JPH0823458B2 - Refrigeration system operation controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] The present invention relates to an operation control device for a refrigeration system provided in a prefabricated cold storage or the like.

2. Description of the Related Art A conventional operation control device for a refrigeration system of this type is, for example, Japanese Utility Model Laid-Open No. 58-188554, which discloses a plurality of refrigeration cycles each having a variable capacity compressor, and each of the compressors. One inverter circuit for driving the drive motor, and a plurality of switches for selectively forming a power supply path from the inverter circuit to each of the drive motors or a power supply to each of the drive motors There is disclosed a refrigeration cycle apparatus including a control unit that controls the switches and the inverter circuit according to the magnitude of the load.

Problems to be Solved by the Invention When the refrigeration cycle device according to the related art is used, for example, in a prefabricated freezer or the like, an indoor side forming a part of the refrigeration cycle is accompanied by a cooling operation by the refrigeration cycle. Frost forms on the heat exchanger. Therefore, in order to defrost this heat exchanger, the refrigerant flow path of the four-way valve is switched, hot gas refrigerant of high temperature and high pressure is made to flow from the compressor to the heat exchanger, and defrosting is performed by the latent heat of this hot gas refrigerant. Defrosting by the hot gas defrost method is started.
However, when the driving power from the inverter circuit during the cooling operation is low, that is, when the operation capacity of the compressor is low, if the cooling operation is switched to the defrosting operation,
The defrosting operation will be started when the operating capacity of the compressor is low, the amount of hot gas refrigerant flowing to the heat exchanger is small, and the defrosting time is longer than when the operating capacity of the compressor is high. Therefore, there is a problem that the temperature inside the chamber rises higher as the time is longer. Especially when the state of frost is not constant over the entire heat exchanger, and when there is a strong or weak frost, there will be a portion where ice frost is melted and a portion where it is not melted, and the refrigerant pipe can be in direct contact with air. If defrosting is continued for a long time, there is a problem in that the temperature inside the refrigerator is significantly increased. In addition, when the drive frequency control by PID control is performed despite the fact that the temperature inside the refrigerator is greatly increased at the end of defrosting, compared to the capacity of the compressor immediately before the start of defrosting operation,
After defrosting, the compressor's capacity rises to zero or slight, and it takes a considerable amount of time during pull-down operation to lower the internal temperature to the set temperature and stabilize it. There is a problem that the stored product is exposed to adverse conditions for a long time, which may impair the quality of the product.

For this reason, the present invention provides an operation control device for performing a piecewise frequency control so that the frequency signal is divided into three regions and changed after the defrosting operation is finished, based on the relationship between the internal temperature and the set temperature. It is a thing.

[Structure of the Invention] Means for Solving the Problems A refrigeration system operation controller according to the present invention includes two refrigeration cycles each including a compressor, a condenser, an evaporator, a flow path switching valve, and the like. A controller that outputs a switching signal for switching the flow path of the flow path switching valve and outputs a frequency signal that is increased / decreased between the minimum frequency and the maximum frequency based on the change in the internal temperature, and the frequency signal from the controller. The controller includes an inverter that increases and decreases the electric power that is input to and supplied to the compressor, and the controller has a first temperature after defrosting that is higher than a preset temperature that can be arbitrarily set by a predetermined temperature p.
When the temperature is higher than the set temperature, the frequency signal of the highest frequency is output, and when the internal temperature is lower than the first set temperature and higher than the second set temperature which is higher than the set temperature by a constant temperature q (<p), the temperature immediately before defrosting is started. A frequency signal having a value higher than the operating frequency signal by the set frequency is output, and when the internal temperature is equal to or lower than the second set temperature, the frequency signal by PID control is output.

By setting the set temperature S that can be arbitrarily set for operation, the first set temperature (t ₁ ) and the second set temperature (t ₂ ) are automatically set, and these two temperatures t ₁ and t ₂ are set. Te, a high temperature region (first region) than t _1, a high temperature region (second region) than t ₂ at t ₁ below, divided into three temperature regions of the t ₂ following temperature region (third region), The frequency signal output from the controller (45) is different for each area. That is, the first
In the area, the highest frequency signal, in the second area, the frequency signal whose value is higher than the frequency just before the start of defrosting by the set frequency ΔHz, and in the third area, the same frequency as that just before the start of defrosting. The cooling capacity of the compressors (5A) and (5B) is determined by outputting the frequency signals by PID control after the frequency signals.

