IEEE Power & Energy Magazine - November/December 2019 - 42

Sites That Disconnected (%)

systems' reliability needs, under NYISO's proposed rules,
priority will be given to maintaining the transmission system's reliability. DER aggregators must work with the DSPs
to meet local reliability criteria and coordinate with NYISO
to deliver the expected services.
Enhanced operational coordination starts two days prior to
the operating day, when the DSP communicates any potential
or expected outages to the DER aggregator. One day prior to
the operating day, aggregators use this information to assess
the availability of the overall aggregation and submit DER
aggregation offers to the NYISO day-ahead market. NYISO
will evaluate these offers with those from other BPS suppliers
and schedule day-ahead market resources. Aggregators report

50
45
40
35
30
25
20
15
10
5
0

Pre-2015
Transition
Post-2016

Zone 1

Zone 2
(a)

Zone 3

Zone 1
Zone 2
Zone 3

(b)

(c)

figure 8. The geographic distribution of the monitored
D-PVs sites disconnecting in New South Wales during the
25 August 2018 event.
42

ieee power & energy magazine

to the DSP their intended dispatch of individual DERs to meet
the NYISO day-ahead market schedule. DSPs can use this
information to identify any potential reliability impacts on
their systems and communicate any restrictions on individual
DER dispatches to the aggregators.
Ongoing communication will be necessary among the
DSPs, DERs, and aggregators after the NYISO day-ahead
market is posted, and it will continue in real time to identify
and address changes in the distribution system conditions and
potential impacts on individual DERs. Aggregators will be
required to communicate aggregation-level changes to NYISO
so that they are reflected in the real-time dispatch. The DSPs
can also request NYISO operations to dispatch DER aggregations to address reliability issues. This enhanced operational
coordination framework recognizes the transmission-distribution system interface and allows DERs to effectively provide
services to both the BPS and DSP.

Managing DERs in Australia
The installed capacity of DERs, particularly D-PVs, is rapidly
growing in Australia's National Electricity Market (NEM),
with more than 6,000 MW installed and a projected increase
to 10-17 GW by 2030 (with peak demand of roughly 35 GW).
The South Australia region of the NEM has been a focus for
analyzing D-PVs integration. This region is geographically
the approximate size of Texas, yet with a demand of 600-
3,000 MW, it has already experienced periods where more
than half of its requirement has been supplied by D-PVs. By
2026-2027, the Australian Energy Market Operator (AEMO)
predicts that the D-PVs capacity may be high enough to periodically supply the region's entire demand. The region is connected to the rest of the NEM via a single double-circuit ac
interconnector, with the expectation that South Australia will
continue to operate as an island if it is separated from the rest
of the network. This raises challenges and questions about how
to successfully operate when the majority of the load is supplied by D-PVs. To explore these challenges, AEMO launched
a program to identify and implement the actions required to
maintain the security and operability of the system.
One of the key focus areas in the program is understanding
and managing the behavior of DERs during grid disturbances.
If a large DER capacity disconnects during a disturbance, the
loss exacerbates the disturbance and could lead to instability. AEMO has been gathering data on DER responses during
grid disturbances and identified the following:
✔ D-PVs are more prone to tripping during grid disturbances than end-use loads.
✔ Net demand post-fault is higher than predisturbance
levels, indicative of D-PVs disconnection.
✔ Data from actual grid disturbances in Victoria, South
Australia, and New South Wales estimated that as
much as 30-40% of the aggregate D-PVs may disconnect during a disturbance.
✔ Laboratory inverter testing showed multiple reasons
for inverter tripping, including voltage phase jumps
november/december 2019

IEEE Power & Energy Magazine - November/December 2019

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