Process control device and process control method

Abstract

To provide a process control device and a process control method capable of properly applying an appropriate control parameter even when a characteristic of a controlled object has changed.SOLUTION: A process control device which controls a controlled variable of a controlled object to a control target value, includes a controller which executes an internal model control being modelled correspondingly to a process characteristic of the controlled object, and outputs an operation quantity to the controlled object. The controller is so configured that the outputs other than the controlled variable to the controlled object are fed back to the controller, and the controller changes the control parameter contained in the internal model control according to the outputs being fed back from the controlled object.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a process control device and a process control method. [Background technology]

[0002] Patent Document 1 listed below discloses a process control device that, for example, in a plant, performs feedback control of a value of a process to be controlled to a predetermined target value. This process control device includes a controller that performs so-called internal model control, which is modeled in accordance with the characteristics of the controlled object. The controller has a proportional controller, a compensator that is a positive feedback element, and an adder. The proportional controller is configured to receive as input the deviation between a control target value (SV) and a controlled variable (PV) of the controlled object, and to perform proportional calculation on the input deviation. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-157002 Summary of the Invention [Problem to be solved by the invention]

[0004] In Patent Document 1, the process model in the controller is fixed, and the gain of the proportional controller, which is a control parameter of the process model, is also fixed. Therefore, it is not possible to apply appropriate control parameters to the characteristics of the controlled object, which vary depending on conditions.

[0005] Therefore, an object of the present disclosure is to provide a process control device and a process control method that are capable of applying appropriate control parameters as needed even if the characteristics of the controlled object fluctuate. [Means for solving the problem]

[0006] Control target A process that isThe process control device according to the present disclosure controls a control variable of the controlled object to a control target value, and includes a controller that executes internal model control modeled in accordance with the process characteristics of the controlled object and outputs an operation variable for the controlled object. The manipulated variable is the amount of liquid introduced into the treatment tank where the process is carried out, and the controlled variable is the liquid level of the liquid introduced into the treatment tank. is fed back to the controller, and the controller ,centre The above feedback Extraction amount The control parameter included in the internal model control is changed in response to The controller has first map data that defines the relationship between the withdrawal amount and the control parameter when the liquid level, which is the controlled variable, is constant at the control target value, and is configured to obtain the control parameter from the first map data using the withdrawal amount as an input. do.

[0007] In the present disclosure, the controller may have a proportional unit that performs a proportional calculation on the deviation between the control target value and the controlled variable, and the control parameter may be a gain of the proportional calculation.

[0008] In the present disclosure, The controller may have, instead of the first map data, second map data that defines the relationship between the manipulated variable and the control parameter when the liquid level, which is the controlled variable, is constant at the control target value, and may be configured to obtain the control parameter from the second map data using the manipulated variable as an input. .

[0009] The process control method according to the present disclosure using the process control device includes: Extraction amount and the relationship between the control parameters The first map data in which an acquisition step of acquiring the feedback signal from the control object to the controller; Operation amount When the value of the variable .theta. First map data After the change using Operation amount and a changing step of changing the control parameter corresponding to the [Effects of the Invention]

[0010] According to the present disclosure, even if the characteristics of the controlled object fluctuate due to a change in output other than the control amount of the controlled object, the optimal manipulated variable for the characteristics of the controlled object can be generated by changing the control parameters of the controller in accordance with the changed output. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a block diagram showing an example of the configuration of a process control device according to a first embodiment. [Figure 2] 1 is a schematic diagram showing an example of a configuration of a controlled object according to the first embodiment. FIG. [Figure 3] 10 is a flowchart illustrating an example of a procedure for a control parameter change process. [Figure 4] FIG. 10 is a diagram showing a map defining the relationship between the extraction amount and the control parameter. [Figure 5] FIG. 10 is a schematic diagram showing an example of the configuration of a controlled object according to a second embodiment. [Figure 6] FIG. 10 is a block diagram showing an example of the configuration of a process control device according to a second embodiment. [Figure 7] FIG. 10 is a diagram showing a map defining the relationship between an operation amount and a control parameter when the control amount is constant. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments will be described with reference to the drawings. Common or corresponding elements in the various drawings will be denoted by the same reference numerals, and descriptions thereof will be simplified or omitted.

