alan d. wright lee j. fingersh national renewable energy laboratory karl a. stol university of...
TRANSCRIPT
Alan D. Wright Alan D. Wright Lee J. FingershLee J. Fingersh
National Renewable Energy LaboratoryNational Renewable Energy Laboratory
Karl A. StolKarl A. StolUniversity of AucklandUniversity of Auckland
2828thth ASME Wind Energy Symposium ASME Wind Energy SymposiumOrlando, Fl.Orlando, Fl.
January 5, 2009January 5, 2009
Field Testing Controls to Mitigate Fatigue Loads in the Controls Advanced Research Turbine
A. Wright 1/5/09 2
Presentation Scope
Show design of region 3 generator torque and blade pitch controller.
Goals: – Region 3 speed regulation– active damping of tower side-side and fore-aft motion
Describe field implementation and tests in the Controls Advanced Research Turbine.
Compare state-space control results to baseline PID control results.
A. Wright 1/5/09 3
Commercial Turbine Control
Generator Speed
Generator Torque
Rotor Collective Pitch
Region 2
Region 3
Wind Disturbances
PID Pitch Controller
Drive-train Damper
T = kw^2
Nonlinear Turbine
Generator Torque
Nacelle Yaw
Blade Pitch
Control Actions
2T k
A. Wright 1/5/09 4
Control of Flexible Modes
Blade2 edge
Tower Side-Side
Rotor Rotation
(b) Frontview
Blade1 edge
Blade-1 Flap
Tower Fore-Aft
Rotor Teeter
(a) Sideview
Blade-2 Flap
Generator Rotation
Drive-train Torsion
A. Wright 1/5/09 5
Region 3 Control Design
Control Actuators: Collective blade pitch, generator torque
Goals:– Collective Blade Pitch Control:
• Speed regulation
• Tower fore-aft damping
– Generator Torque Control:• Tower side-side damping
• Drive-train torsion damping
Two separate control loops:– Collective blade pitch
– Generator torque
A. Wright 1/5/09 6
Questions
Can separate control loops be used to add active damping to two closely spaced modes?
– Tower 1st fore-aft mode (0.87 Hz.)
– Tower 1st side-side mode (0.88 Hz.)
Will these separate loops destabilize each other?
– Two separate control loops:
• Collective blade pitch
• Generator torque
Will adding damping reduce tower fatigue loads?
A. Wright 1/5/09 7
Controller Structure
CART
C onventional Variable - Sp eed
Controller
S tate - Space Torque Controller
S tate - Space P itch Controller
Nominal Generator Torque
Total Gen. Torque
Rotor Coll. Pitch Rate
Added Gen. Torque
y y
y
y
A. Wright 1/5/09 8
Regulate rotor-speed in the presence of wind-speed disturbances and stabilize turbine modes.– Stabilize flexible modes through full state
feedback.– Use state estimation to provide the controller with
needed states (including wind-speed).– Account for uniform wind disturbances
2-Multiple input/single output control loops
Full State Feedback Control
A. Wright 1/5/09 9
Rotor Collective Pitch Control Model
perturbed generator speed
rotor collective pitch angles
perturbed tower-top fore-aft acceleration
y
d d
d d
x Ax Bu B u
y Cx Du D u
rotor collective pitch rateu q
qx
Perturbed structural dofs & rates:
tower f-a
rotor collective flapgenerator-speed
Pitch actuator states
A. Wright 1/5/09 10
Disturbance model
( ) ( )
( ) ( )d d
d d
z t Fz t
u t z t
du uniform wind disturbance
A. Wright 1/5/09 11
Open-loop and Closed-loop Pole Locations
Open-loop poles Closed-loop poles
First flap symmetric mode
−3.63 ± 13.81i −3.66 ± 13.85i
Tower first f-a mode −0.07 ± 5.52i −1.27 ± 5.32i
Generator speed −0.1943 −2.50
( ) ( ) ( ) d du t x t G zG t
A. Wright 1/5/09 12
Generator Torque Control Design Model
perturbed generator speed
perturbed tower-top side-side accelerationy
x Ax Bu
y Cx Du
generator torqueu q
x q
w
Perturbed structural dofs & rates:
tower s-sdrive-train torsiongenerator-speed
filter states
A. Wright 1/5/09 13
Open-loop and Closed-loop Pole Locations
Open-loop poles Closed-loop poles
Tower first s-s mode
−0.002 ± 5.54i −0.140 ± 5.54i
Generator speed −0.102 −0.102
Drive train first torsion
−0.01 ± 22.47i −1.07 ± 22.45i
( ) ( )Gu t x t
A. Wright 1/5/09 14
Testing Strategy
Using two separate uncoupled control loops to add active damping to two closely spaced tower modes
Will these two control loops interact and destabilize the turbine?
Test the tower f-a damping with collective pitch first.
Add tower s-s damping with generator torque.
