Design of robust backstepping controller for unmanned aerial vehicle using analytical redundancy and extended state observer

In current flight control system (FCS) practice for unmanned aerial vehicles(UAVs), flight safety becomes more and more important in extreme weather or in the face of sensor and control effector failures. Flight safety is guaranteed traditionally by specifying functionally redundant control hardware. Compared with extra burden increased by hardware redundancy on UAV, design of analytical redundancy becomes attractive in recent years. This paper proposes a new hybrid design scheme of analytical redundance FCS, which is composed of analytical redundance, core flight control algorithm and uncertainties compensator. Analytical redundancy for attitude angle rates adopts reduced order nonlinear state observer method. The core backstepping flight controller realizes linearization and decoupling of the highly nonlinear and tightly coupled UAV model. For cancelling out uncertainties such as unmodeled dynamics and external disturbances, an extended state observer(ESO) compensator is designed to enhance the robustness of FCS. Pseudoinverse method is applied to establish the mapping between moments and multiple control surfaces. Numerical simulation shows that UAV equipped with the hybrid control scheme has good maneuverability, strong self-learning ability of compensating the unmodeled dynamics and enough robust stability against constraints of actuators.