NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

Active Power Control Testing at the U.S. 

National Wind Technology Center

Erik Ela

Presented at the Wind Power 

Workshop, 27 January 2011, 

Boulder, Colorado

Erik.Ela@nrel.gov

NREL/PR-5500-49785

PIX 16571
National Renewable Energy Laboratory Innovation for Our Energy Future

Current Mainstream Limitations of Wind

• What some of the papers and the anti-wind 

community say about wind...

• It costs too much

• Only competitive when gas prices soar

• Without RPS and PTC revenues would not be enough to 

justify high capital costs

• Causes negative prices in areas where too much wind has 

been built before transmission

• It cannot behave as traditional generators

• It is variable and is more of a detriment to power system 

stability than a benefit

• The word “non-dispatchable” comes to mind
Differences in Perspective

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Operators

Wind 

Owner/Operator

Manufacturer

Sure I desire it, 

but why would I 

ask them to 

provide the 

capability if they 

cannot provide it?

Why would I provide 

that capability if I can’t 

make money from it 

and lose money in the 

energy market?

Sure I can build 

this, but why 

market this 

capability if nobody 

desires it?

Regulator

Why create a

market for that 

capability if it 

currently is given 

for free?

Research and 

Demonstration
Operating Reserves for Active Power Control

Operating 

Reserve

Regulating 

Reserve

Contingency 

Reserve

Load 

Following 

Reserve

Frequency 

Responsive 

Reserve

Replacement 

Reserve

Ramping 

Reserve

Non-event Event

Fast Slow Instantaneous Non-Instantaneous

Spinning Reserve

Non-Spinning Reserve
Operating 

Reserve

Regulating 

Reserve

Contingency 

Reserve

Load 

Following 

Reserve

Frequency 

Responsive 

Reserve

Replacement 

Reserve

Ramping 

Reserve

Non-event Event

Fast Slow Instantaneous Non-Instantaneous

Spinning Reserve

Non-Spinning Reserve

Operating Reserves for Active Power Control
Regulation

• Regulation is provided by units that have automatic generation 

control (AGC)

• AGC signals are developed by the control area operator’s 

energy management system and are sent directly to the 

generator (in some areas loads can also participate)

• In a stand-alone system (island) AGC signals are used to 

correct frequency back to its scheduled setting

• In large interconnected systems, AGC is used to correct area 

control error (ACE) for each area within the interconnection

• ACE is based on each individual areas’ load balance and 

calculated based on tie-line schedule errors considering the 

area’s frequency response

• Maintaining low ACE in all areas will in affect balance frequency 

while also minimizing accounting problems of inadvertent 

interchange between areas

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Area Control Error Signal

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Regulation

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Constant balancing of Area Control Error
Typical generator regulating

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Source: Lazerwicz et al
Regulation from Wind

National Renewable Energy Laboratory Innovation for Our Energy Future

-80

-60

-40

-20

0

20

40

60

80

100

08:52 09:00 09:07 09:14 09:21 09:28 09:36 09:43 09:50 09:57

Total Wind Potential Energy Schedule Set Point Smoothed ACE WIND AGC SCHEDULE
Regulation from Wind

National Renewable Energy Laboratory Innovation for Our Energy Future

-20

-10

0

10

20

30

40

50

10:55 11:02 11:09 11:16 11:24 11:31 11:38 11:45 11:52 12:00

Total Wind Potential Energy Schedule Set Point Smoothed ACE WIND AGC SCHEDULE

Poor Performance due to lack of wind and regulation schedule.
Regulation from Wind

National Renewable Energy Laboratory Innovation for Our Energy Future

-20

-10

0

10

20

30

40

50

10:55 11:02 11:09 11:16 11:24 11:31 11:38 11:45 11:52 12:00

Total Wind Potential Energy Schedule Set Point Smoothed ACE WIND AGC SCHEDULE

Performance now acceptable when system 

operator gives appropriate schedule.
A Lucrative Business

• Regulating is essential to an area; since 

“deregulation” markets have been 

formed to pay for this service along with 

other ancillary services

• Many units take wear and tear hits on 

their machine and turn this into high 

offer costs to provide the service that 

lead to high prices (also efficiency loss 

costs)

• These prices are in $/MWh of capacity, 

the unit will be paid the energy price 

based on where it actually produced in 

addition

• These prices will be paid as long as the 

unit follows the AGC directions in a 

reasonable manner

• The prices can often be higher than 

energy prices and will increasingly be so 

as more low-variable-cost resources 

enter the energy market

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Eastern Date Hour

Pricing 

Region

10 Min 

Sync

10 Min 

Non Sync

30 Min 

Non Sync

Regulatio

n

10/1/2009 0:00 EAST 3.34 3.34 0.25 28

10/1/2009 1:00 EAST 3.35 3.35 0.25 28

10/1/2009 2:00 EAST 3.35 3.35 0.25 28

10/1/2009 3:00 EAST 3.35 3.35 0.25 28

10/1/2009 4:00 EAST 3.35 3.35 0.25 28

10/1/2009 5:00 EAST 3.35 3.35 0.25 45

10/1/2009 6:00 EAST 3.36 3.36 0.25 209.02

10/1/2009 7:00 EAST 7 3.4 0.5 39.5

10/1/2009 8:00 EAST 5 3.38 0.5 43

10/1/2009 9:00 EAST 6.11 3.38 0.5 41.5

10/1/2009 10:00 EAST 6.2 3.36 0.5 41.5

10/1/2009 11:00 EAST 7 3.37 0.5 28

10/1/2009 12:00 EAST 6.11 3.35 0.5 28

10/1/2009 13:00 EAST 6.14 3.35 0.5 28

10/1/2009 14:00 EAST 6.11 3.35 0.5 28

10/1/2009 15:00 EAST 6.1 3.35 0.5 28

10/1/2009 16:00 EAST 6.11 3.32 0.5 41.5

10/1/2009 17:00 EAST 6.1 3.32 0.5 41.5

10/1/2009 18:00 EAST 6.89 3.32 0.69 41.5

10/1/2009 19:00 EAST 9.84 3.34 2 41.5

10/1/2009 20:00 EAST 5 3.32 0.5 41.5

10/1/2009 21:00 EAST 5 3.34 0.5 41.5

10/1/2009 22:00 EAST 5 3.36 0.5 41.5

10/1/2009 23:00 EAST 0.25 0.25 0.25 28

21 cents per kWh just to 

provide capacity!

