Robust control of underwater vehicles: sliding mode vs. LMI synthesis

This paper presents two robust control synthesis methods for an autonomous underwater. The problem statement requires the design of a position and attitude control system for robust vehicle trajectory following. A detailed nonlinear model of the vehicle was derived, an operating point for nominal design was selected, and a multivariable linear model of the vehicle was obtained by linearization around the operating point. The presence of structured uncertainties due to errors in the computation of hydrodynamic coefficients, dynamic linearization and truncation, unknown disturbances, is included in the control synthesis. Two robust controllers were designed: a nonlinear one using a sliding mode approach, and a linear one using linear matrix inequalities (LMI) synthesis techniques. The performance of the two controllers were extensively evaluated and compared in simulation with a full nonlinear model of the vehicle.