Robust Control Of Underwater Vehicles: Sliding Mode Control Vs. Mu Synthesis

This paper presents the results of a controller synthesis where a robust control of an AUV is developed using two different methods. The problem statement requires the design of a position and attitude control system for the vehicle in order to achieve precise trajectory following. Firstly, a detailed nonlinear model of the vehicle was derived. Secondly 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, were considered. Two robust controllers were designed, the first one linear, using standard Mu analysis and synthesis techniques, and the second one nonlinear, using a Sliding Mode approach. The performance of the two controllers were extensively evaluated and compared in simulation with a full nonlinear model of the vehicle.