JPS58191004A - Searching circuit of extreme value - Google Patents

Abstract

PURPOSE:To perform a control to obtain the maximum value of the general efficiency, by changing the direction of the control quantity in response to the direction to the extreme value of the change component between the quantities to be controlled of this time and the previous time which are obtained periodically and then continuing the above-mentioned change of direction to approximate the quantity to be controlled to the extreme value. CONSTITUTION:When an operation start command signal (h) is delivered at a time point TO, a signal (s) is delivered as an output signal (g) from a switch 9 and just for a period TA. A switch 11 delivers the supplied signal as it is for the period TA by a signal (j) and then applies it to an integrator 12. As a result, the signal (s) is applied as it is to the integrator 12 from a generator 8. The signals (h) and (j) are turned off in a period TB, and therefore signals (i) and (k) are held. Then the output signal (k) of the integrator 12 is applied to a PI controller 2, and a new control quantity m1 is decided. Then a new quantity f1 is decided to the quantity m1. In such a way, the sampling time is successively shifted to decide the set value of control quantity in the direction where the quantity to be controlled varies to approximate to the extreme value.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an extreme value search circuit used in a process control system or the like.

Conventional process control systems, such as thermal power plants, employ a constant value control method that keeps a controlled variable constant.

However, regarding boiler control in a thermal power plant, if the boiler efficiency is f Bs turbine efficiency JT and the opening degree of the GR damper is the manipulated variable m, then for example, if the opening degree m is increased, the turbine efficiency increases, but the boiler efficiency decreases. Conversely, if the opening degree m is made small, the boiler efficiency will increase, but the turbine efficiency will decrease.

Therefore, in recent years, instead of simply keeping the controlled variable at a fixed value in thermal power plants, a method has been considered that takes boiler efficiency and turbine efficiency into consideration and attempts to control the controlled variable that maximizes the overall efficiency of the plant. It has reached this point.

Generally, as shown in Fig. 1, a process control system outputs a controlled variable f when a manipulated variable m and a disturbance d are used for a process P. For example, as shown in FIG. 2, the minimum point (or maximum point) of the controlled amount f changes depending on the value of the disturbance d.

When this is considered for the above-mentioned thermal power plant, the difference is that the overall efficiency f is minimized with respect to changes in the manipulated variable, ie, the opening degree m, due to disturbances such as load and fuel ratio. Therefore, in order to control the plant overall efficiency so as to minimize it, it is necessary to change the manipulated variable m and search for an extreme value at which the overall efficiency, which is a controlled variable, is minimized.

An object of the present invention is to provide an extreme value search circuit applicable to the above-mentioned control system.

The extreme value search circuit of the present invention changes the operation amount from a certain operation lid setting value, calculates the difference between the current controlled amount and the previous controlled amount at each predetermined cycle, and calculates the difference value, that is, the amount of change. If the change is in the same direction as the extreme value, the manipulated variable is further changed in the same direction, and conversely, if the change is in the opposite direction to the extreme value, the manipulated variable is changed in the opposite direction from the previous value. The principle is to repeat this operation one after another in order to control the controlled quantity so that it approaches the extreme value.

The present invention will be described in detail below with reference to embodiments shown in nine drawings.

FIG. 3 is a basic block diagram of a process control system in which the extreme value search circuit of the invention is implemented. In the figure, 1 is a process, 2 is a PI controller, 3 is an adder, and 4 is a search circuit. The controlled quantity f, which is the output of the process 1, is added as an input signal to the search circuit 4. In the search circuit 4, the set value of the manipulated variable m is determined based on the controlled variable f.

Manipulated amount mil: Controlled by feedback control by the PI controller 2. This PI controller 2
is already a well-known circuit.

