JPH06324702A - Control system - Google Patents

Abstract

(57) [Summary] [Purpose] Even if some control elements have failed, the operation of each device can be performed without selecting and disconnecting normal control elements and failed control elements. Control continues, which greatly improves system redundancy. [Structure] The PID controllers 2, 3 and 4 take in the measurement results obtained by the flow rate detecting device 5 to calculate the manipulated variable, and supply the manipulated variable to the valve control device 6 to provide an intermediate value ( The opening degree of the valve 9 is controlled based on the second largest value).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control system for controlling process amounts such as temperature, pressure and flow rate to desired values in various plants.

[0002]

2. Description of the Related Art In various plants, temperature, pressure,
As a control system for controlling a process amount such as a flow rate to a desired value, a system in which control elements are parallelized to increase control redundancy has been known.

In this control system, a plurality of control elements are arranged in parallel for each equipment constituting a plant, and when each control element operates normally, one of the control elements arranged in parallel for each equipment Select one to control each device, and when the currently selected control element fails, select the remaining control elements and continue the control, so that even if each control element fails, each The device control is not interrupted.

In addition to such a control system,
For example, there is also known a system in which three or more control elements are arranged in parallel for each device constituting a plant, and a control element that has failed due to a majority logic is separated from these control elements to continue control of each device. ing.

[0005]

However, the above-mentioned conventional control systems have the following problems.

That is, it is necessary to determine which control element is normal and which is abnormal among the control elements provided in parallel for each device.

Therefore, in such a control system,
Although the presence or absence of a failure of each control element is determined by the diagnostic function, such a diagnostic function can detect a failure content predicted in advance, for example, a simple failure such as a stop of the control output. As in recent years, when each control element performs a complicated operation, it is difficult to construct an appropriate diagnostic function, and there is a problem that the reliability of the system decreases.

In view of the above circumstances, the present invention is capable of distinguishing between a normal control element and a defective control element and selecting or disconnecting them from each other, and even when some of the control elements have failed, It is an object of the present invention to provide a control system in which the control of each device can be continued and thereby the reliability of the system can be greatly improved.

[0009]

To achieve the above object, the present invention processes a process signal obtained by a process amount detecting device provided on the site side by a controller to generate an operation signal. In a control system for controlling a controlled object based on an operation signal, based on the same process signal and the same set value, respectively, a controller that independently performs a predetermined arithmetic processing to obtain an operation amount,
1 based on each manipulated variable output from this controller
It is characterized in that it is provided with a synthesizing unit for obtaining one operation amount.

[0010]

In the above structure, a plurality of controllers independently perform predetermined arithmetic processing based on the same process signal and the same set value to obtain the manipulated variable, and the synthesizing section controls the controllers. One operation amount is calculated based on each operation amount output from the control target device.

[0011]

1 is a block diagram showing a first embodiment of a control system according to the present invention.

The control system shown in this figure has a bus line 1
And three PID controllers 2, 3, and 4, a flow rate detection device 5, and a valve control device 6, and each PID
The measurement results obtained by the flow rate detecting device 5 are taken in by the controllers 2, 3 and 4, and the manipulated variable is calculated, and this is supplied to the valve control device 6 to provide an intermediate value (second largest value) of these manipulated variables. The opening of the valve 9 is controlled based on the value.

The flow rate detection device 5 outputs a flow rate measurement result output from a flow rate sensor 8 attached to a pipe 7 in which a fluid to be controlled is flowing every time a transmission request command is input via the bus line 1. Is taken in and converted into a transmission signal of a preset format, and then sent out on the bus line 1 to be supplied to the PID controller which issued the transmission command.

The bus line 1 is laid so as to connect the monitoring room side in which the PID controllers 2, 3 and 4 are installed and the flow rate detecting device 5 and the valve control device 6 installed in the site side. Every time a transmission request command or operation command is output from each of the PID controllers 2, 3 and 4, the PID controller 2, 3 and 4 is taken in and supplied to the flow rate detecting device 5 and the valve control device 6, and the flow rate detecting device 5 is also supplied. Every time a transmission signal is output from the device, it is taken in and supplied to each of the PID controllers 2, 3 and 4.

