Ti. Fossen et Oe. Fjellstad, ROBUST ADAPTIVE-CONTROL OF UNDERWATER VEHICLES - A COMPARATIVE-STUDY, Modeling, identification and control, 17(1), 1996, pp. 47-61
Robust adaptive control of underwater vehicles in 6 DOF is analysed in
the context of measurement noise. The performance of the adaptive con
trol laws of Sadegh and Harowitz (1990) and Slotine and Benedetto (199
0) are compared. Both these schemes require that all states are measur
ed, that is the velocities and positions in surge, sway, heave, roll,
pitch and yaw. However, for underwater vehicles it is difficult to mea
sure the linear velocities whereas angular velocity measurements can b
e obtained by using a 3-axes angular rate sensor. This problem is addr
essed by designing a nonlinear observer for linear velocity state esti
mation. The proposed observer requires that the position and the attit
ude are measured, e.g. by using a hydroacoustic positioning system for
linear positions, two gyros for roll and pitch and a compass for yaw.
In addition angular rate measurements will be assumed available from
a 3-axes rate sensor or a state estimator. It is also assumed that the
measurement rate is limited to 2 Hz for all the sensors. Simulation s
tudies with a 3 DOF AUV model are used to demonstrate the convergence
and robustness of the adaptive control laws and the velocity state obs
erver.