Cascade heat pump unit and control method thereof

Abstract

The invention relates to the technical field of heat pumps, particularly provides a cascade heat pump unit and a control method thereof, and aims to solve the problem that an existing cascade heat pump unit cannot start a low-temperature-stage compressor and a high-temperature-stage compressor in a correct sequence and time interval according to the environment temperature, so that the working performance of the cascade heat pump unit is poor. In order to achieve the purpose, the cascade heat pump unit comprises a low-temperature-stage compressor, a high-temperature-stage compressor and a temperature sensor, and the control method comprises the steps that the temperature sensor is controlled to obtain the environment temperature Tao; the Tao is compared with an environment temperature preset value T1; selectively controlling the low-temperature-stage compressor to be started first or the high-temperature-stage compressor to be started first according to the comparison result; the starting conditions of the compressors which are started later are set based on the starting sequence of the low-temperature-stage compressors and the high-temperature-stage compressors, and therefore the cascade heat pump unit can start the low-temperature-stage compressors and the high-temperature-stage compressors according to the environment temperature in the correct sequence and at the correct time interval.

Description

Technical Field

[0001] The present invention relates to the technical field of heat pumps, and in particular provides a cascade heat pump unit and a control method thereof. Background Art

[0002] The cascade heat pump unit includes a low-temperature heating system and a high-temperature heating system. The two systems are independent systems, both of which have a compressor, an evaporator, a condenser and a throttling device, and are connected through an intermediate plate heat exchanger. In the low-temperature heating system, the low-temperature compressor compresses the refrigerant into a high-temperature and high-pressure gas, and transfers the heat to the intermediate plate heat exchanger, which is equivalent to the low-temperature condenser. In the high-temperature heating system, the refrigerant absorbs heat from the intermediate plate heat exchanger and returns to the high-temperature compressor, which is equivalent to the high-temperature evaporator.

[0003] The operating environment temperature range of the cascade heat pump unit can reach -35℃~+50℃. When the cascade heat pump unit is started, usually, the heating system that starts first needs to exchange heat with the air in the surrounding environment. Different ambient temperature conditions will have different effects on the working performance of the low-temperature heating system and the high-temperature heating system. Therefore, it is necessary to sort the start-up sequence of the low-temperature heating system and the high-temperature heating system according to the ambient temperature to avoid the situation where the cascade heat pump unit cannot exchange heat with the air. On the other hand, in the process of heat exchange between the heating system that starts first and the air, since the heat exchange efficiency of the air cannot meet the heat conduction requirements of the heating system, the heat of the heating system cannot be transferred, which may cause damage to the plate heat exchanger and the compressor.

[0004] Accordingly, the art requires a new control method, control device, cascade heat pump unit and readable storage medium for a cascade heat pump unit to solve the existing problems. Summary of the invention

[0005] The present invention aims to solve the above-mentioned technical problem, that is, to solve the problem that the existing cascade heat pump unit is unable to start the low-temperature stage compressor and the high-temperature stage compressor in the correct order and time interval according to the ambient temperature, which affects the working performance of the cascade heat pump unit and may even cause damage to the plate heat exchanger and the compressor.

[0006] In a first aspect, the present invention provides a control method for a cascade heat pump unit, wherein the cascade heat pump unit includes a low-temperature compressor and a high-temperature compressor, and the control method includes: controlling which of the low-temperature compressor and the high-temperature compressor to start first according to the ambient temperature; and determining the starting conditions of the compressor that is started later based on the starting sequence of the low-temperature compressor and the high-temperature compressor.

[0007] In the specific implementation of the above-mentioned control method for a cascade heat pump unit, the step of "controlling which one of the low-temperature compressor and the high-temperature compressor to start first according to the ambient temperature" further includes: when Tao≥T1, starting the high-temperature compressor first, and then starting the low-temperature compressor; wherein Tao is the ambient temperature, and T1 is the preset value of the ambient temperature.

