KR101397660B1 - Air conditioning system - Google Patents

Abstract

The air conditioning system according to the present invention can improve the stability of the system by changing the control mode of the first expansion valve depending on the operating state.

Air conditioning system, phase separator, injection, refrigerant, valve, superheat degree, intermediate pressure

Description

[0001] Air conditioning system [0002]

The present invention relates to an air conditioning system, and more particularly, to an air conditioning system in which the performance and stability of the system can be improved.

Generally, an air conditioning system is a device that compresses, condenses, expands, and evaporates a refrigerant to cool or heat the indoor space.

The air conditioning system is divided into a normal air conditioning system in which one indoor unit is connected to an outdoor unit and a multi air conditioning system in which a plurality of indoor units are connected to an outdoor unit. In addition, the air conditioning system is divided into a cooling system that only operates the refrigerant cycle in one direction to supply only cool air to the room, and a cooling and heating system that can operate the refrigerant cycle in both directions to supply cold or warm air to the room.

The air conditioning system includes a compressor, a condenser, an expansion valve, and an evaporator. The refrigerant discharged from the compressor is condensed in the condenser, and then expanded in the expansion valve. The expanded refrigerant is evaporated in the evaporator, and then sucked into the compressor. During the cooling operation or the heating operation, the refrigerant is injected into the compressor to improve the performance.

However, in the air conditioning system according to the related art, when the superheat and the intermediate pressure of the refrigerant are not smoothly controlled, the system becomes unstable and the compressor may be damaged.

An object of the present invention is to provide an air conditioning system in which stability and performance of a system can be improved.

The present invention relates to a refrigerating machine comprising a condenser in which a refrigerant is condensed, a first expansion device in which a refrigerant passed through the condenser is throttled, a second expansion device in which a refrigerant having passed through the first expansion device is throttled, A first compression section in which a refrigerant having passed through the evaporator flows and is compressed, a refrigerant having passed through the first compression section, and a second expansion device branched from the first expansion device and the second expansion device, Wherein the control unit controls the first expansion device to the first control mode, and when the operation variable value of at least one operation variable deviates from a predetermined normal operation range, And a control unit for switching to a second control mode different from the first control mode and controlling the first expansion device.

The first control mode may control the opening amount of the first expansion device based on a pre-stored setting value corresponding to the operation variable value. Wherein the at least one operating variable is a plurality of operating variables and the plurality of operating variables independently vary the target opening degree of the first expansion device. The first control mode stores the current degree of opening of the first expansion device in real time.

The second control mode may control the amount of opening of the first expansion device based on the current degree of opening stored in the first control mode upon switching from the first control mode. Wherein the second control mode determines a correction degree of opening based on the operating variable value, and when the mode is switched from the first control mode, the first degree of opening The opening amount of the apparatus can be controlled. Wherein the second control mode stores in real time the current degree of opening of the first expansion device and, during the execution of the second control mode, combines the corrected degree of opening stored in the second control mode with the corrected degree of opening, The opening amount of the apparatus can be controlled.

Wherein the operation parameter value includes a discharge temperature of the refrigerant discharged from the compressor and a temperature of the refrigerant passing through the condenser, and when at least one of the operation parameter values deviates from the normal operation range, And switches to the second control mode.

When the value of the operation variable returns to the normal operation range during the execution of the second control mode, the amount of opening of the first expansion device can be controlled by switching from the second control mode to the first control mode.

The air conditioning system according to the present invention can improve the stability of the system by changing the control mode of the first expansion device depending on the operating state.

The air conditioning system includes a general air conditioning air conditioner for performing only cooling operation, a heating air conditioner for performing only heating operation, a heat pump type air conditioner for performing both cooling and heating operation, a plurality of indoor spaces for cooling / It includes all multi-type air conditioners. Hereinafter, a heat pump type air conditioner (hereinafter referred to as an " air conditioner ") will be described in detail as an embodiment of an air conditioning system.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a configuration diagram of an air conditioner 100 according to an embodiment of the present invention, and FIG. 2 is a block diagram showing a control flow of the air conditioner 100. Referring to FIG.

