Research On Application Of Variable Structure Control Technique To Underwater Vehicles Operating In Current

When Autonomous Underwater Vehicle(AUV) navigate or operate underwater, they are disturbed violently by current, so constructing a motion model and realizing precise motion control for AUV operating in current have become an urgent problem need to be solved in the research field of motion control of AUV.The characteristics of current motion and hydrodynamic forces acted on AUV owing to current are analyzed in the dissertation first, and then the six-degree of freedom motion model of AUV operating in current is derived on the basis of former research and dynamics of AUV. For the need of project research, proper simplification to the model is conducted so the three-degree of freedom motion model of UVs is attained.Then the Sliding Mode Control(SMC) technique is applied to motion control of AUV operating in current on the basis of the motion model constructed above. First the principles and some key issues of SMC are introduced, and then position controllers and velocity controllers are designed for the UV researched in this dissertation. To realize decoupling control, a decentralized sliding mode control strategy is selected when designing the Sliding Mode Control System(SMCS). The mathematical model of AUV is converted into a regular form based on a SMCS design method for controllable multi-input linear system. The switching function of SMCS is devised by pole setting method and a new kind control strategy based on exponential tendency ration is proposed to weaken chattering phenomenon.In conclusion, simulation experiments are carried out. The simulation results show that, on the one hand, the motion model constructed in the dissertation can reflect truly the motion state of AUV operating in current, on the other hand, the SMCS give nice performance in both clam water and current situation.