Nonlinear backstepping control for an underactuated airship

This book proposes a new trajectory tracking control approach for an underactuated stratospheric airship. There is a two-level structure of the proposed controller. A low-level controller based on nonlinear backstepping method with the rigid body dynamics expressed on vector form stabilizes the attitude and velocity of the airship while a high-level controller performs guidance and trajectory tracking task in the three dimensional (3-D) space. Furthermore a control allocation module based on active set algorithm is incorporated into the low-level controller to optimize the practical control inputs under constraints of actuator saturation. The closed-loop trajectory tracking control plant is proved to be globally exponentially stable through Lyapunov theory. Finally simulations show that nonlinear backstepping trajectory tracking controller can achieve desired tracking performances even if the airship is affected by time delay inputs and exogenous disturbances.