The DOE/NREL CART3 test turbine is part of the comprehensive test facilities at the National Wind Technology Centre (NWTC) in Boulder, Colorado. It is an ideal test environment for the evaluation of new and advanced control algorithms of wind turbines, due to its geographical location and easy access to the turbine control system.
“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” said Andrew Scholbrock, Field Test Engineer at 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.”
Alex Woodward, Head of Product Development at ZephIR added that the company has invested significant efforts, over the course of a decade, to be the world first in every application of turbine-mounted lidar. With the assistance of NREL, the University of Stuttgart and DNV GL, ZephIR is helping the wind energy sector to achieve full turbine control, leading to additional benefits of load reduction.
ZephIR’s DM wind lidar is a circularly-scanned, continuous-wave coherent Doppler sensor that offers unmatched benefits in turbine-mounted applications from power curve measurements to full turbine control. It is optimised for installation on a turbine nacelle roof where it generates high-resolution line-of-sight Doppler measurements every 20 milliseconds through a period of a continuous circular scan of 1 second. Previous research has found that this lidar scan geometry and frequency is very well suited to lidar feed-forward turbine control. During tests, the lidar recorded valid signals throughout the 8 month measurement period, operating reliably, without intervention, in a wide range of atmospheric conditions, including heavy blizzards, low cloud and temperatures down to -22°C.
The measurements obtained 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 from 10 m to over 300 m out in front of the turbine. These measurements are key to applications such as Power Curve measurements, turbine optimisation and End of Warranty inspections, in addition to turbine control. Continuous wave lidar and its range focussing approach ensures high sensitivity, permitting measurements even in the very clear air often experienced at the NREL facility.
The ZephIR lidar system can also be used for feed-forward pitch control leading to a reduction of structural turbine loads. This in turn enables OEMs to achieve cost reductions through more optimal turbine design. The successful lidar yaw control means that the yaw direction of the wind turbine can be controlled by a lidar which could lead to a reduction in yaw misalignment and increased power production if the traditional yaw controller has unaccounted errors in it. These errors can include calibration offsets, induced errors by the rotor wake, or due to sensor failures leading to a biased signal as was the case 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.
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