1 and 2, the air conditioner 100 includes a compressor 110, an indoor heat exchanger 120, an outdoor heat exchanger 130, a first expansion valve 141, a second expansion valve 142 A phase separator 150, and a four-way valve 160. The indoor heat exchanger 120 serves as an evaporator during cooling operation and as a condenser during heating operation. The outdoor heat exchanger 130 acts as a condenser during cooling operation and as an evaporator during heating operation. The compressor (110) compresses the introduced low-temperature low-pressure refrigerant into high-temperature high-pressure refrigerant. The compressor 110 includes a first compression unit 111 and a second compression unit 112. The first compression unit 111 compresses the refrigerant introduced from the evaporator and the second compression unit 112 is branched from the refrigerant discharged from the first compression unit 111 and between the evaporator and the condenser The injected refrigerant is mixed and compressed. However, the present invention is not limited to this, and the compressor 110 may have a multi-stage structure having three or more stages.

The four-way valve 160 guides the refrigerant compressed by the compressor 110 to the outdoor heat exchanger 130 when it is cooled, and the indoor heat exchanger (120). The four-way valve 160 and the compressor 110 are connected to a first connection pipe 171. A discharge temperature sensor 181 and a discharge pressure sensor 182 are disposed in the first connection pipe 171 to measure discharge temperature and pressure of the refrigerant discharged from the compressor 110. The indoor heat exchanger 120 is disposed in the room and connected to the four-way valve 160 through a second connection pipe 172.

The phase separator 150 separates the refrigerant flowing into the gas-phase refrigerant and the liquid-phase refrigerant, sends the liquid-phase refrigerant to the evaporator, and sends the gaseous refrigerant to the second compression unit 112. The first connection part 151 of the phase separator 150 and the indoor heat exchanger 120 are connected to the third connection pipe 173. The first connection part 151 is a liquid refrigerant discharge pipe during the cooling operation and a refrigerant inflow pipe during the heating operation.

The first expansion valve 141 is disposed on the third connection pipe 173 and is a second expansion device for exchanging the liquid refrigerant introduced from the phase separator 150 during cooling operation. And is a first expansion device for exchanging the liquid refrigerant introduced from the indoor heat exchanger (120).

The outdoor heat exchanger 130 is disposed outdoors and connected to the second connection unit 152 and the fourth connection pipe 174 of the phase separator 150. The second connection portion 152 is a refrigerant inlet pipe during the cooling operation and a liquid refrigerant discharge pipe during the heating operation.

The second expansion valve 142 is disposed on the fourth connection pipe 174 and is a first expansion device for exchanging the liquid refrigerant introduced from the outdoor heat exchanger 130 during cooling operation. Is a second expansion device for exchanging the liquid refrigerant introduced from the phase separator (150).

The outdoor heat exchanger 130 is connected to the four-way valve 160 through a fifth connection pipe 175. In addition, the four-way valve 160 and the inflow pipe of the compressor 110 are connected to the sixth connection pipe 176. A compressor inlet temperature sensor 184 for measuring the temperature of the inlet side of the compressor 110 is disposed on the sixth connection pipe 176.

The second compression unit 112 is connected to the third connection unit 153 of the phase separator 150 through an injection pipe 180. The third connection part 153 is used as a gaseous refrigerant discharge pipe in the cooling and heating operation. An injection valve 143 is disposed on the injection pipe 180. The injection valve 143 controls the amount of refrigerant injected from the phase separator 150 into the second compression unit 112 and the refrigerant pressure. When the injection valve 143 is opened, the gaseous refrigerant in the phase separator 150 flows into the second compression unit 112 through the injection pipe 180. An injection temperature sensor 183 for measuring the temperature of the injected refrigerant is disposed on the injection pipe 180.

The amount of opening of the first and second expansion valves 141 and 142 and the injection valve 143 is controlled by a control unit 200 that controls the operation of the air conditioner.

