Finite-time Sliding Mode Trajectory Tracking Control Of Autonomous Underwater Vehicles In Complex Interference Environment

The ocean is rich in natural resources and unlike the terrestrial environment,the marine world is full of unknown factors,which bring many challenges to the exploration of the ocean.As an important tool for underwater geological exploration,maritime rescue and other activities,autonomous underwater vehicle(AUV)provides the possibility to study the mysteries of the ocean.Considering the strong nonlinearity,uncertainty,time variability and coupling of AUV,the establishment of AUV model is affected.Due to the particularity of the movement environment,it is inevitable that there will be uncertain disturbances(such as waves and ocean currents)during navigation,which bring difficulties to the motion control of AUV.Thus,it is challenging to design a high-precision controller to complete a given task.Based on sliding mode control,this thesis investigates the trajectory tracking control of AUV under different constraints.The primary contents are summarized as follows:1)The finite-time sliding mode trajectory tracking control problem is investigated for AUV system subject to prescribed performance.A prescribed performance function is first introduced to improve the transient and steady-state performance of the tracking system simultaneously.Then,two new PID-type sliding surfaces are constructed such that the closed-loop system can reach the sliding surface with good performance,on which the developed sliding mode controllers can make the tracking error states converge to zero within a finite time.Finally,the simulation verifies the effectiveness of the proposed control schemes.A large number of simulation experiments demonstrate that compared with the first-order sliding mode control scheme,the proposed finitetime second-order sliding mode control scheme has better control effect.2)The fixed-time trajectory tracking control problem is addressed for AUV system subject to asymmetric prescribed performance and unknown velocity.Considering the performance of AUV system is affected by external disturbances and model uncertainties,asymmetric prescribed performance constraints are introduced to improve the transient and steady-state performance of the tracking error system.Aiming at the difficulties brought by unmeasurable velocity to the controller design,a fixed-time extended state observer is constructed to estimate the unknown velocity and external disturbances.By constructing the sliding surfaces,two continuous output feedback controllers with high control accuracy and low energy consumption are proposed,and then the Lyapunov function is established to analyze the fixed-time stability of the closed-loop system.Finally,the feasibility of the proposed control algorithms is verified by a large number of simulations.3)The finite-time trajectory tracking control problem is studied for AUV system subject to unknown Markovian disturbances and white noise disturbances.In the first step,a disturbance observer is designed for the unknown external disturbances which are modeled by the Markovian jump system.In the second phase,the observer-based sliding mode controller is designed,which effectively resists white noise disturbances,and ensures that the tracking error states reach the sliding mode surface in a finite time,and converge to zero in a fixed time along the designed sliding surface.Further,considering the model uncertainties in the AUV system,the sliding mode controller is designed correspondingly to achieve trajectory tracking.Finally,simulation verifies the feasibility of the proposed control schemes.