JP3015523B2 - Process control equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a proportional / integral / differential (PID) or proportional / integral (PI) method using a control constant for adjustment with respect to a deviation between a control amount signal from a process and its target value. This is a process control device that performs control calculations and outputs a manipulated variable signal to control the process so that the control variable signal follows the target value.Specifically, the target value is changed using the control constant set for disturbance suppression as it is. Even if you do
The present invention relates to a process control device capable of reliably suppressing an oscillating motion.

[0002]

2. Description of the Related Art Conventionally, a proportional / integral / derivative (hereinafter, referred to as PID) controller has been widely used as a controller for controlling a process.

FIG. 7 is a block diagram showing a basic configuration example of this type of PID control device. In FIG. 7, a difference e between a control amount signal (process variable) PV from the process 1 and its target value SV is calculated by a subtracter 2, and the difference e is calculated by a PID control arithmetic processing unit 3 for adjustment control. PID control calculation is performed using constants, and the manipulated variable signal (output signal)
The process 1 is controlled by outputting the MV.

The control formula of the PID control is generally represented by the following formula in the case of the position type. _{MV = K p {e + (} 1 / T I) · [e] dt + T D · de / dt} _{where, K p, T I, T} D is the regulation control constants, respectively proportional gain, integral time, and derivative time , E is the deviation (e = S
V-PV) and SV are target values, PV is a control amount signal, MV is an operation amount signal, and t is time. Also,
[] Dt represents integration.

Now, a PI using such PID control will be described.
The basic functions of the D control device include a disturbance suppression characteristic and a target value tracking characteristic. That is, the former is how to optimally suppress the influence of the disturbance when a disturbance occurs, and the latter is how to optimally follow the target value SV when the value of the process 1 is changed when the target value SV is changed. Are respectively shown.

However, in such a PID control device, the control constants (K _p , T _I , T _D ) for suppressing the influence of the disturbance change and the control constant for the target value change are different. There is such a problem. That is, as to optimally suppress the effect of the disturbance changes, control constants _{(K p, T I, T} D) Setting the target value tracking characteristic vibrational and becomes (overshoot occurs), and conversely, If the control constants (K _p , T _I , and T _D ) are set so as to optimally follow the change in the target value, the disturbance suppression characteristics become weak. Therefore, when the target value SV is changed by using the control constant set for disturbance suppression as it is, it is not possible to suppress the target value following characteristic from becoming an oscillating movement.

[0007]

As described above, in the conventional process control apparatus using PID control, when the target value is changed using the control constant set for disturbance suppression as it is, There has been a problem that the target value following characteristic cannot be suppressed from becoming an oscillating movement.

It is an object of the present invention that the target value follow-up characteristic becomes oscillatory even when the target value is changed using the control constant set for disturbance suppression as it is.
An object of the present invention is to provide an extremely reliable process control device capable of reliably suppressing (overshoot) .

[0009]

In order to achieve the above object, according to the first aspect of the present invention, a deviation between a control amount signal from a process and its target value is determined by using a control constant for adjustment. Performs proportional / integral / differential (PID) control calculations,
In a process control device that controls a process so that an operation amount signal is output and a control amount signal follows a target value,
When the target value is changed, changes in the proportional, integral, and derivative terms are monitored, and the values of the proportional, integral, and derivative terms are changed from the time the target value is changed.
Is calculated separately, the value of (proportional term + derivative term) and the value of integral term
And as a result, the value of the integral term and (proportional term + derivative
When the magnitude relationship with the value of the item (1) is reversed, control constant changing means for changing the control constant for adjustment for a certain period so as to suppress overshoot is provided.

According to the second aspect of the present invention, a proportional-integral (PI) control operation is performed on the deviation between the control amount signal from the process and its target value by using a control constant for adjustment. In a process control device that outputs a quantity signal and controls a process so that a control quantity signal follows a target value, when a target value is changed, a change in a proportional term and an integral term is monitored, and the proportional term and the integral term are monitored. When the magnitude relationship is reversed, control constant changing means for changing the control constant for adjustment for a certain period so as to suppress overshoot is provided.

[0011] Here, in particular examples of the control constant changing unit, for example, as shown in claim 3, the ratio of target value change
Calculate the value of the example term and the integral term individually and calculate the value of the proportional term and the integral term
, And as a result, the value of the integral term and the value of the proportional term
When the magnitude relationship is reversed , the control constant for adjustment is changed so as to suppress overshoot.

