Stall Flutter Suppression for Absolutely Divergent Motions of WindTurbine Blade Base on H-Infinity Mixed-Sensitivity Synthesis Method

This paper is devoted to solve the problem of stall flutter suppression for an absolutely divergent blade of small scale wind turbine. The blade is specially designed with absolutely divergent motions for the purpose of determining the most effective methods of active control for stall flutter suppression. A 2-DOF blade section is considered, with a simplified stall nonlinear aerodynamic model being applied. H-infinity mixed-sensitivity synthesis method with a new three-weight regulation is designed to control the time-domain instability of aeroelastic equations, with a third weight being chosen to weight complementary sensitivity for tracking problems and noise attenuation to robust stabilization in H- infinity control. Effects on flutter suppression are investigated based on different structural and external parameters. Apparent effects of H-infinity mixed-sensitivity method are displayed in the paper, when the other common intelligent control methods fail. The research provides a control way for absolutely divergent turbine blade motions. As typical nonlinear aeroelastic instable vibration, stall flutter is an important reason of fatigue damage for wind turbine. How to effectively avoid flutter instability has become an important subject needed to be investigated. Meanwhile in this area, the investigation of typical blade section based on the simplified stall flutter of 2-DOF flap/lag motions plays an important role due to its simplicity and high efficiency (1). Hence in this study, stall flutter suppression will be depicted based on 2-DOF blade section. In recent years, a number of issues related to the modeling, vibration analysis, and control methods for stall flutter are investigated. Shantanu experimentally studies and demarcates the stall flutter boundaries of an airfoil by measuring the forces and flow fields around the airfoil when it is forced to oscillate (2). S. Sarkar investigates the effect of system parametric uncertainty on the stall flutter bifurcation behavior of a pitching airfoil, with the aerodynamic moment on the two-dimensional rigid airfoil being computed using the ONERA dynamic stall model (3). J. Peiro investigates the dynamics of a typical airfoil section and demonstrates the importance of the added mass terms, with structural behavior being modeled by linear springs and the aerodynamic loading being exerted by Beddoes-Leishman (B-L) model (4). Zhiwei adopts a nonlinear time-domain aeroservoelastic model and designs flutter suppression control systems, with a novel state-space model being descripted for control design (5). Ananth presents a method to predict cascade flutter under subsonic stalled flow condition in a quasi-steady

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