Command-filtered fixed-time trajectory tracking control of surface vehicles based on a disturbance observer

In this paper, we investigate trajectory tracking control of surface vehicles with model parameter uncertainties and external disturbances. The disturbances due to the wind, waves, and ocean currents are combined with the model parameter uncertainties as a compound disturbance. Then, a disturbance observer (DO) is introduced to estimate the compound disturbance, which can be achieved within a finite time independent of the initial estimation error. Based on the DO and, in the context of command filtered control, a novel fixed-time backstepping control scheme is developed, by which the vehicle can track the desired trajectory with all the states globally stabilized in a given fixed time. The effectiveness and performance of the method are demonstrated by numerical simulations.