[0012]

Therefore, in the process control device of the present invention, after the target value is changed, changes in the proportional term, integral term, and derivative term are monitored, and the proportional term, integral term, fine
Calculate the value of the minute term individually and multiply by the value of (proportional term + differential term)
The value of the integral term is compared with the value of the integral term (proportion
Term + differential term), or when the magnitude relation between the proportional term and the integral term is reversed, so as to suppress overshoot for a certain period from the time. By changing the control constant, the movement of the manipulated variable signal is reliably suppressed when the target value is changed, so that a response without overshoot can be obtained as the target value following characteristic. Thus, the control constant set for disturbance suppression can be used as it is even when the target value changes.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the concept of the present invention will be described.

In the above-described PID control device, when the target value is changed, the proportional (P) term and the integral (I) term are used to reduce the deviation between the control amount signal from the process and the target value to zero. , A change appears in each of the differential (D) terms. In this case, the movement of the (P + D) term is as shown in FIG. The movement of the I term is as shown in FIG.
In FIG. 5, t ₀ is the time when the target value is changed. FIG. 5C shows the superimposition of the I term except for the steady-state bias component I ₀ . In FIG. 5C, (P
+ D) Time t at which the waveform of the term and the waveform of the I term intersect for the first time
_{In step 1} , by changing the control constant for a certain period, the operation of the process control device can be changed. FIG.
Indicates that the manipulated variable signal MV is determined by the (P + I + D) term in FIG.

Accordingly, in view of the above, according to the present invention, when the target value is changed, the change of the proportional term, the integral term, and the differential term (or the proportional term or the integral term) is monitored, and whether the target value is changed is determined.
Calculate the values of the proportional, integral, and differential terms individually from
Term + derivative term) and the value of the integral term.
The magnitude relationship between the value of the integral term and the value of the (proportional term + derivative term)
At the time of inversion, or the magnitude relation between the proportional term and the integral term
To suppress overshoot when is reversed
The control constant for adjustment is changed for a certain period from that time . Hereinafter, an embodiment of the present invention based on the above concept will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing a configuration example of a process control device according to the present invention. As shown in FIG. 1, the process control device of the present embodiment has a process input / output (PI /
O) The interface comprises an interface 11, a central processing circuit 12, a memory 13, and a bus 14.

FIG. 2 is a block diagram showing an equivalent circuit configuration of the process control device of FIG. In FIG. 2, a process control device 21 subtracts a deviation e between a control amount signal (process variable) PV from a process 1 and a target value SV from a subtractor 2.
The PID control calculation is performed on the deviation e by the PID control calculation processing unit 23 using a PID control constant for adjustment, and an operation amount signal (output signal) MV is output to output the control amount signal PV. Is controlled so as to follow the target value SV. Further, the PID control calculation processing section 23 has a control constant changing function in addition to the original PID control calculation function. That is, when the target value SV is changed, the control constant changing function sets the P term, the I term,
This function monitors the change of the D term, and changes the adjustment PID control constant for a certain period so as to suppress overshoot when a predetermined relationship is established between the P term, the I term, and the D term. . More specifically, in this embodiment, the target value SV
Calculate the values of P, I and D individually from the time of change,
The value of the (P-term + D-term) is compared with the value of the I-term. As a result, when the magnitude relationship between the value of the I-term and the value of the (P-term + D-term) is reversed, the PID control constant for adjustment is adjusted. Is a function to change for a certain period. Here, the PID control constants (K _p , T _I , T _D ) for adjustment are set in advance so as to optimally suppress the influence of the disturbance change as described above. Next, the operation of the process control device of the present embodiment configured as described above will be described with reference to FIG.

In FIG. 2, in a process control device 21, a deviation e between a control amount signal PV from the process 1 and a target value SV is normally calculated by a subtracter 22, and the deviation e is calculated.
In the PID control arithmetic processing unit 23 to, PID control constants for regulating _{(K p, T I, T} D) PID control calculation is performed using a given process 1 the calculation result as the manipulated variable signal MV Thus, control is performed such that the value of process 1 becomes target value SV.

