In this paper, the trajectory tracking control of underactuated autonomous underwater vehicle without measuring velocity in three-dimensional space and in the presence of unknown disturbances caused by waves and ocean currents is studied based on dynamic surface control for the first time. In order to estimate parametric uncertainties with underwater vehicle dynamic model, radial basis function neural network approximation technique has been proposed. Also, the output feedback control problem is resolved by employing a high-gain observer to estimate the required unmeasurable states. The stability of the proposed controller is investigated by an analysis based on Lyapunov theory and uniform ultimate boundedness stability of states and convergence of tracking errors to a small bound around the origin are guaranteed. Finally, the tracking performance of the proposed control scheme has been verified via computer simulations.

In this paper, the trajectory tracking control problem for a team of nonholonomic tractor-trailer wheeled mob­ile robots has been investigated based on the leader-follower strategy in the presence of structural uncertainties and external disturbances. For this purpose, the kinematic and dynamic equations of the formation of tractor-trailer robots are presented and leader-followerchr('39')s model is produced by defining the state error vector at first. Then, a nonlinear disturbance observer is designed by using the formation dynamic model to estimate and compensate the external disturbance and a new model of the system is obta­ined. In the following, a finite-time dynamic surface controller has been designed and presented by con­sidering an observer-based model. The proposed scheme ensures closed-loop signals boundedness and fast c­o­n­v­er­gence of tracking errors in a limited time. Furthermore, the par­a­m­etric uncertainties are estimated by using a fuzzy adaptive estimator with a great accuracy. Finally, the finite time stability of the closed-loop control system is proved by Lyapunov theory and the effectiveness of proposed algorithm is sho­w­n by simula­tions.

In this paper, the control problem of a finite-time target tracking for an underactuated autonomous submarine is considered in three-dimensional space in the presence of unknown disturbances caused by waves and ocean currents via Dynamic Surface Control (DSC) method. At first, computational complexities of the backstepping method are greatly reduced by employing the DSC technique. Next, by designing a finite-time controller, it can be demonstrated that system errors converge to a small region containing the origin in a finite time. An adaptive robust controller is employed to compensate for unknown vehicle parameters and uncertain nonlinearities. The stability of the proposed controller is demonstrated by an analysis based on Lyapunov theory. Finally, the tracking performance of the proposed control scheme is simulated by MATLAB software and its effectiveness is shown as well.