06 Fakultät Luft- und Raumfahrttechnik und Geodäsie
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/7
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Item Open Access Lidar-assisted wake redirection control(2019) Raach, Steffen; Cheng, Po Wen (Prof. Dr.)Wind energy has developed to a competitive energy source and is intended to play an important role in the world-wide sustainable energy supply. The size of wind turbines has tremendously increased and turbines have been clustered to wind farms in order to share infrastructure and moreover reach energy production capacities of conventional power plants. However, the operation of wind turbines in a wind farm hasn't changed compared to single turbine operation. Possible interactions between wind turbines through the wind are not considered in the operation strategy of the turbines. The wake of a wind turbine can negatively influence the operation of a downwind turbine because the wind speed is reduced and the turbulence intensity is increased in the wake. Currently, each wind turbine is maximizing its power output independently of the other wind turbines. In a total consideration this may result in a suboptimal power output due to the interaction of wind turbines. In the case a wake impinges a second wind turbine, that turbine produces less power and the structural loads may increase. Both effects negatively impact the operation of the wind turbine and therefore it makes sense to avoid wake interactions. This task demands new wind park control concepts which take wind turbine interactions into account. In current research activities the wind farm is treated as the total system. Different investigations in wind farm control have identified two promising operation concepts: axial induction control and wake redirection control. Whereas the concept of induction control tries to minimize the impact of wakes on other wind turbines, the basic idea of wake redirection control is to redirect the wake of a wind turbine by yawing the wind turbine and therefore forcing a misalignment to the wind direction. Using this technique, interactions between wind turbines can be minimized. The current concept is based on an open-loop methodology in which a reduced-order wake model is used to pre-calculate the optimal yaw angles. This results in two disadvantages: The uncertainty which a simplified model introduces and the missing possibility to react to disturbances. This work introduces the concept of lidar-based closed-loop wake redirection control which can adapt to uncertainties and react on disturbances. Therefore it extends the concept of wake redirection control with a new closed-loop methodology. This work contributes various aspects to enable a lidar-based closed-loop wake redirection control. It first presents the general concept. Then it is separated in two subtasks: the measurement and the control tasks. This separation helps to focus on the specific questions of each task. First the measurement task is addressed and solutions are provided to process lidar measurement data to a useful signal for the wake redirection controller. Different methodologies are presented to track the wake position using lidar measurement data and the concept of model-based wake tracking is described in detail. Afterwards the control task is considered. Three different controller synthesis concepts are applied to wake redirection and controllers are synthesized. The different controllers are analyzed and the performances are assessed. Then the controllers are verified in different simulation tools. Mainly simulations are performed with a medium-fidelity computational fluid dynamics simulation tool. In addition the concept is implemented in a Large-Eddy simulation tool to demonstrate the adaption to disturbances and model uncertainties. Altogether the work introduces lidar-based closed-loop wake redirection control. It demonstrates the feasibility of the concept as well as the adaptivity of the controller to model uncertainties and disturbances. The different aspects of the concept are considered and methodologies for wake position estimation are provided and controllers are designed. Finally, recommendations are given to realize the concept in reality, and open questions are highlighted which require deeper investigations.