Sliding Mode Thermal Control System for Space Station Furnace Facility

The space station furnace facility (SSFF) provides the necessary core systems to operate various material processing furnaces. The thermal control system (TCS) is defined as one of the core systems, and its function is to collect excess heat from furnaces and to provide precise cold temperature control of components and of certain furnace zones. Physical interconnection of parallel thermal control subsystems through a common pump implies the description of the whole TCS by coupled nonlinear differential equations in flow and pressure. The report formulates the system equations and develops the sliding mode controllers that cause the interconnected subsystems to operate in the local sliding modes, resulting in control system invariance to interaction disturbances and plant uncertain ties. The desired decoupled flow rate profile tracking is achieved by optimization of the local linear sliding mode equations. Extensive digital simulation results are presented to show the flow rate tracking robustness and invariance to plant nonlinearities, time-varying plant parameters, and variations of the system pressure supplied to the controlled subsystems. A comparison against the popular proportional-plus-derivative-plus-integral (PID) control algorithm is included to demonstrate improved performance over traditional control techniques.