Heat pump system and control method thereof

Abstract

The invention 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 storage device, a main electronic expansion valve and an air side heat exchanger which are sequentially connected to form a refrigerant main loop; and the main electronic expansion valve and the liquid spraying electronic expansion valve are subjected to linkage control when the exhaust temperature is too high. Aiming at the problem that the exhaust temperature of a heat pump system is too high due to severe environmental conditions, through linkage control of the main electronic expansion valve and the liquid spraying electronic expansion valve, the capacity of the system is guaranteed as much as possible while the exhaust temperature is reduced.

Description

Technical Field

[0001] The invention relates to a heat pump system and a control method thereof. Background Art

[0002] With the rapid development of world industry and science and technology, human discovery and environmental problems have become more and more prominent, and the contradiction between energy conservation and environmental protection and people's living needs and comfort requirements has become more and more prominent. The world and our country have attached more and more importance 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 had a very high GWP and was not conducive to environmental protection. Now it is generally replaced by R32 refrigerant, and the exhaust temperature of R32 refrigerant is higher than that of R410A refrigerant. In the case of low ambient temperature and high water temperature heating and high ambient temperature and low water temperature cooling, the exhaust temperature is very high, causing the unit to have to reduce the frequency to protect the compressor, which 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 open the throttle valve appropriately to reduce the superheat of the return air and thus reduce the exhaust temperature. However, this method may cause liquid in the return air, resulting in liquid hammer in the compressor, and has poor reliability. The second is liquid spray cooling, that is, the auxiliary circuit takes liquid from the condenser outlet, passes through the throttle valve to throttle, and then enters the compressor liquid spray port, but the heat pump capacity and energy efficiency of liquid spray cooling is relatively low. The third is to take liquid before replenishing air and increasing enthalpy, that is, the auxiliary circuit takes liquid from the condenser outlet, passes through the throttle valve to throttle, and then exchanges heat with the main circuit through the economizer. The superheated gas is sucked into the compressor replenishing air port. The jet enthalpy increase method has good capacity and energy efficiency at low temperatures, but it is easy to have insufficient replenishing air, resulting in a situation where the exhaust temperature is still very high. 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, not the condensing temperature. When the exhaust temperature is too high, the exhaust temperature cannot be quickly reduced, resulting in a shortened compressor life. Summary of the invention

[0004] In view of the above problems, the present invention provides a heat pump system and a control method thereof, which effectively solve the problems pointed out in the background technology.

[0005] The technical solution adopted by the present invention is:

[0006] A heat pump system, comprising a compressor, a four-way reversing valve, a water-side heat exchanger, a liquid reservoir, a main electronic expansion valve, and an air-side heat exchanger, which are sequentially connected to form a refrigerant main loop; wherein: the four-way reversing valve comprises a control valve port D, a control valve port S, a control valve port E, and a control valve port C, the exhaust port of the compressor is connected to the 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 reservoir, the other end of the liquid reservoir 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 the control valve port E, and the control valve port S is connected to the air intake port of the compressor;

[0007] The air intake port of the compressor is connected to an auxiliary pipeline, the other end of the auxiliary pipeline is located on the pipeline between the liquid reservoir and the main electronic expansion valve, and the auxiliary pipeline is provided with a liquid spraying electronic expansion valve;

[0008] The heat pump system includes a cooling mode and a heating mode.

[0009] Preferably, the heat pump system is in heating mode, the control valve port D is connected to the control valve port C, the control valve port S is connected to the control valve port E, and the refrigerant discharged from the compressor passes through the control valve port D, the control valve port C, the water side heat exchanger, and the liquid storage device in sequence and is divided into the main refrigerant and the auxiliary refrigerant, wherein:

[0010] The main refrigerant passes through the main electronic expansion valve, the air side heat exchanger, the control valve port E, the control valve port S, and the suction port of the compressor in sequence;

[0011] The auxiliary refrigerant passes through the liquid injection electronic expansion valve and the suction port of the compressor in turn.

