JPH0222702A - Process controller - Google Patents

Abstract

PURPOSE:To always keep an optimum controllability by correcting the variation gain of a speed type operation output signal, which is obtained by adding and synthesizing a speed type feedback control signal and a speed type disturbance compensation signal as the feed forward control output, based on a ratio of a position type operation output signal to a position type disturbance compensation signal. CONSTITUTION:Steam evaporated by heating of an evaporation tube 1-2 of a boiler 1 as the control object is supplied to the load side through a steam pipe 4, and the pressure of steam from the boiler 1 is detected by a pressure selector 5, and a steam pressure signal PV and a steam pressure target value signal PS are inputted to a feedback control means 6. The signal PV and the target value signal PS are compared with each other by the means 6 to input a speed type feedback control signal Cn to an adding means 7. The flow rate of steam from the boiler 1 is detected by a flow rate detector 8, and the square root of a steam flow rate signal Fs is extracted by a square root extraction operation means 9, and a linearized signal fs is inputted to a feed forward control model 10 as the disturbance signal, and an influence of the disturbance signal is removed by a gain adapting means 20.

Description

[Detailed description of the invention] [Objective of the invention] (Industrial application field) The present invention constantly optimizes feedback control and feedforward control in response to process gain changes due to qualitative changes in disturbances in intermediate processes. The present invention relates to a process control device that can be maintained.

(Conventional technology) In recent years, in process control, product demand (quantity 1 type 9
Feedback (FB) control, which is the basis of conventional process control, can be used to predict the effects of disturbances such as load changes, so that it can respond flexibly to changes in load and environment due to fluctuations in quality, etc. A combination of advance control, feedforward (FF) control, is being used to improve the response speed to disturbances.

FIG. 7 is a block diagram showing the basic configuration of feedforward/feedback control that combines this type of feedback control and feedforward control. 7th
As shown in the figure, during feedforward control, a disturbance such as a load change is detected, and the process is controlled in advance by M1 while compensating for the influence of this disturbance using the feedforward control output (disturbance compensation signal) from the feedforward control model. , the control deviation caused by this result is corrected in feedback control. In other words, in feedforward/feedback control, when a control deviation occurs as a result of feedforward control, feedback control outputs a feedback control output (adjustment signal) so as to make this control deviation zero; If the forward control realizes the ideal predictive anticipatory control operation, the feedback control function becomes unnecessary. However, when actually controlling the process with feedforward/feedback,
Ideally, feedforward control is affected by (a) errors in the feedforward control model, (b) changes over time, environmental changes, (c) effects of undetected disturbance elements, and (d) other uncertain factors. This is difficult to achieve visually, and requires the assistance of feedback control.

That is, as shown in FIG.
The operation output signal MV of the feedback control is a combination of the feedback control output and the feedforward control output, and when the feedforward control is ideally executed, the (operation output signal MV) command c feedforward control output ), the feedback control output is nearly zero. Therefore, the contribution of feedback control in feedforward/feedback control,
In other words, the larger the feedback control output becomes, the more the suppression characteristic of the influence of disturbance deteriorates.

Therefore, basically, the gain of the feedforward control model is corrected so that it becomes (manipulation output signal MV) - (fieldforward control output), that is, (feedback control output) - 0.

However, how to modify the gain so that it becomes (manipulation output signal MV) - (feedforward control output) depends on the characteristics of the process. This division is shown in FIG. In FIG. 9, the gain adaptive feedforward/feedback control systems have traditionally been type 1 and type 3, that is, for non-mixing processes and for mixed processes, but type 2, which is located between these, That is, there is still no gain-adaptive feedforward/feedback control scheme for intermediate processes (such as boiler steam pressure, which focuses on the "quantity" of disturbances, but also involves quality). However, recently, an increasing number of boilers are using low-grade fuels (wild fuels) whose unit calorific values vary widely, such as pulverized coal and by-product fuels generated in factories, and the controllability of these fuels has become more sophisticated. It has been strongly requested.

(Problems to be Solved by the Invention) As described above, conventionally there has been a problem that there is no optimal process control device for intermediate processes.

