The Nonlinear Adaptive Backstepping Robust Control For Ship Motion

H∞robust control, as an effective method to solve the control problem of model perturbation and parameter uncertainties, has been generally used in the research of ship motion control system.As a simplified H∞, robust control theory, the closed-loop gain shaping algorithm (CGSA) is a simple and direct control algorithm for practical ship motion control engineering. The CGSA can not design the controller for nonlinear system directly; therefore an algorithm combined the CGSA with the Backstepping method is proposed in this paper. For the further research, the stability of the proposed algorithm is proved by the Lyapunov stability theory and linear stability theory, which has provided a solid foundation for the further studies. Furthermore, the above theoretical control strategies have been applied to the ship steering course-keeping system, fin roll control system and rudder/fin joint control system. At last some important conclusions and practical achievements are obtained. The main contributions are as follow:To overcome the disadvantage of the static error of constant disturbance and complexity of the parameters tuning in the ship course-keeping with the traditional Backstepping method, a control scheme combined integral Backstepping algorithm with SISO CGSA is proposed. Furthermore, an integral nonlinear robust controller for ship course-keeping system is designed.The theoretical analysis and simulation results show that the controller designed by the above scheme has nice robustness to the model perturbation and environmental disturbances. Then, in order to overcome the high conservative of the traditional robust control strategy and the hydrodynamic uncertainties of the ship steering system, a new nonlinear adaptive robust control scheme derived from the combination of Backstepping method and the CGSA is proposed in this paper. Finally, a nonlinear adaptive robust controller for ship steering system is designed, and the simulation results show that the adaptive controller has a good performance, strong robustness to the external disturbance.With the consideration of the insufficiencies of the ship roll damping, to improve the security and comfort of the vessel and prevent the capsize of the ship, the active fin roll damping as the most effective roll damping equipment has been found to be very attractive.In the case of training vessel "YUKUN",effective working of advanced scientific research equipments with high-precision is one of the most important requirements. Hence it is important to develop a nonlinear controller for ship fin roll stabilisation system to offer a better performance and stronger robustness.For the further study about the nonlinear fin roll control system of the vessel "YUKUN", the control strategy combined the Backstepping method with SISO CGSA is used to design the two fin roll stabilisation controller:nonlinear robust controller and nonlinear adaptive robust controller. Finally, the numerical simulations to the vessel "YUKUN" clearly show that the two proposed controllers have good control performance and strong robustness to the external disturbance and the model perturbation.At the same time, some important conclusions are obtained.The ship rudder/fin joint control system is a new roll stabilisation equipment derived from the fin roll stabilisation and rudder roll damping, which could improve the effect of the roll stabilization while guaranteeing the course-keeping precision of the ship steering system.Firstly, a nonlinear mathematical model for the rudder/fin joint system, which could describe the nonlinear characteristics of the ship steering system, has been built. Through the further theoretical analysis, a concise nonlinear rudder/fin joint robust control scheme derived from the Backstepping method combined with MIMO CGSA is proposed. Secondly, due to the utility restriction of Backstepping method, a simplified rudder/fin joint nonlinear mathematical model derived from the original model has been built. Then a nonlinear adaptive robust rudder/fin joint controller is proposed with the combination of the adaptive Backstepping method and MIMO CGSA, which could make the design procedure automated and realize the control parameter self-tuning. Finally, with the consideration of the external disturbance and the rudder/fin servo systems, the simulation results show that the nonlinear adaptive robust controller has nice performance and strong robustness.