JPH0259902A - Control device for plant - Google Patents

Abstract

PURPOSE:To prevent a plant from manufacturing defective products or damaging equipments even when an unstable factor is generated in a control system by providing a control device with an evaluation operating means for outputting the influence of a variation in a plant status variable to be exerted upon a variable to be controlled as an evaluation signal. CONSTITUTION:The rise of oil temperature is detected and measured by an oil temperature detector 16, the measured result is inputted to a status variable computing circuit 8 through a status variable input circuit 7 and an inference operation result from the circuit 8 is outputted to a control gain computing circuit 9 as an evaluation signal. The circuit 9 executes the correcting operation of control gain and a compensating variable and outputs the corrected result to a control gain multiplier 4 and a control variable converting circuit 5. Thereby, a signal to be outputted from the converting circuit 5 to a servo valve driving circuit 6 is changed and a driving signal (control signal) to be transmitted to a servo valve 15 is changed in a direction preventing the generation of hunting. Even if an unstable factor is generated in the control system, the plant can be prevented from damaging the equipment or manufacturing defective products and stable plant operation can be attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a control device for a plant equipped with a closed-loop control system, and particularly to a control device that takes into consideration maintaining the stability of the closed-loop control system.

[Conventional technology]

With conventional control devices, when the control system becomes unstable or becomes inoperable, it alerts the operating equipment and maintenance personnel, and the operating equipment and maintenance personnel receive the alert and then decide on the appropriate course of action. , the control gain and control method are changed to prevent the control system from becoming unstable. Japanese Unexamined Patent Publication No. 62-1929
Publication No. 00 describes in detail an alarm management device that takes in an abnormal signal from a plant and outputs it as an alarm. However, this alarm management device is only a means for detecting an abnormality, and subsequent steps to ensure stable plant operation must be taken manually. Also, JP-A-59
Japanese Patent Publication No. 22810 discloses a system in which a control device of an automatic machine monitors conditions that affect its operation, that is, what is usually called an interlock for operation. This system makes sure that the mechanism to be monitored works.
It only controls whether it moves or not.
Although it is good for open-loop control, it is effective for closed-loop control, where the conditions governing plant operation prevent the control system from continuing operation simply by changing the control operation method. isn't it.

[Problem to be solved by the invention]

In the above-mentioned conventional technology, it was usual to take the next action only after the control system became unstable, or sometimes after an operational accident occurred. For this reason,
Damage to plant equipment and defective products could not be avoided. Furthermore, in order to take further action, the equipment had to be stopped for a long period of time in order to consider countermeasures and take appropriate action.

The purpose of the present invention is to automatically detect that the control system has become unstable or will become unstable in the future, and to prevent the production of defective products and equipment damage. and control gains automatically.

[Means for Solving the Problems] The above-mentioned problems include a means for setting a control target value for a controlled quantity, a means for detecting an actual value of the controlled quantity, a means for detecting a plant state quantity, and a means for setting a control target value for a controlled quantity. means for calculating a control signal based on the actual value and the detected actual value and the plant state quantity. evaluation calculation means for outputting the influence as an evaluation signal;
This is achieved by comprising means for calculating a control signal based on the evaluation signal and/or means for changing a circuit for calculating the control signal based on the evaluation signal.

[Effect]

When a change occurs or is about to occur in a plant state quantity that is not directly subject to control, the influence of that variation on the quantity to be controlled is evaluated, and a control signal for the controlled subject is calculated based on the evaluation result. and/or the circuit that calculates the control signal is changed based on the evaluation result.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. 1st
The figure is a diagram showing a hydraulic rolling control device for a rolling mill using an embodiment of the present invention.

Generally, when a control device is designed, the conditions under which the control device operates stably are clarified.

In other words, the factors that cause the control system to become unstable have become clear. In other words, when a factor that inhibits the stability of a control system occurs, what behavior does the control device exhibit?
A reasoning program is programmed into the designer's head as to what needs to be done in order to deal with it. This embodiment has a function in which the control device detects the occurrence of a factor that impedes the stability of the control system, derives a countermeasure in the same way as a human would, and actually sends the result to the control device. This function incorporates the designer's knowledge and the know-how gained at the work site, integrates it with the control device, controls the hydraulic system, and stabilizes the control system. When a change in the state quantity of a mechanical system (including control equipment) occurs that impedes plant operation, rather than simply issuing an alarm, the change in state quantity is avoided or accepted so as not to interfere with plant operation. This allows the gain and control operation method of the control device to be adjusted online.

