A heat pump system and a control method thereof

Abstract

The application discloses a heat pump system and a control method thereof. The heat pump system comprises a compressor, a four-way reversing valve, a water-side heat exchanger, a liquid accumulator, a main electronic expansion valve and an air-side heat exchanger which are sequentially connected to form a refrigerant main circuit. When the heat pump device operates, the main electronic expansion valve and the liquid injection electronic expansion valve are jointly controlled when the exhaust temperature is too high. The application aims at the problem that the exhaust temperature is too high due to the bad environmental conditions of the heat pump system. The joint control of the main electronic expansion valve and the liquid injection electronic expansion valve can reduce the exhaust temperature and ensure the capacity of the system.

Description

Technical Field

[0001] This invention relates to a heat pump system and its control method. Background Technology

[0002] With the rapid development of global industry and technology, human discovery and environmental problems have become increasingly prominent. The contradiction between energy conservation and environmental protection and people's living needs and comfort requirements has also become increasingly prominent. The world and my country are paying more and more attention to environmental protection, and the country has put forward the concept of carbon neutrality. In the past, air conditioning units generally used R410A refrigerant, which has a very high GWP and is not conducive to environmental protection. Now, R32 refrigerant is generally used as a replacement. However, the discharge temperature of R32 refrigerant is higher than that of R410A refrigerant. Under the conditions of low ambient temperature and high water temperature for heating and high ambient temperature and low water temperature for cooling, the discharge temperature is very high, which forces the unit to reduce the frequency to protect the compressor. This leads to a decrease in the unit's capacity and affects comfort.

[0003] There are three main technologies for solving the problem of excessively high exhaust temperature in heat pumps. The first is to appropriately open the throttle valve to reduce the superheat of the return gas and thus lower the exhaust temperature. However, this method may cause liquid to be carried in the return gas, resulting in liquid slugging in the compressor, which has poor reliability. The second is liquid injection cooling, in which the auxiliary circuit takes liquid from the condenser outlet, throttles it through the throttle valve, and then enters the compressor's liquid injection port. However, the heat pump capacity and efficiency of liquid injection cooling are relatively low. The third is to take liquid before enthalpy boosting by injecting gas. In this method, the auxiliary circuit takes liquid from the condenser outlet, throttles it through the throttle valve, and then exchanges heat with the main circuit through the economizer. The superheated gas is then drawn into the compressor's gas injection port. The enthalpy boosting method has good capacity and efficiency at low temperatures, but it is prone to insufficient gas injection, resulting in a still high exhaust temperature. In addition, when controlling the electronic expansion valve, a fixed number of steps is usually used for control, and the exhaust control only considers the water temperature and not the condensing temperature. When the exhaust temperature is too high, it cannot be reduced quickly, which leads to a shortened compressor life. Summary of the Invention

[0004] To address the above problems, this invention provides a heat pump system and its control method, which effectively solves the problems mentioned in the background art.

[0005] The technical solution adopted in this invention is:

[0006] A heat pump system includes a compressor, a four-way reversing valve, a water-side heat exchanger, a liquid receiver, a main electronic expansion valve, and an air-side heat exchanger, connected in sequence to form a refrigerant main circuit; wherein:

[0007] The four-way reversing valve includes control valve port D, control valve port S, control valve port E and control valve port C. The discharge port of the compressor is connected to control valve port D. The control valve port C is connected to the refrigerant inlet of the water-side heat exchanger. The refrigerant outlet of the water-side heat exchanger is connected to one end of the liquid receiver. The other end of the liquid receiver is connected to one end of the main electronic expansion valve. The other end of the main electronic expansion valve is connected to the first port of the air-side heat exchanger. The second port of the air-side heat exchanger is connected to control valve port E. The control valve port S is connected to the suction port of the compressor.

[0008] The compressor's suction port is connected to an auxiliary pipeline, the other end of which is located on the pipeline between the liquid receiver and the main electronic expansion valve. The auxiliary pipeline is equipped with a liquid injection electronic expansion valve.

[0009] The heat pump system includes a cooling mode and a heating mode.

