lee jay fingersh given at cu boulder april 18,...

An introduction to windAn introduction to wind--turbine turbine

electrical systemselectrical systems

Lee Jay FingershLee Jay Fingersh

Given at CU BoulderGiven at CU Boulder

April 18, 2008April 18, 2008

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What does a windWhat does a wind--turbine turbine

electrical system do?electrical system do?

•• Produces our productProduces our product

•• Controls the rotorControls the rotor

•• Interacts with the power gridInteracts with the power grid

•• Protects itself from harmProtects itself from harm

•• Protects the turbine from harmProtects the turbine from harm

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Wind turbine operationWind turbine operation

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Classical wind turbine designClassical wind turbine design

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Alternative train designsAlternative train designs

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Rotating Magnetic FieldsRotating Magnetic Fields

RotatingField.html

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Induction generator torqueInduction generator torque--speed speed

characteristiccharacteristic

-25000

-20000

-15000

-10000

-5000

0

5000

10000

15000

20000

25000

0 300 600 900 1200 1500 1800 2100 2400 2700 3000 3300 3600

HSS speed, RPM

Ge

ne

rato

r T

orq

ue

, N

m

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Synchronous machinesSynchronous machines

•• Very stiff Very stiff –– little dampinglittle damping

•• Can produce rather than Can produce rather than

absorb reactive powerabsorb reactive power

•• Hard to get onlineHard to get online

•• Requires a Requires a ““cushioncushion””

between it an the rotorbetween it an the rotor

•• Fluid couplings can be Fluid couplings can be

dangerousdangerous

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Fluid coupling failureFluid coupling failure

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Torque response Torque response –– constant speedconstant speed

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Torque response Torque response –– variable speedvariable speed

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Torque speed vector for VSTorque speed vector for VS

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What is a power converter?What is a power converter?

Converts Converts

variablevariable--frequency frequency

variablevariable--voltage voltage

into into

constantconstant--frequency frequency

constantconstant--voltagevoltage

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Passive rectificationPassive rectification

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1212--pulsepulse

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FullFull--processingprocessing

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Current linkCurrent link

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DoublyDoubly--fedfed

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WeibullWeibull Probability functionProbability functionWind, Energy

0 5 10 15 20 25 30 35 40

Windspeed (m/s)

Weibull Probability Weibull Betz

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Gearbox efficiencyGearbox efficiency

0%

15

%

30

%

45

%

60

%

75

%

90

%

810

1215

1665

2115

25650%

10%20%30%40%50%60%70%80%90%

100%

Eff

icie

ncy

% of Rated Power

RPM

Variable Speed Gearbox Efficiency Surface

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Generator efficiencyGenerator efficiency

0%

25%

50%

75%

100%

125%

150%

0%5

%10

%15

%20

%25

%30

%35

%40

%45

%50

%55

%60

%

65

%

70

%

75

%

80

%

85

%

90

%

95

%

10

0%

70%

75%

80%

85%

90%

95%

100%

Eff

icie

nc

y

% of rated RPM

% of rated power

Permanent-magnet generator efficiency surface

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Power converter efficiencyPower converter efficiencyVariable Speed Converter Efficiency

0%

20%

40%

60%

80%

100%

120%

0% 20% 40% 60% 80% 100% 120%

Percent of Rated Load

Eff

icie

ncy

Standard Converter

90% Converter

94% Converter

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Interaction with the gridInteraction with the grid

•• Requirements are Requirements are

getting toughergetting tougher

–– Must provide VAR Must provide VAR

compensationcompensation

–– Must rideMust ride--through faultsthrough faults

–– Must provide fault Must provide fault currentcurrent

•• Still no dispatchabilityStill no dispatchability

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The dispatchability issueThe dispatchability issue

Load versus wind

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

0 6 12 18 24

Hour of the day

Meg

aw

att

s

Load

Wind

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What to do about itWhat to do about it

•• Ignore itIgnore it

–– Wind produces 10%Wind produces 10%--20% of 20% of our electricityour electricity

•• Geographical distributionGeographical distribution

•• Add dispatchable loadAdd dispatchable load

•• Add storageAdd storage

–– CAESCAES

–– BatteriesBatteries

–– HydrogenHydrogen

–– V2GV2G

��The problem is cost!!!The problem is cost!!!

