IEEE Power & Energy Magazine - May/June 2021 - 69

and testing live microgrids is best done with time-synchronized PPRs at every IBR and utility point of coupling.
PPRs natively satisfy the microgrid testing standard (IEEE
2030.8-2018); Table 3 summarizes the data-collection
requirements of this standard. These data are collected by
the PPR and sent to a computer to be preserved for the
life of the microgrid. These data-collection methods preserve event data, including islanding, synchronizing, loss
of IBR, faults, open circuits, dispatch controls, and reacceleration, and are essential for any successful microgrid.
There are several phases of the microgrid testing process,
including hardware in the loop, commissioning, and site
acceptance. The data collection presented in Table 3 is used
to document the protection and control system for all phases
of testing and commissioning.
Hardware-in-the-loop testing may be used to validate PPR controls and protection systems in the lab. The
microgrid, including its inverters, gensets, excitation systems, load composition, mechanical loads, and engine
fuel/air delivery systems, is modeled in an electromagnetic transient model and computed in real time. Utility
electric power systems are usually simulated as a single,
large, synchronous generator with properly tuned inertia
and reactance. A simple Thévenin circuit model of a utility is not adequate because it does not contain the inertial,
transient, or subtransient effects of a real utility. Accurate
simulations are necessary to ensure that the PPR at the
PCC adequately tracks frequency, can identify open-circuit upstream conditions, and that adaptive protection systems are functional under all topologies and all combinations of online/offline IBRs.
Commissioning is done by protection experts after the
equipment is installed but before the power system is energized. During this phase, the wiring, current transformers,
voltage transformers, circuit-breaker controls, synchronization programming, and the IBR controls inside the PPR are
tested with current- and voltage-injection tools. Loop checks
are performed to make certain that all of the signals, wiring,
and communication systems are correct. The data collection

table 3. IEEE Standard 2030.8-2018.
IEEE 2030.8-2018
Requirement
PPR Solution

Usage

Sequence of
events

Sequence of
events records

Time-stamped
recordings of all
PPR decisions

Event
oscillography

COMTRADE
event records

Faster than a 4-ms
sample-rate data
collection of all the
disturbances

Continuous data
collection

IEEE C37.118
synchrophasors

Slower than a
16-ms sample-rate
collection for the
life of the microgrid

may/june 2021

presented in Table 3 is mandatory for successful debugging during commissioning.
Site-acceptance testing involves witnessing events like
islanding, synchronization, and safety testing, such as
National Electrical Code-required sensitive earth-ground
testing, and so on. Because of the inherent interdependence
of PPRs and IBRs in the microgrid, it is strongly advised
that dynamic load banks be employed during final siteacceptance testing. For example, to ensure that there are no
underfrequency or directional element-protection misoperations, load banks are used to test full-load acceptance and
rejection on each IBR.

Conclusion
There are two choices with inverter-based microgrids: 1)
Purchase oversized inverters or introduce additional devices
(such as synchronous condensers) to recreate the fault current levels, inertias, and negative-sequence behaviors of synchronous generators; or 2) reduce the cost and complexity
by using advanced inverters and PPRs, as described in this
article. The authors predict that the rapid proliferation of
PPRs and IBRs as renewable energy integrators will become
increasingly competitive in a market driven by low cost and
mandated reliability.

For Further Reading
S. Manson, B. Kennedy, and M. Checksfield, " Solving turbine governor instability at low-load conditions, " in Proc.
62nd Annu. Petrol. Chem. Ind. Techn. Conf., Houston, TX,
Oct. 2015, pp. 1-9. doi: 10.1109/PCICON.2015.7435099.
E. Limpaecher, R. Salcedo, E. Corbett, S. Manson, B.
Nayak, and W. Allen, " Lessons learned from hardware-inthe-loop testing of microgrid control systems, " in Proc. Grid
Future Symp., Cleveland, OH, Oct. 2017, pp. 1-6.
S. Manson, K.G. Ravikumar, and S.K. Raghupathula,
" Microgrid systems: Design, control functions, modeling,
and field experience, " in Proc. Grid Future Symp., Reston,
VA, Oct. 2018, pp. 1-8.
" 1,200 MW fault induced solar photovoltaic resource interruption disturbance report: Southern California 8/16/2016
Event, " NERC, Atlanta, GA, June 2017.
W. Du, R. H. Lasseter, and A. S. Khalsa, " Survivability of autonomous microgrid during overload events, " IEEE
Trans. Smart Grid, vol. 10, no. 4, pp. 3515-3524, Apr. 2018.
doi: 10.1109/TSG.2018.2829438.
IEEE Standard for the Testing of Microgrid Controllers,
IEEE Standard 2030.8-2018, Aug. 24, 2018.

Biographies
Scott Manson is with Schweitzer Engineering Laboratories,
Inc., Pullman, Washington, 99163, USA.
Ed McCullough is with Tesla Energy, Palo Alto, California,
94304, USA.

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