Control method of heat pump system and heat pump system

Abstract

The invention relates to the technical field of household appliances, in particular to a control method of a heat pump system and the heat pump system, and aims to solve the problem that the safety of a compressor is poor in the two-phase injection circulation process of an existing heat pump system. Therefore, the heat pump system comprises a compressor, a condenser, an economizer, a first expansion valve, an evaporator, a gas-liquid separator, a first branch, a second branch and a second expansion valve installed on the first branch, and the control method comprises the steps that the opening degree of the first expansion valve is controlled so that the superheat degree of the evaporator can be within a first preset interval; the opening degree of the second expansion valve is controlled so that the target temperature difference T can be larger than zero degree and smaller than the set temperature; the target temperature difference T is equal to T1-T2, T1 is the temperature of the mixing point in the compressor, and T2 is the saturation temperature corresponding to the pressure of the branch outlet. Through the control, the mixing point in the compressor can be always in an overheat area, the compressor is protected, and the exhaust temperature of the compressor is prevented from being too high.

Description

Technical Field

[0001] The present invention relates to the technical field of household appliances, and in particular provides a control method of a heat pump system and a heat pump system. Background Art

[0002] The use of a quasi-two-stage compression cycle is one of the important technical means to broaden the operating temperature of the heat pump system. Under low-temperature conditions, the steam injection cycle (air supplementation and enthalpy increase) can effectively improve the heating performance of the system. However, under more severe low-temperature conditions (below -15°C), the two-phase injection cycle is more effective than the steam injection cycle in reducing the exhaust temperature of the compressor. The two-phase injection cycle is to inject the gas-liquid two-phase refrigerant at an intermediate pressure into the compressor through the injection port. The mass flow rate of the two-phase injection cycle system can be controlled and optimized by the opening of the electronic expansion valve, the injection pressure (intermediate pressure) and the exhaust superheat, but due to the existence of the wet compression problem, it is crucial to determine the control method and operation strategy of the two-phase injection cycle.

[0003] When the gas-liquid two-phase refrigerant is injected into the compressor, the compressor with an injection port has a wet compression limit. This wet compression limit is related to the manufacturing level of the compressor itself and is generally provided by the compressor manufacturer. In essence, the ideal limit range for safe operation of the compressor is the limit range of wet compression. However, in actual practice, due to the complexity of the heat pump system and the changes in operating conditions, the wet compression limit provided by the manufacturer cannot fully guarantee the safe and stable operation of the heat pump system.

[0004] Therefore, this field needs a new technical solution to solve the above problems. Summary of the invention

[0005] The present invention aims to solve the above technical problem, that is, to solve the problem of poor safety of the compressor of the existing heat pump system during the two-phase injection cycle.

[0006] In a first aspect, the present invention provides a control method for a heat pump system, the heat pump system comprising a compressor, a condenser, an economizer, a first expansion valve, an evaporator and a gas-liquid separator arranged in series in sequence, the compressor having an injection port, the heat pump system further comprising a first branch, a second branch and a second expansion valve installed on the first branch, the two ends of the first branch are respectively connected to the outlet end of the condenser and the branch inlet of the economizer, the two ends of the second branch are respectively connected to the branch outlet of the economizer and the injection port, the control method comprises:

[0007] Controlling the opening of the first expansion valve so that the superheat of the evaporator is within a first preset range;

[0008] Controlling the opening of the second expansion valve so that the target temperature difference ΔT is greater than zero degrees and less than a set temperature;

[0009] Among them, the target temperature difference △T=T1-T2, T1 is the temperature of the mixing point in the compressor, the mixing point refers to the state point after the refrigerant entering the compression chamber of the compressor from the injection port and the gaseous refrigerant entering from the low-pressure inlet of the compressor after primary compression are mixed, and T2 is the saturation temperature corresponding to the pressure of the branch outlet.

[0010] In the preferred technical solution of the control method of the above heat pump system, the control method further includes:

[0011] Acquiring the exhaust temperature of the compressor;

[0012] comparing the exhaust gas temperature with an upper limit exhaust gas temperature of the compressor;

[0013] According to the comparison result, the opening degree of the first expansion valve is selectively increased.

[0014] In the preferred technical solution of the control method of the heat pump system, the step of "selectively increasing the opening of the first expansion valve according to the comparison result" specifically includes:

[0015] If the exhaust gas temperature is greater than or equal to the upper limit exhaust gas temperature, the opening degree of the first expansion valve is increased.