[0010] Preferably, the heat pump system is in heating mode, control valve port D is connected to control valve port C, and control valve port S is connected to control valve port E. The refrigerant discharged from the compressor passes sequentially through control valve port D, control valve port C, water-side heat exchanger, and liquid receiver, and is divided into main refrigerant and auxiliary refrigerant, wherein:

[0011] The main refrigerant passes sequentially through the main electronic expansion valve, the air-side heat exchanger, control valve port E, control valve port S, and the compressor's suction port.

[0012] The auxiliary refrigerant passes sequentially through the liquid injection electronic expansion valve and the compressor's suction port.

[0013] Preferably, the heat pump system is in cooling mode, control valve port D is connected to control valve port E, and control valve port C is connected to control valve port S. The refrigerant discharged from the compressor passes sequentially through control valve port D, control valve port E, air-side heat exchanger, and main electronic expansion valve, and is divided into main refrigerant and auxiliary refrigerant, wherein:

[0014] The main refrigerant passes sequentially through the liquid receiver, water-side heat exchanger, control valve port C, control valve port S, and compressor suction port.

[0015] The auxiliary refrigerant passes sequentially through the liquid injection electronic expansion valve and the compressor's suction port.

[0016] Meanwhile, the present invention also provides a control method for a heat pump system, wherein when the heat pump system is running, the main electronic expansion valve and the liquid injection electronic expansion valve are respectively controlled as follows:

[0017] Main electronic expansion valve:

[0018] When Tpq < 100℃ and lasts for 5 seconds, the main electronic expansion valve operates under normal control.

[0019] When Tpq ≥ 100℃ and remains so for 5 seconds, the main electronic expansion valve enters the exhaust temperature overheat control mode.

[0020] If 100℃≤Tpq<105℃, the main electronic expansion valve will maintain its current opening.

[0021] If Tpq ≥ 105℃, the main electronic expansion valve shall be controlled according to the following rules:

[0022] a. Thj>9℃: The main electronic expansion valve is adjusted every 10 seconds. The opening degree of the main electronic expansion valve is calculated according to the following formula: EXV n =(EXV n-1 )+[KP(Tpq n -100)+KD(Tpq n -Tpq n-1 )];

[0023] b. Thj < 7℃: The main electronic expansion valve is adjusted every 30 seconds. The opening degree of the main electronic expansion valve is calculated according to the following formula:

[0024] EXV n =(EXV n-1 )-[KP(Tpq n -100)+KD(Tpq n -Tpq n-1 )] / 2, the maximum number of valve closing steps is 4 steps. If Pd_t≥55 during the valve closing process, the main electronic expansion valve will remain unchanged.

[0025] c. When Thj is in [7, 9], maintain the previous state. hj Upon first entering [7, 9], execute by pressing 'a';

[0026] d. When Tpq < 100℃, the exhaust temperature overheat control is discontinued, and the main electronic expansion valve operates under normal control.

[0027] Where Tpq is the exhaust temperature, Tpq n The exhaust temperature for this test is Tpq. n-1 The previous exhaust temperature is represented by Thj, the ambient outdoor temperature is represented by EXV, and the main electronic expansion valve opening is represented by EXV. n The opening degree of the main electronic expansion valve at this time, EXV n-1 KP is the previous opening degree of the main electronic expansion valve, KD is the exhaust proportional coefficient of the main electronic expansion valve, and Pd_t is the high-pressure saturation temperature.

[0028] Electronic expansion valve for liquid injection:

[0029] When Tpq < 105℃ and remains so for 5 seconds, the electronic expansion valve for controlling the liquid injection will close.