[0013] Embodiment 1 FIG. 1 is a block diagram showing an example of the configuration of a process control device according to a first embodiment. The process control device 1 is used, for example, in chemical plants such as petrochemical plants, or manufacturing plants for iron, paper, or the like. The process control device 1 controls the value of a process that is a controlled object 2, i.e., the controlled variable PV of the controlled object 2, to a control target value SV. In this embodiment, as shown in FIG. 2, an example will be described in which the controlled variable PV of the controlled object 2 is the liquid level LS of the liquid Lq in the treatment tank Tk measured by the liquid level sensor Ss, and the manipulated variable MV is the amount of liquid introduced into the treatment tank Tk, i.e., the aperture of the valve Va that controls the amount of liquid introduced. Such a controlled object 2 is expressed by the following integral equation (1):

[0014]

number

[0015] In the above equation (1), Kp is a characteristic parameter (gain) of the integral system process, s is a Laplace operator, and Lp is a dead time of the controlled object 2.

[0016] The characteristic parameters Kp and Lp are found in the following way. That is, if the controlled object 2 is a closed loop with no withdrawal amount AE of the liquid Lq, the controlled variable PV increases in proportion to the increase in the manipulated variable MV. The characteristic parameter Kp is found from the relationship between these manipulated variables MV and PV. Lp is a fixed value regardless of the magnitude of the manipulated variable MV, and the fixed value can be determined based on multiple samples with different manipulated variables MV.

[0017] As shown in FIG. 1, the process control device 1 includes a controller 3, a disturbance compensator 4, a first subtractor 5, and a second subtractor 6.

[0018] The controller 3 executes so-called internal model control, which is modeled in accordance with the process characteristics of the controlled object 2. The controller 3 includes a proportional controller 31, a compensator 32, and an adder 33.

[0019] The proportional calculator 31 performs a proportional calculation on the first difference value input from the first subtractor 5, and outputs the calculated value to the adder 33. In the proportional calculation, a proportional gain is used as a control parameter Kc, which will be described later.

[0020] Compensator 32 performs a first-order lag calculation and a dead time calculation on the output of adder 33 fed back from adder 33, and outputs the calculated value to adder 33. The transfer function of compensator 32 is set in consideration of the above equation (1), and specifically, can be expressed by the following equation (2).

[0021]

number

[0022] In the above equation (2), Lc is the dead time of the internal model of the controller 3. Lc is derived using Lp in equation (1).

[0023] The adder 33 adds the output from the proportional unit 31 and the output from the compensator 32 and outputs the sum to the second subtractor 6 .

[0024] The controller 3 corresponds to a computer capable of executing various programs related to process control and may be realized by a processing circuit (not shown). For example, the processing circuit includes at least one processor and at least one memory. The memory stores software or firmware written as various programs, and the processor reads and executes the programs stored in the memory. This enables the functions of the map unit Mp1, proportional controller 31, compensator 32, and adder 33 constituting the controller 3 to be realized. Furthermore, a storage unit (hereinafter referred to as "memory") of the map unit Mp1 readably stores control parameter map data (hereinafter simply referred to as "map data") DMp1, which will be described later. The map unit Mp1 receives an output Op of the controlled object 2, such as a withdrawal amount AE, from a flow rate sensor Sf (described later), and outputs a control parameter Kc to the proportional controller 31. The proportional controller 31 uses the control parameter Kc input from the map unit Mp1 as its proportional gain. This updates the proportional gain of the proportional controller 31. The control parameter Kc is derived using Kp in equation (1).

