Control Of Underactuated Surface Vessels Research Articles

Adaptive Neural Network Control of Underactuated Surface Vessels With Guaranteed Transient Performance: Theory and Experimental Results

In this paper, an adaptive trajectory tracking control algorithm for underactuated unmanned surface vessels (USVs) with guaranteed transient performance is proposed. To meet the realistic dynamical model of USVs, we consider that the mass and damping matrices are not diagonal and the input saturation problem. Neural networks (NNs) are employed to approximate the unknown external disturbances and uncertain hydrodynamics of USVs. Moreover, both full-state feedback control and output feedback control are presented, and the unmeasurable velocities of the output feedback controller are estimated via high-gain observer. Unlike the conventional control methods, we employ the error transformation function to guarantee the transient tracking performance. Both simulation and experimental results are carried out to validate the superior performance via comparing with traditional potential integral control approaches.

Adaptive output-feedback control with prescribed performance for trajectory tracking of underactuated surface vessels

In this paper, we address the problem of trajectory tracking control of underactuated surface vessels in a quantitative method with only position and attitude available. Combined with high-gain observer, parameter compression algorithm and performance function, an adaptive control scheme with prescribed performance is proposed. The high-gain observer is constructed to estimate the velocities, and the parameter compression algorithm is adopted to address persistent perturbations and model uncertainties in a more concise way. By prescribed performance function, the controller can be designed with prescribed performance. The results about system stability is given and proved by using the Lyapunov direct method. The signals concerning with all the errors converge to a bounded set. Compared with the existing methods, the developed scheme can reduce the number of tuning parameters, and guarantee the tracking errors bounded within the prescribed performance constraints in the transformed coordinate, which means the steady errors, convergence rates and maximum overshoots can be guaranteed by the performance function. Comparison and numerical simulations are given to demonstrate the effectiveness of the proposed scheme.

Practical backstepping control for underactuated ship path following associated with disturbances

Robust tracking control of underactuated surface vessels is an important issue in marine control engineering all along. This study intends to enhance the robustness of the motion control system which associates with unknown dynamics and time-varying disturbances. A practical adaptive backstepping control scheme is developed to keep a surface ship along the desired course that generated by a virtual ship. This control scheme can guarantee the error dynamic system to be globally uniformly asymptotically stable by the Lyapunov stability theorem. Furthermore, this algorithm can be implemented without the exact information of the non-linear hydrodynamics and random ocean disturbances. The employed pre-filter can provide a smooth transition of the desired course angle and its derivatives that based on the line-of-sight guidance method when the desired path is a non-smooth curve. The proposed controller can steer the underactuated vessel and follow the reference course accurately whether the desired course is smooth or non-smooth. In addition, this method can effectively reduce the fluctuation of the control moment when the desired path is a non-smooth curve. Two simulation cases are drawn to illustrate the validity of the proposed control strategy.

Adaptive Neural Control of Underactuated Surface Vessels With Prescribed Performance Guarantees.

This paper presents adaptive neural tracking control of underactuated surface vessels with modeling uncertainties and time-varying external disturbances, where the tracking errors consisting of position and orientation errors are required to keep inside their predefined feasible regions in which the controller singularity problem does not happen. To provide the preselected specifications on the transient and steady-state performances of the tracking errors, the boundary functions of the predefined regions are taken as exponentially decaying functions of time. The unknown external disturbances are estimated by disturbance observers and then are compensated in the feedforward control loop to improve the robustness against the disturbances. Based on the dynamic surface control technique, backstepping procedure, logarithmic barrier functions, and control Lyapunov synthesis, singularity-free controllers are presented to guarantee the satisfaction of predefined performance requirements. In addition to the nominal case when the accurate model of a marine vessel is known a priori, the modeling uncertainties in the form of unknown nonlinear functions are also discussed. Adaptive neural control with the compensations of modeling uncertainties and external disturbances is developed to achieve the boundedness of the signals in the closed-loop system with guaranteed transient and steady-state tracking performances. Simulation results show the performance of the vessel control systems.

