IEEE Power & Energy Magazine - March/April 2021 - 24

✔

response of the wind generation resource to low and
high-frequency events.
Voltage and frequency ride-through capability: This
is used to maintain the ability to remain connected to
the grid and for providing the necessary support during
voltage and frequency events of predefined severity.
Dispatchability: This is to ensure that resources follow the dispatch instructions for maintaining or adjusting power output in a timely and precise manner.
Ramping: This is used to limit the ramp rate of each
wind or solar resource to 20% per minute of its nameplate rating (megawatts) when responding to ERCOT
dispatch instructions.
Telemetry: This provides numerous telemetry data
points to ERCOT with a temporal resolution of 2-10 s. These
data points are critical to operation studies and situational awareness tools as well as for offline analysis.

Renewable Generation Forecasting
Renewable production potential forecasting is essential to
the integration of large amounts of renewable generation.
ERCOT acquired its first wind forecast service in 2010 and
added a second in 2017 to provide a centralized prediction
for all renewable generation connected to its transmission
grid. Both of these utilize site-specific meteorological
information, telemetered by wind generation resources,
to generate wind power production forecasts for each
resource. Adding another wind forecasting service provided ERCOT's control room with an ability to enhance
situational awareness and increased resiliency for the provision of this critical information.

60.05

Wind Resource Response to
Low Frequency 13 July 2016

With the addition of the second provider, new capabilities
of forecasting for extreme weather were procured from both
providers and made available to the control room. In addition
to the midterm wind generation forecast, which is delivered
each hour for the next 168 h, ERCOT also has an intrahour
wind forecast, which is delivered at a 5-min resolution for the
next 2 h. The averaged performance, namely the mean absolute percentage error, of day-ahead and 1-h-ahead midterm
wind forecasting in 2019 was 4.6% and 2.7%, respectively
(see Figure 8).
In 2017, ERCOT started solar forecasting for solar generation
with a size greater than 10 MW, connected to the transmission
network. The averaged performance of ERCOT's day-ahead and
1-h-ahead solar power production forecasting in 2019 was 6.55%
and 5.7% mean absolute percentage error, respectively.

Operations Analysis and Studies
To ensure reliable system operation in real time under varying system conditions, the system operator periodically carries out studies and analyses, starting from the day ahead
and going into real time, and uses situational awareness tools
to monitor system conditions (Figure 9).

Day-Ahead Analysis and Studies
✔ Generic transmission limits for the day-ahead market:

In addition to well-defined tools and processes to manage the steady-state constraints, increasingly stabilityrelated constraints also need to be controlled in operations. Generic transmission constraint is a restriction
on one or more grouped transmission elements to manage stability-related limitations. A two-day-ahead

180

60.075

60.025

178

60.056

176

60.038

59.975

174

60.019

59.95

172

59.925

170

59.981

59.9

168

59.963

59.875

166

59.944

59.85
13:25

13:28

13:31

13:34

13:37

164
13:40

Frequency

59.925
16:13

Wind Resource Response to
High Frequency 25 August 2015

140
130
120
110
100
90

16:16

Nominal Frequency

16:19

16:22

16:25

80
16:28

figure 7. The frequency response from wind generation resources in ERCOT.
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IEEE Power & Energy Magazine - March/April 2021

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - March/April 2021