Optimal Coordinated Control of Power Extraction in LES of a Wind Farm with Entrance Effects

Jay Goit,Johan Meyers,Wim Munters

doi:10.3390/en9010029

Abstract

We investigate the use of optimal coordinated control techniques in large eddy simulations of wind farm boundary layer interaction with the aim of increasing the total energy extraction in wind farms. The individual wind turbines are considered as flow actuators, and their energy extraction is dynamically regulated in time, so as to optimally influence the flow field. We extend earlier work on wind farm optimal control in the fully-developed regime (Goit and Meyers 2015, J. Fluid Mech. 768, 5–50) to a ‘finite’ wind farm case, in which entrance effects play an important role. For the optimal control, a receding horizon framework is employed in which turbine thrust coefficients are optimized in time and per turbine. Optimization is performed with a conjugate gradient method, where gradients of the cost functional are obtained using adjoint large eddy simulations. Overall, the energy extraction is increased 7% by the optimal control. This increase in energy extraction is related to faster wake recovery throughout the farm. For the first row of turbines, the optimal control increases turbulence levels and Reynolds stresses in the wake, leading to better wake mixing and an inflow velocity for the second row that is significantly higher than in the uncontrolled case. For downstream rows, the optimal control mainly enhances the sideways mean transport of momentum. This is different from earlier observations by Goit and Meyers (2015) in the fully-developed regime, where mainly vertical transport was enhanced.

Highlights

The size of wind farms has increased rapidly in recent years, and the power production of some of the largest farms is comparable to that of conventional power plants
The power output from the first row is a bit lower compared to the uncontrolled case
The energy extraction of turbines was dynamically controlled in time so as to optimally influence the flow field in the boundary layer

Summary

Introduction

The size of wind farms has increased rapidly in recent years, and the power production of some of the largest farms is comparable to that of conventional power plants. The largest offshore wind farm to date is the 630-MW London Array with 175 turbines spread over an area of 100 km. The largest offshore wind farm to date is the 630-MW London Array with 175 turbines spread over an area of 100 km2 At these sizes, the efficiency of individual turbines in the wind farms differs considerably from that of a lone-standing turbine. The current work investigates coordinated optimal control of wind turbines in a wind farm, focusing on improving energy extraction. To this end, large eddy simulations (LESs) of a wind farm boundary layer are performed, where the LES model itself is used as a control model in a receding horizon optimal control framework. Individual turbines are considered as flow actuators, whose energy extraction can be regulated dynamically in time and per turbine

Methods

Results

Conclusion