IEEE Power & Energy Magazine - September/October 2021 - 23

Connecting generators, original equipment manufacturers,
and network service providers are adapting to operating
in these low system strength conditions.
synchronous plants required to be online in the state of Victoria
in the NEM. The figure shows synchronous generation
plotted against the wind and solar PVs online for 2019 (colored
dots) and 2025 (gray dots). The colors highlight the
number of large synchronous generators online from the
minimum combinations list. The projected generator dispatch
outcomes for 2025 show an increasing likelihood of dispatch
outcomes not delivering the required minimum combination
of synchronous generators in the Victoria region.
AEMO is responsible for determining the minimum levels
of system strength at critical locations in the transmission
system. If these levels are forecast to be breached in the next
five years, AEMO declares a system strength shortfall. The
local utility is then required to procure system strength services
to meet this gap.
A multifaceted approach is needed to manage the impacts
of system strength with the needs of the power system likely
to change as the generation mix changes. Opportunities arise
for technology innovation to offer novel alternatives to traditional
solutions.
In the NEM, consideration is being given to some combination
of the following solutions:
✔ maintaining some minimum level of syst em
strength at key network locations; this may be
achieved by maintaining a minimum combination of
synchronous generators and synchronous condensers
online at all times
✔ actions to support stable
operation of new connecting
IBRs, such as
* performance standards
that ensure an ability to
operate stably down to
some defined level of system
strength
* improved control system
tuning
* network upgrades
* scale-efficient system
st rength solut ions to
enable stable operation
of defined IBR levels
in nominated network
locations
* individual remediation
of local system strength
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issues by new connecting IBRs to ensure stable
system operation
✔ monitoring advancements in new technologies, such
as inverter control systems, to enable stable system
operation to be achieved more efficiently than with
present solutions.
Many of these potential options need to be explored via electromagnetic
transient studies to determine what actions must
be taken. The complexity of studies required to enable transitioning
to operation at lower levels of system strength should
not be underestimated. These challenges are making power
system operations in Australia interesting and exciting. In a
separate article in this issue, " Power System Operation With
a High Share of Inverter-Based Resources: The Australian
Experience, " the challenge of operation in locations with low
system strength is discussed, and implemented measures have
been highlighted.
Variability and Uncertainty in the
Supply and Demand Balance
Increased reliance on wind and solar for energy will increase
the variability and uncertainty in the energy supply. AEMO's
statistical analysis of historical and 2025 projected ramps identified
that hourly net demand ramps will be significantly larger
in magnitude. Some are projected to exceed 5 GW/h beyond
levels previously experienced in the NEM.
Steeper
Shorter and
Earlier
Morning
Peak
Evening Ramp
(>3 GW/h)
Reduction in
Midday Trough
2015 2016 2017 2018 2019 2025
figure 7. The historical versus projected winter NEM average daily net demand
profiles. (Source: AEMO; used with permission.)
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IEEE Power & Energy Magazine - September/October 2021

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