Modelling the Yaw Behaviour of a Small Wind Turbine

Abstract

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.

Experimental study of a small wind turbine for low- and medium-wind regimes

“…This extrapolation is not critical for typical small wind turbine sites with average wind speeds in the 3-8 m s À1 range, but does affect the performance prediction at windier sites. Even though the yawing behavior of wind turbines has been studied in a detailed manner [24,25] and some work has been done in furling of small wind turbines [26], the prediction of the furling behavior is still more of an art than an exact science. For the sake of the present calculations, we have turned to the simplest possible model, assuming that the yawed rotor behaves as the non-yawed rotor but responds only to the wind velocity component normal to the rotor plane, i.e.…”

The Aerodynamic Characterization of Generic Tail Fin Shapes

“…Since the rotating blades of a wind turbine contribute to yaw stability, Miller (1979) and Bechly et al (2002), the main purpose of a tail fin is to provide alignment during starting. This can be a challenging requirement because wind direction changes increase in magnitude and frequency as wind speed decreases, e.g.…”

Analysis of the passive yaw mechanism of small horizontal-axis wind turbines

“…Much of the model that follows is a contextual summary of analytical modeling techniques evident in the literature [7][8][9].…”

“…Through the iterative calculating of these equations, we can get the relationship between the value of and the velocity of wind when the angle is a certain value [9].…”