Design of Robust H_∞ Control for Stabilizing of Stratospheric Airship with Parametric Uncertainty and External Disturbance

Airship is kind of aerial vehicles that has been a significant development of scientific research in recent years. Furthermore, stratospheric airship is in group of lighter-than-air aerial vehicles. This device is designed in order to the ability of unmanned autonomous operation with remote control at a height of 22 kilometers from Earth. With the development of control systems, there are still major challenges in this area. In this paper, in order to stabilizing and trajectory tracking of stratospheric airship, nonlinear H_∞ method has been developed. At first, the dynamic model of an airship is introduced and descriptive equations are presented in an appropriate state-space in order to design a controller based on nonlinear H_∞ method. Then the nonlinear H_∞ controller is designed. In the controller the integral of the position error is considered, allowing the achievement of a null steady-state error when sustained disturbances are acting on the system. The external disturbances are considered as aerodynamic forces and torque. This strategy is designed robustness, against of external disturbance. The results are shown that decrease in steady error and stabilizing system against external disturbance and uncertainties. Also for robustifying of designed control, comparison is done with adaptive control. Simulation results in the presence of aerodynamic disturbances, parametric and structural uncertainties are presented to corroborate the effectiveness and the robustness of the proposed strategy.