Active wake management
For control of wake interactions DNV GL posits two options: axial induction control and wake steering control. Both approaches involve sacrificing power production of some turbines to minimise wake interactions and boost production at other turbines, with the aim of increasing the overall production of the wind farm, and also reducing fatigue loads on wake-affected turbines.
Axial induction control reduces wake interactions by decreasing power set points on some turbines so that others produce more. Wake steering control involves mis-aligning some turbines to the wind. This also sacrifices some power, but has the effect of steering the wake away from downstream turbines, and so reducing wake interactions in that way.
DNV GL has set up field tests on a wind farm doing axial induction control, as part of the EU Horizon 20-20 project ‘CL-Windcon’, and contributed to wake steering tests on the same wind farm. This has provided the opportunity to further develop and validate DNV GL’s ‘LongSim’ software, which is then used to design the controller used in the field tests, and also to test the controller in detailed simulations prior to starting the actual field tests.
DNV GL believes that it is now possible to further reduce the levelised cost of wind energy through systems increasing overall power production from wind farms, while complying with grid system requirements. Existing wind farms should use these advanced control strategies to increase production, reduce operating costs and extend plant lifetimes. New wind farms and wind turbines should be designed so that they can take advantage of these opportunities.
There is a strong interest in wind farm modelling and active wake control techniques, but uncertainties remain. Further validation of models and control strategies is a crucial next step to increase confidence in wind farm control design methods and in the benefits which can be realised.