Now, in such a state, the target value SV
Is changed, the value of the P term, the I term, and the D term are calculated separately from the time point t ₀ when the target value SV is changed. And, based on this calculation result,
The value of the (P-term + D-term) is compared with the value of the I-term, and the time t when the magnitude relationship between the value of the I-term and the value of the (P-term + D-term) is reversed is t ₁ . Then, the PID control constants (K _p , T _I , T _D ) for adjustment in the PID control arithmetic processing unit 23 are changed for a certain period α · t ₁ (α is a constant) from the time t ₁ . Then, during this time, the modified PID control constants _{(K p, T I, T} D) are PID control calculation using performed, by the operation amount signal MV obtained by the operation, the process value of one target value Control is performed to achieve SV.

That is, during the period from time t ₀ to time t ₁ (t <t ₁ ), the P set for disturbance suppression
ID control constants _{(K p, T I, T} D) using, PID control operation is performed by the PID control calculation processing section 23. Further, a period from time t ₁ to time α · t ₁ (t ₁ <t ≦
α · t ₁ ), the changed PID control constant (K
_p , T _I , T _D ) and the PID control arithmetic processing unit 23
Performs a PID control operation. Furthermore, the time in the t ₁ from a certain period alpha · t ₁ elapsed time after _{(α · t 1 <t)} , again the first set PID control constants for disturbance suppression _{(K p, T I, T} D ), The PID control calculation processing section 23 performs the PID control calculation.

In this case, generally, (t ₁ <t ≦ α ·
The lower the gain of the PID control constant during the period of t ₁ ), the better the controllability. The comparison between the value of the (P term + D term) and the value of the I term differs depending on the characteristics of the plant and the direction in which the target value SV is moved. In general, when the target value SV is increased, the value of (P term + D term) Term) ≦ I term is a determination condition for changing the PID control constant.

FIG. 3 shows the manipulated variable signal MV and the controlled variable signal PV when the target value SV is changed from 0 to 50 at time t = 0.
FIG. 4 is a response diagram showing the movement (hereinafter, all are shown by simulation).

FIG. 3A shows a PID adjusted for disturbance suppression.
This shows an example of a response when the control constant is used as it is. In this case, the control amount signal PV once exceeds 50 and is returned to 50. About 10% overshoot is seen.

FIG. 3B shows a PID adjusted for disturbance suppression.
This is a response example in the case of the present embodiment in which the control constant is changed and used when the target value SV changes. In this case, the movement of the operation amount signal MV is suppressed by changing the PID control constant during the period (t ₁ <t ≦ α · t ₁ ) (α = 3 in this example).

FIG. 3C is the same as FIG. 3A, except that P
The terms, I and D are decomposed and shown in addition to FIG. In this case, the manipulated variable signal MV is obtained by MV = (P term) + (I term) + (D term).

FIG. 3D is the same as FIG. 3A,
(P term + D term) and I term are shown in an exploded manner. In this case, the intersection of the (P term + D term) and the I term is the time t ₁ that gives the timing for changing the PID control constant.

On the other hand, FIG. 4A shows the same thing as FIG. 3A. If it is not desired to overshoot the control amount signal PV when the target value SV changes, the PID control constant may be adjusted again. FIG. 4B shows an example in which the overshoot is adjusted. C in FIG.
FIG. 5A and FIG. 4B are shown in an overlapping manner. If the overshoot is not performed, the rise of the control amount signal PV will be poor. FIG. 4D is a diagram in which FIG. 4A and FIG. 3B, which is the response of the present embodiment, are superimposed.
From the figure, it can be seen that the rise, overshoot, control error area, and the like are improved.

As described above, the process control device 21 of this embodiment includes a subtracter 22 for calculating a deviation e between a control amount signal (process variable) PV from the process 1 and its target value SV, PID control calculation is performed using the adjustment PID control constants (K _p , T _I , T _D ) set so as to optimally suppress the influence of disturbance change on the deviation e calculated by step 22. Quantity signal (output signal) MV
And the function of controlling the process 1 so that the control amount signal PV follows the target value SV, and when the target value SV is changed, the P term, I term,
The value of the D term is individually calculated, the value of the (P term + D term) is compared with the value of the I term, and as a result, the value of the I term is compared with the value of the (P term + D term).
Term), when the magnitude relationship with the value of
D control constant is obtained so as to constitute a _{(K p, T I, T} D) of the PID control arithmetic processing unit 23 having a control constant changing function for a period of time changes.