An object of the present invention is to provide a highly reliable process control device that can always maintain optimal feedback control and feedforward control in response to changes in process gain due to qualitative changes in disturbances in intermediate processes. It's about doing.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention inputs a process quantity from a controlled object and a target value signal of this process quantity, and calculates the deviation between the two. A feedback control means that performs the A-section calculation and outputs a speed-type feedback adjustment signal, and a position-type disturbance compensation signal that is obtained by inputting a disturbance signal and multiplying this disturbance signal by a predetermined feedforward gain. feedforward control means that converts the signal into a speed-type signal and outputs it as a speed-type disturbance compensation signal, and a speed-type feedback adjustment signal from the feedback control means and a speed-type disturbance compensation signal from the feedforward control means. means for converting a speed-type manipulated output signal into a position-type signal and output it to a controlled object as a position-type manipulated output signal; and gain correction means for correcting the gain by the change in the gain.

(Function) Therefore, in the present invention, the velocity-type feedback adjustment signal, which is the feedback control output, and the velocity-type disturbance compensation signal, which is the feedforward control output, are determined based on the ratio of the position-type operation output signal and the position-type disturbance compensation signal. By modifying the gain of the change in the speed-type manipulated output signal obtained by addition and synthesis, feedforward control and feedback control can be performed in response to changes in the gain of the controlled object due to qualitative changes in disturbances in intermediate processes. The gain can be automatically modified to always obtain optimal controllability. This makes it possible to maintain stable and optimal control characteristics at all times.

(Example) First, the concept of the present invention will be explained. Here, a case will be described in which the present invention is applied to a process in which the steam pressure of a boiler is detected and the fuel flow rate to the boiler is adjusted so that the steam pressure is constant in response to changes in the steam flow rate.

First, determine the boiler process values as shown in the table below.

is: Enthalpy of steam (Kcal/1on).

iw: Enthalpy of water supply (Kcal/1on).

η: Boiler efficiency FP: Unit calorific value of fuel (Kcal/Nm3) Next, in intermediate processes such as boiler steam pressure control, both feedback control gain and feedforward control gain change in response to qualitative changes in disturbance. Let's talk about that.

Boiler steam pressure P is expressed by the following formula.

dP/dt-PR(77Qp Qs-Pc)/T-Q
R... (1) Here, P: boiler steam pressure, PFL: rated pressure, T:
Boiler time constant, Q8: Rated evaporation amount, η: Efficiency, Q:
Amount of heat supplied, Q: Amount of heat taken out by steam, Pc: Steam pressure adjustment output.

According to equation (1), in order for the boiler steam pressure P to remain unchanged even if the load Qs changes, dP/dt-0, that is, (ηQp -Qs -Pc) -0□"-(2) From equation (2), Qp − (Qs
Ten pages. )/η = (Qs/η) 10(Pc/η)...
(3) is obtained. Here, (Qs/η) represents the feedforward control output, and (Pc/η) represents the feedback control output. Furthermore, using the specifications in the previous table, Qp −Fp XCp −Fps×Cp−f psX
F P(MAX)X CpQs =Fs
is-iw)-fsXFstuAx+X(i5 i
w)... (5) is obtained. Substituting these equations (4) and (5) into equation (3), f psX F P(MAXIX CF= ((fs
XFSIMAXIX (is iw) l
/77)+(Pc/η) Therefore, fps= fFs+uAx+X (is-fw) x
is 1/(ηX Cp X F p+MAX+1+
(Pc / (77×Cp X Fp+uAx+))
= (KI X fs) / (ηXCp) ten (K2
XPC) / (77XCP)... (6
) becomes. Here, (Kz X fs) / (77X
Cp ) is the feedforward control output, (K:zX
Pc)/(ηXCp) respectively represent feedback control outputs. Also, Kt-Fs+uAx+X(is iw)/F P
(MAX)% K2=1/FP(MAX+
is a constant. As is clear from equation (6), both the feedforward control output and the feedback control output change as the boiler efficiency η and the unit calorific value CF of the fuel change.
It can be seen that the gain is similarly affected.

