| Promoting marine science and technology innovation is an indispensable and important measure to achieve a powerful marine country,and underactuated unmanned vehicles(UUVs)with autonomous navigation capabilities and high-precision multi-tasking systems have become a global research hotspot.High-precision path following control technology under severe sea-conditions is a key technology in the design of autonomous control system for UUVs,which is extremely challenging,and not been effectively achieved.In this paper,a guidance-control scheme based on finite-time observers is designed to achieve the accurate path following control of UUVs subjected to time-varying large sideslip angle and unknown external disturbances.Firstly,different from the existing line-of-sight guidance methods,such as integral line-of-sight guidance(ILOS),adaptive line-of-sight guidance(ALOS),etc,this paper completely avoids small angle approximation and slowly time-varying assumption for the sideslip angle.A finite-time sideslip observer(FSO)is created to exactly estimate time-varying large sideslip angle,which makes the observation errors converge to zero in a finite time.Based on the finite-time sideslip observation,a sideslip-tangent line-of-sight(SLOS)guidance scheme is proposed to exactly compensate for the time-varying large sideslip angle,which improves the accuracy and the robustness to the unknown time-varying large sideslip.The stability of the guidance system is strictly proved by the Lyapunov theory,and the simulation results and comparative analysis verify the effectiveness and superiority of the obtained guidance method.Secondly,to eliminate the influence of nonlinear disturbances,unmodeled dynamics and external disturbances on control system,a fuzzy observer(FO)with asymptotic approximation is designed to accurately observe unknown dynamics by constructing an auxiliary dynamic variable and weight parameter adaptive law,and overcomes the limitations of previous fuzzy observers with bounded observation.By virtue of combining auxiliary observation dynamics with adaptive approximation error compensation,the FUO is innovatively devised to accurately complex unknowns rather than bounded observations.FO-based robust adaptive tracking control laws are eventually synthesized and ensure that the guided signals can be globally asymptotically tracked.The simulation results and comparative analysis verify the effectiveness and superiority of the proposed FO-based fuzzy adaptive tracking control law.Then,in order to further improve the observation accuracy of the observers,a finite-time disturbance observer(FDO)is designed to accurately observe unknown disturbances and breaks through the accuracy and converge speed limitations of the previous observers.Combined with the backstepping control technology,robust tracking controllers based on finite-time observer are separately designed to achieve accurate tracking of the guidance signals.This strategy improves the control accuracy and anti-disturbance ability of the control system.Finally,to enhance the overall robustness of the path following control system,the surge and heading tracking controllers are separately designed based on an integral sliding mode(ISM)and a non-singular terminal sliding mode(NTSM).By combining a FDO and finite-time controllers,a finite-time observation-control scheme is designed,which makes all error signals can converge to zero in a short time,and achieves accurate path following control of UUVs under the influence of unknown time-varying large sideslips and complex unknown dynamics.The stability analysis and simulation results verify the effectiveness and superiority of the path-following control strategy for UUVs. |
