JPH0535336B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a refrigeration system used in a prefabricated low-temperature refrigerator or the like, and particularly relates to an operation control device for a compressor and a heater that constitute the refrigeration system.

(b) Prior art For example, Japanese Utility Model Application No. 58-188554 discloses a plurality of refrigeration cycles each having a variable capacity compressor, and one inverter circuit for driving the drive motor of each compressor. and a plurality of switches that selectively form an energization path from the inverter circuit to each of the drive motors or from the power source to each of the drive motors, and control of each of the switches according to the size of the load. Also shown is a refrigeration cycle device including a control unit that controls an inverter circuit.

(c) Problems to be Solved by the Invention In the above conventional technology, for example, when the ambient temperature is low in winter, the load is small and only one refrigeration cycle is operated, and furthermore, the compression of this one refrigeration cycle is reduced. When the drive motor of the machine reaches its lower limit of operation, if the cooling capacity of the refrigeration cycle still exceeds the load, the indoor temperature will drop below the set temperature and the quality of the products stored indoors will deteriorate. A problem had occurred. The present invention aims to solve the above-mentioned problems and to improve temperature control during low load.

(d) Means for Solving the Problems The present invention has been made to solve the above problems, and will be explained below based on an example. , a first frequency and a second frequency lower than this first frequency.
a controller 10 that outputs a frequency signal between the two frequencies; an inverter circuit 11 that inputs the frequency signal from the controller 10 and outputs frequency-controlled power to the compressor 2; When the frequency calculated by the controller 10 becomes slightly lower than the second frequency, the power is supplied by the output from the controller 10, and when the frequency becomes slightly higher than the second frequency, the The present invention provides an operation control device for a refrigeration system that includes a heater 8 that is de-energized by an output from a controller 10.

(e) Effects According to the embodiment, when the cooling load is small, such as during winter, the temperature inside the refrigerator gradually decreases and the calculated value of the controller 10 also gradually decreases. Then, the calculated value becomes the second frequency, the compressor 2 starts operating at the lowest frequency, and the calculated value becomes the second frequency.
When the third frequency is several Hz lower than the frequency, the controller 10 operates to start energizing the heater 8 and start controlling the energization time based on the temperature inside the refrigerator, and from then on, as the temperature inside the refrigerator rises, the above calculation is performed. When the value reaches a fourth frequency that is several Hz higher than the second frequency, the controller 10 operates to stop energizing the heater and shift the compressor 2 from the lowest frequency operation to the operation based on the calculated value, When the calculated value is between the third frequency and the fourth frequency, the lowest frequency operation of the compressor 2 and the energization of the heater 8 are performed in parallel, and the third frequency and the fourth frequency that straddle the second frequency are The surplus cooling heat amount and the heat generation of the heater are offset between the four frequencies, and stable temperature control in the refrigerator is performed.

(F) Embodiment Hereinafter, an embodiment of the present invention will be described in detail based on the drawings.

Reference numeral 1 shown in FIG. 1 is a low-temperature refrigerator which is a prefabricated refrigerator, and A is a refrigeration device for cooling the low-temperature refrigerator.
Here, the refrigeration system A includes, for example, a rotary compressor 2, a condenser C, a refrigerant liquid throttle expansion device 3, and an evaporator 4 installed within the storage, which are connected in a ring shape through refrigerant piping, and a It is composed of blowers 5 and 6, etc. Furthermore, a temperature sensor 7 is installed inside the refrigerator. Incidentally, reference numeral 8 denotes an electric heater, such as a sheathed heater, provided at the lower part of the evaporator 4 for regulating the temperature inside the refrigerator.

10 is a controller that inputs a temperature signal from the temperature sensor 7;
It performs calculations using PID control based on the temperature signal sensed by the sensor, and outputs a frequency signal that is the value resulting from this calculation. Further, 11 is an inverter circuit, which receives a frequency signal from the controller 10 via a frequency signal line 12, and outputs frequency-controlled power based on this frequency signal. This power is then supplied to the compressor 2 via the compressor power supply line 13. Further, 15 is a heater input power supply device, and this heater input power supply device has a built-in solid state relay 16.
A control signal is input from the controller 10 via the heater output control line 17, and energization of the heater 8 is time-controlled based on the signal.

