Tracking Performance of Model-Based Thruster Control of a Remotely Operated Underwater Vehicle

This article compares output feedback control strategies for an underwater thruster. There are a variety of dynamic models for thrusters, some of which can account for fluid-velocity dynamics and others that account for propeller angular velocity dynamics. Here, the contributions of both fluid and propeller velocities are modeled with three levels of complexity: simplified, hydrodynamic linear, and hydrodynamic quadratic models. Multiple methods are presented to estimate axial flow velocity, which is handled as an unmeasured state. The performance of controllers based on these models and estimators is compared for a single thruster as well as for an underwater vehicle with a nonorthogonal multithruster layout. All models, controllers, and estimators are experimentally evaluated in closed-loop experiments using a load cell to measure the tracking performance of an individual thruster. Full vehicle simulations using experimentally characterized models provide additional insights into the control and estimation strategies and their relative merits.