Analysis of Wind Speed Measurements using Continuous Wave LIDAR for Wind Turbine Control

Light Detection and Ranging (LIDAR) systems are able to measure the speed of incoming wind before it interacts with a wind turbine rotor. These preview wind measurements can be used in feedforward control systems designed to reduce turbine loads. However, the degree to which such preview-based control techniques can reduce loads by reacting to turbulence depends on how accurate the incoming wind field can be measured. This study examines the accuracy of different measurement scenarios that rely on coherent continuouswave Doppler LIDAR systems to determine their applicability to feedforward control. In particular, the impacts of measurement range and angular offset from the wind direction are studied for various wind conditions. A realistic case involving a scanning LIDAR unit mounted in the spinner of a wind turbine is studied in depth, with emphasis on choices for scan radius and preview distance. The effects of turbulence parameters on measurement accuracy are studied as well. Nomenclature d measurement preview distance F focal distance k wind velocity wavenumber (m−1) r scan radius for spinning LIDAR RMS root mean square σu standard deviation of u component of wind velocity TI turbulence intensity θ LIDAR measurement angle ū mean u wind speed u ∗ friction velocity U ∗ D average friction velocity over rotor disk φ angle between laser and wind velocity vector ψ angle in the rotor plane ω rotational rate of spinning LIDAR