3 shows the flow of the refrigerant during the heating operation of the air conditioner.

3, the high-temperature, high-pressure gaseous refrigerant discharged from the compressor 110 flows into the indoor heat exchanger 120 via the four-way valve 160. [ The gaseous refrigerant in the indoor heat exchanger (120) undergoes heat exchange with the room air and is condensed. The condensed refrigerant is throttled in the first expansion valve 141, and then flows into the phase separator 160. The liquid refrigerant separated in the phase separator 160 is again throttled by the second expansion valve 142, and then flows into the outdoor heat exchanger 130. In the outdoor heat exchanger (130), the refrigerant evaporates due to heat exchange with the outside air, and the evaporated refrigerant flows into the first compression section (111).

When the operation of gas injection is requested during the heating operation, the control unit 200 opens the injection valve 143. The injection valve 143 is opened and the gaseous refrigerant separated by the phase separator 160 is injected into the second compression unit 112 through the injection pipe 180. [ In the second compression unit 112, the injected refrigerant and the refrigerant from the first compression unit 111 are mixed and then compressed. The refrigerant compressed by the second compression unit 112 is circulated to the four-way valve 160 again.

4 shows the flow of the refrigerant during the cooling operation of the air conditioner.

4, the high-temperature, high-pressure gaseous refrigerant discharged from the compressor 110 flows into the outdoor heat exchanger 130 through the four-way valve 160. In the outdoor heat exchanger (130), the gaseous refrigerant undergoes heat exchange with indoor air and is condensed. The condensed refrigerant is throttled in the second expansion valve 142, and then flows into the phase separator 150. The liquid refrigerant separated in the phase separator 150 is again throttled in the first expansion valve 141 and then flows into the indoor heat exchanger 120. [ In the indoor heat exchanger (120), the refrigerant evaporates due to heat exchange with the outside air, and the evaporated refrigerant flows into the first compression section (111). The control unit 200 shuts the injection valve 143 so that the gaseous refrigerant from the phase separator 150 is not injected into the second compression unit 112. However, the present invention is not limited to this, and the gaseous refrigerant from the phase separator 150 may be injected into the second compression unit 112 even during the cooling operation.

A control method of the air conditioner according to an embodiment of the present invention will now be described.

When the user drives the air conditioner 100 in order to heat and cool the indoor space, the controller 200 senses a driving command. The control unit 200 initializes the first and second expansion valves 141 and 142 and the injection valve 143. That is, the controller 200 completely opens the first and second expansion valves 141 and 142, and shields the injection valve 143. By blocking the injection valve 143, liquid refrigerant can be prevented from flowing into the compressor 110 at the beginning of the operation.

When the initialization of the first and second expansion valves 141 and 142 and the injection valve 143 is completed, the controller 200 determines that the refrigerant of the air conditioner 100 reaches a predetermined target degree of superheat After the superheat degree is adjusted, the refrigerant reaches a predetermined intermediate pressure.

Here, the superheat degree refers to the temperature difference of the refrigerant between the outlet side of the evaporator and the inlet side of the compressor 110. Generally, a refrigerant does not include a liquid refrigerant after passing through the evaporator, but in the case of a sudden change in load, a liquid refrigerant may be included. In this case, when liquid refrigerant flows into the compressor 110, the compressor 110 is damaged. Accordingly, in order to prevent this, the refrigerant having passed through the evaporator is caused to rise in the process of being transferred to the compressor 110, thereby removing the liquid refrigerant. When the amount of the refrigerant flowing into the evaporator is reduced, evaporation of the refrigerant is completed before completely passing through the evaporator, and the gas refrigerant is continuously heated, thereby increasing the degree of superheat. On the other hand, if the amount of refrigerant is increased, the degree of superheat can be reduced. The degree of superheat is determined by a sensor 185 installed in the indoor heat exchanger 120, a sensor 186 installed in the outdoor heat exchanger 130, a compressor inlet temperature sensor 184 installed at the inlet of the compressor 110, Lt; / RTI >

The intermediate pressure is the pressure in the phase separator 160. By setting the intermediate pressure to a predetermined intermediate pressure, it is possible to reduce the work required in the compressor 110 and to increase the efficiency. By adjusting the amount of refrigerant supplied to the phase separator 160 from the condenser, the intermediate pressure can be adjusted. The intermediate pressure can be measured by the injection temperature sensor 183 provided in the injection pipe 180.

