JPH02721B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a process control device that includes an integral element.

For example, a turbine speed control system for a thermal power plant is shown in FIG. That is, the steam Q supplied from the boiler is controlled by the control valve 11, and then supplied to the turbine 12, which imparts rotational torque and rotates the turbine 12. turbine 12
The rotational speed N is detected by the rotational speed detector 13, inputted to the process input/output device 15 in the process control device 14, and predetermined calculation is performed by the arithmetic and control device 16, thereby controlling the control valve 11. do.
The process control device 14 in this case is constituted by a computer system, the functional blocks of which are shown in FIG. This control system operates so that the measured value signal a of the controlled object 17 (turbine rotation speed N) matches the target value _a0 set in the target setting device 18, and this operates as follows. conduct. That is, the target value a ₀ and the measured value signal a are compared by the comparator 19, and the deviation Δa is determined by the proportional element 2
0, a differential element 21, and an integral element 22, and are added by an adder 23 to generate a control signal b. This control signal b is given to the operating device 24 (driving mechanism of the control valve 11) to generate an operating signal c. The controlled object 17 changes in response to this operation signal c, causing the measured value signal a to change.

In such a control system, the integral operation signal d has the function of increasing or decreasing the operation over time when the measurement value signal a differs from the target value _a0 , and eliminates the offset of the deviation Δa. However, if the deviation △a does not disappear for some reason, the integral operation signal d continues to increase (or decrease), and the operation device 24
exceeds the operating range. This phenomenon is generally called integral pressure saturation (reset windup).

If the integration exceeds this saturation state, when shifting to reverse operation, the controller 24 will not operate until this integral value, that is, the integral operation signal d, falls below the saturation point, resulting in a delay in control operation. Become. In order to avoid such a reset windup, a switch means 25 as shown in FIG. 3 is generally provided to kill the so-called integral. That is, the saturation point detection means 26 of the operation device 24 detects that the operation signal c has reached a predetermined limit value, and the switch means determines that saturation has been reached and kills the integral operation of the integral element 22. Open 25.
This eliminates integral pressure saturation in the control system.

However, even if the above-mentioned switch means 25 and saturation point detection means 26 are provided in order to eliminate integral pressure saturation, this only detects the saturation point of the operating device 24, and therefore the limit value of the operating signal c is Inconveniences may occur depending on the setting method. If we focus on suppressing integral pressure saturation,
Even if the operating range of the operating device 24 can be widened, the limit value must be set to a low value, and the range in which the integral element 22 operates becomes narrower.
Further, in that case, since control is performed only by the proportional element 20, the deviation Δa remains or an operation delay occurs.

On the other hand, if the limit value is set to a high value, the integral element 22 may operate beyond the operation range of the controller 24 if there is a disturbance element in the operation signal c or if the time constant of the controlled object 17 is large. Therefore, there is a high possibility that integral pressure saturation will occur. In the end, simply killing the integral element 22 in this way is no longer effective.

An object of the present invention is to provide a process control device that does not have the above-mentioned drawbacks and inconveniences.

An embodiment of the present invention will be described below. First, the basic operation of the present invention is as follows.

Focusing on the polarity reversal of the deviation △a between the measured value signal a and its target value a ₀ , when the polarity of this deviation △a is reversed, the integral value of the integral element 22 is changed to the operating signal c at that time under certain conditions. This is to balance the value of .

a When the polarity of the deviation Δa is reversed from positive to negative, and when the operation signal c<integral operation signal d, the value of the integral operation signal d is made to match the value of the operation signal c at that time for balance.

b When the polarity of the deviation Δa is reversed from negative to positive, and when the operation signal c>integral operation signal d, the value of the integral operation signal d is made to match the value of the operation signal c at that point in time for balance.

c In cases other than a) and b) above, the integral value is applied as is, and no balance processing is performed.

Next, FIG. 4 shows a block configuration of the process control device 14 of the present invention. The polarity reversal detection means 34 detects a polarity change in the deviation Δa between the target value a ₀ set in the target setting device 18 and the measured value signal a, and the integral value balance means 38 is operated.

FIG. 5 is a flowchart showing the operation of the integral value balancing means 38. When the polarity reversal detection means 34 detects that the polarity of the deviation Δa has changed, the integral value balance means 38 obtains the integral operation signal d at that time and stores it as a signal d ₀ (a). Then, it is determined whether the polarity of the deviation △a has been reversed from positive to negative (b), and if the polarity of the deviation △a has been reversed from positive to negative, the polarity of the operation signal c and the above-mentioned Compare with the integral operation signal d ₀ at the time of inversion
(c). As a result of the comparison, the integral operation signal d ₀ is greater than the operation signal c.
If is larger, the integral operation signal d, which is the output of the integral element 22, is made to match (balance) the value of the operation signal c at that time from d0 ( _d ). This takes place via switch means 35. On the other hand, if the operation signal c is larger than the integral operation signal d ₀ (c), no balance processing is performed.

Next, if the deviation △a is not reversed from positive to negative, it is determined whether the deviation △a has been reversed from negative to positive (e), and the deviation △a is reversed from negative to positive. In some cases, the operation signal c is compared with the integral operation signal d ₀ at the time of polarity reversal (f). As a result of the comparison, if the operation signal c is larger than the integral operation signal d ₀ , the integral operation signal d, which is the output of the integral element 22, is made to match (balance) the value of the operation signal c at that time from d ₀ (g).
This takes place via switch means 35. On the other hand, the balance process is not performed when the operation signal c is smaller than the integral operation signal d ₀ or when there is no polarity reversal of the deviation Δa (F) and (E).