Embodiment An embodiment of the present invention will be described below with reference to FIGS.

(1) is a prefabricated refrigerator, and a refrigerating device (2) is provided on one side wall of the prefabricated refrigerator (1).
This refrigeration system (2) comprises an outside unit (3) and an inside unit (4), and the outside unit (3) is a partition plate (3).
The upper heat exchange chamber (3C) and the lower machine room (3D) by B)
The heat exchange chamber (3C) is divided into two parts, the first and second condensers (6
A) (6B), and an axial flow type fan (7) for a condenser are provided. Further, the machine room (3D) is provided with first and second compressors (5A) (5B) and the like which form a part of the refrigeration cycle. In addition, the in-compartment unit (4) includes first and second evaporators (8A) (8B) and
The second evaporator blowers (9A) and (9B) are provided, and the operation of each blower (7) (9A) (9B) causes the refrigeration system (2) to move to the inside or outside of the refrigerator as indicated by the arrow. Air circulates.
Incidentally, (4A) is a drain pan, and (4B) is a drain pipe.

3 and 4 show the first and second refrigeration cycle (11).
FIG. 3 is a refrigerant circuit of (12), and FIG. 3 shows a flow of the refrigerant when both refrigeration cycles (11) and (12) perform a cooling operation, and FIG. 4 shows a second refrigeration cycle (12). Shows the flow of the refrigerant when the cooling operation is performed and the first refrigeration cycle (11) performs the defrosting operation. The first refrigeration cycle (11) includes a first compressor (5A), a first four-way valve (13A) as a first flow path switching valve, a first condenser (6A), a first evaporator (8A), and an accumulator. (14) With pipes connected in a ring,
(15) and (16) are a first check valve and a first capillary tube, respectively, and (17) and (18) are a second check valve and a second capillary tube, respectively. The second refrigeration cycle (12) is the first
It has the same structure as the refrigeration cycle (11) and has a second compressor (5
B), the second four-way valve (13B) as the second flow path switching valve, the second
A condenser (6B), a second evaporator (8B), an accumulator (14), and the like are connected in an annular pipe, and the same reference numerals as those of the first refrigeration cycle (11) indicate the same parts.

Next, a schematic circuit configuration of the operation control device of the refrigeration system of the present invention will be described. (20) is a three-phase AC power supply, (21) is a three-phase full-wave rectifier (hereinafter referred to as bridge circuit), (22) and (23) are smoothing capacitors and choke coils, and (24) is from a controller (45) described later. It is an inverter that converts the DC power that has passed through the bridge circuit (21) into AC power based on the frequency signal. Here, the inverter (24) is composed of a plurality of transistors and diodes. or,
(25S) and (26S) are first and second magnet switches provided between the inverter (24) and the first and second compressors (5A) and (5B), respectively.

Further, (31a) and (31b) are first and second power supply lines connected to the three-phase AC power supply (20), (32) is a motor provided in the condenser blower (7), and (25C) (26C). ) Is the first, respectively
1st paired with 2nd magnet switch (25S) (26S)
The second exciting coil, (33) and (34) respectively control the energization to the first and second exciting coils (25C) and (26C), respectively, and the first and second compressor operating relays (hereinafter, the first and second relays). (35) is the first four-way valve coil, (36) is the motor (hereinafter referred to as the first motor) provided in the first evaporator blower (9A), and (37) is the first refrigeration cycle (11). In the defrosting / cooling switching relay (hereinafter referred to as the third relay), the first four-way valve coil (35) is connected to the defrosting side contact (37a) of the third relay (37),
The motor (36) is the cooling side contact (37b) of the third relay (37).
It is connected to the. Also, (38) is the second four-way valve coil,
(39) is a motor (hereinafter referred to as the second motor) provided in the second evaporator blower (9B), and (41) is a defrosting / cooling switching relay of the second refrigeration cycle (12) (hereinafter referred to as the fourth relay). ), The second four-way valve coil (38) and the second motor (39)
Are connected to the defrosting side contact (41a) and the cooling side contact (41b) of the fourth relay (41), respectively. Reference numeral (42) is a triac, and reference numeral (43) is a heater such as a heating wire for heating the air inside the chamber, the energization of which is controlled by the triac (42).