The PID controllers 2, 3 and 4 are respectively
For each preset cycle (for example, 100 ms),
A transmission request command is generated, sent to the bus line 1 and supplied to the flow rate detecting device 5, a transmission signal is output from this flow rate detecting device 5, and this transmission signal is sent to the bus line 1. At this time, while taking in this, an operation signal is generated by PID calculation, and this is sent out to the bus line 1 and supplied to the valve control device 6.

The valve control device 6 takes in operation signals from the PID controllers 2, 3 and 4 supplied via the bus line 1 and outputs them to the PID controllers 2, 3 and 4.
The latest operation signal of each PID controller 2, 3 and 4 is stored for each preset period (for example, 200 ms), and the intermediate value (2 The opening of the valve 9 is controlled based on the second largest value.

Next, the control operation of this embodiment will be described with reference to the block diagram shown in FIG.

First, each PID controller 2, 3 and 4 has a preset cycle (for example, 100 ms).
For each time, a transmission request command is generated, sent to the bus line 1 and supplied to the flow rate detecting device 5.

As a result, the flow rate detecting device 5 takes in the flow rate measurement result output from the flow rate sensor 8 attached to the pipe 7 through which the fluid to be controlled flows and transmits it as a transmission signal of a preset type. After being converted to, the data is sent to the bus line 1 and supplied to the PID controllers 2, 3 and 4 which issued the transmission command.

The PID controllers 2, 3 and 4 perform PID calculation based on this transmission signal to generate an operation signal, which is sent to the bus line 1 and supplied to the valve control device 6.

On the other hand, the valve control device 6 includes the PID controllers 2, 3, 4 supplied via the bus line 1.
The latest operation signal for each PID controller 2, 3 and 4 is stored by taking in the operation signal from the PID controller 2, 3 and 4 and also to each PID controller 2, 3 and 4 every preset period (for example, 200 ms). The latest operation signals of are compared with each other to determine an intermediate value (second largest value), and the opening of the valve 9 is controlled based on this intermediate value.

As a result, for example, even if one of the PID controllers 2, 3 and 4 outputs a 50% operation signal and one unit fails and outputs a 100% operation signal, the valve control device Since 100% of the operation signal output from this PID controller is ignored by 6 and the valve 9 is controlled based on the intermediate value of 50% of the operation signal, the system is not affected by the defective PID controller. You can avoid it.

Further, at this time, since it is not necessary for the valve control device 6 side to judge which PID controller 2, 3, 4 has failed, the control can be greatly simplified.

As described above, in this embodiment, each PI is
The measurement results obtained by the flow rate detection device 5 are fetched by the D controllers 2, 3 and 4, and the manipulated variable is calculated, and this is supplied to the valve control device 6 to obtain an intermediate value (second largest value) of these manipulated variables. Since the opening of the valve 9 is controlled based on the (value), some PIDs can be selected without distinguishing and selecting a normal PID controller and a defective PID controller. Even if the controller has failed, the control of the valve 9 can be continued, which can greatly improve the reliability of the system.

Further, in the above-mentioned embodiment, the valve 9 is operated based on the intermediate value (second largest value) among the operation signals calculated by the PID controllers 2, 3 and 4 by the valve controller 6. Although the opening is controlled, the opening of the valve 9 may be controlled based on the average value of each operation signal.

In this case, each PID controller 2, 3,
If one of the four fails, the value of the operation signal output from the failed PID controller will temporarily fluctuate from an appropriate value, but it failed because the entire system has a feedback loop configuration. The operation signal output from the PID controller becomes a disturbance to the process, and another normal PID controller can generate an operation signal for correcting the disturbance to reduce the influence of the defective PID controller.

However, when the response of the process is slow, the influence of the occurrence of a failure appears in the process to some extent. Therefore, in such a process, it is preferable to use an intermediate value to control the valve or the like.

Further, in the method using such an average value, the system cannot be made redundant when the range of the operation signal is 0% to 100% and there is no margin of the range over.

