Nonlinear Robust Control Study On Course And Track For Underactuated Marine Surface Vessels

With the development and prosperity of the world's shipping industry, themaritime transportation is more and more dense. In order to ensure the safety of navigation, people have put forward higher requirements for the ship motion control. Sailing in the ocean, in order to reduce the labor intensity of the helmsman, to shorten the sail away, and reduce fuel consumption, it is necessary to implement effective automatic control of the ship's heading or track; In addition, some ships for special operations, such as submarine cable laying and maintenance, etc. need more accurate ship track control especially. Therefore, the ship heading and track control study in both the theory and practice are extremely important.Due to the ship motion's characteristics such as nonlinear, large time delay and inertia, and the ship motion is also susceptible to disturbances of wind, waves and currents, the changes and measurement accuracy of the navigation conditions (such as speed, load and water depth, etc.), make the ship navigation state significant uncertainty. Therefore, the control of the ship heading, track, and other motion is a complex non-linear uncertainty control problem. In addition, most above-water ships are only equipped with the propeller, main propulsion and rudder, when controlling the track, it is necessary to control the ship heading and position (x,y) of ship,3degrees of freedom movement At this time, the ship control system belong to the underactuated system. Underactuated surface ship system is a typical example of second-order nonholonomic constraint dynamic systems. Nonlinear control methods developing with nonholonomic systems, such as linearization, part of the feedback linearization method, cascade system stability analysis theory, sliding mode control theory, is difficult to be directly used in solving underactuated ship's control problem. Therefore, for the control problems of underactuated ships with uncertainties and external disturbances it has not been solved by only a simple control method, but to seek a new control scheme to be adapted to the actual navigation has become a research focus on ship motion control in recent years.In order to solve the containing model uncertainty and disturbance conditions less drive surface ship motion control, this paper completed the following work:1. It introduced the basic knowledge related to this paper, including stability theory, the theory of sliding mode control and active disturbance rejection control theory which are the foundation for following chapters. Second, the surface ship motion mathematical model is established; including the ship horizontal degree of freedom motion model, respond to the mathematical model of ship motion and sea state interference model. The main purpose of modeling is to provide a basic simulation platform to study the characteristics of closed-loop system simulation studies to evaluate the performance of the control system.2. For uncertainties in the ship heading control and poor sea conditions interference, the three kinds of control strategies are applied to design the ship course controller:1) Using strong anti-interference ability ADRC controls technology with the simple algorithm to design the ship course controller. Against outside interference and the actual situation of the system, the traditional ESO has been transformed, so that it can truly estimate the unknown disturbance and eliminate the influence of measurement noise. To solve the problem that ADRC parameters is difficult to be decided, the genetic algorithm is applied to overcome the deficiencies of the hash method. The simulation results show that the ADRC control technology can solve the uncertainty and sea state interference problem very well.2) Adaptive control, fuzzy approximation and sliding mode control technology are applied to the ship course control. The model uncertainty can be solved by applying the fuzzy logic system for uncertainty function approximation and robustnee can be solved by using adaptive sliding mode control. Using the embedded PI control law instead of sliding mode control switch will make the switch continuous which solves the problem of sliding mode chattering. In addition, in order to ensure the control input is bounded, the adaptive algorithm has been improved. The simulation results show that the adaptive fuzzy sliding mode control (AFSMC) has a strong robustness.3) The nonlinear observer (NDO) and Sliding Mode Backstepping Control technology are applied to the ship Course control. Observing the uncertainty and random waves interfere of the system with use of the nonlinear disturbance observer, then, an equal amounts of compensation is introduced in control input, thereby the disturbance completely is fully inhibited. The heading controller is designed with the sliding mode inversion method, not only to ensure the stability of the closed-loop system but also to overcome the system uncertainty and external interference at the same time.3. For the ship track in the control of underactuated and poor sea conditions interfere with, the three kinds of control strategies are applied to design the ship track controller:1) Design the ship linear track controller ADRC control technology. For the underactuated features in the straight track control two TD arrangements are applied for the transition process, and the control law using the error combination with two controlled variables to break through the restrictions of the original ADRC algorithm which is only applicable to SISO systems and solves the underactuated control problem. To verify the robustness, the algorithm has been made a comparative simulation with the other algorithms in the relevant literature under the same conditions which has confirmed the strong robustness characteristics of the control of ADRC.2) Based on two degrees of freedom in the ship model, using the Diffeomorphism transformation and Backstepping, selecting the system output variables as the combinations of the ship course and sway displacement, and applying the state feedback for the design of a rudder control law, it solves underactuated and nonlinear problems of the system. Simulation results demonstrate the effectiveness of the algorithm.3) The Line-of-sight (LOS) navigation systems can transformed the underactuated system into the full-actuated system, so no Brockeets condition limits. Sliding mode control and Backstepping technology are applied to the ship straight line trajectory and curve control, which solved underactuated and nonlinear problems of the system. Simulation results demonstrate the effectiveness of the two algorithm.4. Ship heading(course) and track autopilot control system implementation are introduced briefly. The system hardware, software structure and the system of joint test and test results are also introduced in this paper.In this paper the results can also be applied to underwater vehicle, nonholonomic mobile robots and other systems with underactuated characteristics, which has a good universal.