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Goal of this paper is to present results from wind tunnel tests aimed at evaluating the potential of different wake control strategies for wind farm power maximization and load reduction. The experiments are conducted in a large boundary layer wind tunnel, using up to six servo-actuated and highly sensorized wind turbine scaled models in different wind farm layouts. Two main strategies are considered: the first derates the upstream wind turbines, while the second aims at redirecting wakes away from the downstream machines. The latter strategy is implemented in two alternative ways, using either active yawing or individual blade pitching. The impact on wind farm power and loading of these control strategies is discussed, highlighting the most promising ones

This work is concerned with the design of wind turbine blades with bend-twist-to-feather coupling that self-react to wind fluctuations by reducing the angle of attack, thereby inducing a load mitigation effect. This behavior is obtained here by exploiting the orthotropic properties of composite materials by rotating the fibers away from the pitch axis.The first part of this study investigates the possible configurations for achieving bend-twist coupling. At first, fully coupled blades are designed by rotating the fibers for the whole blade span, and a best compromise solution is found to limit weight increase by rotations both in the spar caps and in the skin. Next, partially coupled blades are designed where fibers are rotated only on the outboard part of the blade, this way achieving good load mitigation capabilities together with weight savings. All blades are designed with a multilevel constrained optimization procedure, on the basis of combined cross-sectional, multibody aero-servo-elastic and three-dimensional finite element models.Finally, the best configuration of the passive coupled blade is combined with an active individual pitch controller. The synergistic use of passive and active load mitigation technologies is shown to allow for significant load reductions while limiting the increase in actuator duty cycle, thanks to the opposite effects on this performance metric of the passive and active control solutions. ABBREVIATIONSADC actuator duty cycle AEP annual energy production BTC bend-twist coupling CAD computer-aided design DEL damage equivalent load DLC design load case EOG extreme operative gust FEM finite element method HAWT horizontal axis wind turbine IPC individual pitch control LQR linear quadratic regulator PID proportional integral derivative SQP sequential quadratic programming