JPS63807B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a level control device that can obtain good control effects for processes in which the process gain is very high and the center value of the manipulated output changes slowly.

A conventional example of level control in this type of process will be explained using tundish level control in continuous casting equipment as an example. Figure 1 is a system diagram of tundish level control. Molten steel 2 is placed in tundish 1, stopper 3 is moved up and down, tundish 1 is
The flow rate of molten steel exiting from the drop port 4 at the bottom of the pipe is controlled. Molten steel coming out of the drop port 4 of the tundish 1 enters a cooling section 5 which also serves as a mold, where it is cooled from the surroundings and solidified into cast steel 6 having a predetermined cross-sectional shape. A continuous process is formed by drawing the cast steel 6 from the lower part of the cooling section 5 by means of rolls 7.

In this process, the opening diameter of the cooling section 5 cannot be made too large considering the cooling effect, and
Since the cast steel 6 is drawn out continuously, the dimension in the height direction of the cooling section 5 cannot be made too long. Also,
The flow rate of molten steel from the drop port 4 of the tundish 1 is determined by the diameter of the drop port 4, the positional relationship of the stopper 3, and the level of the molten steel 2. And cooling section 5
Since the opening diameter of the tundish cannot be made large and the control range of the level of the cooling section 5 is small, the process gain is very high, and since the flow rate depends on the level of molten steel in the tundish 1, the process gain changes. , that is, it becomes unstable. Furthermore, there is another important point to consider when controlling this process. This is the level of the cooling section 5, and if it overflows, high-temperature molten steel will overflow from the cooling section 5, which is dangerous to the operator.On the other hand, if it underflows, the cooling section 5 will overflow, and high-temperature molten steel will flow into the cooling section. It falls without stopping.

If PID control is incorporated into this process having the characteristics described above, on/off control will be performed, resulting in overflow or underflow. Therefore, by setting upper and lower limits on the manipulated output (MV), overflow or underflow is prevented. However, even with this method, due to changes in the level of molten steel in the tundish 1 and the expansion of the drop opening 4 at the bottom of the tundish 1 due to melting of structural materials, the stopper 3
Even if the position is the same, the flow rate of molten steel gradually changes.
Therefore, even if a limit with a fixed range is set for the manipulated output (MV), the manipulated output (MV) will eventually become fixed to one side of the limit.
The level of the cooling unit 5 will overflow or underflow. For this reason, in the prior art, although various attempts have been made, manual operation based on the operator's intuition has been the mainstream.

SUMMARY OF THE INVENTION An object of the present invention is to provide a level control device that can be applied to processes such as those described above in which the process gain is very high and the center value of the manipulated output changes slowly to obtain good control results. do. In the level control device according to the present invention, the central value of the upper and lower limits of the signal limiter that limits the control calculation output output from the controller is set to the upper and lower limits by the average value of the control calculation outputs from the time point appropriately traced back to the present. The limit width is automatically corrected while remaining constant, and is characterized by being able to cope with gradual disturbances over time and gradual changes in process constants.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a block diagram showing an embodiment in which the level control device according to the present invention is applied to tundish level control in continuous casting equipment. In FIG. 2, 11 is a level detector provided in the cooling section 5;
Reference numeral 3 denotes a stopper that changes the flow rate of the molten steel 2 flowing out from the drop port 4 of the tundish 1, which is a tank for temporarily storing the molten steel 2.
change the opening degree. Reference numeral 12 denotes a first subtractor that calculates the difference between the level target value of the cooling unit 5 and the output signal from the level detector 11 indicating the level of the cooling unit 5 .
13 is a controller that performs proportional, integral, and differential calculations on the difference signal from the first subtractor 12 and outputs a control calculation output. The output of this controller 13 is the signal limiter 14
and are respectively input to the first average value calculator 15. The signal limiter 14 limits the output of the controller 13 to a set upper and lower limit range. The first average value calculator 15 calculates the average value of the control calculation output of the controller 13 from a predetermined range back to the present, and sends it to the second subtracter 16 . An upper limit setting device 17 for setting the upper limit value of the signal limiter 14, a lower limit setting device 18 for setting the lower limit value, and a center point setting device 19 for setting the center point of the upper and lower limit values are provided. . A second subtracter 16 subtracts the output of the center point setter 19 from the average value output from the first average value calculator 15 and sends the result to a first adder 20 and a second adder 21, respectively. The first adder 20 adds the output of the upper limit value setter 17 and the output of the second subtracter 16, and adds the output to the signal limiter 14.
Enter this value as the upper limit value. A second adder 21 adds the output of the lower limit value setter 18 and the output of the second subtracter 16 and inputs the result to the signal limiter 14 as a lower limit value. The operation signal from the controller 13, which is limited by the upper and lower limits by the signal limiter 14, operates the stopper 3 of the tundish 1 to change the amount of molten steel flowing out from the descent port 4.

By the way, in the conventional fixed signal limiter, the manipulated output (MV) moves as shown in FIG. Therefore, in a process in which the center value of the control calculation output (MV _c ) moves, the limit width and center value of the signal limiter can be manually adjusted based on changes in the control calculation output (MV _c ) or the control amount (PV). You need to change it. However, in the level control device according to the present invention configured as shown in _FIG . 19 and the second subtractor 16, the limit width is calculated from the average value of the control calculation output (MV _c ) over a certain period from the present to the past, and the upper and lower limits of the signal limiter 14 are changed based on the average value. A mobile signal limiter 14 is used, which is changed continuously. Therefore, the operation output from the signal limiter 14 is as shown in FIG. The reason why the average value was adopted here is that it is impossible to remove vibrations in the control calculation output (MV _c ), and by taking the average value, the moving center value can be automatically adjusted. It's on. That is, as was the case with the prior art, it is difficult to suppress on/off control in a process with a large process gain like the present control target. Therefore, this on-off control is actively used, and the process gain that gradually changes while performing on-off control for each normal control output affects the level of the cooling section 5, and adjusts changes that affect the operating output. It is taken as the average value of a total of 13 control calculation outputs (MV _c ).

