On the dynamic positioning control of underwater vehicles subject to ocean currents

The underwater vehicle control has two problems to deal with: parametric uncertainty and unknown disturbance. Sliding Mode Control (SMC) effectively addresses these issues and is therefore a viable choice for controlling underwater vehicles. On the other hand, this method is known to be susceptible to chatter, which is a high frequency signal induced by the switching control. In this paper a new control methodology called Model-free High Order Sliding Modes Control (HOSMC) is introduced. HOSMC principal characteristic is that it keeps the main advantages of the standard SMC, removing the chattering effects, this advantage is achieved without model knowledge. Simulation results considering the complete 6 DoF (Degrees of Freedom) hydrodynamic model of an underactuated robot, subject to ocean currents, are presented. Real time experiments of a 1 DoF underwater system are conducted to show control effectiveness.