JPH02174593A - Cooling apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention particularly relates to an improvement in a refrigeration system that uses an inverter to control the rotation of a compressor.

[Conventional technology]

A refrigeration system having an inverter controls the rotation of an electric motor that drives a refrigerant compressor by changing the power frequency. By controlling the rotational speed of the compressor in this way, the refrigerating capacity can be changed continuously.

FIG. 3 is a block diagram showing an example of a conventionally commonly used refrigeration system having an inverter, in which refrigerant compressed by a compressor 1 is condensed in a condenser 2 and then expanded in an expansion valve 3. , is evaporated and cooled in the evaporator 4, and is connected in a closed loop with a pipe so that it is returned to the compressor 1.
It constitutes a refrigeration cycle.

On the other hand, 5 is an inverter that changes the frequency of the commercial power source and outputs it. The compressor 1 is driven by supplying the compressor 1.

The electromagnetic contactor 8 and the overcurrent detector 9 are connected in series to a power line between the inverter 5 and the motor of the compressor 1.

Further, the refrigerant pressure on the low pressure side of the compressor 1 is detected by the pressure detection section 7, and the detected output is outputted to the damper output section 6. The control unit 6 is configured to control the output frequency of the inverter 5 according to this detection output.

Next, the operation will be explained. When a power switch (not shown) is turned on, the electromagnetic contactor 8 is closed and the inverter 5
The electric power output from the compressor 1 is supplied to the electric motor (not shown) of the compressor 1, and the compressor 1 is operated.

When compressed refrigerant flows through the refrigeration cycle by operating the compressor 1, cooling is performed by the evaporator 4 as is well known.

Here, when the refrigeration load decreases, the refrigerant pressure on the low pressure side of the refrigeration cycle decreases, and the level of the pressure detection signal output from the pressure detection section 7 to the control section 6 also decreases accordingly.

Since the control section 6 compares the pressure detection signal with the reference value, if the pressure detection signal is lower than the reference value, the control section 6 controls the inverter 5 so that the output frequency is lowered, By lowering the rotation speed of the compressor 1, the cooling capacity is lowered.

In this way, when the cooling capacity is lowered, the refrigerant pressure on the low pressure side of the refrigeration cycle increases and converges to the set pressure.

Further, when the cooling load is high, the refrigerant pressure on the low pressure side of the refrigeration cycle increases, and the pressure detection signal output from the pressure detection section 7 to the control section 6 increases accordingly.

As a result, the control unit 6 controls the inverter 5 so that its output frequency increases, and increases the rotational speed of the compressor 1, thereby increasing the cooling capacity.

Therefore, in a refrigeration system having such an inverter 5, the cooling capacity can be controlled according to the cooling load, and power saving can be achieved.

[Problem to be solved by the invention]

Since the conventional refrigeration system is configured as described above, the output frequency of the inverter 5 when the compressor 1 is restarted after being stopped is fixed at, for example, 40 Hz,
When the refrigeration cycle is stopped, the refrigerant pressure on the low pressure side of the refrigeration cycle increases,
When the pressure detection signal becomes much higher than the reference value, it takes a long time to reach the target refrigerant pressure, which causes the temperature of the cooled object to rise and has the disadvantage that the freshness of the cooled object is not maintained. .

Furthermore, if the refrigerant pressure on the low-pressure side of the refrigeration cycle increases when the compressor 1 is stopped, and the pressure detection signal is almost the same as the reference value, the refrigerant pressure on the low-pressure side will suddenly decrease when the compressor 1 is restarted. This has the disadvantage that the interval between starting and stopping of the compressor 1 becomes shorter, and the life of the compressor 1 becomes shorter.

This invention was made to solve the above-mentioned problems, and aims to provide a refrigeration system that can quickly reach a predetermined pressure and reduce power consumption.

[Means to solve the problem]

The refrigeration system according to the present invention includes: a pressure detection unit that detects refrigerant pressure on the low pressure side of a refrigeration cycle and generates a pressure detection signal; a fuzzy control unit that performs fuzzy inference based on the pressure detection signal; A frequency control section is provided that controls the output frequency of the inverter so that the refrigerant pressure on the low pressure side converges to a predetermined value in accordance with the output fixed value signal.

[For production]

According to the pressure difference between the refrigerant pressure detection signal on the low pressure side of the refrigeration cycle detected by the pressure detection part and the refrigerant pressure to be converged, the fuzzy control part performs fuzzy inference on the inverter output frequency. The refrigerant pressure is made to reach a predetermined pressure by outputting a determined value and controlling the output frequency of the inverter using the frequency control section.

