Wake redirecting using feedback control to improve the power output of wind farms

Abstract

In future, a wind turbine will not only be seen as a single systems operating independently, but also as a component of a larger interacting system, the wind farm. To increase the efficiency of a wind farm, two main concepts have been proposed: axial induction control and wake redirecting. This contribution focuses on the latter. Remote sensing technologies in wind energy applications have opened new ways to control wind turbines. In this contribution, a further step is taken by using a remote sensing device for redirecting the wake of a wind turbine. A controller is proposed which uses the yaw actuator of a wind turbine to steer the wake center of the turbine to a desired position. The wake propagation from the wind turbine to the measurement location is modeled with a time delay. This forms a challenging problem for controller design. The controller follows the idea of the internal model principle and uses a model to predict the system behavior avoiding an overestimation of the error. Further, an adaptive filter is proposed in order to filter uncontrollable frequencies from the wake center estimation. The estimation from lidar measurement data is assumed to be perfect. Closed-loop simulations are conducted using the nominal system and a wind farm simulation tool, which was adapted to the scenario. The results are compared to the uncontrolled baseline case and a statically applied yaw offset. They show an increase in the total power output of the wind farm. Together with wake tracking methods, the approach can be considered as a promising step towards closed-loop wind farm control.