JPH0484201A - Automatic tuning controller - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field This invention relates to a controller used in process control, in particular,
This invention relates to an auto-tuning controller that automatically adjusts its control parameters (PID constants).

(B) Conventional technology Conventionally, as a method for automatically adjusting control parameters, there are two methods: - Determination using the Ziegler-Nichols formula from the constants of the plant's pulse response and individual response.

■The so-called limit sensitivity method uses proportional control to generate a limit vibration that does not dampen, and determines its vibration period by applying the Ziegler-Nichols formula.

■A method of applying identification signals to the plant, statistically processing the responses obtained, estimating parameters, and determining appropriate parameters.

■The so-called limit cycle method, which determines by inserting nonlinear elements into the control system and generating vibrations.

etc.

(c) Problems to be Solved by the Invention In the conventional method (2) described above, when adjusting parameters, it is necessary to open the control system once, resulting in an uncontrolled state, and addition of step and pulse inputs causes disturbances. and disturbs the system. Method (2) generates limit vibrations during parameter adjustment, which disturbs the control system, and limit vibrations are on the verge of divergence of the plant response, which is unfavorable from a safety standpoint. In the method (2), it is advantageous to apply a large-amplitude identification signal for a long time in order to accurately identify the plant for parameter determination, but there is a contradiction in that this causes a large disturbance. Method (2) has the same problems as method (2).

This invention was made by focusing on each of the above-mentioned problems, and it is possible to stably adjust the plant in a normal control state without putting the plant in an uncontrolled state or giving any unnecessary disturbance to the plant. The purpose is to provide an auto-tuning controller.

(d) Means and operation for solving the problems The auto-tuning controller of the present invention includes means for measuring the controlled output, means for calculating the amplitude attenuation rate of the controlled output, and means for calculating the overshoot amount. , a means for calculating an update coefficient for updating a control parameter from the calculated amplitude attenuation rate and an overshoot amount, and a means for updating the parameter with the calculated update coefficient, and while executing PI or PID control, It is comprised of an adjusting means that repeats amplitude attenuation rate calculation, excess amount calculation, update coefficient calculation, and parameter update until the update coefficient reaches a predetermined value.

The autotuning controller of this invention measures the response of the plant while executing PI or PID control without bringing the plant into a non-controlled state, and calculates the amplitude attenuation rate of vibrations caused by various disturbances that occur during control. , calculates the amount of overshoot, calculates a parameter update coefficient from the amplitude attenuation rate and the amount of overshoot, and updates the control parameters (proportional band and integral time) using the update coefficient. By repeating the above procedure until the update coefficient becomes 1, control parameters that obtain the desired plant response are determined. Response measurement is stopped if the peak of vibration does not occur for a certain period of time or longer. Furthermore, if it is predicted that the amplitude attenuation rate will be 1 or more during response measurement, auto-tuning is immediately stopped and the control parameters are updated to predetermined safe values.

The target of controlled variable measurement is the vibration that occurs due to various disturbances in normal control conditions, and it is possible to apply signals to identify the plant and calculate control parameters to cause unnecessary disturbances to the plant. do not have.

Tuning is always performed under control, so the plant remains stable. Response measurement is aborted if a peak does not occur within a certain period of time, so it does not take an unnecessarily long time. If the response of the plant should diverge during tuning, auto-tuning will be immediately stopped as soon as the amplitude attenuation rate is predicted to be 1 or more, and the control parameters will be changed to safe values, ensuring plant safety. Maintains sexuality.

(E) Examples The present invention will be explained in more detail with reference to Examples below.

FIG. 1 is a schematic diagram showing the configuration of an auto-tuning controller according to an embodiment of the present invention. This auto-tuning controller 1 consists of a proportional calculation (P) section 2, an integral calculation (1) section 3, a differential calculation (D) section 4, and an auto-tuning algorithm (control) section 5.
, the integral calculation unit 3 and the differential calculation unit 4 measure the response of the plant 6 while executing PID control, and calculate the process amount (PV).
, control parameters (proportional band P, integral time TI) are automatically adjusted based on the deviation (y) found from the set value (SV).

