JPS60253761A - Method of controlling operation of refrigerator - 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]

This invention relates to an operation control method for a refrigerator used in refrigeration equipment such as refrigeration and refrigerated showcases, and in particular, the refrigerator is configured with a multi-compressor unit, and the multi-compressor unit is controlled by an inverter to compensate for fluctuations in refrigeration load. The present invention relates to an operation control method for a refrigerator that performs refrigerating capacity control accordingly.

[Prior art and its problems]

Since refrigeration equipment such as oven showcases has large fluctuations in refrigeration load throughout the year, recently a multi-compressor unit consisting of multiple compressors has been used as a refrigeration machine, and each refrigeration machine is An operation control method that controls the capacity of the refrigerator in response to fluctuations in the refrigeration load by turning on and off the refrigerator is widely used. In addition, recently, for open showcases for meat, fresh fish, etc. that place emphasis on product temperature control, we have changed from the conventional thermostat on/off control method to adjusting the compressor rotation speed according to refrigeration load fluctuations. An inverter control method that adjusts the refrigerating capacity by changing the cooling capacity is increasingly being adopted. In other words, as is well known, the evaporation pressure in the refrigeration cycle changes depending on the increase or decrease in the refrigeration load.When the refrigerator is operated under certain conditions, when the refrigeration load decreases, the evaporation temperature, that is, the evaporation pressure, decreases, and conversely, the evaporation pressure decreases. As the load increases, the evaporation pressure increases. Therefore, set the compressor suction pressure equivalent to the evaporation pressure corresponding to the rated refrigeration load in advance, and when the detected suction pressure value becomes lower than the set value,
The output frequency of the inverter installed in the compressor's power supply circuit is lowered than the commercial frequency, thereby lowering the rotational speed of the electric compressor and reducing the refrigeration capacity. By doing so, the refrigeration capacity can be finely tuned to follow refrigeration load fluctuations. The temperature inside the showcase can be maintained almost constant. The compressor can also be turned on by inverter control. In addition to preventing off-state losses and rush current, compressor power consumption is proportional to the rotation speed, so when performing low rotation operation control under low refrigeration load conditions, it is possible to reduce power consumption compared to commercial frequency operation. The effect of saving power consumption can be obtained. Next, FIG. 4 shows a refrigeration circuit of an oven showcase employing the above multi-combiner unit, and FIG. 5 shows its conventional operation control circuit. First, in Fig. 4, IA and IB are electric compressors, 2 is a condenser, 3 is an expansion valve, 4 is an evaporator installed in the showcase, 5 is an accumulator, and compressors IA and IB are in the circuit. They are interposed by connecting piping in parallel. Note that 6 is a pressure sensor for detecting suction pressure connected to the compressor suction side of the circuit. In the operation control circuit shown in FIG. 5, 7 is a commercial frequency power supply, 8 is an inverter as a frequency converter, 9 is a regulator that controls the inverter 8 by inputting the detected value of the pressure sensor 6, and 10 is a regulator. Compressor IA, IB
operation and stop control circuits, and 51C+ and 51Cg are electromagnetic contactors installed in the power supply circuits of compressors LA and IB, 63
L+, 63Lz are low pressure switches for compressors IA and IB,
X is an auxiliary relay that is activated by a signal given from the regulator 9 when the inverter 8 is abnormal. Next, the operation control operation of the refrigerator by the above-mentioned circuit will be explained together with the operation characteristic diagram shown in FIG. First, the case load is 100
%, the output frequency of the inverter 8 is set to 60Hz, which is the same as the commercial frequency, and both compressors IA and IB are operated at the commercial frequency, and the rated value is the intersection of the characteristic line of 100% refrigeration capacity and 100% case load. Cooling operation is performed at matching point ■. If the case load decreases here, the compressor I
Compressor IB operates under inverter control while B operates at commercial frequency, and the inverter output frequency is 30Hz, that is, up to point ■ on the characteristic line of refrigeration function cuff 5%, refrigeration is performed under constant pressure according to case load fluctuations. Machine capacity control is performed. When the case load further decreases from here, the suction pressure exceeds the constant pressure control range and fluctuates along the characteristic line of 5% refrigeration function cuff as the case load decreases. If the case load further decreases, the suction pressure becomes less than the cutout setting value of the low pressure switch 63L2 at point (3), the contact of the low pressure switch is turned off, and the compressor IB is stopped. At this point, the output frequency of the inverter remains the original 30Hz, so the refrigeration function is temporarily reduced to the point on the 25% characteristic line.
