JPH11287405A - Water level control device for boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device to prevent the occurrence of unstable control during rise and fall and increase control precision to a high value during normal operation and perform control of a water level to a constant value as the occurrence of overshoot or undershoot during excess combustion or undercombustion is suppressed. SOLUTION: A stabilizing computing part 12 detects reverse reaction phenomenon wherein overshoot or undershoot occurs, reduces a ratio of a control amount of a feedforward system by gradually decreasing the factor (k) of a factor computing part 9 until the phenomenon is prevented from occurring, and increases a ratio of a control amount of a feedback system by gradually increasing the factor of a factor computation part 11. Further, when, during a rise and a fall, a steam generating amount of a boiler 1 is reduced to a value lower than a set value, a factor (k) is limited to a low value, and a ratio of a control amount of the feedforward system is limited to a low value and unstable control is prevented from occurring.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus having a feedback system and a feed-forward system for controlling the flow rate of water supplied to a boiler and controlling the water level of the boiler at a constant level.

[0002]

2. Description of the Related Art Automatic control of a boiler can be roughly divided into three types: combustion control, water supply control, and steam temperature control. Among these, the water supply control enhances the safety and efficiency of the boiler by controlling the water level of the boiler drum at a constant level.

As shown in FIG. 3, a conventional water level control device has a water supply control system in a minor loop, and a feedback system and a feedforward system. Water is supplied to the boiler 1 by water supplied from a water supply pump 2, and the amount of supplied water is controlled by controlling the opening of a supplied water flow control valve 3. In this opening degree control, the water supply amount control unit 4 calculates the difference between the water supply amount command SV and the water supply amount detection value F _K (PV) detected by the water supply amount detector 5 by PID (proportional / integral / differential) calculation. Control amount M
This is performed by feedback control obtained as V.

The water supply amount command SV for the water supply amount control unit 4
Is set to have a feedback system and a feedforward system. The feedback system includes a boiler water level L (PV) detected by the water level control unit 6 and a water level set value and a water level detector 7.
Is calculated as a water level control amount MV by performing a PID (proportional / integral / differential) calculation.

[0005] feedforward system generated by the detection value (the value obtained by converting the amount of water) F _J a coefficient calculation unit 9 of the steam amount detector 8 for detecting the amount of steam generated from the detection boiler 1 is multiplied by the coefficient k steam A water amount decrease (water level decrease) of the boiler 1 according to the amount is predicted, and the prediction signal is transmitted to the water level control unit 6.
The water supply amount compensation according to the generated steam amount is performed by adding to the water level control amount MV from the adder 10 by the adder 10.

[0006] In such a water level control device, the water supply amount control section 4 increases the sensitivity of controlling the water supply amount to the boiler 1. On the other hand, the water level control unit 6 serving as a feedback system sets its sensitivity low according to a gradual change in the water level, and compensates for this control delay by a feedforward system based on the generated steam amount.

[0007]

The conventional water level control device can perform good water level control in a stable combustion state, but has an unstable control state when the boiler starts up or shuts down, or when the combustion is excessive or under combustion. This may cause an abnormality in the boiler water level.

That is, when starting up and shutting down the boiler operation, the amount of generated steam is not stable, which appears as an unstable detection amount in the steam amount detector 8 and becomes a feedforward system. The water level compensation signal from the section 9 changes in an unstable manner, which becomes a disturbance factor for the water supply amount command. At this time, since the sensitivity of the water level control unit 6 is low, the water level control becomes unstable.

Next, during excessive combustion of the boiler, the amount of steam generated suddenly increases, and the sensitivity of the water level control unit 6 is low, so that the water supply command from the adder 10 rapidly increases, and water supply is performed in a state where the water level is rising. As a result, overshoot occurs in the boiler water level. Conversely, when the boiler is under-combusted, an undershoot occurs in the boiler water level due to a sudden decrease in the amount of steam generated.