[0016] In the preferred technical solution of the control method of the above heat pump system, the control method further includes:

[0017] The opening degree of the second expansion valve is controlled so that the superheat degree of the gas-liquid separator is within a second preset range.

[0018] In the preferred technical solution of the control method of the above heat pump system, the control method further includes:

[0019] obtaining the exhaust temperature of the compressor again and comparing it with the upper limit exhaust temperature;

[0020] If the exhaust gas temperature is still greater than or equal to the upper limit exhaust gas temperature, the compressor is stopped.

[0021] In the preferred technical solution of the control method of the above heat pump system, the second preset interval is 3±1°C to 8±1°C.

[0022] In the preferred technical solution of the control method of the heat pump system, when the exhaust temperature is lower than the upper limit exhaust temperature, the control method further comprises:

[0023] Get the load Q provided by the heat pump system h ;

[0024] The load Q provided by the heat pump system h and demand load Q d Make comparisons;

[0025] If the heat pump system provides a load Q h Less than the required load Q d , then increase the operating frequency of the compressor.

[0026] In the preferred technical solution of the control method of the above heat pump system, the first preset interval is 3±1°C to 8±1°C.

[0027] In the preferred technical solution of the control method of the above heat pump system, the set temperature is 5±1°C.

[0028] In a second aspect, the present invention further provides a heat pump system, comprising a controller, wherein the controller is configured to execute the above control method.

[0029] When the above technical scheme is adopted, during the two-phase injection cycle of the heat pump system of the present invention, the opening of the first expansion valve is first controlled to make the superheat of the evaporator within the first preset range, with the purpose of maintaining a certain superheat of the evaporator. After the superheat of the evaporator is within the first preset range by controlling the opening of the first expansion valve, the opening of the second expansion valve is further controlled to make the target temperature difference △T greater than zero and less than the set temperature. By making the target temperature difference △T greater than zero, the mixing point in the compressor can always be in the overheating zone, thereby protecting the compressor and ensuring the smooth and safe operation of the heat pump system. By making the target temperature difference △T less than the set temperature, the exhaust temperature of the compressor can be prevented from being too high, thereby further improving the safety of the heat pump system.

[0030] Furthermore, after controlling the opening of the second expansion valve so that the target temperature difference ΔT is between 0 and the set temperature, it is further determined whether the exhaust temperature of the compressor is too high, so that the exhaust temperature of the compressor can be reduced in time when the exhaust temperature of the compressor is too high, thereby further improving the safety of the heat pump system.

[0031] In addition, the heat pump system further provided by the present invention on the basis of the above technical solution adopts the above control method, thereby having the technical effects possessed by the above control method. Compared with the heat pump system before the improvement, the heat pump system of the present invention is safer. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings, in which:

[0033] Figure 1 is a schematic structural diagram of a heat pump system of the present invention;

[0034] Figure 2 is a flow chart of a control method of a heat pump system of the present invention;

[0035] Figure 3 It is a flow chart of an embodiment of a method for controlling a heat pump system of the present invention.

[0036] List of reference numerals:

[0037] 1. Compressor; 11. Exhaust port; 12. Low pressure inlet; 13. Injection port;

[0038] 2. Condenser;

[0039] 3. Economizer; 31. Main road inlet; 32. Main road outlet; 33. Branch road inlet; 34. Branch road outlet;

[0040] 4. The first expansion valve;

[0041] 5. Evaporator;

[0042] 6. Gas-liquid separator;

[0043] 7. First branch road;

[0044] 8. Second branch road;

[0045] 9. Second expansion valve. DETAILED DESCRIPTION

[0046] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the protection scope of the present invention.

[0047] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that, in the description of the present invention, although the various steps of the control method of the present invention are described in this application in a specific order, these orders are not restrictive, and those skilled in the art may perform the steps in different orders without departing from the basic principles of the present invention.

[0048] It should be noted that in the description of the present invention, the terms "inside", "outside", "left", "right", "top", "bottom" and the like indicating directions or positional relationships are based on the directions or positional relationships shown in the drawings, which are only for the convenience of description, and do not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0049] In addition, it should be noted that in the description of the present invention, unless otherwise clearly specified and limited, the terms "setting", "connection" and "installation" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0050] Specifically, Figure 1 As shown, the heat pump system of the present invention comprises a compressor 1, a condenser 2, an economizer 3, a first expansion valve 4, an evaporator 5 and a gas-liquid separator 6 which are sequentially arranged in series.

