Planar path following nonlinear controller design for an autonomous airship

This paper investigates the planar path following control problem for an autonomous airship taking actuator saturation, actuator dynamics, parameter variation, and wind field into account. Firstly, improved nonlinear models of the airship are introduced and the control objective is formulated. Then, a command filtered backstepping controller combined with nonlinear disturbance observer is derived based on Lyapunov stability theory. The command filter is adopted to approximate the magnitude and rate saturations of actuator. The first-order inertia term is used to approximate the actuator dynamics. And, the nonlinear disturbance observer is employed to handle the disturbance caused by parameter variations and wind field. To guarantee the controller still works when saturations occur, the compensation terms are also designed. It is proved that the proposed controller can drive the airship to track a predefined path under actuator saturation, parameter variations and wind field. Besides, the proposed approach is able to avoid the complex analytic computation of command derivatives which is required in traditional backstepping method. Finally, simulations are carried out to illustrate effectiveness of the proposed controller.