ABSTRACT This paper presents an integrated vertical control method for online identification and compensation of residual buoyancy, designed for full‐ocean‐depth (FOD) autonomous underwater vehicles (AUVs) that rely on vertical thrusters for depth‐keeping or height‐keeping hovering tasks. To address the residual buoyancy drift caused by vehicle hull compression and seawater density variations under extreme hydrostatic pressure, the proposed method constructs a condition‐triggered bidirectional switching framework between velocity and position control modes: During the large‐error stage, a velocity control mode is employed to rapidly drive the vehicle into a low‐speed region. Once the depth error and vertical velocity satisfy predefined threshold conditions, the system switches to a position control mode. In this mode, the equivalent residual buoyancy is estimated online via thruster force equilibrium and applied as feedforward compensation to achieve precise and stable hovering. If operating conditions change, the switching and identification mechanisms can be retriggered to maintain control performance. The proposed method was validated through test‐tank experiments and sea trials for the 1000‐, 7000‐, and 11,000‐m classes using the Wukong FOD AUV. Field results demonstrated that the system achieved average height tracking errors of 0.0124 and 0.0668 m in the test tank and 11,000‐m class trials, respectively. These results verify the effectiveness and engineering applicability of the proposed method in rejecting unknown residual buoyancy disturbances and achieving stable hovering in hadal environments.
Li et al. (2026) studied this question.