Discrete-time quasi-sliding mode control of underwater vehicles

This paper presents a novel discrete-time quasi-sliding mode controller for the multiple-input multiple-output underwater vehicle system. First, according property of slow time-varying dynamics system, an on-line estimation method is used to eliminate the uncertainties of the underwater vehicle systems. Second, combined with the constant term and uncertainties estimation in the dynamics model, the discrete-time quasi-sliding mode control law is designed. And third, the chattering terms in the designed controller are eliminated by using the sliding surface exponential convergence method. Computer simulation is performed for a numerical model of an underwater vehicle in surge, sway, and yaw degrees of freedom. Results show the effectiveness of the proposed control law in the presence of system uncertainties and external disturbances without any predictive control techniques or intelligent control methods.