JPS58146902A - Proportional integrator - Google Patents

Abstract

PURPOSE: To remove dead time at the time of releasing the limitation of a proportional integrator and to improve process control characteristics by setting up an integral value optionally at a proper time from the external through the proportional integrator.

CONSTITUTION: At a time other than the time when a valve 2 is full opened or full closed or a manual/automatic station 16 is in the manual mode, a signal monitor 19 turns its switching signal SW to "1" and an adder 18 makes the output TMH of the proportional integrator 17 coincide with the output YA of itself to make the integrator 17 execute normal integration. Therefore, the spray valve 2 is gradually closed under normal control. When the spray value 2 has been full closed and a main vapor temp. TM also is turned to a value equal to the set value TH, the signal monitor 19 detects the full closed status of the valve 2 and outputs its switching signal SW "0", so that the output YA of the adder 18 is made coincide with the outlet temp. of a temp. reducer, i.e. a feedback signal TA, after a fixed time.

COPYRIGHT: (C)1983,JPO&Japio

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a proportional integrator, and more particularly to a proportional integrator that has a function of allowing the initial value and coefficient of its integral operation to be changed at any time, and is suitable for use in a process control device.

A conventional analog proportional integrator is composed of an integral calculation section A and a proportional calculation section B as shown in FIG. This output■
is expressed with respect to the input (deviation) signal ΔC. Here, KP=R*/Rt is proportional gain,
Tx=1/RxC is an integration time constant and Vrti integration initial value, which is determined by the charging voltage of capacitor C.

A digital proportional integrator also digitally performs the same calculation as in equation (1). However, in this conventional circuit, the initial value of the integral operation ■! It is not possible to arbitrarily change or set the proportional and integral gains during operation, and the proportional and integral gains cannot be arbitrarily set externally. Ta. For this reason, there are problems with the control characteristics of the process control system as described in the following example.

Diagram 2 shows the water and steam system of a thermal power plant, where the water is supplied from the feed water pump 9, and the log is the high pressure feed water heater 1.
The steam is sent to the primary superheater 1 in the boiler 5 via the boiler 5, and is further superheated in the secondary superheater 4 via the desuperheater 3, and sent to the high pressure turbine 6. On the other hand, the log branched from the water supply pump 9 is sprayed to the attemperator 3 via the spray valve 2, but the opening degree of the spray valve 2 is determined by the output T of the attemperator outlet temperature detector 6 and the main steam temperature detection. The main steam temperature T is controlled by a cascade control system as shown in FIG. 3 so that the main steam temperature T is equal to the set value TIIK in accordance with the output of the steam generator 70 and the T blade.

That is, in FIG. 3, the mask proportional integrator 13 detects the main steam temperature setting 1!
Input the detected main steam temperature Tw or the main steam temperature deviation ΔTM obtained from ΔT=T - T, and calculate the set value TMII of the desuperheater outlet temperature T by proportional integration. . Since this loop has a large time constant, the proportional gain and integration time of the proportional integrator 130 are set in accordance with this value.

Next, the set value T determined by the mask proportional integrator 13 is
From the desuperheater outlet temperature T, which is the output of the desuperheater output temperature detector 60, the deviation JT sum = -(TW sum - Tm) is calculated, and this is input to the mask proportional integrator 1.5. Then, the opening degree A- of the spray valve 2 is calculated. Since this loop has a small time constant, the proportional integrator 15
The proportional gain and integral time are set. However, in the manual/automatic station 16, if it is set to automatic mode, the valve opening degree A1 calculated above is output to the spray valve 2, and when the manual mode is set to manual mode, the above calculated 9A- is cut, and the valve opening degree A1 calculated above is output to the spray valve 2. The setting value is output.

In this way, the cascade control allows everyone to independently set the control parameters of the mask and the i-in proportional integrator, so that the control characteristics can be made more suitable.

However, there is a problem in that when the spray valve 2 is fully open or fully closed, the output of the mask proportional integrator 13, that is, the set value TW of the temperature change at the desuperheater outlet is completely exhausted.

