Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer...

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Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer Engineering 1 Wind Generation Technology Short Course October 27, 2010 Iowa State University

Transcript of Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer...

Page 1: Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer Engineering 1 Wind Generation Technology Short Course.

Frequency control (MW-Hz) with wind

James D. McCalleyHarpole Professor of Electrical &

Computer Engineering

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Wind Generation Technology Short CourseOctober 27, 2010

Iowa State University

Page 2: Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer Engineering 1 Wind Generation Technology Short Course.

Outline1. MW-Hz time frames2. Transient frequency control3. Frequency governing4. CPS1, CPS25. Simulations6. Solutions7. Conclusions

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Page 3: Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer Engineering 1 Wind Generation Technology Short Course.

MW-Hz Time Frames

0+<t<2s; Inertial

t=0+; Proximity

2s<t<10s; Speed-governors 10s<t<5m; AGC

5m, ED3

Page 4: Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer Engineering 1 Wind Generation Technology Short Course.

MW-Hz Time Frames

Source: FERC Office of Electric Reliability available at: www.ferc.gov/EventCalendar/Files/20100923101022-Complete%20list%20of%20all%20slides.pdf

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This is load decrease, shown here as a gen increase.

Page 5: Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer Engineering 1 Wind Generation Technology Short Course.

MW-Hz Time Frames

-100

-80

-60

-40

-20

0

20

40

60

80

100

07:00 07:20 07:40 08:00 08:20 08:40 09:00 09:20 09:40 10:00

RE

GU

LA

TIO

N I

N M

EG

AW

AT

TS

Regulation

=

+

Load Following Regulation

Source: Steve Enyeart, “Large Wind Integration Challenges for Operations / System Reliability,” presentation by Bonneville Power Administration, Feb 12, 2008, available athttp://cialab.ee.washington.edu/nwess/2008/presentations/stephen.ppt.

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Page 6: Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer Engineering 1 Wind Generation Technology Short Course.

Transient frequency controlWhat can happen if frequency dips too low?• For f<59.75 Hz, underfrequency relays can trip

load.• For f<59 Hz, loss of life on turbine blades• Violation of NERC criteria with penalties

• N-1: Frequency not below 59.6 Hz for >6 cycles at load buses

• N-2: Frequency not below 59.0 Hz for >6 cycles at load buses

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Page 7: Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer Engineering 1 Wind Generation Technology Short Course.

Transient frequency control

fn

ii

L mH

fP

dt

fd

1

Re

2

60

t

1

mf1

mf2

mf3

Time (sec)

Frequency(Hz)

60-mf1t1

60-mf2t1

60-mf3t1

60

t

1

mf1

mf2

mf3

Time (sec)

Frequency(Hz)

60-mf1t1

60-mf2t1

60-mf3t1

The greater the rate of change of frequency (ROCOF) following loss of a generator ∆PL, the lower will be the frequency dip. ROCOF increases as total system inertia ΣHi decreases.Therefore, frequency dip increases as ΣHi decreases.

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Page 8: Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer Engineering 1 Wind Generation Technology Short Course.

Transient frequency control

49.35

Nadir2.75 sec

sec/227.0475*2

)50(32.4

21

Re HzH

fP

dt

fdm

n

ii

Lf

Example: Ireland: ∆PL =432 MW=4.32 pu. ΣHi =475 sec

1. Governors2. Load frequency sensitivity

50-0.227*2.75=49.38Hz8

Page 9: Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer Engineering 1 Wind Generation Technology Short Course.

Transient frequency controlExample: Estrn Interconnection: ∆PL =2900 MW=29 pu. ΣHi =32286 sec

Nadir59.9828 Hz

59.9725z

sec/0269.032286*2

)60(29

21

Re

Hz

H

fP

dt

fdm

n

ii

Lf

60-0.0269*1.5=59.9597Hz

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Page 10: Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer Engineering 1 Wind Generation Technology Short Course.

Transient frequency control

So what is the issue with wind….?1. Increasing wind penetrations tend to displace

(decommit) conventional generation.2. DFIGs, without specialized control, do not contribute

inertia. This “lightens” the system(decreases denominator) fn

ii

L mH

fP

dt

fd

1

Re

2

Let’s see an example….

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Page 11: Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer Engineering 1 Wind Generation Technology Short Course.