[0008] In the specific implementation of the above-mentioned control method for a cascade heat pump unit, the cascade heat pump unit also includes a high-temperature evaporator, and the step of "determining the starting condition of the compressor to be started based on the starting sequence of the low-temperature compressor and the high-temperature compressor" further includes: when Ts_H≤Ts1, starting the low-temperature compressor; wherein Ts_H is the high-temperature evaporation temperature, and Ts1 is the first preset temperature.

[0009] In the specific implementation of the above-mentioned control method for a cascade heat pump unit, the cascade heat pump unit also includes a low-temperature stage condenser, and the step of "determining the starting condition of the compressor to be started based on the starting sequence of the low-temperature stage compressor and the high-temperature stage compressor" also includes: when Td_L≤Td1, starting the low-temperature stage compressor; wherein Td_L is the low-temperature stage condensing temperature, and Td1 is the second preset temperature.

[0010] In a specific implementation of the control method for the cascade heat pump unit, the control method further includes: if the low temperature compressor is not started after time t1 has passed since the high temperature compressor was started, starting the low temperature compressor.

[0011] In the specific implementation of the above-mentioned control method for a cascade heat pump unit, the step of "controlling which of the low-temperature compressor and the high-temperature compressor to start first according to the ambient temperature" also includes: when Tao<T1, starting the low-temperature compressor first, and then starting the high-temperature compressor.

[0012] In the specific implementation of the above-mentioned control method for a cascade heat pump unit, the cascade heat pump unit also includes a low-temperature stage condenser, and the step of "determining the starting condition of the compressor to be started based on the starting sequence of the low-temperature stage compressor and the high-temperature stage compressor" also includes: when Td_L≥Td2, starting the high-temperature stage compressor; wherein Td_L is the low-temperature stage condensing temperature, and Td2 is the third preset temperature.

[0013] In the specific implementation of the above-mentioned control method for a cascade heat pump unit, the cascade heat pump unit also includes a high-temperature evaporator, and the step of "determining the starting condition of the compressor to be started based on the starting sequence of the low-temperature compressor and the high-temperature compressor" further includes: when Ts_H≥Ts2, starting the high-temperature compressor; wherein Ts_H is the high-temperature evaporation temperature, and Ts2 is the fourth preset temperature.

[0014] In a specific implementation of the control method for the cascade heat pump unit, the control method further includes: if the high-temperature compressor is not started after time t2 has passed since the low-temperature compressor was started, starting the high-temperature compressor.

[0015] The present invention also provides a cascade heat pump unit, which includes a low-temperature compressor, a high-temperature compressor, a low-temperature condenser, a high-temperature evaporator, a first temperature sensor capable of acquiring ambient temperature, a second temperature sensor capable of acquiring high-temperature evaporation temperature, and a third temperature sensor capable of acquiring low-temperature condensation temperature, and can execute any of the control methods for the cascade heat pump unit described in the above technical solutions.

[0016] When the above technical solution is adopted, the cascade heat pump unit of the present invention can start the low-temperature compressor and the high-temperature compressor in the correct order and time interval according to the ambient temperature. Specifically, during the use of the cascade heat pump unit of the present invention, the first temperature sensor is first controlled to obtain the ambient temperature Tao of the cascade heat pump unit, and then the ambient temperature Tao is compared with the ambient temperature preset value T1. When Tao≥T1, the high-temperature compressor is started first, and then the high-temperature evaporation temperature Ts_H and the first preset temperature Ts1 are judged. In order to avoid the high-temperature evaporation temperature being too low, the low-temperature compressor is started when Ts_H≤Ts1. On the other hand, when Tao<T1, the low-temperature compressor is started first, and then the low-temperature condensation temperature Td_L and the third preset temperature Td2 are judged. In order to avoid the low-temperature condensation temperature being too high, the high-temperature compressor is started when Td_L≥Td2, so that the heat exchange between the high-temperature evaporator and the low-temperature condenser can be completed smoothly, thereby ensuring the normal operation of the cascade heat pump unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings, in which:

