JPH0312706A - Feedback controller - Google Patents

Abstract

PURPOSE:To secure the coincidence between the controlled variable and the target value while preventing the hunting and to prevent the occurrence of an offset by performing an integrating operation after choosing the optimum one of two integration times in accordance with the absolute value of the control deviation. CONSTITUTION:The main steam pressure is measured by a pressure gauge 41, and an addition element 12 adds the negative main steam pressure to the target value SV to obtain a control deviation (e). The deviation (e) is inputted to a comparison part 14 and an addition element 18 respectively. The part 14 compares the absolute value ¦e¦ of the deviation (e) with the prescribed value G. Then an integration action part 15 performs an integrating action with use of a comparatively long integration time Ti1 with ¦e¦>G. While an integrating action part 16 performs an integrating action with use of the integration time Ti2 smaller than the time Ti1 with ¦e¦<G respectively. When the value ¦e¦ is reduced less than the value G and the control value PV approximates considerably to the value SV, no hunting phenomenon occurs even with the reduced time Ti. In addition, the value PV is more approximate to the value SV and no offset is caused when the integrating operation is performed with use of the time Ti2.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a feedback control device that performs an integral operation.

(Prior Art) A typical example of a control system for a process having integral characteristics is a main steam pressure control system in a boiler plant. This control system is a system that controls the fuel flow rate and combustion air flow rate to the burner so that the main steam pressure in the boiler is constant.

In such a control system, PID operation is generally performed, but
The transfer function G (S) in this case is G (S) = Kp
[1+1/ (Ti −8) +Td−3]=−(1
) can be expressed as

Here, Kp is a proportional gain, S is a Laplace operator, Ti is an integral time, and Td is a differential time.

Next, a conventional feedback control device that performs the calculation expressed by the above equation (1) will be explained using FIG. 3 showing its algorithm. Control value (PV) and target value (S
V), the control value (PV), which has become a negative value by the proportional element 11, and the target value SV are added by the addition element 12, and the control deviation e is output. Based on this control deviation e, an integral operation is performed in the integral operation section 51 using a transfer function expressed as 1/(Ti-9). Further, using the output value from the proportional element 11, a differential operation is performed in the differential operation section 13 according to a transfer function represented by Td-5. Then, the addition element 18 adds the output value of the integral element 51 and the output value of the differential element 13 to the control deviation e, and outputs the result to the proportional operation section 19. The proportional operation section 19 performs a proportional operation by multiplying this output value by a proportional gain Kp, and outputs the manipulated variable MV to be determined.

(Problems to be Solved by the Invention) However, this conventional feedback control device has the following problems, which will be explained using FIG. 4.

FIG. 4 shows changes in the control value in this control system when a disturbance occurs and a control deviation occurs between the control value and the target value. When the integration time Ti is relatively long, the influence of the integration operation on control is small, and an offset occurs in which the difference does not decrease any further after the control value P■ approaches the target value S■ within a certain range. On the other hand, if the integration time Ti is shortened, a hunting phenomenon will occur in which the control value PV periodically fluctuates up and down, as shown in FIG. 6(b).

As described above, in the past, it was difficult to obtain optimal control characteristics no matter how the length of the integration time Ti was set.

The present invention has been made in view of the above circumstances, so that after the disturbance occurs, the hunting phenomenon can be prevented and the 11 target value S.
An object of the present invention is to provide a feedback control device that can bring a control value PV close to v and match it without causing an offset.

[Structure of the invention]

(Problem to be Solved by the Invention) The feedback control device of the present invention obtains a control deviation based on a control value and a target value, performs an integral operation using this control HI-difference, and outputs the obtained manipulated variable. The feedback control device includes a comparison section that compares the absolute value of the control deviation with a predetermined value, and a first integration time is used when the output of the comparison section indicates that the absolute value of the control deviation is greater than or equal to the predetermined value. On the other hand, if the absolute value of the control deviation is smaller than a predetermined value, the integral operation is performed using a second integration time shorter than the first integration time to calculate the manipulated variable. It is characterized by comprising an integral operation section that outputs an output.