Transient frequency control

• Green: Base Case• Dark Blue: 2% Wind Penetration• Light Blue: 4% Wind Penetration• Red: 8% Wind Penetration

Estrn Interconnection: Frequency dip after 2.9GW Gen drop for Unit De-Commitment scenario at different wind penetration levels (0.6, 2, 4, 8%)

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Page 12: Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer Engineering 1 Wind Generation Technology Short Course.

Transient frequency controlWhy do DFIGs not contribute inertia?

They do not decelerate in response to a frequency drop.

FUELSteam Boiler

Generator

CONTROL SYSTEM

Steam valve controlFuel supply control

MVAR-voltage control

Wind speed

Gear Box

Generator

CONTROL SYSTEM

MVAR-voltage control

Real power output control

STEAM-TURBINE

WIND-TURBINE

The ability to control mech torque applied to the generator using pitch control & electromagnetic torque using rotor current control (to optimize Cp and to avoid gusting) enables avoidance of mismatch between mechanical torque and electromagnetic torque and, therefore, also avoidance of rotor deceleration under network frequency decline.

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Page 13: Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer Engineering 1 Wind Generation Technology Short Course.

Transient frequency controlWhat is the fix for this? Consider DFIG control system

Source: J. Ekanayake, L. Holdsworth, and N. Jenkins, “Control of DFIG Wind Turbines,” Proc. Instl Electr. Eng., Power Eng., vol. 17, no. 1, pp. 28-32, Feb 2003.

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Page 14: Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer Engineering 1 Wind Generation Technology Short Course.

Transient frequency controlAdd “inertial emulation,” a signal dω/dt scaled by 2H

-2H

dω / dt

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Page 15: Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer Engineering 1 Wind Generation Technology Short Course.

Transient frequency controlSeveral European grid operators have imposed requirements on wind plants in regards to inertial emulation, including Nordic countries [1,2]. North American interconnections have so far not imposed requirements on wind farms in regards to frequency contributions, with the exception of Hydro-Quebec.

The Hydro-Quebec requirement states [3, 4], “The frequency control system must reduce large, short-term frequency deviations at least as much as does the inertial response of a conventional generator whose inertia (H) equals 3.5 sec.”

[1] “Wind Turbines Connected to Grids with Voltages above 100 kV – Technical Regulation for the Properties and the Regulation of Wind Turbines, Elkraft System and Eltra Regulation, Draft version TF 3.2.5, Dec., 2004. [2] “Nordic Grid Code 2007 (Nordic Collection of Rules), Nordel. Tech. Rep., Jan 2004, updated 2007. [3] N. Ullah, T. Thiringer, and D. Karlsson, “Temporary Primary Frequency Control Support by Variable Speed Wind Turbines – Potential and Applications,” IEEE Transactions on Power Systems, Vol. 23, No. 2, May 2008. [4] “Technical Requirements for the Connection of Generation Facilities to the Hydro-Quebec Transmission System: Supplementary Requirements for Wind Generation,” Hydro Quebec, Tech. Rp., May 2003, revised 2005.

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Page 16: Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer Engineering 1 Wind Generation Technology Short Course.

Frequency Governing Characteristic, β

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“If Beta were to continue to decline, sudden frequency declines due to loss of large units will bottom out at lower frequencies, and recoveries will take longer.”

β ,

Source: J. Ingleson and E. Allen, “Tracking the Eastern Interconnection Frequency Governing Characteristic,” Proc. of the IEEE PES General Meeting, July 2010.

Page 17: Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer Engineering 1 Wind Generation Technology Short Course.

Reasons for decrease in β

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• Fossil-steam plant changes, motivated to increasing economic efficiency:• Use of larger governor deadband settings, exceeding the historical typical setting

of ±36 millihertz (mHz); • Use of steam turbine sliding pressure controls; • Loading units to 100 percent of capacity leaving no “headroom” for response to

losses of generation; • Blocked governor response (nuclear licensing may also cause this); • Use of once-through boilers; • Gas Turbine inverse response;

• Changes in the frequency response characteristics of the load:• Less heavy manufacturing, therefore less induction motor load• More speed drives which may reduce frequency sensitivity of induction motors

“These changes have been evolving for some time and are not the direct result of the emergence of renewable resources such as wind and solar.”

Source: “Comments Of The North American Electric Reliability Corporation Following September 23 Frequency Response Technical Conference,” Oct. 14, 2010. Seewww.ferc.gov/EventCalendar/EventDetails.aspx?ID=5402&CalType=%20&CalendarID=116&Date=09/23/2010&View=Listview

Page 18: Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer Engineering 1 Wind Generation Technology Short Course.

