An introduction to wind An introduction to wind - - turbine turbine electrical systems electrical systems Lee Jay Fingersh Lee Jay Fingersh Given at CU Boulder Given at CU Boulder April 18, 2008 April 18, 2008
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