Showing papers on "Tip-speed ratio published in 2002"

A comparison of control concepts for wind turbines in terms of energy capture

Abstract: In this study, eight different control concepts for wind turbines are compared in terms of their annual energy capture. In detail, they are a stall controlled single speed concept, a stall controlled two speed concept, an active stall controlled single speed concept, an active stall controlled two speed concept, a pitch controlled single speed concept, a pitch controlled two speed concept, a stall controlled variable speed concept and finally a pitch controlled variable speed concept. In order to be able to expose all these different concepts to exactly the same wind conditions, numerical computer simulation is chosen as the appropriate method to do the comparison, as in reality it is almost impossible to achieve the same wind conditions for different turbines. This approach also prevents all possible differences in rotor layout between the individual concepts from entering into the results, as it is possible to use the same rotor design for all control concepts. Because the influence of time variant quantities such as the turbulent wind flow on a nonlinear system ( e.g. a wind turbine rotor) has to be taken into account, an analytical representation had to be found which allowed a time-step simulation. This especially set some limits on the complexity allowed for the numerical model. Therefore the modeling of all parts of the system (whether they are aerodynamic, mechanic or electric) is kept rather simplistic. As a comparison of general control concepts is the topic of this study, the controllers are not modeled as they are used by a certain manufacturer. Instead they are modeled in an idealized way, each of which covers the ideal performance of one class of control concepts. For each combination of parameters, one time domain simulation was performed. The output data was then weighted and averaged in order to obtain the energy captured from the wind within one year. These energy values are finally arranged in a way which allows an easy comparison between the relative performance of all control concepts under consideration. The results show the differences in the annual energy capture of the eight concepts as a function of site conditions (the annual mean wind speed, the turbulence and the shape parameter of the Weibull distribution assumed for the annual wind speed distribution) as well as their dependence on two design parameters (the design tip speed ratio and the choice of rotor profiles). Due to the rather crude modeling these results have to be seen more qualitatively then quantitatively. However, they show to which extent a comparison between different control concepts depends on the values of different parameters. Hopefully, they also lead to a deeper understanding of the very different results of similar comparisons found in the literature.

Study on maximum power point tracking of wind turbine generator using a flywheel

Abstract: This paper focuses on a maximum power point tracking for wind turbine generator (WTG) with a flywheel. Power coefficient C/sub p/, which has the optimum point, depends on a tip speed ratio (TSR). If we can adjust the angular velocity of WTG to wind speed with the frequency converter, we can realize the maximum power point tracking (MPPT) for WTG. Firstly, this paper explains a mechanism of wind power capture and necessity of flywheel. Secondly, we compare the difference between power ratio with and without a flywheel. We compare between fixed speed rotation operation and MPPT operation with data of the Tappi-zaki WTG system. As a result, a total power increase of up to 2 times has been obtained when the average wind speed is around 6.2 m/s (rated power is 275 kW). Finally, we proposed a simple small WTG system with permanent magnet type synchronous generator (rated power is 150 W) and wind turbine of 3-blades (rotor diameter is 1.24 m). We can make various wind speeds with the electric fan, so that we can evaluate MPPT operation with the experimental studies.

Optimum pitch control for variable-pitch vertical-axis wind turbines by a single stage model on the momentum theory

Abstract: We propose a new approach to realize the optimum control of the pitch angles of the blades on a variable-pitch straight-blade type of vertical-axis wind turbine. After deriving the power coefficient and the tip speed ratio of the turbine by merging the single-stage momentum theory and the blade element analysis, we can solve the stationary problems by using the Calculus of Variations and obtain the optimum pitch-angle control law on a tip speed ratio and calculate the power coefficient.

Vertical axis turbine with wind channeling means

Abstract: The invention relates to a further improved vertical axis wind turbine [FWAT] (1), in which this device mainly consists of a central axis (2), aerodynamic blades (4), spokes (3,5 and 6) and specific connecting parts (7,8), in which all parts are aerodynamically shaped, and in which the so called tip speed ratio λ is optimised between 2.5 and 4, which can be controlled to optimum efficiency without the need for a wind measuring device and in which the aerodynamic parts are of materials that combine a low specific weight with a high tensile strength. Additionally, two diffuser elements (10,11) are placed vertically on either side of rotor, of greater height than the rotor.

Numerical Simulation of the 3D Laminar Viscous Flow on a Horizontal-axis Wind Turbine Blade

Abstract: The aim of this paper is to describe the methodology followed in order to determine the viscous effects of a uniform wind on the blades of small horizontal-axis wind turbines that rotate at a constant angular speed. The numerical calculation of the development of the three-dimensional boundary layer on the surface of the blades is carried out under laminar conditions and considering flow rotation, airfoil curvature and blade twist effects. The adopted geometry for the twisted blades is given by cambered thin blade sections conformed by circular are airfoils with constant chords. The blade is working under stationary conditions at a given tip speed ratio, so that an extensive laminar boundary layer without flow separation is expected. The boundary layer growth is determined on a non-orthogonal curvilinear coordinate system related to the geometry of the blade surface. Since the thickness of the boundary layer grows from the leading edge of the blade and also from the tip to the blade root, a domain transfo...

Iterative Model for the Performance Evaluation of a Horizontal Axis Wind Turbine

Abstract: This paper is based on the studies made on a numerical model for calculating the turbine characteristics at low tip speed ratio for a Horizontal Axis Wind Turbine. The turbine characteristics are analysed for different configurations over the total operating range i.e. from tip speed ratio of zero to a maximum value where CP becomes zero. The simulation model provides acceptable results, however for the blade position near the hub, a non-convergent situation is observed i.e. the flow parameters converge to values outside those associated with turbine operation. This indicates the possibility of a multisolution.