MULTI-OBJECTIVE GAIN-SCHEDULED H ∞ CONTROL OF AN OFFSHORE WIND TURBINE WITH TENSION LEG PLATFORM

Farzaneh Haghjoo, Ehsan Azadi Yazdi, and Mohammad Eghtesad

Keywords

Offshore wind turbine, gain-scheduled H ∞ control, tension legplatform, H ∞ control

Abstract

This paper proposes a gain-scheduled H ∞ control scheme for tension leg platform offshore wind turbines (OWT). A nonlinear dynamic model is developed by considering four rigid body degrees of freedom (DOFs) of the OWT (i.e., surge, heave and pitch of the platform and rotor rotation) and two flexible modes (i.e., the first bending mode of the tower and the torsional mode of the drive train). A multi-objective gain-scheduled H ∞ controller is designed with the aim of tower vibrations attenuation, rotor speed regulation, and generator torque regulation by considering the wind speed as the scheduling variable. The main advantage of the proposed controller is the fatigue life extension of the turbine because of the reduction in tower vibrations. The performance of the gain-scheduled H ∞ controller has been compared with that of a baseline single H ∞ controller through numerical simulations. The gain-scheduled H ∞ controller outperforms the baseline controller because of its inherent ability to compensate for the changes in the dynamic model due to the fluctuations in the wind speed.

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