Considering the actual situation of time-varying interference in the underwater environment, a trajectory tracking control method for an underactuated Unmanned Underwater Vehicle (UUV) underwater exploration based on backstepping sliding mode with fuzzy switching gain is designed in this paper. Firstly, the motion equations of UUV in diving plane are given. Secondly, the virtual control variable is designed to replace the pitch angle to avoid the singular value phenomenon. Combining with the backstepping technique, the fuzzy switching sliding mode controller is proposed. Thirdly, in order to decrease the chattering phenomenon of sliding mode control, the fuzzy rule of sliding mode gain is designed. Fourthly, based on Lyapunov theory and comparison principle, the global asymptotic stability of UUV closed-loop tracking error system is proved. Finally, the simulation results demonstrate the effectiveness and robustness of the proposed controller.

In this paper, the formation control problem for a group of unmanned underwater vehicles (UUVs) is investigated considering collision avoidance and environment disturbances. To address the external force effect of the environment, such as waves and currents, a sliding mode disturbance observer is designed to compensate for the unknown dynamic disturbances in finite time. A bounded artificial potential field is incorporated into the control law to ensure collision avoidance among UUVs. The form of an artificial potential function is much simpler and convenient for engineering applications. A controller is devised to guarantee all the error signals are bounded, and the formation pattern can be achieved in finite time after collision avoidance. The stability of UUV formation with collision avoidance is proven by using the Lyapunov theorem, and the scheme has been shown to be convergent using Barbalat’s lemma. Comparative simulations are presented to demonstrate the effectiveness of the proposed method in 2-D and 3-D environments.

This paper designs an adaptive formation control system for unmanned underwater vehicles (UUVs) in the presence of unmeasurable states and environmental disturbance. To solve the problem of unmeasurable UUV states, a filtered high-gain observer (FHGO) is employed to estimate the states, despite measurement noise. Then, an adaptive control scheme is designed to achieve UUV formation collision avoidance. The radial basis function (RBF) is used to estimate the unknown disturbance. The stability of UUV formation with collision avoidance is proven by using the Lyapunov theorem. Numerical simulation is carried out to demonstrate that the proposed filtered high-gain observer is successful in estimating the states of UUVs. The control law can keep the UUV formation from collision with good performance.

In this paper, we propose a robust tracking control scheme for trajectory tracking of overactuated marine surface vessels subject to environmental disturbances and asymmetric time-varying full-state constraints. The proposed robust control scheme is based on the unified barrier function technique that converts the original constrained dynamic positioning system into an equivalent nonconstrained one. In contrast to barrier Lyapunov function-based methods, the unbreakable requirement on the constraints is less restrictive, and the resultant controller is much simpler in this paper. The effect of environmental disturbances is compensated by a double-layer adaptive sliding mode disturbance observer. On the basis of the proposed adaptive disturbance observer, unknown lumped uncertainty can be estimated in finite time without knowing the upper bounds of the derivative of the lumped uncertainty. Since the surface vessel is overactuated, a control allocation scheme is required to distribute the generalized force signal to the actuators. The enhanced redistributed pseudoinverse algorithm is employed to ensure that the generalized force can be redistributed among the redundant actuators. Lastly, a simulation study is carried out on a dynamic positioning ship to verify the effectiveness of the proposed control method.

In order to overcome the problem that the conventional algorithms cannot be applied in the polar region, a polar initial alignment algorithm for Unmanned Underwater Vehicles (UUVs) with a large misalignment angle is proposed in this paper. The error model, the dynamics model and the observation model of the polar UUV initial alignment algorithm is established under the grid frame. This initial alignment algorithm is designed for the temporary anchoring UUV. According to the complex environment in the polar region, the large misalignment angle is considered instead of the small misalignment angle in other algorithms. An unscented Kalman filter is used to realize the data fusion. Based on the characteristics of the dynamics and the observation model, the unscented Kalman filter is simplified. The errors of the velocity are chosen as the observations. The misalignment angle of UUVs is estimated by the simplified unscented Kalman filter. The results demonstrate that the polar UUV initial alignment algorithm can be effective in improving the initial alignment accuracy, especially when large misalignment angles occur.