This situation will be explained with reference to FIGS. 4 and 5.

FIG. 4 shows how the spray valve 2 is fully closed.

First, when the main steam temperature set value TW becomes larger than the main steam temperature Tx, the attemperator outlet temperature set value TMI increases and the attemperator outlet temperature T becomes larger J), ff ina proportional integrator Is outputs a closed operation signal tube.

Eventually, when 1=1, the i ina proportional integrator ISO output A
1 is zero, that is, the spray valve 2 is fully closed. Here 1
Even after the point of = 1, if Tll > TW, the attemperator outlet temperature T becomes saturated when the spray valve is fully closed, but the attemperator outlet temperature set value T does not increase. continue. That is, the output signal Tax of the mask proportional integrator 13 swings out.

If the spray valve 2 is fully opened, it can be easily inferred that 1M can be blown out in the opposite direction.

When the above-mentioned vibration failure occurs, there is a problem that the opening operation of the spray valve 2 is delayed after the reversal of Tw≧T. This situation is shown in FIG.

In FIG. 5, at the time of tetm, T lid ≧Tm, and the spray valve 2 should start to open, but the mask proportional integrator 13 has completely swung out, and TMII>Tm. Therefore, 1=1. In other words, the spray valve 2ti is not opened until TMI=Tm, and from 1=11 in the figure to 1. Due to this control delay, which results in the occurrence of a control ineffective region leading to , a problem arises in that the main steam temperature TM greatly exceeds its set value T.

Such a phenomenon cannot be avoided in a conventional control device using a proportional integrator because the parameters and initial values cannot be changed from the outside at each calculation time.

We are taking steps to shorten this control ineffective area and increasing the integration time of the master proportional integrator as much as possible (referred to as the reset windup method). Too much control occurs at the point in time,
I can't switch to auto pan press, I shorten the integration time and the time from t1 to t3 is too long, and the control delay is large.

On the other hand, the reset windup detection point is 1Δτ irises = O
% (i.e., ts)], the main steam temperature Tw
Even if the operating end is suddenly opened from the time when the temperature exceeds the set value and starts to rise, the main steam temperature will fluctuate greatly by the amount of the O delay due to the dynamic characteristics of the process.

It is an object of the present invention to eliminate the above-mentioned nine drawbacks of the prior art, to enable automatic pan presses to resume proportional-integral operation without wasting time when the limited operation of plant equipment is released, and to further reduce the gain and integral time to the process amount. The object of the present invention is to provide a proportional integrator that can be set from the outside at any time in accordance with the above.

The present invention uses a digital circuit to facilitate the setting of initial values and parameters, and also detects when the operating end of a process enters a limited operation such as fully opening or closing a valve, and converts it into a mask proportional integrator. This is characterized in that the output of the controller is made to match the actual feedback signal at a speed that can follow the time constant of the process and is put on standby, so that the normal control operation can be performed at the same time as the control operation is released.

The present invention will be explained in detail below using examples. FIG. 6 is a diagram showing an embodiment of the present invention, and the portion surrounded by a chain line is the portion related to the present invention. In this embodiment, the opening degree of the spray valve is controlled by the cascade control system shown in FIG. 3, and its operation is shown in the time chart shown in FIG.

First, in FIGS. 6 and 7, between time t and tl, the main steam temperature TM is small relative to the set temperature Tm (constant), and during this period, the spray valve 2 is opened at a certain degree. It operates in the closing direction.

That is, the valve 2 of the signal monitor (MRY) 19 is fully closed.

When it is neither fully open nor manual/automatic stage opening 16 is in manual mode, the switching signal SW is output.
is 1, and adder 1B (AC) is proportional integrator 1 at this time.
The proportional integrator 17 is caused to perform a normal integration operation by using the output T of the PIC 7 (PIC) as its output Y. Accordingly, the spray valve 2 is gradually closed during normal control operations.

