Extended-Kalman-filter-based equilibrium manifold expansion observer for ramjet nonlinear control

Abstract

A high-accuracy control-oriented model is an important prerequisite for the design of a ramjet controller, which can provide good engine performance and ensure safe and reliable operation under various environments and working conditions. In this study, we established a control-oriented equilibrium manifold expansion (EME) model for ramjets based on engine operation data. Furthermore, according to the EME model, an uncertainty term was introduced to reflect the steady-state error of the system. Meanwhile, in combination with the extended Kalman filter (EKF) algorithm, an EME observer was developed to eliminate the steady-state error and amend the model. Then, we established a model that can reflect the maneuvering characteristics of a ramjet in a large envelope range. Moreover, a feasible nonlinear controller was designed using the EME model and the sliding mode control (SMC) method to further eliminate the influence of model parameter perturbations and enhance the robustness of the control system. A direct control target was designed to further verify the estimation accuracy of the unmeasurable output of the EKF-based EME observer, and to achieve the direct control of the thrust performance and safety performance of a ramjet. Finally, the results of the hardware-in-the-loop (HIL) experiment showed that the state variable tracking error of the EME + EKF SMC system was reduced by at least 40% under continuous variable Mach number instructions, and the tracking error was reduced by more than 70% under more extreme simulation instructions. The control system was robust, and the accuracy of the model significantly improved. In addition, the results of the HIL experiment showed that a EME + EKF SMC control system with high accuracy and stability was established with thrust and inlet stability margin as control objectives.