Oxygen mixing proportional valve calibration and control method

Abstract

The invention provides an oxygen mixing proportional valve calibration and control method which comprises the steps that a current-flow corresponding relation table of an oxygen mixing proportional valve is inquired according to target oxygen flow, and feed-forward opening current of the oxygen mixing proportional valve is obtained; an active-disturbance-rejection controller is adopted, a control loop with an oxygen concentration sensor as a closed loop is adopted, and input current of the oxygen mixing proportional valve is controlled in real time; the current-flow corresponding relation table of the oxygen mixing proportional valve is obtained by performing double-thread calibration on the oxygen mixing proportional valve. The method has the advantages that the oxygen mixing proportional valve is subjected to double-thread calibration, and the processes of oxygen concentration from small to large and from large to small can be accurately controlled; an active-disturbance-rejection control algorithm is adopted, the test process of adjusting PID parameter setting is omitted, and meanwhile the control precision and the measurement precision of a proportional valve-oxygen concentration control system can be met and are both within the error range.

Description

Technical Field

[0001] The present application belongs to the field of respiratory humidification therapy apparatus, and specifically relates to a method for calibrating and controlling an oxygen mixing proportional valve. Background Art

[0002] As a respiratory therapy device, a high-flow respiratory humidification therapy device needs to provide patients with a mixed gas with adjustable oxygen concentration to normalize the patient's blood oxygen and achieve a therapeutic effect. For a high-flow respiratory humidification therapy device realized by a combination of a proportional valve and a fan, when mixing oxygen, the proportional valve and the fan need to be opened at the same time. Since the oxygen connected is a strong gas source, the opening and response time of the proportional valve directly affect the rapidity and stability of the oxygen concentration of the mixed oxygen, and have a certain degree of influence on the fan control. In the prior art, oxygen concentration monitoring is generally carried out using an oxygen concentration sensor, and the oxygen concentration sensor responds slowly, resulting in a slow response of the oxygen concentration control; and there is a difference between the current and flow curves of the mixed oxygen proportional valve, so the mixed oxygen proportional valve needs to be calibrated.

[0003] At present, the calibration method of oxygen concentration proportional valve basically adopts the current-flow relationship curve, but in the calibration process, generally only the current rising curve is calibrated, and the proportional valve usually has a hysteresis loop, that is, there may be a large deviation between the current falling process and the rising process, resulting in a large difference in the oxygen concentration in the process of changing from large to small, and the oxygen concentration control response is slow. After completing the flow calibration, it is necessary to convert the oxygen concentration to the oxygen flow, and further, perform traditional PID control of the oxygen concentration. This control method uses the oxygen concentration sensor as feedback, which has a slow response, and the control parameter setting relies on the experience of engineers. The process is cumbersome and cannot cover all equipment conditions. Summary of the invention

[0004] The purpose of this application is to overcome the defects of the existing oxygen mixing proportional valve, which has slow response, control parameter setting relying on engineer experience, cumbersome process, and cannot cover all equipment working conditions.

[0005] In order to achieve the above purpose, the present application proposes a method for calibrating and controlling an oxygen mixing proportional valve, comprising:

[0006] According to the target oxygen flow rate, the current-flow correspondence table of the mixed oxygen proportional valve is queried to obtain the feedforward opening current of the mixed oxygen proportional valve;

[0007] Adopting the anti-disturbance controller, the control loop with the oxygen concentration sensor as the closed loop is used to control the input current of the oxygen mixing proportional valve in real time;

[0008] The current-flow correspondence table of the oxygen mixing proportional valve is obtained by performing double-thread calibration on the oxygen mixing proportional valve.

[0009] As an improvement of the above method, the dual-thread calibration of the oxygen mixing proportional valve includes: flow rate increase thread calibration and flow rate decrease thread calibration.

