Altitude Optimization of Airborne Wind Energy Systems via Switched Extremum Seeking—Design, Analysis, and Economic Assessment

This paper applies a Lyapunov-based switched extremum seeking (LSES) control algorithm to the application of altitude optimization of airborne wind energy systems. We perform an economic analysis to evaluate the effectiveness of the control scheme. Finding the altitude with the highest energy yield requires energy to be consumed in the search for this optimal altitude. The simultaneous desires to optimize altitude and minimize control energy consumption are balanced in this paper through a variant of ES control, where the periodic perturbation signal is reduced when convergence upon an optimal altitude is detected. The signal is reinstated when the wind speed begins to deviate from its instantaneous optimal value. Because the wind shear profile (wind speed versus altitude) is subject to continual variations, this application represents a challenging case study in LSES control. Using real wind shear data acquired over a 25-day period, the results presented in this paper show that the LSES controller is successful in significantly increasing the net energy production over fixed-altitude and standard ES strategies. The economic advantage of the approach is illustrated through a comparison of achievable wind energy penetration with and without LSES-based altitude optimization in place, using real load demand data.