A. Wright 1/5/09 15
Controllers:
PID State-space1 State-space2
Speed regulation
yes yes yes
Tower f-a damping
no yes yes
Tower s-s damping
no no yes
Drive-train torsion damping
no yes yes
A. Wright 1/5/09 16
Controller Structure
CART
C onventional Variable - Sp eed
Controller
S tate - Space Torque Controller
S tate - Space P itch Controller
Nominal Generator Torque
Total Gen. Torque
Rotor Coll. Pitch Rate
Added Gen. Torque
y y
y
y
A. Wright 1/5/09 17
Results
Statistics and Performance
Measure
Baseline PID Control
(Undamped)(5530 sec.)
State-Space 1 (tower f-a
damping only) (2500 sec.)
State-Space 2 (tower f-a and s-s damping) (3700 sec.)
Tower fore-aft bending(kNm)
mean 1527.5fatigue DEL
1342.2
mean 1525.6fatigue DEL
944.4
mean 1498.9fatigue DEL
928.6
Tower side-side bending(kNm)
mean 122.1fatigue DEL
920.5
mean 293.3fatigue DEL
926.4
mean 360.1fatigue DEL
680.7
Blade pitch rate (deg/s)
avg mag 2.02max 15.1min -15.5
avg mag 2.32max 14.7min -13.9
avg mag 2.33max 14.7min -12.9
Generator torque (Nm)
Std 0.00max 3524min 3524
std 23.1max 3631min 3423
std 115.8max 4177min 2942
A. Wright 1/5/09 18
Results
10 12 14 16 18 20 22 24 26 28 300
0.05
0.1
0.15
0.2
0.25
Windspeed
PDF o
f W
indsp
eed
41.8 42 42.2 42.4 42.6 42.8 43 43.2 43.4 43.6 43.80
0.5
1
1.5
2
2.5
Rotorspeed
PDf of
Rot
orsp
eed
State-space1State-space 2PID
Probability Density Functions:
A. Wright 1/5/09 19
Results
0
0.2
0.4
0.6
0.8
1
1.2
1.4
Low-speed ShaftTorque DEL
(Nm)
Tower s-sbending DEL
(kNm)
Tower f-abending DEL
(kNm)
Blade flap-bending DEL
(kNm)
Load Category
No
rma
lize
d V
alu
e
PID State-space 1
A. Wright 1/5/09 20
Results
0
0.2
0.4
0.6
0.8
1
1.2
1.4
Low-speed ShaftTorque DEL
(Nm)
Tower s-sbending DEL
(kNm)
Tower f-abending DEL
(kNm)
Blade flap-bending DEL
(kNm)
Load Category
No
rma
lize
d V
alu
e
PID State-space 1 State-space 2
A. Wright 1/5/09 21
Results
Tower Bending Moments:
1490 1492 1494 1496 1498 1500 1502 1504 1506 1508
0
500
1000
1500
2000
2500
Time
Tow
er for
e-af
t (k
Nm
)
1490 1492 1494 1496 1498 1500 1502 1504 1506 1508 1510
-500
0
500
1000
Time
Tow
er s
ide-
side
(kNm
)
State-space1
State-space2PID
A. Wright 1/5/09 22
Results
Power Spectral Densities:
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
105
102
108
Frequency, Hz
PSD o
f Tow
er F
ore-
aft
Bend
ing
(kNm
)2/H
z
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
105
102
108
Frequency, Hz
PSD o
f Tow
er S
ide-
side
Be
ndin
g (k
Nm
)2/H
z
State-space1State-space 2PID
1stside-side
1stfore-aft
2P
2P
1P
1P
A. Wright 1/5/09 23
Results
500 510 520 530 540 550 560 570 580 590 600-20
-10
0
10
20
Time
pit
ch1ra
te(d
eg/
s)
500 510 520 530 540 550 560 570 580 590 6002800
3000
3200
3400
3600
3800
4000
4200
Time
GenTor
que
(Nm
)
State-space 1
State-space 2PID
Pitch Rate and Generator Torque:
A. Wright 1/5/09 24
Conclusions
Designed and performed field tests of two separate control loops:
– Rotor collective pitch control• active tower f-a damping • Region 3 speed regulation
– generator torque control• active tower s-s damping• active drive-train torsion damping
Field tests demonstrate 30% reduction in tower f-a and 26% reduction in tower s-s fatigue loads compared to simple PID controls.
Reasons for lack of drive-train torque load mitigation not resolved.
Results showed no undesirable interactions between these separate control loops.
A. Wright 1/5/09 25
Future Work
Resolve issue with drive-train torsion damping and re-test controller.
Implement and field-test independent blade pitch for shear mitigation and generator torque control.
Investigate alternative sensors for independent pitch control – look ahead Lidar
– additional blade sensors
– hub or shaft sensors
A. Wright 1/5/09 26
Acknowledgements
Dr. Michael Robinson – NREL management support
Garth Johnson, Scott Wilde – CART maintenance and support
Marshall Buhl – MCrunch data analysis scripts