Further, (45) is a controller composed of a microcomputer. (46) is a first evaporator (8A) itself or a first defrosting end temperature detection element arranged near the evaporator such as a refrigerant outlet pipe, for example, a negative characteristic defrosting thermistor (hereinafter referred to as a first sensor), ( 47) is a second evaporator (8B) itself or a second defrosting end temperature detecting element arranged in the vicinity thereof, for example, a negative defrosting thermistor (hereinafter referred to as a second sensor), and (48) is an air suction port ( P) or an inside temperature detecting element disposed in the vicinity thereof, for example, an inside thermistor having negative characteristics (hereinafter referred to as a third sensor), each sensor (46) (47) (48) being a controller (45). It is connected to the. First relay (33), second relay (34)
Is turned on / off based on a control signal from the controller (45), and the connection terminals of the third relay (37) and the fourth relay (41) are switched based on a switching signal from the controller (45). Further, the conduction angle of the triac (42) increases or decreases based on the conduction angle control signal from the controller (45). The controller (45) performs proportional, integral, and differential control, that is, PID control based on the internal temperature signal input from the third sensor (48), and outputs the frequency signal by this PID control to the inverter (24). . However, the frequency signal by this PID control is controlled between the highest frequency, for example 60 Hz, and the lowest frequency, for example 30 Hz. Then, the electric power supplied from the inverter (24) to the first compressor (5A) and the second compressor (5B) changes based on the frequency signal. Further, the controller (45) sends a defrost signal for defrosting one of the first evaporator (8A) and the second evaporator (8B) every predetermined time, for example, every two hours after the start of the cooling operation. Output. At this time, the evaporator which has been defrosted once defrosts alternately so that it will be defrosted four hours later.

Next, the operation of the operation control device based on the above configuration will be described.

First, after the key is turned on, both the first and second relays (33) and (34) are turned on by the control signal and the switching signal from the controller (45), and the third and fourth relays (37) and (41) are turned on. Will be described as being both at the cooling side contacts (37b) (41b). At this time, the first and second exciting coils (25C) (26C) are both energized, and the first and second magnet switches (25S) (26S)
S) are both turned on. Therefore, the first compressor (5A)
And, the second compressor (5B) is both ready for driving. On the other hand, the 3rd and 4th relays (37) (41) are the cooling side contacts (37b)
Since it is located at (41b), the first and second four-way valve coils (35)
(38) is de-energized and the first and second four-way valves (13A) (13B)
Both serve as cooling flow paths, and the first and second motors (38, 39) are both energized to provide the first and second blowers (9A).
Both (9B) are in operation. See also Triacs (42)
Is non-conductive and the heater (43) is not energized. Here, the controller (45) outputs a frequency signal by PID control based on the internal temperature signal from the third sensor (48), and passes through the inverter (24) to the first and second compressors (5A).
Change the power supplied to (5B). Then, as shown by the solid line arrow in FIG. 3, the refrigerant circulates in the first and second refrigeration cycles (11) and (12), and the refrigerant is generated by the first evaporator (8A) and the second evaporator (8B). The air in the refrigerator is cooled.

Now, assuming that the controller (45) outputs a frequency signal of a certain frequency, for example, 40 Hz, and that both compressors (5A) (5B) are operating, the controller (45) was set in advance after the cooling operation started. When the time (for example, 2 hours) has elapsed (see time T _{1 in} FIG. 5), the controller (45) causes the third relay to start the defrosting operation of one of the evaporators, for example, the first evaporator (8A). A switching signal is output to (37), and this third relay (37) switches to the defrosting side contact (37a). Therefore, the first motor (36) is de-energized, the first evaporator blower (9A) is stopped, and at the same time, the first four-way valve coil (35) is energized, and the flow path of the first four-way valve (13A) is changed. Switching to the defrosting flow path, the first compressor (5A) operation causes the refrigerant to
As shown by the dotted arrow in the figure, the high-temperature high-pressure hot gas refrigerant that has circulated in the first refrigeration cycle (11) and discharged from the first compressor (5A) flows to the first evaporator (8A), causing frost and frost. Defrosting is performed by exchanging heat. On the other hand, at the same time when the third relay (37) is switched to the defrosting side, the controller (45) sets the defrosting operation frequency slightly lower than the predetermined maximum frequency (60 Hz in this embodiment), for example, a frequency signal of 50 Hz. Is output to the inverter (24), and three-phase AC power (hereinafter referred to as power) corresponding to a frequency of 50 Hz is output from the inverter (24).
This electric power operates both compressors (5A) and (5B). At this time, the first refrigeration cycle (11) performs defrosting operation by the reverse hot gas defrost method in the refrigerant flow path of the first four-way valve (13A), and the second refrigeration cycle (12) continues cooling operation. To do. Incidentally, although an example in which immediately start the defrosting operation be in time T _1, it may be allowed to start the defrosting operation with a slight delay from the time T _1. Although the defrosting operation frequency is set slightly lower than the highest frequency, it may be set to the highest frequency, and the point is that the highest frequency or a frequency close to the highest frequency may be used.