A more detailed block diagram of the search circuit 4 is shown in FIG. In the figure, 5 is a dead time generator, and the dead time TDI of this circuit is set to one cycle period of the sampling timing signal shown in FIG. 5, that is, TA+TB. 6 is a subtracter, which combines the controlled quantity signal a added this time (during sampling) and the dead time generator 5.
The difference c=a−b between the previously applied controlled variable signal is output. This difference output signal C is applied to a multiplier 7. 8 is a signal generator that outputs a constant negative level signal S. Reference numeral 9 denotes a switch that switches between the signal e from the multiplier 7 and the signal S from the signal generator 8 to derive an output signal g. 1
0 is the operation start command output device, and is from the time after Process 1 has stabilized and sufficient time has elapsed (timing TO shown in FIG. 5).

An operation start command signal that is ON for a certain period of time TA is output and applied to the switch 9. The switch 9 outputs the signal S during the period when the operation start command signal 1 is ON, and outputs the signal e as the output signal g during other periods, that is, while the operation command signal 1 is OFF. Reference numeral 11 denotes a switch that receives the output signal g of the switch 9 and derives the output signal i. Further, 12 is an integrator that receives the output signal i of the switch 11 and outputs an output signal k. 15 is a timing signal generator shown in FIG. 5 that outputs a timing signal j for sampling. This timing signal j is sent to the switch 11.
It is adapted to be added to the integrator 12. Switch 11
outputs the output signal g from the switch 9 during the period TA when the timing signal j is ON, and holds the output signal l from the switch 9 during the period TB when the timing signal J is OFF. Output as i. Also, the integrator 12
The input signal i is integrated during the period TA during which the timing signal j is ON, and the period TB during which the timing signal j is OFF is set as a tracking mode.

Hold the output value at the end of the timing period TA,
Each is output as an output signal. This output signal k is applied to the P■:1 controller 2, and the PI controller determines a new set value for the manipulated variable 0m.

Note that the period TA+TB of the timing signal j is set sufficiently to the extent that a new manipulated variable m is set and the post-process is stabilized.

14 is the dead time T when receiving the output signal i of the switching device 11 at the input.
It is a dead time generator with D 2 (TA < TB2 < TB). The output signal l of this dead time generator 14 is applied to a function generator 15. Function generator 15! 6th
As shown in the figure, it has a characteristic that when the input signal l is positive, an output signal n of -100 is derived, and when the input signal l is negative, an output signal n of +100 is derived. The output signal n of this function generator 15
is added to the multiplier 7. The multiplier 7 receives the signal C from the subtracter 6 and the signal n from the function generator 15, multiplies it by 10"0, and applies the output signal e to the switch 9 as described above. The time generator 14, the function generator 15, and the multiplier 7 change the manipulated variable m so as to change the controlled value 1if toward the extreme value at the 9th sampling time. A circuit for applying a positive or negative polarity load is configured.

Next, the operation of the embodiment circuit configured as described above will be explained.

In the circuits shown in FIGS. 3 and 4, it is assumed that the operation start command output device 10 issues an operation start command signal at time TQ after the process has stabilized and a sufficient period of time has elapsed.

The controlled variable at this point is f(To), and the manipulated variable is mO.
shall be. Under this condition, the process is stable, so f
(TO)=f (TO-TDI)=fO, therefore, signal a=double signal, and output signal C of subtractor 6 is 0.
It is. On the other hand, since the TA off period operation start command signal is applied to the switch 9 from time TO, the period switch 9 outputs the signal S from the signal generator 8 as the output signal g.

In addition, the switch 11 outputs the signal input during the TA off period as it is according to the timing signal j, and transfers this signal to the integrator 1.
2, so the signal S from the signal generator 8 is added to the integrator 12.

During the period TA, the signal S from the signal remainder generator 8 is subjected to integration processing. When period TA elapses and period TB begins, both the operation start command signal and timing signal j turn OFF.
Therefore, during the period TB thereafter, the output signal i of the switch 11 and the output signal of the integrator 12 are held at the values at the end of the period TA.

Then, the output signal k of the integrator 12 is applied to the PI controller 2, and the manipulated variable m is determined to a new set value m1. As a result, as shown in the time-operated amount characteristic in FIG. 7 (5) and the time-controlled amount characteristic in FIG. 1, the controlled variable f is set from fO to the value f1 corresponding to the manipulated variable set value m1. Note that the example in FIG. 7 shows a case where the initially controlled amount f changes in a direction that decreases with respect to an increase in the manipulated variable m.

