Abstract
This study investigates an adaptive controller for the flexible air-breathing hypersonic vehicles (AHVs) subject to external disturbances and actuator constraints. The combination of nonlinear disturbance observer and adaptive mechanism is exploited to design an adaptive controller for each subsystem. For the velocity subsystem, an auxiliary system is employed to handle the scramjet input saturation issue. For the altitude subsystem, the magnitude/rate constraints and the dynamics of aerodynamic control surfaces are addressed by the control allocation module. Simulations show the effectiveness of the proposed control.
Highlights
Air-breathing hypersonic vehicles (AHVs) have attracted considerable attention in both military and civil fields
In (1)–(5), velocity V, altitude h, flight path angle (FPA) γ, angle of attack (AoA) α, and pitch rate (PR) Q are system states; g is the acceleration due to gravity; mass m and moment of inertia Iyy are decided by the design and fuel level of AHVs; the disturbances dV, dγ, and dQ are external disturbances with bounded derivatives; ηi is the ith generalized elastic coordinate; ωi and ξi are the natural frequency and the damping ratio for flexible mode ηi, respectively; ψi and ψi′ are coupling coefficients between rigid-body and flexible dynamics; thrust T, lift L, drag D, pitching moment M, and ith generalized force Ni have the following curve-fitted approximations: T
In (7)–(10), scramjet fuel equivalency ratio (FER) Φ, canard deflection angle (CDA) δc, and elevator deflection angle (EDA) δe are three system inputs, respectively; q is the dynamic pressure; S is the reference area; zT is the thrust-to-moment coupling coefficient; c is the mean aerodynamic chord; C∗∗ denotes the fitting coefficients of force and moment
Summary
Air-breathing hypersonic vehicles (AHVs) have attracted considerable attention in both military and civil fields. [16] used the disturbance observer-based (DOB) feedback linearization control to overcome constraints on actuators. A combination of backstepping design and nonlinear disturbance observer (NDO) is utilized to handle actuator constraints [17]. [20] developed a control allocation scheme for fault-tolerant control based on a linear parameter varying (LPV) system. Motivated by the above investigations, this paper proposes a disturbance observer-based adaptive control AHVs with constrained actuators. The main contributions of this paper can be briefly outlined as follows: International Journal of Aerospace Engineering (1) The saturation problem of the scramjet, as well as the dynamics and magnitude/rate constraints of the control surface, is taken into consideration (2) NDO is developed in each step to further improve the disturbance rejection property. The rest of this paper is organized as follows: Section 2 formulates the considered problem; Section 3 presents the design process; Sections 4 and 5 give a stability analysis and a simulation study, respectively; Section 6 concludes this study
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