Showing papers on "Tip-speed ratio published in 1999"

Influence of the Meteorology Mast on a Cup Anemometer

Abstract: In order to measure the efficiency of a wind turbine the non-dimensional power coefficient C{sub p} is measured as a function of the tip speed ratio. The power is non-dimensionalized with respect to the density, the swept area by the rotor and the third power of the wind speed. Since C{sub p} depends on the third power of the wind speed it is very important to measure the wind speed accurately. The wind speed is usually measured by a cup anemometer mounted on a rod which is mounted on a meteorology mast. The mast will often be a lattice construction consisting of three main beams shored up by smaller beams. The mast is a long slender construction, which gives an almost two-dimensional flow round a cross-section at a certain height above the ground. The cylindrical beams will give a local distortion of the wind speed in the vicinity of the mast. If the rod, on which the cup anemometer is mounted, is to short one will measure a wrong wind speed and thus a wrong power coefficient C{sub p}. To the authors knowledge only Cermak and Horn (1968) and Gill et al. (1967) approached the problem experimentally by wind tunnelmore » measurements on scale models. In this paper a simple numerical approach is taken to model the flow around the mast.« less

Design of a wind turbine-generator system considering the conformability to wind velocity fluctuations

Abstract: The conformability of the rated power output of the wind turbine-generator system and of the wind turbine type to wind velocity fluctuations are investigated with a simulation model. The authors examine three types of wind turbines: the Darrieus-Savonius hybrid, the Darrieus proper and the Propeller. These systems are mainly operated at a constant tip speed ratio, which refers to a maximum power coefficient points. As a computed result of the net extracting power, the Darrieus turbine proper has little conformability to wind velocity fluctuations because of its output characteristics. As for the other turbines, large-scale systems do not always have an advantage over small-scale systems as the effect of its dynamic characteristics. Furthermore, it is confirmed that the net extracting power of the Propeller turbine, under wind direction fluctuation, is much reduced when compared with the hybrid wind turbine. Thus, the authors conclude that the appropriate rated power output of the system exists with relation to the wind turbine type for each wind condition.

Control Method for Improved Energy Capture Below Rated Power (Preprint prepared for ASME/JSME)

Abstract: To maximize energy capture, a variable-speed wind turbine should operate continuously at the tip-speed-ratio that results in the maximum power coefficient (Cpo) and, therefore, extracts the maximum energy from the wind. This is the main idea behind improved energy capture from variable-speed operation. However, this goal is only partially achievable due to rapid variations in wind speed and the inertia of the wind turbine rotor. Although it is not possible to operate continuously at maximum efficiency, improvements in energy capture during variable-speed operation can be gained by improved tracking of Cpo. In this paper the aerodynamic torque, estimated by an observer, and rotor speed are used to improve the energy capture of a variable-speed turbine. Two methods are used. The first method uses the torque error for control. The second method is formulated such that the estimated percent power loss is used directly for control. Also, the use of blade pitch below rated power is investigated. A small improvement in energy capture is realized by use of the described control methods. For turbines with a sharp Cp peak or slower time constant, greater improvement would be observed.