Variable capacity heat pump system and control method thereof

Abstract

The present application relates to the technical field of heat pump system, and propose a kind of variable capacity heat pump system and control method thereof, comprising: including compressor, first heat exchanger, second heat exchanger, variable capacity gas-liquid separator and for controlling refrigerant circulation direction's reversing valve;Wherein, the variable capacity gas-liquid separator includes inlet pipe, outlet pipe, first control valve, oil return hole and bottom not intercommunication first liquid storage area and second liquid storage area;The first control valve is arranged at the inlet pipe of the variable capacity gas-liquid separator, for controlling refrigerant inflow first liquid storage area and / or second liquid storage area;The outlet pipe of the variable capacity gas-liquid separator and the oil return hole are arranged in first liquid storage area, and the oil return hole is connected with the oil return pipe of the compressor;The variable capacity heat pump system of present application can give consideration to heat pump system operating efficiency and oil return effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heat pump systems, and more particularly, to a variable-capacity heat pump system and a control method thereof. BACKGROUND

[0002] In order to prevent liquid refrigerant from flowing into the compressor, the existing heat pump system introduces the refrigerant originally directly input into the compressor into the gas-liquid separator, so as to ensure that the refrigerant enters the compressor in the form of gas, thereby avoiding damage to the compressor caused by excessive liquid refrigerant.

[0003] The capacity of the gas-liquid separator in the existing heat pump system is fixed. In order to ensure that the heat pump system has a high efficiency from the refrigerant flowing into the gas-liquid separator to the refrigerant flowing out of the gas-liquid separator in the form of gas during operation, and in order to ensure that oil flowing out of the oil return hole of the gas-liquid separator is used to supplement the lubricating oil of the compressor, and at the same time, excessive liquid refrigerant does not flow into the compressor from the oil return hole of the gas-liquid separator, the capacity of the gas-liquid separator and the size of the oil return hole need to be precisely designed. However, the amount of liquid refrigerant generated by the heat pump system in different operation modes is not fixed. For example, in the defrosting mode, the heat of the refrigerant flowing through the outdoor unit is used to melt the frost layer of the outdoor unit, and more liquid refrigerant enters the gas-liquid separator. When designing the capacity of the gas-liquid separator, if the increased amount of liquid refrigerant in the defrosting mode is not considered in order to maximize the refrigeration or heating efficiency of the heat pump system in the cooling mode and the heating mode, a large amount of liquid refrigerant may flow into the compressor, causing damage to the compressor. However, if the capacity of the gas-liquid separator is simply increased to prevent a large amount of refrigerant from flowing into the compressor in the defrosting mode, the refrigerant may not flow from the gas-liquid separator to the compressor in time, resulting in a decrease in the refrigeration and heating efficiency, and the compressor may not return oil in time or too much liquid refrigerant may flow out of the oil return hole.

[0004] In summary, the existing fixed-capacity gas-liquid separator has the problem of being unable to balance the operation efficiency of the heat pump system and the oil return effect. SUMMARY

[0005] The present application provides a variable-capacity heat pump system and a control method thereof, which can balance the operation efficiency of the heat pump system and the oil return effect.

[0006] To solve the above technical problems, the technical solutions of the present application are as follows:

[0007] A variable-capacity heat pump system, which contains refrigerant, comprises a compressor, a first heat exchanger, a second heat exchanger, a variable-capacity gas-liquid separator, and a reversing valve for controlling the circulation direction of the refrigerant.

