AUTONOMOUS UNDERWATER VEHICLE ROBUST CONTROL

Abstract

ABSTRACTThis paper discusses the autonomous underwater vehicle (AUV) control performanceunder uncertainty using two different methods, linear quadratic (LQ) servo with commandfollowing and sliding mode control (SMC). In spite of the uncertainty in our evaluations ofthe hydrodynamic forces, it is fortunate that the use of feedback control is able to compensatefor this general lack of knowledge and to provide commands to actuators that control andstabilize the motion of underwater vehicles. Robustness is obtained by using feedback of keymotion variables (wind, waves, and current) as measured by sensors to drive actuators which,in turn, manipulate the vehicle's motion so that changes in the behavior of the vehicle can beautomatically compensated. In order to successfully recover or launch a vehicle it will bepreferred for the vehicle to have the capability to compensate for this motion. This paperattempts to investigate a means by which a vehicle may be made to track, in depth, thedynamic motion for launch and recover at some significant depth below the surface. Designtechniques for robust controllers typically use frequency response or state space techniques tospecify control gains and even include observers and model based compensators to replacemissing sensors with virtual sensors. While these techniques have definable robustnessproperties, sliding mode control and (LQ) servo with command following - techniques thatcan compensate for known nonlinear behavior - are convenient and has equally definablerobustness properties.This paper conducts robust control using (LQ) servo with command following andsliding mode control (SMC) which have been found useful and convenient in dealing with theuncertainty and general nonlinear nature of the models developed previously.