[0051] Specifically, the exhaust port 11 of the compressor 1 is connected to the inlet end of the condenser 2 through a refrigerant pipeline (from Figure 1 The right end of condenser 2 (from the top), the outlet end of condenser 2 (from Figure 1 The left end of the condenser 2 as viewed from above) is connected to the main inlet 31 of the economizer 3 through the refrigerant pipeline, and the main outlet 32 ​​of the economizer 3 is connected to the inlet end of the evaporator 5 (from the Figure 1 The first expansion valve 4 is arranged on the refrigerant pipeline between the economizer 3 and the evaporator 5. The first expansion valve 4 can also be called a main valve, and is preferably arranged as an electronic expansion valve. The outlet end (from the outlet of the evaporator 5) of the evaporator 5 is connected to the first expansion valve 4. Figure 1 The right end of the evaporator 5 as seen from above) is connected to the inlet end of the gas-liquid separator 6 through the refrigerant pipeline (from Figure 1 The bottom end of the gas-liquid separator 6 is connected to the outlet end of the gas-liquid separator 6 (from Figure 1 The top of the gas-liquid separator 6 (seen from above) is connected to the low-pressure inlet 12 of the compressor 1.

[0052] like Figure 1 As shown, the heat pump system of the present invention also includes a first branch 7, a second branch 8 and a second expansion valve 9 installed on the first branch 7, the compressor 1 also has an injection port 13, the two ends of the first branch 7 are respectively connected to the outlet end of the condenser 2 and the branch inlet 33 of the economizer 3, and the two ends of the second branch 8 are respectively connected to the branch outlet 34 of the economizer 3 and the injection port 13 of the compressor 1.

[0053] The compressor 1 preferably adopts a scroll compressor, which is relatively less sensitive to wet compression and can allow a small amount of two-phase refrigerant to be injected.

[0054] The main inlet 31 and the branch outlet 34 of the economizer 3 are both located at the first end of the economizer 3 (from Figure 1 The main outlet 32 ​​and the branch inlet 33 of the economizer 3 are both located at the second end of the economizer 3 (from Figure 1 The bottom end of the economizer 3 is shown from above. The refrigerant entering the economizer 3 from the main inlet 31 of the economizer 3 will exchange heat with the refrigerant entering the economizer 3 from the branch inlet 33 of the economizer 3.

[0055] The refrigerant coming out of the condenser 2 is divided into two flow paths: a main path and an injection branch. The refrigerant in the main path enters the economizer 3 from the main path inlet 31 of the economizer 3 along the refrigerant pipeline, and is then discharged from the main path outlet 32 ​​of the economizer 3. The refrigerant discharged from the main path outlet 32 ​​of the economizer 3 returns to the compressor 1 along the refrigerant pipeline through the first expansion valve 4, the evaporator 5 and the gas-liquid separator 6 in sequence. The refrigerant in the injection branch enters the economizer 3 from the branch inlet 33 of the economizer 3 along the first branch 7, and is then discharged from the branch outlet 34 of the economizer 3. The refrigerant discharged from the branch outlet 34 of the economizer 3 is injected into the compressor 1 from the injection port 13 of the compressor 1 along the second branch 8, wherein the mass flow rates of the main path and the injection branch are respectively regulated by the first expansion valve 4 and the second expansion valve 9. The second expansion valve 9 is also called the injection branch valve, and is also preferably set as an electronic expansion valve.

[0056] In the injection branch, if the refrigerant at the branch outlet 34 of the economizer 3 is injected into the compressor 1 in a superheated state, the process is called a vapor injection cycle. If the refrigerant at the branch outlet 34 of the economizer 3 is injected into the compressor 1 in a gas-liquid two-phase state, the process is called a two-phase injection cycle. For the two-phase injection cycle, the refrigerant entering from the low-pressure inlet 12 of the compressor 1 is mixed with the refrigerant entering from the injection port 13 of the compressor 1 in the compression chamber of the compressor 1 after primary compression, and the state point after mixing is the mixing point.