[0008] When the reversing valve controls the circulation direction of the refrigerant to be a heating cycle direction, the reversing valve introduces the refrigerant flowing out of the compressor into the second heat exchanger, the refrigerant sequentially flows through the second heat exchanger, the first heat exchanger and the reversing valve, the reversing valve introduces the refrigerant into the variable-capacity gas-liquid separator, and the refrigerant flows into the compressor after flowing out of the variable-capacity gas-liquid separator;

[0009] When the reversing valve controls the circulation direction of the refrigerant to be a heating cycle direction, the reversing valve introduces the refrigerant flowing out of the compressor into the second heat exchanger, the refrigerant sequentially flows through the second heat exchanger, the first heat exchanger and the reversing valve, the reversing valve introduces the refrigerant into the variable-capacity gas-liquid separator, and the refrigerant flows into the compressor after flowing out of the variable-capacity gas-liquid separator;

[0010] The variable-capacity gas-liquid separator comprises an inlet pipe, an outlet pipe, a first control valve, an oil return hole, and a first liquid storage area and a second liquid storage area which are not communicated at the bottom; the first control valve is arranged at the inlet pipe of the variable-capacity gas-liquid separator and is used to control the refrigerant to flow into the first liquid storage area and / or the second liquid storage area; the outlet pipe of the variable-capacity gas-liquid separator and the oil return hole are arranged in the first liquid storage area, and the oil return hole is connected with an oil return pipe of the compressor.

[0011] The application further provides a variable-capacity heat pump system control method, which applies the above variable-capacity heat pump system and comprises the following steps.

[0012] The variable-capacity heat pump system is continuously detected to determine whether it enters a defrosting state, if yes, the detection is stopped and a defrosting protection operation is performed; otherwise, the variable-capacity heat pump system is continuously detected to determine whether it enters the defrosting state.

[0013] The defrosting protection operation comprises the following steps.

[0014] The liquid level of the refrigerant in the first liquid storage area of the variable-capacity gas-liquid separator is continuously detected, when the liquid level exceeds a preset liquid level threshold, the first control valve is used to make the refrigerant flow into the first liquid storage area and the second liquid storage area, the second control valve is used to make the pipeline between the oil return hole and the compressor be communicated, and the variable-capacity heat pump system is continuously detected to determine whether it exits the defrosting state.

[0015] If the variable-capacity heat pump system does not exit the defrosting state, the variable-capacity heat pump system is continuously detected to determine whether it exits the defrosting state.

[0016] If the variable-capacity heat pump system exits the defrosting state, the defrosting state detection is stopped, the first control valve is used to make the refrigerant flow into the first liquid storage area and not flow into the second liquid storage area, and the difference between the exhaust temperature of the first heat exchanger and the temperature of the refrigerant flowing out of the variable-capacity gas-liquid separator is continuously detected to determine whether it is greater than a preset difference.

[0017] If the difference is greater than a preset difference, a second control valve is used to make the pipeline between the oil return hole and the compressor not communicate; otherwise, it is continuously detected whether the difference is greater than the preset difference.

[0018] Compared with the prior art, the beneficial effects of the technical scheme of the present application are:

[0019] The variable-capacity gas-liquid separator is used to introduce the refrigerant into the first liquid storage area by using the first control valve when the heat pump system operates in the non-defrosting mode, and when designing the capacity of the first liquid storage area and the oil return hole, the maximum operating efficiency of the heat pump system can be considered, without considering the large amount of liquid refrigerant brought by the defrosting mode; when the heat pump system operates in the defrosting mode, the first control valve is used to introduce the refrigerant into the first liquid storage area and the second liquid storage area, and the second liquid storage area shares the excessive liquid refrigerant brought by the defrosting mode, without affecting the design of the oil return hole of the first liquid storage area, so that the operating efficiency of the heat pump system and the oil return effect can be considered, and the control method of the heat pump system is used, so that the operating efficiency of the heat pump system and the oil return effect can be better considered. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The first structure diagram of the variable-capacity heat pump system proposed for example 1 is shown.

[0021] Figure 2 The second structure diagram of the variable-capacity heat pump system proposed for example 1 is shown.

[0022] Figure 3 The principle diagram of the four-way valve proposed for example 1 is shown.

[0023] Figure 4 The defrosting protection control logic diagram proposed for example 2 is shown. DETAILED DESCRIPTION

[0024] The drawings are only used for illustrative description, and cannot be understood as a limitation on the present embodiment;

[0025] In order to better illustrate the present embodiment, some components in the drawings may be omitted, enlarged or reduced, and do not represent the actual product size;

[0026] For those skilled in the art, it is understandable that some known structures and their descriptions in the drawings may be omitted.

