On Fuzzy-approximator-compensator-based Saturated Tracking Control Of Autonomous Underwater Vehicles With Configuration Switching

The ocean is rich in energy,mineral and biological resources,but much of it is still largely unexplored.Especially into the 21 st century,the ocean attracts more and more attentions.Usually,specialized and intelligent marine engineering equipments are required to explore and develop the ocean.As a new kind of marine engineering equipments,autonomous underwater vehicles(AUVs)are now moving towards deeper and wider ocean space with the special mission entrusted by operators.The intelligent motion control technology is one of the core technologies of AUVs.However,the complex and time-varying ocean environment,nonlinear hydrodynamic coefficients of the body,input saturation,actuator dynamics and variable-speed operation render the motion control of AUVs challenging.Therefore,it is of theoretical and practical value to carry out the research on fuzzy-approximator-compensator-based saturated tracking control of AUVs with configuration switching.In this thesis,the state-of-the-art regarding the tracking control of AUVs is first investigated.Then,this thesis takes the exploration type AUV as an example and designs a path following controller for this AUV exposed to configuration switching,dynamics and saturation.Through motion modeling,algorithm design,theory analysis and simulation verification,from two-dimensional decoupling control to three-dimensional coupling control,and from under-actuated configuration to over-actuated configuration,the research is carried out systematically to solve the problem of path following control with system uncertainty,input saturation,actuator dynamics and configuration switching.Specifically,the contributions and main research content of this thesis are summarized as follows:(1)Complete dynamics modeling and thrust performance evaluation based on maneuvering forecast: Based on the existing dynamics modeling of AUVs,this thesis invesitgates the dynamics modeling of the onboard actuators including the rudder surface,main propeller and auxiliary through-body thrusters throughout its full speed profile,especially the nonlinear modeling of the through-body thrusters with the forward speed,and then introduces the intrinsic input saturation and dynamics of these actuators.Based on the complete AUV dynamics model,the maneuvering forecast and thrust performance evaluation of the rudder surface and through-body thrusters throughout its full speed profile is completed,respectively.The speed intervals of low-speed fully-actuation and high-speed under-actuation are determined,and then the intermediate transition interval is connected by using smooth actuator “logic switching flow”,which provides data support and theoretical basis for the subsequent configuration switching.(2)Robust saturated adaptive path following controller based on fuzzy-approximator-compensator: For the under-actuated mode corresponding to the maximum intersection of actuation configurations throughout the speed profile,the moment “delay” characteristic caused by the rudder dynamics increases the order of the dynamics system.To solve this problem,a model-based high-order path following controller is designed based on time-varying line-of-sight guidance and feedback linear backstepping technology.Then,under the consistent framework,adaptive fuzzy approximator and adaptive error estimation technique are used to solve the problem resulted by system uncertainty and high-order complex computation,relaxing the dependence on hydrodynamic coefficients,and avoiding the high order derivative calculation as well as the potential control chattering behavior induced by the dynamics characteristic.Subsequently,an adaptive fuzzy compensator is introduced into the consistent framework to eliminate the potential instable behavior of path following for the under-actuated AUV with input saturation.Finally,compatative simulations among different controllers and using classic AUV model varify the performance of the proposed robust satuarated adaptive controller.(3)Robust saturated path following controller for an AUV with configuration switching: Considering the demand of time-varying forward speed,a unified control architecture for AUV path following with configuration switching is designed,which is composed of active pitch control and passive heave control.The forward speed tracking controller and the normalized pitch moment adaptive controller are designed based on the fuzzy-approximator-compensator method,respectively.A smooth bounded “thrust allocation flow” is designed by combining the smooth actuator “logic switching flow” with the normalized saturated pitch moment.Then,the heave thrust passive control strategy combined with threshold analysis and slipping disturbition is resorted to ensure the uniqueness and boundedness of the horizontal rudder and the through-body thruster commands,so that the actuactor switching control is completed without distortion.Therefore,the stability of the AUV tracking control is relatively independent of the configuration switching.Finally,stability analysis and comparative simulations with different intial postures and environmental disturbances are provided to illustrate the asymptotic stability of the tracking position and attitude errors of the designed two-dimensional path following controller with configuration switching and the characteristic of on-demand bounded thrust allocation.(4)Cascaded three-dimensional accurate path following and switching control based on an improved line-of-sight guidance law: To solve the multi-variable space coupling difficulty in three-dimensional control,this thesis adopts a cascaded tracking control framework composed of the kinematics guidance subsystem and the dynamics tracking subsystem,which avoids the high-order derivative in the entire backstepping design as well as the spatial curvature and torsion calculation.In the kinematics guidance subsystem,the moving path coordinate system is introduced,which eliminates the coupling effect of the third rotation of the space Serrent-Frenet coordinate system around its x axis.The traditional three-dimensional line-of-sight guidance law is modified based on the proposed “equivalence principle” of space coordinate transformation,and the exact coupling nonlinear relationship between the attitude angle and the orientation angle is clarified.By resorting to Lyapunov technology,the position error is decoupled into the attitude angle error.Subsequently,the two-dimensional saturated dynamics tracking control law can be rapidly extended to three-dimensional path following.Based on this idea,the research of three-dimensional path following and switching control of an AUV with multi-variable coupling is carried out,and cascade stability analysis and comparative simulations using classic PID controller,different initial postures and environmental disturbances are given in details.