Abstract-Satisfying actuator constraints is often not considered in the academic literature on the design of ship heading and speed controllers. This paper considers the use of a simplified dynamic window algorithm as a way to ensure that actuator constraints are satisfied. To accomplish this, we use the simplified dynamic window algorithm as a dynamic window-based controller (DWC) to guarantee that the velocities remain within a set of feasible boundaries, while simultaneously respecting the actuator constraints. We also develop a modified nonlinear ship model on which to test the proposed concept. The DWC is compared with a more traditional ship heading and speed controller, using performance metrics which consider both control accuracy and energy use. I. INTRODUCTIONWhen a ship sails the sea, its autopilot system usually leads the ship along the desired heading. Numerous motion controllers and autopilots have been proposed over the years. However, many control algorithms found in the literature do not consider saturation constraints for the actuators. Examples of traditional control designs for ship autopilot systems are given in [1]. Not considering actuator constraints may lead to unsatisfying performance or stability issues. In [2], a gain-scheduled control law is developed and tested for handling actuator constraints for a rudder-roll model of a ship.In [3], the dynamic window (DW) algorithm is suggested as a method to perform collision avoidance and deal with constraints imposed by limited velocities and accelerations for mobile robots. This algorithm first generates a set of possible trajectories. Based on these trajectories, a search space of possible velocities can be approximated. The acceleration constrains are considered by limiting the search space to reachable velocities within a next time interval. To reduce the search space even further, all non-admissible velocities are removed to make the vehicle stop safely before it reaches the closest obstacle on the corresponding trajectory.The DW algorithm is modified for AUVs in [4] and shows promising results for handling magnitude and rate constraints for the actuators. In this paper, we consider a simplification of the DW algorithm in [4], by removing the collision avoidance part of the algorithm. In particular, this DW-based controller (DWC) will be combined with a heading controller based on the design in [5].The contribution of this paperis the proposal of the DWC, which inherently satisfies actuator constraints. Furthermore,

This paper deals with the design and evaluation of four controllers based on backstepping and different adaptive control schemes, which are applied to the motion control of a nonlinear 3 degrees-of-freedom model of a marine surface vessel. The goal is to make a comparative analysis of the controllers in order to find out which one has the best performance. The considered controllers are: Adaptive backstepping, adaptive backstepping with command governor, L 1 adaptive backstepping and L 1 adaptive backstepping with command governor. Numerical simulations are performed for target tracking along both straight-line and circular paths, with uncertain model parameters and an unknown disturbance. Motion control performance is evaluated by performance metrics such as IAE, ISE, ITAE and a novel metric named IAEW which combines control accuracy and energy use in one single metric.

In order to validate relevant dynamic positioning (DP) control algorithms in a realistic environment, a full-scale DP test campaign, the AMOS DP Research Cruise 2016 (ADPRC’16), was organized in a collaboration between the NTNU Centre for Autonomous Marine Operations and Systems (NTNU AMOS) and the company Kongsberg Maritime onboard the research vessel (R/V) Gunnerus. To the authors’ best knowledge, closed-loop DP feedback control algorithms have never been tested full-scale on a ship in an academic research experiment before. However, we have now achieved this by coding our algorithms into a test-module of the DP system, as prepared by Kongsberg Maritime. Among the tested algorithms is an output feedback control law with both good transient and steady-state performance. In another experiment, different adaptive backstepping control laws for DP were tested to compare and contrast their performance and properties. A hybrid state observer with a performance monitoring function proposed to switch between two observers, choosing the best one at any time instant, was also part of the test scope. For this, necessary measurements (including acceleration measurements) were logged to be able to rerun and validate the observer algorithms in post-processing. Finally, several experiments were done to test a pseudo-derivative feedback control law for DP. The feedback mechanism was tested with and without a feedforward disturbance rejection term, called acceleration feedforward. This paper reports the experimental setup, test program, and an overview of results from the ADPRC’16 campaign.

In this paper, combinations of linear and nonlinear feedback terms are investigated for 3 degrees-of-freedom pose and velocity control of ships. Nonlinear control algorithms that are found in the literature often have linear feedback terms, which result in nice globally exponential stability properties when assuming no actuator constraints. However, considering that all actuators have saturation constraints, such stability properties are not feasible in practice. Applying nonlinear feedback terms can be a step to handle such constraints. As a result, this paper explores nonlinear feedback terms for both the kinematic and kinetic control loops. Specifically, three controllers based on a cascaded backstepping control design are implemented and compared through simulations and model-scale experiments in an ocean basin. Stability properties and tuning rules for all the controllers are also provided. Interestingly, the use of nonlinear feedback terms gives the ability to constrain the feedback control inputs globally while simultaneously being able to change the convergence rates locally. The price to be paid is the introduction of additional tuning parameters. The three controller types are compared using performance metrics which consider both control accuracy and energy use. INDEX TERMS Ship motion control, Dynamic positioning, Cascaded backstepping control design, Nonlinear feedback terms, Tuning rules, Performance metrics, Experimental results.

Abstract-This paper presents an approach to obtain fault tolerance in the nonlinear longitudinal motion control of an aircraft. The approach uses an L1 adaptive backstepping controller and fault-dependent control allocation to obtain such tolerance. In the nominal fault-free case, only the elevator will be active. The L1 adaptive backstepping controller provides some robustness to the system by handling uncertainties, which is utilized for fault accommodation if a partial fault occurs. Also, control allocation is used to redistribute control to other available healthy actuators to make the system fault tolerant against more severe faults and even to a total loss of the elevator. Simulations have been conducted on a model of a Cessna 182 and show excellent results for both the nominal and faulty scenarios.