(Function) When the absolute value of the control deviation is greater than a predetermined value (a), by performing an integral operation using a relatively long first integration time, the influence of this integral operation on control is small and the control value fluctuates. The control value gradually approaches the target value while preventing the hunting phenomenon from occurring. When the absolute value of the control deviation becomes smaller than the predetermined value, there is no risk of hunting phenomenon occurring, and it is necessary to make the control deviation closer to each other.
By performing the integration operation using the second integration time shorter than the integration time of S1, the control value approaches and coincides with the target value without an offset.

(Embodiment) A feedback control device according to an embodiment of the present invention will be explained using FIG. 1 showing its algorithm. This shows the configuration when applied to a boiler plant, and controls the fuel flow rate and combustion air flow rate supplied to No. 1 and No. 1 so that the main steam pressure output from the boiler maintains a constant value. It is something.

First, the mutual relationship between the feedback control device 1 and each component of the boiler plant will be explained.

The boiler section 30 includes a boiler 31 containing water 32 and a burner 3.
4, and the high-pressure steam in the boiler 31 is sent as main steam to a plant section such as a steam turbine (not shown). The pressure of this main steam is measured by a pressure gauge 41 and given to the control device 1 as a control amount Pv. Then, PID calculation is performed using this control device 1 or this control RPV, and the operation mMV outputted as the calculation result is given to the control valve 42 and the proportional element 45. The control valve 42 is connected to the burner 3 by the fuel pump 43 from the fuel tank 44.
This is to adjust the fuel flow rate supplied to 4, and operation i
The flow rate of fuel passing through the fuel vibrator 48 per unit time is controlled according to the MV. The flow rate of air required to burn this fuel in the burner 34 is determined by proportional calculation with respect to this fuel flow rate, and the combustion air flow rate is determined from the fuel flow rate given by the proportional element 45, and the air flow rate is determined by the operation damper 46. is output to.

The operating damper 46 controls the amount of air passing through the air vibrator 49 per unit time using the blower 47 so that this combustion air flow rate is supplied to the burner 34 .

Next, the configuration of the feedback control device 1 will be explained. Comparing the calculation elements of this control device 1 with FIG. 3 which shows the conventional case, it is found that in the conventional case, the integral operation was performed by one integral operation section 51 in any case, whereas in this embodiment The absolute value tel of the control deviation and the predetermined value G are compared in the comparison section 14, and depending on the result, the first integration operation section 15 or the second integration operation section 15 having a different length of integration time Ti or
The difference is that either one of the integral operation units 16 is selected to perform the integral operation. That is, the length of the integration time Ti in the transfer function G (S) of the above equation (1) is
It is to be used properly depending on the size of the value of let. Here, the same reference numerals are given to the other same calculation elements, and the explanation thereof will be omitted.

The main steam pressure value measured by the pressure gauge 41 is given to the proportional element 11, and is given as a negative value to the addition element 12 and the differential operation section 13.
given to. In the addition element 12, the negative main steam pressure and the target value SV are added to determine the control deviation e, which is output to the comparison section 14 and the addition drink 18.

The comparator 14 compares the absolute value lel of the control deviation e with a predetermined value G, and when let is greater than or equal to a predetermined value 0, it is sent to the first integral operation section 15, and when it is less than a predetermined 1 direct Second
A control deviation e is given to each of the integral operation units 16.

When let is greater than or equal to the predetermined value G, the first integral operation section 15 performs an integral operation using a relatively long first integral time Til. This allows the PI of integral operation to
The influence on the D control becomes smaller, the control value PV approaches the target value SV while the hunting phenomenon is prevented, and the absolute value lel of the control deviation decreases.

When this lel becomes smaller than the predetermined MG, the second integral operation section 16 adjusts the first integral time T.
The second integration time Ti2, which is shorter than il, is used to perform the integration operation. If the absolute value tel of the control deviation decreases below the predetermined value G and the control value PV approaches the target value SV considerably, there is no possibility of the hunting phenomenon occurring even if the integral time Ti is shortened. Further, in this case, it is necessary to bring the control value PV closer to the target value Sv to prevent offset from occurring. Therefore, a relatively short second integration time T
An integral operation is performed using i2.

