Incorporating thruster dynamics in the control of an underwater vehicle

Abstract

The dynamics of an underwater vehicle are greatly influenced by the dynamics of the thrusters. Precise control, for example to perform repeatable survey or coordinated vehicle/manipulator control, should incorporate knowledge of thruster dynamic behavior. An energy-based lumped parameter model of the nonlinear thruster dynamic response is developed and experimentally verified using static and dynamic thruster relationships. Three controllers to compensate for the nonlinear dynamics are designed including analog lead compensation, model-based computed torque and adaptive sliding control techniques. The proposed controller designs are implemented and evaluated in a hybrid, one degree-of-freedom vehicle simulation using an actual thruster under digital control as the actuator. Controller evaluation and comparison is based on observed vehicle tracking performance. The incorporation of thruster dynamics is shown to significantly improve vehicle tracking performance. Superior, robust tracking performance with significant model uncertainty is demonstrated in the application of the adaptive sliding control technique. The evaluated adaptive controller structure may permit on-line adaptation to complex hydrodynamic phenomena associated with complete vehicle/thruster configurations such as cross-flow and mutual interference.