Two Degree-of-freedom Control for Bi-level Positive Airway Pressure of an Obstructive Sleep Apnea Treatment System

This paper presents a two degree-of-freedom control method for achieving bi-level positive airway pressure (Bi-PAP) of an obstructive sleep apnea (OSA) treatment system. After constructing a closed-loop DC brushless motor which is based on a microchip (dsPIC30F3010) drive together with a blower and an airway module, we develop a pressure control system for achieving Bi-PAP control. A mathematical model of the overall open-loop system is established based on the input-output data and its system parameters are sequentially determined using the recursive least-squares (RLS) approach. A two degree-of-freedom (DOF) controller, including a nonlinear feedforward controller and a feedback proportional-integral-derivative controller (PID controller) with gain scheduling, is proposed to maintain and follow the desired bi-level pressure setpoints. Through experimental results, the proposed control method is shown useful and effective in achieving bi-level airway pressure tracking.