A compact Doppler wind lidar for controlling the operation of wind turbines.

A robust and compact lidar for wind field detection has been developed for operation in the nacelle of wind turbines. The lidar measures wind speed along the line-of-sight of the laser beam with a 15 m range resolution along distances of 100 to 400 m depending on atmospheric aerosol content. An inclined orientation with respect to the rotor axis results in a conical scan of the incoming wind field, from which range-resolved data of the average wind velocity over the scanned cross-section are calculated. Application of the instrument aims at an improved turbine control by optimizing the pitch angle of rotor blades based on remotely sensed data, instead of reacting to wind field fluctuations which have already caused changes in rotational speed or loads. A predictive knowledge of wind conditions also allows for a precise evaluation of turbine power performance. The data are particularly useful for reducing high loads from gusts which otherwise cannot be detected in time.
In this paper, the conceptual layout of Whirlwind 1 is described. Wind speed data are derived from the Doppler shift of backscattered laser radiation from aerosols which is interferometrically detected. Laser source is a diode laser pumped fibre amplifier seeded by a single-frequency diode laser emitting eye-safe radiation at 1.5 micrometre wavelength. The Doppler shifted laser frequency is detected with a Fast Fourier Transform of the signal return and converted to wind speeds in 37 range gates, each of 30 m length with a 50% overlap. The compact aluminium casing includes all components, i.e., the fibre laser, the signal detector, a Field Programmable Gate Array for fast data processing, a 3-axes accelerometer, and a compact industrial PC. First results of wind field measurements obtained with the prototype are presented.