JPH044602B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device that automatically determines whether control operation has become unstable in a closed loop control system that performs feedback control on a process.

In process feedback control equipment,
Adaptive control is known that achieves good control by adapting the control parameters of a controller to the characteristics of a process. As one such adaptive control, for example, in feedback control of a process that had been operating stably until then, when the control operation becomes unstable due to a change in the characteristics of the process and hunting occurs, the hunting is detected. , thereby changing the control parameters of the controller to a weaker one,
Although it is conceivable to return to a stable control operation again, the present invention relates to hunting detection means for control operation that can be used for the above-mentioned applications.

Now, this kind of control operation instability determination device,
In other words, hunting detection devices may be thought of as color-based in principle, but no specific means is known yet.

Therefore, the present invention has been made to meet the above-mentioned technical needs, and an object of the present invention is to provide a process control instability determination device that can be applied to the above-mentioned adaptive control. It's about doing.

The principle of the present invention is briefly as follows. In other words, in process feedback control, the process variable oscillates over time and the oscillation decays slowly, and the manipulated variable also oscillates and decays slowly; It is based on the principle that if the period and the vibration period of the manipulated variable are approximately equal, it is determined that hunting has occurred. Unless the above three conditions are met, for example, just because a process variable oscillates, it is not determined to be hunting because it may be due to noise. Note that slow damping means that the amplitude of each half period of vibration is
When a _i-1 , a _i , a _i+1 , the value of the ratio is a _i /a _i-1 , a _i+1 /a _i or a _i+1 −a _i /a _i a _i-1 is not too small.

Therefore, the main points of the configuration of the present invention include a first means for measuring a process variable and detecting a predetermined number of extreme points in the vibration, and a first means for measuring a manipulated variable from a control section for the process and detecting a predetermined number of extreme points in the vibration. a second means, and a detection time and value of the extreme point detected by the first means and a detection time and value of the extreme point detected by the second means to determine the vibration period of the process variable and the vibration of the manipulated variable. A third means for determining whether or not the deviation from the period is within a predetermined limit; and a third means for determining whether or not the deviation from the period is within a predetermined limit; a fourth means for determining whether the damping rate obtained as the ratio value or the ratio value of the difference in vibration amplitude is larger than a predetermined damping rate; and a pole point similarly detected by the second means. A step of determining whether or not the damping rate obtained as the value of the ratio of the vibration amplitudes for each half period of the manipulated variable or the value of the ratio of the differences in the vibration amplitudes is larger than a predetermined damping rate using the detected value. 5 means,
The present invention is characterized in that when it is determined in each of the third to fifth means that the control operation has become unstable, it is determined that the control operation has become unstable.

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an example of the use of the destabilization determining device according to the present invention. In the figure, 1 is a process, 2 is an adjustment section, 3 is an instability determination means (hunting detection means), 4 is a control parameter adjustment section, and 5 is a determination parameter setting section.

In FIG. 1, a control unit 2 detects a process variable X from a process 1, and accordingly sends a control output (manipulated variable Y) to the process 1, thereby performing so-called feedback control. The destabilization determining means 3 monitors the process variable X and the manipulated variable Y, and when it determines that hunting has occurred in the control system consisting of the process 1 and the adjustment section 2,
The determination result V is sent to the control parameter adjustment section 4. In the adjustment section 4, assuming that the adjustment section 2 is performing PID control, for example, a command W for changing the control parameters (proportional gain, integral time constant, differential time constant) is sent to the adjustment section 2 to change the control parameters. change so that hunting does not occur. Note that the determination parameter setting section 5 is for setting various parameters U necessary for the destabilization determination means 3 to detect hunting.

As mentioned above, the destabilization determining device according to the present invention can be used as the destabilization determining means (hunting detecting means) 3 described above.

Next, the operating principle of the present invention will be specifically explained with reference to FIG.

FIG. 2A is a graph showing an example of a temporal change in the process variable X, and FIG. 2B is a graph showing an example of a temporal change in the manipulated variable Y at the same time.

The values X ₁ , X ₂ , X ₃ and the times of occurrence t _X1 , t _X2 , _t Assume that the values of the extreme points Y ₁ , Y ₂ , Y ₃ and the times of occurrence t _Y1 , t _Y2 , t _Y3 have been found.