In FIG. 1, a rolling mill 1o to be controlled is equipped with a hydraulic rolling down device 11, and the rolling position (controlled amount) of this hydraulic rolling down device 11 is determined by the amount of water discharged from a hydraulic pump 13 and injected into the rolling device 11. The amount of pressure oil injected into the hydraulic pressure lowering device 11 is controlled by the amount of pressure oil injected into the servo valve 1.
Controlled by 5. As detectors for detecting state quantities of the plant mechanical system, there are a reduction position detector 12 for detecting the reduction amount of the reduction device 11, a reduction oil pressure detector 20a for detecting the oil pressure in the reduction device 11, and an operating position of the servo valve 15. A servo valve position detector 17 for detecting, a discharge oil pressure detector 20b for detecting the discharge oil pressure of the hydraulic pump 13, and an oil temperature detector 16 for detecting the oil temperature on the discharge side of the hydraulic pump 13 are provided. As means for detecting the actual value of the controlled quantity, a reduction oil pressure detector 2 for detecting the reduction amount of the reduction device 11 is provided.

As a mechanism for controlling the operating position of the servo valve 15,
A target value setting circuit 1 which is a control target value setting means for setting a target value of the rolling position of the rolling device 11, a deviation calculation circuit 3 connected to the output side of the target value setting circuit 1, and the deviation calculation circuit 3. a control gain multiplier circuit 4 connected to the output side of the
A control amount conversion circuit 5 connected to the output side of the control gain multiplication circuit HI4, and a servo valve drive circuit 6 connected to the output side of the control amount conversion circuit 5 and controlling the operating position of the servo valve 15 are provided. ing. This mechanism further includes a state quantity input circuit 7 into which the outputs of the reduction oil pressure detector 20a, the servo valve position detector 17, the discharge oil pressure detector 20b, and the oil temperature detector 16 are input.

A state quantity calculation circuit 8 connected to the output side of the input circuit 7, a control gain calculation circuit 9 connected to the output side of the state quantity calculation circuit 8, and a control gain calculation circuit 9 connected to the output side of the lowering position detector 12. Feedback value (actual value of controlled quantity) detection circuit 2
The output side of the control gain calculation circuit 9 is connected to the control gain multiplication circuit 4 and the control amount conversion circuit 5, and the output of the feedback value detection circuit 2 is connected to the deviation calculation circuit 3 and the state quantity input circuit 7, respectively. . In addition, target value setting circuit 1
The output side of is also connected to the state quantity input circuit 7. The state quantity input circuit 7 and the state quantity calculation circuit 8 form evaluation calculation means, and the control gain calculation circuit 9, the control gain multiplication circuit 4,
The control amount conversion circuit 9 forms means for calculating a control signal based on the evaluation signal.

Next, the operation of the above-mentioned system will be explained. Target value setting circuit 1
When the reduction position target value is set, a target value signal is output to the deviation calculation circuit 3 and the state quantity input circuit 7. At the same time, the feedback value detection circuit 2 takes in the position signal output from the roll down position detector 12 and outputs a feedback value signal to the deviation calculation circuit 3 and the state quantity input circuit 7.

By differentiating the position signal, the displacement speed of the servo valve can be determined. The deviation calculation circuit 3 calculates the deviation between the input target value signal and the feedback value signal.

It is output to the control gain multiplication circuit 4 as a deviation signal. The deviation signal input to the control gain multiplication circuit 4 is amplified here and output to the control amount conversion circuit 5. This multiplier circuit 4 generally performs proportional control, and the proportional gain used heretofore has been set to a fixed value based on a typical transfer function of each element of the reduction control system.

The signal input to the control amount conversion circuit 5 is shown here.

