JPH0360027B2 - - 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 also 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 driven. When compressed refrigerant flows through the refrigeration cycle by operating the compressor 1, it is cooled by the evaporator 4 as is well known.

Here, when the cooling 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 range of change in the output frequency of No. 5 is constant, it takes a long time to reach the target refrigerant pressure, the temperature of the object to be cooled increases, and the freshness of the object to be cooled is not maintained.

[Summary of the invention]

This invention solves the conventional problems as described above. It detects the refrigerant pressure on the low pressure side and converges the refrigerant pressure to a predetermined value, and also detects the pressure difference between the pressure detection signal and the refrigerant pressure to be converged. depending on,
By controlling the range of change in the inverter output frequency, it is possible to quickly reach the desired pressure and reduce power consumption even when pressure fluctuations are large or when the cooling load is large, such as at the start of operation or after defrosting. It is an object of the present invention to provide a refrigeration device that does the following.

[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, reference numeral 10 denotes a frequency setting section, which sets the frequency so that the refrigerant pressure on the low pressure side converges to a predetermined setting value in response to a pressure detection signal from the pressure detection section 7. Reference numeral 11 denotes a frequency change width setting section, which controls the change width of 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.
Reference numeral 12 denotes a frequency output circuit that outputs a frequency output signal to the inverter 5 by the frequency change width setting section 10 of the frequency setting section 10.

Here, as shown in the flowchart of FIG. 3, the frequency change width setting section 11 sets the change width of the inverter output frequency to the pressure detection signal output from the pressure detection section 7 and the refrigerant pressure to be converged. It can be freely changed according to the pressure difference. In other words, when the pressure difference between the pressure detection signal output from the pressure detection section 7 and the refrigerant pressure to be converged is large, the inverter output frequency is changed every 5 Hz to reduce the pressure output from the pressure detection section 7. When the pressure difference between the detection signal and the refrigerant pressure to be converged is small, the inverter output frequency can be changed every 1 Hz.

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 frequency change width is, for example, 5Hz,
4Hz...1Hz changes to converge the refrigerant pressure.
Until this convergence, the detected refrigerant pressure does not change more than the refrigerant pressure to be converged,
Reach the predetermined pressure quickly. 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 determines the range of change in the inverter output frequency according to the pressure difference. Therefore, even when there are large pressure fluctuations or when the cooling load is large, such as at the start of operation or after defrosting, the predetermined pressure can be quickly reached, reducing power consumption and keeping the temperature of the object to be cooled. 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 frequency change range 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... Frequency change width setting section, 12... Frequency output circuit. Note that the same reference numerals in the figures 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, and the refrigeration cycle described above. a pressure detection section that detects the refrigerant pressure on the low pressure side of the controller and generates a pressure detection signal; and a frequency setting that sets the inverter frequency so that the refrigerant pressure on the low pressure side converges to a predetermined set value according to the pressure detection signal. A refrigeration system comprising: a frequency change width setting section that controls a change width of an inverter output frequency according to a pressure difference between the pressure detection signal and a refrigerant pressure to be converged.