However, after that, the rotation speed of the compressor IA is increased by inverter control to a point (3) that balances with the case load at that time, thereby increasing the refrigerating function. When the case load further decreases from here, the compressor IA follows the steps ①-② and performs refrigeration function control. On the other hand, if the case load increases from point ■, the suction pressure becomes higher than the cut-in pressure setting value of the low pressure switch 63L, compressor IB returns to commercial frequency operation, and the refrigeration function temporarily increases to 100% point ■ From this point, the compressor IA is impark controlled so as to move to a point where it balances with the case load. Further, when the case load decreases extremely, the suction pressure decreases to the cutout pressure setting point (3) of the low pressure switch 63L, and the operation of the compressor IA is controlled so as to stop after pumping down. In addition, in the event that the inverter breaks down during operation, the auxiliary relay
Contacts Xa and Xb inserted in the compressor IA power supply circuit are switched to remove the inverter 8 from the circuit, and the compressor IA receives power directly from the commercial frequency power supply 7 and enters commercial frequency operation, and normal operation control by a thermostat is performed. A protection circuit is configured to ensure that As is clear from the above explanation, the case load exceeds the range of constant pressure control by inverter control and the case load is 75% to 50%.
%, the suction pressure changes with decreasing case load. Therefore, a change in suction pressure, that is, evaporation pressure, directly results in a change in the temperature inside the showcase, which in turn causes a change in the temperature of the products stored in the refrigerator. Generally, a change in evaporation temperature of 1 deg will reduce the product temperature by approximately 0.6 d.
eg change. From this point of view, in order to fully utilize the advantages of the operation control method using inverter control, it is recommended that the fluctuation range of the suction pressure be as small as possible (for this purpose, the low pressure switch 63
It is preferable that the differential between the cut-out and cut-in pressure settings of L+163Lz is set as small as possible unless it causes operational problems. On the other hand, if the differential mentioned above is made extremely small,
Even a slight change in the refrigerating load results in so-called short-cycle operation in which the compressor repeatedly turns on and off, which affects the life of the compressor. Here, we show the appropriate operating pressure setting value of the low pressure switch during inverter control operation for model machines for showcases for meat and fresh fish, as shown in the lower part of Figure 6, obtained from actual machine operation results. Low pressure switch 6 of compressor IA on inverter control operation side
For 3t+, the cant-out and cut-in pressure settings are 1.4 and 2.4 kg/dc, respectively, and the differential is 1.0 kg/ad.The low pressure switch of compressor IB on the commercial frequency operation side Regarding 63L2, the cut-out and cut-in pressure settings are respectively 1.8 and 2.6 kg/csIG, and the differential is 0.8 kg/cd. By the way, as mentioned above, when inverter-controlled operation is performed with the differential of the operating pressure setting value of the low-pressure switch fixedly set to a narrow width, there is a possibility that the inverter should malfunction during operation. When switching from inverter control operation to commercial frequency operation, even a slight change in case load will cause the suction pressure to fluctuate beyond the cant-out and cut-in pressure settings of the low pressure switch 63L+t, especially in the intermediate refrigerating load operation range. for,
Compressor IB frequently turns on and off, resulting in short cycle operation. That is, as shown in Fig. 7, when the case load is 100% and both compressors IA and 1B are operated at the commercial frequency, the case load is reduced to, for example, 80%.
When the suction pressure decreases to 50%, the low pressure switch 63Lz lowers the suction pressure to below the cutout pressure set value and the compressor IB temporarily stops, but on the other hand, the refrigeration function decreases to 50%, so the suction pressure goes back to the low pressure switch 63Lz. 63Lz cuff) The pressure rises above the set value and the circulation is repeated along 10-■-■. In other words, there is no balance between the case load and the refrigeration function, and the refrigeration IB operates in a short cycle, frequently repeating on and off cycles. As a result, there is a risk that the life of the compressor will be shortened, the motor windings of the compressor will be burnt out due to an abnormal temperature rise, and fatigue failure will occur due to shock during restart.

