The focus of control research in wind energy has shifted more and more from individual wind turbines to wind farms due to the potential efficiency improvement in the energy production. In this work, the wind farm control concept “wake redirection” is further investigated. More precisely, the concept of lidar-based closed-loop wake redirection is extended. A lidar-based wake center estimation is assumed and fed back to a controller, which steers the wake by employing the yaw actuator to a desired position. In this work, a ℋ∞ controller design approach for lidar-based closed-loop wake redirection is investigated. The controller is designed using models that are obtained from the wind farm simulation tool WFSim. First, a model identification procedure is applied to derive the controller design models. Then, a ℋ∞ controller design is conducted to obtain a controller for each identified model. The controllers are presented and the performances are analyzed. In a final step, a single controller is implemented in WFSim and closed-loop step simulations are conducted illustrating the desired behavior.@en

Wind turbine wake redirection is a promising concept for wind farm control to increase the total power of a wind farm. Further, the concept aims to avoid partial wake overlap on a downwind wind turbine and hence aims to decrease structural loads. Controller for wake redirection need to account for model uncertainties due to the complexity of wake dynamics. Therefore, this work focuses first on modeling a wind farm using an uncertain plant description and second on the design of a robust H_∞ controller for closed-loop wake redirection by applying standard robust modeling and control techniques on a wind farm. The wake center position is estimated and fed back to a controller which uses the yaw actuator to redirect the wake. For several inflow conditions, step simulations are conducted and system identifications are performed to obtain multiple plant models. This set of models is used to derive a nominal plant and an uncertainty set. Both the nominal model and the uncertainty set define the uncertain plant model. The robust controller is then designed showing promising results in a medium-fidelity CFD simulation model with time-varying inflow conditions.

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The industry’s primary goal for state-of-the-art wind turbine controllers is to maximise the energy capture while keeping the turbine within its operational limits, such as maximum rotor speed or maximum power, which is limited by the generator capacity. To guarantee a reliable operation over the turbine’s lifetime, the structural loads need to be kept within their design limits. In the turbine and controller design process, an increase in energy is evaluated against higher loads; the result is that designers usually make specifications that increase material costs.

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The European Academy of Wind Energy (eawe), representing universities and institutes with a significant wind energy programme in 14 countries, has discussed the long-term research challenges in wind energy. In contrast to research agendas addressing short- to medium-term research activities, this eawe document takes a longer-term perspective, addressing the scientific knowledge base that is required to develop wind energy beyond the applications of today and tomorrow. In other words, this long-term research agenda is driven by problems and curiosity, addressing basic research and fundamental knowledge in 11 research areas, ranging from physics and design to environmental and societal aspects. Because of the very nature of this initiative, this document does not intend to be permanent or complete. It shows the vision of the experts of the eawe, but other views may be possible. We sincerely hope that it will spur an even more intensive discussion worldwide within the wind energy community.@en