In order to control the degree of superheat, the amount of opening of the valve disposed between the phase separator 160 and the evaporator is controlled, and the pressure of the valve disposed between the condenser and the phase separator 160 Adjust the opening amount.

In the heating operation, the first expansion valve 141 serves as a first expansion device for adjusting the intermediate pressure, and the second expansion valve 142 serves as a second expansion device for controlling the superheat degree .

In order to control the degree of superheat, the controller 200 measures the superheat degree of the refrigerant in real time and changes the degree of opening of the second expansion valve 142 accordingly. The control unit 200 is provided with a control unit 200 for controlling the outdoor heat exchanger 130 based on the sensor 186 installed in the outdoor heat exchanger 130 and the overheat measured by the compressor temperature sensor 184, The purge table is stored, and the opening amount of the second expansion valve 142 is determined from the purge table. The control unit 200 measures the degree of superheat of the refrigerant in real time until the degree of superheat of the refrigerant reaches the target degree of superheat and measures the amount of expansion of the second expansion valve 142 based on the measured degree of superheat Continue to change. Therefore, the degree of superheat of the refrigerant can be adjusted more accurately.

5 is a flowchart showing a control method of the first expansion valve when the air conditioner shown in FIG. 1 performs the heating operation.

Referring to FIG. 5, when the initialization of the first expansion valve 141 is completed (S1), the controller 200 adjusts the opening amount of the first expansion valve 141 to adjust the intermediate pressure. The controller 200 controls the first expansion valve 141 in two different control modes.

The controller 200 controls the first expansion valve 141 to the first control mode when the operation variable of the at least one operation variable is within the predetermined normal operation range. On the other hand, when the operating parameter value is out of the preset normal operating range, the first expansion valve 141 is controlled by switching to the second control mode S20 which is different from the first control mode S10. The control unit 200 senses operating parameters such as the discharge temperature of the refrigerant discharged from the compressor 110 and the temperature of the refrigerant passing through the indoor heat exchanger 120 serving as a condenser during the heating operation, If the operating parameter value deviates from a preset normal range, it is determined that a problem such as liquid compression may occur, and the control mode is switched to a second control mode (S20) in which liquid compression or the like can be prevented. The discharge temperature of the refrigerant discharged from the compressor 110 can be measured by the compressor discharge temperature sensor 181 provided on the outlet side of the compressor 110 and the discharge temperature of the refrigerant passing through the indoor heat exchanger 120 The temperature can be measured by a sensor installed on the indoor heat exchanger side.

First, when the operation variable value is within the preset normal operation range, the controller 200 controls the first expansion valve 141 to the first control mode S10. In the first control mode S10, whether or not the gas injection operation in which the refrigerant is injected into the second compression unit 112, the frequency of the compressor 110, the indoor temperature of the air conditioner, And the discharge temperature of the compressor 110. (S11) Then, based on the pre-stored set values corresponding to the operating variable values, (S12), and determines the target degree of opening of the first expansion valve 141 (S13). The set value is predetermined and stored in the form of a table in the controller 200. [ The set value for the frequency of the compressor 110 may be set differently depending on whether the gas injection is operated or not.

The set values for the operating variable values independently vary the target opening. A method for obtaining the target opening degree according to the result is as follows.

Target opening degree = F (A1, A2, A3, A4, A5 .....)

Here, A1 to A5 are the operating variable values. The above F (A1, A2, A3, A4, A5 .....) can be expressed by the following equation.

