The spatial path following control problem of autonomous underwater vehicles (AUVs) is addressed in this paper. In order to realize AUVs’ spatial path following control under systemic variations and ocean current, three adaptive neural network controllers which are based on the Lyapunov stability theorem are introduced to estimate uncertain parameters of the vehicle’s model and unknown current disturbances. These controllers are designed to guarantee that all the error states in the path following system are asymptotically stable. Simulation results demonstrated that the proposed controller was effective in reducing the path following error and was robust against the disturbances caused by vehicle's uncertainty and ocean currents.

Underwater target tracking with signal propagation delay is a major challenge. The widely-used unscented Gauss-Helmert filter (UGHF) algorithm shows good tracking performance in bearing-only filters with signal propagation delay. However, UGHF algorithm is a nonlinear filtering method based on 2-order unscented transformation (UT), which can only match the accuracy of the 3-order Taylor expansion term of Gauss-Hermite model (GHM). Moreover, UGHF is a Gaussian filter, and when the measurement noise presents non-Gaussian characteristics, the tracking accuracy will be reduced. In order to improve the tracking accuracy of underwater bearing-only target, this paper proposes a high-order UGHF (HOUGHF) algorithm using high-order UT instead of 2-order UT. In order to further improve the tracking accuracy of the tracking algorithm under non-Gaussian noise, in this paper, maximum correntropy criterion (MCC) is used to replace the original minimum mean square error (MMSE) to update HOGGHF’s posterior estimation. The maximum correntropy HOGGHF (MCHOGGHF) algorithm is proposed by using MCC based on Gaussian kernel function. At the same time, in order to deal with the change of measurement noise, a method of adaptive Gaussian kernel width is presented. Simulation and sea trial results show that the two algorithm are superior to UGHF algorithm and MCHOGGH algorithm is superior to HOGGHF algorithm in estimation accuracy under non-Gaussian noise.

The research and development of the ocean has been gaining in popularity in recent years, and the problem of target searching and hunting in the unknown marine environment has been a pressing problem. To solve this problem, a distributed dynamic predictive control (DDPC) algorithm based on the idea of predictive control is proposed. The task-environment region information and the input of the AUV state update are obtained by predicting the state of multi-AUV systems and making online task optimization decisions and then locking the search area for the following moment. Once a moving target is found in the search process, the AUV conducts a distributed hunt based on the theory of potential points, which solves the problem of the reasonable distribution of potential points during the hunting process and realizes the formation of hunting rapidly. Compared with other methods, the simulation results show that the algorithm exhibits high efficiency and adaptability.

Due to its highly autonomy, the strapdown inertial navigation system (SINS) is widely used in unmanned underwater vehicles (UUV) navigation. Initial alignment is crucial because the initial alignment results will be used as the initial SINS value, which might affect the subsequent SINS results. Due to the rapid convergence of Earth meridians, there is a calculation overflow in conventional initial alignment algorithms, making conventional initial algorithms are invalid for polar UUV navigation. To overcome these problems, a polar initial alignment algorithm for UUV is proposed in this paper, which consists of coarse and fine alignment algorithms. Based on the principle of the conical slow drift of gravity, the coarse alignment algorithm is derived under the grid frame. By choosing the velocity and attitude as the measurement, the fine alignment with the Kalman filter (KF) is derived under the grid frame. Simulation and experiment are realized among polar, conventional and transversal initial alignment algorithms for polar UUV navigation. Results demonstrate that the proposed polar initial alignment algorithm can complete the initial alignment of UUV in the polar region rapidly and accurately.

This paper focuses on the finite-time formation-control problem of a multi-AUV formation under unknown perturbations with prescribed performance. First, the nonlinear AUV model is transformed into a second-order integral model using feedback linearization. Suitable prescribed performance functions are selected to constrain the control errors of AUVs within a preset range and convert AUV tracking errors into unconstrained tracking errors using an error-conversion function to facilitate controller design. Finite-time sliding-mode disturbance observers are designed for unknown disturbances in the ocean so that they can accurately estimate the unknown disturbances in finite time. Based on the unconstrained tracking error and the unknown disturbance observer, the fast terminal sliding-mode formation controller is designed so that the multi-AUV formation can converge in finite time. Finally, the simulation experimental results show that the finite-time formation-control method with prescribed performance proposed in this paper can better cancel the unknown disturbance in the ocean in finite time and improve the robustness of the multi-AUV formation control.