[0010] As an improvement of the above method, the process of flow rise thread calibration includes:

[0011] The opening of the oxygen mixing proportional valve gradually increases from 0. When the flow sensor detects that the flow is greater than the set threshold, the opening is recorded as the critical opening of the oxygen mixing proportional valve Valve_Open;

[0012] Adjust the opening of the oxygen mixing proportional valve to the maximum value, then gradually reduce the opening, and record the opening of the flow sensor that is lower than the set maximum flow. This opening is the maximum opening of the oxygen mixing proportional valve Valve_Max;

[0013] The oxygen mixing proportional valve is further divided into N equal parts between the critical opening and the maximum opening, that is, the interval between each opening is: Valve_Delta = (Valve Max -Valve Open ) / N, N>0, and set the corresponding opening according to this interval Valve_Delta, and record the data at the same time, where the opening is set to {Valve_Open+Value_Delta, Valve_Open+2*Value_Delta,…, Valve_Open+N*Value_Delta}, and the corresponding flow rate is {y1,y2,…y N}.

[0014] As an improvement of the above method, the process of flow drop thread calibration includes:

[0015] The opening of the oxygen mixing proportional valve gradually decreases from the maximum value. When the flow sensor detects that the flow rate is less than the set threshold, the current is recorded as the critical opening of the oxygen mixing proportional valve Valve_Open;

[0016] Adjust the opening of the oxygen mixing proportional valve to 0, and then gradually increase the opening, and record the opening when the flow sensor is higher than the set maximum flow. This opening is the maximum opening of the oxygen mixing proportional valve Valve_Max;

[0017] The oxygen mixing proportional valve is further divided into N equal parts between the critical opening and the maximum opening, that is, the interval between each opening is: Valve_Delta = (Value Max -Valve Open) / N, N>0, and set the corresponding opening according to this interval Valve_Delta, and record the data at the same time, where the opening is set to {Valve_Open+Value_Delta, Valve_Open+2*Value_Delta,…, Valve_Open+N*Value_Delta}, and the corresponding flow rate is {z1,z2,…z N}.

[0018] As an improvement of the above method, the control loop with the oxygen concentration sensor as a closed loop, the control process includes:

[0019] The oxygen mixing proportional valve obtains the initial opening according to the feedforward opening current limited by the limiting module;

[0020] The real-time oxygen concentration is measured by the oxygen concentration sensor to obtain the oxygen concentration error;

[0021] The anti-disturbance controller is turned on, and the oxygen concentration error is used as the control target. The error e1 is obtained by comparing it with the output value of the linear extended state observer. After passing through the linear state error feedback module, the control quantity u0 is output. After being compensated by the total disturbance estimate z2 obtained by the linear extended state observer, the final control quantity u is obtained after passing through the inverse of the controller gain. u is then output through the limiting module to control the compensation opening of the mixed oxygen proportional valve, and finally the oxygen concentration is controlled.

[0022] As an improvement of the above method, the linear state error feedback module adopts a PD controller, and its controller transfer function is:

[0023] G(s)=k p +k d s

[0024] Among them, k p is the proportionality coefficient; k d is the differential coefficient; s is the complex plane independent variable; the proportional coefficient and differential coefficient are obtained by the ZN setting method.

[0025] As an improvement of the above method, the linear extended state observer is designed as:

[0026]

[0027] Where β1 and β2 represent the pole configuration parameters of the linear extended state observer, which determine the system convergence speed; u represents the system control rate; z is the state variable output matrix of the linear extended state observer, z = [z1z2] T, T represents transposition, z1 tracks the real-time oxygen concentration y output by the system, and after the dynamic control process converges, z1 tends to y; z2 tracks the total disturbance, and after the dynamic control process converges, z2 tends to the total disturbance; b0 = 2.18; Represents the rate of change of the state variable output matrix z; Represents the estimated value of the system's real-time oxygen concentration y.

