Incremental Backstepping for Robust Nonlinear Flight Control
This paper presents a robust nonlinear flight control strategy based on results combining incremental control action and the backstepping design methodology for vehicles described by strict-feedback (cascaded) nonlinear systems. The approach, referred to as incremental backstepping, uses feedback of actuator states and acceleration estimates to allow the design of increments of control action. In combination with backstepping, the proposed approach stabilizes or tracks outer-loop control variables of the nonlinear system incrementally, accounting for large model and parametric uncertainties, besides undesired factors such as external perturbations and aerodynamic modeling errors. With this result, dependency on the modeled aircraft system is greatly reduced, overcoming the major robustness flaw of conventional model-based flight control strategies. This suggested methodology implies a trade-off between accurate knowledge of the dynamic model and accurate knowledge of the vehicle sensors and actuators, which makes it more suitable for practical application than identification or model based adaptive control architectures. Simulation results verify the tracking capability and superior robustness of the proposed controller under aerodynamic uncertainty with respect to standard backstepping methodologies for a simple flight control example.