IEEE Power & Energy Magazine - November/December 2019 - 40

1.2

Bus Voltage (pu)

1.1

DG Netted With Load

1
DG Modeled
0.9

0.8

0.7
0

4
6
8
Bus Voltage (pu)

figure 5. The 230-kV bus voltage close to a three-phase
fault, with and without DER modeled. pu: per unit; DG:
distributed generation.

Net Load and DERs

70
60

Net Load

(MW)

50
40
30
20
10
0

DER Output
0

6
Time (s)

(a)
Voltage

1.2

Voltage (pu)

New York's DER Management

0.8
0.6
0.4

6
Time (s)

(b)
No Model

California Rule 21

IEEE 2018

figure 6. The sensitivities of net load, DER output, and
BPS bus voltage to DER modeling settings.
40

and stability studies for the past three planning cycles to
account for their unique operational characteristics that are
different from the end-use load behavior. This is especially
important for stability studies, since the results between
DERs netted with load versus modeled ones are significantly
different. With a large penetration of DERs in California, study results would be inaccurate if DERs were only
netted with load and would lead to erroneous conclusions.
Retail-scale BTM DERs are modeled in the power flow and
dynamic stability studies as part of a composite load model,
and utility-scale DERs are modeled as aggregated generators on the transmission buses. Figure 5 illustrates these
impacts on transient voltage response following a simulated
BPS fault event. The results are different because modeling
the DER characteristics explicitly (including DER tripping
of legacy equipment) allows the simulation to differentiate
between DERs' response and gross load response. This is
critical as penetration levels of DERs increase, although
DER prevalence has a study impact in all cases, even at low
penetration levels.
CAISO currently uses parameter values for the DER models
based on the Western Electricity Coordinating Council and
North American Electric Reliability Corporation (NERC)
guidelines and performs multiple sensitivity studies to determine the impact that variations in the DER parameters have
on BPS performance. The most sensitive parameters DER
undervoltage trip settings, the fraction of DERs that recover
when voltage returns, and whether DERs provide voltage regulation (and the characteristics of that regulation). Figure 6
illustrates the net load and DER response on a 230-kV bus
and the BPS voltage for a three-phase fault close to the BPS
bus. The plots show the DERs netted with load as well as two
cases of DERs modeled explicitly with different voltage trip
settings. One set uses the IEEE Standard 1547-2018 settings,
and the other uses California Rule 21 settings. The DERs are
on the different feeders and aggregated to the 230-kV bus.
System performance differences are dominated by the different responses of the gross load and DERs. Although the
difference is not that significant for one bus, the aggregate
effect across a large portion of the system has a significant
impact on the study results.

ieee power & energy magazine

New York State is on the cusp of a transformation as it expects
a significant penetration of DERs. New York's Reforming
the Energy Vision and Clean Energy Standard initiatives,
combined with efforts to expand transfer capability on the
BPS, offer a comprehensive energy strategy to achieve its
goal of 50% of its electricity delivered by renewable
energy sources by 2030. New York has also established a
policy to achieve 1,500 MW of energy storage by 2025
and 3,000 MW by 2030.
The New York Independent System Operator (NYISO)
expects DERs to play a significant role in achieving the
state's goals. Due to the expected growth of DERs in the near
november/december 2019

IEEE Power & Energy Magazine - November/December 2019

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