Adaptive output-feedback formation control for underactuated surface vessels

ABSTRACTThis paper investigates the leader–follower formation problem of underactuated surface vessels. Velocities of both leader and follower vessels are unavailable. Model uncertainties and ocean disturbances are also considered. By incorporating adaptive control, neural networks (NNs), the high-gain observer (HGO) and the minimal learning parameter (MLP) algorithm in the backstepping procedure, a novel adaptive output-feedback formation control scheme is developed. We show that formation errors can be guaranteed to be semiglobally uniformly ultimately bounded (SGUUB) with the proposed controller. Compared with existing methods, the formation can be achieved only with position and yaw angle of both leader and follower. Meanwhile, the developed scheme can enhance the robustness of the closed-loop system with less computational effort, where only two online parameters need to be tuned. Simulation and comparison results are provided to illustrate the effectiveness of theoretical results.

Global trajectory tracking control of underactuated surface vessels with non-diagonal inertial and damping matrices

This paper investigates the tracking control problem of underactuated surface vessels with non-diagonal inertia and damping matrices. Based on the inherent cascaded structure of vessel dynamics and the cascaded system theory, the tacking control problem of vessels is converted to the stabilization control problem of two cascaded subsystems. Two trajectory tracking control laws are designed respectively for known and unknown model parameters. The first feedback control law is derived with the aid of Lyapunov method, realizing the global $${\mathscr {K}}$$ -exponential trajectory tracking of vessels with accurate model parameters. As all the state variables in the first law are independent of model parameters, the sliding mode technique is applied to extend the first control scheme to the case of unknown model parameters, resulting into an another tracking control law, which ensures the global $${\mathscr {K}}$$ -exponential stability of the closed-loop error system despite unknown model parameters. Effectiveness of the proposed controllers is demonstrated by numerical simulations.

Adaptive Leader–Follower Formation Control of Underactuated Surface Vessels Under Asymmetric Range and Bearing Constraints

This paper deals with the problem of leader–follower formation control for a group of underactuated surface vessels with partially known control input functions. In the proposed scheme, the problem is formulated as an adaptive feedback control problem for aLine-Of-Sight (LOS) based formation configuration of a leader and a follower. To account for LOS and bearing angle time-varying constraints, asymmetric barrier Lyapunov functions are incorporated with the control design. Furthermore, in order to alleviate required velocity information on the leader, a reconstruction module is designed to estimate the vector velocity of this leader. This reconstruction is accomplished in finite time with zero error, which allows the injection of accurate estimation into the formation controller. The controller is then developed within the framework of the backstepping technique, with the parametric uncertainties and the unknown gains being estimated by a novel structure identifier. The overall closed-loop system, is proved to be semiglobally uniformly ultimately bounded by Lyapunov stability theory. Furthermore, we show under the proposed control scheme that the constraints requirement on the LOS range and bearing angle tracking errors are not violated during the formation process. Finally, the effectiveness and the robustness of the proposed strategy are exhibited through simulations.

Robust adaptive trajectory tracking control of underactuated surface vessel in fields of marine practice

To enhance the control system robustness of an underactuated surface vessel with model uncertainties and environmental disturbances, a robust adaptive trajectory tracking algorithm based on proportional integral (PI) sliding mode control and the backstepping technique is proposed. In this algorithm, a continuous adaptive term is constructed to reduce the chattering magenta phenomenon of the system due to the sliding mode surface, and the backstepping technique is employed to force the ship position and the orientation on the desired values. In addition, we have proved the Lyapunov stability of the closed-loop system under the discontinuous environment disturbances or the thruster discontinuity. Finally, numerical simulations are performed to demonstrate the effectiveness of this novel methodology.

Robust Composite Nonlinear Feedback Path-Following Control for Underactuated Surface Vessels With Desired-Heading Amendment

This paper addresses the transient performance improvement for path-following control of underactuated surface vessels (USVs) in the presence of oceanic disturbances. The traditional practice that chooses the tangent direction of the desired path as the desired heading may deteriorate the tracking performance in the curve following due to the nonzero sideslip angle therein. Also, the disturbances in wave filed greatly affect the transient path-following control. To this end, three contributions are made in this paper: 1) an amendment to the definition of the desired heading using the sideslip-angle compensation is presented to achieve a more accurate path-following maneuver; 2) a novel disturbances observer-based composite nonlinear feedback (DO-CNF) controller is proposed to restrain system overshoots and eliminate steady-state errors while dealing with multiple oceanic disturbances with unknown bounds; and 3) the variation of the yaw-rate reference for path-following objective is handled in the controller design, which can enhance the vessel's robustness to the changing of the path curvature. Comparative simulations verify the reasonability of the desired-heading amendment and the effectiveness of the DO-CNF approach in improving the transient path-following performance of USVs while satisfying actuator saturation considering the unknown disturbances and changing reference.