[0028] Compared with the prior art, the advantages of this application are:

[0029] 1. The oxygen mixing proportional valve is calibrated in two threads, and the process of oxygen concentration from small to large and from large to small can be accurately controlled;

[0030] 2. The use of the anti-disturbance control algorithm not only eliminates the experimental process of adjusting the PID parameters, but also can meet the control accuracy and measurement accuracy of the proportional valve-oxygen concentration control system, so that they are all within the error range. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The figure shows the flow chart of the calibration and control method of the oxygen mixing proportion valve;

[0032] Figure 2 The figure shows the flow chart of the dual-thread calibration method of the mixed oxygen proportion valve;

[0033] Figure 3 Shown is the oxygen concentration control block diagram. DETAILED DESCRIPTION

[0034] The technical solution of the present application is described in detail below with reference to the accompanying drawings.

[0035] like Figure 1 As shown, the calibration and control method of the mixed oxygen proportional valve provided by the present application first performs a dual-thread calibration of the mixed oxygen proportional valve. Using the dual-thread calibration, high-flow respiratory humidification therapy will obtain more accurate oxygen flow control during the oxygen concentration control process, thereby improving the response time of the oxygen concentration control. Furthermore, in the control loop with the oxygen concentration sensor as feedback, the oxygen concentration is controlled by using the oxygen concentration sensor as a closed-loop control loop, avoiding the cumbersome parameter setting process of using PID, while being able to achieve rapidity, and no overshoot in the dynamic process.

[0036] like Figure 2 As shown, the dual-thread calibration process of the mixed oxygen proportional valve includes flow increase thread calibration and flow decrease thread calibration; wherein,

[0037] The flow rate increase thread calibration process is as follows: the proportional valve opening gradually increases from 0. When the flow sensor detects a flow rate > 0.5 LPM, the opening is recorded as the critical opening of the proportional valve Valve_Open. The proportional valve opening is given to the maximum value, and then the opening is gradually reduced. The opening when the flow sensor is lower than the maximum flow rate of 0.5 LPM is recorded. This opening is the maximum opening of the mixed oxygen proportional valve Valve_Max. The proportional valve is further divided into N equal parts between the critical opening and the maximum opening, that is, the interval between each opening is: Valve_Dalta = (Value Max -Valve Open ) / N, N>0, and set the corresponding opening according to this interval Valve_Delta, and record the data at the same time, where the opening is set to {Valve_Open+Value_Delta, Valve_Open+2*Value_Delta,…, Valve_Open+N*Value_Delta}, and the corresponding flow rate is {y1,y2,…y N}.

[0038] The flow rate reduction thread calibration process is opposite to the above flow rate reduction thread, including: the proportional valve opening gradually decreases from the maximum value. When the flow sensor detects a flow rate <0.5LPM, the current is recorded as the critical opening of the proportional valve Valve_Open, the proportional valve opening is adjusted to 0, and then the opening is gradually increased. The opening of the flow sensor when it is higher than the maximum flow rate of 0.5LPM is recorded. This opening is the maximum opening of the mixed oxygen proportional valve Valve_Max. The proportional valve is further divided into N equal parts between the critical opening and the maximum opening, that is, the interval between each opening is: Valve_Delta=(Value Max -Valve Open ) / N, N>0, and set the corresponding opening according to this interval Valve_Delta, and record the data at the same time, where the opening is set to {Valve_Open+Value_Delta, Valve_Open+2*Value_Delta,…, Valve_Open+N*Value_Delta}, and the corresponding flow rate is {z1,z2,…z N}.

[0039] The opening of each proportional valve corresponds to the current allocated to the proportional valve.

[0040] After the calibration is completed, the dual-thread data are linearly smoothed at three points and then piecewise linearly processed to obtain the current size that should be given during the rising process, the falling process and at different flow rates.

[0041] After the flow calibration is completed, the current-flow curve is used as the feedforward of oxygen concentration control and added to the output of the oxygen concentration controller to achieve the purpose of improving the rapidity of oxygen concentration control.

