This paper focuses on the problem of optimal fuzzy output-feedback tracking control for dynamic positioning of marine vessels simultaneously with model uncertainties, unknown disturbances, unavailable velocities and thruster saturations. The control scheme is built by integrating a fuzzy velocity observer, a finite-time disturbance observer, a dynamic auxiliary system, the optimal control strategy with the dynamic surface control. The fuzzy velocity observer is constructed to obtain the unavailable velocities without requiring the certain model dynamics. The finite-time disturbance observer is established to estimate the unknown disturbances. The dynamic auxiliary system is designed to compensate for thruster saturations effects. By incorporating these methods, a disturbance rejection adaptive controller is designed with dynamic surface control. The optimal compensation term is inserted to minimize the cost function of the tracking error system by adaptive dynamic programming. It is shown that the optimal control consisting of the adaptive controller and the optimal compensation term guarantees that all signals in the closed-loop dynamic positioning system are bounded. Finally, simulation results demonstrate the effectiveness of the proposed optimal control scheme.

This paper surveys the recent advances in dynamic positioning (DP) control for marine crafts. DP of marine crafts means that a craft can maintain a fixed position and heading, or move along a predetermined trajectory slowly without the anchoring system, using only its own thruster system to counteract ocean disturbances. The survey is by no means exhaustive but provides a survey of some of the major technological advancements in DP controller design over the years of research and development. Firstly, the model of marine crafts and some difficult problems in DP control are introduced including the impact of multiple source disturbance, unavailable velocity measurement information, resource conservation and performance optimization, destabilizing impact of faults and network security and compound multi-constraint restrictions. Then, the DP control schemes in recent years are summarized and classified in detail. Finally, some theoretical and technical problems are proposed, including online data-driven model-free control, man–machine combination intelligent control and composite hierarchical anti-disturbance control to guide future investigations.

For shipboard boom cranes with the influence of ship roll motion, we develop a new nonlinear antiswing control scheme with a model predictive control (MPC) based auto-tuning mechanism. In this scheme, the superiority of MPC in handling constraints is retained in acquiring time-varying control gains. Compared with trial and error, the efficiency of searching for proper control gains can be improved dramatically while considering optimization. Specifically, by binding the ship rolling angle to the original state variables of shipboard cranes, a coordination transformation is first carried out to facilitate the controller design by excluding the specific expression of ship rollings. Then an energy-based nonlinear controller is proposed, and the system stability can be rigorously guaranteed based on the Lyapunov theory and LaSalle’s invariance principle. To improve the performance of the energy-based controller with gains derived through trial and error tuning, a novel MPC-based auto-tuning mechanism is further established so the optimal and time-varying control gains can be determined more effectively. The other merit of the proposed scheme lying in the state constraints and input saturation are taken into account to enhance the safe operation of shipboard cranes. Finally, numerical simulations are elaborately made, and comparison results are presented to demonstrate the superiority of the proposed scheme, especially in optimality, coordination control performance, and dealing with constraints.

This paper focuses on the platoon formation control for a fleet of unmanned surface vehicles (USVs) with uncertain kinetics, unmeasured velocities, input saturation and dead zone to ensure collision avoidance (CA) and connectivity maintenance (CM). The prescribed performance techniques are implemented to ensure that the formation errors between each USV and its leader are constrained within predefined ranges and angle errors. This enables CA and CM to ultimately remaining within the requested line-of-sight (LOS) range. Moreover, by combining a known smooth function with the extended state observers (ESOs), which cannot only recover relevant velocity information but also compensate for the effects caused by input saturation, dead zone, uncertain kinetics and external disturbances. Consequently, this paper presents a prescribed performance formation control scheme that guarantees uniformly ultimate boundedness of the closed-loop system. Based on the simulation results, it has been confirmed that the developed control strategy is effective.

Dynamic positioning (DP) stands as the keystone underpinning ships’ operations in the abyssal depths and remote oceans. This paper proposes an event-driven disturbance rejection approximate optimal dynamic positioning scheme for surface ships with prescribed performance via reinforcement learning (RL). Firstly, a disturbance observer is established to achieve the online estimations of marine environmental disturbances such that the undesirable disturbance effects on control performance can be reduced. Meanwhile, the positioning error transformations with the prescribed performance function is established to combine with the backstepping method and the virtual controller can be designed to constrain the positioning error. Then, for the velocity error surface, the RL method provides the actor-critic architecture to approximate the actual optimal commanded control law and minimized the specified performance index function. Subsequently, the optimal commanded control design incorporates the event-driven mechanism to avoid communication resource waste as well as actuator wear and tear. By applying the Lyapunov stability theory, it is proven that the designed RL control law forces the ship’s actual position and yaw angle to converge to desired target with prescribed performance while ensuring all signals in the closed-loop system are uniformly ultimately bounded. The feature of this paper is the reasonable integration of prescribed performance and RL, which ensures that the performance index function of the ship is minimized while keeping the DP error within the safety range. Finally, simulations with comparisons based on a sea launch ship show the effectiveness further validating the superiority of the RL control scheme.