JP2911228B2 - Refrigeration cycle control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a refrigeration cycle control device, and more particularly, to a refrigeration cycle control device having a plurality of compressors,
The present invention relates to a refrigeration cycle control device that controls the operation capacity in a stepwise manner by a combination of / OFF.

[0002]

2. Description of the Related Art As a method of controlling a refrigeration cycle of this kind, the ability of a compressor is controlled by an inverter based on the low pressure of the refrigerant, utilizing the fact that the load is reflected on the low pressure of the refrigerant. Control schemes are known. An example is disclosed in Japanese Patent Application Laid-Open No. Sho 59-58182, in which a plurality of low pressure ranges are set, and control specifications are determined for each set range.

[0003]

However, in the conventional control device of this type, in order to perform fine control following a change in load, the setting range of the low pressure is very finely divided. There is a problem that each control specification must be determined. Also, despite the fact that appropriate control specifications differ depending on the type of load, this type of conventional device uses general control specifications, and thus cannot adequately cope with a wide variety of loads. There's a problem.

Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a refrigeration cycle control device which has a high follow-up capability to a load and a sufficiently high responsiveness to various loads. Is to provide.

[0005]

In order to achieve the above object, a compressor unit, a condenser, a decompression device, and an evaporator, which are formed by connecting a plurality of compressors having different rated operation capacities in parallel, are formed by a refrigerant pipe. A refrigeration cycle controller connected to the refrigeration cycle, wherein the on / off operation of the compressor is combined to change the operation capacity of the entire compressor unit in a step-like manner. Pressure detecting means for detecting pressure, pressure setting means for setting a set pressure, and a signal for changing a combination of ON / OFF of the plurality of compressors so that the low pressure becomes the set pressure. and a control operation unit that outputs, this control operation unit based on the pressure deviation and the pressure change speed between the low pressure and the set pressure
Fuzzy inference, and outputs fuzzy inference values.
Of the fuzzy inference value of
And the value corresponding to the range of change in capacity between steps
The value obtained by dividing the fuzzy inference value is the larger of the two values.
The operating capacity of the whole unit when it is larger than the threshold
Is increased to a higher step, and the fuzzy inference value is
If the value is smaller than the smaller of the two values
Reduce the operating capacity of the entire unit to lower steps
If not a little, the operating performance of the whole unit
A determination is made to maintain the force at the same step, and the ON / OFF of the plurality of compressors is
It is characterized by outputting a signal for changing the combination of OFF.

[0006] Since the range of change in the driving ability that can be selected between the steps differs depending on the step, it is desirable to judge the increase or decrease of the driving ability using a value obtained by dividing the fuzzy inference value by the change width.

[0007]

According to the present invention, fuzzy inference is performed based on the pressure deviation of the low pressure of the refrigerant from the set pressure value and the pressure change rate, and based on the inference value obtained as a result, the operation capacity is stepped up or down. It is determined whether to keep it as it is.

[0008]

FIG. 1 shows the configuration of an embodiment of a control device according to the present invention.

In FIG. 1, a compressor unit 1 including three compressors 1a, 1b, 1c connected in parallel, a condenser 3, a liquid receiver 5, an expansion valve 7, an evaporator 9, and an accumulator 11 are connected to a refrigerant pipe. A refrigeration cycle is configured by being connected in a ring at 13. Each of the compressors 1a, 1b, and 1c has a rated operating capacity of, for example, 4HP, 5HP, and 7.5HP. By operating the compressors in combination, the overall operating capacity can be controlled in a stepwise manner. FIG. 2 shows the compressors 1a, 1b,
The relationship between the combination of 1c and the corresponding driving ability is shown.
In the figure, "x" indicates stop and "o" indicates operation, and eight steps of capability selection from A to H are possible by a combination thereof. By making this selection appropriately, control is performed so that the low pressure of the refrigerant matches the predetermined set pressure P0. The control device for that is configured as follows.

As shown in FIG. 1, a pressure sensor 19 detects a low pressure of the refrigerant (for example, an input pressure to the compressor unit 1), and notifies the detection signal processing section 21 of the detected pressure P. The signal processing unit 21 includes an A / D converter and a microprocessor, takes in the detected pressure P every fixed time (for example, 20 seconds), and obtains a deviation PP from the set pressure P0.
0 and the rate of change of this deviation (or detected pressure) dP /
dt is calculated and given to the fuzzy inference unit 23.

The fuzzy inference unit 23 performs fuzzy inference based on the magnitude of the pressure deviation P-P0 and the pressure change rate dP / dt, and outputs a fuzzy inference value F0 as a result. In this case, fine control can be performed by optimally creating a membership function of fuzzy inference and creating rules. The fuzzy inference value F0 output from the fuzzy inference unit 23 is input to the step control unit 25. The step controller 25 determines whether to step up, step down, or maintain the current step from the current step based on the fuzzy inference value F0, and determines a combination of compressors to be operated. I do. Fuzzy
The inference unit 23 and the step control unit 25 constitute a control calculation unit.
To achieve.

FIG. 3 shows a judgment method in the step control section 25. The judgment is made based on a comparison between the fuzzy inference value F0 and two predetermined values L1 and L2. That is, (a) step down if F0 <L1, (b) step up if F0 / k> L2, and (c) step maintenance other than the above. Here, the value k is a capacity change width between the steps shown in FIG. Since the capacity change width k differs between steps, in the case of step-up, the control is likely to undershoot, which is not preferable in terms of energy saving. Further, as the two values L1 and L2, for example, L1 =
Although 0.2 and L2 = 0.5 are typical values, it is desirable to change them to appropriate values according to the control specifications.

