Abstract
Active wake control (AWC) is a strategy for operating wind farms in such a way as to reduce the wake effects on the wind turbines, potentially increasing the overall power production. There are two concepts to AWC: induction control and wake redirection. The former strategy boils down to down-regulating the upstream turbines in order to increase the wind speed in their wakes. This has generally a positive effect on the turbine loading. The wake redirection concept, which relies on intentional yaw misalignment to move wakes away from downstream turbines, has a much more prominent impact and may lead to increased loading. Moreover, the turbines are typically not designed and certified to operate at large yaw misalignments. Even though the potential upsides in terms of power gain are very interesting, the risk for damage or downtime due to increased loading is seen as the main obstacle preventing large scale implementation of this technology. In order to provide good understanding on the impacts of AWC on the turbine loads, this paper presents the results from an in-depth analysis of the fatigue loads on the turbines of an existing wind farm. Even though for some wind turbine components the fatigue loads do increase for some wind conditions under yaw misalignment, it is demonstrated that the wake-induced loading decreases even more so that the lifetime loads under AWC are generally lower.
Highlights
Active wake control (AWC) is a strategy for operating wind farms in such a way that wake effects are mitigated
This paper presents a detailed study on the impacts from wake redirection control on the fatigue loads within a real-life offshore wind farm
The database has been constructed using a large number of simulations with the aeroelastic turbine model Focus/Phatas. These simulations are done for a wide range of representative operational and environmental conditions, including different combinations of wind speeds, turbulence intensities, wake locations, wake deficit width, wake deficit depth, yaw misalignments and pitch angle offsets
Summary
Active wake control (AWC) is a strategy for operating wind farms in such a way that wake effects are mitigated. These simulation results were recently confirmed by field measurements performed with intentionally misaligned turbines by NREL ([26]) and Sandia ([19,27]) These initial studies on the impact of AWC on the farm loads have been limited to one or two turbines. As some fatigue loads are increasing for some yaw misalignment angles, it is important to be able to evaluate the fatigue loads during the complete lifetime of a wind farm To this end, the whole spectrum of wind conditions expected at a given site needs to be considered, and including all wind turbines in the analysis.
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