Finite-time Formation Control Of Under-actuated Ships Using Nonlinear Sliding Mode Control

With the prosperity of global commodity trade,shipping acts as the most fundamental part of the logistics and transportation industry due to its characteristics of larger capacity,lower cost,and higher security.What's more,with the rise of the concept of Unmanned Vehicles,the technologies related to unmanned ships plays a significant role in the development strategies such as Intelligent Transportation and Made in China 2025.Therefore,the application and development of advanced intelligent control algorithms in maritime field is of great and profound importance for the improvement of national comprehensive strength.With regard to most ships used for maritime transportation and offshore operations,their side thrusters usually become invalid while they are sailing at a normal speed.This so-called characteristic of under-actuation,apart from essential nonlinearity,environmental disturbance and parameter perturbation,makes the motion control of surface ships even more challenging.In addition,ship formation proves to have better performance in fault tolerance and robustness for maritime operations,and it also has stronger adaptability and greater efficiency for complex tasks.Therefore,formation control of surface under-actuated ships has attracted widespread attention in recent years.On another hand,in light of the timeliness concerns in practical engineering,finite-time control,as a novel control approach superior than traditional asymptotic control,has developed rapidly due to its faster convergence speed and higher control accuracy.Therefore,how to conduct research on finite-time formation control of surface under-actuated ships based on available theories and methods has become a research focus for the maritime community and the control community.In this thesis,an in-depth research and exploration on achievements for formation control of surface under-actuated ships has been conducted.The main work can be stated as below:Under the framework of leader-following approach,a novel finite-time formation control scheme for under-actuated ships is put forward in this thesis with the utilization of nonlinear sliding mode control method.By means of partition design of control schemes,not only the finite-time formation control objective of surface ships can be ensured,but also the singularity problem occurs in traditional terminal sliding mode control can be overcome.Then,finite-time stability of the formation control algorithm is guaranteed via Lyapunov stability analysis,and effectiveness of the proposed method is also verified through Matlab simulations.Finally,this thesis is summarized,and some key problems for formation control of under-actuated ships are partly given.