FIGS. 4A, 4B and 4C show a pressure deviation P-P0 and a pressure change rate dP used for fuzzy inference in this embodiment.
A typical example of each membership function of / dt and the fuzzy inference value F0 is shown. In the figure, N is negative, Z is zero, and P is a positive membership function. The reason why N and P are asymmetric is that the control is performed at a high speed in a situation where the low pressure is reduced, so that the effect of energy saving is enhanced.

FIG. 5 shows rules used in the fuzzy inference. This rule is expressed in IF-THEN format.
The part of IF ... is called the antecedent part, and the part of THEN ... is called the consequent part. Referring to FIG. 5, for example, IF (P-P0) = N, AND (dP / dt) =
Z, THEN F0 = P or IF (P-P0) =
P, AND (dP / dt) = Z, THEN F0 = N,
It is as follows.

FIG. 6 shows another example of fuzzy inference which can be adopted in this embodiment. This is an example of inference using the MIN / MAX method. For example, a pressure deviation P-P0 = 2.0 and a pressure change rate dP When /dt=0.25, the minimum value of the antecedent part of each rule is taken, the maximum value of each consequent part is taken, and the center of gravity is determined to determine the fuzzy inference value F0.

Next, the operation of the embodiment configured as described above will be described with reference to the flowchart of FIG.

At the start of the operation, the state of the control device is initialized in step 1 and the detected low pressure value P is inputted in step 2 and is set as the previous detected low pressure value P '. Thereafter, in step 3, key scanning of the operation panel (or remote controller) and input of the set pressure value P0 and the detected low pressure value P are performed at regular intervals.
In step 4, the pressure deviation P-P0 and the pressure change speed dP
/ Dt (= P-P ') is calculated. Then, fuzzy inference is performed in step 5 based on the pressure deviation P-P0 and the pressure change rate dP / dt.

In this fuzzy inference, the pressure deviation P-P0
The degree of establishment of the membership function for the antecedent part is determined based on the pressure change rate dP / dt, and the membership function for the antecedent part is weighted based on the degree of establishment, and the weighted value of the membership function for the antecedent part is determined. Is used to determine the fuzzy inference value F0.

Next, at step 6, it is determined whether or not F0 <L1 is satisfied.
Turn on / off the compressors 1a, 1b, 1c
OFF is determined. If F0 <L1 does not hold, the process proceeds to steps 8 and 9, where the current operating capacity HP0 is set.
And the operating capacity HP1 one step higher than the current compressor 1
Calculated from the ON / OFF states of a, 1b, and 1c, the capability change width k between them is obtained in step 10, and it is determined in step 11 whether F0 / k> L2 is satisfied. If this is established, in step 12, ON / OFF of the compressors 1a, 1b, 1c is determined so as to increase the operation capacity by one step.
If F0 / k> L2 is not satisfied, the current driving capability is maintained. Thereafter, in step 13, the input detected low-pressure pressure value P is made the previous detected low-pressure pressure value P '.

The above operation is repeated at regular intervals.
The cycle of this repetition is preferably equal to or longer than the time during which the low pressure of the refrigerant in the refrigeration cycle is stabilized after switching ON / OFF of the compressor, and equal to or shorter than the time that causes a control delay problem. For example, 20 to 30 seconds is appropriate. In addition,
The detected pressure 2 to 3 minutes ago may be used as the previous detected low pressure value P ′.

[0021]

As described above, according to the present invention,
Since the fuzzy inference based on the pressure deviation of the refrigerant low pressure and the pressure change rate is performed, it is possible to cope with various kinds of loads, and to achieve stable and detailed control.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a control device according to the present invention.

FIG. 2 is a diagram showing a relationship between a combination of ON / OFF of a compressor and an overall operation capability.

FIG. 3 is a diagram illustrating a determination method of a step control unit in FIG. 1;

FIGS. 4A, 4B and 4C are diagrams showing examples of membership functions used for fuzzy inference in the embodiment of FIG. 1;

FIG. 5 is a diagram showing an example of a rule used for fuzzy inference in the embodiment of FIG. 1;

FIG. 6 is a diagram showing an example of fuzzy inference using the MIN-MAX method which can be used in the embodiment of FIG. 1;

FIG. 7 is a flowchart showing the operation of the embodiment of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Compressor unit 1a, 1b, 1c Compressor 19 Pressure sensor 21 Signal processing unit 23 Fuzzy inference unit 25 Step control unit

Claims (1)

(57) [Claims] A refrigeration cycle in which a plurality of compressors having different rated operation capacities are connected in parallel, a condenser, a decompression device, and an evaporator are connected in a ring by a refrigerant pipe; In a refrigeration cycle control device configured to change the operation capacity of the entire compressor unit in a step-like manner by combining ON / OFF, a pressure detection means for detecting a low pressure of a refrigerant in the refrigeration cycle;
Pressure setting means for setting a set pressure; and ON / O of the plurality of compressors so that the low pressure becomes the set pressure.
A signal for changing the combination of FF and a control arithmetic unit for outputting to the compressor unit, the control operation unit pressure deviation and the pressure change between the low pressure and the set pressure
Fuzzy inference based on speed and fuzzy inference value
Output, this fuzzy inference value and two preset large and small
Compared to the value of
The value obtained by dividing the fuzzy inference value by the value is the value of the two large and small
If the value is greater than the larger value of the whole unit
Increased the driving ability of the
The inferred value is smaller than the smaller of the two values.
In this case, the operating capacity of the whole unit is
The number of steps is reduced to
A refrigeration cycle control device, which makes a determination to maintain the operating ability of the body at the same step, and outputs a signal for changing the combination of ON / OFF of the plurality of compressors to the compressor unit according to the determination. .