VARIABLE-STRUCTURE CONTROL OF TIME-DELAY SYSTEMS WITH A SIMULATION STUDY ON STABILIZING COMBUSTION IN LIQUID PROPELLANT ROCKET MOTORS

The dynamical model of combustion in liquid propellant rocket motors i s an unstable time-delay system. When it is stabilized by a linear sta te feedback controller, the robustness of the closed-loop system is no t satisfactory. In this paper a variable structure control approach to stabilize the combustion is presented. First, the concept of switchin g functional is introduced, and hence a systematic design method is es tablished for the variable structure control of general time-delay sys tems. Secondly, the proposed theory is applied to the stabilization of combustion in liquid monopropellant rocket motors. Simulation results show that the robustness of the closed-loop system against variations in time lag delta and pressure exponent gamma is considerably improve d. Specifically, the controller designed according to the nominal valu e delta = 1.0 can still stabilize the system with delta = 0, i.e. the system without time delay. This conclusion provides a powerful basis f or the reliable design of rocket motor control systems.