At this time, compare _the period _{of the X} waveform ( _t Determine whether or not. That is, it is determined whether the following equation is satisfied.

_{| ( t _ _} That is, it is determined whether the following equation is satisfied.

|X ₃ −X ₂ |>α・|X ₂ −X ₁ | Similarly, it is determined whether the attenuation rate of the amplitude of the waveform Y is larger than a certain predetermined attenuation rate α. That is, it is determined whether the following equation is satisfied.

|Y ₃ −Y ₂ |>α・|Y ₂ −Y ₁ | When the above three conditions are satisfied, in the present invention, it is determined that the control operation has become unstable, that is, hunting has occurred.

From the above, in the present invention, temporal changes in the process variable X and the manipulated variable Y are monitored,
It will be understood that it is essential to accurately detect at least three extreme points for each, and to perform predetermined calculations on the values and times of the detected extreme points.

FIG. 3 is a block diagram showing one embodiment of the present invention. In the same figure, the block S surrounded by a broken line
is the destabilization determination means 3 in FIG.
DX ₁ is a detection _unit for _the first extreme point in the _process variable send. Similarly, DX ₂ is a detection unit for the second pole (for example, X ₂ in Figure 2 A), and DX ₃ is a detection unit for the third pole (for example, X ₃ in Figure 2 A), and the respective detected values are is sent to the discrimination calculation section E.

DY ₁ , DY ₂ , and DY ₃ are the first, second, and third poles of the manipulated variable Y (in Figure 2 B), respectively.
Y ₁ , Y ₂ , Y ₃ ), and each detection value (Y ₁ and
t _Y1 , Y ₂ and t _Y2 , Y ₃ and t _Y3 ) are sent to the discrimination calculation section E.
The discrimination calculation unit E includes pole detection units DX ₁ to DX ₃ and DY ₁ to
A predetermined calculation is performed on the detection value of each pole given from DY ₃ , and a determination result V of the presence or absence of hunting is thereby output. The determination calculation unit E is set by the setting unit 5 with a determination parameter U necessary for performing a predetermined calculation to determine the presence or absence of hunting. Note that some of the parameters U' are also necessary for detecting the extreme points, so they are further transmitted from the discrimination calculation unit E to the extreme point detection units DX ₁ to DX ₃ , DY ₁ to
Sent to DY ₃ . R is a reset signal.

Whether it is process variable X or manipulated variable Y,
The actual waveform is not a clean waveform as shown in Figure 2, but a waveform with superimposed noise, so a place that is not even a pole may be mistakenly detected as a pole.To avoid this, the detection method This requires special efforts, which will be discussed later.

Next, the above-mentioned discrimination parameter U will be explained.

Once the process to be controlled is determined, the oscillation period T _h of the process variable X (or manipulated variable Y) when hunting occurs can be roughly predicted, so this oscillation period T _h is predicted and determined as one parameter. The types of parameter U are listed below.

T ₁ ... Time width of pole search T ₂ ... Time width T _h when determining that there is no oscillation and stopping further pole search ... Assumed vibration period DX ... If X is vibrating Minimum amplitude to judge (If the amplitude of (If it is smaller, it is considered to be due to noise and is not considered as vibration) ε ₁ ...Tolerance of deviation between each vibration period of X and Y ε ₂ ...Tolerance error between actual vibration period and expected period α... ...Minimum attenuation rate of amplitude to be determined as unstable (determined to be unstable if the attenuation rate of amplitude is equal to or greater than α) Among these, T ₁ and T ₂ are also used as U′.
If the prediction accuracy of T _h is poor, the tolerance ε ₂ is increased or its use is discontinued. It is preferable to set T ₁ to approximately 1/4 of the assumed vibration period T _h and T ₂ to approximately 1/2 of T _h . These T ₁ , T ₂ , T _h , DX,
An example of DY is shown in Figure 2.

Next, the polar point detection operation and subsequent discrimination operation will be explained with reference to FIGS. 2 and 3.

When the pole detection unit DX ₁ starts the pole point determination operation, it examines the change in the process variable X within the time span of T ₁ as a unit, and
At a certain point within _the time span _T1 , the value of the variable When not updated, the time point is t _X1 and the variable X at that time
The amplitude of this is set as X ₁ , and these values are sent to the discrimination calculation unit E and stored as representing the first extreme point.

