Sliding mode control of a direct-injection monopropellant-powered actuator

This paper describes the modeling and control of a direct-injection monopropellant-powered actuator. The actuation system utilizes the catalytic decomposition of a monopropellant, the products of which are directly injected into opposing chambers of a pneumatic cylinder in order to obtain a controllable force source. The system incorporates a pair of proportional liquid fuel valves and a three-way rotary spool valve to control the pressurization and depressurization of each chamber of the actuator. A model of the catalytic decomposition of the monopropellant and the compressible gas dynamics is derived in order to control the output force of the hot gas actuator. Using a Lyapunov function, a model-based sliding mode controller is developed for the multi-input single-output nonlinear system. Experimental results of the actuator force tracking demonstrate the validity of the model of the monopropellant-based actuator and the performance of the nonlinear controller.