Now, as the molten steel 2 from the tundish 1 flows out, the level of molten steel decreases, and the process gain gradually decreases, and the amount of molten steel flowing out from the tundish 1 decreases for the same manipulated variable (MV) output. Therefore, the level of the cooling section 5 decreases, and therefore the control calculation output (MV _c ) of the controller increases even in each on/off control.
In the case of the prior art, the signal limiter continues to be at its maximum limit, causing the problem that the level of the cooling unit 5 drops below the permissible limit. However, in the level control device according to the present invention, the control calculation output (MV _c ) of the controller 13
As becomes larger, the average value of (MV _c ) calculated by the first average value calculator 15 also becomes larger, so the difference between the limit value and the setting value of the center point setter 19 becomes positive, and the second subtracter It will be output from 16. This positive difference output is added to the set value of the upper limit value setter 17 by the first adder 20, and the increased upper limit value is set in the signal limiter 14. Also,
The positive difference output is simultaneously added to the setting value of the lower limit setter 18 by the second adder 21, and the increased lower limit value is set in the signal limiter 14. In other words, the width of the limit value does not change, but the center value of the limit value increases. Therefore, in response to the decrease in process gain, the upper limit value of the manipulated variable (MV) output is increased to reduce the control calculation output (MV _c ).
It is possible to respond to the increase in MV and provide the necessary manipulated variable (MV) output to the operating end without reaching the upper limit value. As a result, the outflow amount can also be increased, making it possible to maintain the level of the cooling section 5 within an acceptable range.

When the process gain increases, the control calculation output (MV _c ) of the controller 13 decreases,
Therefore, the difference output of the second subtractor 16 becomes negative, and contrary to the above case, the upper limit value and lower limit value of the signal limiter 14 are shifted in the direction of decreasing, and the center value of the limit values is also decreased. As a result, the manipulated variable (MV) output is not held down by the lower limit value, but is given to the operating end at the value required by the controller 13, and control corresponding to the increased process gain is performed. As a result, the outflow amount is prevented from becoming excessive, and the level of the cooling section 5 can be maintained within an allowable range.

The movement of the upper and lower limit values of the signal limiter 14 as described above is illustrated in FIG. 5. That is, the width of the limit value (MV _w ) remains constant, while the center value (MV _s ) of the limit value increases or decreases like an arrow.

In the embodiment shown in FIG. 2, a limit value center point setter 19 is provided, and the center point of the limit value set there and the output signal from the first average value calculator 15 are calculated by a second subtractor. As shown in FIG. An average value calculator 22 is provided,
The average value of the upper and lower limit values from the calculator 22 and the output signal from the first average value calculator 15 may be subtracted by the second subtractor 16 to obtain a difference signal.

As described in detail above, according to the present invention, by changing the limit value of the controller output using the average value of the controller output over an appropriate period up to the present time, gradual disturbances and slow process constants can be prevented. Therefore, it is possible to provide a level control device that can deal with random changes and obtain good control effects.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of tundish level control in continuous casting equipment, Fig. 2 is a block diagram showing an embodiment in which a level control device according to the present invention is applied to tundish level control in continuous casting equipment, and Fig. 3 is a system diagram of tundish level control in continuous casting equipment. The figure is a graph showing the fluctuation state of the manipulated output in the conventional fixed signal limiter, Figure 4 is a graph showing the fluctuating state of the manipulated output in the signal limiter of Figure 2, and Figure 5 is the signal A graph explaining the movement of the upper and lower limit values in the limiter, and FIG. 6 is a block diagram showing a modification of the level control device according to the present invention. 11...Level detector, 12...First subtractor,
13...Controller, 14...Signal limiter, 15...
First average value calculator, 16...Second subtractor, 17...
...Upper limit value setter, 18...Lower limit value setter, 19...
...Center point setter, 20...First adder, 21...
Second adder, 22... second average value calculator.

Claims (1)

[Claims] 1 By changing the amount of fluid flowing out from the first tank that temporarily stores the fluid, the fluid level of the second tank that temporarily stores the fluid supplied from the tank and at the same time constantly flows out the fluid is adjusted. In the process of trying to maintain a predetermined value, a first subtraction is performed to calculate the difference between a level detector provided in the second tank, a signal indicating the level from this level detector, and a preset target level. a controller that performs proportional, integral, and differential calculations on the difference signal from the first subtractor and outputs a control calculation output; a signal limiter that limits the output of this controller; and a control calculation for the controller. The first step is to calculate the average value of the output over a certain period of time.
an average value calculator, an upper limit value setter for setting the upper limit value of the signal limiter, a lower limit value setter for setting the lower limit value of the signal limiter, and an upper limit value setter for setting the lower limit value for the signal limiter;
a center point setter that sets the center point of the lower limit value or a second average value calculator that calculates the average value of the set values of the upper and lower limit value setters; a second subtracter that subtracts the output of the point setter or the second average value calculator, and the output of the second subtracter and the output of the upper limit value setter are added together and input as an upper limit value to the signal limiter. First thing to do
an adder; a second adder that adds the output of the second subtracter and the output of the lower limit value setter and inputs the result to the signal limiter as a lower limit value; and an operation output from the signal limiter; and an operating end for changing the outflow amount of the first tank.