As an example, the target degree of opening may be obtained by multiplying the set values corresponding to the operating variable values, and the following equation can be used.

(A1) * f (A2) * f (A3) * f (A4) * f (A5) *

Here, C is a proportional constant, and f (A1), f (A2), .. are the setting values for A1, A2, ..

Since the operating parameters independently vary the target opening degree of the first expansion valve 141, the set values for the respective operating parameters can be easily obtained and the control is easy. However, the present invention is not limited to this, and the target degree of opening may be obtained by adding the set values to each other or by other combinations.

When the target degree of opening of the first expansion valve 141 is determined, the controller 200 increases or decreases the opening degree of the first expansion valve 141 at a time so that the degree of opening of the first expansion valve 141 reaches the target degree of opening (S14) Accordingly, the intermediate pressure of the refrigerant can be quickly reached to the predetermined intermediate pressure.

The controller 200 stores the current degree of opening of the first expansion valve 141 in real time during the execution of the first control mode S10. (S15) In the first control mode S10, 1 The opening degree of the expansion valve 141 is used when switching from the first control mode S10 to the second control mode S20.

The control unit 200 detects whether the operating parameters such as the discharge temperature of the refrigerant discharged from the compressor 110 and the temperature of the refrigerant passing through the indoor heat exchanger 120 are out of a predetermined normal operation range (S2) If the operation parameters such as the discharge temperature of the refrigerant discharged from the compressor 110 and the temperature of the refrigerant passing through the indoor heat exchanger 120 are out of the preset normal operation range, Is switched from the first control mode (S10) to the second control mode (S20) to control the first expansion valve (141).

The control unit 200 measures the refrigerant discharge temperature of the compressor 110 to secure the discharge temperature of the refrigerant discharged from the compressor 110. When the measured refrigerant discharge temperature is out of the preset normal operation range , The control mode is switched to the second control mode (S20). The normal operating range is preset and stored in the controller 200 according to the operating conditions of the air conditioner. (S21) determines the correction degree of opening based on the refrigerant discharge temperature in the second control mode (S20) when switching from the first control mode (S10) (S22), the amount of opening of the first expansion valve 141 is controlled. (S23) Thereafter, when the second control mode (S20) is started, the second control mode (S20) The current degree of opening of the first expansion valve 141 is stored in real time in step S24. Therefore, during the execution of the second control mode S20, Openness is combined.

The second control mode S20 is a method of opening or closing the stored opening degree by the correction opening degree. Accordingly, the opening degree of the first expansion valve 141 is gradually decreased by the correction opening degree until the refrigerant discharge temperature of the compressor 110 becomes the predetermined temperature or more. As the opening degree of the first expansion valve 141 is reduced, the amount of the refrigerant is reduced and the refrigerant discharge temperature of the compressor 110 can be secured. Therefore, liquid compression in the compressor 110 can be prevented.

Meanwhile, when the refrigerant discharge temperature of the compressor 110 returns to the normal operation range during the execution of the second control mode S20, the controller 200 controls the first control mode Mode (S10) to control the amount of opening of the first expansion valve (141).

If the temperature of the refrigerant passing through the indoor heat exchanger 120 is out of the predetermined normal operating range during the execution of the first control mode S10, And switches to the second control mode (S20) to control the amount of opening of the first expansion valve (141). The controller determines the correction degree of opening based on the temperature of the refrigerant which has passed through the indoor heat exchanger 120 in the second control mode S20 at the time of switching from the first control mode S10, The correction opening degree is combined with the opening degree of the first expansion valve 141 stored in step S10. (S22) Then, the opening amount of the first expansion valve 141 is controlled accordingly (S23) Thereafter, during the execution of the second control mode S20, the opening degree of the first expansion valve 141 is stored in real time, and the corrected opening degree is stored in the opening degree stored in the second control mode S20 . The opening degree of the first expansion valve 141 is gradually increased by the correction opening degree until the temperature of the refrigerant passing through the indoor heat exchanger 120 becomes equal to or higher than a predetermined temperature. The temperature of the outlet side of the indoor heat exchanger 120 can be increased by increasing the opening degree of the first expansion valve 141.

