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Title: L1-Optimal Control of Variable-Speed Variable-Pitch Wind Turbines
Author: Jafarnejadsani, Hamidreza
Advisor: Pieper, Jeff
Keywords: Engineering--Mechanical
Issue Date: 30-May-2013
Abstract: The fast-growing technology of large scale wind turbines demands control systems capable of enhancing both the efficiency of capturing wind power, and the useful life of the turbines. Control based on L1 performance is an approach to deal with persistent exogenous disturbances which have bounded magnitude (L1-norm) such as realistic wind disturbances and turbulence profiles. In this study, we use a linear matrix inequality (LMI) approach for solution of the L1-optimal control problem. We develop an LPV model of a variable-speed variable-pitch (VS-VP) wind turbine in the transition region (between power point tracking and power regulation regimes). Then, we derive an LPV L1-optimal controller using LMI methods. We also develop an efficient method for computing the L1-norm of a closed-loop system. As the control synthesis problem is non-convex, we use the proposed method to design optimal output feedback controllers for a linear model of a wind turbine at different operating points using genetic algorithm (GA) optimization. The locally optimized controllers were interpolated using a gain-scheduled technique with guaranteed stability. The controller is tested with comprehensive simulation studies on a 5 MW wind turbine using FAST software. The proposed controller was compared with a well-tuned PI controller. The results show improved power quality, and decrease in the fluctuations of generator torque and rotor speed.
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