[0057] Based on the heat pump system described above, the present invention also provides a control method for the heat pump system, such as Figure 2 As shown, the control method of the present invention comprises the following steps:

[0058] S100: Controlling the opening of the first expansion valve so that the superheat (ΔTevaporation) of the evaporator is within a first preset range;

[0059] S200: Controlling the opening of the second expansion valve so that the target temperature difference ΔT is greater than zero and less than a set temperature.

[0060] The target temperature difference ΔT=T1−T2, where T1 is the temperature of the mixing point in the compressor 1, and T2 is the saturation temperature corresponding to the pressure of the branch outlet 34 of the economizer 3.

[0061] As can be seen from the background technology, in the process of the heat pump system executing the low-temperature heating mode (generally used under the condition where the ambient temperature is lower than -15°C), in order to improve the heating performance of the heat pump system, it is preferred to adopt a two-phase injection cycle, open the second expansion valve 9 and control the opening of the second expansion valve 9 to keep the superheat of the branch outlet 34 of the economizer 3 below zero. In this way, the refrigerant discharged from the branch outlet 34 of the economizer 3 is a gas-liquid two-phase refrigerant.

[0062] During the two-phase injection cycle, in order to improve the safety of the compressor 1, the present invention first controls the opening of the first expansion valve 4 so that the superheat (△Tevaporation) of the evaporator 5 is within the first preset interval, with the purpose of maintaining a certain superheat of the evaporator 5. The present invention does not limit the specific value of the first preset interval, and those skilled in the art can flexibly set it based on experiments or experience. The present invention preferably sets the first preset interval to 3±1°C to 8±1°C, that is, by controlling the opening of the first expansion valve 4, the superheat (△Tevaporation) of the evaporator 5 is between 3±1°C and 8±1°C. Taking the first preset interval of 3°C to 8°C as an example, if the superheat of the evaporator 5 is less than 3°C, it is necessary to reduce the opening of the first expansion valve 4 to increase the superheat of the evaporator 5. Conversely, if the superheat of the evaporator 5 is greater than 8°C, it is necessary to increase the opening of the first expansion valve 4 to reduce the superheat of the evaporator 5.

[0063] Among them, the superheat of the evaporator 5 (△Tevaporation) is the difference between the outlet temperature of the evaporator 5 and the saturation temperature corresponding to the outlet pressure of the evaporator 5. A temperature sensor and a pressure sensor can be set at the outlet end of the evaporator 5 to detect the outlet temperature of the evaporator 5 and the outlet pressure of the evaporator 5 respectively. In specific applications, it can also be replaced by the difference between the outlet temperature of the evaporator 5 and the temperature of the middle coil of the evaporator 5.

[0064] After the superheat (△Tevaporation) of the evaporator 5 is in the first preset range by controlling the opening of the first expansion valve 4, the target temperature difference △T is made greater than zero and less than the set temperature by further controlling the opening of the second expansion valve 9. By making the target temperature difference △T greater than zero, the mixing point in the compressor 1 can always be in the superheat zone, that is, the enthalpy value of the mixing point is greater than or equal to the saturated vapor enthalpy value of the branch outlet 34 of the economizer 3 (the enthalpy value on the saturated vapor line, the saturated vapor line is the phase boundary between the gas-liquid two-phase and the gas phase). In this way, the dryness (referring to the proportion of gaseous refrigerant in the gas-liquid two-phase refrigerant) range of the two-phase injection cycle can be limited to protect The compressor ensures the smooth and safe operation of the heat pump system. By making the target temperature difference △T less than the set temperature, the exhaust temperature of the compressor can be prevented from being too high. The specific value of the set temperature can be set by a person skilled in the art based on experiments or experience. The present invention preferably sets the set temperature to 5±1°C, that is, by controlling the opening of the second expansion valve 9, the target temperature difference △T is between 0°C and 5±1°C. Taking the set temperature of 5°C as an example, if the target temperature difference △T is greater than 5°C, it is necessary to increase the opening of the second expansion valve 9 to reduce the target temperature difference △T. Conversely, if the target temperature difference △T is less than 0°C, it is necessary to reduce the opening of the second expansion valve 9 to increase the target temperature difference △T.

[0065] It should be noted that the temperature T1 of the mixing point in the compressor 1 can be determined based on the enthalpy value H of the mixing point and the pressure P of the mixing point. Specifically, the temperature T1 of the mixing point can be determined by checking a database (eg, REFPROP).

[0066] Ideally, the pressure P at the mixing point is the same as the pressure at the branch outlet 34 of the economizer 3. Therefore, the pressure value at the branch outlet 34 of the economizer 3 detected by the pressure sensor can be used to replace the pressure P at the mixing point.