[0027] The technical scheme of the present application will be further described below in combination with the drawings and examples.

[0028] Example 1

[0029] The present embodiment proposes a variable-capacity heat pump system, Figure 1This is a schematic diagram of the first structure of the variable capacity heat pump system in this embodiment;

[0030] like Figure 1 As shown in this embodiment, a variable capacity heat pump system is proposed. The system contains refrigerant and includes a compressor, a first heat exchanger, a second heat exchanger, a variable capacity gas-liquid separator, and a reversing valve for controlling the refrigerant circulation direction.

[0031] When the reversing valve controls the circulation direction of the refrigerant to the refrigeration circulation direction, the reversing valve introduces the refrigerant flowing out of the compressor into the first heat exchanger. The refrigerant flows through the first heat exchanger, the second heat exchanger and the reversing valve in sequence. The reversing valve introduces the refrigerant into the variable capacity gas-liquid separator. The refrigerant flows out of the variable capacity gas-liquid separator and then into the compressor.

[0032] When the reversing valve controls the circulation direction of the refrigerant to the heating circulation direction, the reversing valve introduces the refrigerant flowing out of the compressor into the second heat exchanger. The refrigerant flows through the second heat exchanger, the first heat exchanger and the reversing valve in sequence. The reversing valve introduces the refrigerant into the variable capacity gas-liquid separator. The refrigerant flows out of the variable capacity gas-liquid separator and then into the compressor.

[0033] The variable capacity gas-liquid separator includes an inlet pipe, an outlet pipe, a first control valve, an oil return hole, and a first liquid storage area and a second liquid storage area that are not interconnected at the bottom. The first control valve is located at the inlet pipe of the variable capacity gas-liquid separator and is used to control the flow of refrigerant into the first liquid storage area and / or the second liquid storage area. The outlet pipe of the variable capacity gas-liquid separator and the oil return hole are located within the first liquid storage area, and the oil return hole is connected to the oil return pipe of the compressor.

[0034] In practical implementation, a variable-capacity gas-liquid separator is used. When the heat pump system is running in non-defrost mode, the first control valve introduces refrigerant into the first liquid storage area. When designing the capacity of the first liquid storage area and the oil return hole, the operating efficiency of the heat pump system can be maximized without considering the large amount of liquid refrigerant brought by the defrost mode. When the heat pump system is running in defrost mode, the first control valve introduces refrigerant into the first liquid storage area and the second liquid storage area. The second liquid storage area shares the excess liquid refrigerant brought by the defrost mode without affecting the design of the oil return hole in the first liquid storage area. This balances the operating efficiency of the heat pump system and the oil return effect. When used in conjunction with the control method of the heat pump system, it can better balance the operating efficiency of the heat pump system and the oil return effect.

[0035] As an example, the reversing valve can be replaced by other devices capable of controlling the direction of refrigerant circulation.

[0036] As an exemplary illustration, the refrigerant circulation direction of the cooling mode and the defrosting mode are both the refrigeration circulation direction, the difference between the cooling mode and the defrosting mode lies in that, in the cooling mode, the first heat exchanger is mainly used for evaporating the liquid refrigerant in the first heat exchanger into gaseous refrigerant, so that the refrigerant entering the gas-liquid separator is mostly gaseous refrigerant; in the defrosting mode, the first heat exchanger is mainly used for removing the frost layer in the first heat exchanger, the temperature fails to make the liquid refrigerant mostly evaporate into gaseous refrigerant, so in the defrosting mode, the amount of liquid refrigerant entering the gas-liquid separator is greater than that in the cooling mode.

[0037] As an exemplary illustration, Figure 1 The position of the electronic expansion valve and its connection relationship in the heat pump system are common designs, which will not be described here.

