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 Comparison of feedforward and model predictive control of wind turbines using LIDAR(2012) Schlipf, David; Pao, Lucy Y.; Cheng, Po WenLIDAR systems are able to provide preview information of wind disturbances at various distances in front of wind turbines. This technology paves the way for new control concepts such as feedforward control and model predictive control. This paper compares a nonlinear model predictive controller and a feedforward controller to a baseline controller. Realistic wind "measurements" are obtained using a detailed simulation of a LIDAR system. A full lifetime comparison shows the advantages of using the wind predictions to reduce wind turbine fatigue loads on the tower and blades as well as to limit the blade pitch rates. The results illustrate that the feedforward controller can be combined with a tower feedback controller to yield similar load reductions as the model predictive controller.Item Open Access Nonlinear model predictive control of floating wind turbines(2013) Schlipf, David; Sandner, Frank; Raach, Steffen; Matha, Denis; Cheng, Po WenIn this work a nonlinear model predictive control method for a floating wind turbine is presented. A reduced nonlinear model including disturbance preview of wind and waves is derived and implemented to compute optimal input trajectories for collective pitch and the generator torque. A cost functional is introduced which fulfills all desired constraints and controller goals for above rated wind conditions. The controller is tested for extreme and fatigue load cases and a significant reduction of the power and rotor speed deviations is obtained. Furthermore, ultimate tower loads and damage equivalent loads on shaft and blades are decreased. Although more detailed testing is necessary, this preliminary results show the advantages of nonlinear model predictive control for floating wind turbines.Item Open Access Nonlinear model predictive control of floating wind turbines with individual pitch control(2014) Raach, Steffen; Schlipf, David; Sandner, Frank; Matha, Denis; Cheng, Po WenIn this work a nonlinear model predictive controller with individual pitch control for a floating offshore wind turbine is presented. An aerodynamic model of the collective pitch control approach is extended by describing pitching and yawing moments based on rotor disk theory. This extension is implemented in a reduced nonlinear model of the floating wind turbine including disturbance preview of wind speed, linear vertical and horizontal wind shear, and wave height to compute optimal input trajectories for the individual pitch control inputs and the generator torque. An extended cost functional for individual pitch control is proposed based on the collective pitch control approach. The controller is evaluated in aero-servo-hydro-elastic simulations of a 5MW reference wind turbine disturbed by a three-dimensional stochastic turbulent wind field. Results show a significant blade fatigue load reduction compared to a baseline controller through minimizing yawing and pitching moments on the rotor hub while maintaining the advantages of the model predictive control approach with collective pitch control.Item Open Access Load analysis of look-ahead collective pitch control using LIDAR(2010) Schlipf, David; Fischer, Tim; Carcangiu, Carlo Enrico; Rossetti, Michele; Bossanyi, ErvinIn a detailed analysis the benefit of LIDAR assisted collective pitch control is evaluated, by using a realistic LIDAR simulator and comparing it to an advanced feedback controller. With the proposed look-ahead controller best load reduction can be observed for high turbulence and high wind speed. Damage equivalent loads on tower and blades are reduced up to 20% and 10%, respectively.Item Open Access LIDAR assisted collective pitch control(2011) Schlipf, David; Bossanyi, Ervin; Carcangiu, Carlo Enrico; Fischer, Tim; Maul, Timo; Rossetti, MicheleNacelle based pulsed LIDAR (Light detection and ranging) systems provide preview information of wind disturbances at various distances in front of wind turbines. In previous work it has been shown that this information can be used to improve the speed regulation of wind turbines by a look-ahead update to the collective pitch control, which indicates load reduction of tower and blades. In the scope of the UpWind project a first fatigue and extreme load analysis has been done to concretize the improvement of look-ahead collective pitch control using LIDAR.Item Open Access Development of a wind turbine LiDAR simulator(2009) Schlipf, David; Trujillo, Juan José; Basterra, Valeria; Kühn, MartinRemote sensing techniques like LiDAR offer many novel applications to the wind energy community, e.g. fast and accurate measurements of inflow and wake wind fields from the turbine nacelle. The prospects of such a new technique are evaluated with a software tool simulating a nacelle-based LiDAR system. The paper presents the implementation and application of a simulator that has been conceived to support the design of wind field scanning procedures. The tool helps to optimize the hardware setup, scanning trajectories and frequency. Furthermore it can be coupled with an aeroelastic code with the aim of developing a predictive control based on remote