[0012] Preferably, the heat pump system is in cooling mode, the control valve port D is connected to the control valve port E, the control valve port C is connected to the control valve port S, and the refrigerant discharged from the compressor passes through the control valve port D, the control valve port E, the air side heat exchanger, and the main electronic expansion valve in sequence and is divided into the main refrigerant and the auxiliary refrigerant, wherein:

[0013] The main refrigerant passes through the liquid receiver, the water side heat exchanger, the control valve port C, the control valve port S, and the suction port of the compressor in sequence;

[0014] The auxiliary refrigerant passes through the liquid injection electronic expansion valve and the suction port of the compressor in turn.

[0015] At the same time, the present invention also provides a control method for a heat pump system. When the heat pump device is running, the main electronic expansion valve and the liquid injection electronic expansion valve are respectively controlled as follows:

[0016] Main electronic expansion valve:

[0017] When Tpq is less than 100℃ and lasts for 5s, the main electronic expansion valve is controlled normally;

[0018] When Tpq≥100℃ and lasts for 5s, the main electronic expansion valve enters the exhaust temperature too high control:

[0019] If 100℃≤Tpq<105℃, the main electronic expansion valve maintains the current opening;

[0020] If Tpq ≥ 105°C, the main electronic expansion valve is controlled according to the following rules:

[0021] a. Thj>9℃: Control the main electronic expansion valve to adjust once every 10s. The opening of the main electronic expansion valve is calculated according to the following formula:

[0022] 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 controlled to adjust once every 30 seconds. The opening 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 is controlled to remain unchanged;

[0025] c. When Thj is in [7, 9], maintain the previous state. If T hj When entering [7, 9] for the first time, press a to execute;

[0026] d. When Tpq is less than 100℃, the exhaust temperature over-control will be terminated and the main electronic expansion valve will be controlled normally;

[0027] Where, Tpq is the exhaust temperature, Tpq n is the exhaust temperature of this time, Tpq n-1 is the last exhaust temperature, Thj is the outdoor ambient temperature, EXV is the opening of the main electronic expansion valve, EXV n The opening degree of the main electronic expansion valve, EXV n-1is the last opening of the main electronic expansion valve, KP is the exhaust proportional coefficient of the main electronic expansion valve, KD is the exhaust differential coefficient of the main electronic expansion valve, and Pd_t is the high-pressure saturation temperature;

[0028] Liquid injection electronic expansion valve:

[0029] When Tpq is less than 105℃ and lasts for 5s, the liquid injection electronic expansion valve is controlled to close;

[0030] When Tpq≥105℃ and lasts for 5s, the liquid injection electronic expansion valve is controlled to open for a duration of t, with the initial opening being EVI1, and then EVI is controlled according to the following rules:

[0031] a. The control liquid injection electronic expansion valve is adjusted every 10 seconds. The opening of the liquid injection 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 is less than 100℃, the liquid injection electronic expansion valve is closed;

[0034] Where, Tpq is the exhaust temperature, Tpq n is the exhaust temperature of this time, Tpq n-1 is the last exhaust temperature, EXI is the opening of the liquid injection electronic expansion valve, EXI n is the current opening of the liquid injection electronic expansion valve, EXI n-1 is the last opening of the liquid injection electronic expansion valve, KA is the exhaust proportional coefficient of the liquid injection electronic expansion valve, and KB is the exhaust differential coefficient of the liquid injection electronic expansion valve.

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

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

[0037] The present invention aims to solve the problem of excessively high exhaust temperature in a heat pump system due to adverse environmental conditions, and reduces the exhaust temperature while ensuring the capacity of the system as much as possible through linkage control of a main electronic expansion valve and a liquid injection electronic expansion valve.