After being corrected, it is output to the servo valve drive circuit 6,
The signal is converted into a servo valve immediate action signal, which is a control signal, and output to the servo valve 15. Conventionally, in the control amount conversion circuit 5, signal correction was performed based on the value of the rolling load. On the other hand, the state quantity signal, target value signal, and feedback value input to the state quantity input circuit 7 are input to the state quantity calculation circuit 8 which monitors the state of the plant, and the calculation result of the state quantity calculation circuit 8 is , is output to the control gain calculation circuit 9 as an evaluation signal. In the control gain calculation circuit 9,
Based on the input evaluation signal, the control gain (proportional gain) used in the control gain multiplication circuit 4 and the gain used for correction in the control amount conversion circuit 5 are changed.

The state quantity arithmetic circuit 8 qualitatively and/or quantitatively captures the state quantities of plans 1 to 1, and infers how the control system will behave in the future based on the captured state quantities. The system derives methods to deal with the behavior according to pre-installed programs. The derived result is an increase in the control gain and/or correction gain,
As an evaluation signal that indicates the decrease, its speed, magnitude, etc.
The signal is output to the control gain calculation circuit 9, where the control gain and correction amount (correction gain) are automatically changed based on the evaluation signal, and the control gain multiplication circuit 4. It is output to the control amount conversion circuit 5. Control gain multiplication circuit 4. Controlled amount conversion circuit 5
Then, the deviation signal is multiplied and converted (corrected) based on the input control gain and correction gain, and is output to the servo valve drive circuit 6.

Here, the transfer function G(S) of the hydraulic system when designing a hydraulic pressure reduction device is G(S)=f(G(FB)・G(SA)・G(L)・G
(SV)-G(PL)・G(K)).

G (FB): Feedback gain G (SA): Gain G (L) of servo valve drive circuit
: Hydraulic circuit transfer function G (SV) : Servo valve transfer function G (PL) : Differential pressure, that is, the difference between the discharge pressure of the hydraulic pump and the oil pressure in the reduction device G (K) : Transmission greater than the control gain of the control device It is well known that among the functions, the G(L,) hydraulic circuit transfer function in particular plays an important role in determining the performance and characteristics of the hydraulic lowering device. Furthermore, this transfer function itself changes in a complex manner depending on fixed parameters (piping diameter, pipe length, etc.) and variable parameters (oil viscosity, oil pressure). Conventional control devices are designed to treat variable parameters as fixed under certain conditions. And so that it doesn't become variable, for example, so that there are no oil pressure changes.

The temperature is controlled so that the viscosity of the oil does not change to prevent the hydraulic system from becoming unstable. However, these are extremely difficult to manage.

Sometimes, the temperature of the oil rises and the damping constant of the entire hydraulic system decreases, causing hunting in the rolling device and making it impossible to control the rolling mill.

The gist of the present invention is to define a controlled object and a controlled amount to be maintained, and to determine a plant state quantity that can be a cause of variation in the controlled object amount, an effect that a fluctuation in the plant state amount has on the controlled object amount, and the effect. a means for detecting a variation in the plant state quantity by combining a method for canceling the change in the state quantity; a means for searching for a method for preventing variation in the controlled quantity based on the detected variation in the state quantity; A control device is provided with a means for applying the method to a closed-loop control system, and when a state variable fluctuation that changes the controlled variable occurs or is progressing, such a control device can be used to prevent such a problem from occurring before a problem occurs. The searched method is executed online at the same time as the state quantity change occurs.

How the control device of the embodiment functions when the oil temperature rises as described above will be explained. The rise in oil temperature is measured and detected by the oil temperature detector 16.

The result is taken into the state quantity input circuit 7, and the value is inputted into the state quantity calculation circuit 8. Here, a controlled quantity to be maintained stored in a storage unit forming a part of the state quantity calculation circuit 8, a plant state quantity that can be a cause of variation in the controlled quantity, and a variation in the plant state quantity that is controlled by the Based on the effect on the target quantity and how to counteract that effect, as humans would judge: 1) Oil temperature has increased. When the oil temperature increases, 2) the viscosity of the oil decreases. If the viscosity of the oil decreases, 3) the damping constant in the transfer function of the hydraulic circuit will decrease. If the damping constant decreases, 4) the phase margin of the entire system will disappear. and 5) hunting occurs.

Such inferences are calculated, and the calculation results are output to the control gain calculation circuit 9 as an evaluation signal. Upon receiving this evaluation signal, the control gain calculation circuit 9 performs calculations for downwardly modifying the control gain and correction amount 5, and outputs the result to the control gain multiplication circuit 4 and the control amount conversion circuit 5. As a result, the signal output from the control amount conversion circuit 5 to the servo valve drive circuit 6 changes, and the servo valve drive signal (control signal) transmitted to the servo valve 15 copes with the decrease in phase margin of the entire system. Changes will be made to prevent hunting from occurring.

