Direct Performance Control Method for Turbofan Afterburning Control with a Nonlinear Fuel Supply System

To improve the anti-interference ability of engine afterburning control, the afterburning closed-loop control based on direct performance value as the controlled quantity has attracted a lot of research. Under the condition of afterburner fuel closed-loop control, the instability of the control system caused by the nonlinearity of the afterburner fuel actuator is more prominent. Traditional afterburning control system inevitably exhibits oscillation phenomenon in the nonlinearity intervals of the actuator. In this paper, the phenomenon of engine state oscillation caused by nonlinear characteristics of the afterburner fuel zonal supply system (FZSS) actuator is studied, and a compound control system based on neural network and & mu; modification control algorithm is proposed to eliminate the oscillation phenomenon. First, the mathematical model of the afterburner FZSS actuator is established on the Simulink platform to simulate the fuel flow discontinuity interval characteristics of the real afterburning system. Second, for the FZSS actuator combined with the mixed exhaust turbofan engine model, a direct performance control system named the compound & mu; correction adaptive control (CCAC) system is proposed with engine thrust as the controlled quantity to control the afterburner fuel flow in closed-loop way. The CCAC system contains multi & mu; modification controllers in the controller group module. If the FZSS actuator works in the fuel flow discontinuity intervals, the CCAC system can modify the engine thrust command and switch the controllers through the design of the controller switching strategy and the adaptive control law of each & mu; modification controller parameter, thus the nonlinear discontinuity intervals can be avoided to realize the smooth transition of turbofan engine states. Finally, the closed-loop numerical simulation is carried out for the designed control system. The simulation results show that the control system can effectively avoid the fuel flow discontinuity intervals and realize the smooth transition of the engine states in the whole operating range of the FZSS actuator. Meanwhile, the control system can improve the control effect adaptively for the engine with degraded performance.