JP2010003071A - Controller for plant - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve responsiveness by compensating delay of compensation operation based on a difference to follow fluctuation of a target value without delay. <P>SOLUTION: This controller 30 for a plant performing feedback control based on the difference between the set target value and a control amount, has a feedforward control means storing in advance an input/output characteristic between a valve opening V input to a valve 13 and a flow rate f output from a controlled object, specifying the valve opening V corresponding to the target value based on the input/output characteristic, and inputting the valve opening V specified from the fluctuating target value to the valve 13 when the target value fluctuates. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a plant control device that computes and outputs an operation amount based on a deviation between a target value and a control amount, and more particularly to control of an adsorption separation device in which a flow rate that is a target value varies greatly with time. The present invention relates to a suitable plant control device.

As a method for selectively separating a specific component from a mixture in a plant, for example, when separating and recovering para-xylene from mixed xylene containing ethylbenzene, an adsorption separation method based on the principle of liquid chromatography is widely practiced. .
As control of the plant using the adsorption separation method, there is an adsorption separation device using the Parex (registered trademark) method of UNIVERSAL OIL PRODUCTS.

As shown in FIG. 8, the adsorption separation device 1 includes an adsorption tower 10 having 20 or more adsorption beds filled with an adsorbent, a line 101 forcibly circulating the fluid in the adsorption tower 10 by a pump 11, A line 102 communicating with each adsorption bed, a rotary valve 20 connected to each line 102 in a time-sharing manner, a mixed xylene, a desorbing agent, a mixed solution of para-xylene and a desorbing agent, etc. Via a line 201 for supplying / withdrawing.
Paraxylene is adsorbed by the adsorbent and separated from other isomers while the mixed xylene flows down through each adsorbent bed.
Furthermore, each adsorption bed is switched by a rotary valve 20 to a zone corresponding to the role of the adsorption separation process every predetermined time, and for each zone, supply of mixed xylene and extraction of a mixed liquid of paraxylene and desorbent are performed. Paraxylene can be continuously recovered by taking out and the like.

In such an adsorption separation apparatus 1, in order to efficiently recover para-xylene, the flow rate of each line 101, 201 is measured by the flow meters 12, 22, so that the optimum flow rate is obtained for each adsorption separation process. It is necessary to perform special control for operating the valves 13 and 21 consisting of electromagnetic valves.
In particular, in the line 101 for circulating the fluid in the adsorption tower 10, the flow rate to be circulated to the uppermost part needs to be changed greatly depending on what zone the lowermost part of the adsorption tower 10 currently functions.

  Such flow rate change control is performed in a plant control device 30 (DCS: digital control device). The control device 30 sets a flow rate as a target value for each zone, and performs feedback control for adjusting the opening of the valve 13 based on the deviation between the actual control amount measured by the flow meter 12 and the target value. It is like that.

Here, as a technique for operating the operation ends such as valves and dampers by feedback control, for example, paying attention to the fact that the operating speed of the operation ends differs between the opening direction and the closing direction of the damper, PID control according to the operation An invention for variably setting PID parameters in operation is disclosed (Patent Document 1).
Further, a process control method is disclosed in which a PID parameter is changed in accordance with quantitative and directional changes in target values (Patent Document 2).