•• CAESCAES–– Current technologyCurrent technology

–– Combined with natural Combined with natural gas electrical plantsgas electrical plants

–– 50% to 70% efficiency50% to 70% efficiency

•• BatteriesBatteries–– Currently expensiveCurrently expensive

–– Efficient (85% to 95%)Efficient (85% to 95%)

•• HydrogenHydrogen–– MassiveMassive

–– Inefficient (25% to 35%)Inefficient (25% to 35%)

•• V2GV2G–– EmergingEmerging

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ApproachApproach

•• Simulation of power grid energySimulation of power grid energy--flowflow

•• Analysis of timeAnalysis of time--series data for 2002series data for 2002

•• California ISO hourly load dataCalifornia ISO hourly load data

•• Lake Benton wind farm hourly power dataLake Benton wind farm hourly power data

•• ComponentsComponents–– Wind Wind –– Current costs ($1,000 / kW)Current costs ($1,000 / kW)

–– Battery Battery –– Projected costsProjected costs

–– Electrolyzer Electrolyzer –– Projected costsProjected costs

–– Fuel Cell Fuel Cell –– Projected costsProjected costs

–– Dispatchable load/curtailmentDispatchable load/curtailment

–– Traditional generationTraditional generation

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Interesting resultInteresting result

•• An optimizer (Excel solver) is used to minimize An optimizer (Excel solver) is used to minimize cost by optimizing the sizes of the componentscost by optimizing the sizes of the components–– ElectrolyzerElectrolyzer

–– Fuel cellFuel cell

–– Control parametersControl parameters

��Hydrogen system is optimized to zero size!Hydrogen system is optimized to zero size!��Cause is the low efficiency of the hydrogen system Cause is the low efficiency of the hydrogen system

compared to the batterycompared to the battery–– Hydrogen system Hydrogen system 37.5% (75% electrolyzer, 50% fuel cell)37.5% (75% electrolyzer, 50% fuel cell)

–– Battery Battery 85.5% (95% charge, 90% discharge)85.5% (95% charge, 90% discharge)

�� True even when costs of hydrogen components True even when costs of hydrogen components (electrolyzer and fuel cell) are set to zero!(electrolyzer and fuel cell) are set to zero!

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Optimized windOptimized wind--battery systembattery system

$0.024

$0.026

$0.028

$0.030

$0.032

$0.034

$0.036

$0.038

$0.040

0% 10% 20% 30% 40% 50% 60% 70%

Capacity Reduction

Co

st

of

En

erg

y

Energy Penetration

2%

Energy Penetration

20%

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What about making hydrogen?What about making hydrogen?

•• Fix the electrolyzer size so the optimizer Fix the electrolyzer size so the optimizer doesndoesn’’t optimize it awayt optimize it away

•• DonDon’’t use the hydrogen to regenerate t use the hydrogen to regenerate electricity onelectricity on--sitesite

•• Sell the hydrogen created as a fuelSell the hydrogen created as a fuel

•• Assume no hydrogen storage neededAssume no hydrogen storage needed

��Result: Hydrogen production is less Result: Hydrogen production is less expensive when electrolyzers are expensive when electrolyzers are combined with wind combined with wind ANDAND batteriesbatteries

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Hydrogen production resultsHydrogen production results

$1.50

$1.75

$2.00

$2.25

$2.50

$2.75

$3.00

$3.25

$3.50

$0 $200 $400 $600 $800 $1,000 $1,200

Electrolyzer cost ($/kW)

Hyd

rog

en

Co

st

($/k

g)

PTC$0.02

0

PTC$0.00

0

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ConclusionsConclusions

��Hydrogen is not economical as an energy Hydrogen is not economical as an energy

storage medium for grid electricitystorage medium for grid electricity

��Batteries are economically competitive for Batteries are economically competitive for

onon--grid electricity storagegrid electricity storage

��Hydrogen can be produced from wind for Hydrogen can be produced from wind for

$1.50 to $3.00 per kg in a hybrid system $1.50 to $3.00 per kg in a hybrid system

(wind(wind--batterybattery--electrolyzerelectrolyzer--grid)grid)

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Wind turbine controlsWind turbine controls

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The controlsThe controls--design processdesign process

DesignDesign

SimulateSimulate

Field TestField Test

AnalyzeAnalyzeModifyModify

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Controls on wind turbinesControls on wind turbines

•• To test controls on To test controls on

wind turbines, we wind turbines, we

needed a controls needed a controls

test bed turbinetest bed turbine

•• Two Westinghouse Two Westinghouse

600kW 43.28 meter 600kW 43.28 meter

twotwo--bladed wind bladed wind

turbines were turbines were

acquired from acquired from

Kahuku point, OahuKahuku point, Oahu

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Turbine shipment/installationTurbine shipment/installation

•• The turbines were The turbines were

brought to the brought to the

NWTC, refurbished NWTC, refurbished

and installedand installed

•• Instrumentation and Instrumentation and

data acquisition data acquisition

equipment were equipment were

addedadded

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Turbine operationTurbine operation

