JP2010026576A - Flow rate control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform satisfactory control by automatically updating a proportional gain when performing proportional control adaptive to a change in a state such as a pressure generated in piping. <P>SOLUTION: For offline, the inverse of a gradient obtained beforehand from a relationship between the opening degree and a flow rate of a control valve 2, the flow rate at the maximum opening degree detected by a rotary encoder 4 attached to the control valve 2, a normalized flow rate obtained by normalizing the flow rate at each opening degree by the flow rate of the maximum opening degree and a normalized proportional constant obtained by dividing the gradient by the flow rate at the maximum opening degree of the control valve 2 are preset. For online, the opening degree and flow rate of the control valve 2 are measured, the normalized flow rate corresponding to the measured opening degree is read from the stored data, and the measured flow rate is divided by the read normalized flow rate, and the flow rate at the maximum opening degree of the control valve 2 after fluctuation is obtained, and a new proportional gradient is calculated by multiplying the obtained flow rate by a preset normalized proportional constant Kz, and a proper proportional gain is obtained form the inverse of the new proportional gradient, and used for a control operation. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a flow rate control method for controlling the flow rate of a fluid.

  In the conventional flow rate control system, many methods using proportional control for controlling the flow rate of fluid have been proposed. In the flow control method using these proportional control operations, when the flow control system is shipped from the factory or installed in the field, a proportional gain that seems to be optimal is fixedly set in the control device, and Based on the flow rate information, the control valve is driven with feedback so that no deviation occurs between the target flow rate and the actual flow rate obtained from the flow meter.

  However, the proportional gain described above is optimized from the relationship between the opening and flow rate of the control valve used in the control system when the pressure on the inlet side of the control valve used in the control system is constant. If the pressure on the inlet side of the engine fluctuates, the optimization condition will not be satisfied. As a result, optimal control with the proportional gain set at the initial stage cannot be guaranteed, and it may be difficult to implement fast response flow control. There is.

  In addition, in the flow control method using a control valve, the rotary motion of the stepping motor is converted into a slide motion to drive a flow control section such as a diaphragm or a needle to adjust the cross-sectional area through which the fluid passes through the control valve. To be done. That is, it is considered that the opening of the control valve can be adjusted by the number of steps input in pulses because the passage cross-sectional area of the fluid is proportional to the distance that the needle or the like slides.

  However, when the drive pulse and the control valve movement are actually linked, a step-out phenomenon in which the control valve does not drive according to the drive pulse often occurs, especially when operating at a high speed, depending on the number of pulses applied. As a result, the opening of the control valve cannot be obtained, and the optimum opening of the control valve cannot be determined uniquely.

  As described above, in the conventional flow rate control method, when the environmental conditions such as the pressure, flow rate, and temperature in the pipe, particularly the pressure on the inlet side of the control valve 2 described above changes greatly, the initially set proportional gain is not necessarily optimal. . Therefore, even if the opening degree of the control valve is to be adjusted, problems such as overshoot and undershoot occur particularly in the case of a small amount of fluid control, and the responsiveness is lowered, and stable flow rate control becomes impossible. In addition, in order to accurately respond to environmental conditions, fine pressure measurement is required, and the control system becomes complicated.

  An object of the present invention is to automatically update to an optimal proportional gain when performing a proportional control operation so as to solve the above-described problems and cope with a change in state of pressure or the like in the pipe. It is to provide a flow rate control method.

  In order to achieve the above object, the flow control method according to the present invention measures the flow rate of a fluid with a flow meter and drives the control valve by a proportional control operation using a proportional gain to perform flow control beforehand. In the flow control method in which the control process conditions are obtained in advance, the proportional gain is updated online using these conditions, and the fluid control is performed using the updated proportional gain. The pressure on the inlet side of the valve was fixed, and the control valve was driven between the fully closed state and the maximum opening, and was obtained from the correspondence between the opening of the control valve and the flow rate obtained from the flow meter. The reciprocal of the gradient, the normalized proportionality constant obtained by dividing the gradient by the flow rate at the maximum opening of the control valve, and each flow rate obtained from the flow meter corresponding to each opening of the control valve Control valve There is a preliminary step of preliminarily inputting the normalized flow rate obtained by dividing by the flow rate at the time of large opening to the control valve opening to the arithmetic control device. A first step of measuring an opening degree during operation and a flow rate corresponding thereto; and a second step of reading out a normalized flow rate that should correspond to the opening degree during operation of the control valve from the previously input data. Measure the actual flow rate corresponding to the operation and the opening of the control valve during operation with a flow meter, and divide the obtained actual flow rate by the normalized flow rate read out in the second step. A third step of calculating the flow rate at the maximum opening of the control valve corresponding to the environment of the control, the flow rate at the maximum opening of the control valve determined in the third step and the offline set Obtained from the relationship between the opening and flow rate of the control valve based on the normalized proportional constant The gradient is calculated, a new proportional gain is obtained from the reciprocal thereof and set in the arithmetic and control unit, and the proportional control operation using the proportional gain while measuring the flow rate with the flow meter. And a fifth step of feedback-controlling the flow rate by driving a control valve, wherein the first to fifth steps are repeated.