The efficiency of a boiler changes with environmental conditions and over time, depending on the size of the load, and the unit calorific value of the fuel also fluctuates more with lower-grade fuels.If the effects of these changes are not automatically compensated for, feedforward control will not work. Both feedback control deviates from the optimum point and the controllability deteriorates. here,(
6) Transforming the equation, f PS"" (KI
, )/ (η XCp) ・・・・・・
・(7) is obtained. From equation (7), it can be seen that the gains of feedforward control and feedback control may be corrected in exactly the same way.

Next, a gain adaptation formula indicating how to modify the gain is determined. FIG. 2 is a diagram showing the temporal movement of the manipulated output signal MV and the position-based disturbance compensation signal FF, where A is the manipulated output signal MV and B is the position-based disturbance compensation signal FF. As described above, the gain may be modified based on the ratio between the operation output signal MY and the positional disturbance compensation signal FF. That is, at the current time (n-1), the feedforward control output FF n-1 is changed to the manipulated output signal M V n-
1 (optimal output signal Xn-1 at time -n-1), that is, the gain adaptation coefficient is k
When n-1, MVn-1-k n-I

Next, the feedforward control output F F n-1 is F
The optimal output signal Xn when changing to Fn is: Become.

Since this equation (9) is a position type calculation formula, it is converted into a velocity type calculation formula.

Xn-Xn-1+ΔXn Therefore, ΔXn = Xn-Xn-1 = (MVn-I
1) MVn-1 = (MVn-1/FF n-1) x (F
Fn −F Fn−1)=(MVn−1/F
F n-1) X ΔFFn... (10
) -kn-LX ΔF Fn...
・(11) In other words, it is sufficient to multiply the current change ΔFFn by the previous gain adaptation coefficient k n-1, and (
Considering that the same gain adaptation coefficient is sufficient for feedforward control and feedback control obtained from equation 7), ΔMVn −kn−I X (ΔFFn +Δ
Cn)...(12). Here, ΔFFn is a feedforward control output and ΔCn feedback control output.

As described above, the present invention attempts to automatically correct the gains of feedforward control and feedback control by skillfully combining position type calculation and velocity type calculation in a feedforward/feedback control system.

Hereinafter, an embodiment of the present invention based on the above-mentioned idea will be described with reference to the drawings.

FIG. 1 is a block diagram showing a configuration example when the present invention is applied to a boiler steam pressure control device.

In FIG. 1, burner 1-
1 is supplied with fuel via a fuel transport pipe 2 from a fuel supply source (not shown), and air is supplied via an air transport pipe 3 from an air supply source (not shown). The burner 1-1 burns the fuel together with the air, heating the evaporation tube 1-2 of the boiler 1, heating and evaporating water, which is the fluid to be heated, and generating steam. It is supplied to a load (customer) side (not shown) via the fuel cell.

On the other hand, the pressure of steam, which is a process amount generated from the boiler 1, is detected by a pressure detector 5, and this steam pressure signal P■ is manually inputted to the feedback adjustment means 6 as a feedback signal. Further, the steam pressure target value signal Ps is inputted to the feedback adjustment means 6. Furthermore, the feedback adjustment means 6 compares the steam pressure signal pv from the pressure detector 5 and the steam pressure target value signal Ps, and performs PID:A clause calculation etc. so that the deviation between the two becomes zero, Velocity type feedback adjustment signal Δ which is the feedback control output
Cn is obtained and inputted to the addition means 7. Due to the above,
It constitutes a feedback control means.

On the other hand, the flow rate detector 8 measures the flow rate of steam generated from the boiler 1.
This steam flow rate signal Fs is linearized by the square root calculation means 9 to obtain a signal fs, which is input to the feedforward control model 10 as a disturbance signal. In general, this feedforward control model 10 has two cases: a case in which only static compensation is performed using a setting coefficient K, and a case in which this static compensation is combined with dynamic compensation in which the influence of sudden changes in disturbance is compensated for by its transfer function. In this embodiment, the former case will be explained for ease of explanation, but the latter case can be similarly applied to the static compensator. That is, in the feedforward control model 10, the steam flow rate signal fs is multiplied by the static compensation coefficient K to obtain the position-type disturbance compensation signal FFn, which is input to the difference calculation means 11 to calculate the velocity-type disturbance compensation which is the change thereof. Signal ΔFFn(
-F F n -F F n-1) and inputs this to the addition means 7 as a feedforward control output.