[Purpose of the invention]

This invention was made in consideration of the above points, and its purpose is to eliminate the drawbacks of conventional operation control methods, and to fully utilize the advantages of inverter control during inverter control operation to improve the product temperature in the showcase. Refrigerating machine operation control that suppresses changes and allows operation to be controlled without shifting the chiller to short cycle operation in the unlikely event that an inverter failure occurs during operation and switching to commercial frequency operation. The goal is to provide a method.

[Key points of the invention]

In order to achieve the above object, the present invention provides 11 parts of the refrigeration circuit.
:#am■ Entering l:I: Rikimoto Seiji Aji Yushufu! The differential setting range of the cut-in and cant-out pressure settings of the low pressure switch for on/off control of the compressor that makes up the Puma 1!7 Ki1 compressor unit is set to a small value during inverter control operation, to prevent inverter failure. During commercial frequency operation associated with this, the setting range of the differential of the low pressure switch is changed over a large range to control the operation.

[Embodiments of the invention]

Figure 1 shows an operation control circuit for implementing the operation control method of the present invention, and Figures 2 and 3 respectively show the operating pressure setting values of the low pressure switch for inverter control operation and commercial frequency operation in Figure 1. It shows. First, in Fig. 1, the operation control circuit of the multi-compressor unit includes each compressor IA whose operating pressure setting value is set as shown in Figs. 2 and 3 in accordance with inverter control operation and commercial frequency operation. Low pressure switches for operation control attached to IB 63t, ++, 63Lz+, and 631;lt,
63Ltz are inserted and connected to the circuits of electromagnetic contactors 51C+ and 51Cz as shown through contacts χ and χ2 of auxiliary relays X, which respectively operate in response to a signal given when an abnormality occurs in inverter 8. Here, as for the low pressure switches 63L++ and 63Lt+ on the inverter control operation side, as shown in FIG. 2, the operating pressure setting values are the same as those shown in FIG. 6 above. On the other hand, for the low pressure switches 63Llz and 63Lz□ on the commercial frequency operation side, the cut-in pressure setting value of the operating pressure setting value is set to 3.0 as shown in Figure 3.
, 3.2kg/aaG, cutout pressure setting value 1.
4.1.6kg/c4 G, the differential setting width is set to 1.6kg/aa. In the above configuration, during inverter control operation when inverter 8 is normal, contact XI+ x of auxiliary relay
is in the position shown, and is the low pressure switch 63L++. 63Lt+ is selected, and as described in FIG. 6, inverter control operation is performed following fluctuations in the refrigeration load. On the other hand, if inverter 8 should fail during this operation, auxiliary relay X is activated based on the detected abnormality, and its contact Xa
The inverter 8 is short-circuited and the compressor IA is switched to commercial frequency operation, and the contact χl+Xg is switched to the low pressure switch 63L+g. 63L is selected and inserted into the circuit. Here, as mentioned earlier, the low pressure switch 63L+z=63 on the commercial frequency operation side
The differential of Lgz is larger than the low pressure switches 63L++, 63Lz+ on the inverter control operation side, so even if there is some fluctuation in the refrigeration load in the intermediate refrigeration load operation range, the suction pressure will be lower than the low pressure switch 63L+z.
Compression 1 because the cutout pressure does not drop below the set value
Although the IIB continues to operate and fluctuations in the suction pressure and therefore the evaporation pressure become larger than during inverter-controlled operation, operation control is performed without easily shifting to so-called short-cycle operation. Low pressure switch 63L+z, 63Lz□ on the commercial frequency operation side
is configured as a mechanical contact type low pressure switch connected to the compressor suction side of the refrigeration circuit, or as an electronic contact type switch incorporated in the regulator 9 that is activated based on the detected value of the pressure sensor 6. You can also do that.

