Improved active disturbance rejection-based full-envelope flight control for a coaxial compound helicopter with multimodal

The coaxial compound helicopter (CCH) system has characteristics such as strong non-linearity, significant coupling, diverse flight modes, as well as control redundancy in the transition mode. This paper proposes a variable-bandwidth extended state observer–based improved active disturbance rejection control (VBADRC) scheme for full-envelope flight control of the CCH. This scheme primarily addresses the influences of disturbances, unmodeled dynamics and parameter uncertainties on the system. A variable-bandwidth extended state observer (VBESO) is proposed to handle the internal unmodeled dynamics and external disturbances of CCH, effectively improving the disturbance-estimation accuracy and mitigating the initial peak phenomenon. To suppress the effects of parameter deviations on the controller in different modes, an adaptive feedback controller incorporating an online adaptive mechanism is proposed to achieve real-time parameter adjustment and disturbance compensation. Furthermore, to manage the control allocation problem during transition flight, a weighted pseudoinverse-based multistage allocation strategy is designed to handle the constantly changing control authorities. The performance of the presented scheme is validated through simulation, demonstrating strong robustness and excellent tracking capability even in the case of external disturbances and internal uncertainties.