JPS61156303A - Process controller - Google Patents

Abstract

PURPOSE:To attain the optimum process control by varying the process time constant, the process gain obtained in a process stable mode and the waste time of a feedforward system respectively according to the process state. CONSTITUTION:The deviation (e) between the control value PV obtained from a control process 12 and the target value SV is obtained by a deviation arithmetic means 11. This deviation (e) is applied to a maximum operating output value output means 14, a deviation holding circuit 15, a control variation arithmetic means 16 and a process time constant correcting means 17 as well as a PID control part 13 forming a feedback system. A gain replacement means 18 obtains the process gain K from the ratio between the operating output value MV and the value PV obtained when the process is stable. Then the process gain is replaced. A waste time replacement means 22 measures the time needed for change of the value PV when a selection circuit 23 is switched to a feedforward system from the feedback control system 13 and replaces the waste time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an improvement in a process control device configured by a feedper control system and a feedper control system.
In particular, the present invention relates to a process control device that performs optimal control by varying a process transfer function according to actual process data.

[Technical background of the invention]

Conventional devices of this type usually have a configuration including a feedback control system K and an auxiliary feedforward control system for disturbance 1, as shown in the WXa diagram, and the main control is PID! This was due to feed control using 1 section meter 2. Specifically, the control value pv output from the process 3 waiting for the transfer function G is read-packed to the deviation calculation element 4, where the control value Pv and the target value SV are
This deviation is converted into PI using PID controller 2.
A feedback control system that performs the D calculation to obtain a manipulated output value Mv that approaches zero to operate and control the process 3, and a feedforward transfer function GC for disturbance compensation to the output of the PID controller 2 as compensation means for the disturbance 1. and transfer function G for disturbance 1 to the process SO output side.
, and a feedforward control system.

[Problems with background technology]

By the way, feedback control is mainstream in the above-mentioned 5 process control devices, and the ΔT meter, which is the transmission amount aGp of process 3 used for feedforward control, is not a method that can be automatically identified during process JO control. Therefore, it is often necessary for humans to separately calculate and measure actual process data to determine and set each parameter, which undeniably complicates operation and also causes a decrease in control responsiveness. .

On the other hand, if the state equation of the plant is clear and all state variables can be easily measured, it is thought that a complete process control device can be realized. Due to the difficulty of measuring all state variables, it is impossible to perform optimal control using conventional equipment.

[Purpose of the invention]

The present invention has been made with the above points in mind, and it executes feedforward control by sequentially varying the process transfer function to an optimal value according to the process state, and further fine-tuning it by feedback control. It is an object of the present invention to provide a process control device that improves the stability of process control and eliminates the effects of delay time.

[Summary of the invention]

The present invention measures the process gain in a stable state of the process, updates the process gain, calculates and corrects the process time constant from the changing state during a transient response, and then switches to the feedforward control system side. This is a process control device that executes feedforward control while varying the process transfer function to an optimal value by measuring the time from when the control value changes and updating the dead time of the process.

[Embodiments of the invention]

Embodiment 1 of the present invention will be described below with reference to FIGS. 1 and 2. Although the process transfer function G is not as simple as expressing it mathematically, it can usually be approximated by K ) with the minimum process dead time and the shortest rise time Tm, the control value pv is changed to the target value SV.
When establishing the operation output value MV as shown in Figure 1
Therefore, it is necessary to control the process. That is, as the operation output value MY, the short startup time 75 xx B・Δ
Between t.

If the process is controlled using the maximum operation output value MH1-, and V is then lowered by Mv-]r (where K is the process gain), the control value PV changes as shown by the dotted line A shown in the 12th line). There is no hunting phenomenon caused by
It is possible to accurately reach the target value SV. For this purpose, it is necessary to vary the necessary 19 parameters T (process time constant), K (process gain), and L (process dead time) of the process transfer function CP according to the process state during feedforward control. .

