Development of an equivalent-input-disturbance based altitude controller for sea-skimming unmanned aerial vehicles

Unmanned aerial vehicles (UAVs) with sea-skimming capability are usually operated at a very low altitude, which require fast yet robust height controller to maintain the desired flight level in order to avoid the vehicle ditching into the sea. Due to the disturbance introduced by sea waves, the measured height information is often noisy and inaccurate, which cannot be directly used by the autopilot. To increase the robustness of the longitude autopilot with respect to unknown external disturbance, we present a novel equivalent-input-disturbance based controller, which enables real time disturbance rejection by considering the external disturbance as an equivalent signal applied to the input channel. Simulation results have shown that the proposed method outperforms the conventional PID based controller in the presence of sea wave disturbances.