[0018] Figure 1 It is a connection relationship diagram of various components of the cascade heat pump unit of the present invention;

[0019] Figure 2 It is a main flow chart of the control method for a cascade heat pump unit of the present invention;

[0020] Figure 3 It is an overall flow chart of the control method for a cascade heat pump unit of the present invention;

[0021] Figure 4 is a flow chart of a first embodiment of a control method for a cascade heat pump unit of the present invention;

[0022] Figure 5 is a flow chart of a second embodiment of the control method for a cascade heat pump unit of the present invention;

[0023] Figure 6 is a flow chart of a third embodiment of a control method for a cascade heat pump unit of the present invention;

[0024] Figure 7 is a flow chart of a fourth embodiment of a control method for a cascade heat pump unit of the present invention;

[0025] Figure 8 is a flow chart of a first preferred embodiment of a control method for a cascade heat pump unit of the present invention;

[0026] Fig. 9 is a flow chart of a second preferred embodiment of the control method for a cascade heat pump unit of the present invention;

[0027] Fig.10 It is a basic flow chart of the control method for a cascade heat pump unit of the present invention.

[0028] List of reference numerals:

[0029] 1- Cascade heat pump unit;

[0030] 11- Low temperature compressor;

[0031] 12-High temperature compressor;

[0032] 13- High temperature evaporator & low temperature condenser & plate heat exchanger;

[0033] 15- high temperature level throttling device;

[0034] 16- low temperature stage throttling device;

[0035] 17- low temperature stage evaporator;

[0036] 18-High temperature stage condenser. DETAILED DESCRIPTION

[0037] 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 scope of protection of the present invention. Those skilled in the art can make adjustments to them as needed to adapt to specific application scenarios.

[0038] First combine Figure 1 The existing cascade heat pump unit 1 is described.

[0039] like Figure 1 As shown, the existing cascade heat pump unit 1 includes a low-temperature heating system and a high-temperature heating system. The two systems are independent systems, both of which have a compressor, an evaporator, a condenser and a throttling device, and are connected through an intermediate plate heat exchanger 13. In the low-temperature heating system, the low-temperature compressor 11 compresses the refrigerant into a high-temperature and high-pressure gas. The high-temperature and high-pressure gaseous refrigerant passes through the plate heat exchanger 13 and transfers heat to the intermediate plate heat exchanger 13. Then, the refrigerant passes through the low-temperature throttling device 16 and the low-temperature evaporator 17 in sequence and returns to the low-temperature compressor 11. The intermediate plate heat exchanger 13 is equivalent to the low-temperature condenser 13. In the high-temperature heating system, the refrigerant flows out of the high-temperature compressor 12, passes through the high-temperature condenser 18 and the high-temperature throttling device 15 in sequence, absorbs heat in the intermediate plate heat exchanger 13, and then returns to the high-temperature compressor 12. The intermediate plate heat exchanger 13 is equivalent to the high-temperature evaporator. The operating environment temperature range of the cascade heat pump unit 1 can reach -35℃~+50℃. When the cascade heat pump unit 1 is started and operated, usually, the heating system that is started first needs to exchange heat with the air in the surrounding environment. Different ambient temperature conditions will have different effects on the working performance of the low-temperature heating system and the high-temperature heating system. Therefore, it is necessary to sort the start-up sequence of the low-temperature heating system and the high-temperature heating system according to the ambient temperature to avoid the situation where the cascade heat pump unit 1 cannot exchange heat with the air. On the other hand, in the process of heat exchange between the heating system that is started first and the air, since the heat exchange efficiency of the air cannot meet the thermal conductivity requirement of the heating system, the heat of the heating system cannot be transferred, which may cause damage to the plate heat exchanger 13 and the compressor. For this reason, the present invention proposes the following technical solution.

