NMPC Design for AUV Dynamic Positioning Control with Incremental Input Constraints

This paper presents a novel nonlinear model pre-dictive control (NMPC) method for the dynamic positioning (DP) problem of general autonomous underwater vehicle (AUV) systems. In addition to common bound constraints on the control input signal, the input increments are particularly considered for smooth actuation. With a Lyapunov-based auxiliary DP con-troller, we show that the input constraints and incremental input constraints can be fully respected. The widely used proportional-integral-derivative (PID) type control law is exploited as the auxiliary DP controller, and then conditions that guarantees the recursive feasibility and closed-loop stability are derived. The feasibility and stability do not rely on the optimality of the control solution, but the control performance improves as the solution approaches to the (local) optimum. Hence, the computational complexity and control performance can be well balanced by the user specified optimizer parameters. Simulation results reveal the effectiveness and advantages of the proposed NMPC method.