A Study On Novel Sliding Mode Control Of Motion Control Of Unmanned Underwater Vehicles

With the globally increasing demand for energy consumption and exhausting of non-renewable energy resources on land,great attention has been increasingly payed to the exploitation of marine resources.This demand pushes the rapid technological advances and wider application of unmanned underwater vehicles(UUV’s)for deep sea explorations.Due to the highly nonlinear vehicle dynamics,unstructured underwater environment,environmental disturbances and modeling uncertainties involved in the hydrodynamic coefficients,development of high performance motion control systems for UUV’s remains a big challenge.Among the existing control methods for nonlinear dynamic systems,sliding mode control has a strong robustness in dealing with model uncertainties and external disturbances.However,the traditional sliding mode control can hardly achieve the desirable performance in some cases.Therefore,advanced sliding mode control methods are proposed,such as terminal sliding mode control,global sliding mode control,second order sliding mode control.However,few of these methods has been experimentally verified in UUV’s motion control.The application of novel sliding mode control method on UUV’s motion control is studied in this thesis.Firstly,the fundamentals of sliding mode control theory are introduced briefly and comparative studies are conducted for several advanced sliding mode control methods via simulations based on Matlab/Simulink.Secondly,a novel nonsingular terminal sliding mode control method combined with global sliding surface is proposed via Lyapunov stability analysis.Compared with the aforementioned advanced sliding mode control methods,the novel approach exhibits superior performance.Finally,to make a further validation,this novel approach is applied in motion control of various types of UUV’s,i.e.depth control of hovering Autonomous Underwater Vehicle(AUV)and combined depth/heading control of DOE HD2+2Remotely Operated Vehicle(ROV).The results of both tank and field tests demonstrate the desirable performance of the motion control systems.