[0040] like Figure 1-Figure 4 , Fig.10As shown, in order to solve the problem that the existing cascade heat pump unit 1 cannot start the low-temperature compressor 11 and the high-temperature compressor 12 in the correct order and time interval according to the ambient temperature, which affects the working performance of the cascade heat pump unit 1 and may even cause damage to the plate heat exchanger 13 and the compressor, the cascade heat pump unit 1 of the present invention includes a low-temperature compressor 11, a high-temperature compressor 12, a high-temperature evaporator 13, a first temperature sensor (not shown in the figure) capable of obtaining the ambient temperature, and a second temperature sensor (not shown in the figure) capable of obtaining the high-temperature evaporation temperature, and the control method includes:

[0041] S01, controlling which of the low-temperature compressor 11 and the high-temperature compressor 12 is started first according to the ambient temperature;

[0042] S02. Determine the starting condition of the compressor to be started later based on the starting sequence of the low-temperature stage compressor 11 and the high-temperature stage compressor 12.

[0043] The control method specifically comprises the following steps:

[0044] S1, controlling the first temperature sensor to obtain the ambient temperature Tao;

[0045] S2, compare the ambient temperature Tao with the ambient temperature preset value T1;

[0046] S3, selectively controlling the low temperature compressor 11 to start first or the high temperature compressor 12 to start first according to the comparison result;

[0047] S4. Setting the starting conditions of the compressor to be started later based on the starting sequence of the low-temperature stage compressor 11 and the high-temperature stage compressor 12.

[0048] In the above steps, step S3 further comprises:

[0049] S31. When Tao ≥ T1, start the high-temperature stage compressor 12 first, and then start the low-temperature stage compressor 11.

[0050] Step S4 further comprises:

[0051] S41, controlling the second temperature sensor to obtain the high temperature stage evaporation temperature Ts_H;

[0052] S42, comparing Ts_H with the first preset temperature Ts1;

[0053] S43. When Ts_H≤Ts1, start the low-temperature stage compressor 11.

[0054] As mentioned above, the cascade heat pump unit 1 includes a low-temperature heating system and a high-temperature heating system. The low-temperature heating system includes a low-temperature compressor 11, and the high-temperature heating system includes a high-temperature compressor 12, a high-temperature evaporator 13 and a second temperature sensor. The above implementation method is proposed on this basis. When the above implementation method is adopted, the first temperature sensor is first controlled to obtain the ambient temperature Tao of the cascade heat pump unit 1, and then the ambient temperature Tao is compared with the preset value T1 of the ambient temperature. When Tao ≥ T1, it means that the ambient temperature is high at this time, which is conducive to the high-temperature evaporator 13 to absorb heat. Therefore, the high-temperature compressor 12 is started first. In the process of heat exchange between the high-temperature evaporator 13 and the air in the environment, the heat in the environment cannot meet the high-temperature evaporator 13. Heat exchange demand is met, and at the same time, the low-temperature compressor 11 is not started, and the low-temperature condensing side cannot actively transfer heat to the high-temperature evaporating side through the intermediate plate heat exchanger 13. Therefore, the high-temperature evaporating temperature will gradually decrease. In order to avoid the high-temperature evaporating temperature being too low, which is less than the set high-temperature minimum evaporating temperature Ts1, resulting in a high-temperature low pressure alarm, the second temperature sensor is controlled to obtain the high-temperature evaporating temperature Ts_H, and the size of the high-temperature evaporating temperature Ts_H and the high-temperature minimum evaporating temperature Ts1 is judged. When Ts_H≤Ts1, the low-temperature compressor 11 is started, and the condensing effect of the low-temperature condenser 13 is used to provide heat to the high-temperature evaporator 13, and the heat of the low-temperature condenser 13 is also conducted, thereby ensuring the normal operation of the high-temperature heating system and the low-temperature heating system.

[0055] Refer to the following Figure 1 , Figure 2 and Figure 5 , the second embodiment of the control method for the cascade heat pump unit 1 of the present invention is introduced. Among them, Figure 5 It is a flow chart of a second embodiment of the control method for the cascade heat pump unit 1 of the present invention.