[0042] According to the user-set oxygen concentration SetO2, the conversion formula of oxygen concentration, total flow Flow and oxygen flow O2Flow can be obtained:

[0043]

[0044] Substitute the target oxygen flow Tar_O2Flow into the set oxygen concentration value in formula (1), use the linearized table lookup method to query the current-flow correspondence table obtained in the dual-thread calibration process of the mixed oxygen proportional valve, and obtain the feedforward opening value of the proportional valve oxygen concentration control. The constant in formula 1 is the algorithm setting.

[0045] On this basis, in order to ensure that the oxygen concentration is controlled without error, a control loop with the oxygen concentration sensor as a closed loop is carried out. The control algorithm adopts ADRC (Active Disturbance Rejection Control) self-disturbance rejection controller, avoiding the tedious parameter setting process of PID, ensuring that the system has no overshoot while meeting the rapidity of system adjustment.

[0046] The control block diagram of the control loop with the oxygen concentration sensor as the closed loop is shown in Figure 3:

[0047] When the proportional valve is given a flow rate according to the feedforward opening, the final proportional valve output opening is obtained through the limiting module. The real-time oxygen concentration is measured by the oxygen concentration sensor to obtain the oxygen concentration error O2Error. At this time, ADRC control is turned on, and the oxygen concentration error is used as the control target. The error e1 is compared with the output value of the linear extended state observer (LESO) to obtain the error. After the designed linear state error feedback module, the module uses the classic PD controller, and its controller transfer function is G(s)=k p +k d s, where k p is the proportionality coefficient, k d is the differential coefficient, which can be obtained by the ZN (Ziegler-Nichols) tuning method according to the system, and s is the independent variable in the complex plane. Its output is the control quantity u0, which is compensated by the total disturbance estimate z2 obtained by the linear extended state observer, and then the inverse of the controller gain is obtained to obtain the final control quantity u, which is then output by the limiting module to compensate the control opening of the proportional valve, and finally realize the rapid and accurate control of oxygen concentration.

[0048] In order to design the linear expansion state observer, a rough mathematical model of the proportional valve needs to be established, and the step response method is used here.

[0049] According to the step response method, the proportional valve is designed to step from the critical opening to 10% of the maximum opening, which is recorded as Δu. The oxygen concentration continuous response curve collected by the oxygen concentration sensor. The initial value of the oxygen concentration is recorded as y(0); after the system tends to be stable, the oxygen concentration value is recorded as y(∞). The response curve is shaped like a typical first-order inertia link plus a delay link. The system model can be established using the two-point method, that is, the oxygen concentration y corresponding to different time points is selected during the rising stage of the response curve. * (t) Establish the proportional valve-oxygen concentration system equation:

[0050]

[0051] Among them, t1 and t2 are two time points selected in the rising stage of the response curve; y(t) is the flow rate corresponding to time t; y * (t) is the ratio of the real-time flow rate to the oxygen concentration after stabilization; τ is the delay time; T is the time constant.

[0052] Usually take typical value: y * (t1)=0.39,y * (2) = 0.63, we can get:

[0053]

[0054] After solving, it can be known that the controlled object gain K = 1.24, the controlled object time common sense T = 0.57, and the controlled object time delay τ = 0.000107. Therefore, the proportional valve-oxygen concentration transfer function model is actually a typical first-order inertia link, and its transfer function expression is:

[0055]

[0056] Where s is the independent variable in the complex plane, which is equivalent to the differential operator. G(s) is converted into the form of a differential equation:

[0057]

[0058] Comparing it with the paradigm of ADRC, we get:

[0059]

[0060] Combining (5)-(6), we can see that b0=2.18, and the total disturbance f=-1.75y.