[0010] These overshoots and undershoots result in an increase or decrease in the volume of steam bubbles in the steam pipe, resulting in an increase or decrease in apparent water holding, and a direction opposite to the control direction for converging the boiler water level to the water level set value. This causes a reverse response phenomenon in which the control amount changes.

If the sensitivity of the feedforward system is reduced to solve these problems, a delay occurs in the water level control, and the accuracy of the constant water level control deteriorates.

An object of the present invention is to start up boiler operation.
An object of the present invention is to provide a control device capable of performing constant water level control that normally has high control accuracy while eliminating unstable control at the time of falling and suppressing overshoot and undershoot at the time of excessive / undercombustion.

[0013]

SUMMARY OF THE INVENTION The present invention makes it possible to adjust the ratio of the control amount by the feedforward system and the control amount by the feedback system in a complementary manner, so that the amount of steam generated at the time of start-up and start-up of the boiler operation is reduced. In the unstable control state, the ratio of the control amount of the feedforward system is reduced by reducing the ratio of the control amount of the feedforward system to obtain a stable control state by the feedback system, and by detecting the reverse response phenomenon due to excessive combustion or undercombustion. Is reduced to suppress overshoot and undershoot, and when the boiler operation is stabilized, the ratio of the control amount of the feedforward system is shifted to the original initial state, and is characterized by the following configuration.

A feedback system for obtaining a water supply amount control signal to the boiler by comparing the water level set value and the water level detection value of the boiler, and a feed forward system for obtaining a water supply amount control signal to the boiler according to the amount of steam generated from the boiler. A water level control device for a boiler, comprising: a water supply amount control device that controls a water supply amount to a boiler in accordance with a water supply amount command obtained by adding a water supply amount control signal from both systems. A control means that can adjust the ratio of the control amount by the system and the control amount by the feedback system complementarily, and a control state in which the steam generation amount is larger than the water supply amount to the boiler and the water level of the boiler is falling, or to the boiler Means for detecting, as a reverse response phenomenon, a control state in which the amount of steam generation is smaller than the amount of water supplied and the water level of the boiler is rising; Processing means for gradually decreasing the rate of control of the feedforward system by the adjusting means when issued, and limiting according to the amount of steam generated when the amount of steam generated from the boiler is lower than a set value. Processing means for limiting the ratio of the control amount of the feedforward system by a value, and the adjusting means when the reverse response phenomenon is not detected and when the amount of steam generated from the boiler exceeds a set value. Processing means for gradually returning the control amount of the feedforward system to the original ratio.

[0015]

FIG. 1 is an apparatus configuration diagram showing an embodiment of the present invention. FIG. 3 differs from FIG. 3 in that a stabilization adjusting means for eliminating an unstable phenomenon of water level control is provided. Therefore, the same reference numerals are given to the same parts as those in FIG.

In FIG. 1, the stabilization adjusting means adjusts the gains of the feedforward system and the feedback system by detecting the reverse response and detecting the amount of steam. ) Is provided, and the coefficient calculator 9 is made to vary its coefficient k, and the coefficient k for these coefficient calculations is converted to a stabilization calculator 12.
Is adjusted according to the reverse response detection and the steam amount detection.

In this configuration, by adjusting the coefficient k (≦ 1), the ratio between the feedback control amount for determining the water level command amount and the feedforward control amount is increased or decreased in a complementary manner. And the ratio of the feedforward control amount increases as the coefficient k increases.

When the stabilization calculation unit 12 detects the reverse response phenomenon, it sequentially decreases the coefficient k until the phenomenon is resolved, and decreases the ratio of the feedforward control amount. Further, when the steam amount increases, the coefficient k is sequentially increased, and the ratio of the feedback control amount is reduced.

The operation of the stabilization operation section 12 in the stabilization adjustment means is realized by the functional configuration shown in FIG. FIG.
Indicates a case where digital operation is performed using a microprocessor.Each detected value is periodically sampled as a digital signal by sampling, and a coefficient k for stabilizing a control system by periodic operation processing is calculated from these sampled values. It is adjusted step by step in the calculation cycle.

