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The control of wind-energy conversion systems (WECSs) is still a challenging task for design engineers. Despite being ubiquitous in the wind industry, the performance of classical proportional-integral-derivative controllers is not ideal, and they require additional notch filters to handle turbine nonlinearity. This has triggered interest toward advanced control concepts that are multiobjective and multivariable. With optimality, feedback, and robustness being prerequisites in developing control policies that guarantee high-integrity and fault-tolerant control systems, H∞ control theory has become a standard design method of choice over the past two decades and is gaining prominence in industrial (and WECS) control applications. Based on the linear matrix inequality approach, this paper presents a comprehensive and systematic way of applying the H∞ control design algorithm for automatically gain-scheduling the linear-parameter-varying turbine plant along parameter trajectories. Control seeks to regulate both power and voltage via a synthesis of two controllers, namely, pitch and generator torque, respectively, for a megawatt-class WECS. Digital simulations executed in a MATLAB/Simulink environment ascertain that the control paradigm meets the objectives of optimizing power conversion throughout the operating envelope, as well as eliminating power oscillations through system damping.
Date of Publication: Jan. 2011