The above constitutes a feedforward control means.

On the other hand, the addition means 7 adds and synthesizes the speed-type feedback adjustment signal ΔCn from the feedback adjustment means 6 and the speed-type disturbance compensation signal ΔFFn from the difference calculation means 11, and outputs this output signal (ΔCn+ΔFFn) as a speed-type operation output. The signal is input to the multiplication means 12 as a signal. Furthermore, the multiplier 12 multiplies the speed-type operation output signal from the adder 7 by a gain adaptation coefficient kn-1, which will be described later, to automatically correct the gain and obtain a signal ΔMVn -kn-I
+ΔFFn). Furthermore, this signal ΔM V n is input to the velocity type/position type signal conversion means 13 to convert it into a position type operation output signal MVn=MVn-1+ΔM V n, which is used as a fuel flow rate command signal fFs to be sent to the fuel flow rate adjustment means. 14.

On the other hand, the flow rate detector 1 measures the flow rate of fuel supplied to the boiler 1.
5, and this fuel flow signal FF is detected by the square root calculating means 16.
is linearized to obtain a signal fF, which is input to the fuel flow m adjustment means 14. Further, in the fuel flow rate adjusting means 14,
and a fuel flow rate command signal fFs from the speed type/position type signal conversion means 13.

Compare the fuel flow rate signal fF from the square root calculation means 16,
By performing Pl adjustment calculation etc. so that the deviation between the two becomes zero, and giving this output signal to the fuel control valve 17 as a fuel command signal for the boiler 1, the fuel flow rate is adjusted and the boiler 1 generates as a whole. It is configured to control the steam pressure to a predetermined value.

On the other hand, the positional disturbance compensation signal FF from the difference calculation means 11
n and the position-type operation output signal M V n from the velocity-type/position-type signal conversion means 13 are input to the dividing means 18, and the ratio between the two is determined to obtain the gain adaptation coefficient kn - MVn /FFn.
is calculated and further manually inputted to the delay means 19 to obtain the gain adaptation coefficient k n-1 of the previous time, that is, the previous time (n-1).
is calculated and inputted to the multiplication means 12 as a multiplication element.

Here, the division means 18 and the delay means 19 constitute a gain adaptation means 20, and the gain adaptation means 20 and the multiplication means 12 constitute a gain modification means.

In the boiler steam pressure control device configured as described above, the pressure of steam generated from the boiler is detected by the pressure detector 5, and the steam pressure signal PV is input to the feedback adjustment means 6. The feedback adjustment means 6 compares the steam pressure signal P■ and the steam pressure target value signal Ps, performs PID adjustment calculations, etc. so that the deviation between the two becomes zero, and generates a speed type feedback adjustment signal which is a feedback control output. ΔCn is input to the adding means 7. Further, the flow rate of steam generated from the boiler is detected by the flow rate detector 8, and the steam flow rate signal Fs is inputted to the feedforward control model 10 as a disturbance signal through the square root calculation means 9. In the feedforward control model 10, the steam flow rate signal fs is multiplied by the static compensation coefficient K to obtain the position-type disturbance compensation signal FFn, which is input to the difference calculation means 11 to generate the velocity-type disturbance compensation signal ΔFFn(-FFn-FFn- 1
) is obtained, which is input to the addition means 7 as a feedforward control output.