Then, with the continuation of the defrosting operation, the ice frost of the first evaporator (8A) is gradually melted, and the radiant heat from the first evaporator (8A) cools the inside temperature of the second refrigeration cycle (12). It rises gradually while driving. Then, the ice frost of the first evaporator (8A) is melted, and the first evaporator (8A)
When the first sensor (46) senses that the temperature has risen to reach the defrosting end temperature, for example, 4 ° C. (see time T _{2 in} FIG. 5), the controller (45) sends a signal from the first sensor (46). A signal for ending the defrosting and starting the cooling operation is output based on the temperature signal, and the third relay (37) is connected to the cooling side contact (37b).
Switch to. Therefore, the first four-way valve coil (35) is de-energized, the first four-way valve (13A) is switched to the cooling flow path, and the refrigerant is driven by the operation of the first compressor (5A) to the solid arrow in FIG. The first refrigeration cycle (11) is circulated as shown in FIG.

On the other hand, the temperature inside the refrigerator, which rises with the defrosting operation, is sensed by the third sensor (48), and the set temperature S (for example, -1
When the temperature inside the refrigerator is higher than the first set temperature (t ₁ ) (0.5 ° C. in this example) which is higher than the predetermined temperature p (for example, 1.5 ° C.) (see time T _{2 in} FIG. 5). , The controller (45) outputs a frequency signal of the highest frequency (here, 60 Hz) to the inverter (24), and the inverter (24) sends electric power corresponding to the frequency of 60 Hz to both compressors (5
A) (5B) is operated at maximum output. In addition, when shifting from the defrosting operation to the cooling operation, the blower for the first evaporator (9A)
If the operation start of (1) is delayed by a delay means such as a timer for a predetermined time (about 1 minute), it is possible to prevent the warm air filled in the inside unit (4) from being discharged into the inside during defrosting.

By continuing the cooling operation with the maximum output of both compressors (5A) and (5B), the temperature inside the chamber rose slightly and then quickly decreased, and the temperature inside the chamber fell below the first set temperature (t ₁ ). Is detected by the third sensor (48) (see time T _{3 in} FIG. 5),
The controller (45) uses, for example, the frequency ΔHz preset from the frequency signal (40 Hz in this example) immediately before the start of defrosting.
Frequency signal with a high value of 10 Hz (which means 50 Hz)
Is output. If the frequency signal immediately before the start of defrosting is 50 Hz or more, the value obtained by adding 10 Hz to the frequency is 60
The frequency signal is up to 60Hz, though it is above Hz.
Then, based on this frequency signal, the inverter (24)
Outputs the previous electric power, reduces the operating capacity of the first and second compressors (5A) (5B), and reduces the refrigeration cycle (12) of the first refrigeration cycle (11) and the second refrigeration cycle (12). Reduces cooling capacity. After that, by continuing the cooling operation with this cooling capacity,
The temperature inside the chamber gradually decreases, and a constant temperature q from the set temperature S
When the third sensor (48) senses that the temperature has fallen below the second preset temperature (t ₂ , which is −0.5 ° C. in this example) which is higher (less than p) (for example, 0.5 ° C.) (fifth temperature). see FIG time T _4), the controller (45) outputs a defrosting start immediately preceding frequency signals (40 Hz in this example). Then, the inverter (24) uses the same electric power as before the start of defrosting, and the first and second compressors (5
Drive A) (5B). After this, the third sensor (48)
The controller (45) based on the internal temperature signal from
PID control is performed to change the frequency signal. For this reason, the internal temperature gradually decreases, and eventually reaches the set temperature S at time T ₅ , and then the PID control is continued so as to maintain the set temperature S (the above is the description of the case of the transition of D ₁ ). () By the way, when there are many stored items in the storage and the latent heat becomes large, the rise in the storage temperature at the time of defrosting changes a gentle curve and changes as shown by the dotted line in Fig. 5 ( the D of ₂ changes), when the defrost is finished at time T _2, the inside temperature is between the first predetermined temperature (t ₁₎ and the second set temperature (t _2), the controller ( 45) outputs a frequency signal of 50 Hz, which is 10 Hz higher than the frequency signal immediately before the start of defrosting. Then, based on this frequency signal, the inverter (24) supplies electric power corresponding to the frequency of 50 Hz to the first and second compressors (5A) (5B). Further, the first four-way valve (13A) is switched to the cooling flow path with the completion of defrosting, the refrigerant circulates to the first refrigeration cycle (11) as shown by the solid arrow, and the second refrigeration cycle (12). The cooling operation is performed as in (1).
When the third sensor (48) senses that the temperature inside the refrigerator has decreased to the second set temperature (t ₂ ) due to the continuation of the cooling operation (see time T _{6 in} FIG. 5), the controller (45) causes the defrosting. The same frequency signal (40 Hz) as that immediately before the start is output, and the inverter (24) supplies electric power corresponding to the frequency signal. Based on this electric power, the operating capacities of the first and second compressors (5A) and (5B) change, and the internal temperature gradually decreases to the set temperature S,
After that, PID control is continued so as to maintain the set temperature.