[0030] When Tpq ≥ 105℃ and remains so for 5 seconds, the electronic expansion valve for liquid injection is opened and remains open for a duration of t, with an initial opening of EVI1. Then, EVI is controlled according to the following rules:

[0031] a. The electronic expansion valve for liquid injection is adjusted every 10 seconds. The opening degree of the electronic expansion valve is calculated according to the following formula:

[0032] EXI n =(EXI n-1 )+[KA(Tpq n -100)+KB(Tpq n -Tpq n-1 )];

[0033] b. When Tpq < 100℃, the electronic expansion valve for liquid injection is closed;

[0034] Where Tpq is the exhaust temperature, Tpq n The exhaust temperature for this test is Tpq. n-1 EXI represents the previous exhaust temperature, and EXI represents the opening degree of the electronic expansion valve for liquid injection. n For the current opening degree of the liquid injection electronic expansion valve, EXI n-1 KA is the previous opening degree of the electronic expansion valve, KB is the exhaust proportional coefficient of the electronic expansion valve, and KB is the exhaust differential coefficient of the electronic expansion valve.

[0035] Preferably, KP is 2, KD is 1, KA is 4, and KB is 2.

[0036] Preferably, the EVI1 is 100 in heating mode and 150 in cooling mode, and t is 60s.

[0037] This invention addresses the problem of excessively high exhaust temperature in heat pump systems under harsh environmental conditions. By linking the main electronic expansion valve and the liquid injection electronic expansion valve, the system can reduce exhaust temperature while maintaining its capacity as much as possible.

[0038] This invention establishes an auxiliary path by setting up a liquid-injecting electronic expansion valve. When the main electronic expansion valve fails to reduce the exhaust temperature, the liquid-injecting electronic expansion valve is opened to lower the exhaust temperature. Since the opening of the liquid-injecting electronic expansion valve affects the energy efficiency of the heat pump system, this invention keeps the liquid-injecting electronic expansion valve closed when the main electronic expansion valve can control the exhaust temperature. When the main electronic expansion valve cannot control the exhaust temperature, the liquid-injecting electronic expansion valve is opened to control the exhaust temperature. Compared with the reduced frequency operation of the heat pump system, the opening of the liquid-injecting electronic expansion valve has a smaller impact on the energy efficiency of the heat pump system. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the structure of the heat pump device of the present invention;

[0040] Figure 2 This is a schematic diagram of the refrigerant flow in the heating state of the present invention;

[0041] Figure 3 This is a schematic diagram of the refrigerant flow in the cooling state of the present invention. Detailed Implementation

[0042] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0043] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0044] Furthermore, in the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0045] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more, unless explicitly defined otherwise.

[0046] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0047] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0048] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings. Example

[0049] like Figure 1 As shown, a heat pump system includes a compressor 1, a four-way reversing valve 2, a water-side heat exchanger 3, a liquid receiver 4, a main electronic expansion valve 5, and an air-side heat exchanger 6, which are connected in sequence to form a refrigerant main circuit; wherein:

[0050] The four-way reversing valve 2 includes control valve port D21, control valve port S22, control valve port E23 and control valve port C24. The discharge port of the compressor 1 is connected to control valve port D21. The control valve port C24 is connected to the refrigerant inlet of the water-side heat exchanger 3. The refrigerant outlet of the water-side heat exchanger 3 is connected to one end of the liquid receiver 4. The other end of the liquid receiver 4 is connected to one end of the main electronic expansion valve 5. The other end of the main electronic expansion valve 5 is connected to the first port of the air-side heat exchanger 6. The second port of the air-side heat exchanger 6 is connected to control valve port E23. The control valve port S22 is connected to the suction port of the compressor 1.

[0051] The compressor 1 has an auxiliary pipeline 7 connected to its suction port. The other end of the auxiliary pipeline 7 is located on the pipeline between the liquid reservoir 4 and the main electronic expansion valve 5. The auxiliary pipeline 7 is equipped with a liquid injection electronic expansion valve 8.

[0052] The heat pump system includes a cooling mode and a heating mode.

[0053] Furthermore, the heat pump system is in heating mode, such as... Figure 2 As shown, control valve port D21 is connected to control valve port C24, and control valve port S22 is connected to control valve port E23. The refrigerant discharged from the compressor 1 passes sequentially through control valve port D21, control valve port C24, water-side heat exchanger 3, and liquid receiver 4, and is divided into main refrigerant and auxiliary refrigerant, wherein:

[0054] The main refrigerant passes sequentially through the main electronic expansion valve 5, the air-side heat exchanger 6, the control valve port E23, the control valve port S22, and the suction port of the compressor 1.

