IEEE Power & Energy Magazine - November/December 2020 - 31

Stage 1-Appendix A: High Penetrations of Distributed
Solar PV" in the "For Further Reading" section.
Frequency Disturbance Case Study

The current inverter interconnection standard requires an
overfrequency droop, or frequency-watt (F-W), response.
At the time the standard was published, in 2015, this was a
world-leading requirement, as the F-W response was generally not mandatory for small-scale systems. An analysis of
real-world operational data from more than 3,000 D-PV systems during a major system disturbance on 25 August 2018
has provided unique insight into the inverter performance of
this F-W function. D-PVs installed under the current standard ("post-2016" systems) appear to have performed the
F-W response adequately, in aggregate (Figures 15 and 16),
providing evidence of D-PVs acting rapidly, autonomously,
and in concert to aid with maintaining power system security. This sort of useful DER response is becoming more
important in regions, such as South Australia, where there is
limited interconnection with neighboring areas and demand
is increasingly met by D-PVs during some periods. However, the separation event on 25 August 2018 also uncovered
concerns regarding inverter compliance. An examination
of individual D-PVs (rather than in aggregate) found that at
least 15% of the systems in Queensland and 30% of those in

South Australia did not appear to perform an F-W response.
High noncompliance rates raise concerns as to whether
inverters can and will perform key functions, such as underfrequency ride-through, when required.
Voltage Disturbance Case Study

D-PV responses to major system voltage disturbances also
pose substantial risks. A 30-40% reduction in the aggregate
D-PV generation has been observed following major voltage disturbances in NEM, including an event in South Australia
on 3 March 2017 following the loss of the Torrens Island gas
generator (steam subcritical, nameplate capacity: 1,280 MW).
During this event, the voltage fell to 0.1 per unit for one
phase in the Torrens Island area, which is in proximity to the
main load center of Adelaide. It is worth noting that the conditions during the disturbance were similar to those experienced prior to the 2016 South Australia system blackout
event and that D-PV losses exacerbated the situation, with
the most extreme D-PV response close to the disturbance
source (Figure 17). A further analysis undertaken by AEMO
in its renewable integration study (RIS) supports a number
of necessary actions. The RIS notes that, in the absence
of these actions, AEMO may require a moratorium on
D-PV installations or the expensive retrofitting of existing
D-PV equipment.

SAPN Systems

Other DNSP Systems

AusNet
Services
Support
Systems

REST Web
Services

IEEE
Standard 2030.5
Utility Server

IEEE
Standard
2030.5

Aggregator
Cloud Platform

Site Energy
Management
System

Gateway

Proprietary
Protocols

API calls support electronic
registration, monitoring,
and constraint publication.

OEM
Protocols

Constraint
Estimator

SAPN API

Time Series
Database

DNSP API

DER
Database

Multiple Connection Options for Market
DER
DER
DER

DER
DER

DER

figure 14. The SAPN technical architecture for flexible export limit communication. Communication between the DNSP
and the server uses a Representational State Transfer (REST) software architecture, while exchanges between the server
and the DERs or the DER controllers employ IEEE Standard 2030.5. API: application programming interface; OEM: original
equipment manufacturer.
november/december 2020

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IEEE Power & Energy Magazine - November/December 2020

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - November/December 2020