JPH0766281B2 - Self-tuning controller - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a self-tuning controller that automatically adjusts at least a proportional (P) constant and an integral (I) constant to optimal values, and more specifically, The present invention relates to a self-tuning controller that observes a waveform of a process amount or a deviation signal between a process amount and a set value, and calculates P and I constants based on the waveform observation result.

(Prior art) In the process PI controller used for feedback control, the PI calculation constant is currently set manually based on the long-term knowledge and experience of the process driver or instrumentation engineer. is there. However, the manual setting causes temporary or steady process disturbances during process startup, load fluctuations, unexpected disturbances, or systems with nonlinear gain characteristics. In some circumstances, it may have caused economic losses.

Therefore, a controller in which the PI calculation constant is self-tuned has been proposed. The self-tuning controllers proposed so far connect the auxiliary controller in parallel to the main controller, increase the gain of the auxiliary controller, cause vibration, and from its amplitude and frequency,
What determines the PI constant based on the so-called ZN limit sensitivity method by Ziegler and Nichols (Proceedings of the Society of Instrument and Control Engineers Vol. Toshiyuki Kitamori), using an on / off generator to generate a limit cycle, and determining the optimum PI calculation constant from its amplitude etc. (Showa 48th 12th Academic Lecture Meeting of the Society of Instrument and Control Engineers) Collection P617 to P624 PID automatic setting type adaptive controller Sumi, Fukuda) etc.

In addition, recently, without making the process into an oscillating state or giving an identification signal, the waveform of the deviation signal between the process amount or the process amount and the set value is observed, and P, P is calculated based on the observation result.
A self-tuning controller that calculates the I constant has also been proposed.

(Problems to be Solved by the Invention) FIG. 4 shows an operation example of a conventional self-tuning controller for observing a waveform of a process amount or a deviation signal between a process amount and a set value and calculating P and I constants. It is a waveform diagram shown.

Now, as shown in (a), a step-like disturbance to the process
When NS is added, the process amount PV is, as shown in (b),
Although it fluctuates at first, it will eventually settle to a steady value due to the self-tuning operation.

Here, when the disturbance NS gradually changes with time as shown in A part of (a), the process amount PV continues to change, and self-tuning is performed to increase the gain, for example, in order to suppress this change. And eventually settles down to a steady value. With self tuning in this way,
When the disturbance NS fluctuates again as shown in part B of (a),
Since the gain has been raised, the process amount will fluctuate unstablely (become an oscillation state) as indicated by C in (b), and there is a possibility that the process amount can be controlled in a dangerous direction. is there. Such a state also occurs when the process characteristics change.

The present invention has been made in view of such problems in the self-tuning controller, and an object thereof is to provide a dangerous direction (for example, a direction in which an oscillation occurs) even when there is a change in process characteristics or disturbance. It is intended to realize a controller that does not perform self-tuning.

(Means for Solving Problems) FIG. 1 is a basic functional block diagram of the self-tuning controller of the present invention. In the figure, 1 is a process, 2
Is the deviation ε between the process amount PV from process 1 and the set value ES
Is input to the process 1, and the manipulated variable MV is output to the process 1, and the PI control means 3 inputs the process amount PV or the deviation signal ε between the process amount and the set value, and its waveform Waveform observing means for observing at a predetermined period, 4 is a memory means for storing the waveform observation result by the waveform observing means 3, and 5 is at least a proportional constant and an integral constant are calculated based on the waveform observing result, and these proportional constant and integral are calculated. Constant
Parameter calculation means to be set in the PI control means 2, 6 inputs the signals from the waveform observing means 3 and the storing means 4, and when the vibration is not observed in the current waveform but the vibration is observed in the previous waveform, the parameters are set. This is an operation instruction means for instructing the operation means 5 not to perform the setting operation of the proportional constant and the integral constant to the PI control means 2.

(Operation) The calculation instructing means 6 determines whether or not there is a change in process characteristics or disturbance from the current waveform observation result and the previous waveform observation result. That is, when there is no vibration in the current waveform and vibration is observed in the previous waveform, the parameter calculation means 5 is instructed not to perform the tuning operation on the assumption that there is a change in the process characteristic or the disturbance.

(Example) FIG. 2 is a configuration block diagram showing an example of an apparatus according to the present invention. In the figure, the same parts as those in FIG. 1 are designated by the same reference numerals.