FIG. 6 is a characteristic diagram thereof. 6A and 6C show the case where the polarity of the deviation Δa is reversed from positive to negative, and FIGS. 6B and D show the case where the polarity of the deviation Δa is reversed from negative to positive. Here, if normal PID control is performed without limiting the integral operation signal d, the integral operation signal d will be
a ₁₁ ^- a ₁₂ ^- a ₁₃ , a ₂₁ ^- a ₂₂ ^- a ₂₃ in Figure 6B, Figure 6C
In this case, it changes as a ₃₁ ^- a ₃₂ ^- a ₃₃ , and in Figure 6 D, it changes as a ₄₁ ^- a ₄₂ ^- a ₄₃ . In this case, when the polarity of the deviation △a is reversed from positive to negative as shown in Fig. 6A and C, that is, when the measured value a exceeds the target value _a0 , the integral operation signal d is larger than the operation signal c. In this case, there is a possibility that there will be a delay in the integral operation when the integral element 22 reversely operates. Also, as shown in Figure 6B, the deviation △
Similarly, when the polarity of a is reversed from negative to positive and the integral operation signal d is smaller than the operation signal c, there is a risk that the integral operation will be delayed.

Therefore, as described above, when the polarity of the deviation △a is reversed from positive to negative and the operation signal c is smaller than the integral operation signal d, the integral operation signal d is made to match the operation signal c, while the deviation △a When the polarity is reversed from negative to positive and the operation signal c is larger than the integral operation signal d, the integral operation signal d is made to match the operation signal c.

Therefore, its characteristics are shown in Figure 6A.
a ₁₁ ^- a ₁₂ ^- a ₁₄ ^- a ₁₅ , a ₂₁ ^- a ₂₂ ^- a ₂₄ ^- a ₂₅ in Figure 6B,
In Figure 6C, it changes as a ₃₁ ^- a ₃₂ ^- a ₃₄ ^- a ₃₅ .
Note that the hatched portion in FIG. 6 indicates the amount of integration that is required to be smaller than when the present invention is not applied, indicating that there is less delay in the integration operation in the reverse operation. In addition, in the case of Fig. 6 D, the deviation △
This is a case where the polarity of a is reversed from negative to positive and the operation signal c is smaller than the integral operation signal d, and in order to make the integral operation work more effectively for control, it is better not to perform balance processing, so balance processing is not performed. do not have.

Next, a steam temperature control system at a boiler outlet in a steam generator (boiler) of a thermal power plant to which the present invention can be applied will be described with reference to FIG. That is, the water supply pump 41 is connected to the boiler 40.
Water compressed by
2, it is heated by a fire 44 of fuel ejected from a burner 43. Thereafter, this fluid (water or steam) is further heated in a superheater 45, and the fluid turned into steam is supplied to the steam turbine 12 via the control valve 11.

In this process, the steam temperature is controlled by the steam temperature measured by the temperature detector 46 as the control target 17.
Considering Ta, the fuel flow rate control valve 47 as the operating device 24 and the change characteristics of the fuel and fluid temperature Tc as the operating signal c, the fluid temperature detected by the detector 48.
Consider Tc. Note that the opening degree of the flow rate control valve 47 is controlled by a control signal b from the process control device 14. The reason why the flow rate of the feed water pump 41 is input to the process control device 14 is to predetermine the fuel flow rate corresponding to the flow rate of the water feed pump 41 in order to maintain the steam temperature Ta at its target value. This is because the time constant of the process in the boiler outlet temperature control system is very long, so the control delay can be suppressed as much as possible.

As described above, the present invention works to minimize the control delay due to the integral operation after the polarity reversal of the deviation Δa. Therefore, it is effective when the range of integral pressure saturation is wide and the integral operation is strongly exerted on control. Further, even when the operation signal c contains a disturbance element, instability due to integration can be eliminated, which is effective.

[Brief explanation of drawings]

Figure 1 is a block diagram of the Durbin rotation speed control system.
2 and 3 are block diagrams of a conventional process control device, FIG. 4 is a block diagram of a process control device of the present invention, FIG. 5 is a flowchart showing the process of the present invention, and FIG. 6 is a block diagram of the process control device of the present invention. Figure 7 is a block diagram of the boiler inlet steam temperature control system. 14... Process control device, 15... Process input/output device, 16... Arithmetic control device, 17... Controlled object, 18... Target setter, 20... Proportional element, 21... Differential element, 22... integral element, 24
...Manipulator, 27...High value priority means, 29...Integral calculation means, 32...Integral pressure saturation removal means, 34
. . . polarity reversal detection means, 36 . . . operation signal determination means, 38 . . . integral value balance means.

Claims (1)

[Claims] 1 A control signal is calculated by an arithmetic and control device including an integral element so that the deviation between the measured value signal of the controlled object and its target value is zero, and this control signal is given to the operating device, thereby obtaining the control signal. In a process control device that controls the controlled object in response to an operation signal, a polarity reversal detection means for detecting that the polarity of the deviation between the measured value signal and its target value is reversed;
When this polarity reversal detection means detects a polarity reversal of the deviation, it compares the operation signal with the output of the integral element, and when the deviation is reversed from positive to negative, the operation signal is greater than the output of the integral element. When the deviation is smaller than the output of the integral element, the integral value of the integral element is used as the value of the operation signal, and on the other hand, when the deviation is reversed from negative to positive and the operation signal is larger than the output of the integral element, the integral value of the integral element is used as the value of the operation signal. 1. A process control device comprising integral value balancing means that uses the value of an operation signal as an integral value balance means.