JPH04138501A - auto 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 The second 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 (PrD constants).

(b) Conventional technology Conventionally, there is a method for automatically adjusting control parameters. ■ A method in which the control parameters are uniquely determined using the Siegler-Nichols formula from the constants of the plant's pulse response and initial response.

■A method of applying an identification signal to the plant, statistically processing the response obtained, estimating the parameters, and determining the parameters to be passed.

■Normal control status 1! The so-called expert method measures the response caused by disturbances entering the control system in a closed loop (closed loop) and updates parameters based on empirical rules from the results.

and so on.

(c) Problems to be Solved by the Invention The conventional method (2) described above is superior to other methods in that it is a stable closed-loop system and does not introduce unnecessary disturbances to the system. There is a problem like this. That is, as a rule of thumb, the parameters of P and I are often first determined from the response waveform, and then the value of D is uniquely determined from the value of I. However, the D operation is easily affected by measurement noise of process quantities, and depending on the plant characteristics and measurement conditions, the response may become too oscillatory with the D operation based on the uniquely determined D parameter.

The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide an auto-tuning controller that is less susceptible to the influence of noise and whose response does not become too vibratory in the D operation.

(d) Means and operation for solving the problems The auto-tuning controller of the present invention has means for setting control parameters of P■D with a dial, means for measuring the response of the controlled output, and means for measuring the response of the output to be measured. Means for updating the control parameters of P and ■ by using P and I set by the dial as initial values based on the response of the control output, means for calculating the parameter of D from the updated parameter of ■, and means for calculating the parameter of D from the updated parameter of ■. It has a means for limiting the parameter of D calculated so that the ratio of the value of and the value of
The apparatus includes an automatic adjustment means that repeatedly updates control parameters while executing ID control until the response of the controlled output becomes a desired response.

In this autotuning controller, when the waveform of the controlled output is observed due to disturbance or the like during normal PID control, the P and r parameters are updated based on empirical rules. Updated ■
The parameters of D are calculated from the parameters of . The calculated parameter of D is a value limited by the ratio of the value of ■ and D set in advance with a dial. The above procedure is repeated until the waveform of the controlled output becomes the desired waveform.

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

FIG. 1 is a block diagram showing the configuration of an autotuning 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 (J) section 3, a differential calculation (D) section 4, and an auto-tuning algorithm (control) section 5.
Integral calculation unit 3 and differential calculation unit 4 perform PID! While executing I+ control, measure the response of plant 6 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 ! ＋! The amount of z overshoot is b=yz/y+, and the maximum waiting time is T, and T1, Tz, and T3 are within T.

)'l % Vt -, )'3 are - respectively 1st to 3rd
Indicates the peak y value, with positive and negative signs 11-)'0
is a positive value of y that provides a condition for starting the auto-tuning process, and when the absolute value of y exceeds yo, the auto-tuning process is started. However, if the time TI from the start of autotuning to the first peak or the time T z , T 3 between each peak is longer than the preset maximum waiting time T (i.e., if no peak is detected), the flowchart described below The values of a and b are separately defined as shown in .

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

First, for a preset yo, lyl>y.

Determine whether or not [Step ST (referred to as ST) 1) y
When l>yo, it is assumed that the control condition is not good and processing is started. The PMDI 11 control continues to measure the response and 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). S
At T2, if there is a peak value within time T, this peak value y
1 is stored as the first peak value (Sr4). and,
Furthermore, it is necessary to determine whether or not there is a peak within T time 5T5
), if there is a peak value, this peak value y2 is stored as the second peak value; if there is no peak value, the current value of y is stored as y
2 and y3 (Sr6).

Next, during the period of waiting for the third sluggishness, it is determined whether "jz = 1" (Sr1). During the response measurement up to the third "j I Fg peak, the current it!" For y (
When the value of y7z)/(y+)'z) became 1, the judgment of Sr1 became YES, and it was judged that a became 1 or more, so the auto-tuning was immediately stopped and the control parameters were set in advance. Change to safe value (S
r22). As a result, even if tuning is not performed properly and the response of the plant tends to diverge, danger can be avoided.

At the start of control, the determination of Sr1 is No, and then it is determined whether there is a peak within time T (5T9), and if there is a peak, the peak value y is memorized as the third peak value (5T9).
11) If there is no peak value, the current value y is set as the third peak value y3 (STIO). Then, calculate a and b from these peak values (Vr, Vz, y3)5T12
), a, b, calculate the update coefficient +, kg according to the range of values (ST13 to 5T19) and kt”kg−1
5T20), and if No, the control parameters P (proportional gain) and TI (integral constant) are multiplied by + and kg, respectively, as new parameter values P,
The TI is updated (Sr21).

Next, TD is calculated from the updated TI using the formula TD-TI/4 (Sr22). Furthermore, if this TD exceeds the upper limit of the following formula, replace it with that upper limit (Sr22
), that is, control (Sr23).

TD upper limit value - (D dial value/■ dial value) ×
(TI after update) Thereafter, parameter updates and calculations are repeatedly executed from the controller side. Then, when calculating the update coefficient kr, kg, kt
-kg-1, the repetition is stopped, parameter updating and calculation are stopped, and auto-tuning is completed. If 'I i >3' o even after completion, tuning is started again. Here, the PID dial is set to a continuous value when the auto-tuning is not used or a safe value that does not cause the plant response to become oscillatory.

Note that in the above embodiment, the parameters of P and I are updated according to an empirical rule, but this empirical rule is not limited to that of the embodiment.

In the example, TD is calculated as 1/4 of TI, but 1/4
Any other suitable value may be used.

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, the specified values of a and b to be set when there is no peak within time T, the inequalities showing the range of cases for a and b, and +
, kg may be different from 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 this invention, the D parameter after auto-tuning is limited by the ratio of the dial ■ and D set in advance. This prevents the plant response from becoming oscillatory. In addition, instead of setting a new limit value for the parameter D, the limit is calculated by calculating the ratio from the conventional operational value or the value determined by the dial as a safety value, so there is no need for extra effort. Furthermore, D is not limited by a fixed value, but by the ratio of ■ and D, so when the values of P and ■ change as a result of auto-tuning, D
The limit value itself also constantly changes to an appropriate value.

[Brief explanation of the drawing]

FIG. 1 shows an auto-tuning mt! according to an embodiment of the present invention. Fig. 2 is a block diagram showing the configuration of the f-meter, Fig. 2 is a diagram showing the closed loop response of the plant, Fig. 3 (A), Fig. 3 (
B) and FIG. 3(C) are flowcharts for explaining the operation of the auto-tuning controller of the embodiment. 2: Proportional operation section, 3: Integral operation section, 4: Differential operation section, 5: Auto-tuning algorithm section. Patent applicant: Shimadzu Corporation Agent
Patent Attorney Shigeru Nakamura Figure (A) Figure (B)

Claims (1)

[Claims] (1) A controller that performs PID control has a means for setting PID control parameters using a dial, a means for measuring the response of the controlled output, and a means for setting the PID control parameters using the dial based on the measured response of the controlled output. means for updating the control parameters of P and I with and I as initial values; means for calculating the parameter of D from the updated parameter of I; It has means for limiting the parameter of D calculated so that it is less than or equal to the ratio of the set value of D and the value of I, and the updated P
An auto-tuning controller characterized by having an automatic adjustment means that repeatedly updates control parameters while executing PID control using ID parameters until a response of a controlled output becomes a desired response.