Design of infinite sliding mode state observer with application to CO2 absorption system of space station

The CO2 absorption system plays the important roles in controlling the partial pressure of CO2 and providing the condensed CO2 for Sabatier reduction device. This paper deals with the design of the state observer of the CO2 absorption system in the environment control and life support system of the space station. The main design difficulty is that the dynamic model of the CO2 absorption system is described by the partial differential equation, which causes to the traditional state observer based on ordinary differential equation is no longer applicable. In order to solve this problem, an infinite dimensional slide mode observer algorithm is proposed. This algorithm firstly uses a new projection approximation method to transform the partial differential equation to ordinary differential equation, and then estimates the system state by using sliding mode observer with better robustness to the model approximation error and external disturbance. Compared with the traditional algorithm, the proposed method not only applies to the more general case, e.g. the case of non-orthogonal basis, but also effectively reduces the influence of approximation error and disturbances. Next, the detail realization procedure is illustrated by using a simulation example. The simulation results show that the new algorithm can effectively estimate the state of the CO2 absorption system and further guarantee robust to the model error and external disturbances.