MULTIVARIABLE SLIDING MODE CONTROL FOR AUTONOMOUS DIVING AND STEERING OF UNMANNED UNDERWATER VEHICLES

A six degree of freedom model for the maneuvering of an underwater vehicle is used and a sliding mode autopilot is designed for the combined steering, diving, and speed control functions. In flight control applications of this kind, difficulties arise because the system to be controlled is highly nonlinear, coupled, and there is a good deal of parameter uncertainty and variation with operational conditions. The development of variable structure control in the form of sliding modes has been shown to provide robustness that is expected to be quite remarkable for AUV autopilot design. This paper shows that a multivariable sliding mode autopilot based on state feedback, designed assuming decoupled modeling, is quite satisfactory for the combined speed, steering, and diving response of a slow speed AUV. The influence of speed, modeling nonlinearity, uncertainty, and disturbances, can be effectively compensated, even for complex maneuvering. Waypoint acquisition based on line of sight guidance is used to achieve path tracking.