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Active Control Systems for Active Control Systems for Wind TurbinesWind Turbines
Avishek Kumar
Supervisor: Dr Karl Stol
The University of Auckland
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OverviewOverview
Wind TurbinesWind Turbines
Power ExtractionPower Extraction
Traditional ControlTraditional Control
Modern ControlModern Control
Future of ControlFuture of Control
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Horizontal Axis Wind TurbinesHorizontal Axis Wind Turbines
Source: US Department of Energy
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5MW (1400-1500 households)5MW (1400-1500 households)
126m Blade Span 126m Blade Span
12.1 rpm12.1 rpm
Power controlled by blade pitchPower controlled by blade pitch
Onshore and offshoreOnshore and offshore
Large Wind TurbinesLarge Wind Turbines
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Power CapturePower CapturePow
er [
kW]
Wind Speed, w
[m/s]
Pwind
w3Ideal turbine
(max. 60% efficient)
Prated
wcut-inwcut-outwrated
Source: Dr. Karl Stol, UoA
Torque Control
Pitch Control
Reg
ion
1
Reg
ion
2
Reg
ion
3
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Power Generation Control Power Generation Control ObjectivesObjectives
Region 1:Region 1: Turbine is stoppedTurbine is stopped
Region 2:Region 2: Maintain constant tip speed Maintain constant tip speed
ratio to produce maximum ratio to produce maximum power below rated wind power below rated wind speed.speed.
Region 3:Region 3: Maintain rated rotor speed Maintain rated rotor speed
and power.and power.P
ower
Coe
ffic
ent,
Cp
(Blade Tip Speed)/Wind Speed, λ
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Classical ControlClassical Control
Use collective pitch and/or generator torque to Use collective pitch and/or generator torque to adjust rotor speed depending on the region.adjust rotor speed depending on the region.
The torque and pitch controllers work The torque and pitch controllers work separately.separately.
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LoadsLoads
Become more significant as turbines get Become more significant as turbines get largerlarger
By reducing loads we can also decrease By reducing loads we can also decrease cost of energy by:cost of energy by: Increasing the lifetime of turbinesIncreasing the lifetime of turbines Reducing structural materialReducing structural material Reducing maintenanceReducing maintenance
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LoadsLoads
High WindsHigh Winds
Stochastic WindsStochastic Winds
Vertical Wind Shear Vertical Wind Shear and Cross Windsand Cross Winds
Inertia and GravityInertia and Gravity
Tower InterferenceTower Interference
Wind Turbulence Wind Turbulence and Gustsand Gusts
Source: E Hau
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Modern ControlModern Control
Traditional Control Modern ControlModern Control
Single control objective
Single input single output
Controllers work separately
Multiple control objective
Multi input multi output
Single centralised controller
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Modern Control Objectives for the Modern Control Objectives for the Wind TurbineWind Turbine
Maintain Rotor SpeedMaintain Rotor Speed Keep the best tip speed ratios in Region 2Keep the best tip speed ratios in Region 2 Not exceed rated velocity in Region 3Not exceed rated velocity in Region 3 Have smooth power outputHave smooth power output
Reducing Reducing DYNAMICDYNAMIC loading on the turbine. loading on the turbine. Blade flapBlade flap Tower fore-aft vibrationTower fore-aft vibration Drive train torsional vibrationDrive train torsional vibration
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Individual Blade PitchingIndividual Blade Pitching
With modern control (MIMO) we can control With modern control (MIMO) we can control the load on each blade individuallythe load on each blade individually
This now allows mitigation of ASSYMETRIC This now allows mitigation of ASSYMETRIC loading:loading: Wind shearWind shear Tower shadowTower shadow Inertial loadsInertial loads Turbulence across the swept areaTurbulence across the swept area
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Simulation ResultsSimulation Results
Stol, Zhao, Wright (2006), Individual Blade Pitch Control for the Controls Advanced Research Turbine (CART), J. of Solar Energy Eng., Transactions of the ASME, v 128, n 4, Nov, 2006, p 498-505
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The ProblemsThe Problems
Model based control tresats a nonlinear Model based control tresats a nonlinear system as a linear onesystem as a linear one
x
y
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The SolutionThe Solution
Nonlinear Control
Allows control over Allows control over the entire operating the entire operating envelopeenvelope
Increase in the Increase in the performance of performance of controlcontrol
Increase in safetyIncrease in safety
More predictable More predictable behaviourbehaviour
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Current State of Nonlinear Current State of Nonlinear ControlControl
Variety of nonlinear controllers are being Variety of nonlinear controllers are being exploredexplored
Simulations show successful SISO power Simulations show successful SISO power controlcontrol
Very little work has been conducted with Very little work has been conducted with multiple control objectives systemsmultiple control objectives systems
No work has been conducted (publicly) with No work has been conducted (publicly) with Individual Blade PitchingIndividual Blade Pitching
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My ResearchMy Research
What:What: Nonlinear controlNonlinear control Individual blade pitchingIndividual blade pitching Multiple control objectivesMultiple control objectives
Why:Why: Reduce cost of energyReduce cost of energy More predictable turbine behaviourMore predictable turbine behaviour Safer turbine behaviourSafer turbine behaviour
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SummarySummaryWind turbines are getting biggerWind turbines are getting bigger
Loads are increasing cost of energyLoads are increasing cost of energy
Modern control (Linear) can mitigate loads AND Modern control (Linear) can mitigate loads AND maintain rated powermaintain rated power
Using individual blade pitch we can mitigate Using individual blade pitch we can mitigate ASSYMETRIC loadsASSYMETRIC loads
Modern Linear Control is only optimal about it’s Modern Linear Control is only optimal about it’s operating regionoperating region
Nonlinear control aims to apply all the above Nonlinear control aims to apply all the above benefits over the entire operating envelopebenefits over the entire operating envelope
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Questions?Questions?
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Wind Energy FactsWind Energy Facts
Wind accounts for currently 2% of our Wind accounts for currently 2% of our electricity.electricity.
Global increase of 25% a year for the last Global increase of 25% a year for the last 5 years.5 years.
321 MW either running or being 321 MW either running or being commissioned in NZ.commissioned in NZ.
Current COE is 5.5-7c/kWhr (2005)Current COE is 5.5-7c/kWhr (2005)
New Zealand Wind Energy Association. (2007, June 28 - last update). [Online]. Available: http://www.windenergy.org.nz/ [2007, July 11]