JPS58219603A - Sampled value pid controller - Google Patents

Abstract

PURPOSE:To eliminate the need for a monitoring person or expensive monitoring facilities by providing a sampled value PID controller with a characteristic variation detection part which detects the characteristic variation of a process and monitoring the characteristic variation of the process on on-line basis. CONSTITUTION:If the characteristic variation of the plant occurs during operation, a direct current for a model error is generated. When the balancing point of the process varies, the direct current for the model error is generated as well. For this purpose, the characteristic variation of the process and the variation of only the balancing point of the process are discriminated in case of the occurrence of the model error. When there is the characteristic variation of the process, a command value is varied impulsively to caluse large variation in model error and when only the balancing point of the process is varied, there is no variation, so a characteristic variation detection part 13 computes the model error to vary the command value impulsively when there is the direct current, checking whether the model error varies greatly or not at this time. When it varies greatly, automatic tuning is carried out. When not, the automatic tuning is not carried out.

Description

[Detailed description of the invention] [Technical field to which the invention pertains] This invention provides a sample value PID that has a function of identifying process dynamic characteristics during close save control and automatically adjusting optimal control constants based on the identification results. The present invention relates to a control device, and particularly to a sample value PID control device that can detect changes in characteristics of a process during operation and automatically readjust control constants.

[Prior art and its problems]

Since the conventional sample value PID control device does not have a restart device for the auto-tuning function, the auto-tuning function must be restarted through acquisition. This resulted in the following problems.

(1) Workers must constantly monitor changes in process characteristics, so manpower cannot be omitted. Furthermore, expensive equipment such as a recorder and a television monitor is required for monitoring.

(2) If the process is operated without noticing changes in the characteristics of the process, there are problems such as deterioration of product quality, deterioration of plant efficiency, and deterioration of safety.

(3) Even if a change in the characteristics of the floss is noticed, the auto-tuning function must be restarted manually, making it impossible to adjust it quickly.

[Purpose of the invention]

In order to solve the above-mentioned problems, the present invention aims to solve the above-mentioned problems by
D. By equipping the control device with a characteristic change detection section for detecting changes in process characteristics and performing online monitoring of changes in process characteristics, it is possible to eliminate the need for monitors or expensive monitoring equipment, which were conventionally required. Furthermore, if there is a change in process characteristics, the auto-tuning function is restarted to ensure that the process is always operated at optimal control constants. In this way, it is possible to fully automate the adjustment of control constants from online monitoring of changes in process characteristics during operation, and to operate the i-plant without deteriorating product quality, plant efficiency, or safety. Our aim is to provide a sample value PID control device that can save manpower.

[Summary of the invention]

In the present invention, if the target value is changed in a pulse-like manner when the characteristics of the process change, the model error will fluctuate greatly, and even if the target value is changed in a pulse-like manner when only the equilibrium point of the process has changed. , the model error changes.

Take advantage of the fact that there is no difference and release f+-. Furthermore, it is a sampling value PID control device that restarts the automatic tuning function depending on the state at this time.

〔Effect of the invention〕

The effects of the Sambuya value Pi and D control device of the present invention will be described below.

fJ) Detection of changes in process characteristics can be automatically monitored on-line, saving manpower and eliminating the need for expensive monitoring equipment.

(2) Since changes in process characteristics are not overlooked, high product quality and plant safety can be maintained at all times.

(3) The readjustment of control constants when process characteristics change can be automated, allowing prompt response. Moreover, manpower at this time can be saved.

[Example of the present invention]

An embodiment of the present invention will be described with reference to FIG.

FIG. 1 is a block diagram showing the configuration of a sample value PID control device of the present invention.

As shown in the figure, the flow process I to be controlled forms a closed-loop four-loop system with the sample value control calculation section. − of r (tl is the target value, e (t) is the deviation, u (t) is the operation signal, Y (t
) is the process output, d(tl indicates a disturbance that changes the equilibrium point of the process. The letter t in parentheses indicates the delayed time signal, and A indicates the signal sampled at sample 24. ing.

Process 1 in operation generates a deviation signal e every sample period 4.
(4) becomes smaller, the sample value control calculation unit 5
Operation signal U (A) ([Jo(41=U
(41) is added and controlled via sample hold 2. The deviation signal e (t) is equal to the target value r (t
It is obtained by adding j and the promos output y(t).