Hereinafter, the operation of the above-mentioned refrigeration system will be explained.
The controller 10 outputs a frequency signal to the inverter circuit 11 based on the temperature signal from the temperature sensor 7, and the frequency signal is output based on the temperature inside the refrigerator, and has a first frequency of 60 Hz and a second frequency of 30 Hz, for example. An arbitrary frequency signal is output between . Note that even if the calculated value based on the internal temperature of the controller 10 is smaller than 30Hz, the controller 1
The frequency signal outputted by 0 is limited to the second frequency of 30Hz. Now, when the calculated value of the controller 10 is, for example, 40Hz, this 40Hz frequency signal is sent to the inverter circuit 11 via the frequency signal line 13,
The inverter circuit 11 outputs 40Hz power determined by the frequency signal to the compressor 2. The compressor 2 is operated based on the power supplied from the inverter circuit 11. Thereafter, the frequency signal output from the controller 10 changes based on the temperature inside the refrigerator, and the frequency of the power supplied from the inverter circuit 11 to the compressor 2 changes, so that the temperature inside the refrigerator reaches approximately the set temperature, for example, in the ice temperature range. The temperature is maintained within the range of -2°C to 0°C.

When the internal temperature is controlled as described above, when the ambient temperature is low in winter, or when a prefabricated refrigerator is installed in a cold region and the ambient temperature is low, the cooling capacity of the refrigeration system is large compared to the cooling load. ,
When the temperature inside the refrigerator tends to be lower than the set temperature, the frequency signal output from the controller 10 gradually decreases. Then, when the calculated value in the controller 10 reaches the second frequency of 30Hz,
The frequency signal becomes 30 Hz, and the compressor 2 starts operating at the lowest frequency using the power from the inverter circuit 11. At this time, if the cooling capacity is still greater than the cooling load and the internal temperature is lower than the set temperature, the calculated value by the controller 10 will be lower than 30 Hz. However, controller 10 is 30
Since the compressor 2 continues to operate at the lowest frequency by continuously outputting the Hz frequency signal, the temperature inside the refrigerator gradually decreases. Then, the calculated value in the controller 10 is slightly lower than the lowest frequency of 30Hz, for example, 2Hz.
When the third low frequency reaches 28 Hz, the controller 10 operates and outputs a control signal to the heater input power supply device 15 via the heater output control line 17,
An on signal is given to the solid state relay 16 of this heater input power supply device, and the heater 8 is energized and generates heat. Here, the heater 8 has a minimum cooling capacity when the compressor 2 is operating at the lowest frequency, that is, a cooling capacity _Q1 when the heater 8 is energized, and an amount of heat dissipated from the low temperature storage to the outside _Q2 (for example, the outside air is 0°C, the inside of the storage (If the set temperature is 9℃, etc., heat will be radiated to the outside of the refrigerator.)
It has a heating capacity W number that is larger than the total value of . That is, the number of required heater W×0.86≧Q ₁ +Q ₂ Kcal/h.

Due to the heat generated by the heater 8, the temperature inside the refrigerator, which had tended to fall below the set temperature, gradually rises, and when the temperature inside the refrigerator stabilizes at the set temperature, the cooling operation by the refrigeration system and the heating operation by controlling the energization time of the heater 8 are resumed. done at the same time. Thereafter, for example, when outside air enters the warehouse due to loading or unloading of stored items, and the internal temperature tends to rise, the calculated value of the controller 10 gradually increases. If the carry-in or carry-out work is completed and outside air infiltration is stopped before the calculated value reaches the heater control stop condition, which is a fourth frequency of 35 Hz, which is slightly higher than the second frequency of 30 Hz, for example, by 5 Hz, The temperature inside the refrigerator tends to decrease due to the cooling operation, and the calculated value of the controller 10 gradually decreases. Furthermore, even when the temperature inside the refrigerator changes as described above, the heater 8 continues the energization time control operation based on the change in the temperature inside the refrigerator, and when the temperature inside the refrigerator increases, the ON time of the solid state relay 16 becomes shorter and the capacity decreases. When the internal temperature decreases, the capacity increases.

Furthermore, when the compressor 2 is operating at the lowest frequency and the heater 8 is operating with energization time control, when loading or unloading of stored items is started again, the temperature inside the refrigerator will drop due to the intrusion of outside air into the refrigerator. gradually rises. Then, as the temperature inside the refrigerator increases, the calculated value of the controller 10 gradually increases. At this time, for example, the carry-in or carry-out work becomes longer and the range of temperature rise in the refrigerator becomes larger than in the above case, so that the calculated value of the controller 10 becomes 35Hz.
When the fourth frequency is reached, controller 1
0 outputs a energization stop signal for the heater 8. This signal is applied to heater input power supply 15, solid state relay 16 is turned off, heater 8 is de-energized, and heat generation stops. Also, the controller 10
outputs a frequency signal calculated by PID control to the inverter circuit 11 instead of the lowest frequency, and frequency-controlled power is output from the inverter circuit 11. Then, the compressor 2 is operated by the electric power, and thereafter, the temperature inside the refrigerator is maintained at approximately the set temperature.

