JPH0132525B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fluid pressure control system suitable for use in a fluid piping system whose pressure distribution changes significantly during operation.

In general, a pressure control method for fluid flowing through a pipe line includes a pressure measuring device that measures the pressure of the fluid flowing through the pipe line, a flow rate operation means (for example, a damper) that manipulates the flow rate of the fluid, and a pressure measuring device that uses the pressure measuring device to control the pressure of the fluid flowing through the pipe line. A feedback control system is used, which comprises a controller that calculates the deviation of the measured pressure value from a target value (set value) and outputs a manipulated output to the flow rate operating means so that the deviation becomes zero. In such conventional control methods, the control parameters of the controller, that is, in the case of a PID controller, proportional gain, integral time,
Parameters such as differential time were always constant during the control operation. On the other hand, the process characteristics (process gain, time constant) of the controlled system including the fluid pipe line change depending on operational factors such as the flow rate and pressure of the fluid supply source, and changes in the pressure loss coefficient in the middle of the pipe. Therefore, even if the controller's control parameters are adjusted and set to optimal values under certain process characteristics, if the process characteristics of the controlled system change due to operational factors, the controller's control parameters will change. Since the value is no longer the optimum value, problems such as hunting occurring in the control operation, or the control operation becoming sluggish and the deviation increasing, have arisen.

This invention was made to solve the problems in the prior art as described above, and therefore, the purpose of this invention is to solve the problems in the prior art as described above. It is an object of the present invention to provide a fluid pressure control method that does not cause problems such as hunting in control operations.

The main points of the configuration of the present invention are that, in the conventional feedback type fluid pressure control system, there is a device for measuring the differential pressure before and after the flow rate operation means for controlling the flow rate of the fluid flowing through the fluid pipe line, and a pressure difference measuring device for measuring the flow rate flowing through the flow rate operation means. A measuring device, a calculation means for calculating a process gain of the controlled system from the measured differential pressure and flow rate, and means for optimally changing the control parameters of the controller according to the calculated gain,
The point is that it is possible to maintain appropriate control operation regardless of changes in process gain.

Next, the present invention will be explained in detail with reference to the drawings.
FIG. 1 is a schematic diagram showing pressure distribution in a fluid pipeline. In the figure, 1 is a flow meter, 2 is a damper, and 3 is a control valve. Further, the flow rate in the flowmeter 1 is f, the pressure loss coefficient in the damper 2 is _r1 , the pressure loss coefficient in the control valve 3 is _r2 , the pressure in the pipe between the flowmeter 1 and the damper 2 is P2, and the pressure between the damper ₂ and the valve is Let P ₁ be the pressure in the pipeline between valve 3 and P ₀ be the pressure on the outlet side of valve 3.

It will be explained with reference to FIG. 1 that changes in the process characteristics (gain) of a controlled system including a fluid pipe line are determined by the differential pressure across the damper and the flow rate therethrough.

Generally, the flow rate f is expressed by the following equation.

f ² = r ₁ ² (P ₂ − P ₁ ) ………(1) = r ₂ ² (P ₁ − P ₀ ) ………(2) In the steady state, the pressure loss coefficient r ₁ has just changed slightly. r ₁ →
(r ₁ +△r ₁ ). △r ₁ is a minute change.

Slightly reducing equation (1) by r ₁ , ∂f ² / ∂r ₁ = 2r ₁ (P ₂ −P ₁ ) + r ₁ ² (∂P ₂ / ∂r ₁ −∂P ₁
/∂r ₁ ) ………(3) Here, since we can set ∂f ² /∂r ₁ =0 and ∂P ₂ /∂r ₁ =0, we can obtain the following equation (4) from equation (3). It will be done.

2r ₁ (P ₂ −P ₁ )−r ₁ ² △P ₁ / △r ₁ = 0 ………(4) Also, if r ₁ is slightly reduced in equation (2) above, ∂f ² / ∂r ₁ = r ₂ ² (∂P ₁ /∂r ₁ −∂P ₀ /∂r ₁ )………(
5) Since we can set ∂f ² /∂r ₁ =0 here, we can finally obtain the following equation (6).