Hereinafter, an embodiment of the process control device according to the present invention realized under the above-mentioned key points will be described with reference to FIG. In the figure, reference numeral 11 denotes a deviation calculation means for calculating the deviation e between the control value Pv obtained from the control process 12 and the target value SV, and the deviation e obtained here is calculated by the feed controller and the PID adjustment unit 13 as a control system. In addition, a maximum operation output value output means 14 that outputs the maximum operation output value MH.
, a deviation holding circuit 15 that always holds the previous deviation 0, a control change value operator R16 that calculates the control change value by subtracting the previous deviation d from the current deviation e, and an f process time constant correction means 1.
It has been introduced in the 1st class.

18 is an r-in updating means, which updates the process control system K based on the ratio of the manipulated output value MY and the control value Pv when the control value SV and the target value SV are stable within a certain range for a predetermined time or more. This update process is supplied to the predetermined operation output value output means 19.

This output means 19 receives a target value of 5V and outputs a manipulated output value that becomes Sv/ as shown in FIG. Each output terminal of the maximum manipulated output value output means 14 and the predetermined manipulated output value output means 19 is selected by a first selection circuit 21 controlled by the maximum manipulated output value output time calculation means 20. The maximum manipulated output value output time calculation means 20 uses the true outputs from the control change value calculation means 16 and the process time constant correction means 11 to calculate the time Ts! for outputting the maximum manipulated output value M'K! I!
It has a function of determining l·Δt, during which time the maximum manipulated output value output means 14 is selected via the first selection circuit 21, and then the predetermined manipulated output value output means 19 is selected. 2
Reference numeral 2 denotes a dead time update means, which is used when the second selection circuit 23 switches from the foot control system to the first selection circuit 21 side when the feed 7# word control system is input, and the control value pv is changed. It has a function of measuring the dead time until the change occurs and closing the @2 selection circuit 23 on the feedforward control system side between L+T.

Next, K, the control value p shown in FIG.
The case of obtaining v will be explained. Always PID adjustment section J
Process 12 is operated and controlled by J, but the 1st r
! When establishing the target value Sv with the shortest rise time d- such as Aω), when the deviation e between the control value pv and the target value SV exceeds a certain value, or as appropriate
Select to switch to the tweed forward control system. At this time, the deviation before switching the feedforward control system is already held in the deviation holding circuit 15 as the previous deviation C. In this state uVc, when the deviation e after switching the feedforward control system exceeds a predetermined value, the maximum manipulated output value output means 14 outputs the maximum manipulated output value MH, and via the first selection circuit 21 fe! 12.

On the other hand, the current deviation e is supplied to the control change value calculation means 16, where the current deviation e and the previous deviation l of the deviation holding circuit 15 are
The control change value h = e - e', which is the difference between
sent to. The maximum operation value output time calculation means 20 is supplied with a correction time constant 'rx'r'+Be- for the current deviation 6 from the process time constant correction means 11. T' is the previous deviation e'Q time constant, and n is a constant determined by the accuracy of the process transfer function. In this way, the control change value h=e
-e' and the correction time constant T=10B1B, the maximum manipulated output value output time calculation means 20 calculates the maximum manipulated output value output time τ shown in FIG. 1(2)K by the following formula.

Ts = m-74! -T log (--1L)
-'' (1) Then, the selection circuit 21 of xi selects the maximum operation output value output terminal gllJ side at this time point (1).

Note that the output time Ts can be derived based on the calculation formula described below. Lose, 4-6-仝-0,3) τB! ! ! l-rd'f...
...The relational expression (4) holds true in the process control system.

However, K is the process dyne, h is the control change value, and 1 is the predetermined control cycle = Therefore, if you transform equation (2), 1 MH - Kd" s + m (-1 for MEI-), this can be expressed by substituting this (6)2K(2) formula.

becomes. Furthermore, when we substitute equation (3) into this equation, d holds true. Therefore, by substituting this m into (4)2, we get
Equation (1) holds true. Therefore, the optimum maximum operation output value output time Ts is determined based on the correction time constant 1 and the control change value, and during this period, the maximum operation output value M1'I becomes 1
given to 2.

Then, after the maximum operation output value output time T1 has elapsed, the first selection circuit 2-1 is connected to the predetermined operation output value output means 19 side. In this means 19, a predetermined operation output of Sv/ is obtained, but in this process dyne, PV
PV when the process is stable when ≧Sv continues for more than a certain period of time
The updated value r in by the ratio of /MV is used.