Further results on global stabilisation and tracking control for underactuated surface vessels with non-diagonal inertia and damping matrices

This paper studies the global uniform stabilisation and exponential tracking problems for an underactuated ship with non-diagonal inertia and damping matrices. For the synthesis of the controller, first, the underactuated ship in question is converted into two cascade connected subsystems by using state and input transformations. Two constructive backstepping design schemes are developed, respectively, to get around the stabilisation burden and tracking burden. Along the way of proving stability analysis, it is shown that the designed control strategies can guarantee the global uniform asymptotic convergence of the state to the origin and global exponential convergence to the desired reference trajectory. Simulation results are provided to demonstrate the effectiveness of the proposed control methodologies.

Stabilization And Tracking Of Underactuated Surface Vessels In Random Waves With Fin Based On Adaptive Hierarchical Sliding Mode Technique

ABSTRACTTrajectory tracking and roll stabilization are both vital practices in ship motion control. Trajectory tracking is a kind of low‐frequency control, while roll stabilization by means of fins is a kind of high‐frequency control. However, they have been studied separately previously; most tracking control of underactuated surface vessels in the previous studies do not account for roll stabilization by means of fins. In reality, however, they are an integral system. In this paper, a simple control strategy is proposed to achieve trajectory tracking and fin roll stabilization simultaneously. Four degrees of freedom derived from a six degrees of freedom mathematical model of a surface vessel is considered, including surge, sway, roll and yaw. Surge force, roll moment and yaw moment are considered as control inputs, while position, yaw angle and roll angle are controlled. The number of control inputs is fewer than the outputs to be controlled. Therefore, we are dealing with an underactuated problem. An adaptive hierarchical sliding mode control technique is employed to deal with the underactuation. Stabilization of underactuated surface vessels is studied as a special case. Random waves are applied to test the robustness of the designed controllers. Lyapunov stability theory is used to show the stability of closed‐loop system. The simulation results verify the effectiveness of the proposed strategy.

LMI-Based Model Predictive Control for Underactuated Surface Vessels with Input Constraints

A nonlinear model predictive control (MPC) is proposed for underactuated surface vessel (USV) with constrained inputs. Aimed at the special structure of USV, a state-dependent coefficient (SDC) under the given USV is constructed in terms of diffeomorphism and state-dependent Riccati equation (SDRE) theory. Based on linear matrix inequalities (LMIs), the states of the USV are steered into an operating region around zero. When the states reach the region, the control law is switched to stabilize the system. And the constrained control input of the considered system is solved by convex optimization based on MPC involving LMIs. The simulation results verified the effectiveness of the proposed method. It is shown that, based on LMIs, it is easy to get the MPC for the USV with input constraints.

Cooperative control of underactuated surface vessels

This study considers the cooperative control of a group of underactuated surface vessels using the relative information between neighbour's information such that the group of surface vessels come into a desired geometric pattern whose centroid moves along a desired tajectory. With the aid of results from graph theory and Lyapunov techniques, decentralised cooperative control laws are proposed for different communication scenarios. The effect of communication delays on the proposed controllers is analysed. Simulation results show the effectiveness of the proposed control laws.

Global stabilisation and tracking control of underactuated surface vessels

In this study, the authors solve the problem of uniform global asymptotic stabilisation and global exponential tracking for an underactuated ship with only two propellers. A unified backstepping design methodology is proposed to tackle both the stabilisation and tracking problems. The obvious advantage of this framework is that the controller design procedure is systematic and analytically simple. The study also addresses the tracking problem with constant bias of environmental disturbances. Simulation results are provided to validate our theoretical results.

On the dynamic properties and control of underactuated surface vessels

In the present work we study the problem of controlling the planar position and orientation of an autonomous surface vessel using two independent thrusters. It is first shown that although the system is not asymptotically stabilisable to a given equilibrium configuration using a time-invariant continuous feedback, it is strongly accessible and Small Time Locally Controllable (STLC) at any equilibrium. A discontinuous time invariant controller is then constructed to almost exponentially stabilises the system to the desired configuration. Simulation and concluding remarks are then exposed.