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This paper focuses on the altitude tracking issue for air-breathing hypersonic vehicles. It proposes a rapid altitude tracking method with synthetical consideration on the angle of attack constraint, which is crucial to keep the scramjet away from the inlet unstart. For the inner-loop, the novel compensator is considered in the conjunction of the backstepping approach to design a flight path angle tracking controller. The compensator helps the controller to limit the angle of attack with the uncertainties. For the out-loop of the control system, the altitude controller involves the combination of Bang-Bang control and the sliding mode technique to generate the command which accommodates the constraint on the angle of attack. The atmosphere density model is taken into account, which makes the proposed method more adaptable to the altitude variation. The effectiveness of the proposed control method is evaluated in the simulations. INDEX TERMS Bang-bang control, sliding mode control, backstepping, inlet unstart, angle of attack constraint.

Aiming at the static unstable Hypersonic vehicle, a method for designing H∞ autopilot to satisfy gain margin and phase margin is proposed. Structured H∞ synthesis is used to synthesize the autopilot under the fixed structure. The gain margin and phase margin were constrained by using H∞ norm of the complementary of the scaled plant. The requirement for the gain margin and phase margin is represented by the distance between the open loop Nyquist curve and the circle that represents the gain margin and phase margin in the complex plane. The distance is adjusted by tuning the parameter of performance specifications automatically to reduce the conservatism of the controller. The present method is applicable to both static stable vehicle and static unstable vehicle, and a three loops acceleration tracking autopilot is design. The numerical simulations have demonstrated that the autopilot satisfys the performance specifications, gain margin and phase margin simultaneously.

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