[0038] In an optional embodiment, the variable-capacity gas-liquid separator further comprises a second control valve, which is used to control the communication or non-communication of the oil return hole and the compressor.

[0039] As an exemplary illustration, the first control valve comprises a first electromagnetic valve, and the second control valve comprises a second electromagnetic valve.

[0040] In an optional embodiment, the inlet pipe of the variable-capacity gas-liquid separator is divided into a first inlet branch pipe and a second inlet branch pipe, wherein the first inlet branch pipe communicates with the first liquid storage area, the first electromagnetic valve is arranged on the second inlet branch pipe, and the first electromagnetic valve is used to control the communication or non-communication of the second inlet branch pipe and the second liquid storage area.

[0041] In an optional embodiment, the variable-capacity gas-liquid separator further comprises a liquid level detector arranged in the first liquid storage area.

[0042] In an optional embodiment, a first temperature detector is arranged on the outlet pipe of the variable-capacity gas-liquid separator; and a second temperature detector is arranged on the first heat exchanger.

[0043] In an optional embodiment, the first heat exchanger comprises a finned heat exchanger.

[0044] In an optional embodiment, the second heat exchanger comprises a double-pipe heat exchanger.

[0045] In an optional embodiment, the reversing valve comprises a four-way reversing valve.

[0046] As an exemplary illustration, Figure 2 A second structural diagram of the variable-capacity heat pump system according to the present embodiment, Figure 2The connection state of each device of the heat pump system using the four-way reversing valve is shown, wherein the electromagnetic valve 1 represents the first control valve, and the electromagnetic valve 2 represents the second control valve; the electronic expansion valve and its position are designed as the common design of the heat pump system, and thus no further description is given herein.

[0047] As an exemplary illustration, as shown in Figure 2 the first end of the four-way valve is connected with the outlet pipe of the compressor, the second end of the four-way valve is connected with the second heat exchanger, the third end of the four-way valve is connected with the inlet pipe of the variable-capacity gas-liquid separator, the outlet pipe of the variable-capacity gas-liquid separator is connected with the inlet pipe of the compressor, the fourth end of the four-way valve is connected with the first heat exchanger, and the first heat exchanger is connected with the second heat exchanger;

[0048] As an exemplary illustration, Figure 3 the principle diagram of the four-way valve proposed in the embodiment is shown; Figure 3 the refrigerant flow direction controlled by the four-way valve in the refrigeration cycle direction is shown, Figure 3 the outdoor unit corresponds to the first heat exchanger, Figure 3 the indoor unit corresponds to the second heat exchanger, Figure 3 the position of the variable-capacity gas-liquid separator is not shown, and Figure 3 A, B, C and D respectively represent the first end, the second end, the third end and the fourth end of the four-way valve; when the heat pump system is in the refrigeration state, the four-way valve is not powered, the four-way valve is in the state of AD communication and BC communication, the refrigerant is compressed by the compressor to become a high-temperature and high-pressure gas, is discharged from the D port through the A port of the four-way valve, enters the outdoor heat exchanger (the first heat exchanger, used as a condenser), becomes a medium-temperature and high-pressure liquid after heat absorption and heat release in the condenser, becomes a low-temperature and low-pressure liquid after passing through the expansion valve, becomes a low-temperature and low-pressure gas after heat absorption and heat release in the indoor heat exchanger (the second heat exchanger, used as an evaporator), and returns to the compressor through the C port of the four-way valve B port, and then continues to circulate; when the heat pump system is in the heating state, the four-way valve is powered, the piston moves to the right to make AB communication and CD communication, the refrigerant is compressed by the compressor to become a high-temperature and high-pressure gas, is discharged from the B port through the A port of the four-way valve, enters the indoor heat exchanger (the condenser), becomes a medium-temperature and high-pressure liquid after heat absorption and heat release in the condenser, becomes a low-temperature and low-pressure liquid after passing through the expansion valve, becomes a low-temperature and low-pressure gas after heat absorption and heat release in the outdoor heat exchanger (the evaporator), and returns to the compressor through the C port of the four-way valve D port, and then continues to circulate.

