Back-stepping sliding mode control for pressure regulation of oxygen mask based on an extended state observer.

Robust control laws based on the back-stepping sliding mode control (SMC) and extended state observer (ESO) are designed for pressure regulation of the oxygen mask in an oxygen supply system (OSS) which is non-linear in mechanical dynamics. Firstly, the structure and working principle of OSS are introduced; the electronic oxygen regulator (EOR) used in this system is a new type of EOR with proportional flow valve as throttle valve. Then, the highly nonlinear mathematical model of oxygen mask is analyzed. Next, an ESO is applied to deal with highly nonlinear problems caused by disturbances and uncertainties. Based on the back-stepping SMC technique, the corresponding controller is designed to control the throttle valve. Further, the stability of ESO and SMC are analyzed and proven theoretically. The effectiveness of this method is illustrated by extensive comparative simulations. The simulation results show that compared with the traditional PID control method, SMC control method can achieve accurate pressure regulation under superior lower inspiratory resistance.