[0067] According to the law of conservation of energy, the enthalpy value H of the mixing point satisfies the following conditions: H×M=H1×M1+H2×M2, wherein M is the mass flow rate at the mixing point, M1 is the mass flow rate of the refrigerant in the main circuit, which can be detected by setting a mass flow meter on the refrigerant pipeline between the condenser 2 and the main circuit inlet 31 of the economizer 3, and M2 is the mass flow rate of the refrigerant in the injection branch, which can be detected by setting a mass flow meter on the first branch 7. According to the law of conservation of mass, M=M1+M2, H1 is the enthalpy value of the gaseous refrigerant after primary compression of the refrigerant entering from the low-pressure inlet 12 of the compressor 1, and H2 is the enthalpy value of the refrigerant at the branch outlet 34 of the economizer 3.

[0068] Where, H1=H0+[K / (K+1)]×P0×V0×[(P1 / P0) (C-1) / C-1], H0 is the enthalpy value of the refrigerant at the outlet of the gas-liquid separator 6 (in KJ / Kg), which can be determined according to the pressure P0 and temperature T0 at the outlet of the gas-liquid separator 6. The specific value of H0 can be determined by checking the database (such as REFPROP), C is the adiabatic index of the refrigerant, and the adiabatic index is related to the type of refrigerant. Once the refrigerant is determined, the adiabatic index is also determined. For example, the adiabatic index of R22 refrigerant is about 1.19, and the adiabatic index of R134a refrigerant is about 1.11. P0 is the pressure at the outlet of the gas-liquid separator 6 (in MPa), which can be detected by setting a pressure sensor at the outlet of the gas-liquid separator 6. V0 is the specific volume of the refrigerant at the outlet of the gas-liquid separator 6 (in m 3 / kg), or it can be determined according to the pressure P0 and temperature T0 at the outlet of the gas-liquid separator 6. Specifically, the specific value of V0 can be determined by checking the database (such as REFPROP). P1 is the pressure of the gaseous refrigerant after the refrigerant enters from the low-pressure inlet 12 of the compressor 1 and is compressed by the primary compression. This pressure is also the same as the pressure of the branch outlet 34 of the economizer 3. Therefore, P1 can also be replaced by the pressure value of the branch outlet 34 of the economizer 3 detected by the pressure sensor.

[0069] The enthalpy value H2 of the refrigerant at the branch outlet 34 of the economizer 3 can be determined based on the saturated gaseous enthalpy value and the saturated liquid enthalpy value of the refrigerant at the branch outlet 34 of the economizer 3, H2 = X × (H vap -H lip )+H lip , X is the dryness of the refrigerant at the branch outlet 34 of the economizer 3. The dryness of the refrigerant refers to the proportion of the gaseous refrigerant in the gas-liquid two-phase refrigerant. The dryness X is generally between 0.8 and 1. H vap is the saturated gaseous enthalpy of the refrigerant at the branch outlet 34 of the economizer 3, H vap It can be calculated by looking up the database (such as REFPROP) according to the pressure of the branch outlet 34 of the economizer 3, H lip is the saturated liquid enthalpy of the refrigerant at the branch outlet 34 of the economizer 3, H lip It can also be calculated based on the pressure of the branch outlet 34 of the economizer 3 by looking up a database (eg REFPROP).

[0070] When calculating H2, first select a value between 0.8 and 1 as the value of dryness X, for example, dryness X = 0.9, then calculate the value of H2, and finally calculate the enthalpy value H of the mixing point, and then determine whether the enthalpy value H of the mixing point meets the set boundary conditions. The boundary condition is that the enthalpy value H of the mixing point ≥ H vap , thus the specific range of dryness X can be inferred, and the specific calculation process can be achieved through the mathematical software MATLAB.

[0071] In addition, it should be noted that, in actual applications, those skilled in the art may set a pressure sensor at the branch outlet 34 of the economizer 3 to detect the pressure of the branch outlet 34 of the economizer 3, and then obtain the saturation temperature T2 corresponding to the pressure of the branch outlet 34 of the economizer 3.

[0072] Preferably, the control method of the present invention further comprises the following steps:

[0073] Obtaining the exhaust temperature Td1 of the compressor;

[0074] comparing the exhaust temperature Td1 with the upper limit exhaust temperature Td0 of the compressor;

[0075] According to the comparison result, the opening degree of the first expansion valve is selectively increased.