[0055] The auxiliary refrigerant passes sequentially through the liquid injection electronic expansion valve 8 and the suction port of compressor 1.

[0056] Furthermore, the heat pump system is in cooling mode, such as... Figure 3 As shown, control valve port D21 is connected to control valve port E23, and control valve port C24 is connected to control valve port S22. The refrigerant discharged from compressor 1 passes sequentially through control valve port D21, control valve port E23, air-side heat exchanger 6, and main electronic expansion valve 5, and is divided into main refrigerant and auxiliary refrigerant.

[0057] The main refrigerant passes sequentially through the liquid receiver 4, the water-side heat exchanger 3, the control valve port C24, the control valve port S22, and the suction port of the compressor 1.

[0058] The auxiliary refrigerant passes sequentially through the liquid injection electronic expansion valve 8 and the suction port of compressor 1.

[0059] Furthermore, for this heat pump system, the present invention also provides a control method for the heat pump system, wherein during the operation of the heat pump system, the main electronic expansion valve and the liquid injection electronic expansion valve are respectively controlled as follows:

[0060] Main electronic expansion valve:

[0061] When Tpq < 100℃ and lasts for 5 seconds, the main electronic expansion valve operates under normal control.

[0062] When Tpq ≥ 100℃ and remains so for 5 seconds, the main electronic expansion valve enters the exhaust temperature overheat control mode.

[0063] If 100℃≤Tpq<105℃, the main electronic expansion valve will maintain its current opening.

[0064] If Tpq ≥ 105℃, the main electronic expansion valve shall be controlled according to the following rules:

[0065] a. Thj>9℃: Adjust the opening of the main electronic expansion valve according to PID control to bring the exhaust temperature closer to 100℃. Specifically, adjust the main electronic expansion valve every 10 seconds. The opening of the main electronic expansion valve is calculated according to the following formula: EXV n =(EXV n-1 )+[KP(Tpq n -100)+KD(Tpq n -Tpq n-1 )];

[0066] b. Thj < 7℃: Adjust the opening of the main electronic expansion valve according to PID control to bring the exhaust temperature closer to 100℃. Specifically, adjust the main electronic expansion valve every 30 seconds. The opening of the main electronic expansion valve is calculated according to the following formula:

[0067] EXV n =(EXV n-1 )-[KP(Tpq n -100)+KD(Tpq n -Tpq n-1 )] / 2, the maximum number of valve closing steps is 4 steps. If Pd_t≥55 during the valve closing process, the main electronic expansion valve will remain unchanged.

[0068] c. When Thj is in [7, 9], maintain the previous state. hj Upon first entering [7, 9], execute by pressing 'a';

[0069] d. When Tpq < 100℃, the exhaust temperature overheat control is discontinued, and the main electronic expansion valve operates under normal control.

[0070] Where Tpq is the exhaust temperature, Tpq n The exhaust temperature for this test is Tpq. n-1 The previous exhaust temperature is represented by Thj, the ambient outdoor temperature is represented by EXV, and the main electronic expansion valve opening is represented by EXV. n The opening degree of the main electronic expansion valve at this time, EXV n-1 KP is the previous opening degree of the main electronic expansion valve, KD is the exhaust proportional coefficient of the main electronic expansion valve (default is 2), KD is the exhaust differential coefficient of the main electronic expansion valve (default is 1), and Pd_t is the high-pressure saturation temperature.

[0071] Electronic expansion valve for liquid injection:

[0072] When Tpq < 105℃ and remains so for 5 seconds, the electronic expansion valve for controlling the liquid injection will close.

