Wind Engineering

This paper describes a dynamic model of a wind farm and its nearest utility grid. It is intended to use this model in studies addressing the dynamic interaction between a wind farm and a power system, both during normal operation of the wind farm and during transient grid fault events. The model comprises the substation where the wind farm is connected, the internal power collection system of the wind farm, the electrical, mechanical and aerodynamic models for the wind turbines, and a wind model. The integrated model is built to enable the assessment of power quality and control strategies. It is implemented in the commercial dedicated power system simulation tool DIgSILENT.

Wind turbines for electricity production have two seemingly opposing constraints; they need to be structural secure yet of low cost. To meet the first constraint, it would be an obvious choice to design a stiff structure of consequently large mass but this would drive up the cost. By reducing the mass a more cost effective turbine can be realized. However, such lightweight structures are by definition more flexible. To design a cost effective flexible system, thorough understanding of the dynamics is essential. This paper reviews the theoretical basics of the dynamic design options and applies these to realistic situations, including offshore machines under wave action. The wind energy converter and the support structure form an integrated dynamic system that must be developed in mutual interdependency and close co-operation. This paper provides a contribution to this integration process by extending the design approach initiated in the Opti-OWECS study [1] and the work of Kühn [2].

This paper develops a mathematical model for a small wind turbine responding to changes in the wind direction. Here “small” implies that the turbine has a tail fin. Good yaw behaviour, in terms of tracking the changes in wind direction, is necessary to maximize power extraction. However large rates of change of yaw can lead to large stresses in the turbine components. The unsteady tail fin loads are more complex than implied by the “pseudo-static” assumption that the steady-state lift and drag act instantaneously. The aerodynamic model is applied first to data obtained from a 5 kW experimental turbine when it was not extracting power, because this almost removes the effect of the blades from the yaw behaviour. MATLAB's systems identification toolbox was used to optimise the fit of the model parameters to the data. The resulting values of a number of the parameters are shown to be in good agreement with earlier wind tunnel tests of the tail fin design. Some details of the comparisons, mainly in terms of the higher frequency components, suggest the need to characterise similarly the dynamics of wind vanes. When the turbine was extracting power, the flexible blades were deflected backwards by the aerodynamic loads. A blade element analysis suggests that the stabilizing moment due to this “coning” does not alter the form of the yaw response equation. The optimised fit of the model equations gave changes in the parameters broadly in agreement with the blade element analysis, but the quasi-steady analysis did not predict the measured increase in the damping associated with power extraction.

Stand-alone wind power systems provide a solution for the electrification of isolated families. However, optimal sizing is usually based on simplified cost analysis of the initial installation. In this paper, a complete long-term energy production cost investigation is developed. This considers the fixed and variable costs of maintenance, operation and financing, in addition to initial costs. The new model includes local economic parameters, technological improvements concerning the system components and the local wind characteristics. By using the proposed model, the requirements and costs of the appropriate stand-alone system are recalculated and then compared with those based only on the initial installation. According to the results obtained, the proposed configuration uses larger wind turbines and smaller batteries than that the installation-only scenario. Finally, the energy production values are compared to available operational data from autonomous thermal power plant on various small Greek islands.

A global optimum design model for a HAWT rotor blade is presented in this paper. The model refers to the wind speed distribution function on the specific wind site, with the objective to satisfy the maximum annual energy output, using a complex method to carry on the global optimum searching. For obtaining more accurate performance data, strip theory is applied to calculate the aerodynamic performance. For obtaining aerodynamic data of the airfoil, an airfoil database is designed. Based on these factors, an aerodynamic performance and structure CAD software “BladeDesign for Windows” is setup. A 600kW wind turbine is designed and the results are compared with that of a 600kW commercial wind turbine. Satisfactory agreement is obtained.