  The flow control method according to the present invention automatically obtains an optimal proportional gain using a simple control system and performs good flow control.

  The present invention will be described in detail based on the embodiments shown in the drawings.

  FIG. 1 is a configuration diagram of a flow rate control system. For example, a control valve 2 having a needle and a flow meter 3 for adjusting the opening degree are arranged in series in the pipe 1 through which the fluid flows. The control valve 2 is provided with a rotary encoder 4 for detecting the opening, the output of the flow meter 3 and the output of the rotary encoder 4 are connected to the arithmetic control device 5, and the output of the arithmetic control device 5 is connected to the control valve 2. ing.

  The fluid flows from the pipe inlet 6 of the pipe 1, the flow rate is adjusted by the control valve 2, the flow rate is measured by the flow meter 3, and reaches the pipe outlet 7.

  The flow value measured by the flow meter 3 is sequentially sent to the arithmetic and control unit 5, and information from the rotary encoder 4 that measures the opening degree of the control valve 2 is also sent to the arithmetic and control unit 5 and sequentially processed.

  Various types of control valves for controlling the flow rate can be used. In this embodiment, a needle valve is used. Various types of flowmeters can be used, but an ultrasonic flowmeter is used in this embodiment.

  The eye of this embodiment is to appropriately update the proportional gain of the proportional control operation (P operation) that has deviated from the optimum value due to the pressure change at the pipe inlet 6 online. In the proportional control operation, the opening degree of the control valve 2 is accurately grasped by the rotary encoder 4, the normalized flow rate with respect to the opening degree inputted in advance is read, and the maximum opening of the control valve 2 estimated after the environmental change is read. The flow rate in degrees is calculated, and feedback control is performed using the proportional gain updated based on the result.

  FIG. 2 is a graph showing the flow rate F obtained by changing the opening degree d of the control valve 2 under the pressure P at the pipe inlet 6. Accordingly, the gradient K and the maximum flow rate Fp when the control valve 2 is opened from the initial rising portion to the maximum opening degree dp are defined.

  FIG. 3 is a graph when the pressure at the pipe inlet 6 is changed from Pa to Pd. From FIG. 3, the gradients Ka, Kb, Kc, Kd at the respective pressures and the flow rates Fap, Fbp, Fcp, Fdp at the maximum opening are obtained.

FIG. 4 shows the flow rate values Fa, Fb, Fc, and Fd obtained at each opening when the pressure at the inlet 6 changes, with the maximum opening of the control valve 2 determined corresponding to the opening at that time. The normalized flow rates obtained by dividing the flow rates Fap, Fbp, Fcp, and Fdp are graphed. FIG. 4 shows that even if the pressure at the pipe inlet 6 changes, the flow rate with respect to each opening degree becomes constant by normalization. From this, it can be seen that equation (1) holds.
Fa / Fap = Fb / Fbp = Fc / Fcp = Fd / Fdp (1)

Therefore, if the flow rate during operation is Fe, the flow rate Fep at the maximum opening of the control valve 2 corresponding thereto is obtained from the equation (2) obtained by converting the equation (1).
Fep = Fe / (Fa / Fap) (2)

  That is, equation (2) shows that the maximum opening of the control valve 2 when the pressure at the pipe inlet 6 fluctuates due to environmental changes and the flow rate fluctuates from Fa to Fe even if the opening of the control valve 2 is fixed. The flow rate at V f also varies from Fap to Fep, and this value indicates that if the normalized flow rate (Fa / Fap) is known, it can be estimated by calculation together with the actual flow rate Fe.