JP-A-6-259105 JP-A-6-236201

However, since the feedback control is a follow-up control that eliminates the deviation based on the occurrence of the deviation, the responsiveness is poor in the process control in which the target value is rapidly changed.
In particular, the adsorption tower 10 of the adsorption / separation apparatus 1 has a large capacity, and the flow rate output with respect to the opening degree of the valve 13 is not in a proportional relationship, and a dead time or delay until a change in the target value appears as a control amount. Since it is a non-linear control target having time, the general PID control for calculating the manipulated variable based on the deviation has a poor response and cannot efficiently recover paraxylene.
Furthermore, since the fluid is supplied / extracted from the adsorption tower 10 via a plurality of lines 102, a disturbance in which the internal pressure of the adsorption tower 10 changes for each zone occurs, and the flow rate is not stable. For this reason, if the PID parameter is set so that the disturbance response characteristic is emphasized, the target value responsiveness is deteriorated and the setting is unbalanced.
For example, FIG. 9 shows measured data by conventional PID control. A broken line in the figure is a target value set by the control device 30 and shows a temporal change in the flow rate. A solid line is a control amount measured by the flow meter 12 based on PID control.
Comparing these, it can be seen that the time (settling time) required for the control amount to converge to a predetermined range with respect to the target value is long (about 2 minutes) and the responsiveness is poor.

  The present invention has been proposed in order to solve the above-described problem, and by directly inputting an operation amount corresponding to a change in the target value to the operation end, the compensation operation delay based on the deviation is compensated. It aims at providing the control apparatus of the plant which improves a responsiveness.

  In order to achieve the above object, a plant control apparatus according to the present invention is a plant control apparatus that performs feedback control of a predetermined control object based on a deviation between a set target value and a control amount, and includes a predetermined operation. A storage unit that pre-stores input / output characteristics of an operation amount input to the end and a control amount output from the control target with respect to the operation amount, and an operation amount corresponding to a target value is specified based on the input / output characteristics And a feedforward control means having an output unit that outputs an operation amount specified from the fluctuating target value to the operation end at a timing when the target value fluctuates.

  According to the plant control apparatus of the present invention, it is possible to compensate for the delay of the compensation operation based on the deviation, follow the fluctuation of the target value without delay, and improve the responsiveness.

Hereinafter, a preferred embodiment of a plant control apparatus according to the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram including a plant control device according to the present embodiment, and FIG. 2 is a block diagram showing a PID calculation unit and a delay unit of the plant control device according to the present embodiment.
FIG. 3 is a diagram showing a temporal change in a target value (flow rate) set by the plant control apparatus according to the present embodiment, and FIG. 4 is executed by the plant control apparatus according to the present embodiment. It is the figure which showed the concept of feedforward control.

The plant control apparatus according to this embodiment is the control apparatus 30 that controls the adsorption separation apparatus 1 shown in FIG.
As described above, the adsorption / separation apparatus 1 of FIG. 8 has the lowest part of the adsorption tower 10 currently functioning as any zone in the line 101 for circulating the fluid in the adsorption tower 10 from the lowermost part to the uppermost part. Depending on whether or not, the flow rate circulating to the uppermost part is changed greatly.
Specifically, as shown in FIG. 3, the flow rate circulated to the uppermost portion is changed according to zones 1 to 4 in which the lowermost portion functions.
In the present embodiment, such a change in the flow rate is output as a change in the target value by the control device 30 every predetermined time.
And the control apparatus 30 of this embodiment draws the fluid in the adsorption tower 10 from the lowest part based on the deviation of the target value which changes every predetermined time in this way, and the controlled variable measured in the flowmeter 12. The amount of operation for opening and closing the valve 13 for adjusting the flow rate of the fluid circulated to the top is calculated, and feedback control is performed to eliminate the deviation.

Specifically, the plant control apparatus 30 of the present embodiment is configured by a computer having storage means such as a CPU, ROM, and RAM, an I / O, and the like, as shown in FIG. 1 and FIG. The flow rate circulated from the lowermost part to the uppermost part of a certain adsorption tower 10 is measured by the flow meter 12, and the valve 13 for adjusting the flow rate of the circulated fluid, which is the operation end, is operated based on the measured control amount PV.
Specifically, the controller 30 switches the output of a plurality of flow rates set as the target value SV1 every predetermined time, and outputs the target value SV1 output after delaying the feedback control. Unit 302, a second PID calculation unit 303 that PID calculates target value SV1 and outputs target value SV2, and calculates deviation E from target value SV2 output from PID calculation unit 303 and measured control amount PV Subtracting section 304, first PID calculating section 305 that calculates and outputs an operation amount based on deviation E, feedforward control section 306 that is a feedforward means of the present invention, and feedforward control section 306 And an addition unit 307 for adding the operation amount from the PID calculation unit 305 and outputting the operation amount MV to the valve 13 is provided. That.