The PI control means 2 includes a multiplexer 20, a comparator 21,
It is composed of a microprocessor 22, a D / A converter 23 that converts a digital signal from the processor 22 into an analog signal, and a sample hold circuit 24 that holds the output of the D / A converter. Reference numeral 7 is a RAM storing various data, 8 is a system ROM storing a program of an operation performed by the microprocessor 22, 9 is a user ROM storing a program created by a user according to a process, 10 is a display keyboard, These are microprocessors via the data bus DB
Is bound to 22. Here, the system ROM 8 stores programs for the microprocessor 22 to perform the functions of the waveform observing means 3, the parameter calculating means 5 and the controlling means 6 shown in FIG. 1, and the CPU 22 executes these programs. Each function is realized by executing it. Further, the storage means 4 for the data showing the waveform observation result is provided in a part of the RAM 7.

FIG. 3 is a flow chart showing an example of the operation of the controller thus configured.

The flowchart shown here is a schematic flowchart, and its cycle period (control period) is, for example, 100 mS.
It is started with, and as explained next,
Operations such as A / D conversion, waveform observation, PI control calculation, and output of the calculation result to the process are performed in this control cycle.

While performing such a series of operations, analysis of the waveform observation of the process amount or deviation signal ends (For example, in the analysis of the observed waveform, the A / D converted process amount is trended for a certain period of time. The analysis is completed when a few peaks are detected, and although it depends on the type of process, normally, for the waveform observation of the process amount or deviation signal,
If it takes a long time of several minutes or more), steps 3, 4, and 5 for calculating the PI calculation parameter will be activated.

First, the microprocessor 22 selects and extracts the process amount PV1 and the set value es applied to the multiplexer 20 according to the system program stored in the system ROM 8, and at the same time outputs these signals to the comparator 21, the processor 22, and the processor 22. The digital signal is converted by the A / D conversion loop formed by the D / A converter 23 (step 1).

Then, according to the system program functioning as the waveform observing means 3 in FIG. 1, the waveform of the deviation signal ε between the process amount PV or the process amount PV and the set value es is observed (step 2). By observing this waveform, for example, the peak value of the process amount PV or the deviation signal ε, or the time until the peak value is reached, information such as the overshoot amount, the deviation area non-decreasing rate, and the vibration cycle that represents the waveform is obtained. . Information on these waveform observation results is stored in the RAM 7 (storage unit 4). Next, it is judged whether or not the above-mentioned waveform analysis is completed (step 20), and when the analysis is completed, the process proceeds to step 3.

Here, the processor 22 determines whether or not there is a vibration in the waveform from the current waveform observation result according to the system program functioning as the calculation instruction means 6 (step 3).
If no vibration is recognized in the waveform, it is determined from the previous waveform observation result stored in the ROM 7 (storage unit 4) whether or not the previous waveform has vibration (step 4).
If it is determined that there is vibration, the parameter calculation means 5 is instructed not to perform a new P, I constant setting operation for the PI control means 2. That is, step 5 described below is skipped.

In step 3, “this time” means the waveform observation of the process amount or deviation signal of this time when it is judged that the analysis is completed in step 20 (YES judgment), and in step 4, the previous time is analyzed in step 20 It refers to the waveform observation of the process amount or deviation signal at the last time when it was judged that the process was completed.

When there is vibration in the current waveform in step 3, and when there is no vibration in the previous waveform in step 4, the processor 22 uses the waveform observation result in accordance with the system program functioning as the parameter calculation means 5 to obtain an optimum response. The P and I constants shown are calculated, and a tuning operation for setting the obtained P and I constants in the PI control means 2 is performed (step 5).

Next, the processor 22 performs PI control calculation by the system program functioning as the PI control means 2 (step 6), and the obtained PI calculation result (manipulation amount: MV) is D / A converter 23 and sample hold. Output to process 1 via circuit 24 (step 7). After that, the process returns to step 1 and the operations up to step 7 are repeated in a predetermined cycle.

In the waveform observation performed in step 2 and step 20,
For example, the peak value of the observed waveform is detected, and the vibration period (TP), overshoot amount (OVS), damping value (DMP), etc. of the observed waveform are obtained. Whether or not the waveform is vibrated in steps 3 and 4 is determined by the vibration period (TP) and overshoot (OV
S), damping value (DMP) and other values (for example, whether the overshoot amount is greater than a predetermined value, whether the vibration cycle is greater than a certain value, etc.) to decide.