From the time when the detection of the first pole point is completed (t ₁ in the graph of FIG. 2A), the second pole point is searched for in the same manner as described above.

If the second pole is not detected even after the time interval _T2 has elapsed after the detection of the first pole is completed, it is assumed that the process variable X is not oscillating;
Make a determination and return to the above.

When the second extreme point is detected by the extreme point detection section DX ₂ , its value and time (X ₂ and t _X2 in FIG. 2) are sent to the discrimination calculation section E and stored.

The time when detection of the second pole ended (in Figure 2)
t ₂ ), the third pole (X ₃ ,
If you cannot find it even after searching for _tX3 ), return to .

In this way, if the first pole is the top of a mountain, then the three poles are (mountain, valley, mountain), and if the first pole is the bottom of a valley, then the three poles are (valley, mountain, valley). Seek.

When the three extreme points are determined in this way, the discriminator E compares the values of adjacent extreme points, and if the difference is not more than a predetermined difference, the first extreme point is discarded and the second and third extreme points are discarded. Each pole is moved to the first and second poles, and the third pole is newly found. For example, |X ₁ −X ₂ |DX or |X ₂ −X ₃ |DX
...If (1) holds true, the discriminant calculation unit E proceeds to the next discriminant calculation, but if the above (1) does not hold, the three obtained extreme points [X ₁ , X ₂ , X ₃ ] are X ₂ , X ₃ , *] to find the third pole *.

For the manipulated variable Y, find the three extreme points in exactly the same way |Y ₁ −Y ₂ |DY or |Y ₂ −Y ₃ |DY
...Determine (2), and if it does not hold, discard the first pole, move the second and third poles to the first and second poles, and find the third pole anew.

When three extreme points are detected for both the process variable X and the manipulated variable Y, they are used to examine whether the following discriminant holds true.

_{｜ t X3 −t _ _ _ _ _ _ _} |>α·|Y ₂ −Y ₁ | (5) When all the above discriminants are satisfied, it is determined that hunting is occurring, and the discriminator E outputs the determination result V. However, if any one of the above three discriminants does not hold, the next extreme point is searched in the same way as in .

If no pole point is detected during the above search operation, the process returns to the above process.

In addition to the above discrimination conditions (3), (4), and (5), if the period T _h of unstable vibration is given with high precision for some reason, |t _X3 −t _X1 /T _h −1 |ε ₂ ...(6) |t _Y3 −t _Y1 /T _h −1|ε ₂ ...(7) The reliability of the discrimination can also be improved by further adding the following conditions.

The method for determining T ₁ and T ₂ was explained earlier, but
The following may be determined in relation to the accuracy of the predicted vibration period T _h . T ₁ is set to be larger than the period of the noise and smaller than T _h /4, and if the accuracy of T _h is high, it is set as close to T _h /4 as possible. T ₂ is made larger than T _h /2, and if T _h has high accuracy, it is made as close to T _h /2 as possible.

Next, we will discuss the role of the time width T ₁ of the pole search in the fourth section.
This will be explained with reference to the figures.

FIG. 4 is a graph showing temporal changes in the process variable X, and it is assumed that noise causes a peak M that is confusing to be a pole. However, by appropriately determining the time width T ₁ of the pole search, this M point will not be mistaken as a pole. In this case, since the maximum value of the process variable X has been updated at the time when point N has passed within the time span _T1 , point M is not determined to be the extreme point.

Figure 5 is _a graph showing temporal changes in process _variable For example, since it is determined that _the ^process variable As a result, the second pole searching operation does not continue indefinitely, and the quick response of the unstable vibration discrimination operation is guaranteed.

Figures 6 to 10 each show the process variable
and graphs showing examples of temporal changes in the manipulated variable Y. How to determine the minimum attenuation rate α, which is one of the discrimination parameters, will be explained with reference to these graphs.

Generally, the response of process variable X and manipulated variable Y is
It is said that the ideal situation would be as shown in FIG. 6, in which case the damping ratio a ₂ /a ₁ would be about 0.25, and such vibration damping is called 25% damping. When the damping factor is smaller than this value of 0.25, the vibration becomes stable, and when it becomes very small, it is said to be overdamped, and the control action lacks quick response. Conversely, when the damping factor is greater than 0.25, the vibration becomes unstable. When the vibration oscillates as shown in FIG. 7, the damping factor is larger than 1.0, and when the damping is poor as shown in FIG. 8, the damping factor is close to 1.0.