The setting unit 301 is set with flow rates as target values corresponding to at least four zones, and varies and outputs the target value SV1 according to the switching timing of the rotary valve 20 shown in FIG. Target value SV1 is input to delay unit 302 and feedforward control unit 306, respectively.
As illustrated in FIG. 2, the delay unit 302 functions as a first-order lag filter, and can delay the rise in which the target value SV <b> 1 output from the setting unit 301 is input to the PID calculation unit 302.
The rise delay time can be adjusted by changing the time constant parameter Tj.

As shown in FIG. 2, the PID calculation unit 303 includes a proportional element 303a, an integral element 303b, a differential element 303c, and a calculus common element 303d.
The target value SV1 transmitted with a delay by the delay unit 302 is first input to the proportional element 302, the integral element 302b, and the differential element 302c, and the outputs from the integral element 302b and the differential element 302c are input to the calculus common element 302d. Is done. The outputs from the proportional element 302 and the calculus common element 302d are added and output as the target value SV2.

As shown in FIG. 2, the PID calculation unit 305 includes a proportional integration element 305 a and a differentiation element 305 b that perform differential leading type PID calculation processing.
The deviation E is input to the proportional integration element 305a, and the control amount PV is input to the differentiation element 305b in advance.
The difference between the proportional integration element 305 a and the differentiation element 305 b is output to the adding unit 307.

  As described above, in this embodiment, two PID calculation units, the PID calculation unit 303 and the PID calculation unit 305, are provided. Thereby, the plant control apparatus 30 of the present embodiment has the target value parameters α, β, γ provided in the proportional, integral, and differential elements in the PID calculation unit 303 and the proportionality in the PID calculation unit 305, respectively. The PID parameters (Kp, Ti, Td) provided for the integration and differentiation elements are individually adjusted to control the control object 10 so as to function as a so-called two-degree-of-freedom PID control device. Yes.

Specifically, the control response of the block diagram shown in FIG. 1 is expressed by the following equation.
PV = [(F + H · G1 · G2) · P / (1 + G1 · P)] × SV1
+ [P / (1 + G1 · P)] × D (1)
Note that F, H, G1, G2, and P indicate transfer functions of the feedforward control unit 306, the delay unit 302, the PID calculation unit 305, the PID calculation unit 303, and the controlled object 10, respectively, as shown in FIG.

As can be seen from the equation (1), the PID control operations acting on the target value SV1 of the first term on the right side are the transfer function G1 and the transfer function G2, while on the other hand, for the disturbance D of the second term on the right side. The transfer function G2 is not involved and only the transfer function G1 acts.
As a result, the PID parameters (Kp, Ti, Td) of the PID calculation unit 305 related to the transfer function G1 are set to a state in which the influence can be immediately suppressed when the disturbance D is applied, that is, the disturbance suppression optimum state. The target value parameters α, β, and γ of the PID calculation unit 303 related to the transfer function G2 can be set to the optimum characteristic state to follow the fluctuation of the target value SV1, that is, the target value tracking optimum state.
Thus, the plant control device 30 of the present invention is configured as a two-degree-of-freedom PID control device that can individually adjust the response characteristics of the PID operation with respect to the response of the target value SV1 and the disturbance D, As a result, an optimal response can be obtained for the controlled object 10.

