15 Fakultätsübergreifend / Sonstige Einrichtung
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/16
Browse
8 results
Search Results
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 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 Modeling and identification of nonlinear systems using SISO LEM-Hammerstein and LEM-Wiener model structures(2006) Bolognese Fernandes, Pedro; Schlipf, David; Trierweiler, Jorge O.This paper applies the concept of linearization around the equilibrium manifold (LEM) already presented in the literature in order to construct model structures that can be viewed as extensions of the conventional Wiener and Hammerstein models. Instead of linear time-invariant subsystems in association with static nonlinearities, these extensions exhibit variable dynamic character and can therefore model a broader class of systems than the conventional cited approaches. Moreover, the identification strategy already used with LEM systems can be applied in order to construct such models from experiments, and the techniques destined for analysis and control of Wiener and Hammerstein systems can be applied promptly. To application of these concepts to the modeling and identification is demonstrated with a numerical example, considering a heat exchange system.Item Open Access Load reduction potential of variable speed control approaches for fixed pitch tidal current turbines(2015) Arnold, Matthias; Biskup, Frank; Cheng, Po WenThe present paper compares control strategies for fixed pitch Tidal Current Turbines and introduces the underspeed control technique. The state of the art approach of overspeed control for fixed pitch turbine increases the tip speed ratio to limit the power output of the turbine. This leads to a high fatigue loading as the number of load cycles increases and requires a specific rotor design not to increase the thrust coefficient as well. The underspeed controller on the other side reduces the tip speed ratio resulting in a reduced thrust coefficient and a reduced number of load cycles. However, this point of operation is unstable based on the characteristic curves of the rotor and needs to be stabilized by the controller. The basic structure of the controller as well as the calculated stability limits will be shown in the paper. Further, the performance of the underspeed controller regarding loads is compared to state of the art fixed and variable pitch controllers. The paper concludes with an analysis of the impacts on the turbine design and further potential and issues arising with the underspeed control approach.