Regulation/Protection Control Strategy Design For Ramjet Engine Under Airframe/Propulsion Integration

In over half a century, the great interest in hypersonic vehicles powered byair-breathing ramjet engine still continues in aeronautics and astronautics fields,with several experimental vehicles built and launched. The supersonic/hypersonicinlet, an important component of ramjet, determines the characteristics of capturedflow. Inlet unstart phenomenon is an inherent characteristic belonged to ramjet and asevere issue, and unstart might lead to an abnormal operation of engine, even amission failure. Hence, an integrated control scheme and a regulation/protectioncontrol stragtegy were proposed in this paper.Firstly, a longitudinal rigid dynamics for an air-breathing hypersonic vehiclewas developed and the corresponding aerodynamic parameters were analyzed. Thenonlinear vehicle model was linearized about a specific trim condition by Jacobianlinearization method. An integrated control scheme, which contained a separateengine control system, was presented for dynamic pressure and accelerationcommand, and the vehicle controller was designed for pitch-attitude stabilizationand altitude command input tracking.Secondly, a ramjet first principle model was developed and its detailedsubmodels can capture the physics of interaction between inlet and combustor,namely, the unstart oscillation phenomenon which is caused by high backpressure.With curve-fitted approximation method, a parameterized, high-fidelity enginemodel was obtained by replacing some complex functions, and engine system’s openloop characteristics, for instance, the constraints on fuel equivalence ratio, weregiven.Thirdly, a class of bumpless transfer design method based on linear quadraticwas systematically carried out. For engine thrust regulation/inlet unstart safetymargin protection issue, an integral augmentation2-DOF bumpless transfer wasapplied into the built engine model and the corresponding simulations demostratedthe effectiveness of control scheme.Finaly, the coupling between airframe and propulsion system, stemming fromthe complexity of dynamics of air-breathing hypersonic vehicles, are extraordinarilystrong. The work of analyzing the main coupling approaches under inlet start, andtwo factors inducing inlet unstart, were conducted via dynamic equation analysiscombined with simulation results.