Abstract:
The unexpected centroid shift of an aircraft can alter model parameters by introducing additional moments that degrade controller performance. This can lead to failed command tracking or flight accidents. To address these challenges, in this study, an L1 adaptive robust control strategy is proposed based on nonlinear dynamic inversion (NDI). By leveraging the time-scale separation principle, the method integrates L1 adaptive dynamic inversion (L1-NDI) with incremental nonlinear dynamic inversion (INDI) control, thereby substantially enhancing the stability and robustness of the attitude controller. The design concurrently satisfies INDI’s requirements for state derivatives while applying filters to the adaptive control to prevent controller-induced high-frequency oscillations caused by abrupt model parameter changes. First, a dynamic model of the aircraft accounting for centroid shift is constructed. Assuming that the aircraft is a rigid body with constant mass, the net external force and net external moment acting on it after the centroid shift are calculated using Newtonian mechanics, thereby deriving the angular velocity dynamics. In this model, the effects induced by a sudden centroid shift are treated as disturbance terms, thereby establishing an accurate aircraft model with a centroid shift for subsequent simulations. Additionally, the dynamic equations of the attitude angles and angular rates are transformed into an affine nonlinear form to facilitate controller design. Next, a cascaded dual-loop nonlinear controller is designed for attitude angle and angular velocity regulation. This hierarchical architecture achieves precise and stable control of the aircraft attitude via a hierarchical control strategy. A core control algorithm based on the NDI is adopted in the design of the inner-loop control system. By constructing precise nonlinear state feedback channels, it compensates for the strong nonlinear coupling characteristics present in an aircraft's dynamic system in real time, thereby transforming the originally complex nonlinear system into a globally linearized system. Recognizing that NDI performance is fundamentally dependent on the availability of an accurate system model, an L1 adaptive control architecture is incorporated. This hybrid control approach guarantees system stability in the presence of disturbances through its L1-norm condition, while simultaneously resolving the high-frequency oscillation issues characteristic of conventional adaptive control schemes. The combined structure maintains rapid response characteristics while significantly enhancing robust performance. The outer loop for attitude-angle control uses incremental nonlinear dynamic inversion control. This is because the derivatives of the state variables can be readily obtained in the outer loop. This in turn makes the incremental nonlinear dynamic inversion control method particularly suitable owing to its simple structure and strong robustness. Finally, the stability of the incremental nonlinear dynamic inversion and L1 adaptive dynamic inversion control algorithms is rigorously proven based on the Lyapunov theory. Numerical simulations demonstrated that for angular rate tracking, the system successfully re-establishes command tracking within 0.5 s after centroid shift while maintaining minimal error bounds. Regarding attitude angle tracking, the system requires only 0.8 s to stabilize from the instant of centroid shift, achieving a maximum tracking error of merely 0.7°. These results conclusively validate that the proposed control framework not only delivers satisfactory control performance but also exhibits a strong disturbance rejection capability with respect to perturbations induced by an abrupt centroid shift.