The detection of the reverse response phenomenon is performed in processing block A. The deviation (F _J −F _K ) between the detected steam amount F _J and the detected water supply value F _K is obtained (S1), and the moving average Y ₁ is obtained to eliminate the detection abnormality due to the change in noise (S2). ), And determine whether the moving average Y ₁ is positive or negative (S3, S
4). In this determination, when the moving average value Y ₁ is positive,
The amount of steam generated is larger than the amount of water supplied to the boiler 1, and it is determined that the control state is such that the amount of water supplied to the boiler 1 is insufficient. Conversely when the moving average value Y ₁ is negative, determines that the water supply amount excessive control state of the boiler 1.

Meanwhile, Searching for the moving average value Y ₂ in order to eliminate the abnormality detection due to noise of the changes with respect to the water level detection value L of the boiler 1 (S5), previous and current difference for the moving average value Y ₂ ΔY ₂ is obtained (S6), and the sign of the difference ΔY ₂ is determined (S7, S8). When the water level difference ΔY ₂ becomes positive in this determination, it is determined that the water level of the boiler 1 is rising. Conversely, when the difference ΔY ₂ is negative,
It is determined that the water level of the boiler 1 is falling.

Based on the result of the positive / negative determination of the moving average value Y ₁ and the difference ΔY ₂ , the water level is falling (ΔY ₂ <0) in a control state in which the amount of water supplied to the boiler is insufficient (Y ₁ ≧ 0). Is determined as an AND condition (S9) to determine the reverse response phenomenon. In a control state where the amount of water supplied to the boiler is excessive (Y ₁ <0), the reverse response phenomenon is determined by determining that the water level is rising (ΔY ₂ ≧ 0) as an AND condition (S10). obtain.

The result of the determination of the reverse response phenomenon is detected in any case as an OR condition (S11), and it is confirmed that the reverse response phenomenon has occurred when the predetermined time period T set by the digital timer is continued (S12).

When the occurrence of the above-mentioned reverse response phenomenon is confirmed, the coefficient k which is currently set is reduced every calculation cycle of the set value n, that is, the calculation of k = k−Δk is performed (S13).
After limiting the lower limit of the coefficient k to 0 and the upper limit to the set value z (S14), the coefficient k of the coefficient calculators 9 and 11 is determined (S15).

By continuing the adjustment to decrease the coefficient k, the ratio of the feedforward control amount decreases and the ratio of the feedback control amount increases, resulting from the feedforward control during excessive combustion or undercombustion. It is possible to suppress the occurrence of the reverse response phenomenon, stabilize the water supply amount control to the boiler, and eventually the water level control mainly by feedback control, and prevent overshoot and undershoot.

When the reverse response phenomenon has been resolved, the coefficient k is gradually returned to the original initial state by the processes S18 and S19 described later, and the desired control accuracy can be obtained.

Next, when unstable control at the time of startup or shutdown of the boiler operation is predicted, the coefficient k is limited to a small value in conjunction with the amount of generated steam to stabilize the control. This control eliminates unstable control at the time of startup or shutdown of the boiler operation.

In the above control, the ratio Y ₃ of the detected steam value F _J to the rated steam amount F _JT is determined (S16), and the ratio Y ₃
Check whether ₃ is higher than the set ratio X (%) (S
17) If the ratio Y ₃ is lower than the fixed ratio X, a limiter calculation process is performed having a limit value k _max (or as table data) with a smaller value as the ratio Y ₃ is smaller (S20). Upper and lower limit processing of k _max (S1
The limit value of the coefficient k in 4) is used. When the boiler is started, the coefficient k is initially set to a value corresponding to the limit value k _max in the ratio X.

As described above, the generation ratio Y ₃ of the steam generation amount F _J
Is smaller than the fixed ratio X, that is, when the steam generation amount is low but unstablely changes at the start of the boiler operation start, or when the steam generation amount is low but unstable at the end of the boiler operation start-up. At this time, the value of the coefficient k is limited to a small value.