[Example] Hereinafter, an example of the refrigeration apparatus of the present invention will be described based on the drawings. FIG. 1 is a block diagram showing one embodiment of the present invention, and the same parts as in FIG. 3 are denoted by the same reference numerals to avoid redundant explanation of the structure.

In this FIG. 1, the parts indicated by symbols 1 to 5, and 7 to 9 are the same as in FIG. The inverter output frequency during the compressor operation is controlled based on a fixed value signal output from the fuzzy control section 11 which performs fuzzy inference according to the pressure difference between the refrigerant pressure and the refrigerant pressure.

Next, the fuzzy control section 11 according to the present invention will be explained below. The fuzzy control unit 11 performs forward fuzzy inference (-sulfurized Modus Bonens) and draws a conclusion.

The rules are four production rules, listed as the following rules ■ to rule ■.

Rule ■ If the detected pressure is much higher than the set pressure, increase the output frequency more, Rule■ If the detected pressure is a little higher than the set pressure, increase the output frequency a little, Lulu■ The detected pressure is the set pressure If the detected pressure is much lower than the set pressure, reduce the output frequency a little. Rule ■ If the detected pressure is much lower than the set pressure, reduce the output frequency even more. The extent to which the pressure detection signal, which is a fact, matches the antecedent part of the rule is checked using a preset linear function. Next, the consequent part of the rule is adopted depending on the degree to which the above-mentioned fact matches the conditions of the rule.

Naturally, the consequent of the rule is cut when there is a certain degree of match. Using this idea, we obtain inference results for each rule,
Take the logical sum of the four rules. Finally, defuzzification is performed to take the center of gravity of the menhashic function that represents the final inference result.

The details will be explained with reference to FIG. First, let us assume that there is a fact that the low pressure is now higher than the set temperature (target value). Consider the extent to which this fact matches the antecedent part of Rule ■, "If the pressure is much higher than the set pressure."

As shown in Figure 2 (a), the peak value of the overlapping part (hatched area) of the two menhash functions is the grade of soft matching, and the degree to which the fact matches (matches) the rule ■ (grade) For example, it is 0.7.

Next, according to the grade of soft matching of the antecedent part, rule (2), which is the consequent part, "increase the frequency more" is adopted. In other words, α cut (remove the head) the consequent by 0.7.
However, only the two shaded areas in FIG. 2 [el] are adopted. This is the inference result obtained from the facts and the rule■.

In the same way, Fig. 2 (overlapping partial opening of bl, Fig. 2 (
The overlapped part C1 of C1, the hatched part E of Fig. 2 ffl corresponding to the case where there is no overlapped part of Fig. 2 (d+), the hatched part of Fig. 2 (gl), the hatched part of Fig. 2 (h) As in the case without the shaded area, make inferences between the rules ■, ■, ■ and the facts, and take the logical sum of the obtained results (Figure 2 (1)
) Based on this result, the center of gravity k in Figure 2 (1) is determined as a definite value.
(perform defasification of fuzzy inference) and set the value at this center of gravity as the definite value.

The determined value outputted here is input to the frequency control section 10 to change the current frequency, and is input to the inverter 5 to control the rotation speed of the compressor 10.

〔Effect of the invention〕

As described above, according to the present invention, the pressure detection unit detects the refrigerant pressure on the low pressure side of the refrigeration cycle, and the fuzzy control unit performs fuzzy inference in response to the pressure detection signal and outputs a determined value. However, the frequency controller is configured to control the output frequency of the inverter so that the refrigerant pressure on the low pressure side converges to a predetermined set value based on the determined value.
The inverter output frequency of the compressor can be controlled according to the pressure difference between the pressure detection signal and the target refrigerant pressure to be converged. It has the effect of maintaining the freshness of the food.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a refrigeration system according to an embodiment of the present invention;
FIG. 2 is a diagram showing soft matching and defuzzification according to the present invention, and FIG. 3 is a configuration diagram of a conventional refrigeration system. 1... Compressor, 2... Condenser, 3... Expansion valve, 4
. . . Fuji generator, 5. Inverter, 7. Pressure detection section, 10. Frequency control section, 11. Fuzzy control section. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] A refrigeration cycle consisting of a variable wave number inverter, a compressor driven by the output of this inverter, a condenser, an expansion valve, and an evaporator connected in a closed loop, and the refrigerant pressure on the low pressure side of this refrigeration cycle. a pressure detection unit that detects the pressure and generates a pressure detection signal, a fuzzy control unit that performs fuzzy reasoning so that the refrigerant pressure on the low pressure side converges to a predetermined set value in response to the pressure detection signal, and this fuzzy control a frequency control section that controls an output frequency of the inverter based on a determined value output from the section.