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As wind turbine rated power increase, the potential danger of the vibration is bigger result of the rotor diameter and the hub height is longer and higher. Wind turbine vibrations will cause futile mechanical loads, such vibration loads maybe result to serious damage of wind turbine. In order to achieve vibration suppression, taking the uncertainty of turbulence which the operate environment of wind turbine into consider, control methods is utilized in wind turbine to achieve reduction of coupled load. The state space of wind turbine in cycle life is established. Effectiveness of controller based on the control in vibration control field is verified by GH-Bladed and Matlab. Simulation results and validation results show that the purposed control strategy is effective in terms of wind turbine tower vibration. Introduction The basic control requirements for a wind turbine are to regulate rotor speed and electric power aiming to reduce detrimental dynamic loads and to maximize efficiency on energy conversion [2] . In most wind turbine, the speed of generator must be controlled to restrict speed variations since the generator is directly connected to fixed-frequency electrical net. Another important control objective is to reduce the influence of wind fluctuation and ripple torque on wind at any rotation speed, whose introduce unavoidable vibrations along drive train line with detrimental effects on wind turbine. The vibration issues have become a key problem that cannot be ignored in the wind turbine’s life cycle. The advanced control system is considered as a promising way to improve wind turbine conversion system and to decrease wind turbine cost. Wind turbine is a nonlinear system, because of complex multi-body structure which is consists with the rigid structures like nacelle, hub, tower and the flexible structures like rotor. System analyze issue also is the fluid-structure interaction with high linearity. The conventional approach to introducing additional damping is by adding separate single-input signal-output (SISO) control loops to the existing baseline control loop for each new control objective. Although the classical methods for wind turbine vibration control like tuned mass damper (TMD) for wind turbine has been applied in vibration control field, but the control method existed do not offer a completely satisfactory solution to decrease vibration, since they do not assure the robustness for both stability and performance, especially the stability fitting for various wind condition. Considering that wind turbine objectives can be easily specified in terms of maximum allowable gain in the disturbance to output transfer functions, H∞ and H2 methodologies consist in good options to control design for wind turbine. Active control of H∞ control takes the vibration information, e.g. Velocity, acceleration, as the feedback to achieve vibration suppress. It is based on a modern multi-input multi-output (MIMO) controller described by the state function to design the controller. This approach has also been shown effective for reducing loads and suppressing vibration. In this paper, H∞ control methodologies are utilized on feedback controller for a multivariable wind turbine. The section 2 shows the linearized wind turbine model, the section 3 presents the H∞ control methodologies design. Section 4 shows the dynamic response and the performance of close-loop system simulating results using a nonlinear model of a wind turbine. Section 5 presents some conclusions, which from simulation results the H∞ controllers can achieve vibration control of wind turbine. 197 Wind Turbine Model Wind turbine model is a complex nonlinear model. In order to conduct the control analyses, the first is linearized the wind turbine model. The linear system is the system can be described as a linear differential equation. And it is should satisfy the superposition principle, that is, ( ) ( ) f ax af x = (1) 1 2 1 2 ( ) ( ) ( ) f x x f x f x + = + (2) Wind turbine is consists of rotor, nacelle, tower, drive train, generator and foundation, Figure 1 shows the model of wind turbine. The power of wind turbine Pr, the aerodynamics torque Taero and the thrust force Faero are functions of the air density ρ, the velocity V, the rotational speedωr, the power coefficient Cp, the thrust coefficients CT and the torque coefficient CQ, 2 3 1 ( , ) 2 r P P R C v ρπ λ β = (3) 3 2 e 1 π , 2 r aero Q R T R C V V ω ρ β   =     (4) 2 2 e 1 π , 2 r T T R F R C V V ω ρ β   =     (5) Where Ris the radius of the rotor blades,Ve is the actual wind speed, and the tip speed ratioλ, the ratio of the blade tip linear speed to the wind speed. Figure 1. The drive train model The drive train model of wind turbine can be described as, ( ) ( ) s r g s r r ae r g ro d T J dt B K ω ω ω θ θ − = + − + (6) ( ) ( ) g g s g r s g r g d J B K dt T ω ω ω θ θ − + − + − = (7) Where Jr is the wind rotor inertia, Jg is the generator inertia, Bs is the transmission damping, Ks is the transmission stiffness. The pitch control in linearized aero is, 1 1 r β β β β β τ τ = − + (8) Whereτβ the time is constant, usually equals 0.2s, βr is the control input pitch angle. The nonlinear generator torque can be linearized as,

Controlling Structural Vibration in Wind Turbine by H∞ Controlling Structural Vibration in Wind Turbine by H Control