JPS63204401A - Pid controller - Google Patents

Abstract

PURPOSE:To realize the response with improved controllability for a PID controller by calculating the waste time and a primary delay time with process identification for comparison between both times and applying the PID control to a process based on the set optimum parameters. CONSTITUTION:A process identifying means 2 calculates the waste time L and the primary delay time TL and a parameter setting means 3 compares both times L and TL with each other to decide whether a process is controlled by the time L or the time TL. Based on this deciding result, the gain K, the integration time Ti and the differentiation time Td serving as the PID (proportion, integration and differentiation) parameters are calculated. Then a PID control means 4 calculates the manipulated variable MV corresponding to the input deviation from those parameters K, Ti and Td and outputs the MV to perform the control to the process. Thus it is possible to attain the response with improved controllability.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a controller that performs PID (proportional-integral-derivative) control over a process, and particularly relates to a controller that performs self-tuning.

[Conventional technology]

PID control combines the advantages of PI control and PD control, and has the advantage that the response is more centrifugal than in the case of only P operation. As a controller in such PID control, PID parameters (K, Ti,
Self-tuning controllers that automatically set Td) are already known.

[Problem that the invention seeks to solve]

However, in conventional self-tuning controllers, the values obtained as a result of determining the optimum PID parameters of the controller through process identification or similar operations are not always the optimum values for various process characteristics. Ta. In other words, the responsiveness may not be optimal for some processes.

Further, even with a controller in which two degrees of freedom or more are given to the PID parameter calculation formula, there are cases where the optimum value cannot be output due to changes in process characteristics.

In such cases, a problem arises in that the controllability over the process is reduced.

[Means for solving problems]

The PID controller of the present invention has been developed in view of the above-mentioned problems, and the PID controller adjusts the operation i1MV so as to reduce the deviation e between the process control amount P■ and the set value SP.
an ID control means, a process identification means for identifying characteristics of the process based on a set value SP, a controlled variable PV, and a manipulated variable MV, and calculating a dead time and a primary lag time T of the process, and the dead time. First-order delay time TL
From the magnitude relationship of
and parameter setting means for calculating PID parameters to be given to the ID control means.

[Effect]

Based on the dead time and the first-order delay time TL calculated by the process identification means, the parameter setting means determines whether the process is dominated by the dead time or the second-order delay time, and based on that judgment, Optimal PID parameters are automatically set. Then, the PID control means controls the PI for the process based on the PID parameters set by the parameter setting means.
Perform D control.

〔Example〕

Hereinafter, the present invention will be described in detail along with examples.

FIG. 1 is a block diagram showing one embodiment of the present invention.

The PID controller 1 includes a process identification means 2, a parameter setting means 3, and a PI according to its functional classification.
D control means 4 is present.

The process identification means 2 identifies the process characteristics of the controlled object (process) 5 by observing the values of the set value SP, the controlled variable pv, and the manipulated variable MV. That is, here, the process is divided into dead time and first-order delay time Tt.
L and TL are determined by the identification results.

In addition, the parameter setting means 3 also uses the process identification means 2.
From the dead time and first-order lag time TLO values obtained from
Determine the values of i and differential time Td. At this time, a system in which dead time is dominant and a system in which first-order delay time TL is dominant cause a large difference in process characteristics, so these two systems will be considered separately. In other words, the process 5
Determine which system belongs to.

For example, when L≧TL, the system is defined as system (i) where dead time is dominant, and when L<TL, the system is defined as system (ii) where first-order delay time TL is dominant. .

Then, according to the calculation formula shown in Table 1, the system (i),
Set the PID parameters of system (ii).

The PID control means 4 uses Ti and Td as new PID parameters set by the parameter setting means 3, and calculates and outputs the manipulated variable MV from the input deviation e. This operation iMV is given to process 5, and process 5
The control amount P■ approaches the set value SP.

FIG. 2 is a flowchart when a microcomputer is installed in the PID controller l.

First, the values of dead time and first-order delay time TL are determined by process identification (step 101).

Next, the magnitude of the obtained dead time and the first-order lag time TLO value are compared, and when L≧TL, the calculation formula used for system (i) where the dead time is dominant (see Table 1). ), the PID parameters are Ti, Td
is calculated (step 103). In judgment 102, if L<TL, the PID parameters, that is, K, Ti, Td
is calculated (step 104). Then, Ti and Td obtained in this way are set as new PID parameters (step 105).

The PID controller 1 calculates and outputs the operation iMV according to the manually input deviation e (=set value SP - control amount PV) using the new PID parameters.

Table 1 [Effects of the Invention] As explained above, according to the PID controller of the present invention, the process identification means calculates the dead time and the first-order delay time TL as process characteristics by on-line identification. Based on the value of TL, the parameter setting means determines whether the process is dominated by dead time or -next delay time, and then automatically sets optimal PID parameters. Since the PID control means performs PID control based on the PID parameters set in this way, it is possible to recognize changes in characteristics due to the passage of time or load fluctuations in the process, making it possible to perform optimal control according to the process characteristics. . Therefore, it is possible to realize a response with improved controllability compared to a conventional PID controller.

[Brief explanation of the drawing]

The first volume is a block diagram showing an embodiment of the present invention, and FIG. 2 is a flow chart when the present invention is implemented by a microcomputer. DESCRIPTION OF SYMBOLS 1... PID controller, 2... Process identification means, 3... Parameter setting means, 4... PID control means, 5... Process.

Claims (1)

[Claims] PID control means that adjusts the manipulated variable MV to reduce the deviation e between the controlled variable PV and the set value SP of the process; and a PID control means that identifies the characteristics of the process based on the set value SP, the controlled variable PV, and the manipulated variable MV. , a process identification means for calculating the dead time L and the first-order lag time T_L of the process, and whether the process is a system dominated by the dead time or the first-order lag based on the magnitude relationship between the dead time L and the first-order lag time T_L. A PID controller comprising parameter setting means for recognizing whether the system is controlled by time and calculating PID parameters to be given to the PID control means based on a calculation formula according to this recognition.