If the temperature of the refrigerant that has passed through the indoor heat exchanger 120 during the execution of the second control mode S20 returns to the preset temperature or more, The first expansion valve 141 is switched to the first control mode S10 and the opening amount of the first expansion valve 141 is controlled.

When the discharge temperature of the compressor 110 is out of the predetermined normal operating range during the execution of the first control mode S10, the controller 200 determines that the first control mode (S10) Mode (S20) to control the amount of opening of the first expansion valve (141). In the second control mode S20, the correction opening degree is determined based on the discharge temperature of the compressor 110, and in step S21, the opening degree of the first expansion valve 141 stored in the first control mode S10 (S22), the opening amount of the first expansion valve 141 is controlled. (S23) Thereafter, during the execution of the second control mode S20, the first expansion valve (S24), and compares the correction degree with the stored degree of opening in the second control mode (S20). The opening degree of the first expansion valve (141) is gradually increased by the correction opening degree until the discharge temperature of the compressor (110) becomes a predetermined temperature or lower. By increasing the opening degree of the first expansion valve (141), it is possible to prevent the discharge temperature of the compressor (110) from rising. Therefore, damage or the like of the compressor 110 can be prevented.

When the refrigerant discharge temperature of the compressor 110 falls below a predetermined temperature during the execution of the second control mode S20, the controller 200 determines whether the refrigerant discharged from the second control mode S20 to the first control mode S10) to control the amount of opening of the first expansion valve (141).

The first control mode S10 sets the target opening degree regardless of the opening degree of the first expansion valve 141 and reaches the target opening degree at a time. Accordingly, when the first expansion valve 141 is controlled to the first control mode (S10) in the normal operation state, quick control can be performed. On the other hand, in the second control mode S20, the opening degree of the first expansion valve 141 is gradually decreased or gradually increased. Therefore, when the engine is not in the normal operating state, the amount of opening of the first expansion valve 141 is controlled more accurately according to the operating state, so that return to the normal operating state can be facilitated.

After the initialization of the second expansion valve 142, the controller 200 corrects the target superheat degree to secure the discharge temperature of the compressor 110, You can control the dosage. That is, after the initialization of the second expansion valve 142, when the discharge temperature of the compressor 110 is lower than a preset temperature, the controller 200 corrects a predetermined value to a predetermined target superheat degree, The degree of superheat can be set and the opening amount of the second expansion valve 142 can be controlled accordingly. Therefore, after the initialization of the second expansion valve 142, the discharge temperature of the compressor 110 can be secured.

Thereafter, when the discharge temperature of the compressor 110 reaches a predetermined temperature or more, the controller 200 may control the amount of opening of the second expansion valve 142 so as to reach a preset target superheat degree.

On the other hand, in the cooling operation, the second expansion valve 142 serves as a first expansion device for adjusting the intermediate pressure, and the first expansion valve 141 serves as a second expansion device for controlling the superheating degree . Accordingly, in the cooling operation, the second expansion valve 142 can be controlled in different control modes according to the operation state. When the operating variable value is within the normal operation range, the second expansion valve 142 is controlled to the first control mode (S10). When the operation variable value is out of the normal operation range, the first control mode (S10) to the second control mode (S20) to control the amount of opening of the second expansion valve (142).

That is, when the refrigerant discharge temperature of the compressor 110 is out of the normal operating range and is lower than a predetermined temperature, the second control mode S20 determines the correction opening degree according to the refrigerant discharge temperature. Then, the opening degree of the second expansion valve 142 is gradually decreased by the correction opening degree until the refrigerant discharge temperature becomes the predetermined temperature or more. The refrigerant discharge temperature of the compressor 110 can be secured while the second expansion valve 142 is gradually closed.

