Nonlinear control of three‐dimensional underactuated vehicles

This paper presents the derivation of robust trajectory‐tracking nonlinear control laws for general three‐dimensional vehicle models with one degree of underactuation where all of the state tracking errors are stabilized. The method is based on a novel transformation of the trajectory tracking problem into a reduced‐order error dynamics. Two traditional nonlinear controllers based on sliding mode and backstepping approaches are developed and shown to stabilize the trajectory tracking errors in presence of modeling uncertainties and bounded disturbances. The performance of the two controllers are compared in absence and presence of disturbances.