Next, regarding the auto-tuning function that determines the control constants of the sample value control calculation section, see \Maru[Sample value PID controller J/II! It is described in detail in i'Gan Sho 55-113030. Here, the outline will be explained, and in particular, the characteristic change detection section related to the present invention will be described in detail.

First, when performing auto-tuning, the initial values of the proportional gain, integral time constant, and differential time constant (
Kco, Tio, Tdo), and also the Forgetting Factor λ of the bus transfer function generator 9,
Then, the amplitude of the identification signal from the identification signal generating section 7 is determined, and each block of the sample value PID control device is activated as shown by the dotted line in the figure.

In this way, the operation signal U. Is (') a persistent and exciting identification signal that satisfies all the identification conditions for closed-loop processes? . (A) is added and injected into the process as shown.

At this time, the input signal U (A) of the process and the sampler 8
By processing the sampled process output signal y (Al) in time series in a pulse transfer function identification unit 9 (to be described later), a Z-domain pulse transfer function is calculated, and the result is sent to a transfer function calculation unit 10 to calculate an S-domain pulse transfer function. From the 8 low-order parameters of the pulse transfer function, the sample value control constant calculation unit 11 calculates the PID.
Calculate control constants and perform sample value control calculations! Set to I55.

By performing the following processing sequentially every four sampling periods, it is possible to determine the optimum control constants that match the characteristics of the process to be controlled.

Here, as the process identification progresses, the parameters of the transfer function in the S region become constant values, so the identification end determination unit 13 determines this and stops the auto-tuning function.

The identification signal 'o ('1
By stopping the injection of the signal UO(A), only the signal UO(A) which is purely controlled is applied to the process 1.

Furthermore, Forgettin of the pulse transfer function identification section 9
Set gFactorλ to 1. (Forgctting
Factor is set within the range of 0 and λ≦1.0. λ
The larger is,′,.

(It is possible to identify a process whose characteristics change rapidly, and λ = 1.0 identifies a process whose characteristics do not change.) Therefore, there is a strong signal in process 1 during operation. Therefore, the characteristics of the process cannot be identified.

Next, a method of detecting a change in characteristics of the process 1 during operation according to the present invention will be described in detail.

'First, the present invention uses a pulse transfer function unit 9 that identifies the equilibrium point D (including tl) of process l.

A process model of the pulse transfer function identification section 9 is shown in FIG.

As shown, process model, noise model, and equilibrium point 1! - A disturbance model that changes the system is defined. Here, U (ru) is an operation signal, Z (A) is white noise, D is a DC signal, and Y (A) is a process output.

The process model shown in FIG. 2 can be identified as shown in the following equation.

Here, Yo is the equilibrium point of the process output, and Uo is the process output.

indicates the equilibrium point of the process input.

Transforming equation (1), Y (A) = θ ψ ('-1) + 6 (A)
...(3) 'jjT=' (at l ”' * 曾m, b, l ”, +T)-+CI+ ”, +Cm
, 6) ”' (41ψTTA)=(-Y(A-1
), -, -Y(mu-m), U('-1-1).

,, ,U('-/-m), g(A-1>,・
-, ε('-m), 1)...(5) The pulse transfer function Gp(Z'') of the zero process to be identified becomes the following.

The sample value PID control constant is 2 meters (1=:
1...m), gt (t=i...n). In the identification of the parameter model used in the present invention, the equilibrium point of the process can also be identified.

Next, a method for detecting characteristic changes in the process of the present invention will be explained in detail.

As mentioned above, after the process identification is completed, the parameter A (
Z), B(, Z), and D are known and can be measured by a key operator or professional who does not change the process characteristics.

Can do all calculations.

The characteristic change detection unit 13 in FIG. 1 is a block that calculates equation (7).

If there are characteristic changes in the process during operation, a DC component will occur in the model error. Also, if the process equilibrium point changes, a DC component will occur in the model error. If only the equilibrium point of the process changes, there will be no problem because the PID controller will regulate it.

Therefore, when a model error occurs, it is necessary to separate whether it is due to a change in the characteristics of the process or only a change in the equilibrium point of the process.

This separation method is shown in FIG. The figure shows the occurrence of model errors obtained by the characteristic change detection section 13 of the present invention. As can be seen from the figure, there is a difference between a case where there is only a change in the equilibrium point and a case where there is a change in process characteristics due to changing the target value in a pulsed manner when a model error occurs.

