Underwater vehicle autopilot system for controlling depth and pitch: Maneuvering through near-surface waves and environmental disturbances

Abstract

This paper introduces a control algorithm for autonomous underwater vehicles (AUVs) designed to perform missions under complex near-surface wave conditions. The algorithm enables the AUV to control depth and pitch in response to changing environmental conditions and speed of the AUV. The proposed control system targets the specific case of a Joubert BB2 vehicle, utilizing control inputs from the tail planes, sail plane, and hover tank. The control system combines a Linear Quadratic Regulator (LQR) with $L_1$ adaptive autopilot augmentation. The LQR controller, designed to address wave disturbances, incorporates a filtering technique that mitigates the effects of such disturbances on the vehicle’s actuators without affecting the robustness of the autopilot. The $L_1$ adaptive augmentation deals with low-frequency disturbance and model uncertainties, and ensures asymptotic stability of depth and pitch dynamics in the presence of such disturbance. This advanced control strategy for underwater vehicles significantly enhances their functionality across various marine operations. The effectiveness of the proposed control system has been validated through comprehensive simulations using a reduced order model of the Joubert BB2 vehicle, which was developed in our previous work. This validation confirms the potential of the control system to improve AUV performance in demanding underwater conditions.