Therefore, even when the target value SV is changed by using the PID control constant set for disturbance suppression as it is, the target value following characteristic has an oscillatory motion (overshoot).
Can be reliably suppressed. That is,
The PID control constant for disturbance suppression can be used as it is even when the target value SV changes, and a power saving effect can be obtained. Further, when the target value SV changes, the oscillating movement (overshoot) of the target value follow-up characteristic can be suppressed, thereby contributing to safe operation of the plant, resource saving, high quality of products, and the like.

In the above embodiment, the case where the present invention is applied to a PID control device has been described. However, the present invention is not limited to this case.
The present invention can be applied in the same manner. That is, generally, the determination of the timing t ₁ of the change of the PID control constant is determined by a × (P term) + b × (D term) and c
× (I term) + d. Where a, b, c,
d is a constant.

Further, in the above-described embodiment, the case where the timing of returning the changed PID control constant to the original state is determined by time such as α · t ₁ is described. What is necessary is just to be able to judge that the process 1 is calm (stable) such that the deviation e between the PV and the target value SV is equal to or less than a certain value.

[0032]

As described above, according to the present invention, after the target value is changed, the change of the proportional term, the integral term, and the differential term (or the proportional term or the integral term) is monitored, and when the target value is changed, From
Calculate the values of the proportional term, integral term and differential term individually (proportional term
+ Differential term) and the value of the integral term.
The magnitude relationship between the value of the integral term and the value of the (proportional term + derivative term) is reversed
At the time of the change (or the magnitude relation between the proportional and integral terms)
In the case where the rotation is reversed), the control constant for adjustment is changed only for a certain period from that point to suppress the overshoot. Therefore, the target value is changed using the control constant set for disturbance suppression as it is. Even in such a case, it is possible to provide an extremely reliable process control device that can reliably suppress the target value following characteristic from becoming an oscillating movement (overshoot).

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a process control device according to the present invention.

FIG. 2 is a block diagram showing an equivalent circuit in the embodiment.

FIG. 3 is a response waveform chart for explaining the operation in the embodiment.

FIG. 4 is a response waveform chart for explaining effects in the embodiment.

FIG. 5 is a conceptual diagram for explaining the concept of the present invention.

FIG. 6 is a conceptual diagram for explaining the concept of the present invention.

FIG. 7 is a block diagram showing a basic configuration example of a PID control device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Process, 2 ... Subtractor, 3 ... PID control arithmetic processing part, 11 ... Process input / output (PI / O) interface, 12 ... Central processing circuit, 13 ... Memory, 14 ... Bus,
21: Process control device, 22: Subtractor, 23: PID
Control operation processing unit.

────────────────────────────────────────────────── ─── Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G05B 13/00-13/02 G05B ⁷ /00-7/02 G05B 11/42 JICST file (JOIS)

Claims (3)

(57) [Claims] 1. A proportional / integral / differential (PID) control operation is performed on a deviation between a control amount signal from a process and its target value using a control constant for adjustment, and an operation amount signal is output by outputting the operation amount signal. In a process control device that controls the process so that a control amount signal follows a target value, when the target value is changed, a change in a proportional term, an integral term, and a differential term is monitored, and the change is proportional to the target value. The values of the term, the integral term, and the derivative term are individually calculated, and the value of the (proportional term + derivative term) is compared with the value of the integral term. As a result, the value of the integral term is compared with the value of the (proportional term + derivative term). A process control device, comprising: control constant changing means for changing the control constant for adjustment for a certain period of time so as to suppress overshoot when the magnitude relationship with the value is reversed. 2. A proportional-integral (PI) control operation is performed on a deviation between a control amount signal from a process and its target value using a control constant for adjustment, and an operation amount signal is output to output the control amount signal. In a process control device that controls the process so that the signal follows a target value, when the target value is changed, a proportional term and a change in an integral term are monitored, and the magnitude relation between the proportional term and the integral term is reversed. In case,
A process control apparatus comprising: control constant changing means for changing the control constant for adjustment for a certain period so as to suppress overshoot. 3. The control constant changing means calculates the value of the proportional term and the value of the integral term individually from the time of changing the target value and compares the value of the proportional term with the value of the integral term. 3. The process control according to claim 2, wherein when the magnitude relation between the value of the term and the value of the proportional term is reversed, the control constant for adjustment is changed so as to suppress overshoot. apparatus.