That is, when one faulty PID controller outputs a 0% operation signal, even if another normal PID controller outputs a 100% operation signal, the average value is set to 100%. Therefore, in the system using such an average value, the range of the operation signal output from each PID controller 2, 3, 4 is -1.
It is desirable to set the average value to 00% to + 200% and limit the average value to a preset range on the valve control device 6 side, for example, 0% to 100%.

As a result, even if the defective PID controller outputs an operation signal of -100%, the other two PID controllers are
Since the ID controller outputs a + 200% operation signal, the average value can be set to + 100%.

Further, in the above-described embodiment, the valve control device 6 obtains a representative value such as an intermediate value or an average value from the respective operation signals. A representative value such as an intermediate value or an average value may be obtained and supplied to the valve control device 6 to control the valve.

FIG. 2 is a block diagram showing a second embodiment of the control system according to the present invention.

The control system shown in this figure comprises a plurality of voltage output type PID controllers 20 and a plurality of resistors 21, and the output of a sensor 24 for detecting the state of a process 23 to be controlled by each PID controller 20 ( Process variable) and perform PID calculation.
A plurality of manipulated variables are obtained, the respective manipulated variables are weighted and combined by the resistors 21, and one manipulated variable thus obtained is supplied to the manipulated end 22 to control the control target process 23.

Each PID controller 20 is composed of the same hardware, and takes in preset setting values, and takes in these setting values and the process variable output from the sensor 24.
After the PID calculation is performed according to these differences to obtain the manipulated variables, these manipulated variables are set to 1 via the corresponding resistor 21.
In summary, this is supplied to the operating end 22.

In this case, all PID controllers 20
Is normal, all manipulated variables have the same value,
When one of these PID controllers 20 fails and has an inappropriate value, the input impedance of the operating end 22 is sufficiently high, and when all the resistors 21 have the same resistance value, one operation obtained by each resistor 21 is performed. The amount is the value shown in the following formula.

MV = {(N-1) MV1 + MV2} / N where MV1: the value of the manipulated variable output from the normal PID controller 20.

MV2: Defective PID controller 20
Value of manipulated variable output from.

MV: The value of one manipulated variable obtained by each resistor 21.

N: Total number of PID controllers 20.

From a different point of view, this equation gives the normal operation output of the PID controller 20 as (N-1) / N
Is applied to the controlled object process 23,
It is in the form of a disturbance called (MV2 / N). Therefore, even in such a case, if N is a sufficiently large value, the function of the feedback control normally operates and even if the process variable output from the sensor 24 temporarily fluctuates to some extent, It has no significant effect on control.

For example, the value MV of the manipulated variable at the normal time is 1 to 5 VDC, and the PID controller 20 has a value of 0.
In the case of a system having an output capacity of up to 6VDC and having six such PID controllers 20, all six operate normally, and at this time, the values MV1 to MV6 of all manipulated variables are 1
It is assumed that the output is stable at a constant output of 00%, that is, 5 VDC.

In this state, one PID controller 2
If 0 fails and outputs a constant value of 0V, the other 5 PID controllers 20 continue to operate at 5VDC.
Is output, the value MV of the total manipulated variable decreases to [(6-1) × 5 + 0] / 6 = approximately 4.17V.

However, when the feedback control function of the system operates, the five normal PID controllers 20 increase the operation amount value MV1 to reach the upper limit of 6 V, [(6-1) × 6 + 0]. / 6 = 5V, and the overall manipulated variable value MV returns to the normal value. Further, from this, when the output of 0 to 6 VDC is possible for the 1 to 5 VDC range, in order to build a redundant system, at least 6 PID controllers 20 are required.
It turns out that is needed.

In another case, each PID controller 20 has a range of -3 to + 9VD for a range of 1 to 5VDC.
If C can be output, a redundant system can be configured with three units as shown in the following equation.

[(3-1) × 9 + (-3)] / 3 = 5V Further, -3 to + 9VDC for the 1 to 5VDC range.
If six PID controllers 20 capable of outputting are used, a system that can be normally controlled even if two PID controllers 20 fail as shown in the following equation can be configured.

