Cascade heat pump unit and control method thereof

Abstract

The present application relates to the technical field of heat pump, and particularly provides a cascade heat pump unit and a control method thereof, aiming at solving the problem that the existing cascade heat pump unit cannot start the low-temperature stage compressor and the high-temperature stage compressor according to the correct order and time interval based on the ambient temperature, resulting in poor working performance of the cascade heat pump unit. For this purpose, the cascade heat pump unit of the present application comprises a low-temperature stage compressor, a high-temperature stage compressor and a temperature sensor, and the control method comprises: controlling the temperature sensor to obtain the ambient temperature Tao; comparing the size of Tao and a preset ambient temperature value T1; selectively controlling the low-temperature stage compressor to start first or the high-temperature stage compressor to start first according to the comparison result; and setting the start condition of the compressor started later based on the start order of the low-temperature stage compressor and the high-temperature stage compressor, so that the cascade heat pump unit can start the low-temperature stage compressor and the high-temperature stage compressor according to the correct order and time interval based on the ambient temperature.

Description

Technical Field

[0001] This invention relates to the field of heat pump technology, specifically providing a cascade heat pump unit and its control method. Background Technology

[0002] A cascade heat pump unit consists of a low-temperature stage heating system and a high-temperature stage heating system. These two systems are independent and each has a compressor, evaporator, condenser, and throttling device, connected by an intermediate plate heat exchanger. In the low-temperature stage heating system, the low-temperature stage compressor compresses the refrigerant into a high-temperature, high-pressure gas, transferring heat to the intermediate plate heat exchanger, which acts as the condenser for the low-temperature stage. In the high-temperature stage heating system, the refrigerant absorbs heat from the intermediate plate heat exchanger and returns to the high-temperature stage compressor; the intermediate plate heat exchanger acts as the evaporator for the high-temperature stage.

[0003] Cascade heat pump units can operate in ambient temperatures ranging from -35℃ to +50℃. During startup, the heating system, which starts first, typically needs to exchange heat with the surrounding air. Different ambient temperatures will have different effects on the performance of the low-temperature and high-temperature heating systems. Therefore, the startup order of the low-temperature and high-temperature heating systems needs to be determined according to the ambient temperature to avoid situations where the cascade heat pump unit cannot exchange heat with the air. On the other hand, during the heat exchange process between the first-starting heating system and the air, if the air's heat exchange efficiency cannot meet the heat conduction requirements of the heating system, the heat from the heating system may not be transferred, potentially damaging the plate heat exchanger and compressor.

[0004] Accordingly, there is a need in the art for a new control method, control device, cascade heat pump unit, and readable storage medium for cascade heat pump units to solve the existing problems. Summary of the Invention

[0005] The present invention aims to solve the above-mentioned technical problems, namely, to solve the problem that existing cascade heat pump units cannot start the low-temperature stage compressor and the high-temperature stage compressor in the correct sequence 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 compressor.

[0006] In a first aspect, the present invention provides a control method for a cascade heat pump unit, the cascade heat pump unit including a low-temperature stage compressor and a high-temperature stage compressor, the control method comprising: controlling which of the low-temperature stage compressor and the high-temperature stage compressor to start first based on the ambient temperature; and determining the starting conditions of the compressor to be started later based on the starting order of the low-temperature stage compressor and the high-temperature stage compressor.

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

[0008] In a specific embodiment of the control method for the cascade heat pump unit described above, the cascade heat pump unit further includes a high-temperature stage evaporator. The step of "determining the starting conditions of the compressor after the starting sequence of the low-temperature stage compressor and the high-temperature stage compressor is determined" further includes: when Ts_H≤Ts1, the low-temperature stage compressor is started; wherein, Ts_H is the high-temperature stage evaporation temperature, and Ts1 is the first preset temperature.

[0009] In a specific embodiment of the control method for the cascade heat pump unit described above, the cascade heat pump unit further includes a low-temperature stage condenser. The step of "determining the starting conditions of the compressor after the starting sequence of the low-temperature stage compressor and the high-temperature stage compressor is determined" further includes: starting the low-temperature stage compressor when Td_L≤Td1; wherein Td_L is the low-temperature stage condensing temperature and Td1 is the second preset temperature.

[0010] In a specific embodiment of the control method for the above-mentioned cascade heat pump unit, the control method further includes: if the low-temperature stage compressor has not started after time t1, then the low-temperature stage compressor is started.