•• Both turbines were Both turbines were placed into placed into operationoperation

•• ART (left) ART (left) –– 19991999–– ConstantConstant--speedspeed

–– LIST experimentLIST experiment

•• CART (right) CART (right) –– 20012001–– Constant or variableConstant or variable--

speedspeed

–– Controls testingControls testing

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CART CapabilitiesCART Capabilities

•• Turbine heavily Turbine heavily modified for controls modified for controls testingtesting–– HighHigh--speed independent speed independent

pitch controlpitch control

–– ConstantConstant--speed modespeed mode

–– Full variableFull variable--speedspeed

–– Flexible controller (PCFlexible controller (PC--based)based)

–– Fast data acquisition Fast data acquisition (100 Hz, 90 channels)(100 Hz, 90 channels)

•• InstrumentationInstrumentation

–– PerformancePerformance

•• HSS, LSS torqueHSS, LSS torque

•• Power, current, voltagePower, current, voltage

–– LoadsLoads

•• Blade root loadsBlade root loads

•• Tower bendingTower bending

•• AccelerationsAccelerations

•• RateRate--gyrosgyros

–– MeteorologicalMeteorological

•• UpUp--wind vertical arraywind vertical array

•• Sonic anemometerSonic anemometer

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Turbine characterizationTurbine characterization

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0 5 10 15 20

TSR

Cp

Constant Speed - LSS Predicted

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Adaptive controllerAdaptive controller

0 50 100 150 200 250 300 3500.5

1.0

1.5

2.0

No

rma

lize

d M

(M

/M+)

0 50 100 150 200 250 300 350

0.3

0.4

0.5

Fra

cti

on

al A

ve

rag

e P

ow

er

Time (hours)5 10 15 20

0

100

200

300

400

500

600

Gri

d P

ow

er

(kW

)

Mean Equivalent Wind Speed (m/s)

Standard ControlAdaptive Control

Region 3Region 2

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““StateState--spacespace”” controlcontrol

•• StateState--space control allows the designer great flexibilityspace control allows the designer great flexibility

–– Multiple inputs (RPM, blade bending, nacelle acceleration, etc.)Multiple inputs (RPM, blade bending, nacelle acceleration, etc.)

–– Multiple outputs (shaft torque, individual blade pitch)Multiple outputs (shaft torque, individual blade pitch)

•• Ability to Ability to dramaticallydramatically reduce turbine vibrationsreduce turbine vibrations

Measured Shaft Torque

60

80

100

120

140

160

180

200

0 5 10 15 20 25 30

Time (sec)

Lo

w-S

pe

ed

Sh

aft

To

rqu

e

PI Control

State-space (FAST) controller

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Why do we need to reduce Why do we need to reduce

vibrations?vibrations?

•• Turbines are getting Turbines are getting muchmuchlarger in response to the need larger in response to the need to meet LWST goalsto meet LWST goals

–– Increased economies of scaleIncreased economies of scale

–– Stretched rotors for more Stretched rotors for more energy captureenergy capture

•• Physics dictates that a larger Physics dictates that a larger machine made out of the same machine made out of the same materials will be more flexiblematerials will be more flexible

•• More flexibility = More flexibility = More vibrations = More vibrations = More loads = More loads = More costMore cost

��Controls may be the most Controls may be the most important solution to reducing important solution to reducing cost cost

Boeing 747-200

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PreliminaryPreliminary StateState--space resultsspace results

306306

((--21%)21%)385385

BladeBlade--root flap fatigue root flap fatigue DEL [DEL [kNmkNm]]

2525

((--40%)40%)4242

LowLow--speed shaft torque speed shaft torque fatigue DEL [fatigue DEL [kNmkNm]]

15861586

((--30%)30%)22662266

Tower foreTower fore--aft fatigue aft fatigue DEL [DEL [kNmkNm]]

RMS pitch current [A]RMS pitch current [A]

15.515.514.914.9Max. pitch rate [deg/s]Max. pitch rate [deg/s]

.380.380.389.389RMS speed error [RPM]RMS speed error [RPM]

SymDynSymDyn StateState--SpaceSpaceControllerController

((SimulationSimulation))

Baseline PI Baseline PI ControllerController

((SimulationSimulation))

Performance MeasurePerformance Measure

8686

((--32%)32%)126126

7.77.7

((--51%)51%)15.815.8

272272

((--53%)53%)578578

16.016.0

((--44%)44%)28.828.8

9.49.413.713.7

.213.213.233.233

SymDynSymDyn StateState--SpaceSpaceControllerController

((Field TestField Test))

Baseline PI Baseline PI ControllerController

((Field TestField Test))

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Questions and commentsQuestions and comments