Lidar controlled turbine
US-based lidar wind measurement specialist ZephIR claims that an industry ‘landmark’ moment has been confirmed thanks to NREL, Stuttgart University and DNV GL with the control of an operational wind turbine with a ZephIR wind lidar.
While the tests were conducted on an onshore test turbine, ZephIR’s previous work with offshore lidars and DNV GL’s involvement with the project suggest that progress will be quickly translated offshore.
“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. 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.” said Andrew Scholbrock, Field Test Engineer at NREL.
ZephIR claims that the usage of the ZephIR lidar system for feed-forward pitch control delivers a reduction of structural turbine loads enabling OEMs with the opportunities to achieve a lower cost of energy for the industry through more optimal turbine design.
The field testing was conducted on the US DOE/NREL CART3 test turbine, which is part of the comprehensive test facilities at the National Wind Technology Center (NWTC) in Boulder, Colorado. The geographical location 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.
The ZephIR DM wind lidar is a circularly-scanned, continuous-wave coherent Doppler sensor. Zephir Ltd. notes that the ZephIR DM wind lidar offers unique and unmatched benefits in turbine-mounted applications from power curve measurements to full turbine control as demonstrated in this project. Optimised for installation on a nacelle roof, ZephIR DM generates high-resolution line-of-sight Doppler measurements every 20 ms through a period of a continuous circular scan of 1 second. 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 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 this NREL facility. The ZephIR DM 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 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.
By Jake Frith
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