Taking this into account, the minimum attenuation rate α should be set to a value slightly smaller than 1.0 (for example, 0.8).
0.7) is appropriate, and if you want to avoid vibration to the extreme, you can set it to a smaller value.

In an actual control system, the vibration of the manipulated variable Y may lag or advance with respect to the vibration of the process variable In some cases, the relationships are as shown in FIGS. 9 and 10. In other words, Fig. 9 is a graph when the vibration phases of process variable X and manipulated variable Y are out of phase by 180 degrees, and Fig. 10 is a graph when the phase relationship is unclear. However, it is needless to explain that hunting can be detected by the present invention. This point is also an advantage of the present invention.

According to the destabilization determining device of the present invention, the determining conditions are simple and the program capacity required therefor is also small, so that it can be implemented in a small-capacity digital control system at the microcomputer level. In addition, since it is determined based on the vibration status of both the process variable and the manipulated variable, it can be determined within a short period of time, within two cycles of vibration (more specifically, the 1.5 cycles required to find the three extreme points), and stably (malfunctions due to noise). This has the advantage of being able to identify hunting without having to

If the destabilization determination device according to the present invention is incorporated into a process feedback control device, the control operation can be strengthened to the maximum extent possible to the point just before hunting occurs, and responsiveness can be improved. This is because even if hunting occurs due to a slight change in process characteristics, it can be quickly detected and the control parameters of the controller can be changed to prevent hunting.

In the application example shown in FIG. 1, the control parameter adjustment section 4 is configured to output a command to change the control operation to the adjustment section 2. The present invention can be similarly utilized as a configuration in which this function is strengthened to provide a function to provide setting values to be changed for the control parameters used in the adjustment section 2. In that case, the adjustment section 2 can be replaced with a simple one. It becomes possible to do this.

Furthermore, the present invention can be applied to many types of feedback control systems in addition to the commonly employed PID feedback control system.

[Brief explanation of drawings]

Figure 1 is a block diagram showing an example of the use of the destabilization determination device according to the present invention, and Figure 2A is a diagram showing a process variable X.
Figure 2B is a graph showing an example of a temporal change in the manipulated variable Y.
Fig. 3 is a block diagram showing an embodiment of the present invention, Fig. ₄ is a graph of _the process variable 6 to 10 are graphs showing examples of vibrations of the process variable X and the manipulated variable Y, respectively. Explanation of symbols, 1...Process, 2...Adjustment section, 3
... Unstable determination means, 4... Control parameter adjustment section, 5... Parameter setting section for discrimination, X... Process variable, Y... Manipulated variable, U... Parameter for discrimination, V... Discrimination result, W... Control parameter change command, DX ₁ to DX ₃ ... Extreme point detection unit for process variable X, DY ₁ to DY ₃ ... Extreme point detection unit for manipulated variable Y, E... Discrimination calculation unit.

Claims (1)

[Scope of Claims] 1. A device for determining that a control operation in process feedback control has become unstable, comprising: a first means for measuring a process variable and detecting a predetermined number of extreme points in the vibration; a second means for measuring the manipulated variable from the adjustment section and detecting a predetermined number of extreme points in the vibration; a detection time and value of the extreme point detected by the first means; and the extreme point detected by the second means. a third means for determining whether or not the deviation between the vibration period of the process variable and the vibration period of the manipulated variable is within a predetermined limit using the detection time and value of; Using the detected value of the pole point, it is determined whether the damping rate obtained as the value of the ratio of the vibration amplitude for each half cycle of the process variable or the value of the ratio of the difference in the vibration amplitude is larger than a predetermined damping rate. Using the fourth means for detecting the vibration amplitude and the detected value of the pole point similarly detected by the second means, it is determined as a value of the ratio of the vibration amplitude for each half cycle of the manipulated variable or a value of the ratio of the difference in the vibration amplitude. and fifth means for determining whether or not the attenuation rate is greater than a predetermined attenuation rate, and when each of the third to fifth means determines that the attenuation rate is present, the control operation is performed. An instability determination device for process control, characterized in that it determines whether instability has occurred.