Two Comments1. Wind is small now, so the NERC comment that

decreasing β is not due to wind is correct, but…this will not be true if, at higher wind penetrations, non-wind units with speed governing are displaced with wind units without speed governing.

2. Decreasing β will risk violation of NERC Standard BAL-001-0.1a — Real Power Balancing Control Performance

Each Balancing Authority shall achieve, as a minimum,• Requirement 1: CPS1 compliance of 100%• Requirement 2: CPS2 compliance of 90%and $ penalties apply for non-compliance.

So what are CPS1 and CPS2?Ref: N. Jaleeli and L. Van Slyck, “NERC’s New Control Performance Standards,” IEEE Transactions on Pwr Systems, Vol 14, No 3, Aug 1999.

Page 19: Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer Engineering 1 Wind Generation Technology Short Course.

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CPS1 is a measure of a balancing area’s long term (12 month)

frequency performance. The targeted control objective underlying CPS1 is to bound excursions of 1-minute average frequency error over 12 months in the interconnection. As the interconnection frequency error is proportional to the sum of all balancing areas’ ACEs, maintaining averages of ACEs within proper statistical bounds will therefore maintain the corresponding averages of frequency error within related bounds. With the interconnection frequency control responsibilities being distributed among balancing areas, CPS1 measures control performance by comparing how well a balancing area’s ACE performs in conjunction with the frequency error of the interconnection.

ε1 is maximum acceptable steady-state freq deviation- 0.018Hz in east interconnection.

FBPPACE atiestie ||)( ,,

%100)2(1 CFCPS

21

12min1

)(

)(

MonthCP

CF

min1min1

min1 ||10F

B

ACECP

Page 20: Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer Engineering 1 Wind Generation Technology Short Course.

CPS1 If ACE is positive, the control area will be increasing its generation, and if ACE is negative, the control area will be decreasing its generation. If ∆F is positive, then the overall interconnection needs to decrease its generation, and if ∆F is negative, then the overall interconnection needs to increase its generation. Therefore if the sign of the product ACE×∆F is positive, then the control area is hindering the needed frequency correction, and if the sign of the product ACE×∆F is negative, then the control area is contributing to the needed frequency correction. The minimum score of CPS1 compliance is 100%. If an area has a compliance of 100%, they are supplying exactly the amount of frequency support required. Anything above 100 is “helping” interconnection frequency whereas anything below 100 is “hurting” interconnection frequency.

Page 21: Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer Engineering 1 Wind Generation Technology Short Course.

CPS2is a measure of a balancing area’s ACE over all 10-minute periods in a month. The control objective is to bound unscheduled power flows between balancing areas. It was put in place to address the concern that a balancing area could grossly over- or under-generate (as long as it was opposite the frequency error) and get very good CPS1, yet impact its neighbors with excessive flows.

1010min2

10min

100(1 )%

Num ACE LCPS

Num all ACE

10 101.65 10 10i sL B B

• Num(.) denotes “number of times that…” over 1 month.

• (ACE) 10min is the 10 min average of ACE• L10 describes the interval within which |(ACE) 10min| should be controlled.• BS=sum of B values for all control areas.• ε10 =targeted 10-minute average frequency error bound

for Interconnection

Page 22: Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer Engineering 1 Wind Generation Technology Short Course.

Simulation System•Two Area System (Area A and Area B)

Wind power is assumed in area A •Each area consists of 10 conventional units, with inertia and with speed governing• 24 hour UC is run based on a load and wind forecast•Wind penetration levels- 6%, 10%, 25%, and 31% (Pw/Pnw) are considered (by capacity), without inertia or speed governing (would be 5, 9, 20, 24% Pw/(Pw+Pnw)).• Wind is assumed to displace conventional units• Actual sec-by-sec p.u. value of load and of wind power data from one wind farm is used.

A BWind

ConCon

Page 23: Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer Engineering 1 Wind Generation Technology Short Course.

Simulation Results

0% 6% 15% 25% 30%0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

120.00%

140.00%

160.00%

180.00%

CPS1 Score under different wind pene-tration levelsMinimum CPS1 score for CPS1 com-pliance

Wind Penetration Level

CPS1

0% 6% 15% 25% 30%0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

120.00%

CPS2 Score under different wind penetration levels

Minimum CPS2 score for CPS1 compliance

Wind Penetration Level

CPS2

Page 24: Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer Engineering 1 Wind Generation Technology Short Course.

