Research Papers

Adaptive Pitch Control of Variable-Speed Wind Turbines

[+] Author and Article Information
Kathryn E. Johnson

Colorado School of Mines, Division of Engineering, 1600 Illinois Street, Golden, CO 80401kjohnson@mines.edu

Lee Jay Fingersh

National Renewable Energy Laboratory, National Wind Technology Center, MS 3811, 1617 Cole Boulevard, Golden, CO 80401

J. Sol. Energy Eng 130(3), 031012 (Jul 02, 2008) (7 pages) doi:10.1115/1.2931505 History: Received February 13, 2007; Revised August 31, 2007; Published July 02, 2008

The aerodynamic efficiency of a variable-speed wind turbine operating in Region 2, or below-rated wind speeds, is greatly affected by the identification of accurate parameters for the controller. In particular, the power coefficient (Cp) surface must be well known for optimal efficiency to be achieved with a constant-gain controller. However, adaptive control can overcome the inefficiencies caused by inaccurate knowledge of the Cp surface. Previous work focused on adaptive torque gain control to cause a variable-speed turbine to operate, on average, at the tip-speed ratio λ* for which the maximum Cp occurs. This paper considers the effects of adaptive blade pitch angle control on a turbine’s aerodynamic efficiency. Computer simulations and tests on a field turbine are used to verify the adaptive pitch control scheme. Simulation and field test results demonstrate that the adaptive pitch controller causes the pitch angle to approach its optimal value. Adaptive pitch control can be used to seek the optimal pitch angle for energy capture in Region 2 operation. Additional field operation is required before a statistically significant improvement in energy capture can be demonstrated.

Copyright © 2008 by American Society of Mechanical Engineers
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Figure 1

CART operating at the National Renewable Energy Laboratory’s National Wind Technology Center in Golden, CO. The CART is a test bed for advanced turbine control experiments.

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Figure 2

Cp surface and steady-state operating curves. The vertical line indicates the range of steady-state operating values for the previously developed adaptive torque control, while the near-horizontal curve indicates the range of steady-state operating values for the adaptive pitch control.

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Figure 3

Power coefficient Cp versus blade pitch angle β. This curve is a slice of the three-dimensional contour plot shown in Fig. 2.

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Figure 4

Simulation model. The “CART Aerodynamic Model” and “CART Rigid-Body Model” blocks make up the CART model, and both the torque and pitch control feedback loops are shown. The “turbine data” signals include rotor speed, acceleration, tip-speed ratio, and captured power.

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Figure 5

Results from constant-wind speed adaptive pitch simulation. The simulation used a constant-wind speed input of 8m∕s and a 5min adaptation period.

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Figure 6

Wind input files used in simulations. Each file contains 300s of 100Hz wind speed data measured with a cup anemometer at the National Wind Technology Center. Characteristics of each input file can be found in Table 1.

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Figure 7

Optimal pitch angle and customized power coefficient versus mean wind speed for CART model with ten different wind inputs. The optimal pitch angle is approximately 0.4deg in low wind speeds, and increases as the mean wind speed increases.

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Figure 8

Optimal pitch angle and customized power coefficient versus turbulence intensity for CART model with ten different wind inputs. The optimal pitch angle increases as the turbulence intensity increases.

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Figure 9

Adaptive pitch angle and customized power coefficient Cpc versus time for simulated CART adaptive pitch controller. The maximum power coefficient Cpmax for the simulation is 0.448.

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Figure 10

Adaptive pitch angle and customized power coefficient Cpc field data versus time in Region 2. The CART’s optimal power coefficient Cpmax is uncertain but is approximately 0.45.

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Figure 11

10min power coefficients Cp versus mean pitch angle from CART field data. Cp is computed using the measurement of the CART’s low-speed shaft power and the sonic anemometer’s wind speed measurement.



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