Disturbance Observation Based Composite Trajectory Tracking Control Of Unmanned Underwater Vehicles

Recently,with the increasing complexity of underwater operation task,the requirements of the trajectory tracking control algorithm have raised since the onefold control schemes are not able to solve the multi-indexes optimal control issue for trajectory tracking of unmanned underwater vehicle under the condition of system internal uncertainties and external distur-bances.In this dissertation,to obtain trajectory tracking performance of fast convergence,high accuracy and robustness for unmanned underwater vehicle in complex environment,together with disturbance observation based control,several control schemes have been pro-posed to cope with high-quality trajectory tracking of unmanned underwater vehicles,the main research results are summarized as follows:For the model construction issue of unmanned underwater vehicles under complex un-derwater environment,using the Lagrange model framework,an unmanned underwater ve-hicle dynamic model is constructed with the actuator saturation limits,whereby the paramet-ric uncertainty,structural uncertainty,external perturbations caused by underwater waves,currents and unknown flow fields are assembled into a lumped disturbance term.For the robust adaptive trajectory tracking control issue of unmanned underwater ve-hicles with complex external disturbance,parametric uncertainty,unconstructed dynamic-s and actuator saturation,using the dynamic surface control framework,a succinct fuzzy neural disturbance observer with matching-,generating-,pruning-,and merging of rules,is proposed to accurately online capture the lumped disturbance term,and an auxiliary system is aslo introduced to handle the effect of actuator saturation,such that the closed-loop stabil-ity and boundedness of signals are guaranteed.Numerical simulations demonstrate that the proposed control scheme can provide fast,accurate and strong robust tracking performance.To improve the real time of control system,for the finite time trajectory tracking prob-lem of unmanned underwater vehicles,under the dynamic surface control framework,by introducing input saturation error to be a component of internal disturbance,then the lumped disturbance term is identified by using a nonlinear disturbance observer,the second-order sliding surface and control law is proposed as well,such that the finite time stability of closed-loop system and the finite time convergence of signals therein are guaranteed.The numerical simulations demonstrate that the proposed control scheme can not only ensure the accuracy and robustness,but also can effectively improve the system fast-convergence.To further improve the real time of control system on the basis of finite time control and to eliminate the relationship between convergence time and system initial states,for the fixed time trajectory tracking problem of unmanned underwater vehicles,a fixed time distur bance observer is proposed based on super-twisting algorithm to online estimate the lumped disturbance term which contains the input saturation error.Moreover,using the reaching law control,a variable-gain fixed time reaching control law is proposed to guarantee the fixed time stability of closed-loop system and fixed time convergence of signals.Numerical simulations demonstrate that the proposed control scheme can provided the control perfor mance of finite time control,and a further improvement on system fast convergence is also provided.The bounded stability,finite-time stability and fixed-time stability can be ensured by above mentioned schemes such that the speedability,accuracy and strong robustness require-ments of unmanned underwater vehicles in specific underwater missions can be satisfied.