In addition, when the flow rate is normalized from the relationship shown in FIG. 4, the flow rate is almost coincident with the opening degree of the control valve 2 and is represented by a single curve. From the part, it is possible to define a normalized proportionality constant Kz that does not depend on the inlet pressure. This normalized proportional constant Kz corresponds to the ratio between the gradient (Ka to Kd) corresponding to each inlet side pressure shown in FIG. 3 and the flow rate (Fap to Fdp) at the maximum opening of each control valve 2. It can be expressed by the following equation (3).
Kz = Ka / Fap = Kb / Fbp = Kc / Fcp = Kd / Fdp (3)

As can be seen from FIG. 3, if the environmental conditions at the time of flow rate control change and the pressure becomes, for example, Pe (not shown), the gradient Ke at that time and the proportional gain (1 / Ke) that is the inverse thereof should also change. It is. At this time, the gradient Ke can be expressed by the following equation (4) obtained by converting the equation (3).
Ke = Kz × Fep (4)

  From equation (4), it can be seen that the gradient Ke to be obtained can be obtained by multiplying the normalized proportionality constant Kz by the flow rate Fep at the maximum opening of the control valve 2 obtained by equation (2). Among these, the normalized proportionality constant Kz is obtained from, for example, the relationship between the opening degree dj and the flow rate Fj under a constant pressure Pj, and the gradient and the flow rate Fjp at the maximum opening degree of the control valve 2 corresponding to the opening degree. be able to.

  However, it is virtually impossible to measure the flow rate at the maximum opening of the control valve 2 every time during the control operation. In order to solve the problem, in this embodiment, the opening degree of the control valve 2 during operation, which is accurately obtained using the rotary encoder 4, the flow rate corresponding to the opening value, and the normalized flow rate are obtained and calculated. The flow rate at the maximum opening of the control valve 2 after the fluctuation is calculated by inputting in advance to the control device and substituting it into the equation (2) together with the actual flow rate.

  Next, the flow rate at the maximum opening of the control valve 2 obtained according to the equation (4) is multiplied by the normalized proportionality constant Kz that has also been input in advance to obtain the gradient after the environment has changed, A new proportional gain (1 / Ke) is calculated from the reciprocal.

  In the description so far, the maximum opening of the control valve 2 and the corresponding flow rate are defined as the maximum flow rate. However, the maximum opening does not necessarily have to be the opening when the control valve 2 is fully opened. An opening range in which 2 is normally controlled may be defined, and the opening in the most open state within the opening range may be used.

  The first embodiment will be described with reference to the flowchart shown in FIG. In the flowchart of FIG. 5, the value of each opening degree d up to the maximum opening degree of the control valve 2 is accurately obtained in advance in step S <b> 1 offline using the rotary encoder 4. The flow rate Fj corresponding to this opening, the flow rate Fjp at the maximum opening of the control valve, and the normalized flow rate (Fj / Fjp) obtained by dividing each flow rate by the flow rate Fjp at the maximum opening of the control valve 2 Data corresponding to each opening degree of the control valve 2, the gradient Kj of the linear part in the relational expression between the opening degree and the flow rate of the control valve 2 and the proportional gain (1 / Kj) which is the inverse thereof, and the opening of the control valve 2 A normalized proportionality constant Kz, which is the gradient of the relational expression between the degree and the normalized flow rate, is predetermined and input to the arithmetic and control unit 5. In creating the data, it is desirable to measure as many openings and corresponding flow rates as possible.

  In this embodiment, the opening degree of the control valve 2 is obtained by using the rotary encoder 4, but it can also be measured by counting the drive pulses of the pulse motor that drives the control valve 2.

  On-line, in step S2, the opening dk of the control valve 2 during operation is measured by the rotary encoder 4, the flow rate Fk is obtained by the flow meter 3, and is taken into the arithmetic and control unit 5 as data. Next, the process proceeds to step S3, and the normalized flow rate (Fj / Fjp) that should correspond to the actual flow rate Fk corresponding to the opening degree dk of the operating control valve 2 is read from the input normalized flow rate data.

