Adaptive tracking control of longitudinal trajectory for underwater vehicle

For the underwater vehicle trajectory tracking with strong nonlinearity and large pitch angle movement, a class of nonlinear adaptive control schemes were proposed in this paper. Firstly, the nonlinear movement model was adopted directly, a saturation function was induced in the process of controller design, and the assumption limit that the pitch angle was a small-angle was broken through the Maclaurin expansion formula. Then, taking into account that the precise nonlinear motion model of the vehicle was difficult to establish and there were many modeling errors in the actual vehicle model, the online adaptive method was used to approximate the nonlinear model. Finally, a nonlinear adaptive controller was designed by using Backstepping method, and its stability was proved by Lyapunov's theory. The hardware-in-the-loop simulation results show that the tracking errors of all three types of tracks given in the paper are less than 0.5 m, the pitch rudder partials are less than 15°, and the pitch moments are within 10⁵ N·m order of magnitude in consideration of measurement noises and parameter uncertainties, These results prove that the control algorithm in this article has a strong robustness and can meet the requirement of tracking performance.