[0025] The disturbance compensator 4 performs a predetermined filter operation on the control amount PV input from the controlled object 2, and outputs the operation value to the second subtractor 6. The compensator 4 is adjusted so that the closed-loop transfer function from the disturbance actually applied to the controlled object 2 to the control amount PV approaches the stability limit. Note that the disturbance is, for example, lightning, and cannot be detected in advance.

[0026] The first subtractor 5 subtracts the control amount PV of the controlled object 2 from the control target value SV, and outputs the difference value, that is, a first difference value, to the proportional controller 31.

[0027] The second subtractor 6 subtracts the calculated value input from the disturbance compensator 4 from the sum input from the adder 33, and outputs the resulting difference, that is, a second difference value, to the controlled object 2 as the manipulated variable MV.

[0028] In the process shown in Figure 2, the control object 2 outputs an output OP different from the controlled variable PV, which is the withdrawal amount AE withdrawn from the treatment tank Tk. The withdrawal amount AE corresponds to the amount withdrawn from the treatment tank Tk. The withdrawal amount AE is measured by the flow rate sensor Sf and affects the control object 2. For example, if the withdrawal amount AE changes significantly, the manipulated variable MV must be increased to keep the controlled variable PV of the control object 2 constant. In this case, the relationship between the withdrawal amount AE and the manipulated variable MV can be approximated as a linear relationship.

[0029] Here, if the withdrawal amount AE changes during the process operation, the characteristics of the controlled object 2 will fluctuate, making it impossible to generate an optimal manipulated variable MV.

[0030] Therefore, in this embodiment, the extraction amount AE is fed back to the controller 3, and the controller 3 changes the control parameter Kc in accordance with the fed back extraction amount AE. The control parameter Kc is changed at the timing when the extraction amount AE is changed.

[0031] 3 is a flowchart showing an example of a procedure for changing the control parameter Kc. The flowchart is repeatedly executed by the controller 3 during operation of the process. Furthermore, during operation of the process, the withdrawal amount AE is constantly fed back to the controller 3.

[0032] First, the map unit Mp1 of the controller 3 acquires the extraction amount AE (step S10).

[0033] Next, it is determined whether or not there has been a change in the extraction amount AE (step S11). In step S11, for example, if the absolute value of the difference between the extraction amount AE newly acquired in this step S10 and the extraction amount AE acquired in the previous step S10 is equal to or greater than a predetermined value, it is determined that there has been a change in the extraction amount AE (YES in step S11), and if the absolute value is less than the predetermined value, it is determined that there has been no change in the extraction amount AE (NO in step S11). If there has been no change in the extraction amount AE, this process is temporarily terminated. If there has been a change in the extraction amount AE, the process proceeds to step S12. The process of step S11 corresponds to the determination step.

[0034] In step S12, map data DMp1 is read from the memory of the map unit Mp1. The process of step S12 corresponds to an acquisition step. As shown in FIG. 4, the map data DMp1 defines a relationship between the extraction amount AE and the control parameter Kc. In the map data DMp1, as the extraction amount AE increases from AE1 to AE2, the control parameter Kc also increases linearly from Kc1 to Kc2. In the map data DMp1, when the extraction amount AE is equal to or less than AE1, the control parameter Kc is fixed to a minimum value Kc1. In addition, when the extraction amount AE is equal to or greater than AE2, the control parameter Kc is fixed to a maximum value Kc2. By restricting the range of the control parameter Kc to be changed in this manner, it is possible to prevent excessive load from being imposed on the controlled object 2. It is also possible to meet the demand in a plant to change (update) the control parameter Kc with a margin. In determining the control parameter Kc, for example, Kc2 is positioned as the maximum value of the control parameter related to the manipulated variable MV of the controlled object 2 in this embodiment. The manipulated variable MV may be determined so as not to exceed the allowable value of the manipulated object (e.g., the opening of the valve Va) or the allowable value of the controlled object (e.g., the amount of liquid introduced into the treatment tank Tk). Also, for example, the minimum value Kc1 may be determined based on the allowable accuracy of the controlled object 2 in the region below the withdrawal amount AE1.