In other words, ■ When the process characteristics change, if the target value is changed in a pulsed manner, the model error will fluctuate greatly.

■ When only the equilibrium point of the process changes, there is no change in the model error even if the target value is changed in a pulse-like manner.In the present invention, by utilizing the characteristics shown in Fig. 3, the model error is first detected in the characteristic change detection section. Calculate and change the target value in a pulse-like manner if the model error is outside DC, and check whether the model error changes significantly at that time. Then, when there is a large variation, there is a change in process characteristics, so auto-tuning is performed. When there is no fluctuation, auto-tuning is not performed.

The flow of this process of the present invention is shown in the time chart of FIG. In the sump I value PID control device of the present invention, if auto-tuning is first performed manually as shown in the figure, if the characteristics of the process change during operation, the auto-tuning function can be activated immediately.

FIG. 5 shows a specific determination unit that distinguishes between a change in process characteristics and a change in only the equilibrium point of the process based on a change in model error.

The low level determining section in the figure detects the occurrence of a model error, and the high level determining section detects the occurrence of a model error when the target value is changed in a pulsed manner.

This determination section is performed by the controller 14 shown in FIG.

As will be clear from the detailed description, the 7-pull value PID control device of the present invention can automatically perform auto-tuning in response to changes in process characteristics. The functionality of the PID controller can be greatly improved.

[Other Embodiments of the Invention] In the present invention, the target value is changed in a pulse-like manner when there is a model error, but as shown in FIG. Even if you add a pulse signal to (')),
Effects similar to those of the present invention can be obtained.

[Brief explanation of drawings]

FIG. 1 is a four-dimensional diagram showing the configuration of the sample value PID control device of the present invention, and FIG. 2 is an explanatory diagram of a process model for parameter identification used in the sample value PID control device of the present invention.
FIG. 3 is an explanatory diagram of characteristic change detection in the process of the present invention, FIG. 4 is a time chart of the Zump v value PID control device of the present invention, and FIG. 5 is a circuit diagram of characteristic change determination of the present invention.
FIG. 6 is another embodiment of the present invention. 1...Process, 2...Sample hold, 5...
Sample value control calculation unit, 7...Identification signal generation unit, 9...Pulse transfer function identification unit, 10...Transfer function calculation unit, 11...Sample value control constant calculation unit, 12...Identification end Judgment unit, 13...Characteristic change detection unit, 14...Control unit. Agent: Patent Attorney Noriyuki Chika (and 1 other person) 2nd
Figure 3 Figure 4 Figure 5

Claims (2)

[Claims] (1) In a device having a sample value PID control calculation unit that controls the sample V value of the process to be controlled,
In the control loop controlled by the sample l value PID control calculation section, there is an identification signal generation section that applies an identification signal consisting of a systematic exciting signal, and an identification signal generation section that applies an identification signal consisting of a systematic exciting signal. The sample value PID
Input the operation signal obtained by adding it to the output signal of the control calculation unit and the process signal obtained by sampling the control amount of the process, and identify the parameters of the process from these operation signals and process signals. The region of the 2-plus operator S is calculated from the result of Laplace transform of the response obtained by connecting the step response of the pulse transfer function identification part of the process obtained by the pulse transfer function identification part and this process's process's transfer function identification part with a straight line. a transfer function calculation unit that calculates a transfer function of the transfer function calculation unit; a sample value control constant calculation unit that calculates a control constant of the sample value PID control calculation unit from the calculation/result of the transfer function calculation unit; an identification end determination section that determines the end of identification from the results; and a characteristic change detection section that calculates a model error of the process from the parameters of the pulse transfer function identification section after the end of the identification, and the operation signal and process signal of the process after the end of the identification. and determines that a model Fl/error has occurred in the calculation result of this characteristic change detection section,
a controller Fl/unit that generates a deviation signal that is an input signal of the sample value PID control calculation unit when there is a model error and adds a pulse-like signal to the addition point of the target value signal and the process signal; Depending on whether or not there is a change in the model error of the characteristic change detection section, a function is activated to adjust the control constant when there is a change, and when there is no change, the sample value PID control is performed using the same control constant. sampled value PID controller. (2) 4! The pulse signal is configured to be added to the output signal of the sample value PID control calculation section. A sample value PIT) control device according to claim 1.