On the other hand, the adding means 7 adds and synthesizes the speed-type feedback adjustment signal ΔCn from the feedback adjustment means 6 and the speed-type disturbance compensation signal ΔFFn from the difference calculation means 11 to obtain a speed-type operation output signal (ΔCn+ΔFFn). , this is multiplied by the gain adaptation coefficient k n-1 from the gain adaptation means 20 in the multiplication means 12 to obtain a signal ΔMVn −
kn-IX(ΔCn+ΔFFn) is obtained. Then, this signal ΔM V n is converted into a position type operation output signal MVn−MVn−1+ΔMV by the velocity type/position type signal conversion means 13.
n1. : is converted and inputted to the fuel flow rate adjustment means 14 as the fuel flow rate command signal f's. Further, the flow rate of fuel supplied to the boiler 1 is detected by the flow rate detector 15, and this fuel flow rate signal FF is inputted to the fuel flow rate adjustment means 14 through the square root calculation means 16. The fuel flow ffi adjustment means 14 compares the fuel flow rate command signal f's and the fuel flow rate signal fF, performs PI adjustment calculation etc. so that the deviation between the two becomes zero, and adjusts the fuel command signal to the fuel control valve. 17, the fuel flow rate to the boiler 1 is adjusted so that the steam pressure generated by the boiler 1 is controlled to a predetermined value.

In this case, the multiplier 12 multiplies the speed-type operation output signal (ΔCn+ΔFFn) by a gain adaptation coefficient k n-1 as follows. In other words, the gain adaptation coefficient k n-1 is the ratio (MVn/FFn) between the position-based disturbance compensation signal FFn and the position-based manipulated output signal MV n.
The division means 18 calculates n as
9, it is obtained as the previous (n-1) gain adaptation coefficient k n-1. Therefore, boiler 1
When there is no qualitative change in the disturbance at Shape operation output signal (ΔCn+Δ
FFn) is multiplied by a gain adaptation coefficient kn-1 of 1, that is, the speed-type operation output signal (ΔCn+ΔFFn) from the adding means 12 is input to the speed-type/position-type signal conversion means 13 with the same magnitude. will be done.

On the other hand, when the gain of the boiler 1, which is the controlled object, changes due to a qualitative change in the disturbance in the boiler 1, since the magnitudes of the position-based disturbance compensation signal FFn and the position-based operation output signal M V n are different, both The ratio (M V n/
F F n ) has a size other than 1, and the multiplication means 12
Then, for the speed-type manipulated output signal (ΔCn+ΔFFn), a gain adaptation coefficient k n-1 whose size corresponds to the ratio of both is set.
is multiplied, that is, the gain of the change in the velocity type operation output signal (ΔCn+ΔFFn) from the adding means 12 is corrected and inputted to the velocity type/position type signal conversion means 13.

As described above, in the boiler steam pressure control device of this embodiment, the speed type feedback adjustment signal, which is the feedback control output, is adjusted in response to the change in the gain of the boiler 1 as the control target due to the qualitative change in the disturbance in the intermediate process. A gain adaptation coefficient k is added to the velocity-type operation output signal (ΔCn+ΔFFn) obtained by adding and combining ΔCn and the velocity-type disturbance compensation signal ΔFFn, which is the feedforward control output.
Since the gain is corrected by multiplying it by n-1, (a) the gain of the feedforward control model 10 can be optimized more quickly, and the feedforward control function is always maximized. It becomes possible to do so.

(b) By simultaneously correcting the feedback control gain, it is possible to ensure control stability and prevent a decrease in controllability.

This extremely excellent effect can be obtained.

As described above, the boiler steam pressure control device can be made more sophisticated, and this advancement makes it possible to supply stable and high-quality steam.

Furthermore, it is predicted that the use of low-grade fuels such as pulverized coal and by-product fuels will increase in the future due to limited oil resources and rising energy costs, but the boiler steam pressure control system of this example will be applied. By doing so, controllability can be improved, and it can be expected to greatly contribute to the development of industry.

It should be noted that the present invention is not limited to the above-mentioned embodiments, but can be similarly implemented in the following manner.

(a) The gain adaptation means is not limited to the configuration shown in FIG. 1; for example, as shown in FIG.
is composed of two delay means 21 and 22 and a division means 18, and the previous value M V n-1 of the position-type operation output signal is divided by the previous value F F n-1 of the position-type disturbance compensation signal ( MVn-1/F F n-1) may be output as the gain adaptation coefficient kn-1 (7).

(b) The gain adaptation means is not limited to the structure shown in FIG. 1; for example, as shown in FIG.
It is composed of a 0 dividing means 18 and a delay means 19, and also includes a filter means 23, and smoothes the gain adaptation coefficient k n-1, which is the output signal from the gain adaptation means 20, to obtain k
n-1, and this may be output as the gain adaptation coefficient kn-1. This allows the gain to be corrected gradually.

