Sliding mode heading control of an over-actuated, hover-capable autonomous underwater vehicle with experimental verification

A sliding mode heading control system is developed for over-actuated, hover-capable AUVs operating over a range of forward speeds. A simplified switching function is introduced, and simulation studies are proposed accordingly. The results with this novel switching function show a significant improvement in the chattering problem when compared to other conventional switching function candidates. Studies on sensitivities to a range of hydrodynamic parameter uncertainties are presented, and the parameters that have major influences on the sliding mode control performance are highlighted. The proposed control system is also proven in the field trials to enhance vehicle response, yielding consistent and robust performance over the entire range of vehicle's speeds, even when subjected to external disturbance. It also shows superior heading tracking performance when compared to a P-D approach implemented on the same vehicle. However, this improved performance requires intense control actions as a trade-o_, causing the AUV to expend more energy than with the P-D approach. Path following trials, where the AUV is demanded to follow a set of GPS coordinates at the water surface, are presented. These demonstrate the applicability of the proposed heading control system in a practical operation. The presented SMC scheme can be applied to any vehicle straightforwardly, but the control allocation part may need to be modified regarding the actuator configuration of that vehicle.