consequences of load mitigation control strategies for a floating … · 2020. 1. 22. · 3p....
TRANSCRIPT
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Consequences of load mitigation control strategies for a floating wind turbine
Chern Fong Lee, NTNUErin E. Bachynski, NTNU ([email protected]) Amir R. Nejad, NTNU
mailto:[email protected]
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Control-induced resonance
1. Platform pitches forward2. Nacelle sees an increase in
relative wind speed3. Controller regulates blade
pitch to reduce rotor speed4. Thrust is reduced
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Load-mitigation control strategies for FWTs
• AD: Nacelle velocity feedback (added damping)– Lackner, 2007– Modify rotor speed reference with nacelle velocity measurement
𝐻𝐻𝑃𝑃𝑃𝑃∆Ω𝐴𝐴𝐴𝐴
Ω𝑟𝑟
+
-
𝐻𝐻𝑊𝑊𝑊𝑊
∆𝜃𝜃+
K�̇�𝑥
Ω0
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Load-mitigation control strategies for FWTs
• ES: Energy shaping controller– Pedersen, 2017– Modify rotor speed reference using the deviation of nacelle
velocity from its value in equilibrium
+
D𝛿𝛿�̇�𝑥 𝐾𝐾𝐸𝐸𝐸𝐸
𝐻𝐻𝑃𝑃𝑃𝑃Ω0∆Ω𝐸𝐸𝐸𝐸
Ω𝑟𝑟
+
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𝐻𝐻𝑊𝑊𝑊𝑊
∆𝜃𝜃IPC
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Load-mitigation control strategies for FWTs
• AD: Nacelle velocity feedback (added damping)– Lackner, 2007– Modify rotor speed reference with nacelle velocity measurement
• ES w/o IPC: Energy shaping controller– Pedersen, 2017
• ES w/IPC: Energy shaping controller with IPC– Try to reduce individual blade root bending moments– IPC follows Lackner and van Kuik, 2009
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Known consequences of load-mitigating control strategies• AD: reduction in pitch motion, increased variations in
power and rotor speed• ES: stable control, expected reductions in pitch motions• IPC: reduce blade root bending moments, increase pitch
actuator use
What about the drivetrain?
Image: Nejad et al., 2016
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Outline
• Methodology• Global analysis results• Drivetrain loads• Conclusions
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Methodology: Decoupled simulations
Image: Nejad et al., 2016
Global analysis: SIMA Drivetrain analysis: SIMPACK
EC 1 EC 2 EC 3
Significant wave height, Hs [m] 5.0 4.0 5.5
Peak period, Tp [s] 12.0 10.0 14.0
Mean wind speed, U [m/s] 12.0 14.0 20.0
Turbulence intensity, I [-] 0.15 0.14 0.12
6x1hr1x1hr
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Performance indicators
• Tower base 1-hr fatigue damage– Stresses from global analysis, rainflow counting, SN curve,
Miner’s rule• Gear root 1-hr fatigue damage
– Forces from MBS analysis, load duration distribution method• Bearing 1-hr fatigue damage
– Forces from MBS analysis, load duration distribution method• Standard deviation of power output
– Direct result from global analysis
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Global motions, EC1
0 0.2 0.4 0.6 0.8
Frequency [rad/s]
0
50
100
150
200
250
300
350
400
S() [
m2
s/ra
d]
Baseline
ES w/o IPC
ES w IPC
AD
0 0.2 0.4 0.6 0.8 1 1.2
Frequency [rad/s]
0
10
20
30
40
50
60
S()[r
ad2
s/ra
d]
0.3 0.4 0.5 0.6
0
1
2
0.3 0.4 0.5 0.6
Frequency [rad/s]
0
10
Surge Pitchsurge
pitch
wave
pitch
wave
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Tower base fore-aft bending moments
wave
tower 3p
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Gearbox topology
Image: Nejad et al., 2016
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Sun gear circumferential force
wave
1P
3P
tower
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Tower top side-side force
tower
wave 1P
pitch
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Bearing INPB
axial
radial1P
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Conclusions• Global and drivetrain responses of a spar floating wind turbine• Three control modifications
– active damping (AD)– energy shaping control (ES w/o IPC),– energy shaping control with individual blade pitch (ES w/IPC).
• Improved platform motion responses in surge and pitch• ES adds some responses at i.e. wave frequency • IPC reduces blade root flap-wise bending, but introduces
excitation of tower top shear force at rotor frequency.• The reduced blade root moment therefore comes with a cost
of increased radial load resonance in drivetrain gears and bearings.
• Drivetrain should be considered when assessing control performance
Consequences of load mitigation control strategies for a floating wind turbineControl-induced resonanceLoad-mitigation control strategies for FWTsLoad-mitigation control strategies for FWTsLoad-mitigation control strategies for FWTsKnown consequences of load-mitigating control strategiesOutlineMethodology: Decoupled simulationsPerformance indicatorsGlobal motions, EC1Tower base fore-aft bending momentsGearbox topologySun gear circumferential forceTower top side-side forceBearing INPBSlide Number 16Conclusions