[0035] Alternatively, instead of the map data DMp1, a relational expression describing the relationship between the extraction amount AE and the control parameter Kc may be stored in the memory of the map section Mp1, and the relational expression may be read from the memory. In this case, in step S13 described later, the control parameter Kc is calculated using the read relational expression, and the control parameter Kc is changed to the calculated control parameter Kc.

[0036] Next, the map unit Mp1 of the controller 3 refers to the read map data DMp1 to determine the control parameter Kc corresponding to the extraction amount AE fed back (i.e., acquired in this step S10), and changes (updates) the control parameter Kc of the proportioner 31 (step S13). The process of step S13 corresponds to the changing step. Thereafter, this process is temporarily terminated.

[0037] According to this embodiment, even if the characteristics of the controlled object 2 fluctuate due to a change in the withdrawal amount AE during process operation, by changing the control parameter Kc of the controller 3 in accordance with the withdrawal amount AE, it is possible to generate an optimum manipulated variable MV for the characteristics of the controlled object 2. In other words, even if the characteristics of the controlled object 2 fluctuate, it is possible to appropriately apply an appropriate control parameter Kc to generate the manipulated variable MV.

[0038] Embodiment 2 Fig. 5 is a schematic diagram showing an example of the configuration of a controlled object according to embodiment 2. The process shown in Fig. 5 differs from embodiment 1 in that there is no flow sensor Sf that measures the withdrawal amount AE, that is, the withdrawal amount AE is unknown.

[0039] Figure 6 is a block diagram showing an example of the configuration of a process control device according to embodiment 2. In Figure 6, elements having the same functions as those in Figure 1 are given the same reference numerals, and their explanation will be omitted. The following explanation will focus on the differences from Figure 1.

[0040] The process control device 1A of the second embodiment has a controller 3A instead of the controller 3 of FIG. 1. The controller 3A has a map section Mp2 instead of the map section Mp1 of FIG. 1. Furthermore, the second difference value, which is the output of the second subtractor 6, is output to the controlled object 2 as the manipulated variable MV and is also input to the map section Mp2 in the controller 3A. Map data DMp2, which defines the relationship between the manipulated variable MV and the control parameter Kc, is readably stored in the memory of the map section Mp2, as will be described later. The map section Mp2 determines the control parameter Kc corresponding to the manipulated variable MV and outputs the determined control parameter Kc to the proportional controller 31. The proportional controller 31 uses the control parameter Kc input from the map section Mp2 as a proportional gain. As a result, the proportional gain of the proportional controller 31 is changed.

[0041] In this embodiment, as shown in FIG. 7(a), when the controlled variable PV is constant (for example, the controlled variable PV is PV1), the relationship between the manipulated variable MV and the control parameter Kc can be uniquely determined. Therefore, map data DMp2, as shown in FIG. 7(b), is created and stored in the memory of the map section Mp2. For example, as shown in FIG. 7(a), when the controlled variable PV is constant at the controlled variable PV1, the appropriate control parameter Kc for the extracted amount (estimated value) AE11 is Kc11, and the manipulated variable MV at this time is MV11. Also, as shown in FIG. 7(a), for a constant controlled variable PV1, the extracted amount AE gradually increases, and the appropriate control parameter Kc for the extracted amount AE21 is Kc21, and the manipulated variable MV at this time is MV21. In this case, the control parameter Kc can be determined as a function of the manipulated variable MV, as shown in FIG. 7(b). Therefore, if map data DMp2 defining the relationship between the manipulated variable MV and the control parameter Kc shown in Fig. 7(b) is stored in the map section Mp2, an appropriate control parameter Kc can be obtained by inputting the manipulated variable MV. That is, an appropriate control parameter Kc can be obtained by the function Kc = fkc(MV).

