The controller for the ventilator should match the airway pressure to a set pressure waveform.[^1] The airway pressure has a sensor that can be fed back into the controller.[^1] This controller uses a feedforward component.[^1]
The desired response is a quick rise to the desired pressure plateau, and no extreme overshoots.[^1] The steady state error between the target plateau and the patient’s lung plateau should be less than 2 mbar.[^1] The rise time should be 200ms, and the maximum flow rate overshoot should be less than 2 L/m.[^1]
An integral controller is good as it suppresses low-frequency disturbances, rolls-off the high frequencies and has a stabilizing slope for the entire bandwidth.[^2] The gains for the controller will need to be scheduled to meet the required rise times and overshoot thresholds.[^1]
Where
$$\phi(Q_{pat})=\cases{
0, \ |Q_{pat}|\leq \delta \
\alpha, |Q_{pat}> \delta’
}$$
a good value for delta is 6 L/min. With the switching gain the transfer function of the Lur’e-type system is.[^1]
$$e=p_{set}-p_{aw}=\frac{P_p(s)C(s)}{1+P_p(s)C(s)}u+\frac{1-P_p(s)}{1+P_p(s)C(s)}p_{set}$$
$$e:=G_{eu}(s)u+G_{ep}(s)p_{set}$$
Which is input-to-state stable if:[^1]
- \(G_{eu}(s)\) is Hurwitz,
- \(Re[G_{eu}(j\omega)]>-1/\alpha\)
- \(1+G_{eu}(\infty)>0\)
Be sure to vary the parameters of hose-lung combinations to ensure robustness of the controller to modeling uncertainties and differences between patients.[^1]
[[Ventilator Pressure Waveform]]
Source
- “Controller design for respiratory ventilators | Collimator.” Accessed: Mar. 31, 2023. [Online]. Available: https://www.collimator.ai/tutorials/controller-design-for-respiratory-ventilators
Backlinks
[[Feedforward Control]]
Gain Scheduling
[[Pressure Controlled Positive Pressure Ventilation]]