[0038] The present invention forms an auxiliary circuit by arranging a liquid-spraying electronic expansion valve. When the main electronic expansion valve cannot lower the exhaust temperature, the exhaust temperature is lowered by opening the liquid-spraying electronic expansion valve. Since the liquid-spraying electronic expansion valve will affect the capacity and energy efficiency of the heat pump system when it is opened, the present invention closes the liquid-spraying electronic expansion valve when the main electronic expansion valve can control the exhaust temperature to meet the requirements. When the main electronic expansion valve cannot control the exhaust temperature to meet the requirements, the exhaust temperature is controlled by opening the liquid-spraying electronic expansion valve. Compared with the frequency reduction operation of the heat pump system, the opening of the liquid-spraying electronic expansion valve has less impact on the capacity and energy efficiency of the heat pump system. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0041] Figure 3 It is a schematic diagram of the refrigerant flow in the refrigeration state of the present invention. DETAILED DESCRIPTION

[0042] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0043] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0044] In addition, in the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0045] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "plurality" means two or more, unless otherwise clearly specified.

[0046] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0047] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0048] The present invention is further described in detail below through specific embodiments in conjunction with the accompanying drawings.

[0049] Example 1

[0050] 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 storage tank 4, a main electronic expansion valve 5, and an air-side heat exchanger 6, which are sequentially connected to form a refrigerant main circuit; wherein:

[0051] The four-way reversing valve 2 includes a control valve port D21, a control valve port S22, a control valve port E23 and a control valve port C24. The exhaust port of the compressor 1 is connected to the 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 reservoir 4, the other end of the liquid reservoir 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 the control valve port E23, and the control valve port S22 is connected to the air intake port of the compressor 1;

[0052] The air intake port of the compressor 1 is 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, and a liquid injection electronic expansion valve 8 is provided on the auxiliary pipeline 7;

[0053] The heat pump system includes a cooling mode and a heating mode.

[0054] Furthermore, the heat pump system is in heating mode, such as Figure 2 As shown, the control valve port D21 is connected to the control valve port C24, the control valve port S22 is connected to the control valve port E23, and the refrigerant discharged from the compressor 1 passes through the control valve port D21, the control valve port C24, the water side heat exchanger 3, and the liquid storage tank 4 in sequence and is divided into the main refrigerant and the auxiliary refrigerant, wherein:

[0055] The main refrigerant passes 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 air intake port of the compressor 1 in sequence;

[0056] The auxiliary refrigerant passes through the liquid injection electronic expansion valve 8 and the suction port of the compressor 1 in sequence.

[0057] Furthermore, the heat pump system is in cooling mode, such as Figure 3 As shown, the control valve port D21 is connected to the control valve port E23, the control valve port C24 is connected to the control valve port S22, and the refrigerant discharged from the compressor 1 passes through the control valve port D21, the control valve port E23, the air side heat exchanger 6, and the main electronic expansion valve 5 in sequence and is divided into the main refrigerant and the auxiliary refrigerant, wherein:

[0058] The main refrigerant passes through the liquid storage tank 4, the water side heat exchanger 3, the control valve port C24, the control valve port S22, and the air intake port of the compressor 1 in sequence;

[0059] The auxiliary refrigerant passes through the liquid injection electronic expansion valve 8 and the suction port of the compressor 1 in sequence.

[0060] At the same time, for the heat pump system, the present invention also provides a control method for the heat pump system, when the heat pump device is running, the main electronic expansion valve and the liquid injection electronic expansion valve are respectively controlled as follows:

[0061] Main electronic expansion valve:

[0062] When Tpq is less than 100℃ and lasts for 5s, the main electronic expansion valve is controlled normally;

[0063] When Tpq≥100℃ and lasts for 5s, the main electronic expansion valve enters the exhaust temperature too high control:

[0064] If 100℃≤Tpq<105℃, the main electronic expansion valve maintains the current opening;

[0065] If Tpq ≥ 105°C, the main electronic expansion valve is controlled according to the following rules:

[0066] a. Thj>9℃: According to PID control, adjust the opening of the main electronic expansion valve so that the exhaust temperature approaches 100℃. Specifically, control the main electronic expansion valve to adjust once every 10s. 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 )];

[0068] b. Thj<7℃: adjust the opening of the main electronic expansion valve according to PID control to make the exhaust temperature close to 100℃. Specifically: control the main electronic expansion valve to adjust once every 30s. The opening of the main electronic expansion valve is calculated according to the following formula:

