Experimental testing of an adaptive controller for USVs with uncertain displacement and drag

The automatic launch and recovery of an AUV from a USV presents a challenging control problem because control parameters are chosen based on the dynamics of the vehicle, which can change abruptly and significantly when an AUV is jettisoned or docked. Tight control of the vehicle state is required to conduct an underway recovery, with looser requirements for the launch. Experimental testing of an unmanned surface vehicle has been performed to evaluate the performance of several low-level controllers when displacement and drag properties are time-varying and uncertain. Variable mass and drag tests show that the vehicle is best controlled by a model reference adaptive backstepping speed and heading controller. The backstepping controller developed by Liao et. al (2010) is modified to account for an overprediction of necessary control action and motor saturation. It is shown that when an adaptive algorithm is implemented for the surge control subsystem of the modified backstepping controller, the effects of variable mass and drag are mitigated.