[(6-2) × 9 + 2 × (−3)] / 6 = 5V As described above, in this embodiment, the output of the sensor 24 that detects the state of the process 23 to be controlled by each PID controller 20 (process Each variable) and perform PID calculation to obtain a plurality of manipulated variables,
These operation amounts are weighted and combined by the respective resistors 21, and one operation amount obtained by this is combined with the operation end 22.
Are supplied to the control target process 23 to control the control target process 23. Therefore, some control elements can be selected without distinguishing and selecting a normal control element and a defective control element. Even in the state of failure, the control of each device can be continued, which can greatly improve the reliability of the system.

Further, in this embodiment, simply increasing the number of PID controllers 20 connected in parallel,
Not only one of N units but also multiple PID controllers 2
It is possible to provide a system in which control is not hindered even if 0 fails, and online maintenance can be performed by removing one to a plurality of PID controllers 20 during operation.

FIG. 3 is a block diagram showing a third embodiment of the control system according to the present invention. In addition, in this figure,
The same parts as those in FIG. 2 are designated by the same reference numerals.

The control system shown in this figure differs from the system shown in FIG. 2 in that the voltage type PID controller 20 is used.
Instead of this, a current type PID controller 25 is used, and a resistor 26 for converting the current output from the PID controller 25 into a voltage is further provided at the operating end 22.

In this case, the voltage type PID controller 2
When it is 0, the combined output becomes the average value and the current type PI
In the case of the D controller 25, since the combined output has an added value, by using the current type PID controller 25, when the current is converted to 1 to 5 VDC at the operating end 22 and used, 4 to 20 mA DC is used. It suffices to connect N PID controllers 25 capable of outputting the above in parallel, and connect 250 pieces of 250Ω resistors 26 in parallel at the operating end 22.

Further, the operating end 22 itself is set to 4 to 20 mA DC.
(4 / N) to (20 / N) mAD when driven by
PID controller 2 capable of outputting C current
N units of 5 may be connected in parallel and used.

When manipulating the value MV of the manipulated variable manually, it is necessary to instruct all PID controllers 25 at the same time. In such a case, PI
Use the communication function between D controllers 25
The D controller 25 can be controlled simultaneously. A separate bus line may be provided for this communication, but each P
The operation amount line of the ID controller 25 may be used as a communication line, and a digital signal may be superimposed on an analog signal of each PID controller 25 to perform communication between the PID controllers 25.

Further, in the second embodiment shown in FIG. 2 and the third embodiment shown in FIG. 3, a voltage type PID controller 20 and a current type PID controller 25 which are generally used are connected in parallel. Although the system is constructed, the respective PID controllers 20 and 25 themselves may be of a redundant system compatible type and connected in parallel.

In this case, the PID controllers 20 and 25
As a method of making the system compatible with the redundant system, for example, as shown in FIG. 4A, a fixed resistor 27 is arranged on the output stage side inside the PID controllers 20 and 25, and FIG.
As shown in FIG. 4, a method of disposing a diode 28 for preventing backflow on the output stage side of the PID controllers 20 and 25, FIG.
A method for providing a parallel connection terminal 30 at the output end 29 of the PID controllers 20 and 25 as shown in FIG.
As shown in FIG. 5, a method of providing a switch 31 for disconnecting the output of the operation amount of the PID controller 20 or 25 at the time of abnormality or power off is provided.

In addition to the methods for dealing with these redundant systems, a relay control circuit 33 is provided on the output stage side inside the PID controllers 20 and 25 as shown in FIG. 5A, for example.
After the relay 34 and the reading circuit 35 are provided, the voltage of the external manipulated variable line 36 is monitored by the reading circuit 35 when the power is turned on, and the value MV of the own manipulated variable is set to that value based on the monitoring result. The relay control circuit 33 controls the relay 34 to connect its own manipulated variable line to an external line so that a normal control operation is performed thereafter, whereby the manipulated variable does not suddenly change.
The D controllers 20 and 25 may be used.