Then, whether the transition is D _{1 or} D ₂ , if the preset time (2 hours) has passed since defrosting was started,
In order to start the defrosting operation of the second evaporator (8B), the controller (45) outputs a switching signal to the fourth relay (41),
Move the relay (41) from the cooling side contact (41b) to the defrosting side contact (41b).
Switch to a). Further, the controller (45) outputs a signal of the defrosting operation frequency (50 Hz), and the inverter (24) outputs electric power corresponding to this frequency. This electric power drives both compressors (5A) (5B), but the 4th relay (4A
In 1), the second four-way valve coil (38) is energized, and the second
Since the four-way valve (13b) is switched to the defrosting flow path, the first refrigeration cycle (11) continuously performs the cooling operation and the second refrigeration cycle (12) performs the defrosting operation. After that, the second refrigeration cycle (12) is cooled from defrosting in the same transition order as in the case of transition from the defrosting operation of the first evaporator (8A) of the first refrigeration cycle (11) described above to the cooling operation. Then, the frequency signal from the controller (45) is changed so as to quickly decrease the internal temperature to the set temperature and maintain the set temperature.

In addition, after defrosting of the second evaporator (8B) is started, 2
After a lapse of time, the first evaporator (8A) is defrosted again, and thereafter the evaporators are defrosted alternately with the lapse of time to prevent a decrease in cooling due to long-term use. .

As described above, the first set temperature (t ₁ ) which is higher than the set temperature S set by the user by the predetermined temperature p and the second set temperature (t ₂ ) which is higher than the set temperature S by the constant temperature q (p> q). ) And are stored in the controller (45) according to the setting of the set temperature S, and the frequency signal immediately before defrosting is stored, and both evaporators (5A) and (5B) are cooled after the defrosting operation ends. The controller (45) outputs a signal for switching the refrigerant flow path to be used by the controller (45). When the temperature inside the refrigerator at the time of pulling down after defrosting is higher than the first set temperature (t ₁ ), the controller (45) outputs the frequency signal of the highest frequency, and both compressions are performed via the inverter (24). Both refrigeration cycles (11) (12) by operating the machines (5A) (5B) with maximum operating capacity
By giving the highest cooling capacity to the chamber, the temperature inside the chamber after the defrosting operation is finished can be suppressed slightly, and the temperature inside the chamber can be quickly lowered. On the other hand, the internal temperature is the first
When the temperature is lower than the set temperature (t ₁ ) and higher than the second set temperature (t ₂ ), the controller (45) sets the preset frequency ΔHz.
Only the frequency signal higher than the frequency immediately before defrosting is started is output, and both compressors (5A) and (5B) are operated through the inverter (24) to have a higher operating capacity than the capacity immediately before defrosting, and the temperature inside the refrigerator decreases. Is set to be higher than immediately before defrosting, so that the internal cold storage temperature is lowered to the set temperature faster. On the other hand, when the temperature inside the refrigerator is equal to or lower than the second set temperature (t ₂ ), the controller (45) outputs the frequency signal immediately before the start of defrosting, and thereafter outputs the frequency signal based on the PID control based on the temperature inside the refrigerator. In this way, by changing the operation capacity of the compressor via the inverter (24), the overshoot phenomenon in the temperature change from the second set temperature (t ₂ ) to the set temperature S is made small, and the required power is reduced. And the set temperature can be maintained.

