Research Papers

Nonlinear Systems Analysis and Control of Variable Speed Wind Turbines for Multiregime Operation

[+] Author and Article Information
Greg Semrau

Moog Inc.,
East Aurora, NY 14052

Sigitas Rimkus

Department of Mechanical
and Aerospace Engineering,
University of Central Florida,
Orlando, FL 32816

Tuhin Das

Department of Mechanical
and Aerospace Engineering,
University of Central Florida,
Orlando, FL 32816
e-mail: Tuhin.Das@ucf.edu

1Corresponding author.

Contributed by the Dynamic Systems Division of ASME for publication in the JOURNAL OF DYNAMIC SYSTEMS, MEASUREMENT, AND CONTROL. Manuscript received December 31, 2013; final manuscript received October 7, 2014; published online November 7, 2014. Assoc. Editor: Ryozo Nagamune.

J. Dyn. Sys., Meas., Control 137(4), 041007 (Apr 01, 2015) (10 pages) Paper No: DS-13-1537; doi: 10.1115/1.4028775 History: Received December 31, 2013; Revised October 07, 2014

The key control problems associated with variable speed wind turbines are maximization of extracted energy when operating below the rated wind speed, and power and speed regulation when operating above the rated wind speed. In this paper, we develop a nonlinear systems framework to address these problems. The framework is used to visualize and analyze the equilibria of the wind turbine as its operating regimes and controllers change. For both below rated and above rated wind speeds, we adopt nonlinear controllers, analyze the stability property of the resulting equilibria, and establish the criterion for switching between control regimes. Further, the regions of attraction of the resulting equilibria are determined, and the existence of a common region of attraction, which allows stable switching between operating regimes, is shown. The control input maintains continuity at the point of switching. We next provide a method for blade pitch modulation to control rotor speed at high wind speeds. Through Lyapunov stability analysis, we prove stability of the equilibria in the presence of the two independently functioning torque- and pitch-control feedback loops. Simulation results are presented and the controller is compared with existing works from the literature.

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Fig. 1

Rotor efficiency surface as a function of tip speed ratio and blade pitch angle

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Fig. 2

Drive train model with a gearbox

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Fig. 3

Operating regimes of variable speed wind turbine

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Fig. 4

Equilibrium points for below rated wind speed under control law, Eq. (9)

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Fig. 5

Equilibrium points for above rated wind speed under control law, Eq. (15)

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Fig. 6

Switching point between regimes 2 and 3

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Fig. 7

Common equilibrium at switching point

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Fig. 8

Equilibrium points under β modulation

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Fig. 9

Response of wind turbine to step changes in wind speed

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Fig. 10

Simulation results for combined regimes 2 and 3 operation

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Fig. 11

Wind profile, controller state, blade pitch, and power

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Fig. 12

Simulations for comparison with Ref. [15]



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