Robust missile longitudinal autopilot design based on equivalent-input-disturbance and generalized extended state observer approach

This paper presents a new robust design for the longitudinal autopilot of a tail-controlled, skid-to-turn missile based on equivalent-input-disturbance (EID) and generalized extended state observer (GESO) approach. Firstly, the nonlinear missile longitudinal dynamics is modeled as a linear formulation for angle-of-attack tracking with uncertainties and disturbances. Next, as a new method, EID-GESO-based control is proposed for disturbance rejection. The method regards the uncertainties and disturbances as a lumped disturbance, named as EID, and simultaneously attenuates it through estimation of linear GESO and simple feedback. Closed-loop stability of the method is also proved. The most important feature of the proposed method over the others is that there is no requirement for system transformation, differentiation of the measured output, full system state available, exact plant model or any information about uncertainties and disturbances. Subsequently, the method is applied to robust longitudinal autopilot design and the feasibility is illustrated by numerical simulations. Finally, a performance comparison with some notable designs under considerable uncertainties and disturbances is implemented to demonstrate the effectiveness and robustness of the proposed design.