Discrete-time quasi-sliding mode control of an autonomous underwater vehicle

This paper presents a discrete-time quasi-sliding mode controller for an au tonomous underwater vehicle (AUV) in the presence of parameter uncertaintie s and a long sampling interval. The AUV, named VORAM, is used as a model fo r the verification of the proposed control algorithm, Simulations of depth control and contouring control are performed for a numerical model of the A UV with full nonlinear equations of motion to verify the effectiveness of t he proposed control schemes when the vehicle has a long sampling interval. By using the discrete-time quiasi-sliding mode control law, experiments on depth control of the AUV are performed in a towing tank. The controller mak es the system stable in the presence of system uncertainties and even exter nal disturbances without any observer nor any predictor producing high rate estimates of vehicle states. As the sampling interval becomes large, the e ffectiveness of the proposed control law is more prominent when compared wi th the conventional sliding mode controller.