Composite hovering control of underwater vehicles via variable ballast systems

In this paper, a composite hovering control scheme is proposed to improve the disturbance rejection performance of underwater vehicles via variable ballast systems (VBSs). A nonlinear disturbance observer (NDOB) based feedforward controller, which estimates and then compensates the resultant force of external disturbances, is augmented to the conventional proportional plus derivative (PD) based feedback control system. Both stability and convergence of the overall system have been guaranteed via Lyapunov analysis. Simulation results show that the NDOB based composite hovering control system exhibits more desirable performance in disturbance rejection than conventional PD control system.