Quasi-static closed-loop wind-farm control for combined power and fatigue optimization

We develop a methodology for combined power and loads optimization by coupling a surrogate loads model with an analytical quasi-static Gaussian wake merging model. The look-up table based fatigue model is developed offline through a series of OpenFast simulations, covering different operational states of a DTU 10 MW reference wind turbine, and verified against large eddy simulations with aeroelastic coupling. Subsequently, optimal control set points for the TotalControl reference wind power plant are obtained using the analytical model, and tested in a wind farm emulator that is based on large eddy simulations. The wake model is calibrated online using in a quasi-static closed-loop manner. Benefits of the closed-loop controller are exhibited via comparison of farm performance against greedy operation and against open-loop control results obtained without feedback or calibration. Results show that the closed-loop control out performs open-loop control, with farm configurations with deep turbine arrays showcasing the highest gains. Inclusion of fatigue in the cost function through the developed LUT also leads to interesting insights, with reduced blade root fatigue loading without significant decrease in power production when compared to open-loop control. A case study is also performed which showcases real world applications for the developed closed-loop controller and the load LUT, in which the closed-loop controller is shown to react to scenarios with turbine operation shut-down, optimizing the yaw angles online to maximize performance for the new layout.