JPH06259104A - Pid control method and cooling device applying the control method - Google Patents

Abstract

PURPOSE:To provide a PID control method which can set the priority of the differential control operation of a control system in response to the attribute to which the differential value, i.e., an input signal is optionally defined and also to provide a cooling device which applies the PID control method in regard of the PID control where the proportional control, the integral control and the differential control are carried out together or selectively. CONSTITUTION:A cooling device which applies a PID control method consists of a controller O, an expansion valve V, and an evaporator R. The controller O is set at different priority levels of a D operation in accordance with the attribute of the differential value, i.e., the positive or negative value.

Description

Detailed Description of the Invention

[0001]

[Object of the Invention]

BACKGROUND OF THE INVENTION The present invention relates to a novel P. I. The present invention relates to D control and a cooling device to which the D control is applied.

[0002]

BACKGROUND OF THE INVENTION For example, in a cooling device, a so-called P.P. I. Many control the opening and closing of the expansion valve using D control. And P. I. The D control controls the expansion valve with a proportional operation (hereinafter referred to as P operation) as a main operation, and an integral operation (hereinafter referred to as I operation) and a differential operation (hereinafter referred to as D operation) perform insufficient control in the P operation. It is a supplement. And a specific P. I. The control output from the D controller is output by appropriately selecting the priority of these P, I, and D operations.

However, in the system in which the priorities of the P, I, and D operations are appropriately selected and output, particularly in the D operation, the response of the controlled system varies depending on the attribute of the sampled differential value. In this case, the priority had to adopt a compromise value that was not optimal for both parties. For example, in the case of the temperature characteristic of the cooling device as shown in FIG. 3 (a), when the temperature rises and passes the inflection point, the temperature starts to sharply decrease, greatly falls below the set value, and it takes time to recover to the set value. .
When viewed from the differential value for detecting this situation, such a tendency occurs at once when the differential value changes from positive to negative. Therefore, it is required that the D operation be controlled more predominantly. On the contrary, when the temperature falls and rises gently after passing the inflection point, that is, when the differential value changes from negative to positive, it is required that the P operation dominates the control. However, the conventional P. I. In the D control, the priority cannot be set by the attribute of the differential value, so that the priority uses a compromise value that is not optimal for both sides, and as a result, accurate control cannot be performed.

[0004]

[Technical Items Attempted to Develop] The present invention has been made in view of such a background, and the priorities of the D motions are different according to arbitrary attributes of the differential value which is a sample during the D motions. This is an attempt to develop a new cooling device controlled by a configurable PID controller.

[0005]

[Constitution of the invention]

[Means for Achieving the Object] The first invention according to the present application, P.
I. The D control method is a P.D. method that performs proportional control, integral control, and derivative control in a combined or selective manner. I. In the D control, the priority of the differential control operation can be set according to an arbitrarily defined attribute of the differential value as an input signal.

A second invention according to the present application, P. I.
The cooling device to which the D control method is applied is a P.I. system that performs proportional control, integral control, and derivative control in a combined or selective manner. I. In a device in which the heat exchange output is controlled by receiving the D control, the priority of the differential control operation in the control system can be set according to an arbitrarily defined attribute of the differential value as the input signal. Then, the above means is used to achieve the above object.

[0007]

The operation of the present invention will be described with respect to the cooling device. When the opening / closing of the expansion valve is controlled, the differential value of the output difference (hereinafter referred to as superheat degree) of the two temperature sensors provided in the evaporator. For example, when the degree of superheat corresponding to the positive differential value is high, the priority of the D operation is lowered to make the P operation dominant, and when the degree of superheat is negative corresponding to the negative differential value, the priority of the D operation is set. It can be set higher so that the D motion is dominant.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings by taking a cooling device to which the present invention is applied as an example. A reference numeral P in FIG. 1 is a refrigerant pipe in which a refrigerant L such as CFC is supplied.
The refrigerant pipe P, which circulates, passes through the evaporator C installed in the cooling action part F from the compressor C via the control valve V and enters the compressor C again. Temperature sensors T1 and T2 are installed in the evaporator R, and these are connected to a controller O. The controller O adjusts the degree of opening of the expansion valve V by the signals from T1 and T2, adjusts the amount of the refrigerant liquefied by the compressor C sent to the evaporator R, and controls the degree of superheat in the cooling action part F. .

First, the relationship between the amount of refrigerant L in the evaporator R and the degree of superheat will be described. FIG. 2A shows the change in superheat degree. 2B shows the amount of the refrigerant L in the evaporator R at points of and in FIG. In the state shown in FIG. 2B, the amount of refrigerant is insufficient and the temperature is above the set temperature. Figure 2 (b)-
The state shown in is the theoretical operating state and the set temperature. In the state shown in FIG. 2B, the amount of the refrigerant L is excessive and the temperature is below the set temperature. Based on these, the case where the control operation of the controller C is the PD operation (proportional + differential operation) will be described.