In FIG. 2, the closed loop response of the plant (the waveform of the deviation of the controlled variable), the amplitude attenuation rate a, and the overshoot amount are defined. That is, the amplitude attenuation rate a is: ygo -yt 'lr Vz The amount of overshoot is b"" Yz / 'I l ,
When the maximum waiting time is T, T+', Tt, and Ts are T
within

yl, y2, and y3 each indicate the y value of the first to third peaks, and have positive and negative signs. yo is a positive value of y that provides the conditions for starting the auto-tuning process, and y
When the absolute value of exceeds yo, auto-tuning processing is started. However, the time TI from the start of auto-tuning to the first peak, or the time Tz between each peak,
When T3, . . . is larger than the preset maximum waiting time T (that is, when no peak is detected), the values of a and b are separately defined as shown in the flowchart described later.

Next, the operation of the embodiment auto-tuning controller will be explained with reference to flowcharts shown in FIGS. 3(A) and 3(B).

First, for a preset yo, lyl>y.

It is determined whether or not [step ST (referred to as ST]■)].

When yl>yo, it is assumed that the control condition is not good and processing is started. Measure the response while continuing PID control,
Find the peak value. That is, it is determined whether or not there is a peak within time T (ST2). If a peak cannot be detected within a certain time, a and b are set as specified values (ST3). ST
2, if there is a peak value within time T, this peak value y1
is stored as the first peak value (ST4). Then, it is further determined whether there is a peak within T time 5T5)
, if there is no peak value, set a and b to the specified values 5T6)
, if there is a peak value, this peak value y2 is stored as the second peak value.

)'+'lz At the start of control, this determination is NO, and then it is determined whether or not there is a peak within time T (5T9), NO.

If so, set the current value of y to y, and if there is a peak, store the peak value ys as the third peak value (STI
I). Furthermore, if there is no peak value, the current value y is set as the third peak value y (STIO).

And these peaky direct('/I% Yz,)'s
), calculate a and b from
5T19) Then, it is necessary to judge whether kl=kz=1 or not.5T
20), if No, update P and TI by setting the values obtained by multiplying the control parameters P (proportional gain) and TI (integral constant) by , k as new parameter values (S
T21). Thereafter, the process from response measurement to parameter update is repeatedly executed. Then, when calculating the update coefficient, k2, when k,=2=1, the repetition is stopped, parameter updating is stopped, and auto-tuning is completed. Even after completion, if lyl>yO, tuning is started again. During response measurement, when the value of (y-y2)/(yl-y2) becomes 1 for the current value y, the judgment in ST8 becomes YES, and it is determined that a is greater than or equal to 1. Cancel auto-tuning and change the control parameters to preset safe values (S
T22).

As a result, even if tuning is not performed properly and the response of the plant tends to diverge, danger can be avoided.

Note that although PID control is used in the above embodiment, this may be replaced with PI control.

Furthermore, the maximum waiting time T in the above embodiment merely defines the time limit of response measurement, and does not make the time between peaks, that is, the vibration period itself, a necessary condition for tuning.

In addition, there are also inequalities that indicate the range of cases for a and b, and +
, kz may be different from those in the above embodiment depending on the system to which it is applied.

Furthermore, stopping auto-tuning and setting parameters to safe values when an amplitude attenuation rate of 1 or more is predicted is a safety function in case of an emergency, and is not a necessary condition for tuning.

(F) Effects of the Invention According to the present invention, tuning can be performed stably in a normal control state without causing unnecessary disturbance to the plant, compared to conventional methods.

In the embodiment, if a peak is not detected for a certain period of time or more, the response measurement is aborted and the process moves on to calculating the update coefficient, so that an unnecessarily long time is not required. Furthermore, if the plant tends to diverge during response measurement, the control parameters are immediately changed to safe values, so safety is ensured.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an autotuning controller according to an embodiment of the present invention, FIG. 2 is a diagram showing the closed loop response of the plant, FIG. 3 (A), FIG. 3 (B)
FIG. 2 is a flowchart for explaining the operation of the auto-tuning controller according to the embodiment. 2: Proportional calculation section, 3: Integral calculation section, 4: Differential calculation section, 5: Auto-tuning algorithm section.

Claims (1)

[Claims] (1) In a controller that performs PI or PID control, a means for measuring the controlled output, a means for calculating the amplitude attenuation rate of the controlled output, a means for calculating the overshoot amount, and the calculated amplitude attenuation rate. It has a means for calculating an update coefficient for updating the control parameter from the overshoot amount and a means for updating the parameter with the calculated update coefficient, and while executing PI or PID control, until the update coefficient reaches a predetermined value. Amplitude attenuation rate calculation, excess amount calculation, update coefficient calculation,
An auto-tuning controller characterized by having an adjustment means that repeatedly updates parameters.