IEEE Power & Energy Magazine - November/December 2020 - 32

Solutions
Interconnection Standards

for new D-PV installations in South Australia to aid in managing extreme abnormal system conditions during periods of
high D-PV contribution.

In Australia, DERs are predominantly small systems connected to the LV grid through inverter energy systems, with
requirements for their function and performance specified in
Standard for Grid Connection of Energy Systems via Inverters-Part 2: Inverter Requirements, AS/NZS4777.2:2015.
In June 2019, AEMO submitted a proposal to review AS/
NZS4777.2 to address the key challenges resulting from the
increasing penetration of D-PVs by aligning the aggregate
behavior requirements for these systems with wider power
system security objectives as well as distribution-level
protection, power quality, and safety requirements. The
proposed changes align with recent developments in international standards, such as IEEE 1547-2018 and Association of Electrical Engineering 4105 (Germany), which have
implemented "smart" inverter functionality to support system security. As of July 2020, a revision of AS/NZS 4777.2
is out for public consultation, with expected publication in
early 2021. This revision was developed through close collaboration between AEMO, DNSPs, inverter manufacturers,
and other key stakeholders. In addition, AEMO is seeking to
mandate minimum device-level curtailability requirements

Disturbance Withstand Capabilities
As previously described, an analysis of recent system disturbances in NEM has highlighted the increasingly significant
and unpredictable behavior of D-PVs during these events.
The analysis shows that some of the currently installed
inverters behaved in unexpected ways. Potential noncompliance with the expected operation under the current standard
could have caused unforeseen reductions and losses of generation, thus increasing the event severity. With increasing
DER levels, the unpredictable and potentially damaging
behavior of D-PVs creates a growing risk and uncertainty
that (in the absence of improved DER capabilities) will drive
a need for AEMO to take increasingly conservative actions
in managing the power system. Under the most extreme DER
generation levels, AEMO might otherwise lose the ability to
maintain line flows and restore operational stability. To continue to securely manage the power system as the penetration
of inverter-connected DERs continues to grow, disturbancewithstanding requirements are being clarified and defined
in AS/NZS4777.2. The proposed changes seek to define

50.5

1:34 p.m.

1:32 p.m.

1:30 p.m.

1:28 p.m.

1:26 p.m.

48.5

1:24 p.m.

0.6

1:22 p.m.

1:20 p.m.

0.7

1:18 p.m.

49.5

1:16 p.m.

0.8

1:14 p.m.

1:12 p.m.

0.9

1:10 p.m.

Normalized Power
(MW/MW at 1:10:55 p.m.)

Frequency Peak: 50.866 Hz at 1:11:44 p.m.
Frequency: <50.15 Hz for 60 s
Beginning at 1:26:10 p.m. and
Frequency: >50.25 Hz at
Ending at 1:27:10 p.m.
1:11:42 p.m.

Frequency (Hz)

1.1

Australian Eastern Standard Time
AS/NZS4777.2:2015-Specified Response

AS/NZS4777.2:2015-Specified Response (1-min Average)

Observed Power: <30 kW, 878 Sites

Observed Power: 30-100 kW, 92 Sites

Queensland Frequency

50.25 Hz

50.15 Hz

figure 15. Queensland's post-2016 inverter-over-frequency-droop response during the 25 August 2018 event. The average aggregate power is compared with the specified profile. For further details, please refer to "Technical Integration of
Distributed Energy Resources" in the "For Further Reading" section.
32

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