When the inlet side temperature of the indoor heat exchanger 120 serving as the evaporator is out of the normal operation range and is lower than a predetermined temperature, the inlet side of the indoor heat exchanger 120 in the second control mode (S20) The correction opening is determined according to the temperature. The opening degree of the second expansion valve 142 is gradually increased by the correction opening degree until the inlet side temperature of the indoor heat exchanger 120 reaches the normal operation range. Therefore, the inlet pipe of the indoor heat exchanger 120 can be prevented from freezing.

When the discharge temperature of the compressor 110 exceeds the predetermined operating temperature range, the second control mode S20 determines a correction degree of opening according to the discharge temperature of the compressor 110 . The opening degree of the second expansion valve 142 is gradually increased by the correction opening degree until the discharge temperature of the compressor 110 becomes equal to or lower than the predetermined temperature. Therefore, the discharge temperature of the compressor 110 can be prevented from rising excessively.

When the air conditioner 100 is overloaded, a predetermined target superheat degree is corrected to set a new target superheat degree, thereby controlling the opening amount of the first expansion valve 141 have. Therefore, it is possible to cope with an overload of the air conditioner 100. [

1 is a configuration diagram of an air conditioner according to an embodiment of the present invention.

FIG. 2 is a block diagram showing the control flow of the air conditioner shown in FIG. 1. FIG.

3 is a configuration diagram showing the flow of the refrigerant during the heating operation of the air conditioner shown in Fig.

FIG. 4 is a configuration diagram showing the flow of the refrigerant during the cooling operation of the air conditioner shown in FIG.

5 is a flowchart showing a control method of the first expansion valve when the air conditioner shown in Fig. 1 performs heating operation.

BRIEF DESCRIPTION OF THE DRAWINGS Fig.

100: air conditioner 110: compressor

120: indoor heat exchanger 130: outdoor heat exchanger

141: first expansion valve 142: second expansion valve

143: Injection valve 150: Phase separator

160: Four-way valve 180: Injection piping

200:

Claims (9)

A condenser for condensing the refrigerant; A first expansion device through which the refrigerant passing through the condenser is throttled; A second expansion device in which the refrigerant having passed through the first expansion device is throttled; An evaporator through which the refrigerant having passed through the second expansion device is evaporated; A first compression unit into which the refrigerant having passed through the evaporator flows and is compressed; and a refrigerant that has passed through the first compression unit and a refrigerant branched and injected between the first expansion device and the second expansion device, A compressor having a second compression section; When the operation variable value of at least one operation variable deviates from a predetermined normal operation range, the first expansion mode is switched to the second control mode different from the first control mode, And a control unit for controlling the expansion device. The method according to claim 1, Wherein the first control mode determines a target opening degree of the first expansion device based on a pre-stored setting value corresponding to the operating variable value. The method of claim 2, Wherein the at least one operating parameter is a plurality of operating parameters, Wherein the plurality of operating variables independently vary the target opening degree of the first expansion device. The method according to claim 1, Wherein the first control mode stores the current degree of opening of the first expansion device in real time. The method of claim 4, And the second control mode controls the amount of opening of the first expansion device based on the current degree of opening stored in the first control mode upon switching from the first control mode. The method of claim 4, Wherein the second control mode determines a correction opening degree based on the operation variable value, And controls the opening amount of the first expansion device by combining the correction opening degree with the current opening degree stored in the first control mode upon switching from the first control mode. The method of claim 6, Wherein the second control mode stores the current degree of opening of the first expansion device in real time, And controls the opening amount of the first expansion device by combining the correction opening degree with the current opening degree stored in the second control mode during the execution of the second control mode. The method according to claim 1, Wherein the operation parameter includes a discharge temperature of the refrigerant discharged from the compressor and a temperature of the refrigerant passing through the condenser, And switches from the first control mode to the second control mode when at least one of the operating parameter values deviates from the normal operation range. The method of claim 8, Wherein when the value of the operating variable returns to the normal operation range during execution of the second control mode, the amount of opening of the first expansion device is controlled by switching from the second control mode to the first control mode.

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