When twtl is reached, spray valve 2 is fully closed (As=0%
), the main steam temperature Tw also becomes equal to its set value T. At this time, the signal monitor 19 detects that the valve 2 is fully closed, and the switching signal 5W=O is output, which causes the adder 18
The output Y of the output signal TaK coincides with the attemperator outlet temperature, that is, the feedback signal TaK, over a certain period of time. This 5W-OO
In this track mode, the initial value of the proportional integrator 17 is matched with the ride pack signal T, and when the next control is restarted, the conventional fifth
This is a mode in which the TMI is kept on standby so that the TMI does not run out as shown in the figure.

ζNow, the reason why it takes a certain amount of time to approach YhtT in this track mode is that if you do this instantly,
Ina proportional integrator 1! According to the proportional amount of s, the output changes from fully open to fully closed and ceases to be a fully closed signal, enters the normal control mode (automatic mode) with 5W=1, and repeats the operation of fully open or fully open again. This occurs because the operating time constant of the spray valve 2 is finite, so it is necessary to take a certain amount of time to follow the operating time constant of the spray valve 2.

Next [, 1=1. When the main steam temperature TM is higher than the set temperature TI, the output of the signal monitor 19 becomes 5W=
1, the output Y of the adder 18 is instantly switched from T to a proportionally integrated signal of ΔTm, and the spray valve 2 is opened. It will output a signal to operate in the direction.

FIG. 8 is a flowchart of the operation of the proportional integrator 17 in the embodiment described above. First, in step 20, each input signal IT, T, SW, Y^, etc. is input, and in step 21, It is determined whether the switching signal 5W=1. 5W=OO
In the manual mode, it takes a certain period of time in the calculation step 22 to output TMII=Tm from the signal output step 24. When 9.3W-1, normal proportional-integral calculation is performed in automatic mode calculation step 23, and the result is output from step 24. In this way, when switching from manual mode to automatic mode, for example, the initial integral value becomes the process amount immediately before switching, and the switching can be performed without wasting time.

As mentioned above, if the proportional integrator of the present invention is used, the integral value can be set externally at any time and as desired, eliminating wasted time when the proportional integrator's restriction operation is released, and furthermore, the proportional integral operation can be performed on the auto pan press. Moreover, the gain and integration time of the proportional integrator can be set externally in accordance with the process amount, and the process control characteristics can be improved.

[Brief explanation of drawings]

Figure 1 is a diagram showing a conventional proportional integrator, Figure 2 is a schematic diagram of a steam system in a thermal power plant, Figure 3 is a diagram of a conventional cascade control system, and Figures 4 and 5 are a diagram of a conventional system. 6 is a diagram showing an embodiment of the present invention, FIG. 7 is an explanatory diagram of the operation of the embodiment of FIG. 6, and FIG. 8 is a diagram illustrating the operation of the proportional integrator in manual/automatic mode. - is a figure showing. 2... Spray valve, 6... Attemperator outlet temperature detector,
7... Main steam temperature detector, ll... Main steam temperature setter, 17... Proportional integrator, 18... Adder, 19-
signal monitor. Agent Patent Attorney Masami Akimoto 11) Figure 1 '$ 2 Figure $ 3 Figure 4121 '$ 5 Figure $ 61 v, 7 Toryo grv /MH

Claims (1)

[Claims] 1. In a proportional integrator for process control that performs proportional integral operation by digital calculation and is configured so that the initial value of the integral and each constant of proportionality and integral can be set externally at each calculation time, its output The output signal changes to the feedback signal at the time of a limited operation in which the operating end, which is controlled by the deviation between the signal and the feedback signal representing the controlled quantity of the process, reaches the limit of its operating range or its operation is limited by an external operation. The initial integral value is made to follow the feedback signal to prevent the output signal from overshooting, and when the control operation is canceled, the output signal is used as the initial integral value at the time of the next calculation to perform normal proportional integral operation. An initial value setting means is provided to enable the operation of the operating end, and effective control of the operating end can be immediately started without wasting time when the restricted operation of the operating end is canceled by the operation of the initial value setting means. Features a proportional integrator.