Elegant Anti-disturbance Control For Dynamic Positioning System Of Ships

In the process of sailing in the complex marine environment,the ship is inevitably affected by the disturbances from the oceans,such as wind,waves,currents and other uncertain marine environment factors,which will reduce the control performance and even make the dynamic positioning(DP)control system unstable.Therefore,high anti-disturbance control capability and strong robustness are important aspects in the DP ship control research.Based on this background,by using disturbance observer-based control(DOBC)method,elegant anti-disturbance control(EADC)for the DP system of ships under the disturbance of several different marine environments is studied.The main content is divided into the following four aspects:Firstly,the anti-disturbance control problem of the DP system of ships with slowly varying environmental disturbances caused by second-order wave drift,wind,ocean currents and unmodeled dynamics is considered.The disturbance observer is established to online estimate slowly varying environmental disturbances with partially known information,which are modelled by adopting stochastic modeling method(first-order Markov process).Then,an EADC strategy is proposed and the stability analysis of the composite system is carried out by using stochastic theory.The slowly varying environmental disturbances can be rejected and attenuated so that the ship from the initial position to the desired position with arbitrary precision.Secondly,the EADC strategy is investigated for the DP system of ships with multiple heterogeneous disturbances,which include slowly varying environmental disturbances,first-order wave-induced disturbances and norm bounded disturbances.Both the velocity and low-frequency position and the bias states(slowly varying environmental disturbances)are estimated online by designing the state and disturbance observer,respectively.Subsequently,a robust filter(RF)is constructed to deal with the first-order waveinduced disturbances,which assures a prescribed performance level for the filter error system.The EADC strategy is proposed through integrating stochastic DOBC theory,RF method and H_? technology such that the high anti-disturbance control accuracy of the DP system can be ensured.Thirdly,the problem of anti-disturbance control is discussed for dynamic positioning system of ships with uncertain model parameters and slowly varying environmental disturbances.The fuzzy logic system is used to approximate the unknown model uncertainties in the dynamic positioning system of ships,and the adaptive disturbance observer is designed to estimate the slowly varying environmental disturbances.Based on which,an EADC scheme based on DOBC method and fuzzy control is proposed,such that higher control accuracy can be achieved.The simulation results on supply ship model are presented to demonstrate the effectiveness of the proposed strategy.Fourthly,this part studies the problem of anti-disturbance control for a class of DP systems with multiple heterogeneous disturbances,which include the white noise and the non-harmonic disturbance with unknown nonlinear function.An adaptive disturbance observer is constructed to estimate the non-harmonic disturbances with unknown nonlinear function,which is approximated by neural network.An EADC scheme is designed by integrated Lyapunov function and linear matrix inequality,such that the expected dynamic performance of the composite system is achieved.