JPH0360028B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a refrigeration system, and more particularly to an improvement of a refrigeration system that uses an inverter to control the rotation of a compressor.

[Prior art]

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

FIG. 1 is a block diagram showing an example of a conventionally commonly used refrigeration system having an inverter, in which 1 is a compressor for compressing refrigerant, 2 is a condenser, and 3
4 is an expansion valve, and 4 is an evaporator, which are connected to a closed loop via a pipe to constitute a refrigeration cycle. Reference numeral 5 denotes an inverter that outputs a variable frequency of the commercial power supply, and 6 a control unit that controls the inverter 5 in accordance with an output signal from a pressure detection unit 7 that detects the refrigerant pressure on the low pressure side of the compressor 1. 8 is an electromagnetic contactor provided on the power line connecting the inverter 5 and the compressor 1, and 9 is an overcurrent relay similarly provided in series with the power line.

In the conventional refrigeration system configured as described above, when a power switch (not shown) is turned on, the electromagnetic contactor 8 is closed and the power output from the inverter 5 is supplied to the electric motor (not shown) of the compressor 1. , 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 detector 7 to the control unit 6 also decreases accordingly. The control unit 6 compares the pressure detection signal with the reference value, so if the pressure detection signal is lower than the reference value, the control unit 6 controls the inverter 5 so that the output frequency decreases, and the compression By lowering the rotation speed of machine 1, the cooling capacity is lowered. When the cooling capacity is lowered in this way, 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
The cooling capacity is increased by controlling the output frequency of the compressor 1 to increase the rotational speed of the compressor 1.

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.

However, in the conventional refrigeration equipment described above, when the refrigerant pressure fluctuates greatly, or when the refrigerant pressure is higher than the refrigerant pressure to be converged, such as at the start of operation or during pulldown after defrosting, the inverter Since the setting time of the output frequency of No. 5 is constant, it takes a long time to reach the target refrigerant pressure, which causes the temperature of the object to be cooled to rise and the freshness of the object to be cooled to be cooled to be not maintained.

[Summary of the invention]

This invention solves the conventional problems as described above, and detects the refrigerant pressure on the low pressure side, converges the refrigerant pressure to a predetermined value, and detects the pressure difference between the pressure detection signal and the refrigerant pressure to be converged. By controlling the output time of the inverter output frequency, that is, the time until the inverter output frequency is changed according to the It is an object of the present invention to provide a refrigeration system that can quickly reach a predetermined pressure and reduce power consumption.

[Embodiments of the invention]

FIG. 2 is a block diagram showing an embodiment of the refrigeration system according to the present invention, and the same parts as in FIG. 1 are indicated using the same symbols. In the figure, 10 is a frequency setting section, which sets the inverter output frequency according to the pressure difference between the pressure detection signal output from the pressure detection section 7 and the refrigerant pressure to be converged. Further, 11 is a time setting section,
The time for outputting the frequency set by the frequency setting section 10 is determined according to the pressure difference between the output detection signal output from the pressure detection section 7 and the refrigerant pressure to be converged. 12 is a frequency output circuit that outputs a frequency output signal to the inverter 5, and is configured to output the frequency set by the frequency setting section 10 for a period of time set by the time setting section 11. ing. here,
As shown in the flowchart of FIG. 3, the time setting unit 11 determines the time required for changing the inverter output frequency, which is the pressure difference between the pressure detection signal output from the pressure detection unit 7 and the refrigerant pressure to be converged. It can be changed freely depending on the situation. That is, when the pressure difference between the pressure detection signal output from the pressure detection unit 7 and the refrigerant pressure to be converged is large, the output time of the inverter output frequency is
If the pressure difference between the pressure detection signal output from the pressure detection unit 7 and the refrigerant pressure to be converged is small, the output time of the inverter output frequency can be set to 5 seconds.

Moreover, the refrigerant pressure in the operating state is constantly detected and compared with the refrigerant pressure to be converged.
Depending on the pressure difference, the output time changes to, for example, 1 second, 2 seconds, . . . 5 seconds, and the refrigerant pressure is converged. The detected refrigerant pressure until convergence does not change more than the refrigerant pressure to be converged, and quickly reaches the predetermined pressure. After reaching the predetermined pressure, the compressor 1 continues to operate at the frequency at which the predetermined pressure was reached.

〔Effect of the invention〕

As explained above, the refrigeration system according to the present invention constantly detects the pressure detection signal output from the pressure detection section and the refrigerant pressure to be converged, and the output time of the inverter output frequency is set according to the pressure difference. This allows the predetermined pressure to be quickly reached even when there are large pressure fluctuations or when the cooling load is large, such as at the start of operation or after defrosting, reducing power consumption and reducing the temperature of the cooled object. It becomes constant and freshness is maintained.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a conventional refrigeration system, FIG. 2 is a block diagram showing an embodiment of the refrigeration system according to the present invention, and FIG. 3 is a flowchart showing the operation of a time setting section. 1... Compressor, 2... Condenser, 3... Expansion valve,
4... Evaporator, 5... Inverter, 6... Control section, 7... Pressure detection section, 10... Frequency setting section,
11...Time setting section, 12...Frequency output circuit.
In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A refrigeration cycle configured by connecting a compressor, a condenser, an expansion valve, and an evaporator in a closed loop; an inverter that varies the power frequency and supplies it to an electric motor that drives the compressor; A pressure detection unit that detects the refrigerant pressure on the low pressure side of the cycle and generates a pressure detection signal, and an inverter output frequency that sets the refrigerant pressure on the low pressure side to a predetermined set value according to the pressure detection signal. and a time setting section that controls the output time of the output frequency of the inverter according to the pressure difference between the pressure detection signal and the refrigerant pressure to be converged. .