Research On Trajectory Tracking Control For Underactuated UUV With Nonlinear Constrained Factors

With the gradual deepening of marine development and more sophisticated unmanned undersea vehicle(UUV)technology,underactuated UUVs have become one of indispensable equipments in exploration of marine resources,marine scientific research and maritime military operations.The UUV's motion control technology is the necessary prerequisite to perform various missions.Compared to other forms of motion,the trajectory tracking of UUV belongs to a high maneuverability motion problem.Its research is still in theoretical explora-tion stage.Therefore,this thesis will choose the very challenging control problem for trajectory tracking of an underactuated UUV as the core of the research.Through analyzing in depth domestic and foreign research achievements regarding the trajectory tracking control for marine vehicle(including surface vessel,USV,UUV/AUV,ROV and so on),it is possible to summarize the challenges of trajectory tracking control for an underactuated UUV and the various nonlinear factor constraints that affect the trajectory tracking control performance.Then,the trajectory tracking issues of an underactuated UUV with various nonlinear factors are studied using the bio-inspired filtered backstepping,the nonlinear integral sliding mode control(SMC),the equivalent output injection sliding mode observer(SMO)and so on.This thesis intends to undertake the following works:Firstly,the standard motion equations for an underactuated UUV are derived based on the kinematics and dynamics of rigid body and the maneuvering theory.Furthermore,considering itself structural characteristics for the subject,its motion model is obtained by simplifying the standard motion equations for an underactuated UUV.Then,the models of various nonlinear factor constraints are established by analyzing their influence in the motion of an underactuated UUV.Finally,the second-order nonholonomic property and small-time local controllability of an underactuated UUV are analyzed by using the dynamics of rigid body and differential geometry.Secondly,for the problem of the trajectory tracking control for underactuated UUVs with constant unknown ocean current,a three-dimensional tracking controller is proposed based on the bio-inspired filtered backstepping and the current observer.The tracking errors in the inertial coordinate frame are converted into the body-fixed coordinate frame by introducing the orthogonal coordinate transformation.Then,two three-dimensional tracking controllers are developed based on the traditional backstepping and bio-inspired filtered backstepping,respectively.Further,considering the ocean current that affects an underactucated UUV in actual operations is difficult to be measured accurately,it is necessary to design the current observer to estimate the velocity of unknown current.Thus,the current observer is introduced into the trajectory tracking controller to compensate the influence of ocean current.Finally,the convergence of the tracking errors under the tracking controller is analyzed based on the Lyapunov stability theory.Thirdly,for the problem of the trajectory tracking control for underactuated UUVs with parameter perturbation,a globally finite-time tracking controller is developed based on the “virtual vehicle” tracking guidance laws and the nonlinear PID integral SMC.Because the parameter perturbation makes it become more complicated and the UUV motion can be approximated as horizontal when performing most missions,the problem of the horizontal trajectory tracking is studied first.And then,the research results are extended three-dimensional situation.Firstly,the horizontal trajecotry tracking guidance law of an underactucated UUV is constructed based on the “virtual vehicle” method,calculated its desired states.Furthermore,the tracking error equations of the horizontal trajectory are build-ed.Then,the tracking errors of the linear velocities are chosen as the virtual control variable,and these controllers are designed based on the equivalent control law of the first-order PI integral SMC.The dynamic equations of the tracking errors are converted to the cascade form by introducing the errors between the tracking errors of the linear velocities and their desired values.Further,the dynamic tracking controllers are derived using the nonlinear PID integral SMC,to achieve an UUV to track the desired trajectory.The stability of the designed horizontal tracking controllers is analyzed based on the finite-time Lyapunov stability theory.Then,the “virtual vehicle” tracking guidance laws are extended from the two-dimension to the three-dimension,to make the present point on the reference trajectory map to the desired states of an UUV.Then,a globally finite-time three-dimensional tracking controller developed based on the nonlinear PID integral SMC.The parameter perturbation is reduced effectively by the reaching law with the gain regarding the upper bound of parameter perturbation.Finally,for the problem of the trajectory tracking control for underactuated UUVs with unobservable linear and angular velocities,a finite-time output feedback tracking controller is developed based on the equivalent output injection SMO and the first-order integral SMC.The motion state observer of an UUV is developed based on the equivalent output injection SMO,to estimate the linear and angular velocities.Then,the dynamic controller is designed by using the first-order integral SMC,to achieve the tracking errors converge to zero in the finite time.Using the finite-time Lyapunov stability theory,the output feedback tracking controller is analyzed.Finally,the anti-windup control method is used to develop the tracking controller to compensate the input saturation nonlinearity by introducing a stable auxiliary system into the three control channels of the surge velocity,pitch angle velocity and yaw angle velocity respectively.