[0073] When Tpq ≥ 105℃ and remains so for 5 seconds, the electronic expansion valve for liquid injection is opened and held for a duration of t, preferably 60 seconds. The initial opening degree is EVI1, which is 100 in heating mode and 150 in cooling mode. Then, EVI is controlled according to the following rules:

[0074] a. Adjust the opening of the electronic expansion valve for liquid injection according to PID control to bring the exhaust temperature closer to 100℃. Specifically, control the electronic expansion valve to adjust every 10 seconds. The opening of the electronic expansion valve is calculated according to the following formula:

[0075] EXI n =(EXI n-1 )+[KA(Tpq n -100)+KB(Tpq n -Tpq n-1 )];

[0076] b. When Tpq < 100℃, the electronic expansion valve for liquid injection is closed;

[0077] Where Tpq is the exhaust temperature, Tpq n The exhaust temperature for this test is Tpq. n-1 EXI represents the previous exhaust temperature, and EXI represents the opening degree of the electronic expansion valve for liquid injection. n For the current opening degree of the liquid injection electronic expansion valve, EXI n-1 KA represents the previous opening degree of the electronic expansion valve, KA represents the exhaust proportional coefficient of the electronic expansion valve (default value is 4), and KB represents the exhaust differential coefficient of the electronic expansion valve (default value is 2).

[0078] This invention utilizes the coordinated control of the main electronic expansion valve and the liquid injection electronic expansion valve to rapidly reduce exhaust temperature. On one hand, it prevents the unit from reducing its air conditioning capacity and affecting comfort due to excessively high exhaust temperature. On the other hand, it prevents the compressor from overheating, ensuring long-term reliable operation of the unit. Furthermore, it prioritizes the use of the main electronic expansion valve to control the exhaust temperature, and opens the liquid injection electronic expansion valve for control when the main electronic expansion valve fails, thereby maximizing the energy efficiency of the heat pump system.

[0079] Finally, it should be noted that the above examples are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments and many variations are possible. All variations that can be directly derived or conceived by those skilled in the art from the disclosure of this invention should be considered within the scope of protection of this invention.

