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J. Mar. Sci. Eng. 2018, 6(4), 151; https://doi.org/10.3390/jmse6040151

Linear Quadratic Optimal Control of a Spar-Type Floating Offshore Wind Turbine in the Presence of Turbulent Wind and Different Sea States

Federal University of ABC (UFABC), Center of Engineering, Modeling and Applied Social Sciences, Av. dos Estados, 5001, Bairro Santa Terezinha, Santo André, SP 09210-580, Brazil
Received: 29 November 2018 / Revised: 4 December 2018 / Accepted: 5 December 2018 / Published: 7 December 2018
(This article belongs to the Special Issue Advances in Offshore Wind Energy)
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Abstract

This paper presents the design of a linear quadratic (LQ) optimal controller for a spar-type floating offshore wind turbine (FOWT). The FOWT is exposed to different sea states and constant wind turbulence intensity above rated wind speed. A new LQ control objective is specified for the floater-turbine coupled control, in accordance with standard requirements, to reduce both rotor speed fluctuations and floater pitch motion in each relevant sea state compared with a baseline proportional-integral (PI) controller. The LQ weighting matrices are selected using time series of the wind/wave disturbances generated for the relevant sea states. A linearized state-space model is developed, including the floater surge/pitch motions, rotor speed, collective blade pitch actuation, and unmeasured environmental disturbances. The wind disturbance modeling is based on the Kaimal spectrum and aerodynamic thrust/torque coefficients. The wave disturbance modeling is based on the Pierson–Moskowitz spectrum and linearized Morison equation. A high-fidelity FOWT simulator is used to verify the control-oriented model. The simulation results for the OC3-Hywind FOWT subjected to turbulent wind show that a single LQ controller can yield both rotor speed fluctuation reduction of 32–72% and floater pitch motion reduction of 22–44% in moderate to very rough sea states compared with the baseline PI controller. View Full-Text
Keywords: floating offshore wind turbine; spar; floater-turbine coupled control; control-oriented modeling; linear quadratic (LQ) optimal control; turbulent wind; sea states; disturbance modeling floating offshore wind turbine; spar; floater-turbine coupled control; control-oriented modeling; linear quadratic (LQ) optimal control; turbulent wind; sea states; disturbance modeling
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Ramos, R.L. Linear Quadratic Optimal Control of a Spar-Type Floating Offshore Wind Turbine in the Presence of Turbulent Wind and Different Sea States. J. Mar. Sci. Eng. 2018, 6, 151.

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