[0049] Embodiment 2

[0050] Based on the variable-capacity heat pump system proposed in Embodiment 1, the following specific implementation examples are proposed in the embodiment.

[0051] Traditional heat pump air conditioning unit without economizer defrosting often accompanied by the influx of refrigerant, resulting in thinning of the compressor oil film or even wear off, resulting in compressor over temperature or over current. Figure 4 The defrosting protection control logic diagram for the present embodiment is shown in Figure 4 As shown, the present embodiment introduces two solenoid valves, the evaporated refrigerant is controlled by one solenoid valve into the variable capacity gas, the other solenoid valve is used for defrosting control oil return, the mainboard monitors the unit state, when the unit enters defrosting, liquid refrigerant level determination will be carried out, if the refrigerant exceeds the liquid level detection device, trigger the first logic, solenoid valve 1 (first control valve) open to store excess refrigerant, prevent excessive influx of compressor, at the same time, solenoid valve 2 is opened for oil return, because of the difference in density between the compressor and the refrigerant, oil will be on top of the refrigerant, at this time, a little refrigerant will bring oil into the compressor for oil return. When the unit exits defrosting, solenoid valve 2 (second control valve) is closed, at this time, the exhaust temperature T and the saturated condensation temperature T1 are detected every 30s, if the difference between the two is > 30℃, solenoid valve 1 is closed, until the next time the unit defrosting is opened, the stored refrigerant will also be gradually evaporated in the process of circulation.

[0052] The present embodiment relates to the problem of excessive refrigerant flowing into the compressor during the defrosting process of the traditional heat pump air conditioner, which can avoid overcurrent of the traditional heat pump air conditioner, store more with less, and improve the safety factor of the unit.

[0053] When the traditional heat pump air conditioning unit without economizer uses R32 (a kind of refrigerant), it will face the problem of exhaust. The refrigerant quantity will be 10% more than usual, and the problems caused by excessive refrigerant will also increase. Currently, most compressors use rotor compressors, which are high-pressure chambers in the compressor, i.e. high-speed motion area of the compressor. During the defrosting process of the unit, the frequency will be reduced, and the oil cannot be supplied to the compressor in time. Instead, the closing of the fan will cause a large amount of refrigerant to be unable to evaporate and enter the compressor in liquid state. Too large or too small gas division will cause liquid refrigerant to flow into the compressor. Especially when the gas division is small, a large amount of liquid refrigerant will directly enter the high-pressure chamber, and the refrigerant will continuously flush the oil film of the compressor bearing. After repeated flushing, the oil film gap of the compressor will be broken and disappeared. At this time, it is equivalent to the direct friction between the bearings, which will directly cause the compressor to overheat and overcurrent. The unit will frequently report faults, affecting the normal use of the unit. To solve this problem, the present application can also prevent the influx of a large amount of refrigerant during defrosting while supplementing lubricating oil to the compressor according to the density of the compressor oil and the refrigerant.

[0054] Embodiment 3

[0055] The present embodiment proposes a variable capacity heat pump system for realizing the variable capacity heat pump system proposed in embodiment 1.

[0056] The variable-capacity heat pump system control method comprises the following steps:

[0057] Continuously detecting whether the variable-capacity heat pump system enters a defrosting state, if yes, stopping the detection and performing a defrosting protection operation; otherwise, continuously detecting whether the variable-capacity heat pump system enters the defrosting state;

[0058] The defrosting protection operation comprises the following steps:

[0059] Continuously detecting a refrigerant liquid level in a first liquid storage area in the variable-capacity gas-liquid separator, when the refrigerant liquid level exceeds a preset liquid level threshold, using a first control valve to make the refrigerant flow into the first liquid storage area and a second liquid storage area, and using a second control valve to make a pipeline between the oil return hole and the compressor communicate, and continuously detecting whether the variable-capacity heat pump system exits the defrosting state;

[0060] If the defrosting state is not exited, continuously detecting whether the variable-capacity heat pump system exits the defrosting state;

[0061] If the defrosting state is exited, stopping the defrosting state detection, using the first control valve to make the refrigerant flow into the first liquid storage area and not flow into the second liquid storage area, and continuously detecting whether a difference between an exhaust temperature of the first heat exchanger and a refrigerant temperature flowing out of the variable-capacity gas-liquid separator is greater than a preset difference value;

[0062] If the difference is greater than the preset difference value, using the second control valve to make the pipeline between the oil return hole and the compressor not communicate; otherwise, continuously detecting whether the difference is greater than the preset difference value.

