JPS5965319A - Control method for fluid pressure - Google Patents

Abstract

PURPOSE:To always ensure a stable control response, by calculating the linear conversion model characteristic value of a fluid to be controlled and performing automatic control based on said calculated characteristic value so as to obtain a constant crossing angle frequency of the control response time. CONSTITUTION:The water, i.e., a fluid to be controlled is discharged from a pump 1 and distributed to a consumer house 4. A water flow rate detector 6, an opening detector 5 of the valve 3 and a water pressure detector 7 are provided at the secondary side of the valve 3 to detect each process data. These data are supplied to an electronic computer 10 via an input device 9 together with the pressure target value given from a set data input device 8. Based on the result of calculation of the computer 10, the valve 3 is operated via an output device 11 and a pressure control valve opening controller 12. With this operation the characteristic value of a linear model is calculated from each process data mentioned above, and a control parameter is automatically controlled based on said characteristic value so as to obtain a constant crossing angle frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a fluid pressure control method, and more particularly to a fluid pressure control method using a proportional, integral, differential (PID) control method.

[Technical background of the invention and its problems]

Generally, the so-called PID control method is used in which the integral and differential of the deviation between the detected pressure value of the controlled fluid and the preset pressure target value are multiplied by a certain control parameter, and the valve opening of the pressure control valve is adjusted using the sum of the integrals and derivatives. In the conventional fluid pressure control method used, the control parameters used for these calculations are fixed parameters. However, when the fluid pressure is PID controlled using a fixed control/4' parameter, the relationship between the pressure change of the controlled fluid and the valve opening of the pressure control valve becomes non-linear, which is why it has always been desirable to It was extremely difficult to obtain a control response.

[Purpose of the invention]

The present invention has been made to overcome the above problems.
SUMMARY OF THE INVENTION In order to achieve the above object, the present invention has the following features: Find the characteristic values of a linear model between the pressure of the controlled fluid and the valve opening in which the process quantities are the flow rate of the controlled fluid and the valve opening of the pressure control valve within a minute pressure change of the controlled fluid. Based on 1
It is characterized by automatically adjusting control parameters so that the difference angular frequency of the liU response time is constant.

[Embodiments of the invention]

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Figures 1 to 4 are all for explaining one embodiment of the present invention. Figure 1 is a diagram showing a water pressure control system in a water supply distribution system as an embodiment, and Figure 2 is a diagram showing a water pressure control system in a water supply distribution system as an embodiment. This is a diagram showing a linear model of water pressure and pressure control valve opening. Figure 3 is a diagram that combines the linear model of Figure 2 with a PI control model, and Figure 4 shows the computer algorithm of the same example. It is a diagram.

What is indicated by the symbol 1 in FIG. 1 is νJ? is a
The water discharged from the pump 1 is transferred to the pipe line 2 and the pressure control valve 311.
:Water is distributed to customer 4. As shown in the figure, this control system includes, on the secondary side of the pressure control valve 3, an opening detector 5 for detecting the valve opening of the pressure control valve 3, a flow rate detector 6 for detecting the flow rate of water, and a flow rate detector 6 for detecting the flow rate of water. A pressure detector 7 for detecting pressure is installed. The process data detected by these detectors 5, 6, 7 is input to the computer 10 via the input device 9 together with the pressure target value supplied from the setting data input device 8. The electronic computer 10 inputs the process data of the detectors 5, 6.7 input via the input device 9 and the pressure target value stored in the setting data input device *S using a built-in predetermined logic described below. The calculation result is supplied to the pressure control valve opening control device 12 as an operation command signal via the output device 11. As a result, the pressure control valve opening degree control device J2 operates the valve opening degree of the pressure control valve 3 based on the operation command signal supplied from the electronic computer 10, and controls the water pressure to the target setting and pressure level. .