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

[0012] In a specific embodiment of the control method for the cascade heat pump unit described above, the cascade heat pump unit further includes a low-temperature stage condenser. The step of "determining the starting conditions of the compressor after the starting sequence of the low-temperature stage compressor and the high-temperature stage compressor is determined" further includes: starting the high-temperature stage compressor when Td_L≥Td2; wherein Td_L is the low-temperature stage condensing temperature and Td2 is the third preset temperature.

[0013] In a specific embodiment of the control method for the cascade heat pump unit described above, the cascade heat pump unit further includes a high-temperature stage evaporator. The step of "determining the starting conditions of the compressor after the starting sequence of the low-temperature stage compressor and the high-temperature stage compressor is determined" further includes: starting the high-temperature stage compressor when Ts_H≥Ts2; wherein, Ts_H is the high-temperature stage evaporation temperature and Ts2 is the fourth preset temperature.

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

[0015] The present invention also provides a cascade heat pump unit, which includes a low-temperature stage compressor, a high-temperature stage compressor, a low-temperature stage condenser, a high-temperature stage evaporator, a first temperature sensor capable of acquiring ambient temperature, a second temperature sensor capable of acquiring high-temperature stage evaporation temperature, and a third temperature sensor capable of acquiring low-temperature stage condensation temperature, and is capable of executing the control method for the cascade heat pump unit described in any of 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 stage compressor and the high-temperature stage compressor in the correct sequence and time interval according to the ambient temperature. Specifically, in the operation of the cascade heat pump unit of the present invention, the first temperature sensor is controlled to obtain the ambient temperature Tao of the cascade heat pump unit. Then, the ambient temperature Tao is compared with the preset ambient temperature T1. When Tao ≥ T1, the high-temperature stage compressor is started first. Then, the high-temperature stage evaporation temperature Ts_H is compared with the first preset temperature Ts1. In order to avoid the high-temperature stage evaporation temperature being too low, the low-temperature stage compressor is started when Ts_H ≤ Ts1. On the other hand, when Tao < T1, the low-temperature stage compressor is started first. Then, the low-temperature stage condensation temperature Td_L is compared with the third preset temperature Td2. In order to avoid the low-temperature stage condensation temperature being too high, the high-temperature stage compressor is started when Td_L ≥ Td2. This allows the high-temperature stage evaporator and the low-temperature stage condenser to complete heat exchange smoothly, ensuring the normal operation of the cascade heat pump unit. Attached Figure Description

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

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

[0019] Figure 2 This is a main flowchart of the control method for cascade heat pump units of the present invention;

[0020] Figure 3 This is an overall flowchart of the control method for cascade heat pump units of the present invention;

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

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

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

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

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

[0026] Figure 9 This is a flowchart of a second preferred embodiment of the control method for a cascade heat pump unit of the present invention;

[0027] Figure 10 This is a basic flowchart of the control method for cascade heat pump units of the present invention.

[0028] List of reference numerals in the attached diagram:

[0029] 1-Cascade heat pump unit;

[0030] 11- Cryogenic stage compressor;

[0031] 12-High temperature stage compressor;

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

[0033] 15 - High-temperature throttling device;

[0034] 16 - Low-temperature stage throttling device;

[0035] 17 - Low-temperature stage evaporator;

[0036] 18 - High-temperature condenser. Detailed Implementation

[0037] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the invention and are not intended to limit the scope of protection of the invention. Those skilled in the art can make adjustments as needed to adapt to specific applications.