  In step S4, the flow rate Fkp at the maximum opening of the control valve 2 that has fluctuated due to environmental changes is calculated from the actual flow rate Fk measured by the flow meter 3 and the normalized flow rate (Fj / Fjp) that has been input as data (2 ) Determined by the formula. If the flow rate at the maximum opening of the control valve 2 calculated in this way is substituted into the equation (4) together with a known normalized proportional constant Kz, the proportional gradient Kk to be updated in step S5 is obtained, and in step S6. The proportional gain (1 / Kk) that is the inverse of the proportional gradient Kk is updated.

  As described above, when the optimum proportional gain (1 / Kk) corresponding to the situation at that time is obtained and the automatic update is repeated, the flow rate control with a quick response can be continuously performed.

  FIG. 6 is a graph showing the relationship between the opening of the control valve 2 and the flow rate as in FIG. In FIG. 6, the differential coefficient F ′ of the flow rate F calculated corresponding to each opening degree is displayed on the curve showing the correspondence between the opening degree and the flow rate. The differential coefficient F ′ of the flow rate is obtained from the relationship between the opening degree of the control valve 2 and the flow rate, approximated by an approximate expression, and the adjacent opening degree and the gradient of the flow rate measured successively. However, the differential coefficient F 'of the flow rate may be obtained by approximating the relationship between the opening degree of the control valve 2 and the flow rate to a higher order equation and using a mathematical differential method therefrom.

  In the control method based on the second embodiment, the first embodiment directly uses the information on the opening degree of the control valve 2, whereas the differential coefficient F ′ of the flow rate is used.

  FIG. 7 is a flowchart showing the control flow of the second embodiment. In advance, in offline step S <b> 1, the opening degree and flow rate data of the control valve 2 are measured, and the linear portion gradient Kj and the proportional gain (1 / Kj) that is the reciprocal thereof in the relational expression thereof, A normalized flow rate obtained by normalizing each flow rate by obtaining a flow rate at the maximum opening degree, and a normalized proportional constant Kz that is a gradient of a linear portion in a relational expression between the opening degree of the control valve 2 and the normalized flow rate are determined. An approximate expression is obtained from the input opening degree and flow rate data, a differential coefficient of the flow rate at each opening degree is calculated from the approximate expression, and the normalized differential coefficient normalized with the maximum opening flow rate of the control valve 2 together with them. Are input to the arithmetic and control unit 5 as data.

  Next, in step S 2, the plurality of openings dm of the operating control valve 2 are accurately measured by the rotary encoder 4 and the flow rate Fm is measured by the flow meter 3 in step S 2. Further, the normalized differential coefficient (Fj ′ / Fjp) of the flow rate Fm corresponding to the opening degree dm of the control valve 2 measured in step 3 is read from the input normalized differential coefficient data.

When the differential coefficient is used, as data of the flow rate Fm with respect to the opening degree dm of the control valve 2, two points in the relational expression between the continuous opening degree and the flow rate, for example, (d3, F3) and (d4, F4) are obtained. It is done. The flow rate Fmp at the maximum opening of the control valve 2 under this environment is the gradient (F4-F3) / (d4-d3) actually measured at the current opening and the normalized differential coefficient corresponding to the opening. Is obtained from data stored in advance, and obtained from the following equation (5).
Fmp = {(F4-F3) / (d4-d3)} / (Fj ′ / Fjp) (5)

  Thus, in the flowchart of FIG. 7, the gradient obtained from the data measured in step S4 is divided by the normalized differential coefficient, and the flow rate Fmp at the maximum opening corresponding to the actual opening of the control valve 2 is expressed as ( 5) Estimate according to equation. When the flow rate Fmp at the time of the maximum opening of the control valve 2 is obtained, the process proceeds to step S5 and is substituted into the equation (4) together with the input normalized proportional constant Kz to calculate a new gradient Km.

  In step S6, a new proportional gain (1 / Km) is calculated from the reciprocal of the obtained new gradient Km, and the control valve 2 is controlled by the obtained new proportional gain.