The logic built into the electronic computer 10 can be roughly divided into two types. The first is linearization of the water pressure and pressure control valve opening within the minute pressure changes of the water supply, which is the control target, and the second is control from the characteristic values of the nine magnetization model obtained by the first logic. This is an algorithm for determining parameters.

First, linearization of water pressure and pressure control valve opening degree within a small pressure change of waterworks will be explained. Generally, the pressure balance equation for a fluid pressure control system as shown in FIG. 1 is expressed as the following equation: 0 However, in the above equation, h! : Pump discharge pressure h2 : Secondary side pressure of the pressure control valve U : Pressure control valve opening f (u) : Head loss coefficient q of the pressure control valve : Flow rate through the pipe fo : Pipe friction loss coefficient fc : Inertia Loss coefficient nym: A constant specific to the 7' runt. Here, since the values of the third and fourth terms on the right side of equation (1) are relatively small, equation (1) can be approximated as equation (2).

h, −h, = tu<u>−q”・・−・−・・−(2
) As is clear from equation (2), the pump discharge pressure h! The pressure difference between the pressure control valve 30 secondary pressure h2 and the flow iq flowing through the pipe line 2 to the nth power and the pressure control valve opening degree u'jF! : Expressed as a product of the head loss coefficient fu(u) of the pressure control valve 3 as a variable, and the relationship between the pressure difference and the valve opening degree U is non-linear.

Therefore, in order to linearize this relationship, it is sufficient to obtain the pressure control valve opening degree U and the flow rate q within a minute change in the pressure difference as process variables. That is, assuming that the target range of the control fluid is near a certain equilibrium point, the following equation holds true.

bso-h2gWju(u)aqon+*・・・−・−・
・(3) (hlo+Δhx) (hso+Δha)−
fu (uo + ΔU) (qo + Δq) n・・・・・・・・・
・ (4) However, in the above equation, uo: Pressure/force control valve opening Δu when Zorones is at a certain equilibrium point: Deviation from the pressure control valve opening when the process is at a certain equilibrium point qo: Flow rate Δq when the process is at a certain equilibrium point: Deviation hl from the flow rate when the process is at a certain equilibrium point. : Pump discharge pressure when the process is at a certain equilibrium point Δh1: Deviation from the pump discharge pressure when the process is at a certain equilibrium point hzo: 2 of the pressure control valve when the process is at a certain equilibrium point Next side pressure Δh2: 0 which is the deviation from the secondary -j pressure of the pressure control valve when the process is at a certain equilibrium point.Other symbols are the same as in equation (1).

Here, in equation (4), ignoring the term ΔU・Δh2, (
By substituting into equation 3), equation (5) is obtained.

9, -Δb2=fu'(uo) "q"Δu...
...As is clear from equations (5) and (6), Δh, -Δh
2 is linear with respect to ΔU and Δh2, and this linear model is illustrated in FIG. 2. Note that in the figure, K is a characteristic value of the linear model, which is expressed as follows from equation (5).

K=fu'(uo) ``q''``''-(6)
Therefore, this model is expressed as a proportional system, and as mentioned above, the pressure control valve opening degree u6 and the flow rate q
If o is obtained as a process variable, fu' is a function -, and n is a constant that can be set in advance, so a characteristic value K of a linear control model can be obtained.

Next, an algorithm for determining control parameters for PID control from characteristic value K will be explained.

Note that, since differential control may have an undesirable effect on noise, a case where proportional/integral control is applied will be described here.

As shown in Figure 3, in a system where the controlled object is proportional, PI-
When controlled, the open-loop transfer function of this system is expressed as follows.

G(5)=Kp@-I・(1+T!S)・・・・・・
... (7) However, in the same figure and equation (7),
and TI are the proportional gain and integral time as control parameters, S is the Lagrass operator, and Δhr is the target value of the pressure deviation Δh. Here, as is clear from equation (6), the characteristic values of the linear model include the valve opening degree u6 and the flow rate (t
Varies depending on o. Therefore, in this embodiment, in order to keep the control response constant against this variation, a pointer like an arrow is set. Pointer 1: In order to keep the control response time constant, a proportional gain is set to keep the crossing angular frequency ωc constant. and 0 guideline 2 to determine the integration time TI”:
Since there is a term (1+TI) in equation (7), the rise is 9
In order to stabilize the response time, it is set to l/TIt-3ωC or more.