[0061] Select state variables x1, x2, where make The derivative of the total disturbance of the system, y, is the oxygen concentration output of the system, which is converted into a state space expression:

[0062]

[0063] Where: C=[1,0],D=[0],

[0064] Design the corresponding linear expansion state controller as follows:

[0065]

[0066] Where: z is the state variable output matrix of the linear extended state observer, z = [z1z2] T , where z1 output will track the oxygen concentration set value x1, that is, the real-time oxygen concentration y output by the system. After the dynamic control process converges, z1 tends to y, and z2 will track x2, that is, the total disturbance f, that is, after the dynamic control process converges, z2 tends to f, L = [β1β2] T Configure parameters for the two undetermined poles of the linear extended state observer, and then the linear extended state observer is designed as:

[0067]

[0068] Among them, β1 and β2 represent the pole configuration parameters of the linear extended state observer, which determine the system convergence speed; u represents the system control rate; Represents the rate of change of the state variable output matrix z; Represents the estimated value of the system's real-time oxygen concentration y.

[0069] The linear extended state observer can obtain the total disturbance f,z2→f, and introduce the total disturbance f into u.

[0070]

[0071] Substituting (8) into (7), we get: The above model can be transformed into a single integral model, and its open-loop transfer function is: G1(s) = ω c / s, where ω c is the system bandwidth, s is a complex variable, s=σ+jω, σ∈R + is the real part, ω∈R is the imaginary part, R and R + denote the real number domain and the positive real number domain respectively. The closed-loop transfer function is:

[0072]

[0073] Time constant T = 1 / ω c ,According to the time domain system response, the closed-loop output of the system can reach 99% of the set value of oxygen concentration at 5T. According to the oxygen concentration control requirements, 1s is set to reach the set value, then it can be known that: ω c=5rad / s.

[0074] Design the bandwidth ω of the linear extended state observer o , since the controlled object is set as a single integral model, the observer bandwidth needs to be larger than the controller bandwidth, so it can be set to (3~5)*ω c , depending on the system. In the process of proportional valve-oxygen concentration control, 5ω is used c According to the bandwidth method:

[0075]

[0076] To verify the above calibration and control methods, the ventilation flow rate of the high-flow humidification therapy device was set to 35L / min, and three groups of oxygen concentration parameters were set, namely 30%, 60%, and 90%. The initial current value of the proportional valve of the high-flow humidification therapy device, the actual oxygen concentration RTO2 monitored by the oxygen concentration sensor, and the SensorO2 of the third-party monitoring equipment were recorded. At the same time, the response time of each parameter was recorded. The specific data are shown in the table below.

[0077] Table 1 Oxygen mixing proportion valve calibration and control algorithm verification

[0078]

[0079] It can be seen that the mixed oxygen proportional valve is accurately calibrated, with an absolute error of ±1L / min, which can meet the feedforward requirements of the mixed oxygen control system; the use of the self-disturbance rejection control algorithm not only eliminates the test process of adjusting the PID parameters, but also can meet the control accuracy and measurement accuracy of the proportional valve-oxygen concentration control system, so that they are all within the error range.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present application and are not intended to limit it. Although the present application is described in detail with reference to the embodiments, a person skilled in the art should understand that any modification or equivalent replacement of the technical solution of the present application does not depart from the spirit and scope of the technical solution of the present application and should be included in the scope of the claims of the present application.

Claims

1. A method for calibrating and controlling an oxygen mixing proportional valve, comprising: According to the target oxygen flow rate, the current-flow correspondence table of the mixed oxygen proportional valve is queried to obtain the feedforward opening current of the mixed oxygen proportional valve; Adopting the anti-disturbance controller, the control loop with the oxygen concentration sensor as the closed loop is used to control the input current of the oxygen mixing proportional valve in real time; The current-flow correspondence table of the oxygen mixing proportional valve is obtained by performing double-thread calibration on the oxygen mixing proportional valve.

2. The method for calibrating and controlling an oxygen mixing proportion valve according to claim 1, characterized in that: The dual-thread calibration of the oxygen mixing proportional valve includes: flow rate increase thread calibration and flow rate decrease thread calibration.