The controller C controls the expansion valve V by using T2-T1 (degree of superheat) as a detection signal and tries to bring the state close to the ideal operating state shown in FIG. 2 (b). FIG. 3A shows the change in superheat degree. Further, at this time, the opening degree of the expansion valve V controlled by the P operation becomes an opening degree proportional to the difference between the set superheat degree and the superheat degree at that time as shown in FIG. At temperature, the openness is 50%. However, the relations of FIGS. 3 (a) and 3 (b) are theoretical values in which the transmission time of the refrigerant L and the like are ignored, and in reality, for example, before a large amount of the refrigerant supplied at the point X is completely vaporized in the evaporator R, Y Refrigerant is also supplied at the point of, and the decrease in superheat becomes a sharp curve. Further, at this time, the refrigerant is excessively present in the evaporator R, so that the refrigerant remains in a liquid state and the compressor C
The so-called liquid back phenomenon occurs, which causes damage to the compressor C.

In order to prevent the liquid back phenomenon described above, control by the D operation is required. That is, it is required to sensitively reflect the change rate (differential value) of the degree of superheat and output the control signal. FIG. 3C shows the opening degree of the expansion valve V controlled by the D operation. In this case, a large amount of the refrigerant supplied at the point of X is vaporized in the evaporator R, and the supply of the refrigerant is stopped at the point of Z at which the degree of superheat starts to decrease.
The excessive supply of the refrigerant into the inside is prevented, and the liquid back phenomenon can be prevented. The point to be noted here is when the once lowered superheat degree starts to rise due to the lack of refrigerant. If the point indicated by W in the figure is in this state and the priority for the D operation is the same as when the superheat degree is decreasing, that is, when the differential value is negative, the open degree of the valve suddenly becomes high open degree and the evaporator R Since a large amount of the refrigerant L is supplied into the inside, the operating state of the device becomes unstable.

Here, as a characteristic method of the present invention, the priority of the D operation is changed depending on the attribute of the change rate (differential value) of the degree of superheat, specifically, whether the differential value is positive or negative. Figure 3
(D) shows the degree of opening of the expansion valve V at this time. Where W
Point, that is, when the differential value is positive, the priority of the D operation is set low so that the P operation becomes dominant, while when the differential value is negative, the priority of the D operation becomes dominant. Set higher. As a result, the operating state of the device can be stabilized. In this example, positive and negative are used as the attribute of the differential value, but the absolute value of the difference is
It is also possible to use the size of the n-th power or the like as an attribute.

[0013]

EFFECT OF THE INVENTION I. In the D control, when the response of the controlled system differs depending on the attribute of the differential value, for example,
When the differential value is positive, the priority of the D operation is lowered and the P operation is dominant, while when the differential value is negative, the priority of the D operation is high and the D operation is dominant. Accurate control is possible even when it is necessary to make settings. Further, when controlling the opening and closing of the expansion valve V, the cooling device of the present invention lowers the priority of the D operation when the superheat degree corresponding to the positive differential value rises, depending on whether the differential value of the superheat degree is positive or negative, It is possible to make the P operation dominant and, on the other hand, set the priority of the D operation to be high when the degree of superheat is decreased when the differential value is negative, so that the D operation can be made dominant. As a result, it is possible to prevent excessive supply of the refrigerant L, stabilize the operating state of the device, and reduce power consumption.

[Brief description of drawings]

FIG. 1 shows the P. I. It is a block diagram of the cooling device to which the D control method is applied.

FIG. 2 is a perspective view showing a graph showing changes in superheat degree and a refrigerant in the evaporator at that time.

FIG. 3 is a graph showing changes in superheat and P, D, P
It is a graph which shows the valve opening degree by D control.

[Explanation of symbols]

 C Compressor F Cooling part L Refrigerant O Controller P Refrigerant pipe R Evaporator T1 Temperature sensor T2 Temperature sensor V Expansion valve

Claims (2)

[Claims] 1. A P.I. that performs proportional control, integral control and derivative control in combination or selectively. I. In the D control, the priority of the differential control operation can be set according to an arbitrarily defined attribute of the differential value as the input signal. I. D control method. 2. A P.I. which performs proportional control, integral control and derivative control synthetically or selectively. I. In a device in which a heat exchange output is controlled by receiving D control, the priority of differential control operation in a control system can be set according to an arbitrarily defined attribute of a differential value as an input signal. .