IEEE Power & Energy Magazine - March/April 2021 - 82

Frequency-response security maps have been widely used
by AEMO in its 2020 Renewables Integration Study and
implemented in AEMO's control room in Western Australia
for the real-time online security assessment of low-inertia

ROCOF Requirement
0

2,50

Nadir Requirement

PFR (MW)

0
2,00

Static Requirement

0
1,50
0

1,00

500

In

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figure 3. A frequency-response security map to comply
with the desired nadir, ROCOF, and quasi-steady-state
frequency limits considering variable contingency size
(adapted from Puschel et al., 2020).

conditions for the Wholesale Electricity Market operated in
the South West Interconnected System. These maps can also
be used to assess the implications of using fast frequencyresponse resources to support slower generation units or
modulate the size of the largest contingency in the system to
decrease the incumbent security requirements.
In this respect, Figure 3 illustrates a 3D security map
considering the interaction of a variable contingency size,
with the amount of inertia and PFR shown. From the example, it can be appreciated how the ROCOF and nadir requirements decrease greatly (for the nadir, very nonlinearly) with
the contingency size. This suggests that ramping down the
output of the largest online generator could significantly help
meet security requirements, and this effect is much larger for
decreasing inertia conditions.
A natural implementation of the multiparametric security maps discussed previously is the development of a frequency-response, security-constrained, optimal power-flow
tool that could co-optimize energy, PFR (and fast frequency
response), inertia, and the largest system contingency. The
largest contingency may refer to generation/demand loss as
well as, more generally, to interconnector flows in case there
is a risk of system split. Such tools are now being considered
for implementation in both the NEM and Western Australia.
There are also various progressive approaches undertaken by AEMO to deal with variability and uncertainty
by using data-driven artificial intelligence algorithms. For

table 1. The fragility of low-carbon grids: Challenges and potential solutions.

82

Risk

Emergence

Mitigations

Frequency
control and
inertia

* Sustained frequency excursions
(regulation)
* High ROCOF following contingency
* Insufficient regional inertia
* Insufficient PFR
* The risk of low inertia and insufficient PFR
after separation

*
*
*
*

Variability and
uncertainty

* A large variation in net demand
* Insufficient short- and medium-term and
ramping reserves

* Better forecasting
* Machine learning to assess reserves (e.g., dynamic Bayesian
belief network tools)
* The use of more flexible resources, including energy storage
(e.g., pumped hydro)

DER visibility

* Photovoltaic generation (and generally
DERs) trip following transmission
frequency and voltage events
* Commercial security issues related to fast
price-driven response from DERs

* Connection standards
* The setup of distributed marketplaces for DERs to interact
with wholesale markets
* Advanced transmission system operator/distribution system
operator interface and coordination

System strength

*
*
*
*

* Minimum levels of inertia and fault current (out-of-merit
dispatch of conventional generators)
* Synchronous condensers
* Static synchronous compensator and static VAR
compensators to improve voltage stability
* Improvements of internal generator controls (especially in
solar and wind farms)
* Grid-forming converters and virtual synchronous machines

Fault current shortage
Voltage instability
Sustained voltage oscillations after fault
Fault ride-through issues

ieee power & energy magazine

Minimum inertia levels
Compulsory droop-based governor response
An additional amount of PFR
The co-optimization of energy, frequency response, and
(regional and system-level) inertia
* The regional allocation of reserves
* New sources of fast frequency response (e.g., batteries,
electrolyzers)
* The management of largest contingency and interconnector
flows (system at risk of regional separation)

march/april 2021
IEEE Power & Energy Magazine - March/April 2021

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - March/April 2021