NYISO pricing data www.nyiso.com
NYISO Regulation Prices

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$0

$50

$100

$150

$200

$250

$300

0:001:002:003:004:005:006:007:008:009:00

10:0011:0012:0013:0014:0015:0016:0017:0018:0019:0020:0021:0022:0023:00

Regulation Exceeds Energy
Example

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Steam Generators: 5 with minimum gen = 100 MW, 

maximum = 300 MW, 2 MW/min ramp rate; all must stay 

on at night due to commitment constraints

Wind: blowing at 300 MW

Load: 800 MW

Regulation Requirement: 50 MW/5min up and down, 

Current Solution: Steam generators all operate at 110 MW, 

wind is curtailed to 250 MW. (Energy price = $0, regulation 

price >> $0)

Wind on Regulation: Steam generators all operate at 100 

MW, Wind is not curtailed.

Thus reducing costs and emissions
Primary Response and Inertia

• Inertia of synchronous machines provide initial response to 

disturbances of supply-demand balance

• More inertia on the system will decrease the rate of change of 

frequency decline during disturbances

• Primary response (e.g., frequency response, governor control) 

adjusts mechanical input after sensing frequency deviations

• Primary response used to stabilize frequency to some level

• Primary response based on governor control of traditional 

hydro-thermal generating units

• Response based on droop (∆f/∆P in pu), frequency dead band, 

and MW capacity head room (Pmax – Pgen)

• Both services essential to reduce the impact of frequency 

decline (or increase) and avoiding the need to shed load based 

on under-frequency load shedding relays

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Frequency Response Basics 

(Using a 1400 MW generation loss event as an example)

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

Time (Seconds)

Governor/Load Response (MW)

59.60

59.65

59.70

59.75

59.80

59.85

59.90

59.95

60.00

60.05

60.10

Frequency (Hz)

Governor Response

 Load Response

Frequency

A

B

C

NERC Frequency Response =

 Generation Loss (MW) 

FrequencyPoint A-FrequencyPoint B

Slope of the dark green line 

illustrates the System Inertia 

(Generation and Load). 

The slope is ΔP/(D+2H)

Pre Event Frequency

Frequency Nadir:

Generation and Load Response equals 

the generation loss

Settling Frequency: 

Primary Response is almost all deployed

Taken from FERC Technical Conference on Frequency Response, Sept, 2010
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Current Status

• Europe: UCTE requires 3000 MW of primary response 

throughout interconnection, distributed based on load/gen ratio

• N.America: No requirement for primary response, only a 

requirement for frequency bias as part of ACE equation 

(1%peak load/0.1Hz)

• Current decline of the North American Eastern Interconnection 

of about 60-70 MW/0.1 Hz per year (Ingleson and Nagle 98, 

Ingleson and Ellis 2004)

• Eastern Interconnection currently has no “C” point

• Reasons for decline

• Governor dead bands

• Stepped droop rather than proportional curve

• Blocked governors

• Generator modes (sliding pressure, exhaust temperature control mode)

• If enough wind displaces and de-commits units 

providing this, and wind does not provide these 

capabilities, this can cause a further decline
Response with Wind contribution

National Renewable Energy Laboratory Innovation for Our Energy Future

Miller et. al, “Impact of Frequency Responsive Wind Plant Controls on Grid 

Performance,” 9th International Conference on transmission networks and offshore wind. 

Quebec, Canada, October 2010.
NREL project

National Renewable Energy Laboratory Innovation for Our Energy Future

• NREL and EPRI joint project, to test at NWTC facilities

• Computer simulations

• CART machine field test

• DOE wind turbine test and demonstration (1.5 MW)

• Regulation signal with actual ACE input

• Inertial response with synthetic/real frequency input

• Primary response with synthetic/real frequency input

• Parameter adjustments (dead bands, ramp rates, droop 

characteristic, etc.)

• Different wind speeds, upward and downward, high varying wind

• All three responses together

• Publish results and demonstrate to regulators, operators, wind 

owner/operators, and manufacturers
Schedule

Currently setting up project roles, literature reviews.

Early 2011: Simulations for different procedures

September 2011: Interim project report

September 2012: Final project report, demonstrations

National Renewable Energy Laboratory Innovation for Our Energy Future
And the result

• If tested, and reports show wind turbine providing 

capability satisfactorily...

• It costs too much?

• Additional revenues per wind plant would possibly be in the 

millions should they choose to participate and market rules 

are correctly designed

• Help wind compete with other generation when subsidies are 

no longer given

• It cannot behave as other generators?

• Studies may show it providing the finest scale of active 

power control capability on a better quality than other 

generation

• Obviously, more questions and issues will arise once 

it is shown to be a feasible option, but this would be a 

very good starting point

National Renewable Energy Laboratory Innovation for Our Energy Future
Questions

Erik.Ela@nrel.gov

National Renewable Energy Laboratory Innovation for Our Energy Future