[HTML][HTML] Optimal closed-loop wake steering–Part 1: Conventionally neutral atmospheric boundary layer conditions

MF Howland, AS Ghate, SK Lele… - Wind Energy …, 2020 - wes.copernicus.org
Wind Energy Science, 2020wes.copernicus.org
Strategies for wake loss mitigation through the use of dynamic closed-loop wake steering
are investigated using large eddy simulations of conventionally neutral atmospheric
boundary layer conditions in which the neutral boundary layer is capped by an inversion
and a stable free atmosphere. The closed-loop controller synthesized in this study consists
of a physics-based lifting line wake model combined with a data-driven ensemble Kalman
filter (EnKF) state estimation technique to calibrate the wake model as a function of time in a …
Abstract
Strategies for wake loss mitigation through the use of dynamic closed-loop wake steering are investigated using large eddy simulations of conventionally neutral atmospheric boundary layer conditions in which the neutral boundary layer is capped by an inversion and a stable free atmosphere. The closed-loop controller synthesized in this study consists of a physics-based lifting line wake model combined with a data-driven ensemble Kalman filter (EnKF) state estimation technique to calibrate the wake model as a function of time in a generalized transient atmospheric flow environment. Computationally efficient gradient ascent yaw misalignment selection along with efficient state estimation enables the dynamic yaw calculation for real-time wind farm control. The wake steering controller is tested in a six-turbine array embedded in a statistically quasi-stationary, conventionally neutral flow with geostrophic forcing and Coriolis effects included. The controller statistically significantly increases power production compared to the baseline, greedy, yaw-aligned control provided that the EnKF estimation is constrained and informed with a physics-based prior belief of the wake model parameters. The influence of the model for the coefficient of power as a function of the yaw misalignment is characterized. Errors in estimation of the power reduction as a function of yaw misalignment are shown to result in yaw steering configurations that underperform the baseline yaw-aligned configuration. Overestimating the power reduction due to yaw misalignment leads to increased power over the greedy operation, while underestimating the power reduction leads to decreased power; therefore, in an application where the influence of yaw misalignment on is unknown, a conservative estimate should be taken. The EnKF-augmented wake model predicts the power production in yaw misalignment with a mean absolute error over the turbines in the farm of , with as the power of the leading turbine at the farm. A standard wake model with wake spreading based on an empirical turbulence intensity relationship leads to a mean absolute error of , demonstrating that state estimation improves the predictive capabilities of simplified wake models.
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