Concurrent Optimal Control and Design of an Airborne Wind Energy System

Recent years have seen a growing interest in airborne wind energy systems (AWESs), which pursue higher electricity generation by harvesting faster winds at higher altitudes. Particular attention has been given to a single aircraft that flies crosswind, reeling out a tether wound around a winch connected to a ground-based generator. The research has been strongly focussed on tackling the control problem, both optimal (trajectory generation/path planning) and feedback, with the development of dedicated optimization and tracking approaches respectively. However, the optimal design of these systems has been studied less although the design depends on the control and vice versa. This issue can be attributed to the strongly dynamic nature of the mission profile, which inhibits conventional static design routines. Therefore, this paper examines the concurrent optimal control and design of a AWES. To realize this multidisciplinary design problem a nested optimization problem is formulated and solved to discover integrated solutions that surpass those attainable through a decoupled approach. The nested formulation permits using dedicated trajectory optimization routines for AWES in the interior loop, such as the penality-based interior point homotopy (PIPH) approach, and data-efficient design optimization routines, such as fail-safe constrained Bayesian optimization, in the outer loop. The result is an optimal design and trajectory for an airborne wind energy system that outperforms a baseline design in power generation by 60%.