[0069] 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. During the valve closing process, if Pd_t≥55, the main electronic expansion valve is controlled to remain unchanged;

[0070] c. When Thj is in [7, 9], maintain the previous state. If T hj When entering [7, 9] for the first time, press a to execute;

[0071] d. When Tpq is less than 100℃, the exhaust temperature over-control will be terminated and the main electronic expansion valve will be controlled normally;

[0072] Where, Tpq is the exhaust temperature, Tpq n is the exhaust temperature of this time, Tpq n-1 is the last exhaust temperature, Thj is the outdoor ambient temperature, EXV is the opening of the main electronic expansion valve, EXV n The opening degree of the main electronic expansion valve, EXV n-1 is the last opening of the main electronic expansion valve, KP is the exhaust proportional coefficient of the main electronic expansion valve, the default value is 2, KD is the exhaust differential coefficient of the main electronic expansion valve, the default value is 1, and Pd_t is the high pressure saturation temperature;

[0073] Liquid injection electronic expansion valve:

[0074] When Tpq is less than 105℃ and lasts for 5s, the liquid injection electronic expansion valve is controlled to close;

[0075] When Tpq≥105℃ and lasts for 5s, the liquid injection electronic expansion valve is controlled to open for a duration of t, preferably 60s, with an initial opening of EVI1, which is 100 in heating mode and 150 in cooling mode. Then EVI is controlled according to the following rules:

[0076] a. According to PID control, adjust the opening of the liquid-spraying electronic expansion valve so that the exhaust temperature approaches 100°C. Specifically, control the liquid-spraying electronic expansion valve to adjust once every 10 seconds. The opening of the liquid-spraying electronic expansion valve is calculated according to the following formula:

[0077] EXI n =(EXI n-1 )+[KA(Tpq n -100)+KB(Tpq n -Tpq n-1 )];

[0078] b. When Tpq is less than 100℃, the liquid injection electronic expansion valve is closed;

[0079] Where, Tpq is the exhaust temperature, Tpq n is the exhaust temperature of this time, Tpq n-1 is the last exhaust temperature, EXI is the opening of the liquid injection electronic expansion valve, EXI n is the current opening of the liquid injection electronic expansion valve, EXI n-1 is the last opening of the liquid injection electronic expansion valve, KA is the exhaust proportional coefficient of the liquid injection electronic expansion valve, the default value is 4, KB is the exhaust differential coefficient of the liquid injection electronic expansion valve, the default value is 2.

[0080] The present invention controls the main electronic expansion valve and the liquid injection electronic expansion valve in linkage to quickly reduce the exhaust temperature. On the one hand, it can avoid the reduction of air-conditioning capacity due to frequency reduction of the unit due to excessively high exhaust temperature, thereby affecting comfort; on the other hand, it can prevent the compressor from overheating, thereby ensuring the long-term reliable operation of the unit, and preferentially using the main electronic expansion valve to control the exhaust temperature. When the main electronic expansion valve cannot be controlled, the liquid injection electronic expansion valve is opened for control, thereby maximizing the capacity and energy efficiency of the heat pump system.

[0081] Finally, it should be noted that the above examples are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and there are many variations. All variations that can be directly derived or associated with the content disclosed by a person skilled in the art should be considered as the protection scope of the present invention.

Claims

1. A heat pump system, characterized in that: The invention comprises a compressor (1), a four-way reversing valve (2), a water-side heat exchanger (3), a liquid storage device (4), a main electronic expansion valve (5), and an air-side heat exchanger (6) which are sequentially connected to form a refrigerant main circuit; wherein: The four-way reversing valve (2) comprises a control valve port D (21), a control valve port S (22), a control valve port E (23) and a control valve port C (24); the exhaust port of the compressor (1) is connected to the 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 reservoir (4); the other end of the liquid reservoir (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 the control valve port E (23); and the control valve port S (22) is connected to the air intake port of the compressor (1); The air intake port of the compressor (1) is connected to an auxiliary pipeline (7), the other end of the auxiliary pipeline (7) is located on the pipeline between the liquid storage device (4) and the main electronic expansion valve (5), and a liquid injection electronic expansion valve (8) is provided on the auxiliary pipeline (7); The heat pump system includes a cooling mode and a heating mode.

