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 IEA Wind Task 32: Wind Lidar : identifying and mitigating barriers to the adoption of wind lidar(2018) Clifton, Andrew; Clive, Peter; Gottschall, Julia; Schlipf, David; Simley, Eric; Simmons, Luke; Stein, Detlef; Trabucchi, Davide; Vasiljevic, Nikola; Würth, InesIEA Wind Task 32 exists to identify and mitigate barriers to the adoption of lidar for wind energy applications. It leverages ongoing international research and development activities in academia and industry to investigate site assessment, power performance testing, controls and loads, and complex flows. Since its initiation in 2011, Task 32 has been responsible for several recommended practices and expert reports that have contributed to the adoption of ground-based, nacelle-based, and floating lidar by the wind industry. Future challenges include the development of lidar uncertainty models, best practices for data management, and developing community-based tools for data analysis, planning of lidar measurements and lidar configuration. This paper describes the barriers that Task 32 identified to the deployment of wind lidar in each of these application areas, and the steps that have been taken to confirm or mitigate the barriers. Task 32 will continue to be a meeting point for the international wind lidar community until at least 2020 and welcomes old and new participants.Item Open Access Optimization of floating offshore wind turbine platforms with a self-tuning controller(2017) Lemmer, Frank; Müller, Kolja; Yu, Wei; Schlipf, David; Cheng, Po WenThe dynamic response of floating offshore wind turbines is complex and requires numerous design iterations in order to converge at a cost-efficient hull shape with reduced responses to wind and waves. In this article, a framework is presented, which allows the optimization of design parameters with respect to user-defined criteria such as load reduction and material costs. The optimization uses a simplified nonlinear model of the floating wind turbine and a self-tuning model-based controller. The results are shown for a concrete three-column semi-submersible and a 10MW wind turbine, for which a reduction of the fluctuating wind and wave loads is possible through the optimization. However, this happens at increased material costs for the platform due to voluminous heave plates or increased column spacing.Item Open Access Flatness-based feedforward control of wind turbines using Lidar(2014) Schlipf, David; Cheng, Po WenCurrent lidar technology is offering a promising opportunity to take a fresh look at wind turbine control. This work evaluates a flatness-based feedforward approach, that allows to calculate the control action based on trajectories of the rotor speed and tower motion using wind measurements. The trajectories are planned online considering actuator constrains to regulate the rotor speed and minimize tower movements. The feedforward signals of the collective pitch and generator torque update can be combined with conventional feedback controllers. This facilitates the application on commercial wind turbines. Simulations using a realistic lidar simulator and a full aero-elastic model show considerable reduction of tower and shaft loads.Item Open Access Realistic simulations of extreme load cases with lidar-based feedforward control(2017) Hagemann, Tim; Haizmann, Florian; Schlipf, David; Cheng, Po WenThis work presents the development of a simulation environment which allows to simulate realistic extreme events with lidar-based feedforward control. This environment includes turbulent wind fields including extreme events, wind evolution and wind field scanning with a nacelle-based lidar system. It is designed to simulate lidar-based controllers in a realistic environment. In addition, a controller extension is proposed to identify and mitigate extreme events in wind fields based on lidar measurements. The combination of this extreme event controller with the realistic simulation environment is a promising tool for load reductions in wind turbines.Item Open Access Lidar-based wake tracking for closed-loop wind farm control(2017) Raach, Steffen; Schlipf, David; Cheng, Po WenThis work presents two advancements towards closed-loop wake redirection of a wind turbine. First, a model-based wake-tracking approach is presented, which uses a nacelle-based lidar system facing downwind to obtain information about the wake. The method uses a reduced-order wake model to track the wake. The wake tracking is demonstrated with lidar measurement data from an offshore campaign and with simulated lidar data from a simulation with the Simulator fOr Wind Farm Applications (SOWFA). Second, a controller for closed-loop wake steering is presented. It uses the wake-tracking information to set the yaw actuator of the wind turbine to redirect the wake to a desired position. Altogether, the two approaches enable a closed-loop wake redirection.Item Open Access Statistical load estimation using a nacelle-based lidar system(2010) Bischoff, Oliver; Hofsäß, Martin; Rettenmeier, Andreas; Schlipf, David; Siegmeier, BjörnThe paper presents the results of statistical load analyses based on data measured at the 5MW AREVA Wind M5000 onshore prototype. Measurements with standard meteorological measurement devices are analysed and compared to measurements with a pulsed LIDAR system which is enhanced with a multi-purpose scanning device installed on the top of the nacelle of the turbine. Based on these measurements statistical summaries of relevant meteorological parameters have been used for normative procedures to calculate the mechanical