After further reducing the control gain, the output of the target value setting circuit 1 and the output of the feedback value detection circuit 2 are monitored by the state quantity calculation circuit 8 to determine the stability of the system. If the measures are insufficient and the stability of the system cannot be maintained, repeat the measures until appropriate measures are taken.

In addition, a reduction oil pressure detector 20a, a discharge oil pressure detector 2
Select an appropriate gain according to the pressure difference detected by 0b, or select the servo valve operating position indicated by the position signal of the servo valve position detector 17 and the servo valve operation instructed by the servo valve drive signal. It is also possible to change the gain of the control device by comparing the positions and monitoring changes in the characteristics of the servo valve 15.

Further, as in the second embodiment shown in FIG. 2, two control gain calculation circuits are arranged in parallel on the output side of the deviation calculation circuit 3, one calculation circuit 4a is used as a proportional control circuit, and the other calculation circuit 4a is used as a proportional control circuit. The arithmetic circuit 4b is set as a proportional-integral control circuit or an integral control circuit, and the control gain arithmetic circuit 9 is normally controlled by the evaluation signal output from the state quantity arithmetic circuit 8 using the arithmetic circuit 4a.
It is also possible to instruct switching to the arithmetic circuit 4b.

As described above, online automatic adjustment of the control device is realized by adding a control gain corresponding to changes in the state quantity of the mechanical system and a means for instructing the control operation method to the control device. In other words, the stable operation of equipment, which has traditionally been supported by human knowledge (know-how), is now an inference process that derives the best way to respond to changes in the state quantities of plant mechanical systems from human knowledge, that is, changes in the state quantities of plant mechanical systems. By programming this and integrating it into the plant's control equipment, the actions that the control equipment should take are automatically determined based on changes in the state quantity, and the actions can be taken without stopping the equipment. maintained without going through the
This has the effect of improving equipment operation rates and reducing the burden on equipment maintenance personnel.

〔Effect of the invention〕

According to the present invention, knowledge regarding destabilization of the plant control system in response to changes in the state quantity of the plant and how to deal with the destabilization is stored in a control device of a plant that is subjected to feedback control, and A means for predicting unstable changes in the state quantities of the plant using the state quantities and deriving countermeasures is provided, and the control operation method and/or control gain of the control signal calculation means can be automatically corrected based on the derived results. Even if an unstable factor occurs in the plant's control system, it can be dealt with online, and stable plant operation is possible without stopping plant operation, preventing equipment damage or product defects. This has the effect of improving plant operation rates and reducing the burden on equipment maintenance staff.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing a first embodiment of the invention, and FIG. 2 is a system diagram showing a second embodiment of the invention. 1... Control target value setting means (target value setting circuit), 3.
...Means for calculating control signals (deviation calculation circuit), 4...
・Means for calculating the control signal based on the evaluation signal (control gain multiplication circuit), 5...Means for calculating the control signal based on the evaluation signal (control amount conversion circuit), 6...Calculating the control signal Means (servo valve floating circuit), 7...Evaluation calculation means (state quantity input circuit). 8... Evaluation calculating means (state quantity calculating circuit), 9... Means for calculating a control signal based on the evaluation signal (control gain calculating circuit), 12... Means for detecting the actual value of the controlled quantity (reduction position detector), 16... Plant state quantity detection means (oil temperature detector), 17... Plant state quantity detection means (servo valve position detector), 20a... Plant state quantity detection means ( Reduction oil pressure detector), 20b... Plant state quantity detection means (discharge oil pressure detector).

Claims (1)

[Claims] 1. Control objective value setting means for the controlled quantity, means for detecting the actual value of the controlled quantity, plant state quantity detection means, the set control target value, the detected actual value, and the plant state quantity. In a plant control device, the means for calculating the control signal includes an evaluation calculation means for outputting an influence of fluctuations in the plant state quantity on the controlled quantity as an evaluation signal. , means for calculating a control signal based on the evaluation signal, and/or means for changing a circuit for calculating the control signal based on the evaluation signal.