LIDAR controls turbine yaw to boost power production

The ZephIR DM wind LIDAR is a circularly-scanned, continuous-wave coherent Doppler sensor, offering benefits in turbine-mounted applications from power curve measurements to full turbine control.

The field testing was conducted on the US DOE/NREL CART3 test turbine, at the National Wind Technology Center (NWTC) in Boulder, Colorado. The exposed location in the foothills of the Rocky mountains, and the easy access to the turbine’s control system, make the CART3 an optimal test environment for the evaluation of new and advanced control algorithms of wind turbines.

Designed for installation on a nacelle roof, ZephIR DM generates high-res line-of-sight Doppler measurements every 20ms through a period of a continuous circular scan of 1s. Industry research demonstrates that this LIDAR scan geometry and frequency is very well suited to LIDAR feed-forward turbine control. The measurements taken by ZephIR calculate various wind field quantities, such as rotor equivalent and hub height horizontal wind speeds, vertical wind shear, wind veer and wind yaw misalignment relative to the turbine axis at ranges of 10-300m out in front of the turbine.

In addition to turbine control, these measurements are key to applications such as Power Curve measurements, turbine optimisation and End of Warranty inspections. Continuous wave LIDAR and its range focussing approach ensures high sensitivity, allowing measurements even in the very clear air often experienced at the NREL (National Renewable Energy Laboratory) facility. The ZephIR DM LIDAR recorded valid signals throughout the eight month measurement period, operating reliably, without intervention, in a wide range of atmospheric conditions, including heavy blizzards, low cloud and temperatures as low as -22°C.

The successful LIDAR yaw control could lead to a reduction in yaw misalignment and increased power production, if the traditional yaw controller contains as-yet-unaccounted-for errors such as calibration offsets, induced errors by the rotor wake, or sensor failures leading to a biased signal. The latter phenomenon occured in this deployment, where ZephIR DM was able to aid in a health-check for the vane sensor and help to target the root cause of the variance in performance.

Further, the successful collective pitch control means that an approximate 25% reduction of the rotor speed variation could be seen in standard deviation. Collectively, the success of these pitch turbine control experiments has paved the way for subsequent trials on larger, 2MW class, onshore turbines.

“ZephIR is the perfect LIDAR technology choice for turbine control,” noted Alex Woodward, Head of Product Development, ZephIR. “For a decade we have invested significant efforts to be the world first in each and every application of turbine-mounted LIDAR. Now, with the dedication of NREL, the University of Stuttgart and DNV GL and their passionate team of industry experts, we can help the sector achieve full turbine control. Additional benefits of load reduction can then also be realised. High resolution, continuous wave, coherent technology is second to none in this application and ZephIR is the only LIDAR built on this robust, lower cost laser design.”

“This new installation of a ZephIR DM has taken a new direction in reducing yaw misalignment by providing the opportunity for full turbine yaw control through LIDAR measurements,” added Andrew Scholbrock, Field Test Engineer, NREL. “Working with a group of experts within each field on this project - wind turbines, controls and LIDARs - has delivered a landmark moment for the industry and one we are all very proud of. We eagerly anticipate the next steps in LIDAR Controlled Turbine.”