Further, the plant control apparatus 30 of the present embodiment compensates for a delay in the compensation operation based on the deviation E, and feedforward is feedforward means that directly inputs the manipulated variable MV corresponding to the fluctuation of the target value SV1 to the valve 13. A control unit 306 is provided.
The feedforward control unit 306 inputs and outputs a valve opening V that is an operation amount MV input to the valve 13 and a control amount PV that is output from the control target 10 and is measured by the flow meter 12. A storage 306a that stores characteristics in advance, a specifying unit 306b that specifies the valve opening degree V corresponding to the target value SV1 based on the input / output characteristics, and a target that changes at the timing when the setting unit 301 changes the target value SV1 The output part 306c etc. which directly output the valve opening degree V specified from the value SV1 to the valve 13 are comprised.

The input / output characteristics of the valve opening degree V and the flow rate f stored in the storage unit 306a are determined based on previously measured data.
FIG. 5 is actual measurement data showing the relationship between the valve opening V and the flow rate f. FIG. 6A is a graph showing the valve opening V on the horizontal axis and the flow rate f on the vertical axis. FIG. FIG. 6B shows the input / output characteristic equation calculated as an approximate expression based on the actual measurement data while the flow rate f is the horizontal axis, the valve opening degree V is the vertical axis, and FIG. 5 is shown in the graph. FIG.
As shown in these figures, the relationship between the valve opening degree V and the flow rate f has a non-linear characteristic that does not become a proportional relationship. Therefore, from the measured valve opening V and flow f data, as shown in the following equation, by substituting the flow rate f, an approximate expression that can calculate the valve opening V is flow rate f−valve opening. A degree V characteristic equation can be obtained.
V = U (f)
= Af ⁵ + bf ⁴ + cf ³ + df ² + ef + g (2)
However, ag is a constant calculated | required from the measured data of the valve opening degree V and the flow volume f in FIG.
The storage unit 306a stores the fV characteristic equation as an input / output characteristic.
The specifying unit 306b specifies the valve opening degree V corresponding to the fluctuation of the flow rate f that is the target value SV1 based on the fV characteristic equation.

Specifically, as shown in FIG. 4, the specifying unit 306b uses the previous target value SV1 (n−1) set by the setting unit 301 and the current target value SV1 (n) newly set. Substituting each flow rate f into the fV characteristic equation, corresponding to the valve opening V (n-1) corresponding to the previous target value SV1 (n-1) and the current target value SV1 (n). The calculated valve opening V (n) is calculated.
Further, the specifying unit 306b calculates a difference ΔV (= V (n) −V (n−1)) between the previous valve opening V (n−1) and the current valve opening V (n). The difference ΔV is specified as an operation amount to be output to the valve 13.
As described above, since the operation amount is specified from the approximate expression based on the actually measured data, the operation amount is not far from the characteristic that the operation end and the control target actually have. Further, since the manipulated variable is specified from the approximate expression based on the actually measured data, the present invention can be applied to a controlled object whose input / output characteristics have nonlinearity.

Next, the output unit 306c outputs the difference ΔV to the adding unit 307 illustrated in FIG. 1 as the operation amount of the valve 13 at the timing when the setting unit 301 outputs the target value SV1 that fluctuates.
As a result, in the adding unit 307, the output from the PID calculating unit 305 and the output from the feedforward control unit 306 are added, and this added value is input to the valve 13 as the operation amount MV.
However, since the rise of the fluctuation of the target value SV1 transmitted to the feedback control via the delay unit 302 is delayed, the output from the feedforward control unit 306 is output at the timing when the setting unit 301 outputs the fluctuating target value SV1. Is input to the valve 13 first.
Thus, since the feedforward control part 306 inputs the operation amount according to the fluctuation | variation of target value SV1 directly to the valve | bulb 13, the response characteristic with respect to the fluctuation | variation of target value SV1 can be improved greatly.
Further, the output from the feedforward control unit 306 is a difference ΔV between the previous valve opening V (n−1) and the current valve opening V (n). Therefore, the absolute error can be reduced.

