JPS5971507A - Process controller - Google Patents

Abstract

PURPOSE:To prevent the overshoot with a simple constitution by changing the level of a control output signal depending on a deviation from a prescribed value, in a process controller preventing the generation of overshoot. CONSTITUTION:Since a controlled variable PV1 of a controlled system 5 is different largely from a control objective SP at the start of control, the deviation epsilon is larger than a compared value BAND. Thus, the multiplication factor of a multiplier 4 is set to 1 with an output signal of a comparator 3, an output signal MV2 of the multiplier 4 becomes the same value as a control output signal MV1 and the controlled variable approaches rapidly to the control objective. When the deviation epsilon is smaller than the compared value BAND, since the multiplication factor of the multiplier 4 is set to a prescribed value smaller than 1 with an output signal of the comparator 3, the output signal MV2 of the multiplier 4 becomes a smaller value than the control output signal MV1, the change in the controlled variable PV1 is gentle, allowing to attain minute following of the controlled variable.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a process control device that prevents overshoot from occurring.

In general, process control is designed to compare the control target value of the controlled object with the control amount that is actually occurring, find the amount of deviation, and perform the operation that minimizes this amount of deviation. In many control systems, even if control is performed to cancel the deviation, changes in the controlled variable occur after a time delay, resulting in excessive control and overshoot. For this reason, various methods for preventing overshoot have been proposed, but all of them are complicated and therefore uneconomical.

Therefore, it is an object of the present invention to provide a process control device that is simple and economical and can prevent overshoot.

In order to achieve this object, the present invention changes the magnitude of the control output signal supplied to the controlled object depending on whether the deviation amount is large or small by a predetermined value F. Hereinafter, the present invention will be described in detail using drawings showing embodiments.

FIG. 1 is a block diagram showing one embodiment of the present invention.

In the figure, 1 is a subtracter, 2 is a proportional/integral/differential calculation circuit (hereinafter referred to as PID calculation circuit) 3Vi, a comparator,
4 is a multiplier, 5 is a controlled object, and 6 is a detection circuit. The subtracter 1 receives the control target value SP and the detection signal PV2 of the detection circuit 6.
The deviation amount ε is calculated by subtracting the difference ε. The PID calculation circuit 2 is designed to generate a control output signal corresponding to the deviation amount ε. Also, comparator 3Ff:,
The deviation amount ε is compared with a comparison value BAND k, which is a value determined by the characteristics of the controlled object, and a signal for controlling the multiplier 4 is generated based on the difference in magnitude as follows. In other words, when the comparator 3 has a deviation amount ε equal to the comparison value BAND, and 11) is also large, the multiplier 40 multiplier becomes "1", and the deviation amount ε becomes the comparison value BA.
ND! When the coefficient is also small, the multiplier 40 generates a coefficient signal so that the multiplication factor becomes a predetermined value determined by the characteristics of the controlled object with a value smaller than 11, for example, about 0.7 to 0.9. It has become. As a result, multiplier 4 has PID
The control output signal MVI supplied from the arithmetic circuit 2 is multiplied by a multiplication factor determined by the coefficient signal supplied from the comparator 3, and a new control output signal MVZ is output. Then, the control amount PV of the controlled object 5 controlled according to the control output signal MV2
I is fed back to the subtracter 1 via the detection circuit 6 as a detection signal PV2.

The operation of the apparatus according to the present invention configured as described above is as follows.
1 is significantly different from the control target value SP, so the deviation amount ε
is thicker than the comparison value BAND. Therefore, the multiplier 40 multiplication factor is set to 11'' by the output signal of the comparator 3, so the output signal MV2 of the multiplier 4 is equal to the control output signal MVI.
becomes the same value as BAND, and the control amount rapidly approaches the control target value. When the deviation amount ε becomes smaller than the comparison value BAND, the multiplier of the multiplier 4 is adjusted to the output signal of the comparator 3 to Since it is set to a predetermined value smaller than "1",
The output signal MV2 of the multiplier 4 is equal to the control output signal MVI
If the value is small, the change in the control amount PVI becomes gradual. Therefore, it is possible to prevent the control amount from overshooting, which makes it possible to follow the control amount more closely.

Figure 2 shows a simulation example of process control characteristics when this device is not used, and Figure 3 shows a simulation example of process control characteristics when this device is used, where A is the control output signal (MV2) and B is the control output signal. quantity (pvi), C is the control target value (SP'), and D is the comparison value (BAND). In FIGS. 2 and 3, dead time L=15 seconds and time constant T=100 seconds. From these figures, according to the device of the present invention, when the comparison value BAND becomes less than a predetermined value, the control output signal (curve A) decreases rapidly and the control rKJ amount (curve B) does not exhibit an overshoot. Recognize.

Although the above embodiment has been described with respect to an analog processing process control device, it can also be applied to a digital processing device, and in this case, the deviation calculation, comparator K, PID calculation, and multiplication are performed by a computer. The present invention can also be applied to prevent overshoot that occurs when changing from gradient control to constant value control in program control. In this case, the deviation between the control target value and the control amount in constant value control is calculated as a comparison value BAND. Just compare. Further, it has been confirmed through experiments that it is preferable to set the comparison value BANDO value to about half of the proportional band used for the control.

As explained above, the overshoot prevention device according to the present invention is configured to change the magnitude of the control output signal supplied to the controlled object depending on whether the deviation amount is larger than a predetermined value or smaller than a predetermined value. Therefore, fine control can be performed when the control amount is close to the control target value, and overshoot can be prevented with a simple device, so it is economical. have

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a graph showing an example of process control characteristic simulation of a conventionally used device, and Fig. 3 is a process control characteristic simulation of the device according to the present invention. Figure 2 is a graph showing an example. 1... Subtractor, 2... PID calculation circuit, 3...
... Comparator, 4 ... Multiplier, 5 ... Controlled object, 6
...Fist detection circuit.

Claims (1)

[Claims] A process control device that generates a control output signal by performing proportional, integral, and differential calculations according to the deviation amount, which is the deviation between the control target value of the controlled object and the actual controlled amount, and controls the controlled object using this control output signal. a comparator that outputs signals of different values when the deviation amount is smaller than and larger than a predetermined value determined by the characteristics of the controlled object; and a multiplier that outputs a new control output signal with a total change in magnitude, and the process control device is characterized in that the controlled object is controlled by the new control output signal.