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This paper proposes a dynamic output feedback decentralized pitch controller for flexible wind turbines. Both collective and cyclic (individual) pitch controllers are considered. The collective pitch controller aims at improving the rotor speed regulation and maximizing the harvested electrical power, without violating the pitch actuator limits. On the other hand, the cyclic (individual) pitch controller targets mitigating the fatigue relevant loads caused by aerodynamic forces. Both controllers are designed based on a polytopic model. The design constraints include (H∞ problem, H2 problem and pole clustering). Initially, an LMI-based feasible controller is designed, and then a final feasible controller is reached via local optimization iterative algorithm. The performance of the proposed controller is compared to a gain scheduled PI controller. The results are validated by testing on a nonlinear flexible multi-MW wind turbine model against a realistic extreme turbulence wind profile.