In this paper, a robust sliding mode tracking controller with prescribed performance is developed for an underactuated surface vehicle (USV) with time-varying external disturbances. Firstly, to guarantee the transient and steady-state performance of the closed-loop system, the error transformation technique is presented. Further, the design of the prescribed performance function implements predefined tracking performance constraints, which eliminate the requirement for prior knowledge about the initial errors. Then, a Lyapunov stability synthesis shows that all closed-loop signals remain bounded and the tracking errors remain strictly within the predefined bounds. Finally, simulations and a comparative study are performed to illustrate the robustness and effectiveness of the proposed robust sliding mode control scheme.
In this paper, a six degrees-of-freedom unified model of ship is established based on one dynamic positioning (DP) vessel, in which sea environment models of wind, current and waves are included.Then, the controller of DP ship based on a kind of nonlinear model predictive control algorithm is designed. By choosing an appropriate predictive period, the DP ship can move to the desired position and heading quickly and accurately. Finally, the stability of the developed control system for dynamic positioning of ships is proved by theoretical and simulation studies.
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