In addition, the time constant Tj in the first-order lag filter of the delay unit 302 is substantially the same as the response characteristic and phase of the flow rate output from the control target 10 with respect to the operation amount directly input to the valve 13 from the output unit 306c. Set to match.
That is, since the control target 10 has a delay time and a dead time, the response is delayed even when the feedforward control unit 306 performs a direct operation. A constant Tj is set.
As a result, the temporal change of the target value fluctuation transmitted to the feedback control via the delay unit 302 and the response characteristic with respect to the target value fluctuation caused by the output from the output unit 306c of the feedforward control unit 306 are in phase. Therefore, the occurrence of the deviation E can be suppressed at the timing when the target value fluctuates, and the PID calculation unit 305 hardly operates.
That is, the PID calculation unit 305 functions as a PID control unit that is responsible for quick settling of the deviation E and suppression of the disturbance D after the target value fluctuates.

FIG. 7 shows an actual control result based on the control in the plant control apparatus 30 of the present embodiment.
FIG. 7 is a diagram illustrating the response characteristics of the actually measured control amount (solid line) with respect to fluctuations in the target value (broken line) output from the setting unit 301.
Compared with FIG. 9 described above, the time required for the controlled variable to converge to a predetermined range with respect to the target value (settling time) is less than half (about 1 minute), and the responsiveness is greatly improved. I understand that.
Thus, in the plant control apparatus 30 of the present invention, the feedforward control unit 306 can speed up the response of the control target 10 by directly inputting the operation amount corresponding to the fluctuation of the target value SV1 to the valve 13. In addition, by delaying the phase by the delay unit 302, optimal control can be performed without interfering with the compensation operation by the PID calculation unit 305.

Further, in the present embodiment, a variable unit that changes the operation amount output from the feedforward control unit 306 is provided.
Specifically, in the fV characteristic equation (Equation (2)) stored in the storage unit 306a described above, the adaptive gain Ka and the switching coefficient M are set as the following equations as adjustable parameters. ing.
V = Ka · M · U (f) (3)
In the equation (3), the adaptive gain Ka is set as a parameter for adjusting the operation amount output from the output unit 306c of the feedforward control unit 306.
On the other hand, as the switching coefficient M, either “0” or “1” is set as a selectable parameter.
Thereby, the output from the feedforward control part 306 can also be made zero. That is, the function of the feedforward control unit 306 can be switched to a stopped state or an operating state.

That is, it is possible to select whether or not to perform the feedforward control depending on the operation status of the adsorption separation apparatus 1 and the difference in the target flow rate to be varied.
In addition, a switching unit that prevents the delay unit 302 from functioning when the feedforward control unit 306 is in a stopped state may be provided.
Further, the target value parameters α, β, and γ of the second PID calculation unit 303 are also set to α = 1, β = 0, and γ = 0 as shown in FIG. The transfer function can be set to “1”, whereby a PID control device including only the PID calculation unit 305 can be obtained.
As described above, the plant control device 30 according to the present embodiment adjusts the above-described parameters so that the operation status of the adsorption separation device 1, the difference in the target value flow rate to be varied, and the control target having different response characteristics are different. Can also respond.

  As described above, according to the plant control apparatus of the present invention, the operation amount corresponding to the fluctuation of the target value is directly input to the operation end, thereby compensating for the delay of the compensation operation based on the deviation and improving the responsiveness. Can be made. In particular, the target value fluctuates greatly, and the operation amount input to the operation end and the control amount output corresponding to the operation amount are non-linear, and the control target having delay time and dead time is optimally controlled. can do.

