IEEE Power & Energy Magazine - September/October 2021 - 55

otherwise be required if no FFR was available, which results
in a reduced need for synchronous unit directions.
During low-demand conditions when there is a need to
reduce the amount of grid-connected generation, such a
measure provides a twofold benefit. It allows a smaller number
of synchronous units online while also maximizing the
overall frequency control capability of a region.
The Need for Enhanced Modeling
and System Testing
Secure power system operation requires the use of fit-for-purpose,
accurate, and validated power system simulation models.
The use of wide-area EMT modeling has become a necessity.
Conventional power system models cannot accurately represent
complex interactions and overall system response under
scenarios with a high share of IBRs. All of the studies discussed
in this article and the operational measures taken are
based on the wide-area EMT models that AEMO has developed.
While AEMO does not currently integrate EMT analysis
into control room tools for real-time assessments, it does
use these models extensively to determine the secure operating
envelope of the power system with a high share of IBRs and
power system limits under various system conditions.
Considering the novelty of some of the experienced phenomena
and increased complexities in actual power systems
and simulation models, it is important to validate these models
to ensure they represent the actual behavior of the system
and its elements. Field measurements recorded during
system disturbances provide a good opportunity to validate
the overall system model against network faults that may not
otherwise be practicable.
Over the last few years, AEMO and relevant asset owners
have carried out field tests in an area with a high share of IBRs.
The aim is to observe the collective response of several IBRs
and their interactions with the wider network and measure key
quantities that can be later used for validating models. Examples
of such tests were shown in Figures 5 and 7.
Summary
Operating a power system with a high share of IBRs has
presented AEMO with several new and complex system
security challenges. This has necessitated developing many
novel solutions backed by detailed and fit-for-purpose power
system modeling and simulation studies.
SA, one of five NEM regions, has the highest share of IBRs
at both the transmission and distribution levels. For this reason,
many actions currently implemented in the NEM were
first operationalized in SA and then implemented in other
regions (recognizing that other NEM regions experience
unique phenomena). Actions discussed in this article are
✔ establishing minimum must-run synchronous units
at all times during both system intact and islanded
conditions
✔ installing strategically located synchronous condensers
to reduce the need for the directed dispatch of synchronous
generators, which otherwise naturally tend
to be offline during high IBR periods, hence, reducing
the cost of market interventions
✔ determining and managing the size of sympathetic
disconnection of uncontrolled distributed PVs to avoid
creating a larger contingency than would otherwise
need to be accounted for
✔ identifying the value of FFR provided by IBRs, and
its complementary value concerning physical inertia
provided by synchronous generators, to securely operate
a normally interconnected power system with high
IBRs share as an island.
The article also presents an example of adverse control system
interactions between multiple electrically close IBRs, all
in remote parts of the network and far from large synchronous
generators. Such phenomena have been experienced frequently
in remote parts of the network with high IBR shares. Methods
implemented in the short and long term to address the resulting
low-frequency oscillations include a reduction in the number
of online inverters, use of nearby synchronous condensers, and
control system tuning for the impacted IBRs to operate stably
under lower system strength conditions that would not be possible
with the original control system.
For Further Reading
B. Badrzadeh, S. Grogan, and N Modi, " Minimum system
strength for secure operation of large-scale power systems
with high penetration of non-synchronous generation, " in
Proc. CIGRE Paris Symp., 2018.
A. Jalali, B. Badrzadeh, J. Lu, N. Modi, and M. Gordon,
" System strength challenges and solutions developed for a
remote area of Australian power system with high penetration
of inverter-based resources, " CIGRE Sci. Eng. J., pp.
27-37, Feb. 2021.
" South Australian electricity report, " AEMO, Melbourne,
Australia, Nov. 2020. [Online]. Available: https://www.aemo
.com.au/-/media/files/electr icity/nem/planning_and
_forecasting/nem_esoo/2020/2020-electricity-statement-of
-opportunities.pdf?la=en
Biographies
Babak Badrzadeh is with Aurecon Group, Melbourne, Victoria,
3008, Australia.
Nilesh Modi is with Australian Energy Market Operator,
Brisbane, Queensland, 4000, Australia.
James Lindley is with Australian Energy Market Operator,
Brisbane, Queensland, 4000, Australia.
Ahvand Jalali is with Australian Energy Market Operator,
Melbourne, Victoria, 3000, Australia.
Jingwei Lu is with Aurecon Group, Melbourne, Victoria,
3008, Australia.
p&e
september/october 2021
ieee power & energy magazine
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IEEE Power & Energy Magazine - September/October 2021

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