[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 stage heating system and a high-temperature stage heating system. These two systems are independent and each has a compressor, evaporator, condenser, and throttling device, connected by an intermediate plate heat exchanger 13. In the low-temperature stage heating system, the low-temperature stage compressor 11 compresses the refrigerant into a high-temperature, high-pressure gas. The high-temperature, high-pressure gaseous refrigerant transfers heat to the intermediate plate heat exchanger 13 after passing through the plate heat exchanger 13. Then, the refrigerant passes through the low-temperature stage throttling device 16 and the low-temperature stage evaporator 17 before returning to the low-temperature stage compressor 11. The intermediate plate heat exchanger 13 is equivalent to the low-temperature stage condenser 13. In the high-temperature stage heating system, the refrigerant flows out from the high-temperature stage compressor 12, passes through the high-temperature stage condenser 18 and the high-temperature stage throttling device 15, absorbs heat in the intermediate plate heat exchanger 13, and then returns to the high-temperature stage compressor 12. The intermediate plate heat exchanger 13 is equivalent to the high-temperature stage evaporator. The cascade heat pump unit 1 can operate in an ambient temperature range of -35℃ to +50℃. During startup, the heating system that starts first typically needs to exchange heat with the surrounding air. Different ambient temperatures will have different effects on the performance of the low-temperature heating system and the high-temperature heating system. Therefore, the startup order of the low-temperature heating system and the high-temperature heating system needs to be sorted 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, during the heat exchange process between the first-starting heating system and the air, if the heat exchange efficiency of the air cannot meet the heat conduction requirements of the heating system, the heat of the heating system will not be transferred, which may damage the plate heat exchanger 13 and the compressor. To address this, the present invention proposes the following technical solution.

[0040] like Figures 1-4 , Figure 10As shown, to address the problem that existing cascade heat pump units 1 cannot start the low-temperature stage compressor 11 and high-temperature stage compressor 12 in the correct sequence and time interval according to the ambient temperature, thus affecting the working performance of the cascade heat pump unit 1 and potentially causing damage to the plate heat exchanger 13 and compressor, the cascade heat pump unit 1 of the present invention includes a low-temperature stage compressor 11, a high-temperature stage compressor 12, a high-temperature stage evaporator 13, a first temperature sensor (not shown in the figure) capable of acquiring the ambient temperature, and a second temperature sensor (not shown in the figure) capable of acquiring the high-temperature stage evaporation temperature. The control method includes:

[0041] S01. Based on the ambient temperature, determine which of the low-temperature stage compressor 11 and the high-temperature stage compressor 12 should be started first;

[0042] S02. Start-up conditions of the compressors that are started after the start-up sequence of the low-temperature compressor 11 and the high-temperature compressor 12 is determined.

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

[0044] S1. Control the first temperature sensor to acquire the ambient temperature Tao;

[0045] S2. Compare the ambient temperature Tao with the preset ambient temperature value T1;

[0046] S3. Based on the comparison results, selectively control the low-temperature stage compressor 11 to start first or the high-temperature stage compressor 12 to start first;

[0047] S4. Start-up conditions for the compressors that start after the start-up sequence of the low-temperature compressor 11 and the high-temperature compressor 12 is set.

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

[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 includes:

[0051] S41. Control the second temperature sensor to obtain the high-temperature stage evaporation temperature Ts_H;

[0052] S42. Compare the magnitude of Ts_H with the first preset temperature Ts1;

[0053] S43. When Ts_H≤Ts1, start the cryogenic stage compressor 11.

[0054] As mentioned above, the cascade heat pump unit 1 includes a low-temperature stage heating system and a high-temperature stage heating system. The low-temperature stage heating system includes a low-temperature stage compressor 11, and the high-temperature stage heating system includes a high-temperature stage compressor 12, a high-temperature stage evaporator 13, and a second temperature sensor. Based on this, the above-mentioned implementation method is proposed. In this implementation method, the first temperature sensor is first controlled to acquire the ambient temperature Tao of the cascade heat pump unit 1. Then, the ambient temperature Tao is compared with a preset ambient temperature value T1. When Tao ≥ T1, it indicates that the ambient temperature is relatively high, which is conducive to the high-temperature stage evaporator 13 absorbing heat. Therefore, the high-temperature stage compressor 12 is started first. During the heat exchange process between the high-temperature stage evaporator 13 and the ambient air, the heat in the environment cannot meet the heat requirements of the high-temperature stage evaporator 13. Due to heat exchange requirements, and with the low-temperature stage compressor 11 not running, the low-temperature stage condenser cannot actively transfer heat to the high-temperature stage evaporator through the intermediate plate heat exchanger 13. Therefore, the high-temperature stage evaporation temperature will gradually decrease. To prevent the high-temperature stage evaporation temperature from being too low and falling below the set minimum high-temperature stage evaporation temperature Ts1, which would trigger a low-pressure alarm, the second temperature sensor is controlled to acquire the high-temperature stage evaporation temperature Ts_H. The sensor then compares the high-temperature stage evaporation temperature Ts_H with the minimum high-temperature stage evaporation temperature Ts1. When Ts_H ≤ Ts1, the low-temperature stage compressor 11 is started. The condensation effect of the low-temperature stage condenser 13 provides heat to the high-temperature stage evaporator 13, while also conducting the heat from the low-temperature stage condenser 13, thus ensuring the normal operation of both the high-temperature stage heating system and the low-temperature stage heating system.