Claims

1. A control method for a heat pump system, characterized in that, The heat pump system comprises a compressor (1), a four-way reversing valve (2), a water-side heat exchanger (3), a liquid receiver (4), a main electronic expansion valve (5), and an air-side heat exchanger (6), which are connected in sequence to form the refrigerant main circuit; wherein: The four-way reversing valve (2) includes control valve port D (21), control valve port S (22), control valve port E (23) and control valve port C (24). The exhaust port of the compressor (1) is connected to control valve port D (21). The control valve port C (24) is connected to the refrigerant inlet of the water-side heat exchanger (3). The refrigerant outlet of the water-side heat exchanger (3) is connected to one end of the liquid receiver (4). The other end of the liquid receiver (4) is connected to one end of the main electronic expansion valve (5). The other end of the main electronic expansion valve (5) is connected to the first port of the air-side heat exchanger (6). The second port of the air-side heat exchanger (6) is connected to control valve port E (23). The control valve port S (22) is connected to the suction port of the compressor (1). The compressor (1) has an air intake connected to an auxiliary pipeline (7). The other end of the auxiliary pipeline (7) is located on the pipeline between the liquid reservoir (4) and the main electronic expansion valve (5). The auxiliary pipeline (7) is equipped with a liquid injection electronic expansion valve (8). The heat pump system includes a cooling mode and a heating mode; During the operation of the heat pump system, the main electronic expansion valve and the liquid injection electronic expansion valve are controlled as follows: Main electronic expansion valve: When Tpq < 100℃ and lasts for 5 seconds, the main electronic expansion valve operates under normal control. When Tpq ≥ 100℃ and remains so for 5 seconds, the main electronic expansion valve enters the exhaust temperature overheat control mode. If 100℃≤Tpq<105℃, the main electronic expansion valve will maintain its current opening. If Tpq ≥ 105℃, the main electronic expansion valve shall be controlled according to the following rules: a. Thj>9℃: The main electronic expansion valve is adjusted every 10 seconds. The opening degree of the main electronic expansion valve is calculated according to the following formula: EXV n =(EXV n-1 )+[KP(Tpq n -100)+KD(Tpq n -Tpq n-1 )]; b. Thj < 7℃: The main electronic expansion valve is adjusted every 30 seconds. The opening degree of the main electronic expansion valve is calculated according to the following formula: EXV n =(EXV n-1 )-[KP(Tpq n -100)+KD(Tpq n -Tpq n-1 )] / 2, the maximum number of valve closing steps is 4 steps. If Pd_t≥55 during the valve closing process, the main electronic expansion valve will remain unchanged. c. When Thj is in [7, 9], maintain the previous state. hj Upon first entering [7, 9], execute by pressing 'a'; d. When Tpq < 100℃, the exhaust temperature overheat control is discontinued, and the main electronic expansion valve operates under normal control. Where Tpq is the exhaust temperature, Tpq n The exhaust temperature for this test is Tpq. n-1 The previous exhaust temperature is represented by Thj, the ambient outdoor temperature is represented by EXV, and the main electronic expansion valve opening is represented by EXV. n The opening degree of the main electronic expansion valve at this time, EXV n-1 KP is the previous opening degree of the main electronic expansion valve, KD is the exhaust proportional coefficient of the main electronic expansion valve, and Pd_t is the high-pressure saturation temperature. Electronic expansion valve for liquid injection: When Tpq < 105℃ and remains so for 5 seconds, the electronic expansion valve for controlling the liquid injection will close. When Tpq ≥ 105℃ and remains so for 5 seconds, the electronic expansion valve for liquid injection is opened and remains open for a duration of t, with an initial opening of EVI1. Then, EVI is controlled according to the following rules: a. The electronic expansion valve for liquid injection is adjusted every 10 seconds. The opening degree of the electronic expansion valve is calculated according to the following formula: EXI n =(EXI n-1 )+[KA(Tpq n -100)+KB(Tpq n -Tpq n-1 )]; b. When Tpq < 100℃, the electronic expansion valve for liquid injection is closed; Where Tpq is the exhaust temperature, Tpq n The exhaust temperature for this test is Tpq. n-1 EXI represents the previous exhaust temperature, and EXI represents the opening degree of the electronic expansion valve for liquid injection. n For the current opening degree of the liquid injection electronic expansion valve, EXI n-1 KA is the previous opening degree of the electronic expansion valve, KB is the exhaust proportional coefficient of the electronic expansion valve, and KB is the exhaust differential coefficient of the electronic expansion valve.

2. A heat pump system according to claim 1, characterized in that, The heat pump system is in heating mode. The control valve port D (21) is connected to the control valve port C (24), and the control valve port S (22) is connected to the control valve port E (23). The refrigerant discharged from the compressor (1) passes through the control valve port D (21), the control valve port C (24), the water-side heat exchanger (3), and the liquid receiver (4) in sequence and is divided into main refrigerant and auxiliary refrigerant, wherein: The main refrigerant passes sequentially through the main electronic expansion valve (5), the air-side heat exchanger (6), the control valve port E (23), the control valve port S (22), and the suction port of the compressor (1); The auxiliary refrigerant passes sequentially through the liquid injection electronic expansion valve (8) and the suction port of the compressor (1).

3. A heat pump system according to claim 1, characterized in that, The heat pump system is in cooling mode. The control valve port D (21) is connected to the control valve port E (23), and the control valve port C (24) is connected to the control valve port S (22). The refrigerant discharged by the compressor (1) passes through the control valve port D (21), the control valve port E (23), the air-side heat exchanger (6), and the main electronic expansion valve (5) in sequence and is divided into main refrigerant and auxiliary refrigerant, wherein: The main refrigerant passes sequentially through the liquid receiver (4), the water-side heat exchanger (3), the control valve port C (24), the control valve port S (22), and the suction port of the compressor (1); The auxiliary refrigerant passes sequentially through the liquid injection electronic expansion valve (8) and the suction port of the compressor (1).

4. The control method for a heat pump system according to claim 1, characterized in that, The values ​​are KP = 2, KD = 1, KA = 4, and KB = 2.

5. The control method for a heat pump system according to claim 1, characterized in that, The EVI1 is 100 in heating mode and 150 in cooling mode, and t is 60s.

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