Guideline 3: In order to maintain stability in the steady state, the dyne characteristic ω in the frequency response of the open-loop transfer function G(S) is
The slope near C should be -20 dB/dec.

If you follow these guidelines 1 to 3, the crossing angular frequency ωC will be constant from equation (7) so that ωC==−, taking /TX into account.
The control norm Kp + T 1 is determined as follows.

Therefore, in the electronic computer 1o, based on the above-mentioned logic, as shown in FIG.
C is set, and the characteristic value K of the controlled object is calculated and detected. Then, the proportional gain, which is the control norm of the PI control, and the integral time TX are determined based on the finger hooks 1 to 3, and the operation output signal is calculated.

As described above, according to this embodiment, the discharge pressure of the pump 1 and the pressure cuff 17! The characteristic value Kt'' of the linear model in which the pressure control valve opening u6 and the flow rate qo are the process amount when the pressure difference with the secondary side pressure of the I control valve 3 is within a minute change is determined, and based on this characteristic value K, the crossing angular frequency is calculated. By automatically adjusting the pressure control parameters and TIt so that ωC remains constant, stable control and response are always possible.

Note that in this embodiment, taking into account the noise of the process signal, the PI
Although the case where control is applied has been described, according to the present invention, the input signal from the process may be inputted through all the filters.

In this way, the noise contained in the process signal is completely reduced, and when applied to PIDID control, a more stable control response can be obtained. Furthermore, the present invention is not limited to the above-mentioned water supply distribution system; 1. For example, fluid pressure and force in fluid transfer equipment such as plants can be controlled in a similar manner.

〔Effect of the invention〕

As explained above, according to the present invention, a linearized model characteristic value is calculated in which the pressure control valve opening degree and flow rate in a minute pressure change of the controlled fluid are processed, and the control response is calculated based on this characteristic value. Since the control parameters are automatically adjusted so that the time crossing angular frequency is constant, the fluid test adjustment time can be shortened, and a highly practical fluid pressure control system that always provides the desired control response can be provided. can.

[Brief explanation of the drawing]

Figures 1 to 4 are all diagrams for explaining one embodiment of the present invention. Figure 1 is a block diagram showing a water pressure control system in a water supply distribution system as an embodiment, and Figure 2 is a block diagram showing a water pressure control system in a water supply distribution system as an embodiment. Model diagram showing a linear model of pressure change and pressure control valve opening,
FIG. 3 is a model diagram combining the linear model KPI control model of FIG. 2, and FIG. 4 is a flowchart showing an electronic calculation-like algorithm. 1... Ponder, 2... Pipe line, 3... Pressure control valve,
5... Valve opening degree detector, 6... Flow rate detector, 7...
Pressure detector, 8... Setting rotor input device, 10...
Electronic calculation, 12...Pressure control valve opening control device. Applicant's representative Patent attorney Takehiko Suzue Figure 1 Figure 2

Claims (1)

[Claims] In the fluid pressure control method, the integral and differential of the deviation between the detected pressure value of the controlled fluid and a preset pressure target value are multiplied by a control parameter, and the valve opening degree of the pressure control valve is adjusted using the sum of the integrated and differentiated deviations between the detected pressure value of the controlled fluid and a preset pressure target value. Characteristics of a linear model of the pressure change of the controlled fluid and the valve opening of the pressure control valve in which the flow rate of the controlled fluid and the valve opening of the pressure control valve are process quantities within a minute pressure change of the control fluid. A fluid pressure control method characterized in that the control parameter is adjusted based on the characteristic value so that the crossing angular frequency of the control response time is constant.