[0056] In a second embodiment of the present invention, the cascade heat pump unit 1 further includes a low-temperature stage condenser 13 and a third temperature sensor (not shown in the figure) capable of obtaining the low-temperature stage condensation temperature. The control method for the cascade heat pump unit 1 includes:

[0057] S4. Setting the starting conditions of the compressor to be started later based on the starting sequence of the low-temperature stage compressor 11 and the high-temperature stage compressor 12.

[0058] Step S4 further comprises:

[0059] S44, controlling the third temperature sensor to obtain the low-temperature stage condensation temperature Td_L;

[0060] S45, comparing Td_L with the second preset temperature Td1;

[0061] S46: When Td_L≤Td1, start the low temperature stage compressor 11.

[0062] As mentioned above, when the low-temperature compressor 11 is not started, the low-temperature condensing side cannot actively transfer heat to the high-temperature evaporating side through the intermediate plate heat exchanger 13. However, at this time, the high-temperature heating system will continuously absorb heat from the low-temperature condensing side through the intermediate plate heat exchanger 13, thereby passively and gradually reducing the low-temperature condensing temperature. In order to prevent the low-temperature condensing temperature from being too low and less than the minimum condensing temperature Tmin of the low-temperature stage, resulting in an alarm for too low a high pressure, the above-mentioned implementation method is proposed. When the above-mentioned implementation method is adopted, in the process of gradually decreasing the low-temperature condensing temperature, the third temperature sensor is controlled to obtain the low-temperature condensing temperature Td_L, and the low-temperature condensing temperature Td_L is compared with the second preset temperature Td1 (Td1=Tmin+5°C). When Td_L≤Td1, the low-temperature compressor 11 is started, and the low-temperature condensing temperature is increased by the condensing effect of the low-temperature condenser 13, thereby avoiding an alarm for too low a high pressure caused by the low-temperature condensing temperature. In addition, those skilled in the art will appreciate that the purpose of setting the judgment condition for starting the low-temperature stage compressor 11 to the low-temperature stage condensing temperature Td_L being less than or equal to the low-temperature stage minimum condensing temperature Tmin+5°C is to enable the low-temperature stage compressor 11 to start early and begin heating up, thereby avoiding the low-temperature stage condensing temperature from dropping below the low-temperature stage minimum condensing temperature, thereby avoiding damage to the plate heat exchanger 13 and the low-temperature stage compressor 11.

[0063] like Figure 8 As shown, in a possible implementation manner, the control method for the cascade heat pump unit 1 further includes:

[0064] S47: If the low-temperature stage compressor 11 is not started after a time t1 has passed since the high-temperature stage compressor 12 was started, the low-temperature stage compressor 11 is started.

[0065] Although the above mentioned starting condition of further starting the low-temperature stage compressor 11 after starting the high-temperature stage compressor 12, this is a protection condition set to avoid adverse consequences. On this basis, in order to ensure the normal operation of the cascade heat pump unit 1, the present embodiment is proposed. If the low-temperature stage compressor 11 has not started after the high-temperature stage compressor 12 has started for a period of time t1, the low-temperature stage compressor 11 is started. In this way, the cascade heat pump unit 1 can be started and used normally under the premise of ensuring that the components are not damaged, thereby avoiding the situation where the low-temperature stage compressor 11 does not start after the high-temperature stage compressor 12 is started.

[0066] The above has already introduced the situation where the ambient temperature is high when Tao ≥ T1. Next, the situation where the ambient temperature is low when Tao < T1 will be explained. Figure 1 , Figure 2 , Figure 6 , the third embodiment of the control method for the cascade heat pump unit 1 of the present invention is introduced. Among them, Figure 6 It is a flow chart of the third embodiment of the control method for the cascade heat pump unit 1 of the present invention.

[0067] In a third embodiment of the present invention, a control method for a cascade heat pump unit 1 includes:

[0068] S3, selectively controlling the low temperature compressor 11 to start first or the high temperature compressor 12 to start first according to the comparison result;

[0069] S4. Setting the starting conditions of the compressor to be started later based on the starting sequence of the low-temperature stage compressor 11 and the high-temperature stage compressor 12.

