JPH04303201A - Controller - Google Patents

Abstract

PURPOSE:To always keep a high control performance regardless of the state change of a control object by always inferring the parameter of a control object model in a Smith controller so that it follows up with the state change of the actual control object. CONSTITUTION:A manipulated variable output (u) of a linear or nonlinear control part 11 is inputted to the control object 10, and the control object 10 is divided into a control object 10a before the intermediate state and a control object 10b subsequent to the intermediate state. Control data (x) of the intermediate state is taken out and inputted to control object models 12 and 13 subsequent to the intermediate state. The control object model 13 is a general primary time lag system, and the control model 12 expresses a dead time. That is, this system controls the control object having the dead time, and the parameter of the control model is inferred based on a set value and the state of the control object and is changed in real time to prevent mismatching between the actual control object and the control object model.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device capable of controlling a controlled object including dead time by following changes in its state.

0002

2. Description of the Related Art It is extremely difficult to control a system that includes dead time such as a heat exchanger using a normal PID control system. It is the dead time function e−L within the closed loop of the control system.
This is because S is included. Therefore, the Smith controller incorporates a model of the controlled object into the control device, removes the dead time from the closed loop, and enables control similar to normal one-time delay and two-time delay systems. That is,
The Smith controller is designed to feed back the output of a general first-order delay system or second-order delay system control device via a controlled object model. A controlled object model generally consists of a first-order delay system + dead time. FIG. 8 is a diagram showing the configuration of a control system using the general Smith method. The object to be controlled is a water heater. The input water amount sf, the input water temperature Ti, and the set temperature r are input as set values, and the aforementioned wf, Ti, and r-y-z are input to the control section 31 (transfer function Gc(s)). That is, by adding the predicted deviation z, which is obtained by taking in the dead time in advance from the actual control deviation ry, it is possible to control a controlled object having a dead time. This predicted deviation z is calculated by converting the manipulated variable output of the control unit 31 into a transfer function (1-e-LS) of the controlled object model 32.
This is the value obtained by inputting G(s).

0003

[Problem to be solved by the invention] As described above, by using the Smith controller, it is possible to easily control a controlled object that has dead time, but the actual controlled object and the controlled object model must match. be. When a plant is installed, it is necessary to adjust this model on site, but this adjustment requires skill and is extremely time-consuming. Furthermore, because conventional controlled object models were adjusted at the time of plant installation and then fixed, they had the disadvantage that if there was a change in the state of the controlled object, a mismatch between the model and the object would occur, resulting in an extremely poor control performance. there were. In the control system of Figure 8, the water volume of the water heater is set to 2 liters,
FIGS. 9A to 9C show graphs of changes when the temperature is controlled by changing the temperature to 6 liters and 9 liters. In addition,
The controlled object model 32 is a model for a case where the amount of water is 6 liters. When the water volume is 6 liters as shown in Figure (A), the water temperature settles almost immediately, but when the water volume is 9 liters as shown in Figure (B), the settling time is longer; In the case of 2 liters of water shown in C), control is no longer possible. As described above, the conventional Smith controller has a drawback in that it has extremely poor ability to follow changes in the controlled object.

An object of the present invention is to provide a control device that solves the above problems by inferring a controlled object model in accordance with control conditions.

[0005]

[Means for Solving the Problems] The present invention provides a control device for controlling a controlled object including dead time, which includes a sensor for detecting an intermediate state of the controlled object, and a control device that receives the detected amount of the sensor as input. a Smith controller having a target model; a detection unit into which state data of the controlled target and/or setting values for the target are input; and an inference unit for inferring parameters of the controlled target model based on detected values of the detection unit. It is characterized by having the following.

[0006]

[Operation] The control device of the present invention is provided with an inference device for inferring the parameters of the controlled object model within the Smith controller. Inputs for inference are state data and set values of the controlled object; for example, when the controlled object is a water heater, they are the amount of water input, the temperature of water input, the set temperature, and the like. When these values change, the inference means infers the parameters of the controlled object model that are suitable for the controlled object at that time. This results in
Mismatches between the controlled object model and the actual controlled object can be prevented, and control accuracy can be maintained at a high level.

Furthermore, in the present invention, the intermediate state of the controlled object is detected by the sensor, and this value is input into the controlled object model. That is, the model for the controlled object after the intermediate state is used as the controlled object model. By doing so, even if a change occurs in the state of the controlled object, the steady-state gain remains approximately constant, so model mismatch is less likely to occur, and it is possible to prevent a decrease in control performance due to a change in the characteristics of the controlled object.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing a water heater system in which a control device 5 according to an embodiment of the present invention is used. The water heater 1 has a heat exchanger 2, and a temperature sensor 2a is provided approximately in the middle of the heat exchanger 2. A burner 3 is provided at the bottom of the water heater 2. Burner 3 has valve 6,
The gas supplied via 4 is combusted. The valve 4 is a proportional valve that opens and closes steplessly under the control of the control device 5. Target values and control variables are input to the control device 5.