【Effect of the invention】

As described above, according to the present invention, in a multi-compressor unit consisting of electric compressors of the same type, at least one compressor is operated under inverter control, the other compressors are operated at commercial frequency, and the refrigeration cycle is controlled. The suction pressure is used as a control detection value, and in combination with the on/off operation of each compressor to turn on and off the low pressure switch, and the compressor rotation speed control by inverter control, the capacity of the chiller can be adjusted in accordance with fluctuations in the chiller load. In the operation control method of the refrigerator, the differential setting range of the cut-in and cant-out pressure setting values of the low pressure switch is set to a small value during inverter control operation, and the low pressure that occurs during commercial frequency operation due to inverter failure is set to a small value. By controlling the operation by changing the differential setting range of the switch to a large value, during normal inverter control operation, the differential setting range of the low pressure switch pressure setting value is narrowed to prevent refrigeration load fluctuations in the intermediate load range. This suppresses changes in evaporation pressure, that is, changes in temperature of products in the showcase,
On the other hand, if the inverter is activated during operation, it is possible to prevent damage to the compressor by preventing the shift to short-cycle operation. A useful refrigerator operation control method can be provided.

[Brief explanation of drawings]

Fig. 1 is an operation control circuit diagram of a refrigerator according to an embodiment of the present invention, and Figs. 2 and 3 show operating pressure settings of the low pressure switch on the inverter control operation side and commercial frequency operation side in Fig. 1, respectively. Figure 4 is a refrigeration circuit diagram of a refrigerator that uses a multi-compressor unit.
FIG. 5 is a conventional refrigerator operation control circuit diagram, and FIGS. 6 and 7 are diagrams of operating characteristics of the refrigerator under inverter control and commercial frequency operation, respectively. IA, IB; Compressor, 6: Pressure sensor, 7: Commercial frequency power supply, 8: Inverter, 9: u @ controller, 10: Operation control circuit, 51C+, 51Cz: Magnetic contactor, 63L
I ++ 63Lit: Low pressure switch on the inverter control operation side, 63L+z, 63L2□: Low pressure switch on the commercial frequency operation side, X: Auxiliary relay that operates when the inverter is abnormal. Figure 3 Figure 5

Claims (1)

[Claims] 1) Out of a multi-compressor unit consisting of a plurality of electric compressors installed in a refrigeration circuit by connecting pipes in parallel to each other, at least one compressor is operated under in-hark control; By operating the compressor at a commercial frequency and using the suction pressure of the refrigeration cycle as the control detection value, the system operates and stops each compressor by turning on and off the low pressure switch, and controls the rotation speed of the compressor by controlling the inverter. In a refrigerating machine operation control method that controls the capacity of the refrigerating machine in accordance with fluctuations in the refrigerating load, the differential setting range of the cut-in and cut-out pressure setting values of the low pressure switch is set to a small value during inverter control operation. An operation control method for a refrigerator, characterized in that the operation is controlled by greatly changing the differential setting width of the low pressure switch during commercial frequency operation due to an inverter failure. 2. In the operation control method described in claim 1, the operation control circuit of the multi-compressor unit has its operating pressure set value corresponding to inverter control operation and commercial frequency operation due to inverter failure. A low pressure switch is provided for each set compressor, and the low pressure switch for inverter control operation is normally selected, and when the inverter fails, the low pressure switch for commercial frequency operation is selected and connected to the circuit. Operating the refrigerator