JPH05346805A - Control method for process - Google Patents

Abstract

PURPOSE:To operate the scheduling of a PID constant, and to steppedly and automatically switch and set it to the optimal PID constant, according to the change of an objective function due to the change of each kind of condition. CONSTITUTION:In a process control mechanism 10 being a system in which the objective function is rapidly changed due to the change of each kind of condition, a scheduling means 16 selects the optimal value of the PID constant based on the detection signal of the change of the quantity and direction of the objective function based on the change of each kind of condition, and derives the signal of the optimal value to a PID control part 11. At that time, the scheduling means 16 executes the procedure of steppedly and automatically switching and setting the PID constant. Thus, a controllability can be maintained even in the system in which the objective function is rapidly changed due to a disturbance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a process control method for a system in which an objective function changes rapidly due to a disturbance.

[0002]

2. Description of the Related Art Conventionally, a PID control system has been widely adopted for various control mechanisms. This PID is shown in Figure 2.
The block diagram of the control mechanism 1 of the process to which the control method is applied is shown. The control mechanism 1 of this process includes a PID control unit 2, an operation unit 3, a control target 4, and a detection unit 5 that detects and feeds back a control amount output from the control target 4, and a feedback signal and a setting thereof. The deviation is obtained from the set target value, and the PID control is performed from the PID control section 2 to the operation section 3 based on the deviation to perform the PID control. In this case, the PID control constant in the PID control unit 2
Each coefficient of the proportional term, the integral term, and the derivative term is preset as a fixed constant so as to show the controllability of a certain range in the entire control range.

[0003]

However, among various control mechanisms, there is one in which the objective function changes due to changes in various conditions (control amount, elements other than the control amount and the direction of change). For example, in the cooling water control mechanism 6 in the cogeneration system shown in FIG. 3, a change in the power generation amount, which is an element other than the control amount, affects the cooling water temperature. That is, in this system, the cooling water temperature changes under the influence of both the change in the amount of power generation and the change in the cooling water flow rate. In other words, it can be seen that the cooling water control mechanism 6 is a system in which the objective function changes according to factors other than the control amount, because the temperature changes with changes in the amount of power generation. On the other hand, the predetermined number of the cooling water temperature change response due to the change of the cooling water flow rate is significantly different depending on the changing direction, as shown in FIGS. 4, 5, and 6. In the figure, the arrow indicates the direction of change. In this way, the objective function changes due to changes in various conditions (control amount, elements other than the control amount, and the direction of change). Therefore, it is difficult to maintain controllability with a PID control constant fixed in advance. The present invention has been made in view of the above problems, and an object thereof is to provide a process control method capable of switching and setting a PID constant to an optimum value in accordance with a change in an objective function due to a change in various conditions. And

[0004]

In order to solve the above-mentioned problems, the present invention relates to a control mechanism of a process for performing PID control, in which the objective function is quantitatively and directionally based on changes in various conditions due to external factors. It is characterized in that a change is detected, a PID constant is scheduled on the basis of a detection signal relating to this quantitative or directional change, and the PID constant is stepwise and automatically switched to an optimum value.

[0005]

First, the control mechanism is actually operated, and during operation,
When various conditions due to external factors change and quantitative or directional changes in the objective function are detected, the optimum value of the PID constant is selected according to the degree of change in the objective function and the direction of change. This allows the process control mechanism to
PID control is performed based on the optimum value of the D constant. In the process control mechanism in which the objective function changes abruptly due to changes in various conditions, the PID constants are automatically switched in steps to perform PID control.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A process control method according to the present invention will now be described with reference to the accompanying drawings showing an embodiment of a process control mechanism for carrying out the method. In FIG. 1, reference numeral 10 indicates a block diagram of a control mechanism of the process, and the control mechanism 10 of the process is shown.
Indicates a system in which the objective function changes abruptly due to changes in various conditions, and the PID control unit 11, the operation unit 12, and the controlled object 1
3 and a detector 14 that detects and feeds back the control amount output from the controlled object 13, and obtains the deviation from the feedback signal and the set target value,
It is derived to the ID control unit 11 to perform PID control. Further, the control mechanism 10 of this process includes a disturbance change determination unit 15 that detects a quantitative and directional change in the objective function based on a change in various conditions due to external factors, and a detection signal related to the quantitative and directional change. Based on the above, a scheduling means 16 is provided for selecting an optimum value of a preset PID constant and deriving a signal related to the optimum value to the PID control unit 11. The scheduling means 16 executes the procedure of stepwise switching and setting the PID constant. The scheduling means 16
Is equipped with an appropriate storage means and can store the optimum value of the PID constant corresponding to the change of various conditions obtained as a result of actually operating the apparatus as data.

In the process control mechanism 10 as described above, first, assuming a change in various conditions, the process control mechanism 10 is subjected to a test operation, and P corresponding to each change is performed.
The optimum value of the ID constant is calculated and stored. The optimum value of the PID constant can be calculated manually, or the auto-tuning function for automatically calculating the optimum value can be applied. However, any other method may be used. The process control mechanism 10 is actually operated, and during the operation, the disturbance change determination means 15 monitors whether or not various conditions are changed, and the various conditions are changed and the objective function is quantitatively or directionally changed. When is detected, the scheduling means 16 selects and sets the optimum value of the PID constant according to the degree and direction of change,
A signal relating to the optimum value of the PID constant is sent to the PID control unit 11, and the process control mechanism 10 performs PID control. Since the control mechanism 10 of the process is a system in which the objective function changes abruptly according to changes in various conditions, the scheduling means 16 executes a procedure for automatically and stepwise setting the PID constant. To do. This is because, in a system where the objective function changes rapidly, unless the PID constant is changed stepwise, due to the delay,
This is because system control becomes unstable and it takes time to stabilize. As described above, even if various conditions change due to disturbance or the like and the objective function changes quantitatively or directionally, the control can always be executed by the PID constant having the optimum value, so that controllability is maintained. Therefore, the process control mechanism 10 can perform stable control operation against disturbances.

Although the process control method according to the present invention has been described above with reference to the embodiment of the process control mechanism 10, it can be applied to various known control systems.

[0009]

As described above, according to the present invention, the PID constant can be freely selected and set to the optimum value according to the change of the objective function due to the change of various conditions. The controllability can be maintained even for a system that changes to, and it is resistant to disturbance and stable control is possible.

[0010]

[Brief description of drawings]

FIG. 1 is a block diagram of a process control mechanism for carrying out a process control method according to the present invention.

FIG. 2 is a block diagram of a conventional process control mechanism.

FIG. 3 is an explanatory diagram showing an example of a system in which an objective function changes according to changes in various conditions.

FIG. 4 is a graph showing the relationship between the power generation amount and the cooling water amount and the process gain indicating the cooling water temperature change response in the system shown in FIG.

5 is a graph showing the relationship between the power generation amount and the cooling water amount and the time constant indicating the cooling water temperature change response in the system shown in FIG.

FIG. 6 is a graph showing the relationship between the amount of power generation and the amount of cooling water and the dead time indicating the response to changes in cooling water temperature in the system shown in FIG.

[Explanation of symbols]

 10 Process Control Mechanism 11 PID Control Section 12 Operation Section 13 Control Target 14 Detection Section 15 Disturbance Change Discrimination Means 16 Scheduling Means

Claims (1)

[Claims] 1. A control mechanism of a process for performing PID control detects a quantitative or directional change of an objective function based on a change of various conditions due to an external factor, and a detection signal relating to the quantitative or directional change. A method for controlling a process, characterized in that a PID constant is scheduled based on the above, and is automatically and stepwise set to an optimum value.