Simulation ResultsMeasures CPS1 CPS2

0% wind penetration 160% 100%

Reference case at 25% wind penetration 78.80% 88.89%

Provide primary frequency control to wind turbines 98.84% 83.33%

Provide wind with inertial emulation & primary frequency control 109.58% 88.89%

Increase ramp rate of committed non-wind units by 50% 116.04% 94.44%

Increase ramp rate of committed non-wind units by 100% 156.02%100.00%

Control fast variations of wind power within +- 2% of forecast 91.92% 88.89%

Control fast variations of wind power within +- 1% of forecast 124.64% 94.44%Conclusion:Wind degrades frequency performance due to inertia, no control, and variability. These 3 issues need to be and can be addressed.

Page 25: Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer Engineering 1 Wind Generation Technology Short Course.

Regulation via rotor speed & pitch controlFUEL

Steam Boiler

Generator

CONTROL SYSTEM

Steam valve controlFuel supply control

MVAR-voltage control

Wind speed

Gear Box

Generator

CONTROL SYSTEM

MVAR-voltage control

Real power output control

STEAM-TURBINE

WIND-TURBINE

Rotor speed control is well suited for continuous, fine, frequency regulation; blade pitch control provides fast acting, coarse control both for frequency regulation as well as emergency spinning reserve.

Pitch control

Rotor speed control

Sources: Rogério G. de Almeida and J. A. Peças Lopes, “Participation of Doubly Fed Induction Wind Generators in System Frequency Regulation,” IEEE Trans On Pwr Sys, Vol. 22, No. 3, Aug. 2007. B. Fox, D. Flynn, L. Bryans, N. Jenkins, D. Milborrow, M. O’Malley, R. Watson, and O. Anaya-Lara, “Wind Power Integration: Connection and system operational aspects,” Institution of engineering and technology, 2007.

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Page 26: Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer Engineering 1 Wind Generation Technology Short Course.

Manufacturers & some wind farms have it

See http://www.gepower.com/prod_serv/products/wind_turbines/en/downloads/wind_plant_perf2.pdf.

Then why don’t they use it?

Page 27: Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer Engineering 1 Wind Generation Technology Short Course.

Regulation via rotor speed & pitch control

[1] “Wind Generation Interconnection Requirements,” Technical Workshop, November 7, 2007, available at www.bctc.com/NR/rdonlyres/13465E96-E02C-47C2-B634-F3BCC715D602/0/November7WindInterconnectionWorkshop.pdf. [2] [North American Electric Reliability Corporation, “Special Report: Accommodating High Levels of Variable Generation,” April 2009, available at http://www.nerc.com/files/IVGTF_Report_041609.pdf.

Review of the websites from TSOs (in Europe), reliability councils (i.e., NERC and regional organizations) and ISOs (in North America) suggest that there are no hard requirements regarding use of primary frequency control in wind turbines.There are soft requirements [1]:• BCTC will specify “on a site by site basis,” • Hydro Quebec requires that wind turbines be “designed so that they can

be equipped with a frequency control system (>10MW)”• Manitoba Hydro “reserves the right for future wind generators”

NERC [2], said, “Interconnection procedures and standards should be enhanced to address voltage and frequency ride-through, reactive and real power control, frequency and inertial response and must be applied in a consistent manner to all generation technologies.”

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Page 28: Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer Engineering 1 Wind Generation Technology Short Course.

Regulation via rotor speed & pitch control

[15] Draft White Paper, “Wind Generation White Paper: Governor Response Requirement,” Feb, 2009, available at www.ercot.com/content/meetings/ros/keydocs/2009/0331/WIND_GENERATION_GOVERNOR_RESPONSE_REQUIREMENT_draft.doc..

ERCOT says [1], “…as wind generation becomes a bigger percentage of the on line generation, wind generation will have to contribute to automatic frequency control. Wind generator control systems can provide an automatic response to frequency that is similar to governor response on steam turbine generators. The following draft protocol/operating guide concept is proposed for all new wind generators: All WGRs with signed interconnect agreements dated after March 1, 2009 shall have an automatic response to frequency deviations. …”

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Page 29: Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer Engineering 1 Wind Generation Technology Short Course.