Calculation of the PI constant performed in step 5 is performed by, for example,
The method disclosed in Japanese Patent Laid-Open No. 62-108306 is applied.

That is, the ratio R between the integration constant (TI) set in the PI control means 2 and the vibration period (TP) obtained as a result of analysis of the observed waveform.
(= TI / TP), damping value (DMP) and ratio (R)
The proportional constant and the integral constant are calculated using a predetermined arithmetic expression selected according to the size of. Then, the obtained new proportional constant and integral constant are set in the PI control means 2.

Here, even if the judgment is “NO” in both Steps 3 and 4, in Step 5, the PI constants are calculated and set in the PI control means. The reason is as follows. Is.

That is, in Steps 3 and 4, it is only judged whether or not there is vibration in the observed waveform at this time and the previous time. There are many observed waveforms of the process amount or deviation signal that take a path that does not oscillate (oscillate) and gradually settle to a constant value, as in normal responses.
Waveform observations are performed and analysis results are obtained. Even in such a case, it is necessary to repeatedly perform the operation of calculating PI constants based on the analysis result and setting them in the PI control means 2 until the optimum response result is obtained.

If the waveform is for a normal response that does not vibrate, both steps 3 and 4 are judged as "NO", and step 5
At, the PI constants are newly calculated based on the analysis result of the observed waveform, and these PI constants are set in the PI control means 2. In steps 6 and 7, this time, the PI calculation result based on the newly set PI constant is output to the process.
After that, returning to step 1, this time, the process quantity or the reaction (response) of the deviation signal based on the new PI constant is observed again, and the same operation is repeated several times to finally obtain the optimum PI constant. It can be set in the PI control means 2.

It should be noted that in both Steps 3 and 4, it is determined whether or not there is vibration in the waveform, but if it is also determined in combination with the direction of vibration, the process characteristics or the change characteristics of the disturbance can be more accurately determined. Can be captured.

If the process characteristics change or the disturbance changes due to the above operation (that is, No is determined in step 3 and Yes is determined in step 4), the self-tuning operation is performed. It skips, performs PI control calculation according to the previously set PI constant, and outputs the manipulated variable MV that stays in a safe direction.

(Effect of the invention) As described above, in the present invention, the PI constant is calculated based on the process amount or the waveform observation result of the deviation signal,
In the controller in which it is set in the PI control means and the operation of observing the process amount or the response of the deviation signal based on the PI control means is repeated several times to finally obtain the optimum PI constant, the parameter calculation means has 5 Is configured to skip the calculation of PI constant and the setting operation of PI constant once when the vibration is generated in the previous waveform analysis even if the vibration is not generated in the current waveform analysis. Is.

That is, in order to eliminate the possibility that a PI constant that emphasizes oscillation is set when there is vibration in the previous waveform observation, even if no vibration has occurred in this waveform analysis. , The PI constant setting operation is skipped once for the completion of analysis of the observed waveform (waiting until the completion of the analysis of the next waveform observation), and the disturbance or process characteristics change. In such a process, a self-tuning controller that can always safely control the process can be realized.

[Brief description of drawings]

FIG. 1 is a basic functional block diagram of the self-tuning controller of the present invention, FIG. 2 is a configuration block diagram showing an example of the device of the present invention, and FIG. 3 is a flow chart showing an example of operation.
FIG. 4 is a waveform diagram showing an operation example of the conventional device. 1 ... Process, 2 ... PI control means, 3 ... Waveform observation means, 4 ... Storage means, 5 ... Parameter calculation means, 6 ...
... Calculation instruction means.

Continuation of the front page (56) References JP-A-60-215208 (JP, A) JP-A-62-236004 (JP, A) JP-A-62-135902 (JP, A) US Patent 4602326 (US, A)

Claims (1)

[Claims] 1. PI control means for performing at least proportional and integral calculation on a deviation signal between a process amount and a set value from a process and outputting the obtained manipulated variable to the process, and a waveform of the process amount or the deviation signal. And a storage means for storing a waveform observation result by the waveform observation means, and at least a proportional constant and an integral constant are calculated based on the waveform observation result, and the proportional constant and the integral constant are calculated by the PI control means. Input the signals from the waveform observing means and the storage means, and the waveform observing means does not show any waveform vibration in the current waveform analysis result. If waveform vibration is observed in the result, the setting operation of the new proportional constant and integral constant to the PI control means by the parameter calculation means is not performed. A self-tuning controller, which is provided with a calculation instructing means for instructing the self-tuning.