15 Fakultätsübergreifend / Sonstige Einrichtung
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/16
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Item Open Access Detection of wind evolution and lidar trajectory optimization for lidar-assisted wind turbine control(2015) Schlipf, David; Haizmann, Florian; Cosack, Nicolai; Siebers, Tom; 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 Design and evaluation of a lidar-based feedforward controller for the INNWIND.EU 10 MW wind turbine(2015) Fürst, Holger; Schlipf, David; Iribas Latour, Mikel; Cheng, Po WenFor the development of the next generation of multi megawatt wind turbines, advanced control concepts are one of the major tasks. Reduction of fatigue and extreme loading could help to improve the overall design process and make plants more cost effective. This work deals with the application of the promising methodology of feedforward control using nacelle-based lidar sensor measurements on a 10 MW wind turbine concept. After lidar data processing has been described, the feedforward controller is designed such that disturbances from the changing wind speed to the generator speed are compensated by adding an update to the collective pitch rate signal of the normal feedback controller. The evaluation of the feedforward controller is done in two steps: Firstly, simulations using perfect lidar data measurements are applied to check the robustness of the controller against model uncertainties. After that, simulations with realistic lidar measurements are investigated. To improve control performance, the scanning configuration of the used lidar system is optimized. Over all it can be shown that lidar-assisted control leads to significant load reductions, especially in the full load region of the 10 MW turbine.Item Open Access Comparison of linear and nonlinear model predictive control of wind turbines using LIDAR(2014) Schlipf, David; Grau, Patrick; Raach, Steffen; Duraiski, Ricardo; Trierweiler, Jorge; Cheng, Po WenRecent developments in remote sensing are offering a promising opportunity to rethink conventional control strategies of wind turbines. With technologies such as LIDAR, the information about the incoming wind field - the main disturbance to the system - can be made available ahead of time. Feedforward control can be easily combined with traditional collective pitch feedback controllers and has been successfully tested on real systems. Nonlinear model predictive controllers adjusting both collective pitch and generator torque can further reduce structural loads in simulations but have higher computational times compared to feedforward or linear model predictive controller. This paper compares a linear and a commercial nonlinear model predictive controller to a baseline controller. On the one hand simulations show that both controller have significant improvements if used along with the preview of the rotor effective wind speed. On the other hand the nonlinear model predictive controller can achieve better results compared to the linear model close to the rated wind speed.Item Open Access An adaptive data processing technique for lidar-assisted control to bridge the gap between lidar systems and wind turbines(2015) Schlipf, David; Fleming, Paul; Raach, Steffen; Scholbrock, Andrew; Haizmann, Florian; Krishnamurthy, Raghu; Boquet, Matthieu; Cheng, Po WenThis paper presents first steps toward an adaptive lidar data processing technique crucial for lidar-assisted control in wind turbines. The prediction time and the quality of the wind preview from lidar measurements depend on several factors and are not constant. If the data processing is not continually adjusted, the benefit of lidar-assisted control cannot be fully exploited or can even result in harmful control action. An online analysis of the lidar and turbine data is necessary to continually reassess the prediction time and lidar data quality. In this work, a structured process to develop an analysis tool for the prediction time and a new hardware setup for lidar-assisted control are presented. The tool consists of an online estimation of the rotor effective wind speed from lidar and turbine data and the implementation of an online cross-correlation to determine the time shift between both signals. Further, we present initial results from an ongoing campaign in which this system was employed for providing lidar preview for feedforward pitch control.Item Open Access Improved tank test procedures for scaled floating offshore wind turbines(2014) Müller, Kolja; Sandner, Frank; Bredmose, Henrik; Azcona, José; Manjock, Andreas; Pereira, RicardoThis study collects issues from previous tank test campaigns of scaled Floating Offshore Wind Turbines (FOWT), compares the different scaling methodologies, points out critical aspects and shows possible alternatives and recommendations for future tests depending on the specific objective. Furthermore, it gives practical recommendations for the modeling and construction of scaled rotors. The presented scaling procedure will be applied in tank tests within the EU Seventh Framework Program InnWind (ENERGY.2012.2.3.1 "Innovative wind conversion systems (10-20MW) for offshore applications").Item Open Access Field testing of feedforward collective pitch control on the CART2 using a nacelle-based lidar