[0063] As an exemplary illustration, the preset difference value is designed according to actual conditions, and as an exemplary illustration, the preset difference value can be set to 30 degrees Celsius.

[0064] As an exemplary illustration, the heat pump system detects whether the mainboard monitoring unit enters the defrosting state; the heat pump system detects the refrigerant liquid level through a liquid level detector in the first liquid storage area, when the refrigerant liquid level in the first liquid storage area touches the liquid level detector, the refrigerant liquid level is considered to exceed the preset liquid level threshold; the heat pump system detects the exhaust temperature of the first heat exchanger through a second temperature detector of the first heat exchanger; the heat pump system detects the refrigerant temperature flowing out of the variable-capacity gas-liquid separator through a first temperature detector on an outlet pipe of the variable-capacity gas-liquid separator.

[0065] In an optional embodiment, when continuously detecting whether the variable-capacity heat pump system enters the defrosting state, detection is performed once every first preset time length;

[0066] Continuously detecting whether the variable-capacity heat pump system exits the defrosting state, and detecting every second preset time interval;

[0067] Continuously detecting whether the difference between the exhaust temperature of the first heat exchanger and the refrigerant temperature flowing out of the variable-capacity gas-liquid separator is greater than a preset difference, and detecting every third preset time interval.

[0068] As an exemplary illustration, the first, second, and third preset time intervals are designed according to actual needs. As an exemplary illustration, the first preset time interval can be set to 1 minute, the second preset time interval can be set to 1 minute, and the third preset time interval can be set to 30 seconds.

[0069] It can be understood that the variable-capacity heat pump system control method of the embodiment applies the system of Embodiment 1, and the optional items in the above-mentioned Embodiment 1 are also applicable to the present embodiment, so they will not be described again here.

[0070] The same or similar reference signs correspond to the same or similar components;

[0071] The terms describing the positional relationship in the drawings are only used for exemplary illustration, and should not be understood as a limitation on the present embodiment;

[0072] Obviously, the above-described embodiments of the present application are only examples for clearly illustrating the present application, and are not intended to limit the embodiments of the present application. Based on the above description, other different forms of changes or variations can be made by those of ordinary skill in the art. Here, it is not necessary or possible to exhaust all the embodiments. Any modification, equivalent replacement, and improvement made within the spirit and principles of the present application should be included in the protection scope of the claims of the present application.

Claims

1. A variable capacity heat pump system, said system containing a refrigerant, characterized by, The variable-capacity heat pump system comprises a compressor, a first heat exchanger, a second heat exchanger, a variable-capacity gas-liquid separator, and a reversing valve for controlling the circulation direction of refrigerant. When the reversing valve controls the circulation direction of the refrigerant to be a refrigeration cycle direction, the reversing valve introduces refrigerant flowing out of the compressor into the first heat exchanger, the refrigerant sequentially flows through the first heat exchanger, the second heat exchanger, and the reversing valve, the reversing valve introduces the refrigerant into the variable-capacity gas-liquid separator, and the refrigerant flows into the compressor after flowing out of the variable-capacity gas-liquid separator. When the reversing valve controls the circulation direction of the refrigerant to be a heating cycle direction, the reversing valve introduces refrigerant flowing out of the compressor into the second heat exchanger, the refrigerant sequentially flows through the second heat exchanger, the first heat exchanger, and the reversing valve, the reversing valve introduces the refrigerant into the variable-capacity gas-liquid separator, and the refrigerant flows into the compressor after flowing out of the variable-capacity gas-liquid separator. The variable-capacity gas-liquid separator comprises an inlet pipe, an outlet pipe, a first control valve, an oil return hole, and a first liquid storage area and a second liquid storage area that are not in communication at the bottom; the first control valve is arranged at the inlet pipe of the variable-capacity gas-liquid separator and is used to control the flow of refrigerant into the first liquid storage area and / or the second liquid storage area; the outlet pipe and the oil return hole of the variable-capacity gas-liquid separator are arranged in the first liquid storage area, and the oil return hole is connected with an oil return pipe of the compressor.

