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

Abstract

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.wind velocity wavenumber (m −1 ) r scan radius for spinning LIDAR RMS root mean square σ u standard deviation of u component of wind velocity TI turbulence intensity θ LIDAR measurement anglē u 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 * This work was supported in part by the US National Renewable Energy Laboratory. Additional industrial support is also greatly appreciated. The authors also thank Alan Wright, Fiona Dunne, and Jason Laks for discussions on desired characteristics of wind speed measurement devices that can enable preview-based control methods for wind turbines.

Comparison of Two Independent Lidar-Based Pitch Control Designs

“…For example, the feedback gains are different, and while they use the same pitch rate limit, they differ slightly in the way the rate limit is implemented (referred to as feedback controllers A [1] and B [2]). The two feedforward controllers were also each developed with their own LIDAR (Light Detection and Ranging) configuration, which are referred to as LIDAR configuration A [1,9] and LIDAR configuration B [2].…”

LIDAR Wind Speed Measurements of Evolving Wind Fields

“…A previous study 7 examined measurement errors for a hub-mounted LIDAR scanning a circle of wind with radius r in front of the turbine as a function of preview distance D (see Fig. 2).…”

“…Wind conditions generated by TurbSim using the Great Plains-Low Level Jet (GP LLJ) spectral model 9 were used in previous studies 6,7,14 to evaluate LIDAR measurements and controller performance. The wind fields are designed to be used with NREL's 5-MW turbine model with a hub height of 90 m and a rotor radius of 63 m. We have chosen one of these conditions as a wind field to which wind evolution can be introduced.…”

“…In this paper we combine our existing model 7 of LIDAR measurements with a model of wind evolution to study the degree to which wind inflow can be accurately measured and the scenarios that provide the best measurements.…”

Real-time wind field reconstruction from LiDAR measurements using a dynamic wind model and state estimation

“…Such difficulty in resolving wind direction and magnitude from line-of-sight velocity data is commonly referred to as the 'cyclops' dilemma, and has been reported by several authors. 4,13,14 Extra information is therefore required in order to resolve wind magnitude and direction from line-of-sight velocity measurements and as will be shown in this paper, such information may be teased out from a physical model that captures the spatio-temporal dynamics of the wind.…”