IEEE Power & Energy Magazine - November/December 2021 - 83

System operators need to be aware of this paradigm shift
and understand that some weather events currently deemed
benign will lead to system stress. The focus should not merely
be on events that drive extreme loads, but, rather, it should shift
to looking at events driving extreme net loads.
Smarter Procurement of Regulation
Requirements at the CAISO
As renewable penetration grows on the CAISO system, it
has become more important to develop methodologies to
incorporate products into the CAISO market optimization
to assist with uncertainty from the increasing capacity of
renewable resources. The CAISO products to assist with
uncertainty include regulation or operating reserves, flexible
ramp requirement, and a new product in development:
imbalance reserves. These can provide the flexibility needed
to assist with forecast deviations or movement between different
periods. For this discussion, the focus is on smarter
procurement of regulation requirements or operating reserves.
Regulation requirements account for active power capacity
held above or below expected average energy schedules to respond
to changing system conditions under operational timeframes. For
the California ISO, the focus is the prior 5 min to the current system
condition. Regulation requirements are held for many reasons-maintaining
frequency, reducing area control error (ACE),
power plant contingencies, forecast error for demand, behind-themeter
generation, and large-scale renewable generation. In the past
few years, the CAISO has partnered with multiple research partners
to develop and trial methodologies to optimize the regulation
capacity required during operating hours when the need is less but
increase operating reserves when it is greater.
The current methodology utilized is based on a statistical
analysis of the ACE signals and actual regulation applied to
Regulation Required
30,000
25,000
20,000
15,000
10,000
5,000
-5,000
-10,000
-15,000
-20,000
4,300
3,300
2,300
1,300
300
-700
-1,700
the system to correct ACEs. The sum of ACEs and actual
regulation applied to the system to correct ACEs is referred
to as ACE*. The base statistical analysis is updated monthly
at a minimum. Figure 6 shows the last 30 days of ACE*
(red lines) in combination with the regulation recommendation
(gray and yellow lines). The risk tolerance percentiles
forming the regulation recommendation within Figure 6 are
for the 98% (gray lines) and 95% (yellow lines) confidence
bands. Note that the risk tolerance percentiles are configurable.
If the CAISO finds that the regulation requirement
recommendation hits outside the bands, impacting operational
conditions, it indicates the potential need for adjustment
of the risk tolerance parameter.
Figure 7 shows an additional tool that allows the CAISO
to further analyze certain days and look at some of the main
Regulation Required
2,000
1,000
-1,000
-2,000
0246 810121416182022
Time of Day
figure 6. An example of a monthly look at ACE* alongside
requirement recommendations.
Solar RTD Forecast
Solar Actual (Raw)
Load Actual
Wind RTD Forecast
Wind Actual (Raw)
Load RTD Forecast
Net Load RTD Forecast
Net Load Actual
ACE* (-ACE + Regulation)
Regulation Up 95%
Regulation Down 95%
Regulation Up 98%
Regulation Down 98%
figure 7. A postanalysis from the perspective of the regulation needed for a day in March 2021. RTD: real time dispatch.
november/december 2021
ieee power & energy magazine
83
Load, Wind, and Solar Forecasts Versus Actual (MW)
AGC Requested (MW)
Regulation Recommendation Versus ACE* (MW)

IEEE Power & Energy Magazine - November/December 2021

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