Analysis of light detection and ranging wind speed measurements for wind turbine control

Abstract

Light detection and ranging (LIDAR) systems are able to measure the speed of incoming wind before it reaches a wind turbine rotor. These preview wind measurements can be used in feedforward control systems designed to reduce turbine structural loads. However, the degree to which such preview-based control techniques can reduce loads by reacting to turbulence depends on how accurately the incoming wind field can be measured. This study examines the accuracy of different measurement scenarios that rely on coherent continuous-wave or pulsed Doppler LIDAR systems, in terms of root-mean-square measurement error, to determine their applicability to feedforward control. In particular, the impacts of measurement range, angular offset of the LIDAR beam from the wind direction, and measurement noise are studied for various wind conditions. A realistic simulation case involving a scanning LIDAR unit mounted in the spinner of a MW-scale wind turbine is studied in depth, with emphasis on preview distances that provide minimum measurement error for a specific scan radius. Measurement error is analyzed for LIDAR-based estimates of point wind speeds at the rotor as well as spanwise averaged blade effective wind speeds. The impact of turbulence structures with high coherent turbulent kinetic energy on measurement error is discussed as well.

Reducing LIDAR wind speed measurement error with optimal filtering

“…The LIDAR model includes the estimation of this wind component based on a line-of-sight measurement containing along-wind, horizontal, and vertical wind speeds using the assumption that the wind speeds are confined to the along-wind direction. The spatial averaging of wind speeds along the laser beam due to the LIDAR optics [7] are also modeled (see Fig. 2).…”

“…2). Additional details regarding the LIDAR measurement scenario are provided in [7]. A preview distance of d = 90 m and a scan radius of r = 44.1 m are used (resulting in a LIDAR focus distance of 100.2 m).…”

“…Distortion caused by the LIDAR measurement [7] and the evolution of the wind [8] as it advects toward the turbine both cause measurement error. In the past few years, controller designs based on simulation have begun to incorporate realistic LIDAR models to introduce the spatial averaging effect of LIDAR as well as the detection of transverse and vertical wind speeds through line-of-sight velocity This work was supported in part by the US National Renewable Energy Laboratory.…”

“…of Electrical, Computer, and Energy Engineering, University of Colorado, Boulder, CO 80309, e-mail: eric.simley@colorado.edu 2 Lucy Pao is the Richard & Joy Dorf Professor in the Dept. of Electrical, Computer, and Energy Engineering, University of Colorado, Boulder, CO 80309, e-mail: pao@colorado.edu measurement [3]- [7]. Taylor's frozen turbulence hypothesis, which describes turbulence as remaining unchanged while traveling at the mean wind speed [9], is usually assumed for simulation purposes.…”

Lidar arc scan uncertainty reduction through scanning geometry optimization

“…Lidars also have applications in wind energy resource estimation and wake characterization (Banta et al, 2013;Barthelmie et al, 2013) due to their ability to accurately and precisely measure flow structures both in front of and in the wake of a wind turbine (Simley et al, 2013;Aitken et al, 2014) and spatial variability of wind speeds over prospective wind farms .…”