Thus, at the start of boiler operation start-up or at the end of the shutdown, the ratio of the feedforward control amount is reduced, and the ratio of the feedback control amount is increased. Control.

The limit value k _max of the coefficient k increases exponentially as the steam generation ratio Y ₃ approaches the ratio X, and when the steam generation ratio Y ₃ exceeds the ratio X, it is determined that the reverse response phenomenon has not occurred. (S18) When the condition is satisfied, the coefficient k
Is incremented every n operation cycles, that is, the calculation of k = k + Δk is performed (S19), and after the upper and lower limit limiting process of the coefficient k is performed (S14), the coefficient k of the coefficient calculators 9 and 11 is determined (S15). .

That is, when in the stable combustion control state near the end of the start-up of the boiler operation or in the stable combustion control state at the start of the shutdown of the boiler operation, the coefficient k is gradually increased by the arithmetic processing S19. To the original stable control state.

Incidentally, the increase of the coefficient k by the processing S19 is as follows.
After the reverse response phenomenon occurs in the control state where the steam generation ratio Y ₃ exceeds the ratio X, when the reverse response phenomenon is eliminated, the control is executed to return to the original control state.

In step S17, the case where the magnitude of the amount of generated steam is determined by the ratio is shown. However, this may be determined by the amount of generated steam itself.

[0035]

As described above, according to the present invention, the ratio of the control amount by the feedforward system and the control amount by the feedback system can be adjusted in a complementary manner, so that steam is generated when the boiler starts up and shuts down. In the control state where the amount becomes unstable, the ratio of the control amount of the feedforward system is reduced, and the ratio of the control amount of the feedforward system is reduced by detecting the reverse response phenomenon caused by excessive combustion or undercombustion, and the boiler operation is stabilized. In such a case, the control ratio of the feedforward system is shifted to the original initial state, so that a stable control state by the feedback system is obtained even when starting up and shutting down the boiler operation, and overshoot also occurs during excessive combustion and undercombustion Normally, water level control can be performed with high accuracy while suppressing undershoot.

[Brief description of the drawings]

FIG. 1 is an apparatus configuration diagram showing an embodiment of the present invention.

FIG. 2 is a processing block diagram of a stabilization calculation unit 12 in the embodiment.

FIG. 3 is a configuration diagram of a conventional apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Boiler 4 ... Water supply amount control part 5 ... Water supply amount detector 6 ... Water level control part 7 ... Water level detector 8 ... Steam amount detector 9, 11 ... Coefficient calculation part 10 ... Adder 12 ... Stabilization calculation part

Claims (1)

[Claims] 1. A feedback system for obtaining a water supply amount control signal for a boiler by comparing a water level set value and a water level detection value of a boiler, and a feedforward for obtaining a water supply amount control signal for a boiler according to the amount of steam generated from the boiler. A water level control device for a boiler, comprising a system and a water supply amount control device that controls a water supply amount to the boiler in accordance with a water supply amount command obtained by adding a water supply amount control signal from both systems. An adjusting means capable of complementarily adjusting the ratio of the control amount by the feedforward system and the control amount by the feedback system; and a control state in which the steam generation amount is larger than the water supply amount to the boiler and the water level of the boiler is falling, or Means for detecting, as a reverse response phenomenon, a control state in which the amount of steam generation is smaller than the amount of water supplied to the boiler and the water level of the boiler is rising; Processing means for gradually decreasing the ratio of the control amount of the feed-forward system by the adjusting means when is detected, and responding to the steam generation amount when the steam generation amount from the boiler is lower than a set value. Processing means for limiting the ratio of the control amount of the feedforward system with a limit value, and when the reverse response phenomenon is not detected, and when the amount of steam generated from the boiler exceeds a set value, the adjusting means A water level control device for a boiler, comprising: processing means for gradually returning the control amount of the feedforward system to an original ratio.