A discrete adaptive variable-structure controller for MIMO systems, and its application to an underwater ROV

This paper addresses discrete-time variable structure control for multiple input-multiple output (MIMO) systems. Two control algorithms are presented, obtained extending to the multivariable case two control techniques previously proposed by the authors (1995) for single input-single output (SISO) systems. Both techniques consist of variable structure control laws cascaded to a generalized minimum variance controller. The former algorithm refers to a completely known system, while the latter has been designed to deal with parameter uncertainties in the plant. In this case, the connection with a MIMO online parameter estimator has been considered. Proofs are provided about the convergence of the proposed control laws. The presented algorithms have been applied to the problem of position and orientation control of an underwater remotely operated vehicle (ROV) used in the exploitation of combustible gas deposits at great water depths. Resulting performances have been tested by simulation, modeling the ROV with a nonlinear differential equations system. Results have been discussed and compared with recent literature