Solutions to degraded frequency performance

1. Increase control of the wind generationa. Provide wind with inertial emulation & speed governingb. Limit wind generation ramp rates

• Limit of increasing ramp is easy to do• Limit of decreasing ramp is harder, but good

forecasting can warn of impending decrease and plant can begin decreasing in advance

2. Increase non-wind MW ramping capability during periods of expected high variability using one or more of the below:a. Conventional generation b. Load controlc. Storage

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Steam turbine plants 1- 5 %/minNuclear plants 1- 5 %/minGT Combined Cycle 5 -10 %/min Combustion turbines 20 %/min Diesel engines 40 %/min

Page 30: Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer Engineering 1 Wind Generation Technology Short Course.

Hybrid Wind Systems – Save Money, Enhance

Frequency Regulation

HOLDEN REDBRIDG CHENAUX CHFALLSMARTDALE

HUNTVILL

NANTCOKE

WALDEN COBDEN MTOWN

GOLDEN BVILLE STRATFRDJVILLE

WVILLE

STINSON

PICTON

CEYLON RICHVIEWLAKEVIEW

MITCHELL

PARKHILL

BRIGHTON

HANOVERKINCARD

HEARN

DOUGLAS

Number of buses 60Number of generators 25Number of branches 96Peak Load 6,110MWTotal Generation Capacity 10,995MW

Wind Power Capacity 545MW

CAESPower Capacity

Compressor 30MW

Gas Turbine 75MW

CAES Energy Capacity 17,000MWh

NaS Battery Power Capacity 5.5MW

NaS Battery Energy Capacity 1.25MWh

0 200 400 600 800 1000 1200 1400 1600 1800-50

0

50

100

150

200

250

300

350

400

Time (s)

Pow

er C

omm

and

(M

W)

Wind Power CAES Power NaS Battery Power ×10

0 200 400 600 800 1000 1200 1400 1600 180059.96

59.97

59.98

59.99

60

60.01

60.02

60.03

60.04

Time (S)

Sys

tem

Fre

que

ncy

(Hz)

Wind plant Hybrid Wind Systems

0 200 400 600 800 1000 1200 1400 1600 18002

4

6

8

10

12

Time (s)

Win

d S

pee

d (

s)

Cost ($M)Saving ($M)

Investment Cost Operation Cost

155.15 221.83 481.40

Life time: 20 years 0 200 400 600 800 1000 1200 1400 1600 1800-100

-80

-60

-40

-20

0

20

40

60

80

100

Mis

mat

ch (

MW

)

With StorageNo Storage

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Page 31: Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer Engineering 1 Wind Generation Technology Short Course.

How to decide?First, primary frequency control for over-frequency conditions, which requires generation reduction, can be effectively handled by pitching the blades and thus reducing the power output of the machine. Although this action “spills” wind, it is effective in providing the necessary frequency control. Second, primary frequency control for under-frequency conditions requires some “headroom” so that the wind turbine can increase its power output. This means that it must be operating below its maximum power production capability on a continuous basis. This also implies a “spilling” of wind.Question: Should we “spill” wind in order to provide frequency control, in contrast to using all wind energy and relying on some other means to provide the frequency control? Answer: Need to compare system economics between increased production costs from spilled wind, and increased production and investment costs from using storage and conventional generation.

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Page 32: Frequency control (MW-Hz) with wind James D. McCalley Harpole Professor of Electrical & Computer Engineering 1 Wind Generation Technology Short Course.

Conclusion: Select solution portfolioWind energy attrbute

Grid prblemcaused by wind attrbute

SolutionsDFIG Control Inc.

reservesStorage Load Cntrl Stoch-

asticUnit Cmmtprgrm

Dec fore-cast error

Wind plant remote trip (SPS)

HVDC control

Geo-diversity of wind

Inrtialemu-lation

Freq reg via pitch+ cnvrtr

Fast rmping

Spnng/10 min

1 hour Fast Slow Fast Slow

Estimated relative costs/MW of solution technology (to be refined)5 5 6 10 10 9 9 9 9 4 4 6 10 10

Decreased inertia

Transient frequency dips, CPS2 perfrmance

√ √ √ √Increased 1 min MW variability

CPS2 perfrmance √ √ √ √ √ √

Increased 10 min MW variability

CPS1, CPS2 perfrmance √ √ √ √ √ √ √ √

Increased 1 hr MW variability

Balancing market perfrmance √ √ √ √ √ √ √

Increased day-ahead MW variability

Day-ahead market perfrmance √ √ √ √ √ √ √

Increased transmission loading

Increased need for transmssion

√ √ √Low, variable capacity factor

More planning uncertainty √ √ √ √32