Robust constraint backstepping control for high-performance aircraft with account of unsteady aerodynamic effects

Abstract

This paper presents a robust constraint backstepping control scheme for high performance aircraft attitude tracking in the presence of physical constraints, model uncertainties and unsteady effects. The six-degree-of-freedom aircraft model with unsteady aerodynamics is first established, of which the characteristics are investigated through open-loop analysis. Based on the immersion and invariance approach, a state observer is developed to estimate the unmeasurable unsteady aerodynamic states. The unsteady effects are then compensated in the controller design where the bounds of estimate errors and model uncertainties are used to increase robustness. In addition, a command filter is introduced to impose physical constraints on states and control inputs and overcome the ‘explosion of terms’ problem. An auxiliary system of which the states are applied to the controller design is constructed as well to evaluate the constraint effects. Furthermore, stability of the closed-loop system and convergence of the tracking error are proven by Lyapunov stability theorem. Finally, several numerical simulations are performed to verify the effectiveness and robustness of the proposed control scheme.

Observer-based dynamic surface control for high-performance aircraft subjected to unsteady aerodynamics and actuator saturation

“…Simulation results are presented in Figure 2. For the quasi-steady model, incidence angles undergo smaller amplitude and faster convergence rate at low AOA, which are consistent with the results reported in Wang et al 30,31 However, the disturbance results in much differences at high AOA. The incidence angles show acute changes and do not return to the initial condition for both models.…”

“… β r , p sr are set to zero to neglect the coupled responses. Since the longitudinal unsteady effects mainly focus on α ∈ [ 30 ∘ , 60 ∘ ] , 30 α r is selected as a piecewise constant command expressed as…”

“…The design parameters and initial conditions are kept unchanged in this simulation. Herbst maneuver is simulated to account for the couplings between longitudinal and lateral motions, and α r , β r , p sr are defined in Zhou et al 30 To perform fair comparisons, the command filter in CFBC is replaced by first-order filters which have same parameters as that in CDSC. Moreover, the way of addressing unsteady effects and model uncertainties are identical in both control schemes, and the only difference is the saturation compensation mechanism.…”

“…Therefore, unsteady effects are added to enhance the model accuracy. By identifying the forced-oscillation test data, unsteady aerodynamics can be modeled in the following form 30,31…”

“…with b i > 0 , a i , b i , i = Y , Z , l , m , n are fitting polynomials whose expressions and coefficients are given in Zhou et al 30 Note that the unsteady effects will converge to zero exponentially as maneuver ends because equation (6) is stable.…”