[0070] In the above steps, step S3 further comprises:

[0071] S32. When Tao<T1, start the low-temperature compressor 11 first, and then start the high-temperature compressor 12.

[0072] Step S4 further comprises:

[0073] S401, controlling the third temperature sensor to obtain the low temperature stage condensation temperature Td_L;

[0074] S402, comparing Td_L with a third preset temperature Td2;

[0075] S403: When Td_L≥Td2, start the high temperature stage compressor 12.

[0076] When Tao<T1, the temperature of the surrounding environment is low, which is conducive to the heat release of the low-temperature condenser 13. Therefore, the low-temperature compressor 11 is started first. In the process of heat exchange between the low-temperature condenser 13 and the air in the environment, due to the limited heat exchange capacity of the air in the environment, when the high-temperature compressor 12 is not started, the high-temperature evaporation side cannot actively absorb the heat of the low-temperature condensation side through the intermediate plate heat exchanger 13. At this time, the low-temperature condensation temperature will continue to rise. In order to prevent the low-temperature condensation temperature from being too high and greater than the set low-temperature maximum condensation temperature Td2, resulting in a low-temperature high pressure alarm, the third temperature sensor is controlled to obtain the low-temperature condensation temperature Td_L, and the low-temperature condensation temperature Td_L is compared with the third preset temperature Td2. When Td_L≥Td2, the high-temperature compressor 12 is started to absorb the heat of the low-temperature condenser 13 through the evaporation of the high-temperature evaporator 13, and also provide heat for the high-temperature evaporator 13 to evaporate, thereby ensuring the normal operation of the high-temperature heating system and the low-temperature heating system.

[0077] Refer to the following Figure 1 , Figure 2 , Figure 7 , the fourth embodiment of the control method for the cascade heat pump unit 1 of the present invention is introduced. Among them, Figure 7 It is a flow chart of a fourth embodiment of the control method for a cascade heat pump unit 1 of the present invention.

[0078] In a fourth embodiment of the present invention, a control method for a cascade heat pump unit 1 includes:

[0079] S4. Setting the starting conditions of the compressor to be started later based on the starting sequence of the low-temperature stage compressor 11 and the high-temperature stage compressor 12.

[0080] Step S4 further comprises:

[0081] S404, controlling the second temperature sensor to obtain the high temperature stage evaporation temperature Ts_H;

[0082] S405, comparing Ts_H with the fourth preset temperature Ts2;

[0083] S406: When Ts_H≥Ts2, start the high temperature stage compressor 12.

[0084] As mentioned above, when the high-temperature stage compressor 12 is not started, the low-temperature stage heating system will continuously release heat to the high-temperature stage evaporation side through the intermediate plate heat exchanger 13, and the high-temperature stage evaporation temperature will passively increase gradually. In order to prevent the high-temperature stage evaporation temperature from being too high and higher than the high-temperature stage maximum evaporation temperature Tmax, resulting in a low-pressure excessive alarm, the above-mentioned implementation method is proposed. When the above-mentioned implementation method is adopted, in the process of gradually increasing the high-temperature stage evaporation temperature, the second temperature sensor is controlled to obtain the high-temperature stage evaporation temperature Ts_H, and the size of Ts_H and the fourth preset temperature Ts2 (Ts2=Tmax-5°C) is judged. When Ts_H≥Ts2, the high-temperature stage compressor 12 is started, and the high-temperature stage evaporation temperature is reduced by the evaporation action of the high-temperature stage evaporator 13, thereby avoiding the high-temperature stage evaporation temperature from being too high and causing a low-pressure excessive alarm. In addition, those skilled in the art will appreciate that the purpose of setting the judgment condition for starting the high-temperature stage compressor 12 to the high-temperature stage evaporating temperature being greater than or equal to the high-temperature stage maximum evaporating temperature Tmax-5°C is to enable the high-temperature stage compressor 12 to start early and begin cooling down, thereby avoiding the high-temperature stage evaporating temperature from rising above the high-temperature stage maximum evaporating temperature, thereby avoiding damage to the plate heat exchanger 13 and the high-temperature stage compressor 12.

