On Dynamic Surface Control And Backstepping Applied In Course Control Of Ships

The ship course control system directly influences the economy and security of ship navigation. The movement of ship has large inertia and nonlinear characteristics. Since the speed and load of ship as well as the marine environment often change, there is obviously uncertainty in the ship maneuvering system dynamics and disturbance. It is an important issue to develop a feasible, adaptive and robust nonlinear ship course control strategy in ship control field.Based on Backstepping design tool, dynamic surface control and Nussbaum function, this thesis developes three nonlinear ship course control strategies which are adaptive and robust. To solve the parameter uncertainties of nonlinear ship maneuvering system, an adaptive nonlinear ship course-keeping control law is designed, which can guarantee the closed-loop system asymptotic stability. To take the disturbances into consideration, an adaptive and robust nonlinear ship course-tracking control law is designed, which can guarantee the global uniform boundedness of all signals of the resulting closed-loop ship course-tracking control system and make the course tracking error arbitrarily small by appropriate choice of the design parameters. Since actuator physical constraints can severely degrade the closed-loop system performance, considering actuator saturation, an adaptive and robust nonlinear ship course-tracking control law is designed, which can guarantee the global uniform boundedness of all signals of the resulting ship course-tracking control system and make the course tracking error arbitrarily small by appropriate choice of the design parameters. Nussbaum function is used to deal with the unknown sign of uncertain control gain and avoid the possible controller singularity problem. Dynamic surface control is combined with backstepping technique to overcome the problem of "explosion of terms". By means of Lyapunov function and Nussbaum function lemmas, it is proved theoretically that the designed adaptive nonlinear controller can guarantee the stability of close-loop control system. The simulations on two ships are carried out. The simulation results demonstrate the effectiveness of the proposed control scheme.