△P ₁ / △r ₁ −△P ₀ / △r ₁ = 0 ………(6) From equations (4) and (6) above, △P ₀ / △r ₁ = −2 (P _{1 −} P ₂ ) /r ₁ =-2(P ₁ −P ₂ ) ^3/
2 /f ......(7) Pressure loss coefficient r ₁ in damper 2 and damper 2
Assuming that there is ^a linear relationship between _the damper opening _x and _the opening It can be seen that the control parameters of a controller (not shown) for operating 2 may be determined by adapting them to the values of P ₁ , P ₂ , and f.

FIG. 2 is a schematic configuration diagram showing an embodiment of the present invention. In the figure, A and B are supply sources of different types of fluids, and the fluids supplied from these sources are mixed at a mixing location C and sent to a demand source D. There are control valves 3, 3a, 3b and dampers 2 along the way for various purposes, causing pressure loss. At this time, set the pressure P ₀ after the control valve 3 to a certain target value.
Consider a piping system controlled by damper 2.

The pressure before and after the damper 2 is measured by pressure transmitters 5 and 6 to obtain the differential pressure ΔP. Furthermore, the flow rate f flowing through the damper 2 is measured by the flow meter 1. Using this differential pressure △P and flow rate f, the calculation device 7
Adaptive calculation of the control parameters of the controller 8 is performed. Next, the pressure transmitter 4 measures the pressure P ₀ and detects the deviation from the target value. Based on this deviation, the controller 8 inputs an operation output to the damper operating device 9 to operate the damper 2 using the control parameters previously determined by the arithmetic unit 7.

The content of the calculation device 7 differs depending on the controller, but it is common that the control parameters are calculated by determining the damper gain ratio from the pressure difference ΔP before and after the damper. The case of a PI controller will be explained below.

The process gain when the differential pressure △P _s and the flow rate f _s is
Let K _ps be the control gain of the PI controller, and K _cs be the control gain of the PI controller.

Next, when the differential pressure is △P and the flow rate is f, the process gain K _p becomes K _p = K _ps f _s / f (△ P / △ P _s ) ^3/2 , and the control gain K _c is calculated using the following formula. It would be better to change it so that it is given to you.

K _c = K _cs K _ps / K _p = K _cs (△P _s / △P ₀ ) ^3/2 (f/f _s ) With this invention, it is possible to determine the optimal control parameters corresponding to changes in process gain during operation. Since it can be set on the controller, controllability is greatly improved. The effect of this invention will be clarified by comparing it with a conventional method in which control parameters are always kept constant.

It is assumed that the flow rate f is constant and the differential pressure ΔP varies due to changes in the pressure loss coefficient during the process.

If the control parameters of the controller are adjusted and fixed to the optimum differential pressure △P _s , the control operation will be as follows.

(A) When △P<△P _s , the closed loop gain becomes large, so hunting occurs as shown in Fig. 3A.

(b) When △P<△P _s , the closed loop gain becomes small, so as shown in Fig. 3 (b), the control operation becomes slow and the deviation becomes large.

On the other hand, if the control parameters are adapted to changes in process gain, good control results can always be obtained even if ΔP varies, as shown in FIG. 3C.

The present invention can be applied to pressure control of fluid piping systems such as gas recovery equipment and gas mixing equipment.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing pressure distribution in a fluid pipeline, FIG. 2 is a schematic diagram of a configuration showing an embodiment of the present invention, and FIG. 3 is a diagram showing fluid pressure control characteristics when using the system of the present invention. FIG. 3 is a characteristic comparison diagram showing a comparison between the case of the conventional method and the case of the conventional method. In the figure, 1 is a flow meter, 2 is a damper, 3 is a valve, 4 to 6 are pressure transmitters, 7 is an arithmetic unit, 8 is a controller, and 9 is a damper operating device.

Claims (1)

[Claims] 1. A pressure measuring device that measures the pressure of fluid flowing through a pipe, a flow rate operating means that manipulates the flow rate of the fluid, and determining the deviation of the value measured by the pressure measuring device from a target value until the deviation becomes zero. A fluid pressure control method comprising: a controller that outputs a manipulated output to the flow rate operation means; a measuring device for measuring the differential pressure before and after the flow rate operation means; and a measuring device for measuring the flow rate flowing through the flow rate operation means. a calculation means for calculating the gain of the process including the fluid pipe line from the measured differential pressure and flow rate, and means for changing the control parameter of the controller according to the calculated gain. Characteristic fluid pressure control method.