Therefore, the predetermined manipulated output value SV/K is given to the process 12 from the predetermined manipulated output value output means 19 .

On the other hand, the dead time updating means 22 measures the time from switching to the feedforward control system until the process 120 control value changes, takes into account the response delay time Ts, and during that time the selection circuit 23 of wc2 Select and hold the forward control system side.

In this way, the process constants used in the feedforward control system are identified from time to time, and the feedforward control is performed using the optimum/dalameter without the hunting phenomenon. Note that during the operation of this feedforward control, if the % feedback control is operated, an overshoot will occur, so to prevent this, no operation using the feedback control is performed during the feedforward control operation.

However, even when feedforward control is performed, control deviations occur due to unclear plant characteristics, so the second selection circuit 23 switches to the feedforward control system and performs feedback control to control the Adjustment control is performed.

Therefore, according to the above configuration, the transfer function of Derosés is ``1+TS e-'', of which K,
'r.

Approximate the process with a first-order delay system using a nocrameter of L to perform feedforward control, and at the same time
The deviation due to the depletion meter is PID due to K, -dopa,
Since the fine adjustment operation is carried out by the control, the control value can be established as the target value with the shortest rise time and without causing any hunting phenomenon.

Special K: In a feedback control system when there is process waste time, it is necessary to wait until a response appears in the control value, but with feedforward control, there is no need for this, and control is performed by anticipating the waste time in advance. can be applied, and the establishment time can be shortened accordingly.

In the above embodiment, a feedforward control system was used in which the process transfer function was approximated by 1+T8e-'', and a feedforward control system using K PID control for fine adjustment was used. Instead of tID control, it may be possible to control the sample P1.I-PD, etc. Furthermore, it may include a control system in which the process control device shown in FIG. 2 is added with feedforward control for disturbances. , process transfer function "= TAT'
-'' T, K, and L may be functions of the control value, the manipulated output value, or the target value, respectively, and the present invention can be implemented with various modifications without departing from the gist thereof.

〔Effect of the invention〕

As detailed above, according to the present invention, feedforward control is performed while sequentially varying the process transfer function by measuring the process dyne in a stable state and identifying the process from the deviation during a transient response. A process control device that can eliminate control delays caused by wasted time in the process due to forwarding, eliminate hunting phenomena, and also ensure process stability by adding fine adjustments using feedpaper control after feedforward control. can be provided.

[Brief explanation of the drawing]

1 and 2 are for explaining one embodiment of a process control device according to the present invention. Figure 1 is a diagram showing the relationship between the manipulated output value and the process control value.
FIG. 2 is a schematic configuration diagram of the apparatus of the present invention, and FIG. 3 is a schematic diagram of a conventional process control apparatus including a feedforward control system expressed using a transfer function. 1. Deviation calculation means, 12. Process, 13.
... PID adjustment unit, 14-... Maximum operation output value output means, 15... Deviation holding circuit %16... Control change value calculation means, 11... Time constant correction means, 18... r-in Update means, 19... Predetermined operation output value output means, 20...
- Maximum operation output value output time calculation means, 22...dead time updating means. Representative Patent Attorney Takehiko Suzue Figure 1

Claims (1)

[Scope of Claims] A process control device in which a feedforward control system for preventing a hunting phenomenon of control values is added to a process feedback control system, wherein the feedforward control system is configured to obtain a control value based on a control value and a target value. time constant correction means for calculating a process time constant based on the current deviation, and when the deviation is greater than or equal to a predetermined value;
The maximum operation output value output time is determined using the difference signal between the current deviation and the previous deviation and the correction process time constant obtained by the time constant correction means, and a maximum operation output value output time is determined for the process during this time. a second manipulated output value output means for providing the process with a predetermined manipulated output value determined by the process gain K and the target value when the process is stable after the maximum manipulated output value output time has elapsed; , dead time updating means for measuring the time from when the feedforward control system is activated until the control value of the process changes, and updating dead time L of the feedforward control system; At least the parameters K, T, L of the transfer function
A process control device characterized by controlling a process while sequentially varying.