2. The variable capacity heat pump system of claim 1, wherein, The variable-capacity gas-liquid separator further comprises a second control valve, which is used to control the communication or non-communication of the pipeline between the oil return hole and the compressor.

3. The variable capacity heat pump system of claim 1, wherein, The inlet pipe of the variable-capacity gas-liquid separator is divided into a first inlet branch pipe and a second inlet branch pipe, wherein the first inlet branch pipe is in communication with the first liquid storage area, the first control valve is arranged on the second inlet branch pipe, and the first control valve is used to control the communication or non-communication of the second inlet branch pipe with the second liquid storage area.

4. The variable capacity heat pump system of claim 1, wherein, The variable-capacity gas-liquid separator further comprises a liquid level detector, which is arranged in the first liquid storage area.

5. The variable capacity heat pump system of claim 1, wherein, A first temperature detector is arranged on the outlet pipe of the variable-capacity gas-liquid separator; and a second temperature detector is arranged on the first heat exchanger.

6. The variable capacity heat pump system of claim 1, wherein, The first heat exchanger comprises a fin heat exchanger.

7. The variable capacity heat pump system of claim 1 wherein, The second heat exchanger comprises a tube-in-tube heat exchanger.

8. The variable capacity heat pump system according to any one of claims 1 to 7, wherein The reversing valve comprises a four-way reversing valve.

9. A variable capacity heat pump system control method for use with the variable capacity heat pump system of any one of claims 2 to 8, wherein The method comprises the following steps: continuously detecting whether the variable-capacity heat pump system enters a defrosting state, if yes, stopping the detection and performing a defrosting protection operation; otherwise, continuously detecting whether the variable-capacity heat pump system enters a defrosting state; The defrosting protection operation comprises the following steps: continuously detecting the refrigerant liquid level in the first liquid storage area of the variable-capacity gas-liquid separator, when the refrigerant liquid level exceeds a preset liquid level threshold, using the first control valve to make the refrigerant flow into the first liquid storage area and the second liquid storage area, using the second control valve to make the pipeline between the oil return hole and the compressor be in communication, and continuously detecting whether the variable-capacity heat pump system exits the defrosting state; if the variable-capacity heat pump system does not exit the defrosting state, continuously detecting whether the variable-capacity heat pump system exits the defrosting state; If the defrosting state is exited, the defrosting state detection is stopped, the first control valve is used to make the refrigerant flow into the first liquid storage area and not flow into the second liquid storage area, and it is continuously detected whether the difference between the exhaust temperature of the first heat exchanger and the refrigerant temperature flowing out of the variable capacity gas-liquid separator is greater than a preset difference value; If the difference is greater than the preset difference value, the second control valve is used to make the pipeline between the oil return hole and the compressor not communicate; otherwise, it is continuously detected whether the difference is greater than the preset difference value.

10. The variable-capacity heat pump system control method according to claim 9, characterized by, When it is continuously detected whether the variable capacity heat pump system enters the defrosting state, it is detected once every first preset time interval; When it is continuously detected whether the variable capacity heat pump system exits the defrosting state, it is detected once every second preset time interval; When it is continuously detected whether the difference between the exhaust temperature of the first heat exchanger and the refrigerant temperature flowing out of the variable capacity gas-liquid separator is greater than a preset difference value, it is detected once every third preset time interval.

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