[0076] That is, after the target temperature difference ΔT is between 0 and the set temperature by controlling the opening of the second expansion valve 9, it is further determined whether the exhaust temperature of the compressor 1 is too high.

[0077] The upper limit exhaust temperature Td0 of the compressor 1 is the maximum exhaust temperature of the compressor 1 , which is generally related to the manufacturing level of the compressor 1 . The upper limit exhaust temperature of the compressor will be recorded in the specification of the compressor.

[0078] Preferably, the step of "selectively increasing the opening of the first expansion valve according to the comparison result" specifically includes:

[0079] If the exhaust gas temperature Td1 is greater than or equal to the upper limit exhaust gas temperature Td0, the opening degree of the first expansion valve is increased.

[0080] For example, Td0 = 120°C. If Td1 ≥ 120°C, the opening of the first expansion valve 4 needs to be increased to reduce the exhaust temperature of the compressor 1.

[0081] Preferably, the control method of the present invention further comprises: controlling the opening of the second expansion valve so that the superheat (ΔT gas ) of the gas-liquid separator is within a second preset range.

[0082] That is to say, when the exhaust temperature of the compressor 1 is higher than the upper limit exhaust temperature, it is also necessary to control the superheat (ΔT gas fraction) of the gas-liquid separator 6 to reduce the exhaust temperature of the compressor 1 .

[0083] Specifically, the superheat (△T gas fraction) of the gas-liquid separator 6 can be adjusted by controlling the opening of the second expansion valve 9, so that the superheat (△T gas fraction) of the gas-liquid separator 6 is within the second preset interval. The present invention does not limit the specific value of the second preset interval, and technical personnel in this field can flexibly set it based on experiments or experience. The present invention preferably sets the second preset interval to 3±1°C to 8±1°C, that is, by controlling the opening of the second expansion valve 9, the superheat (△T gas fraction) of the gas-liquid separator 6 is between 3±1°C and 8±1°C. Taking the second preset interval of 3°C to 8°C as an example, if the superheat (△T gas fraction) of the gas-liquid separator 6 is less than 3°C, it is necessary to reduce the opening of the second expansion valve 9 to increase the superheat of the gas-liquid separator 6. Conversely, if the superheat (△T gas fraction) of the gas-liquid separator 6 is greater than 8°C, it is necessary to increase the opening of the second expansion valve 9 to reduce the superheat of the gas-liquid separator 6.

[0084] Among them, the superheat of the gas-liquid separator 6 is the difference between the outlet temperature of the gas-liquid separator 6 and the saturation temperature corresponding to the outlet pressure of the gas-liquid separator 6. A temperature sensor and a pressure sensor can be set at the outlet of the gas-liquid separator 6 to detect the outlet temperature and the outlet pressure of the gas-liquid separator 6 respectively.

[0085] It should be noted that, in practical applications, in addition to controlling the opening of the second expansion valve 9 to control the superheat of the gas-liquid separator 6, the superheat of the gas-liquid separator 6 can also be controlled by controlling the first expansion valve 4 and the second expansion valve 9 in linkage.

[0086] Preferably, the control method of the present invention further includes:

[0087] Obtaining the exhaust temperature Td1 of the compressor again and comparing it with the upper limit exhaust temperature Td0;

[0088] If the exhaust gas temperature Td1 is still greater than or equal to the upper limit exhaust gas temperature Td0, the compressor is stopped.

[0089] That is to say, after controlling the opening of the second expansion valve 9 to make the superheat of the gas-liquid separator 6 within the second preset interval, it is necessary to determine again whether the exhaust temperature of the compressor 1 exceeds the upper limit exhaust temperature. If the exhaust temperature of the compressor 1 is still greater than or equal to the upper limit exhaust temperature, the compressor 1 needs to be stopped to avoid safety accidents. Of course, if the exhaust temperature of the compressor 1 drops below the upper limit exhaust temperature, the heat pump system can continue to operate with the current parameters.

[0090] Preferably, after the target temperature difference ΔT is between 0 and the set temperature by controlling the opening of the second expansion valve, if the exhaust temperature Td1 of the compressor is less than the upper limit exhaust temperature Td0, there is no need to increase the opening of the first expansion valve. In this case, the control method of the present invention further includes:

[0091] Get the load Q provided by the heat pump system h ;

[0092] The load Q provided by the heat pump system h and demand load Q d Make comparisons;

[0093] If the heat pump system provides a load Q h Less than the required load Q d , then increase the operating frequency of the compressor.