Therefore, the frequency of the electric power supplied to the compressor 2 is controlled based on the temperature inside the refrigerator, and when the temperature inside the refrigerator is being controlled, the cooling load also decreases due to a decrease in the ambient temperature, for example, and the controller 10 After the output frequency signal reaches the second frequency of 30 Hz, if the calculated value of the controller 10 becomes lower than 30 Hz, the controller 10 continues to output the 30 Hz frequency signal. When the temperature inside the refrigerator tends to decrease despite the cooling operation at the lowest capacity, and the calculated value of the controller 10 reaches a third frequency of 28 Hz, which is lower than the lowest frequency, the controller 10 operates to increase the temperature to the heater 8. The electricity starts, and the inside of the refrigerator is heated by the heat generated by the heater 8, so the surplus cooling capacity of the refrigeration system and the heat generated by the heater 8 are offset, preventing the inside of the refrigerator from getting too cold. Of course, it is possible to maintain the temperature approximately at the set temperature, and as mentioned above, when the calculated value of the controller 10 reaches the third frequency, which is lower than the second frequency, due to the temperature drop in the refrigerator due to the lowest frequency operation of the compressor 2, the heater 8 Since the heater generates electricity, if the internal temperature tends to rise and exceeds the set temperature, overshoot can be suppressed slightly.

Also, when the heater 8 is energized, the calculated value of the controller 10 is 35Hz, which is 5Hz higher than the second frequency of 30Hz.
After reaching the fourth frequency of The energization to the heater 8 is immediately stopped due to a shoot, etc., and thereafter the energization and de-energization of the heater 8 are repeated, and as a result of this repetition, the changes in the calculated value and the fluctuation in the temperature inside the refrigerator become large, and the temperature inside the refrigerator It is possible to prevent the temperature from becoming unstable, thereby making it possible to stabilize the internal temperature at approximately the set temperature, and as a result, it is possible to maintain good quality of stored products for a long period of time.

Further, Fig. 2 is an operation control flowchart during low cooling load, and Fig. 3 is a characteristic diagram showing the calculated value of the controller 10, the operating frequency of the compressor 2, and the temperature change inside the refrigerator, also during low cooling. be.

Note that in the above embodiment, the inverter circuit 11
Although the description has been made regarding a refrigeration system that supplies power from the inverter circuit 11 to one compressor 2, the compressors provided in a plurality of refrigeration systems can be operated in the same manner as in the above embodiment even when the compressors provided in a plurality of refrigeration systems are operated by power from the inverter circuit 11. Similar effects can be obtained through control. Further, the first to fourth frequencies preset in the controller 10 are not limited to those in the above embodiment.

(G) Effects of the Invention Since the present invention is an operation control device for a refrigeration system as explained in the above embodiment, when the ambient temperature drops such as in winter and the cooling load is small, the frequency signal from the controller changes to the second frequency. When the frequency calculated by the controller reaches a third frequency, which is slightly lower than the second frequency, the heater starts to be energized, and the calculated value increases as the temperature inside the refrigerator increases due to the heat generated by the heater. In this case, the heater is de-energized at a fourth frequency that is slightly higher than the second frequency, so that the temperature rises when the frequency calculated by the controller becomes the third frequency and the heater is energized. In other words, not only can overshoot be reduced, but also the excess cooling heat generated by the refrigeration system and the heat generated by the heater can be offset over the second frequency, which is the lowest frequency of compressor operation, to prevent the interior of the refrigerator from becoming too cold. , when the heater is de-energized, even if the internal temperature drops slightly due to the latent heat of the load, the calculated value will not drop to the third frequency, and as a result, the heater It is possible to avoid repeated energization and de-energization of the compressor, and to minimize changes in the temperature inside the refrigerator due to switching between energization and de-energization. The temperature inside the refrigerator can be stabilized at approximately the set temperature, and as a result, the quality of stored items can be maintained at good quality over a long period of time.

[Brief explanation of the drawing]

1 to 3 show an embodiment of the present invention,
Figure 1 is a block diagram of the operation control of the refrigeration system, Figure 2 is a flowchart of operation control at low cooling loads, and Figure 3 is the calculated values of the controller, operating frequency of the compressor, and internal temperature at low cooling loads. It is a characteristic diagram showing changes. 1... Low temperature storage, A... Freezer, 2... Compressor, 4... Evaporator, C... Condenser, 8... Heater, 10... Controller, 11... Inverter circuit.

Claims (1)

[Claims] 1 In a refrigeration system in which a compressor, condenser, and evaporator are connected via piping, the
A controller that calculates a frequency under PID control and outputs a frequency signal between a first frequency and a second frequency lower than the first frequency; An inverter circuit that outputs an output to the compressor and an inverter circuit that is provided in the evaporator and is energized by the output from the controller when the frequency calculated by the controller becomes slightly lower than the second frequency; An operation control device for a refrigeration system, comprising: a heater that is de-energized by an output from the controller when the frequency becomes slightly higher than the second frequency.