Then, the calculation result of the integral operation by the first or second integral element is given to the adding element 18 via the adding element 17.

This addition element 18 includes addition element 1 as in the conventional case.
2 gives the control deviation e, and the differential element 13 gives the calculation result of the differential operation. The value obtained by adding these three calculation results from the addition element 18 is the proportional operation unit 1.
given to 9. In the proportional operation section 19, this given value is multiplied by a proportional gain Kp to find the operation In M V to be found. This value is then given as the output value of the feedback control device 1 to the control valve 42 and the proportional element 45 as described above.

Next, FIG. 2 shows changes in the control value PV when a feedback control device that performs such an operation is used. In this figure, in section 10, the state in which the control amount PV matches the target value Sv is maintained. Then, when some disturbance that changes the main steam pressure occurs at the time when the period changes from to to tl, a control deviation e occurs between the control amount Pv and the target value SV. In this case, the absolute value e1 of the control deviation
is larger than the predetermined value G (section tl), the relatively long first integration time Tit is used to gradually approach the target value SV while preventing the hunting phenomenon from occurring. If the value of lel becomes smaller than the predetermined value G (
In the interval t2), the integration operation is performed using the second integration time Ti2, which is lfi, and almost completely coincides with the target value S■ without any offset occurring. Similarly, if a disturbance occurs again and the controlled variable PV fluctuates greatly, the absolute 1 of the control deviation
The length of the integration time is used differently depending on the size of iatel, and the first integration time Tit is used while the value deviates significantly from the predetermined value 0 or more (section t3), and after it becomes smaller than the predetermined value G ( The interval t4) is made to coincide with the 1'' target value SV by using the second integration time Ti2.

In this way, according to this embodiment, by selecting the optimal one of the two integration times and performing the integration operation according to the magnitude of the absolute value of the control deviation, hunting can be prevented and the i1mPV can be controlled. Since it is possible to make the value coincide with the target value SV and prevent offset from occurring, extremely good control characteristics can be obtained for a process having integral characteristics.

The embodiments described above are merely examples and do not limit the present invention. For example, although this embodiment is applied to a boiler blunt, it can be applied to any process that has any integral characteristic.

Further, it is not necessarily necessary to include an arithmetic element that performs a proportional operation or a differential operation other than the proportional operation. Regarding the integration time, it is sufficient to use different sizes depending on the magnitude of the absolute value of the control deviation, and it is possible to use not only two types but three or more types of integration times. good.

〔Effect of the invention〕

As explained above, the feedback control device of the present invention uses a relatively long first integration time when the absolute value of the control deviation is greater than or equal to a predetermined value, and uses the first integration time when the absolute value of the control deviation becomes smaller than the predetermined value. Since the control is performed by performing an integral operation using the second integral time shorter than the f1 time, it is possible to prevent the hunting phenomenon from occurring and to make the control value match the f1 target value without causing an offset. Excellent characteristics.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a feedback control device according to an embodiment of the present invention, FIG. 2 is an explanatory diagram showing the control characteristics of the device, and FIG. 3 is a block diagram showing the configuration of a conventional feedback control device. , FIG. 4 is an explanatory diagram showing the control characteristics of the device. 1... Feedback control device, 11.45... Proportional element, 12, 17.18... Addition element,] 3...
Differential action section, 14... Comparison section, 15... First integral action section, 16... Second integral action section, one... Proportional action section, 30... Boiler section, 41 ...Pressure gauge, 42
...Control valve, 43...Fuel pump, 44...
Fuel tank, 46... operation damper, 47... blower. Figure 2 V

Claims (1)

[Scope of Claims] A feedback control device that obtains a control deviation based on a control value and a target value, performs an integral operation using this control deviation, and outputs the obtained manipulated variable. a comparison section that compares the control deviation with a predetermined value; and when the output of the comparison section indicates that the absolute value of the control deviation is greater than or equal to the predetermined value, an integration operation is performed using a first integration time. On the other hand, when the absolute value of the control deviation is smaller than the predetermined value, an integral operation is performed using a second integral time shorter than the first integral time, and the manipulated variable is output. A feedback control device comprising: an integral action section.