Robust control design based on uncertainty and disturbance estimation for a thruster-actuated axisymmetric AUV with a four-quadrant propulsion model

Thruster-driven autonomous underwater vehicles (AUVs) are designed to maneuver at low speeds and carry out dynamic station keeping operations. In this paper, a dynamic model of a thruster-actuated axisymmetric AUV operating at low speed is presented along with a four-quadrant thruster model. The hydrodynamics of the AUV were estimated using Semi-empirical formulation and computational fluid dynamics simulations. To simulate realistic thruster forces, a four-quadrant thruster model is integrated into the AUV’s maneuvering dynamics. A robust control strategy based on the uncertainty and disturbance estimation (UDE) method is formulated for depth, pitch, and heading control of a thruster-driven AUV. UDE control consists of nominal feedback plus the estimator which utilizes a low-pass filter with a proper bandwidth to estimate the unmodeled dynamics and unknown external disturbances. We introduce an optimization framework for tuning the filter time constant value to improve the performance and energy efficiency. The effectiveness of the proposed control system is demonstrated through numerical simulations considering model uncertainty, thruster nonlinear model, input saturation, external disturbances, and measurement noises. The proposed UDE control design is compared with Time Delay Estimation (TDE) control and Sliding Mode Control (SMC), and implementation issues are addressed. The comparative analysis shows that the UDE control provides enhanced robustness and performance across various maneuvering scenarios, making it a viable solution for the AUV motion control. Experiments were conducted on a testbed AUV for trajectory tracking in depth and yaw degrees of freedom to demonstrate practical realization of the UDE control. The experimental results confirm the effectiveness of the proposed control strategy in presence of system uncertainties.