Motion Tracking Control Of Underwater Vehicle

The21st century is the time in which man investigate, develop and utilize the sea.Underwater vehicles are important tools for exploring and exploiting the underwaterresources. Underwater vehicles can be applied to explore unknown underwater worldand accomplish appointed underwater missions. From1950s, with the development ofmodern science and technology, exploration of sea as well, underwater vehicles havebeen paid attention to by lots of research institutes all over the world. The applicationsof underwater vehicles concern to commercial, military, scientific aims.To accomplish kinds of complicated underwater missions, it requires automationand safety of the underwater vehicles, which can be achieved by appropriate design ofcontrol systems. The underwater motion of an underwater vehicle is a complicatednonlinear system with six degrees of freedom, including surge, sway, heave, roll, pitchand yaw. State variables in subsystems are coupling with each other. Some externaldisturbances such as non-uniform current may affect the motion of underwater vehicle.It requires the high performance of control system including tracking system andpositioning system. Research on the control system of underwater vehicle has been oneof hot researches in the world.To guarantee the stability and robustness of control system, many advancedcontrol strategies have been proposed for the control of underwater vehicles, forexample, adaptive control, fuzzy control, sliding variable structure control, H-infinitycontrol and artificial intelligent control (such as neural network based and genealgorithm based etc.) Each control strategy has its advantage and disadvantage. Ahybrid controller in which several control strategies involve provides an effective wayto improve the performance of control system.With the help of theories of linear feedback, Lyapunov stability and L2-gaindesign, a tracking control system is proposed. First, to a certain six-degree-of-freedommathematical model, a tracking control system is designed by inversely dynamiccompensation. In the control system, tracking error and filtered tracking error isintroduced; assistant control input is also designed by using recursive Lyapunov function. Second, uncertain external disturbance, which refers to the environmentalforce, is considered in the plant. L2-gain design is adopted to suppress this disturbance.Also, controller is obtained by using recursive Lyapunov function.