Response-Tunable Adaptive LOS-Based Guidance for Depth-Tracking Control of Underactuated AUVs in the Presence of Time-Varying Disturbances

Autonomous underwater vehicles (AUVs) have been extensively employed in diverse marine applications, where depth-tracking control remains a critical technical challenge. Although previous studies have investigated various guidance law designs for underactuated AUVs, compensation for the attack-angle effect induced by heave velocity remains underexplored, particularly in the presence of extreme time-varying external disturbances and sharp path curvature variations. Existing line-of-sight (LOS) based methods, including integral LOS (ILOS) and adaptive LOS (ALOS), rely solely on the integral action of the pitch-tracking error to estimate the attack angle, which inevitably introduces inherent time-delay characteristics and induces overshoot and chattering in the depth-tracking response. Given that a system’s position and its velocity are uniquely determined by its acceleration, a response-tunable adaptive LOS (RTALOS) guidance design is proposed for AUV depth-tracking control task. This guidance law incorporates both the depth-tracking error and its velocity term as boundary constraints, generating an acceleration reference through a time-based planning polynomial to achieve accurate attack-angle estimation. The proposed method redefines attack-angle estimation as a new paradigm based on a second-order depth-tracking kinematic system, where the introduced velocity term acts as an adjustable damping effect to effectively suppress the depth-tracking overshoot and oscillation. Simulations were conducted to verify that the proposed guidance design could make the depth-tracking motion converge within a given time duration if the state-constrained acceleration was promptly executed. Compared to the selected ILOS and ALOS methods, the proposed RTALOS method can rapidly and accurately compensate for time-varying attack-angle effects via the estimation of attack angle, resulting in precise depth-tracking control performance, even under severe time-varying disturbances and when the pitch-tracking control performance is unsatisfactory.