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), the control valve port S (22) is connected to the control valve port E (23), and 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 storage device (4) in sequence and is divided into a main refrigerant and an auxiliary refrigerant, wherein: the main refrigerant passes 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 air intake port of the compressor (1) in sequence; The auxiliary refrigerant passes through the liquid spray electronic expansion valve (8) and the air intake port of the compressor (1) in sequence.

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), the control valve port C (24) is connected to the control valve port S (22), and the refrigerant discharged from 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 a main refrigerant and an auxiliary refrigerant, wherein: The main refrigerant passes through the liquid storage device (4), the water side heat exchanger (3), the control valve port C (24), the control valve port S (22), and the air intake port of the compressor (1) in sequence; The auxiliary refrigerant passes through the liquid spray electronic expansion valve (8) and the air intake port of the compressor (1) in sequence.

4. A control method for a heat pump system according to any one of claims 1 to 2, characterized in that: When the heat pump device is running, the main electronic expansion valve and the liquid injection electronic expansion valve are controlled as follows: Main electronic expansion valve: When Tpq is less than 100℃ and lasts for 5s, the main electronic expansion valve is controlled normally; When Tpq≥100℃ and lasts for 5s, the main electronic expansion valve enters the exhaust temperature too high control: If 100℃≤Tpq<105℃, the main electronic expansion valve maintains the current opening; If Tpq ≥ 105°C, the main electronic expansion valve is controlled according to the following rules: a. Thj>9℃: Control the main electronic expansion valve to adjust once every 10s. 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 )]; b. Thj<7℃: The main electronic expansion valve is controlled to adjust once every 30 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 )] / 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 is controlled to remain unchanged; c. When Thj is in [7, 9], maintain the previous state. If T hj When entering [7, 9] for the first time, press a to execute; d. When Tpq is less than 100℃, the exhaust temperature over-control will be terminated and the main electronic expansion valve will be controlled normally; Where, Tpq is the exhaust temperature, Tpq n is the exhaust temperature of this time, Tpq n-1 is the last exhaust temperature, Thj is the outdoor ambient temperature, EXV is the opening of the main electronic expansion valve, EXV n The opening degree of the main electronic expansion valve, EXV n-1 is the last opening of the main electronic expansion valve, KP is the exhaust proportional coefficient of the main electronic expansion valve, KD is the exhaust differential coefficient of the main electronic expansion valve, and Pd_t is the high-pressure saturation temperature; Liquid injection electronic expansion valve: When Tpq is less than 105℃ and lasts for 5s, the liquid injection electronic expansion valve is controlled to close; When Tpq≥105℃ and lasts for 5s, the liquid injection electronic expansion valve is controlled to open for a duration of t, with the initial opening being EVI1, and then EVI is controlled according to the following rules: a. The control liquid injection electronic expansion valve is adjusted every 10 seconds. The opening of the liquid injection 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 is less than 100℃, the liquid injection electronic expansion valve is closed; Where, Tpq is the exhaust temperature, Tpq n is the exhaust temperature of this time, Tpq n-1 is the last exhaust temperature, EXI is the opening of the liquid injection electronic expansion valve, EXI n is the current opening of the liquid injection electronic expansion valve, EXI n-1 is the last opening of the liquid injection electronic expansion valve, KA is the exhaust proportional coefficient of the liquid injection electronic expansion valve, and KB is the exhaust differential coefficient of the liquid injection electronic expansion valve.

5. A control method for a heat pump system according to claim 4, characterized in that: The KP is 2, the KD is 1, the KA is 4, and the KB is 2.

6. A control method for a heat pump system according to claim 4, characterized in that: The EVI1 is 100 in heating mode and 150 in cooling mode, and the t is 60s.

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