[Effects of the Invention] As described in detail above, according to the present invention, since the internal cold storage temperature rises with the defrosting operation, two refrigerating cycles are provided, and one system is cooled during defrosting, etc. The system is defrosted so that the internal temperature rise is kept low. In addition, immediately after defrosting, PI
Instead of performing cooling operation by D control, when the temperature inside the refrigerator is higher than the first set temperature, which is higher than the set temperature that can be set arbitrarily, by a predetermined temperature, the controller outputs the frequency signal of the highest frequency and the compressor compresses both. Since the capacity of the machine is maximized and the cooling capacity of both refrigeration cycles is maximized, the inside of the refrigerator can be rapidly cooled. On the other hand, the internal temperature is the first
When the temperature is below the set temperature and higher than the second set temperature, the controller outputs a frequency signal that is higher than the frequency immediately before the start of defrost by the set frequency, and determines that the capacity of both compressors is higher than the capacity immediately before defrost through the inverter. Therefore, the operating capacity of the PID control determined by the difference between the set temperature and the internal temperature can be made larger, and the internal temperature can be reduced to near the set temperature earlier. On the other hand, when the temperature inside the refrigerator is below the second set temperature, the controller outputs the same frequency signal as immediately before the start of defrosting, and thereafter outputs the frequency signal based on the PID control based on the temperature inside the refrigerator to operate both compressors. Since the capability is adjusted appropriately, the overshoot phenomenon until the temperature stabilizes at the set temperature can be made small, and the required power can be saved and the temperature can be finely maintained.

[Brief description of drawings]

Each drawing shows an embodiment of the present invention, FIG. 1 is a schematic electric circuit diagram of an operation control device of a refrigerating apparatus, FIG. 2 is a schematic vertical sectional view of a prefabricated refrigerator, and FIGS. In the refrigerant circuit diagram of the cycle, FIG. 3 shows the flow of the refrigerant in the case of both cooling operations, and FIG. 4 shows the flow of the refrigerant in the case of one cooling operation and the other in the defrosting operation. The figure is a transition diagram showing changes in the internal cold storage temperature before defrosting, during defrosting, and after defrosting, and changes in the refrigeration operation control state. (1) …… Prefabricated refrigerator, (2) …… Refrigerator, (5
A) …… First compressor, (5B) …… Second compressor, (8A)…
… First evaporator, (8B) …… Second evaporator, (11) …… First
Refrigeration cycle, (12) …… Second refrigeration cycle, (13A)
…… First four-way valve, (13B) …… Second second four-way valve, (24) ……
Inverter, (33) …… first relay, (34) …… second relay, (37) …… third relay, (41) …… fourth relay,
(42) …… Triac, (45) …… Controller,
(46) …… First sensor, (47) …… Second sensor, (48)
...... Third sensor.

Claims (1)

[Claims] 1. A refrigeration cycle of two systems each comprising a compressor, a condenser, an evaporator, a flow path switching valve, and the like, and a switching signal for switching the flow path of the flow path switching valve and a temperature inside the refrigerator. A controller that outputs a frequency signal that is increased / decreased between the lowest frequency and the highest frequency based on a change in the, and an inverter that inputs the frequency signal from the controller and increases / decreases the power supplied to the compressor. In the operation control device of the refrigeration system, the controller outputs the frequency signal of the highest frequency after the defrosting and when the internal temperature is higher than the first preset temperature which is higher by a predetermined temperature p than the preset temperature that can be arbitrarily set. When the internal temperature is lower than the first set temperature and higher than the second set temperature by a constant temperature q (<p) higher than the set temperature, the set frequency is set from the operating frequency signal immediately before the start of defrosting. Only it outputs a frequency signal of a high value, when the inside temperature is less than or equal to the second predetermined temperature, the operation control device for a refrigeration system and outputs a frequency signal by the PID control.