IEEE Power & Energy Magazine - May/June 2021 - 59

The control and protection of microgrids are highly interdependent, and to solve this challenge, modern PPRs have
taken on a larger role than traditional PPRs for utility grids.
Depending on the application, PPRs are placed in switchgear, the yard, or a control room. PPRs contain large numbers of protocols and physical hardware input/output, allowing them to control and monitor inverters simultaneously
to circuit breakers, tap changers, and so on. As shown in
Figure 1, a PPR interrupts currents by tripping circuit breakers, and it reconnects to the system by closing breakers once
synchronization is confirmed. A PPR and/or a combination
of inverter controls may also control (dispatch) inverters,
monitor inverters to enhance protection, and simultaneously
provide comprehensive situational awareness through visualization, archiving, oscillography, and error-logging systems.
This consolidation of more features into fewer electronic
devices is a proven method for improving a power system's
resilience and reliability and has been employed to overcome
microgrid protection challenges.
This consolidation of functionality has also reduced the
costs of operating installed
microgrids. For example, a single
PPR can replace a programmable
logic controller, load-sharing
system, digital automatic voltage regulator, digital governor,
on-load tap changer controller,
automatic transfer switch controller, computer, fault recorder,
oscilloscope, (multiple) singlefunction relays, and so forth.
Because PPRs are the most reliable microprocessor-based electronics on the power system and
protection is mandatory, it is
natural that PPRs replace other
lower-reliability components.
This article provides several
solutions for a low-cost, reliable, and safe PPR-based protection system for microgrids.
It shows that using PPRs allows
the user to increase the use of
inverters and renewable generation sources without impacti n g t h e s a fe t y of h u m a n s ,
processes, equipment, or the
environment. To fully realize
the advantages of this, the engineers designing microgrids and
selecting IBRs, circuit breakers, switchgear, and cybersecurity systems must be experienced in PPR techniques.
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processes that produce revenue. What store, factory, or home
can operate without electric power?
PPRs are the microprocessor devices most closely coupled to all utility grids and microgrids. PPRs are required
to protect life, the environment, and assets from damage
on both utility grids and microgrids. PPRs commonly perform only protection functions on utility grids, whereas they
commonly provide both protection and control functions
on microgrids. PPRs are digital protective relays with userprogrammable logic, synchronized metering, oscillographic
data collection, sequence-of-events collection, high-speed
communication protocols, and so forth. PPRs came to the
market in the mid-1990s as high-voltage transmission-class
digital protective relays and have evolved into small-formfactor devices for the industrial and medium-voltage distribution market. PPRs for small microgrids are frequently
used as both a protective relay and microgrid controller. For
larger microgrid jobs, PPRs provide a hard-wired physical
connection for remote and centralized microgrid controllers.

may/june 2021

ieee power & energy magazine

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IEEE Power & Energy Magazine - May/June 2021

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