A robust reel-in controller using active depower control

Abstract

Airborne Wind Energy (AWE) generates renewable power by using tethered flying devices to access stronger winds at high altitudes. The Kitepower system uses a soft-wing kite that produces electricity during cyclic crosswind operation: energy is generated as the tether reels out under high tension, while the reel-in phase consumes less energy due to lower aerodynamic forces. However, the reel-in phase remains inefficient and susceptible to stall under low apparent wind conditions. This thesis develops control strategies to improve reel-in performance using active depower control, which adjusts the kite’s angle of attack. A non-linear four-point kite model was analysed to obtain trimmed parking states for linearisation. Quasi-steady reel-in trimming proved inconclusive, revealing methodological limitations. Controllers designed using H∞ synthesis improved stability under wind disturbances and reduced reliance on winch actuation. Results show active depower control enhances stability and efficiency, providing a foundation for future robust control development across broader operating conditions.