(C) The gain adaptation means is not limited to the configuration shown in FIG. 1; for example, as shown in FIG. 5, the gain adaptation means 20 having the configuration shown in FIG. The gain adaptation coefficient k n-1, which is the output signal of the adaptation means 20, may be smoothed to k n-1, and this may be output as the gain adaptation coefficient k n-1.

This allows the gain to be corrected gradually.

(d) In the above embodiment, the case where the feedforward control model 10 only compensates for the static characteristics of disturbance is described, but this is not limited to this, and dynamic characteristic compensation may also be added. As shown in the figure. That is, the disturbance static compensation signal FFn is input to the dynamic characteristic compensation means 25 and the output signal obtained by incomplete differentiation is applied to the gain adaptation means 20 by the multiplication means 26.
After multiplying by the gain adaptation coefficient k n-1 which is the output signal of , the addition means 27 may add j7 to the positional operation output signal M V n.

(e) In the above embodiment, the present invention is applied to a boiler steam pressure control device, but the present invention is not limited to this and can be similarly applied to other process control devices that control intermediate processes.

〔Effect of the invention〕

As explained above, according to the present invention, the velocity type feedback 1''J8 node signal which is the feedback control output,
The gain for the change in the velocity-type manipulated output signal obtained by adding and combining the velocity-type disturbance compensation signal, which is the feedforward control output, is corrected based on the ratio of the position-type manipulated output signal and the position-type disturbance compensation signal. This provides an extremely reliable process control device that can always maintain optimal feedback control and feedforward control in response to changes in process gain due to qualitative changes in disturbances in intermediate processes. can.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention applied to a boiler steam pressure control device, Fig. 2 is a diagram for explaining the operation of the embodiment, and Figs. Main part block diagrams showing other embodiments when the invention is applied to a boiler steam flow rate control device, FIG. 7 is a block diagram showing the basic configuration of feedforward/feedback control, and FIG. 8 is a block diagram showing the basic configuration of feedforward/feedback control. FIG. 9 is a diagram illustrating the structure of the operation output signal of the conventional method. DESCRIPTION OF SYMBOLS 1... Boiler, 1-1... Burner, 1-2... Evaporation pipe, 2... Fuel transport pipe, 3... Air transport pipe, 4...
...Steam vibrator, 5...Pressure detector, 6...Feedback adjustment means, 7...Addition means, 8...Flow rate detector, 9...Square root calculation means, 10...Feedforward Control model, 11... Difference calculation means, 12...
- Multiplying means, 13... Velocity type/position type signal conversion means,
14...Fuel flow rate adjustment means, 15...Flow rate detector,
16... Square root calculation means, 17... Fuel control valve, 18
...Dividing means, 19... Delay means, 20... Gain adaptation means, 21.22... Delay means, 23.24.
... Filter means, 25... Dynamic characteristic compensation means, 26.
...Multiplication means, 27...Addition means. Applicant's agent: Patent attorney Takehiko Suzue 100s. Figure 2 Figure 1 Figure Figure

Claims (1)

[Scope of Claims] Feedback control means that inputs a process quantity from a controlled object and a target value signal of this process quantity, performs adjustment calculations so that the deviation between the two becomes zero, and outputs a speed-type feedback adjustment signal. and feedforward control means for inputting a disturbance signal and converting a position-type disturbance compensation signal obtained by multiplying the disturbance signal by a predetermined feedforward gain into a velocity-type signal and outputting the same as a velocity-type disturbance compensation signal; A velocity-type operation output signal obtained by adding and combining the velocity-type feedback adjustment signal from the feedback control means and the velocity-type disturbance compensation signal from the feedforward control means is converted into a position-type signal, and the above-mentioned position-type operation output signal is converted into a position-type signal. a means for outputting the output to the controlled object; and a gain modification means for modifying the gain of the change in the speed-type operation output signal based on the ratio of the position-type operation output signal and the position-type disturbance compensation signal. A process control device characterized by: