Non-linear controller with switched control law for tracking control of non-cruising AUV

Noncruising AUVs have to be controlled directly by thrusters placed in suitable directions. Some of the problems for controlling noncruising AUVs in precise maneuver are: nonlinear dynamics of AUV, uncertain output from thruster in nonsteady condition, slow response during thruster reversal, and substantial noise in sensor data when the quantity to be measured is small. Practically when plant parameters are uncertain, tracking performance deteriorates significantly when the output is corrupted by noise for most controller design methods. Based on sliding control methodology, a nonlinear, robust controller with switched control law is proposed for the tracking control of noncruising AUV. Controller design can be done with only rudimentary knowledge of the dynamics of the system, without the need of accurate parameter identification. In this system output error feedback is switched on and off by looking at the measurement output and its derivatives. Since the derivatives are not used directly in the feedback, chattering can be reduced. Position tracking is possible in realistic conditions with noisy measurement data. Although identification model is not necessary for the design, performance can be further improved by including such model as feed forward controller. To fine tune the performance of the controller, methods of successfully using identification model and digital filters is discussed. The controller is implemented on the noncruising AUV `Twin-Burger´ of the University of Tokyo and experiments are carried out to verify the performance of the controller