loads which occur at the wind energy turbine. It could be verified that LIDAR systems can substitute standard measurement devices for a load estimation of wind energy turbines.Item Open Access Optimization of a feed-forward controller using a CW-lidar system on the CART3(2015) Haizmann, Florian; Schlipf, David; Raach, Steffen; Scholbrock, Andrew; Wright, Alan; Slinger, Chris; Medley, John; Harris, Michael; Bossanyi, Ervin; Cheng, Po WenThis work presents results from a new field-testing campaign conducted on the three-bladed Controls Advanced Research Turbine (CART3) at the National Renewable Energy Laboratory in 2014. Tests were conducted using a commercially available, nacelle-mounted continuous-wave lidar system from ZephIR Lidar for the implementation of a lidar-based collective pitch feed-forward controller. During the campaign, the data processing of the lidar system was optimized for higher availability. Furthermore, the optimal scan distance was investigated for the CART3 by means of a spectra-based analytical model and found to match the lidar's capabilities well. Throughout the campaign the predicted correlation between the lidar measurements and the turbine's reaction was confirmed from the measured data. Additionally, the baseline feedback controller's gains were tuned based on a simulation study that included the lidar system to achieve further load reductions. This led to some promising first results, which are presented at the end of this paper.Item Open Access Multi-variable feedforward control for floating wind turbines using lidar(2020) Schlipf, David; Lemmer, Frank; Raach, SteffenIn this work a multi-variable feedforward controller for floating wind turbines is presented. The feedforward controller provides a pitch rate and a torque update to a conventional feedback controller based on a wind speed preview. A 10 MW reference wind turbine is used on a semi submersible floating platform to study the potential of the controller. An open-source simulation tool is extended with an realistic lidar simulator and the lidar data processing, feedforward controller, and feedback controller are implemented in modular setup. The lidar measurements are fully motion compensated and combined to provide a preview of the rotor-effective wind speed to the controller. The feedforward controller is designed to minimize structural loads and to decrease the platform pitch motion. In verification and simulation studies the concept is demonstrated and the multi-variable feedforward controller shows a promising improvement in speed regulation and load reduction on the floating wind turbine.Item Open Access Prospects of linear model predictive control on a 10MW floating wind turbine(2015) Lemmer, Frank; Raach, Steffen; Schlipf, David; Cheng, Po WenThe presented research has the objective of supporting the integrated conceptual design of floating offshore wind turbines (FOWT). The dynamics of the multidisciplinary coupled system with the aerodynamics, hydrodynamics, structural dynamics, the catenary mooring lines and the controller shall be represented in simulation models adapted to the current design stage. Here, a linear model-predictive controller (MPC) as an optimal multiple input-multiple output (MIMO) controller is designed for a novel concept of the floating foundation for a 10MW wind turbine. The performance of this controller is easily adjustable by a cost function with multiple objectives. Therefore, the MPC can be seen as a benchmark controller in the concept phase, based on a simplified coupled simulation model with only approximate model information. The linear model is verified against its nonlinear counterpart and the performance of the MPC compared to a SISO PI-controller, which is also designed in this work. The developed models show to be well suited and the linear MPC shows a reduction of the rotor speed overshoot and tower bending from a deterministic gust.Item Open Access Investigation on the potential of individual blade control for lifetime extension(2018) Pettas, Vasilis; Salari, Mohammad; Schlipf, David; Cheng, Po WenIn recent years the focus of wind energy industry is on reducing levelized cost of energy by rotor upscaling. Moreover, a current topic of interest to both industry and academia is the extension of lifetime to existing wind turbines approaching the end of initial design span. Thus, the need for load alleviation technologies integrated in the design process or for retrofit purposes is becoming more relevant. One of these is individual blade pitch control, a recurring topic in research, with known advantages and weaknesses namely the pitch actuator and bearing wear. The present work suggests such a system incorporating three independent controllers with input the root bending moments on the rotating frame. The linear system used for controller design is based on black box identification of non-linear simulations and filters are used both for the input and output. Different setups of the independent blade control scheme are applied on a 10 MW reference turbine, with a large and highly flexible rotor representative of the current industrial status, under wind conditions as defined by relevant certification standards. The investigation aims on evaluating the system’s performance based on the fatigue load alleviation potential for different components as well as identifying the tradeoff for each design choice. Finally, based on basic assumptions the reductions are translated to possible life time extension for each component based on a combined operation where the new controllers are applied for a percentage of the initial 20 year lifetime.