ROBUST ADAPTIVE-CONTROL OF UNDERWATER VEHICLES - A COMPARATIVE-STUDY

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.