Active robust control scheme for uncertainty and flexibility suppression of air-breathing hypersonic vehicles

Inevitable uncertainties and cross couplings between rigid and flexible modes pose huge challenges to control design for flexible air-breathing hypersonic vehicles. This paper addresses an active robust control scheme that can simultaneously suppress uncertainties and flexible modes using active approaches rather than inherent system robustness. Couplings between different rigid and flexible modes are analyzed, providing insights into internal coupling behaviors. Generally, the active robust control scheme consists of two components: a nonlinear extended state observer (ESO) and a notch filter. The ESO is designed to estimate and compensate diverse uncertainties. For specific high-frequency uncertainties, the ESO estimated values could excite the flexible modes and then cause instabilities. So the notch filter is designed to actively suppress the specific high-frequency estimated signals induced by ESO. Both nonlinear and linear approaches are discussed for the notch filter design. At last, several representative simulations are conducted to demonstrate the advantages of the proposed active robust control scheme.