Wind Farm Loads under Wake Redirection Control

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.

Review of wake management techniques for wind turbines

“…Both optimization techniques 3,36,102,103,111,114,119,120,128,137,140,145,148–150,157,158,161,163–165 and trial and error comparisons 108,123,164 of different arrangements of yaw misalignment angles have been tested and have arrived at different conclusions. Several studies have found that total power is optimized when the upstream turbines are misaligned the most and the misalignment angle is decreased as turbines are located farther downstream 3,108,123,146,164 . Gebraad et al 136 used a game theoretic approach and found that a 3 × 2 wind farm was optimized when the front row had misalignment angles of about 25°, the second row about 40°, and the back row was not misaligned as usual.…”

“…Under these optimizations, lifetime power was increased as much as 1.9% and the lifetime of the wind farms increased as much as 0.9%. In another evaluation of the lifetime effects of wake steering, Kanev et al 146 simulated a wind farm over a complete range of conditions and found that virtually all fatigue loads were reduced across the lifetime of the wind farm using wake steering. Ultimately, Kanev has shown that, although wake steering does increase some loads, it reduces turbulence levels at downstream rotors.…”

LES verification of HAWC2Farm aeroelastic wind farm simulations with wake steering and load analysis

“…Despite the promising results in terms of power gain, there are very few studies that identify the dynamic loading experienced by the turbines when such control strategies are implemented. Past studies suggest that wake steering can lead to varying loading in both the upstream [5] and downstream turbines [6], for example. Axial induction and wake steering control can either alleviate or exacerbate structural loading in wind turbines depending on the scenario, for which further research is needed for a deeper understanding [7,8,9].…”

Probabilistic surrogates for flow control using combined control strategies

“…Depending on the control and sensing solution utilised, the strategy for implementing each technology can differ significantly. The literature contains an abundance of examples leveraging these technologies for one or several objectives such as power maximisation (a comprehensive review can be found in [2]), load alleviation [3,4,5,6], provision of ancillary services (e.g. power tracking [7]), revenue maximisation [8] and beyond.…”