Output-Feedback Control for Cooperative Diving of Saucer-Type Underwater Gliders Based on a Fuzzy Observer and Event-Triggered Communication

This paper presents an output-feedback control method for cooperative diving of multiple homogenous under-actuated saucer-type autonomous underwater gliders (AUGs) subject to unmeasured velocities, model uncertainties, as well as unknown environmental disturbances. A robust cooperative diving controller is constructed by using a modular back-stepping design method. First, a fuzzy observer combined with a low-frequency learning scheme is presented to identify the unknown AUG dynamics as well as to estimate the unmeasured velocities. Second, a commanded guidance law is designed based on the observed velocities and a vertical line-of-sight guidance scheme at the kinematic level, and fuzzy dynamic control law is developed at the kinetic level. Finally, a non-periodic path update law based on an event-triggered mechanism is designed to reduce the communication frequency. By using the cascade theory, the stability of the closed-loop system is analyzed. The simulation results are provided to show the effectiveness of the proposed output-feedback control approach for saucer-type AUGs.