[0085] like Fig. 9 As shown, in a possible implementation manner, the control method for the cascade heat pump unit (1) further includes:

[0086] S407: If the high-temperature compressor (12) has not started after a time t2 has passed since the low-temperature compressor (11) was started, the high-temperature compressor (12) is started.

[0087] Although the aforementioned starting condition of further starting the high-temperature compressor (12) after starting the low-temperature compressor (11) is mentioned, this is a protection condition set to avoid adverse consequences. On this basis, in order to ensure the normal operation of the cascade heat pump unit (1), the present embodiment is proposed. If the high-temperature compressor (12) has not started after the low-temperature compressor (11) has started for a period of time t2, the high-temperature compressor (12) is started. In this way, the cascade heat pump unit (1) can be started and used normally under the premise of ensuring that the components of the cascade heat pump unit (1) are not damaged, thereby avoiding the situation where the high-temperature compressor (12) does not start after the low-temperature compressor (11) is started.

[0088] In addition, regarding the priorities of the above-mentioned steps S41-S43, S44-S46 and S7, and the priorities of steps S401-S403, S404-S406 and S407, those skilled in the art can understand that the priorities of steps S41-S43 and steps S44-S46 are higher than that of step S7, and steps S41-S43 and steps S44-S46 can be judged at the same time, and the priorities of steps S401-S403 and steps S404-S406 are higher than that of step S407, and steps S401-S403 and steps S404-S406 can be judged at the same time. Of course, those skilled in the art can also adjust the priorities of the above steps according to the needs in actual use, and these changes do not exceed the scope of protection of the present invention.

[0089] It should be noted that the above-mentioned implementation mode is only used to illustrate the principle of the present invention and is not intended to limit the scope of protection of the present invention. Without departing from the principle of the present invention, those skilled in the art can adjust the above-mentioned structure so that the present invention can be applied to more specific application scenarios.

[0090] Those skilled in the art can understand that the above-mentioned cascade heat pump unit 1 also includes some other well-known structures, such as a processor, a controller, a memory, etc., wherein the memory includes but is not limited to a random access memory, a flash memory, a read-only memory, a programmable read-only memory, a volatile memory, a non-volatile memory, a serial memory, a parallel memory or a register, etc., and the processor includes but is not limited to a CPLD / FPGA, a DSP, an ARM processor, a MIPS processor, etc. In order to unnecessarily obscure the embodiments of the present disclosure, these well-known structures are not shown in the drawings.

[0091] In addition, the present invention also provides a control device for a cascade heat pump unit 1, the control device comprising a processor and a memory storing program instructions, the processor being configured to execute any one of the control methods for the cascade heat pump unit 1 in the above technical solutions when running the program instructions.

[0092] In addition, the present invention also provides a cascade heat pump unit 1, which includes a low-temperature stage compressor 11, a high-temperature stage compressor 12, a low-temperature stage condenser 13, a high-temperature stage evaporator 13, a first temperature sensor capable of obtaining ambient temperature, a second temperature sensor capable of obtaining high-temperature stage evaporation temperature, a third temperature sensor capable of obtaining low-temperature stage condensation temperature, and a control device for the cascade heat pump unit 1 in the above technical solution.

[0093] In addition, the present invention also provides a readable storage medium, in which a plurality of program codes are stored, and the program codes are suitable for being loaded and run by a processor to execute any one of the control methods for air conditioning refrigerant diversion in the above-mentioned technical aspects.

