Robust Hierarchical Hovering Control of Autonomous Underwater Vehicles via Variable Ballast System

Hovering control of autonomous underwater vehicles (AUVs) via a variable ballast system (VBS) is challenging owing to the difficulty in precisely estimating related hydrodynamic coefficients and vertical disturbance. In this work, a hierarchical control strategy is proposed which comprises an upper layer-the proportional-integral-derivative (PID) type ballast water mass planner generating the desired ballast mass, and a lower layer-the continuous mass flowrate controller adjusting the actual ballast mass. The resulting flowrate algorithm endows the system with local uniform asymptotic stability and robustness to both modeling errors and vertical disturbance. Numerical results verify the feasibility and effectiveness of the proposed hierarchical hovering control strategy.