As mentioned above, although preferable embodiment of the control apparatus of the plant of this invention was described, the control apparatus of the plant which concerns on this invention is not limited only to embodiment mentioned above, A various change implementation is carried out in the scope of this invention. It goes without saying that it is possible.
For example, in the present embodiment, the plant control device is applied to the adsorption separation device. However, from a control target for the operation amount of the operation end, such as a flow control generally having a wide setting range or a damper control of a heating furnace. It can be applied to control of a plant whose output characteristics are nonlinear.
In the present embodiment, as the two-degree-of-freedom PID control, the second PID calculation unit is provided after the setting unit 301. However, since the two-degree-of-freedom PID control has been proposed in various configurations, It is only necessary to individually adjust the parameter that acts on the fluctuation of the value and the parameter that acts on the suppression of the disturbance, and the configuration of the present embodiment is not limited.
Further, the operation end is not limited to the valve because it changes depending on the control target. For example, the present invention can be applied to an operation end in which an operation amount of a damper or the like and an output control amount are nonlinear.

  The present invention can be widely used as a plant control device.

It is a block diagram including the control apparatus of the plant which concerns on one Embodiment of this invention. It is a block diagram which shows the PID calculating part and delay part of the control apparatus of the plant which concern on one Embodiment of this invention. It is a figure which shows the time change of the target value set with the control apparatus of the plant which concerns on one Embodiment of this invention. It is the figure which showed the concept of the feedforward control performed with the control apparatus of the plant which concerns on one Embodiment of this invention. It is a figure which shows the actual value of the control amount output from a control object corresponding to the operation amount input into the operation end which concerns on one Embodiment of this invention. The relationship between the operation amount and the control amount of the operation end which concerns on one Embodiment of this invention is shown, (a) is the figure shown on the graph by making a valve opening degree into a horizontal axis and making a flow volume into a vertical axis | shaft, (b ) Is a graph showing the flow rate on the horizontal axis and the valve opening on the vertical axis, and a graph showing the characteristic equation of flow rate (f) −valve opening (V). It is a figure which shows the relationship between the target value set with the control apparatus of the plant which concerns on one Embodiment of this invention, and the control amount measured. It is a schematic diagram of an adsorption separation device to which a control device of a plant concerning one embodiment of the present invention is applied. It is a figure which shows the relationship between the target value set by the conventional PID control, and the measured control amount.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Adsorption / separation device 12 Flow meter 13 Valve 30 Control device 302 Delay unit 303 PID calculation unit 305 PID calculation unit 306 Feedforward control unit

Claims (9)

A plant control apparatus that performs feedback control of a predetermined control object based on a deviation between a set target value and a control amount,
A storage unit that stores in advance input / output characteristics of an operation amount input to a predetermined operation end and a control amount output from the control target with respect to the operation amount;
A specifying unit for specifying an operation amount corresponding to a target value based on the input / output characteristics;
An apparatus for controlling a plant, comprising: a feedforward control unit having an output unit that outputs an operation amount specified from a changing target value to the operation end at a timing at which the target value changes.   The plant control apparatus according to claim 1, wherein the specifying unit specifies a difference between a previous operation amount corresponding to a target value before change and a current operation amount corresponding to a target value after change as an operation amount.   The said plant is an adsorption separation apparatus which adsorb | sucks and isolate | separates a specific component from a mixture, Comprising: The said control object is the adsorption tower which changes the flow volume of the fluid to circulate every predetermined time. Plant control device.   The plant control device according to claim 3, wherein the operation end is a valve for adjusting a flow rate of a fluid to be circulated in the adsorption tower.   The plant control apparatus according to any one of claims 1 to 4, wherein an object whose input / output characteristics are nonlinear is a control object.   The plant control apparatus according to any one of claims 1 to 5, wherein the input / output characteristic includes an approximate expression calculated based on actual measurement data.   The plant according to claim 1, further comprising a delay unit that delays a timing at which a fluctuation of a target value is transmitted to the feedback control from a timing at which an operation amount is input to the operation end from the output unit. Control device.   The plant control apparatus according to any one of claims 1 to 7, further comprising a two-degree-of-freedom PID calculation unit capable of individually adjusting a response characteristic corresponding to a target value and disturbance.   The plant control apparatus according to any one of claims 1 to 8, further comprising variable means for changing an operation amount input from the output unit to an operation end.

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