When the period TB passes and the next sampling time T1 is reached, the controlled quantity f(TI) decreases with respect to f(T[]), so the output signal C of the subtractor O, that is, the change in the controlled quantity is It becomes a negative value. On the other hand, the output signal of the switch 11 when the period TA has elapsed in the T1 cycle! Since is a negative level signal, the signal l output to the dead time generator 14 at sampling time T1 is also negative, so +100 is derived as the output signal n of the function generator 15, and this +
100 signals are applied to multiplier 7. The two input signals applied to the multiplier 7 are negative and positive, and the output signals e and C・1
00, the negative output signal C of the subtracter 6 is derived as is from ' `` 100 ''. At timing T1, the start command signal is OFF, so the multiplier 7
The output signal e, that is, the change in the controlled variable passes through the switch 9 as it is, and further passes through the switch 11 during the period TA and is added to the integrator 12. The change in the controlled amount is integrated by the integrator 12 during the period TAO. When the period TB begins, the outputs of the switch 11 and the integrator 12 are held until the next sampling time T2. The output signal of the integrator 12 is applied to the PI controller 2 in the same manner as at the sampling time TO, and the manipulated variable m is set to a new set value m2. Then, as shown in FIG. 7(A), at the next sampling time T2t, the manipulated variable m changes to the new set value m2, and as shown in FIG. 7(B), the controlled variable f changes from fl to the manipulated variable. It is set to a value f2 corresponding to the set value m2.

Note that since the output signal i of the switch 11 in this operation cycle is also a negative level signal, the output signal n of the function generator 15 becomes +100, that is, a positive signal. Even at the next sampling time T2, the controlled amount f(T2) is in the decreasing direction with respect to f(TI), so the change is in the minimum direction, similar to the sampling time T1 described above, so the subsequent operation is also further controlled by the controlled amount f progress in the direction of lowering. i.e. 9 multipliers 7
The output of the subtractor 6 is a negative signal, that is, the signal C from the subtractor 6 is directly derived as the output signal e, and the switch 9. and switch 1
1 is passed through the integrator 1 for the change in this controlled quantity.
2 performs integration processing, and further uses the output signal of this integrator 12 to increase the manipulated variable m in the positive direction and change the setting. Then, as in the case of the above-mentioned sampling times TO and TI, FIG.
6), by the next sampling time T3, the manipulated variable m changes to the new set value m3, and as shown in FIG. 7(B), the controlled variable f changes from f2 to the manipulated variable set value m3. It is set to the value C3.

Next, moving on to the operation during the sampling time T5, in the example shown in FIG. 7, the controlled amount f also increases as the manipulated variable m increases in the operation cycle from 72 to T3.

That is, the controlled amount f changes from a decreasing direction to an increasing direction. This means that the controlled variable f is between the manipulated variables m2 and m3.
This means that there is a point that minimizes (Figure 7 (C)
) Manipulated amount-controlled amount characteristic reference 1 Therefore, at the sampling time T3, the manipulated variable m is lowered to lower the controlled amount f.

At sampling time T3, the controlled quantity f (T3) is f
Since it is in the increasing direction with respect to (T2), the output of subtractor B.

In other words, the amount of change in the controlled amount is a positive value. This signal C is applied to the multiplier 7. It is directly applied to the integrator 12 via the switch 9 and the switch 11, and is subjected to integration processing by the integrator 12 to derive a positive output signal k, which is applied to the PI controller 2, and the manipulated variable m is changed to a new set value. It can be decided on m4. Since the signal applied to the PI controller 2 is a positive signal, this new manipulated variable set value m4 is set to the previous cycle's set value m5.
becomes smaller than By the next sampling time T4, the manipulated variable m is set to a new set value m4, and the controlled variable f is set from f3 to a value f4 corresponding to the manipulated variable set value m4.

