functionalced d
van an
* National Laboratories and Testing Labs
Ad grids n
ity requirements. One aspect of
ro
tio
* State Agencies for Smart Grid R&D
Mic rotec
this evolution is the consideration
* Electric Utilities and Industry
P
of additional functionalities and
complexities related to energy stority
age and inverter-based resources in
tric
Activities*
lec
E
R&D, Security,
f
s
microgrids. Technical functions and
e o ion
Protocols, Testing, Tools,
ffic licat
O
value limits set by Rule 21 include
and Specifications
y pp
erg A
En New
✔✔ technical operating paramf
to -
en &D
eters
rtm rid R
a
ep og
✔✔ certification and testing criStandards Developments*
. D icr
Primary Advocates*
U.S M
* IEEE
teria
* IEC
✔✔ technical requirements for
* Underwriters Laboratories/Test Laboratories
inverters
* State Agencies for Renewable/Alternative Energy
✔✔ provisions specific to net
* National Fire Protection Association
energy metered facilities
* Note: There are others. These are example lists.
✔ ✔ metering and monitoring
requirements.
figure 1. Microgrid growth on the path to protection.
may/june 2021	

ieee power & energy magazine 	

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IEEE Power & Energy Magazine - May/June 2021

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