[0094] That is to say, when the exhaust temperature of compressor 1 is normal, it is further determined whether the load provided by the heat pump system can meet the required load. If the load Q provided by the heat pump system is h Less than the required load Q d , indicating that the load provided by the heat pump system cannot meet the required load. In this case, it is necessary to increase the operating frequency of compressor 1 to increase the load provided by the heat pump system.

[0095] Among them, the load provided by the heat pump system can be obtained by the conventional calculation method in this field, that is, it is calculated according to the inlet and outlet temperature difference and flow rate of the condenser 2, and the demand load depends on the area of ​​the room where the heat pump system is located. It is a fixed value, which is calculated by the staff and stored in the controller of the heat pump system for retrieval and use at any time.

[0096] Combine the following Figure 3 A specific embodiment of the control method of the present invention is introduced.

[0097] like Figure 3 As shown, the control method of the present invention comprises the following steps:

[0098] S110: adjusting the opening of the first expansion valve;

[0099] The superheat degree of the evaporator 5 is adjusted by adjusting the opening degree of the first expansion valve 4 .

[0100] S120: Determine whether ΔTevaporation is between 3°C and 8°C;

[0101] If 3°C≤ΔTevaporation≤8°C, then step S210 is executed; otherwise, if ΔTevaporation<3°C or ΔTevaporation>8°C, then the process returns to step S110.

[0102] S210: Adjust the opening degree of the second expansion valve;

[0103] Adjust the target temperature difference △T by adjusting the opening degree of the second expansion valve 9.

[0104] S220: Determine whether the target temperature difference △T is between 0°C and 5°C;

[0105] If 0°C < △T < 5°C, then proceed to step S300. Conversely, if △T ≤ 0°C or △T ≥ 5°C, then return and continue to execute step S210.

[0106] S300: Determine whether the exhaust gas temperature Td1 is less than 120°C;

[0107] This step is mainly used to determine whether the exhaust gas temperature of the compressor 1 is too high. If Td1 < 120°C, it means that the exhaust gas temperature of the compressor 1 is not high, then proceed to step S800; conversely, if Td1 ≥ 120°C, it means that the exhaust gas temperature of the compressor 1 is too high, then proceed to step S400.

[0108] S400: Increase the opening degree of the first expansion valve;

[0109] When the exhaust gas temperature of the compressor 1 reaches or exceeds 120°C, first increase the opening degree of the first expansion valve 4 to achieve the purpose of reducing the exhaust gas temperature of the compressor 1.

[0110] S500: Determine whether △T of the gas-liquid separator is between 3°C and 8°C;

[0111] When the exhaust gas temperature of the compressor 1 reaches or exceeds 120°C, it is also necessary to control the superheat degree of the gas-liquid separator 6. Specifically, the superheat degree of the gas-liquid separator 6 can be adjusted by controlling the opening degree of the second expansion valve 9. After the superheat degree of the gas-liquid separator 6 satisfies 3°C ≤ △T of the gas-liquid separator ≤ 8°C, proceed to step S600.

[0112] S600: Determine whether the exhaust gas temperature Td2 is less than 120°C;

[0113] After making the superheat degree of the gas-liquid separator 6 in the second preset interval (3°C to 8°C), it is necessary to determine again whether the exhaust gas temperature of the compressor 1 is too high. If Td2 ≥ 120°C, it means that the exhaust gas temperature of the compressor 1 is still too high. In this case, step S700 needs to be executed, that is, stop the compressor 1. Conversely, if Td2 < 120°C, it means that the above adjustment has played a role in reducing the exhaust gas temperature of the compressor 1. In this case, the heat pump system can continue to operate according to the current operating parameters.

[0114] S700: Stop the compressor;

[0115] In the case where the above-mentioned adjustment fails to reduce the exhaust temperature of the compressor 1, the compressor 1 can be stopped to avoid safety accidents, thereby further improving the safety of the heat pump system.

[0116] S800: Determine the load Q provided by the heat pump system h Is it greater than or equal to the demand load Q d ;

[0117] If Q h ≥Q d , indicating that the load provided by the heat pump system can meet the demand. In this case, the heat pump system can continue to operate according to the current operating parameters. On the contrary, if Q h <Q d , indicating that the load provided by the heat pump system cannot meet the requirements, and step S900 needs to be executed next.

