The Design Of CPAP Ventilator Controller Based On PI Control Algorithm

As an important clinical application, ventilator which helps patients complete the process of respiratory ventilation and provides the adjuvant treatment, has played an irreplaceable role. Upon analyzing the requirements and the domestic demand for the portable CPAP (Continuous Positive Airway Pressure) ventilator, this paper makes demonstration and designs a portable CPAP ventilator for home use.This paper focus on the hardware design of the CPAP ventilator, finishes completing the design of signal acquisition circuit, the motor control circuit and power circuit. Through a series of improvement measures, not only we improve the precision of pressure signal acquisition and the motor control, but also enhance the stability and reliability of the power supply. By using low cost and high-performance chips, it greatly reduces the overall cost in the context of insuring a good performance. By using the new chips, it reduces the external circuit and the size of the controller, which makes it meet the portability requirements. Different from the habit that there are two sensors in the CPAP, there is only one pressure sensor in our design, which is used to complete the functions of signal acquisition and closed-loop control. Designing in this way can reduce the machine cost, the board space, closed-loop control loop cycle and the pressure signal acquisition circuit complexity. In order to improve control accuracy and efficiency, we exploit the industrial IC MC33035 and MC33039 to ensure the control effect. Otherwise on the design of power supply, we emphasize on the design of the isolation, the anti-interference and the stability. With separating the power board and the signal board, it avoids the electrostatic coupling and the high-frequency electromagnetic interference effects on the control panel. The incremental limiting type PI algorithm avoids the problem that the traditional PID control algorithm easily produces some noise to influence control accuracy, reduces the response time of control loop. In addition, the algorithm just takes some milliseconds to ensure the system stable output, and improves the control accuracy of the system.Throughout the test, this paper finishes the design of the ventilator controller, whose functions can meet the design requirements and the whole equipment can operate normally. During the normal time (8 hours), the ventilator controller shows a strong stability, and the temperature of all the hardware chips is non-drift. Moreover, each hardware module can operate normally as expected. As for the control accuracy, the error is less than 0.5 cmH2O, which has achieved the domestic leading level.