AUTONOMOUS UNDERWATER VEHICLE ROBUST CONTROL

ABSTRACT
This paper discusses the autonomous underwater vehicle (AUV) control performance
under uncertainty using two different methods, linear quadratic (LQ) servo with command
following and sliding mode control (SMC). In spite of the uncertainty in our evaluations of
the hydrodynamic forces, it is fortunate that the use of feedback control is able to compensate
for this general lack of knowledge and to provide commands to actuators that control and
stabilize the motion of underwater vehicles. Robustness is obtained by using feedback of key
motion 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 be
automatically compensated. In order to successfully recover or launch a vehicle it will be
preferred for the vehicle to have the capability to compensate for this motion. This paper
attempts to investigate a means by which a vehicle may be made to track, in depth, the
dynamic motion for launch and recover at some significant depth below the surface. Design
techniques for robust controllers typically use frequency response or state space techniques to
specify control gains and even include observers and model based compensators to replace
missing sensors with virtual sensors. While these techniques have definable robustness
properties, sliding mode control and (LQ) servo with command following - techniques that
can compensate for known nonlinear behavior - are convenient and has equally definable
robustness properties.
This paper conducts robust control using (LQ) servo with command following and
sliding mode control (SMC) which have been found useful and convenient in dealing with the
uncertainty and general nonlinear nature of the models developed previously.