An overview of active load control techniques for wind turbines with an emphasis on microtabs

Abstract

This paper outlines the benefi ts and challenges of utilizing active fl ow control (AFC) for wind turbines. The goal of AFC is to mitigate damaging loads and control the aeroelastic response of wind turbine blades. This can be accomplished by sensing changes in turbine operation and activating devices to adjust the sectional lift coeffi cient and/or local angle of attack. Fifteen AFC devices are introduced, and four are described in more detail. Non-traditional trailing-edge fl aps, plasma actuators, vortex generator jets and microtabs are examples of devices that hold promise for wind turbine control. The microtab system is discussed in further detail including recent experimental results demonstrating its effectiveness in a three-dimensional environment. Wind tunnel tests indicated that a nearly constant change in C L over a wide range of angles of attack is possible with microtab control. Using an angle of attack of 5 degrees as a reference, microtabs with a height of 1.5%c were capable of increasing CL by +0.21 (37%) and decreasing CL by −0.23 (−40%). The results are consistent with fi ndings from past two-dimensional experiments and numerical efforts. Through comparisons to other load control studies, the controllable range of this micro-tab system is determined to be suitable for smart blade applications.Equation (1) illustrates that there are several distinct approaches that can be taken to lower the COE. One way is to make more reliable turbines, thereby reducing the downtime and O&M costs. Another is to reduce the amount of materials or improve manufacturing techniques to decrease capital cost. COE can also be reduced by increasing the rotor diameter and turbine size; this has been occurring since the beginning of the commercial wind industry. A larger turbine can capture more energy throughout its lifetime, and although the cost of the turbine will increase and O&M may increase as well, the COE has been declining.Signifi cant growth of wind turbine size and weight over the past few decades has made it impossible to control turbines passively as they were controlled in the past. Modern turbines rely on sophisticated control systems that assure safe and optimal operation under a variety of atmospheric conditions. As turbines grow in size, the structural and fatigue loads become more pronounced. Implementing new and innovative load control techniques could decrease RESEARCH ARTICLE Wind Energ. 2010; 13:239-253

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