[0094] 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 cascade heat pump unit (1), characterized in that: The cascade heat pump unit (1) comprises a low-temperature compressor (11) and a high-temperature compressor (12), and the control method comprises: Controlling which of the low-temperature compressor (11) and the high-temperature compressor (12) is started first according to the ambient temperature; The starting condition of the compressor to be started later is determined based on the starting sequence of the low-temperature stage compressor (11) and the high-temperature stage compressor (12).

2. The control method for a cascade heat pump unit (1) according to claim 1, characterized in that: The step of "controlling which of the low-temperature compressor (11) and the high-temperature compressor (12) is started first according to the ambient temperature" further includes: When Tao ≥ T1, the high temperature stage compressor (12) is started first, and then the low temperature stage compressor (11) is started; Among them, Tao is the ambient temperature and T1 is the preset value of the ambient temperature.

3. The control method for a cascade heat pump unit (1) according to claim 2, characterized in that: The cascade heat pump unit (1) further comprises a high-temperature evaporator (13), and the step of "determining the starting condition of the compressor to be started later based on the starting sequence of the low-temperature compressor (11) and the high-temperature compressor (12)" further comprises: When Ts_H≤Ts1, starting the low temperature stage compressor (11); Wherein, Ts_H is the high temperature stage evaporation temperature, and Ts1 is the first preset temperature.

4. The control method for a cascade heat pump unit (1) according to claim 2, characterized in that: The cascade heat pump unit (1) further comprises a low-temperature stage condenser (13), and the step of "determining the starting condition of the compressor to be started later based on the starting sequence of the low-temperature stage compressor (11) and the high-temperature stage compressor (12)" further comprises: When Td_L≤Td1, starting the low temperature stage compressor (11); Wherein, Td_L is the low temperature stage condensation temperature, and Td1 is the second preset temperature.

5. The control method for a cascade heat pump unit (1) according to claim 2, characterized in that: The control method further comprises: If the low-temperature stage compressor (11) has not started after a time t1 has passed since the high-temperature stage compressor (12) was started, the low-temperature stage compressor (11) is started.

6. The control method for a cascade heat pump unit (1) according to claim 2, characterized in that: The step of "controlling which of the low-temperature compressor (11) and the high-temperature compressor (12) is started first according to the ambient temperature" also includes: When Tao<T1, the low temperature stage compressor (11) is started first, and then the high temperature stage compressor (12) is started.

7. The control method for a cascade heat pump unit (1) according to claim 6, characterized in that: The cascade heat pump unit (1) further comprises a low-temperature stage condenser (13), and the step of "determining the starting condition of the compressor to be started later based on the starting sequence of the low-temperature stage compressor (11) and the high-temperature stage compressor (12)" further comprises: When Td_L≥Td2, starting the high temperature stage compressor (12); Wherein, Td_L is the low temperature stage condensation temperature, and Td2 is the third preset temperature.

8. The control method for a cascade heat pump unit (1) according to claim 7, characterized in that: The cascade heat pump unit (1) further comprises a high-temperature evaporator (13), and the step of "determining the starting condition of the compressor to be started later based on the starting sequence of the low-temperature compressor (11) and the high-temperature compressor (12)" further comprises: When Ts_H≥Ts2, starting the high temperature stage compressor (12); Wherein, Ts_H is the high temperature stage evaporation temperature, and Ts2 is the fourth preset temperature.

9. The control method for a cascade heat pump unit (1) according to claim 6, characterized in that: The control method further comprises: If the high-temperature compressor (12) has not started after a time t2 has passed since the low-temperature compressor (11) was started, the high-temperature compressor (12) is started.

10. A cascade heat pump unit (1), characterized in that: The cascade heat pump unit (1) comprises a low-temperature stage compressor (11), a high-temperature stage compressor (12), a low-temperature stage condenser (13), a high-temperature stage evaporator (13), a first temperature sensor capable of acquiring an ambient temperature, a second temperature sensor capable of acquiring a high-temperature stage evaporation temperature, and a third temperature sensor capable of acquiring a low-temperature stage condensation temperature, and is capable of executing the control method for the cascade heat pump unit (1) described in any one of claims 1 to 9.

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