An improved predictor LOS-based global fixed-time prescribed performance controller for the path following of underactuated marine surface vehicles with input saturation

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A fixed-time controller based on improved fixed-time predictor line-of-sight (FxTPLOS) guidance and a nonsymmetrical prescribed performance constrained controller is designed for the path-following of underactuated marine surface vehicles (MSVs) in the presence of unknown external disturbances and uncertainties. First, a fixed-time error prediction model is established, and an internal model-controlled observer is designed to observe the sideslip angle, which can extend the estimated range of the sideslip angle to any range. Second, a nonlogarithmic performance function is introduced that can converge the error to a prescribed range, and a fixed-time controller is designed by error transformation. A new input saturation function is added to solve the problem of input saturation, and a new filter is added to avoid differentiating the virtual control law. Third, a novel fixed-time lumped disturbance observer is proposed for estimating the model uncertainty and external disturbances. It is possible to achieve accurate disturbance compensation. By using Lyapunov theory to analyze the stability of the closed-loop control system, it is proven that the system can be uniformly globally fixed-time stable (UGFxTS). Finally, simulation experiments prove that the control strategy proposed in this paper is effective.