[0042] If the appropriate control parameter Kc changes even for the same manipulated variable MV due to fluctuations in the manipulated variable PV, map data or functions (relational expressions) defining the relationship between each manipulated variable MV and the control parameter Kc for multiple manipulated variables PV (for example, multiple manipulated variables PV between the lower and upper limits of the assumed manipulated variable PV) are stored in the memory of the map unit Mp2, and the map unit Mp2 is configured to input the manipulated variable PV as well.The control parameter Kc is then configured to be found as a function of the manipulated variable MV and the manipulated variable PV.That is, the appropriate control parameter Kc can be found using the function Kc=fkc(MV, PV). For example, when it is desired to find the control parameter Kc(x, y) when the control volume PV(x) and the manipulated variable MV(y) are given, the control parameter Kc may be found by complementing the value of the control parameter Kc=fkc(MV, PV+) found from a function that indicates the relationship between the manipulated variable MV(x+), which is equal to or greater than the control volume PV(x) and closest to the control volume PV(x), and the value of the control parameter Kc=fkc(MV, PV-) found from a function that indicates the relationship between the manipulated variable MV(x-), which is equal to or less than the control volume PV(x) and closest to the control volume PV(x), and the control parameter Kc.

[0043] According to this embodiment, even when the withdrawal amount AE cannot be measured, the control parameter Kc of the controller 3 can be changed to a value corresponding to the withdrawal amount AE. Therefore, as in the above-described first embodiment, even if the characteristics of the controlled object 2 fluctuate due to changes in the withdrawal amount AE during process operation, an appropriate manipulated variable MV can be generated. Furthermore, as in the above-described first embodiment, by restricting the range of the control parameter Kc to be changed to the range from the minimum value Kc1 to the maximum value Kc2, it is possible to prevent an excessive load from being imposed on the controlled object 2.

[0044] In the above-described first and second embodiments, the controlled variable PV is the liquid level LS of the liquid Lq introduced into the treatment tank Tk, but this is not limiting. The controlled variable PV may be, for example, another process value such as temperature, flow rate, or pressure. In this case, the output OP from the controlled object 2 is not limited to the extraction amount AE, and may be anything that varies the characteristics of the controlled object 2. Furthermore, the map data DMp1 and DMp2 may be stored in a memory that is accessible outside the controller 3. [Explanation of symbols]

[0045] 1...process control device, 2...controlled object, 3...controller, 31...proportional regulator, AE...withdrawal amount, Kc...control parameter, gain of proportional regulator 31, Lq...liquid, LS...liquid level, MV...operated variable, OP...output, PV...controlled variable, SV...control target value, Tk...treatment tank

Claims

1. A process control device that controls a control amount of a process to be controlled to a control target value, a controller that executes an internal model control modeled in correspondence with a process characteristic of the controlled object and outputs a manipulated variable for the controlled object; wherein the manipulated variable is the amount of liquid introduced into a treatment tank where the process is performed, and the controlled variable is the liquid surface level of the liquid introduced into the treatment tank; The amount of the liquid extracted from the treatment tank is fed back to the controller; the controller is configured to change a control parameter included in the internal model control in response to the feedback of the withdrawal amount; The controller a first map data defining a relationship between the withdrawal amount and the control parameter when the liquid level, which is the controlled variable, is constant at the control target value; a process control device configured to obtain the control parameter from the first map data using the withdrawal amount as an input;

2. 2. The process control device according to claim 1, wherein the controller has a proportional unit that performs a proportional operation on a deviation between the control target value and the controlled variable, The process control device wherein the control parameter is a gain of the proportional operation.

3. In the process control device according to claim 1, The controller Instead of the first map data, second map data is provided which defines a relationship between the manipulated variable and the control parameter when the liquid level, which is the controlled variable, is constant at the control target value, and The process control device is configured to obtain the control parameter from the second map data using the manipulated variable as an input.

4. A process control method using the process control device according to any one of claims 1 to 3, comprising: an acquisition step of acquiring the first map data defining the relationship between the extraction amount and the control parameter; a changing step of changing, when the manipulated variable fed back from the controlled object to the controller changes, the control parameter to correspond to the manipulated variable after the change, using the first map data acquired in the acquiring step.

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