Further, for example, as shown in FIG.
Subtraction for calculating the difference between the output of the PID calculator 38 for performing PID calculation based on the difference between the process amount and the set value obtained by the subtractor 37 on the output side of the controller 20, 25 and the external manipulated variable line 36. Circuit 39 and this subtractor 3
PID calculator 4 for performing PID calculation based on the output of 9
0 is provided, PID calculation is performed based on the difference between the manipulated variable (internal manipulated variable) obtained by the PID calculator 40 and the manipulated variable on the external manipulated variable line 36, and the manipulated variable thus obtained is calculated. It may be supplied to the operating end via a resistor 41 provided outside.

In addition, the PID controllers 20 and 25
Then, the resistor 41 is provided outside the PID controllers 20 and 25.
Are provided, but as shown in FIG.
The resistor 42 may be provided inside the D controllers 20 and 25.

When these so-called cascade controls are performed, the PID controllers 20, 2 are generally used.
Since the response of the manipulated variable obtained when 5 is connected in parallel is much faster than the response of the process to be controlled, the correction operation at the time of failure occurrence becomes faster, and the effect of the failure on the process is reduced to be realistic. , It is possible to prevent almost no control disturbance.

Further, for example, as shown in FIG. 6, the microprocessor is operated in a time-division manner, and P having N control functions 46 is provided.
Configure the ID controller 45, use M of this,
For each loop, each control function 46 is connected in parallel and N (N
> M) loops may be controlled.

By doing so, even if the number of loops to be controlled is N, in the case where M redundant redundancy is normally performed, N × M controllers are normally required. The N PID controllers 45 can control N loops.

In each of the above-mentioned embodiments, each PID controller 20, 25, 45 used in the system is used.
Hardware and software of the PID controller 20, 25, 41
Hardware and software may be different from each other.

By doing so, even if a lot of parts is defective or a software bug occurs, control of the entire system can be maintained in a normal state.

In the above embodiment, the PID
Although the control system is constructed by using the controllers 20, 25, 41, the control system may be constructed by using a controller that performs other control calculation.

[0064]

As described above, according to the present invention, some control elements fail without the operation of separately selecting and disconnecting a normal control element and a failed control element. Even in this state, the control of each device can be continued, and the redundancy of the system can be greatly improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of a control system according to the present invention.

FIG. 2 is a block diagram showing a second embodiment of the control system according to the present invention.

FIG. 3 is a block diagram showing a third embodiment of the control system according to the present invention.

FIG. 4 is a block diagram showing another example of a PID controller used in the present invention.

FIG. 5 is a block diagram showing another example of a PID controller used in the present invention.

FIG. 6 is a block diagram showing another example of a PID controller used in the present invention.

[Explanation of symbols]

 2, 3, 4 PID controller (controller) 5 Flow rate detection device (process amount detection device) 6 Valve control device (synthesis unit) 9 Valve (controlled device) 20 PID controller (controller) 21 Resistance (synthesis unit) 24 Sensor ( Process amount detection device) 25 PID controller (controller) 26 Resistance (combining unit) 45 PID controller (controller) 46 Control function

Claims (4)

[Claims] 1. A control system in which a controller processes a process signal obtained by a process amount detection device provided on the site side to generate an operation signal and controls a controlled object based on the operation signal, Based on the process signal and the same set value,
A controller that independently performs a predetermined calculation process to obtain a manipulated variable, and 1 based on each manipulated variable output from this controller.
A control system comprising: a synthesizing unit that obtains one operation amount. 2. The controller outputs the operation amount obtained by the arithmetic processing in a voltage format or a current format, and the combining unit adds or averages the operation amounts output from the controllers to combine them. 1. The control system according to 1. 3. Each of the controllers has a plurality of control functions configured by a microprocessor, performs arithmetic processing for each control function to calculate an operation amount, and a synthesizing unit adds the operation amounts of each function. Or average and combine,
The control system according to claim 1. 4. Each controller independently performs a predetermined arithmetic processing based on the same process signal and the same set value to individually generate an operation signal, and the synthesizing unit outputs the operation signal from each controller. The control system according to claim 1, wherein a representative value of each output operation signal is obtained, and the control target device is controlled based on the representative value.