FIG. 2 is a block diagram of the control device for the water heater system. The manipulated variable output u of the linear or non-linear controller 11 is input to the controlled object 10. Controlled object 10
is divided into a controlled object 10a before the intermediate state and a controlled object 10b after the intermediate state. The controlled variable data x in this intermediate state is extracted and input to the controlled object models 12 and 13 in the intermediate state and thereafter. The controlled object model 13 is a general first-order lag system, and the transfer function G(s) = K/(1
+sT). Moreover, the controlled object model 12 is
It expresses the dead time, and L included in the index is the estimated value of the dead time of the controlled object 10b (Gp2(s).Here, the controlled object 10a before the intermediate state also includes dead time. However, in the case of a water heater heat exchanger, the dead time is small in the first half and the dead time is larger in the second half, so ignoring the dead time in the first half will have a large negative impact on control performance. A model inference section 14 is connected to the controlled object models 12 and 13.The model inference section is a device that infers the parameters of the controlled object model by fuzzy inference.The fuzzy inference is performed as shown in FIGS.
It is executed based on the rules and membership functions shown in FIG.

FIG. 3 is a diagram showing the configuration of the control device 11. This control device is composed of fuzzy control systems 20-22, PID control systems 23-27, and feedforward control system 28. The fuzzy control system consists of a fuzzy inference device 20, an amplifier 21, and a distributor 22. The fuzzy control device 20 includes fuzzy rules and membership functions for performing general temperature control. The distributor 22 is a circuit for adjusting the degree of contribution between the PID control system and this fuzzy control system. The PID control system is composed of a proportional controller 23, a differential controller 24, and an integral controller 25. This output is input to a distributor 27 for adjusting the degree of contribution to the fuzzy control system. These outputs and the output of the feedforward control system 28 are all added together to calculate the manipulated variable output u.

FIGS. 4 to 6 are diagrams for explaining the fuzzy inference method executed by the model inference section 14. Figure 4
shows the rules used for fuzzy inference, FIG. 5 shows the membership function of input variables, and FIG. 6 shows the membership function of output variables. FIG. 4A shows a rule that determines the dead time L, time constant T, and steady gain K of the controlled object models 12 and 13 based only on the condition of the inflow water flow rate Wf. In other words, the characteristics of the controlled model are almost determined by the incoming water flow rate. The membership function of the incoming water flow rate is as shown in Figure 5(A), and the output variables are dead time L, time constant T,
The membership functions of steady gain K are shown in Figures 6(A) to (C).
As shown below. Furthermore, FIG. 4(B) shows the set temperature r
Steady gain K and time constant T based on the input water temperature Ti
This is a rule for correcting. The membership function for determining the correction value, which is an output variable, is as shown in FIG. 6(D).

In this way, by correcting the controlled object models 12 and 13 based on the state of the controlled object such as the incoming water flow rate, the control device 5 is able to adjust the control object even when the incoming water flow rate changes from 2 liters to 6 liters to 9 liters. , as shown in FIGS. 7(A) to 7(C), it becomes possible to provide settling characteristics that are almost practical.

[0013]

[Effects of the Invention] As described above, in the control device of this invention,
By constantly inferring the parameters of the controlled object model in the Smith controller so as to follow changes in the state of the actual controlled object, control accuracy can be improved by following this no matter how the controlled object or its setting values change. can be kept high.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a water heater system that is an embodiment of the present invention;

[Figure 2] is a control diagram of the same water heater system.

FIG. 3 is a diagram showing the configuration of the control device of the water heater system;

FIG. 4 is a diagram showing fuzzy rules used in the model inference section of the water heater system.

FIG. 5 is a diagram showing the input membership functions used in the model inference section,

FIG. 6 is a diagram showing the output membership function used in the model inference section,

FIG. 7 is a diagram illustrating control characteristics when the amount of water input is changed in the same water heater system.

FIG. 8 is a diagram showing the configuration of a conventional Smith controller;

FIG. 9 is a diagram showing control characteristics when the amount of water input is changed using the conventional Smith controller.

[Explanation of symbols]

11-control device, 10a, 10b-controlled object, 12,1
3-Controlled object model, 14-Model inference section.

Claims (1)

[Claims] 1. A control device for controlling a controlled object including dead time, comprising: a sensor for detecting an intermediate state of the controlled object; and a Smith controller having a controlled object model inputting a detection amount of the sensor; It is characterized by comprising a detection means into which state data of the controlled object and/or setting values for the object are input, and an inference means for inferring parameters of the controlled object model based on the detected value of the detection means. control device.