LIDAR-based wind turbine control system
There’s been a little bit of interest in laser based anemometry, or LIDAR, wind turbine control systems. It’s been the precept of Risoe’s Windscanner program below, and several Risoe-DTU papers at EWEC 2009. It even made this month’s Economist technology quarterly. As rotors get bigger, I believe this concept will become more and more import – both for energy production optimisation, and for loads reduction on the blades and drive train.

So what is LIDAR? LIDAR is simply the use of a laser in the same way a RADAR is used, by measuring the time it takes for pulses to return after they have bounced off minute particulates carried in the air, a profile of the wind speed can be developed. If used in an array, a three-dimensional picture of the column of approaching wind can be more accurately estimated.

How does this help a wind turbine? At the moment, wind turbines estimate the wind speed based on a nacelle-based anemometer – typically ultrasonic, or a traditional cup anemometers. The wind speed measured here is used as the basis for the controller to estimate the wind speed over the entire rotor and set the appropriate pitch setting of the blades to optimise the angle of attack. Wind turbine blades operate most efficiently at only one angle of attack setting – too much, or too little reduces the aerodynamic efficiency and therefore the energy output.

The bigger rotors get, the less accurate it is to estimate the entire wind speed of the column of wind based on one single anemometer input. So, a LIDAR can help by providing a more accurate distribution of wind speeds of the incoming wind. Armed with this, the controller can then anticipate more accurately the pitch settings to use (possibly even individual blade pitch settings). In the case of an extreme gust, the blades could then feather and dramatically reduce the loads on the turbine, where as a traditional system will only know a gust after it’s experienced it.

There are some definite practical engineering problems with integrating this system however. If you base it on the ground, how do you yaw it efficiently to align with the turbine? If you base it on the nacelle, you have to place it in the rotating hub and allow for the complications of rotating a delicate laser array continuously. Whether or not the increased cost and complication of this system will be balanced by the production increase and possible cost reduction in structure optimisation: only industry experience will tell.

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