scanner(2012) Schlipf, David; Fleming, Paul; Haizmann, Florian; Scholbrock, Andrew; Hofsäß, Martin; Wright, Alan; Cheng, Po WenThis work presents the first results from a field test to proof the concept of LIDAR assisted collective pitch control using a scanning LIDAR device installed on the nacelle of a research turbine. The purpose of the campaign was to show that a reduction of rotor speed variation is feasible with a feedforward update without changing the feedback controller. Although only a small amount of data could be collected, positive effects can be observed not only on the rotor speed but also on tower, blade and shaft loads in the case that the correlation of the wind preview and the turbine reaction is taken into account.Item Open Access Modeling and identification of nonlinear systems using MIMO LEM-Hammerstein structure(2006) Schlipf, David; Bolognese Fernandes, Pedro; Trierweiler, Jorge O.This paper extends the LEM-Hammerstein models already presented in the literature to MIMO systems. Instead of linear time-invariant subsystems in association with static nonlinearities, LEM-Hammerstein and LEM-Wiener systems exhibit nonlinear static features and operating-point dependent dynamics, and can therefore model a broader class of system than the conventional block-oriented models. In order to avoid the problem of solving the partial differential equations necessary for the construction of the steady-state mapping that appears in the model, a modified controller normal form is proposed, and the model is constructed on the basis of an extended, non-minimal state-space realization. Moreover, the identification strategy already used with LEM systems can be applied in order to construct such models from experimental data, and the techniques destined for analysis and control of Hammerstein systems can be applied promptly. An application of these concepts to the modeling and identification is demonstrated in the numerical example of a level system constituted by six connected tanks.Item Open Access Impact of structural flexibility on loads on tidal current turbines(2015) Arnold, Matthias; Biskup, Frank; Cheng, Po WenIn the development of tidal current turbines there are two common approaches regarding the required level of detail for load simulations. Those two are either to simulate the pressure field in detail with computational fluid dynamics (CFD) and assume a rigid geometry or to use a high fidelity structural model and simulate the hydrodynamic blade loads with the semi-empirical blade element momentum theory. Within the present research this simplification and the impact of fluid-structure-interaction (FSI) on the loads on tidal current turbines are analysed. Based on coupled CFD and multibody simulations the FSI is simulated for the Voith HyTide®1000-13 turbine. This method allows taking the detailed structure of the full turbine into account, while also simulating the detailed pressure field. Transient simulations of a representative point of operation are performed taking the structural flexibility of the tower, rotor blades, drivetrain and other components into account. This comparison is used to quantify the individual and combined effect of flexibilities on the loads and performance. Therefore, the Voith HyTide®1000-13 turbine is simulated within this research in varying levels of detail to analyse the required level of modelling detail for load simulations of tidal current turbines and increases the understanding of fluid-structure-interaction in tidal current turbine applications.Item Open Access Simulation of rotor-foundation-interaction on tidal current turbines with computational fluid dynamics(2013) Arnold, Matthias; Biskup, Frank; Matha, Denis; Cheng, Po WenIn this research the interaction of the rotor hydrodynamics with the foundation of a Tidal Energy Converter (TEC) are investigated. A detailed model of the turbine is built up and simulated with Computational Fluid Dynamics (CFD). The results of these simulations are used to compare the 4 load states of up- and downstream, below and above rated operation with respect to the rotor performance coefficients. The paper concludes with a comparison to results of simplified models and shows that the interaction can be simulated by an empirical approach.Item Open Access Determination of stationary and dynamical power curves using a nacelle-based lidar system(2012) Würth, Ines; Rettenmeier, Andreas; Schlipf, David; Cheng, Po Wen; Wächter, Matthias; Rinn, Philip; Peinke, JoachimThis paper investigates the determination of stationary and dynamical power curves using a nacelle-based lidar system. Wind speed measurements on one of the REpower 5MW turbines at the German offshore test site "alpha ventus" were carried out with a pulsed lidar system that is capable of measuring the wind field at different measurement planes over the rotor swept area. The results show that the stationary lidar-based power curve has a small scatter but is shifted towards lower wind speeds compared to a conventional power curve measured with a cup anemometer from a met mast. The new approach of calculating dynamical power curves shows short-time dynamics of the turbine and allows a quick detection of changes such as the icing of an anemometer or the reduction in the maximum power output of the wind turbine.