A Velocity Form Model Predictive Control of an Autonomous Underwater Vehicle

This article presents a model-predictive control (MPC) scheme to achieve 3-D trajectory tracking control and point stabilization of an autonomous underwater vehicle (AUV) subject to environmental disturbances. The AUV is modeled as a coupled nonlinear system. The control scheme is developed using a linear parameter-varying formulation of the nonlinear model in velocity form to obtain an optimization control problem with efficient online solvers and does not require model augmentation that can potentially increase computational efforts. The control strategy inherently provides offset-free control when tracking piecewise constant reference signals, ensures feasibility for trajectories containing unreachable points, and is relatively simple to implement, as parameterization of all equilibria is not required. A simple switching law is proposed for task switching between the 3-D trajectory tracking and point stabilization. The MPC is designed to ensure the closed-loop stability of the vehicle in both motion control tasks via the imposition of terminal constraints. Through simulations of the coupled nonlinear Naminow-D AUV under ocean current and wave disturbances, the effectiveness of the control strategy in trajectory tracking and point stabilization is demonstrated.