sensing.Item Open Access Testing of frozen turbulence hypothesis for wind turbine applications with a scanning LIDAR system(2011) Schlipf, David; Trabucchi, Davide; Bischoff, Oliver; Hofsäß, Martin; Mann, Jakob; Mikkelsen, Torben; Rettenmeier, Andreas; Trujillo, Juan José; Kühn, MartinTaylor’s frozen turbulence hypothesis is tested in its applicability for wind turbine applications. In this research full field measurements are performed at a test site for multi-megawatt wind turbines by means of a pulsed LIDAR with a scanning device. The system is installed at the top of the nacelle of a 5MW wind turbine. It provides simultaneous wind speed, with a maximum sampling rate of 5 Hz, at different stations parallel to the mean wind. Measurements in a range between 0.4 and 1.6 rotor diameter are performed following several two and three dimensional trajectories. The spectral characteristics of measurements taken simultaneously at different separation distances are studied. The scanning strategy which maximizes the wavenumber region where results are consistent with Taylor’s hypothesis is assessed. The best results are achieved by a horizontal sliding trajectory with valid wavenumbers up to 0.125 rad/m.Item Open Access Collective pitch feedforward control of floating wind turbines using lidar(2015) Schlipf, David; Simley, Eric; Lemmer, Frank; Pao, Lucy; Cheng, Po WenIn this work a collective pitch feedforward controller for floating wind turbines is presented. The feedforward controller provides a pitch rate update to a conventional feedback controller based on a wind speed preview. The controller is designed similar to the one for onshore turbines, which has proven its capability to improve wind turbine control performance in field tests. In a first design step, perfect wind preview and a calm sea is assumed. Under these assumptions the feedforward controller is able to compensate almost perfectly the effect of changing wind speed to the rotor speed of a full nonlinear model over the entire full load region. In a second step, a nacelle-based lidar is simulated scanning the same wind field which is used also for the aero-hydro-servo-elastic simulation. With model-based wind field reconstruction methods, the rotor effective wind speed is estimated from the raw lidar data and is used in the feedforward controller after filtering out the uncorrelated frequencies. Simulation results show that even with a more realistic wind preview, the feedforward controller is able to significantly reduce rotor speed and power variations. Furthermore, structural loads on the tower, rotor shaft, and blades are decreased. A comparison to a theoretical investigation shows that the reduction in rotor speed regulation is close to the optimum.Item Open Access Lidar technology for the German offshore test site "alpha ventus" - joint project in measurement development(2008) Rettenmeier, Andreas; Schlipf, David; Wächter, Matthias; Käsler, Yvonne; Mellinghoff, Harald; Siegmeier, Björn; Reeder, Lennard; Kühn, MartinThis paper describes the content of the joint research project "Development of LiDAR measurement techniques for the German offshore test site" and its first results. The objective is to develop reliable and standardised remote sensing techniques for various new applications in the wind energy community and to support other RAVE1 projects at the German offshore test site "alpha ventus". The first measurement campaign dealt with the comparison of wind parameters measured by common anemometry in a height of up to 103 m and LiDAR data measured up to 220 m height. The first results show very good agreement when the two techniques are compared as to wind speed, wind direction and power curve determination at a 5 MW wind turbine. The status of the development of a wind field scanner for nacelle-based LiDAR measurements is described and an outlook to the forthcoming work is given.Item Open Access Direct speed control using LIDAR and turbine data(2013) Schlipf, David; Fleming, Paul; Kapp, Stefan; Scholbrock, Andrew; Haizmann, Florian; Belen, Fred; Wright, Alan; Cheng, Po WenLIDAR systems are able to provide preview information of the wind speed in front of wind turbines. One proposed use of this information is to increase the energy capture of the turbine by adjusting the rotor speed directly to maintain operation at the optimal tip-speed ratio, a technique referred to as Direct Speed Control (DSC). Previous work has indicated that for large turbines the marginal benefit of the direct speed controller in terms of increased power does not compensate for the increase of the shaft loads. However, the technique has not yet been adequately tested to make this determination conclusively. Further, it is possible that applying DSC to smaller turbines could be worthwhile because of the higher rotor speed fluctuations and the small rotor inertia. This paper extends the previous work on direct speed controllers. A DSC is developed for a 600 kW experimental turbine and is evaluated theoretically and in simulation. Because the actual turbine has a mounted LIDAR, data collected from the turbine and LIDAR during operation are used to perform a hybrid simulation. This technique allows a realistic simulation to be performed, which provides good agreement with theoretical predictions.