In order to obtain the flow rate at the maximum opening degree of the control valve 2 so far, the method of using the control valve opening degree and the flow rate itself is used in the first embodiment, and the opening degree and flow rate of the control valve 2 in the second embodiment. The method using the derivative of is shown. On the other hand, in Example 3, the flow rate at the maximum opening degree obtained from the relationship between the opening degree and the flow rate of the control valve 2 and the maximum opening degree obtained from the relationship between the opening degree of the control valve 2 and the differential coefficient of the flow rate. Control is performed by using the equation (6) that weights and averages each flow rate.
Fpav = (Fp1 × ρ1 + Fp2 × ρ2) / (ρ1 + ρ2) (6)

Here, Fpav is the flow rate at the maximum opening obtained by weighted averaging calculation.
Fp1 is the flow rate at the maximum opening degree of the control valve 2 obtained from the opening degree and the flow rate.
ρ1 is a weight coefficient for the flow rate at the maximum opening degree estimated from the opening degree and the flow rate.
Fp2 is the flow rate at the maximum opening obtained from the opening degree of the control valve 2 and the differential coefficient F ′ of the flow rate.
ρ2 is a weighting factor for the flow rate at the maximum opening degree estimated by the differential coefficient F ′ of the opening degree and flow rate of the control valve 2.

It is a block diagram of a control system. It is a graph of the relationship between the opening degree of the control valve and the flow rate at a constant pressure. It is a graph of the relationship between the opening degree of the control valve and the flow rate based on a plurality of input pressures. It is a graph of the relationship between the flow volume after normalization and the opening degree of a control valve. FIG. 3 is a flowchart of a control flow according to the first embodiment. It is the graph which displayed the differential coefficient of the flow volume with respect to each opening degree in the approximate expression of the opening degree and flow volume in a fixed pressure. It is a flowchart figure of the flow of control of Example 2.

Explanation of symbols

1 Piping 2 Control valve 3 Flow meter 4 Rotary encoder 5 Arithmetic control device 6 Piping inlet 7 Piping outlet

Claims (5)

When the flow rate of fluid is measured by a flow meter and the control valve is driven by proportional control operation using proportional gain to perform flow control, the control process conditions are obtained offline in advance, and these conditions are set online. In the flow rate control method in which the proportional gain is updated using and the fluid control is performed using the updated proportional gain.
In the offline mode, the pressure on the inlet side of the control valve is made constant, the control valve is driven between the fully closed state and the maximum opening, and the opening of the control valve and the flow rate obtained from the flow meter And the flow rate meter corresponding to each opening degree of the control valve, a reciprocal of the slope obtained from the correspondence relationship, a normalized proportionality constant obtained by dividing the slope by the flow rate at the maximum opening degree of the control valve, and There is a preliminary step of previously inputting into the arithmetic and control unit the data obtained by dividing each flow rate obtained from the above by the flow rate at the maximum opening degree of the control valve and the data corresponding to the opening degree of the control valve. And
In the online, a first step of measuring the opening degree of the control valve during operation and the corresponding flow rate;
A second step of reading out the normalized flow rate that should correspond to the opening during operation of the control valve from the previously input data;
The actual flow rate corresponding to the opening degree of the control valve during operation is measured with a flow meter, and the obtained actual flow rate is divided by the normalized flow rate read out in the second step, to the operating environment. A third step of calculating the flow rate at the maximum opening of the corresponding control valve by calculation;
The gradient obtained from the relationship between the opening degree and the flow rate of the control valve is calculated based on the flow rate at the maximum opening degree of the control valve obtained in the third step and the normalized proportionality constant set offline. A fourth step of obtaining a new proportional gain from the reciprocal and setting it in the arithmetic control device;
The control valve is driven by a proportional control operation using the proportional gain while measuring the flow rate with the flow meter, and includes a fifth step of feedback controlling the flow rate,
A flow rate control method characterized by repeating the first to fifth steps.   When the flow rate of fluid is controlled by proportional action using the proportional gain while measuring the flow rate of fluid with a flow meter, the relationship between the flow rates corresponding to the multiple openings of the control valve is approximated by an approximate expression, The flow rate at the maximum opening degree of the control valve is calculated by obtaining the differential coefficient of the flow rate corresponding to the opening degree and the normalized differential coefficient of the flow rate, and using this, the proportional gain is obtained. The flow rate control method according to 1.   The flow rate at the maximum opening of the control valve corresponding to the opening is the flow rate at the maximum opening obtained using the flow rate at the maximum opening obtained using the flow rate and the differential coefficient of the flow rate. The flow rate control method according to claim 2, wherein each is obtained by multiplying each by a weight coefficient and averaging.   The flow rate control method according to claim 1, wherein the flow rate at the maximum opening of the control valve is a maximum flow rate at a maximum opening in an opening range in which the control valve is used.   The flow rate control method according to claim 1, wherein the opening degree of the control valve is obtained by a rotary encoder.

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