[0118] S900: Increase the operating frequency of the compressor.

[0119] When the load provided by the heat pump system cannot meet the demand, the load increased by the heat pump system can be increased by increasing the operating frequency of the compressor 1 to meet the demand.

[0120] It should be noted that after increasing the operating frequency of the compressor 1 , it is preferred to return to step S110 and execute the above steps again to ensure that the compressor 1 can operate safely.

[0121] Finally, it should be noted that the heat pump system of the present invention includes a controller, which is configured to execute the above-mentioned control method.

[0122] It should be noted that the control method provided in this embodiment can be stored as a program in a computer-readable storage medium. The storage medium includes a number of instructions for enabling a computer device (which may be a personal computer, a server, or a network device, etc.) or a processor to perform some steps of the methods of various embodiments of the present invention. The aforementioned storage medium includes: a U disk, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a disk or an optical disk, and other media that can store program codes.

[0123] Those skilled in the art will appreciate that, although some embodiments described herein include certain features included in other embodiments but not other features, the combination of features of different embodiments is meant to be within the scope of the present application and form different embodiments. For example, in the claims of the present application, any one of the claimed embodiments may be used in any combination.

[0124] So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

Claims

1. A control method for a heat pump system, characterized in that: The heat pump system comprises a compressor, a condenser, an economizer, a first expansion valve, an evaporator and a gas-liquid separator which are sequentially connected in series, the compressor having an injection port, the heat pump system further comprising a first branch, a second branch and a second expansion valve installed on the first branch, the two ends of the first branch are respectively connected to the outlet end of the condenser and the branch inlet of the economizer, the two ends of the second branch are respectively connected to the branch outlet of the economizer and the injection port, the control method comprises: Controlling the opening of the first expansion valve so that the superheat of the evaporator is within a first preset range; Controlling the opening of the second expansion valve so that the target temperature difference ΔT is greater than zero degrees and less than a set temperature; Among them, the target temperature difference △T=T1-T2, T1 is the temperature of the mixing point in the compressor, the mixing point refers to the state point after the refrigerant entering the compression chamber of the compressor from the injection port and the gaseous refrigerant entering from the low-pressure inlet of the compressor after primary compression are mixed, and T2 is the saturation temperature corresponding to the pressure of the branch outlet.

2. The control method of the heat pump system according to claim 1, characterized in that: The control method further comprises: Acquiring the exhaust temperature of the compressor; comparing the exhaust gas temperature with an upper limit exhaust gas temperature of the compressor; According to the comparison result, the opening degree of the first expansion valve is selectively increased.

3. The control method of the heat pump system according to claim 2, characterized in that: The step of "selectively increasing the opening of the first expansion valve according to the comparison result" specifically includes: If the exhaust gas temperature is greater than or equal to the upper limit exhaust gas temperature, the opening degree of the first expansion valve is increased.

4. The control method of the heat pump system according to claim 3, characterized in that: The control method further comprises: The opening degree of the second expansion valve is controlled so that the superheat degree of the gas-liquid separator is within a second preset range.

5. The control method of the heat pump system according to claim 4, characterized in that: The control method further comprises: obtaining the exhaust temperature of the compressor again and comparing it with the upper limit exhaust temperature; If the exhaust gas temperature is still greater than or equal to the upper limit exhaust gas temperature, the compressor is stopped.

6. The control method of the heat pump system according to claim 4, characterized in that: The second preset range is 3±1°C to 8±1°C.

7. The control method of the heat pump system according to claim 2, characterized in that: When the exhaust temperature is lower than the upper limit exhaust temperature, the control method further includes: Get the load Q provided by the heat pump system h ; The load Q provided by the heat pump system h and demand load Q d Make comparisons; If the heat pump system provides a load Q h Less than the required load Q d , then increase the operating frequency of the compressor.

8. The control method of a heat pump system according to any one of claims 1 to 7, characterized in that: The first preset interval is 3±1°C to 8±1°C.

9. The control method of a heat pump system according to any one of claims 1 to 7, characterized in that: The set temperature is 5±1°C.

10. A heat pump system, comprising a controller, characterized in that: The controller is configured to be able to execute the control method according to any one of claims 1 to 9.

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