Note that the output signal i of the switch 11 in this operation cycle
Since n is a positive level signal, the output signal n of the function generator 15 becomes -100, that is, a negative signal.

Therefore, at the next sampling time T4, the sign of the output signal C of the subtractor B, that is, the change in the controlled quantity is reversed by the 9 multiplier 7. At sampling time T4, the controlled quantity f
Since (T4) is decreasing with respect to f (T5), the change in the controlled amount is negative, so the output signal e of the 9 multiplier 7 is positive. 11, is applied to an integrator 12, is subjected to integration processing, and is then outputted as an output signal in the direction of further decreasing the manipulated variable m, and is applied to the PI controller 2.

As above, for each sampling time.

Find the change in the controlled variable at the current sampling time compared to the previous time, and based on this change, determine the next manipulated variable setting value in the direction in which the 9th order controlled variable approaches the minimum value, and perform this operation. By repeating this process, the point where the controlled variable becomes the minimum value is searched for.

In the above embodiment, the case where the point where the controlled amount is the minimum is searched is explained, but when the input to the function generator 15 is positive, the output is +100. When the input is negative, the output is -10
By using a characteristic that is 0, it is possible to search for a point where the controlled amount has the maximum value.

As described above, according to the present invention, it is possible to search for the extreme value of the controlled variable by sequentially changing the manipulated variable, so it is possible to perform optimal control that suits the purpose of the control system without being affected by disturbances. I can do it.

Furthermore, the circuit can be realized using functional blocks built into general controllers, such as subtracters, switches, integrators, and dead time generators, so there is no need to create special complicated programs. The entire 9 circuits can be obtained easily and inexpensively.

[Brief explanation of drawings]

Fig. 1 is a diagram showing a general process control system, Fig. 2 is a diagram showing an example of operation-controlled quantity characteristics of the process control system,
FIG. 6 is a basic block diagram of a process control system in which the extreme value search circuit of the present invention is implemented. Figure 4 is a block diagram showing the search circuit of the process control system shown in Figure 3 in more detail, Figure 5 is a timing signal waveform diagram of the circuit shown in Figure 4, and Figure 6 is the search circuit shown in Figure 4. Figure 7 is a diagram showing the input-output characteristics of the function generator of the circuit.
Figure 7(A) is a diagram showing the time-operated amount characteristic, and Figure 7(B) is a diagram showing the time-operated amount characteristic on one side of the characteristic diagram for explaining the operation of the circuit shown in Figure 4. Diagram showing control amount characteristics, 7th
Figure G) is a diagram showing the manipulated variable-controlled variable characteristics. 1: Process, 2: PI controller. 6: Adder, 4: Search circuit, 5/14: Dead time generator, 6: Subtractor, 7: Multiplier. 8: Signal generator, 9/11: Switch. 10: Operation start command signal output device, 12: Integrator,
13: Timing signal generator. 15: Function generator. Patent applicant Shimadzu Corporation Representative Patent attorney Shigeru Nakamura

Claims (1)

[Claims] (1) An extreme value search circuit for a controlled variable in a control system in which the extreme value of the controlled variable relative to the manipulated variable changes in response to disturbances. a subtraction means that receives the input of the controlled quantity and calculates and outputs the difference between the currently input controlled quantity and the previously input controlled quantity at a predetermined cycle; a signal generating means that outputs a signal at a predetermined level; means for outputting a start command; receiving signals from the subtracting means and the signal generating means; outputting a signal from the signal generating means when the operation start command signal from the operation start command output means is ON; A first switching means outputs the signal from the subtraction means when the operation start command signal is OFF, and a predetermined first period in each cycle outputs the signal from the first switching means during a second period. a second switching means that holds and outputs its own output; receiving the output of the second switching means; the first period performs an integral calculation; the second period holds the output value; an integrating means that uses the output value as a signal for updating the manipulated variable setting value, and a signal from the subtracter to the first switching means in the primary cycle based on the polarity of the current output signal of the second switching means. at the signal. An extreme value search circuit comprising means for imparting polarity so that the manipulated variable changes in a direction in which the controlled variable approaches the extreme value.