3. The method for calibrating and controlling an oxygen mixing proportion valve according to claim 2, characterized in that: The process of flow rise thread calibration includes: The opening of the oxygen mixing proportional valve gradually increases from 0. When the flow sensor detects that the flow is greater than the set threshold, the opening is recorded as the critical opening of the oxygen mixing proportional valve Valve_Open; Adjust the opening of the oxygen mixing proportional valve to the maximum value, then gradually reduce the opening, and record the opening of the flow sensor below the set maximum flow. This opening is the maximum opening Valv of the oxygen mixing proportional valve. e Ma x The oxygen mixing proportional valve is further divided into N equal parts between the critical opening and the maximum opening, that is, the interval between each opening is: Valve_Delta = (Value Max -Valve Open ) / N, N>0, and set the corresponding opening according to this interval Valve_Delta, and record the data at the same time, where the opening is set to {Valve_Open+Value_Delta, Valve_Open+2*Value_Delta, …, Valve_Open+N*Value_Delta}, and the corresponding flow rate is {y1, y2, …y N }.

4. The method for calibrating and controlling an oxygen mixing proportion valve according to claim 2, characterized in that: The process of flow drop thread calibration includes: The opening of the oxygen mixing proportional valve gradually decreases from the maximum value. When the flow sensor detects that the flow rate is less than the set threshold, the current is recorded as the critical opening of the oxygen mixing proportional valve Valve_Open; Adjust the opening of the oxygen mixing proportional valve to 0, and then gradually increase the opening, and record the opening when the flow sensor is higher than the set maximum flow. This opening is the maximum opening of the oxygen mixing proportional valve Valve_Max The oxygen mixing proportional valve is further divided into N equal parts between the critical opening and the maximum opening, that is, the interval between each opening is: Valve_Delta = (Value Max -Valve Open ) / N, N>0, and set the corresponding opening according to this interval Valve_Delta, and record the data at the same time, where the opening is set to {Valve_Open+Value_Delta, Valve_Open+2*Value_Delta, …, Valve_Open+N*Value_Delta}, and the corresponding flow rate is {z1, z2, …z N }.

5. The method for calibrating and controlling an oxygen mixing proportion valve according to claim 1, characterized in that: The control process of the control loop with the oxygen concentration sensor as a closed loop includes: The oxygen mixing proportional valve obtains the initial opening according to the feedforward opening current limited by the limiting module; The real-time oxygen concentration is measured by the oxygen concentration sensor to obtain the oxygen concentration error; The anti-disturbance controller is turned on, and the oxygen concentration error is used as the control target. The error e1 is obtained by comparing it with the output value of the linear extended state observer. After passing through the linear state error feedback module, the control quantity u0 is output. After being compensated by the total disturbance estimate z2 obtained by the linear extended state observer, the final control quantity u is obtained after passing through the inverse of the controller gain. u is then output through the limiting module to control the compensation opening of the mixed oxygen proportional valve, and finally the oxygen concentration is controlled.

6. The method for calibrating and controlling an oxygen mixing proportion valve according to claim 5, characterized in that: The linear state error feedback module adopts a PD controller, and its controller transfer function is: G(s)=k p +k d s Among them, k p is the proportionality coefficient; k d is the differential coefficient; s is the complex plane independent variable; the proportional coefficient and differential coefficient are obtained by the ZN setting method.

7. The method for calibrating and controlling an oxygen mixing proportion valve according to claim 5, characterized in that: The linear extended state observer is designed as: Where β1 and β2 represent the pole configuration parameters of the linear extended state observer, which determine the system convergence speed; u represents the system control rate; z is the state variable output matrix of the linear extended state observer, z = [z1 z2] T , T represents transposition, z1 tracks the real-time oxygen concentration y output by the system, and after the dynamic control process converges, z1 tends to y; z2 tracks the total disturbance, and after the dynamic control process converges, z2 tends to the total disturbance; b0 = 2.18; Represents the rate of change of the state variable output matrix z; Represents the estimated value of the system's real-time oxygen concentration y.

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