[0055] The following reference Figure 1 , Figure 2 and Figure 5 A second embodiment of the control method for a cascade heat pump unit 1 of the present invention will be described. In this embodiment, Figure 5 This is a flowchart of a second embodiment of the control method for a cascade heat pump unit 1 according to 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 acquiring the low-temperature stage condensation temperature. The control method for the cascade heat pump unit 1 includes:

[0057] S4. Start-up conditions for the compressors that start after the start-up sequence of the low-temperature compressor 11 and the high-temperature compressor 12 is set.

[0058] Step S4 further includes:

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

[0060] S45. Compare the magnitude of Td_L with the second preset temperature Td1;

[0061] S46. When Td_L≤Td1, start the cryogenic stage compressor 11.

[0062] As mentioned above, when the low-temperature stage compressor 11 is not started, the low-temperature stage condenser side cannot actively transfer heat to the high-temperature stage evaporator side through the intermediate plate heat exchanger 13. However, at this time, the high-temperature stage heating system will continuously absorb heat from the low-temperature stage condenser side through the intermediate plate heat exchanger 13, thereby causing the low-temperature stage condensing temperature to gradually decrease passively. In order to prevent the low-temperature stage condensing temperature from being too low and falling below the minimum low-temperature stage condensing temperature Tmin, which would lead to a high-pressure low alarm, the above-mentioned implementation method is proposed. When the above-mentioned implementation method is adopted, during the process of the low-temperature stage condensing temperature gradually decreasing, the third temperature sensor is controlled to obtain the low-temperature stage condensing temperature Td_L, and the low-temperature stage condensing temperature Td_L is compared with the second preset temperature Td1 (Td1 = Tmin + 5℃). When Td_L ≤ Td1, the low-temperature stage compressor 11 is started, and the low-temperature stage condensing temperature is increased by the condensing effect of the low-temperature stage condenser 13, thereby avoiding the low-temperature stage condensing temperature from being too low and causing a high-pressure low alarm. Furthermore, those skilled in the art will understand that setting the criterion for starting the cryogenic compressor 11 to be less than or equal to the cryogenic condensing temperature Td_L and the cryogenic minimum condensing temperature Tmin+5°C is intended to enable the cryogenic compressor 11 to start and begin heating in advance, thus preventing the cryogenic condensing temperature from dropping below the cryogenic minimum condensing temperature and thereby avoiding damage to the plate heat exchanger 13 and the cryogenic compressor 11.

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

[0064] S47. If the low-temperature compressor 11 has not started after time t1 since the high-temperature compressor 12 was started, then the low-temperature compressor 11 shall be started.

[0065] Although the aforementioned start-up conditions for starting the low-temperature compressor 11 after starting the high-temperature compressor 12 were mentioned, these are protective conditions set to avoid adverse consequences. Based on this, this embodiment is proposed to ensure the normal operation of the cascade heat pump unit 1. If the low-temperature compressor 11 has not started after time t1 since the high-temperature compressor 12 started, then the low-temperature compressor 11 is started. In this way, the cascade heat pump unit 1 can be started and used normally without damage to its components, avoiding the situation where the low-temperature compressor 11 does not start after the high-temperature compressor 12 starts.

[0066] The above has already described the case where the ambient temperature is too high when Tao ≥ T1. Next, we will explain the case where the ambient temperature is too low when Tao < T1. Please refer to the following... Figure 1 , Figure 2 , Figure 6 A third embodiment of the control method for a cascade heat pump unit 1 of the present invention will be described. Figure 6 This is a flowchart of a third embodiment of the control method for a cascade heat pump unit 1 according to the present invention.

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

[0068] S3. Based on the comparison results, selectively control the low-temperature stage compressor 11 to start first or the high-temperature stage compressor 12 to start first;

[0069] S4. Start-up conditions for the compressors that start after the start-up sequence of the low-temperature compressor 11 and the high-temperature compressor 12 is set.

[0070] Of the above steps, step S3 further includes:

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

[0072] Step S4 further includes:

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

[0074] S402. Compare the magnitude of Td_L with the third preset temperature Td2;

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

[0076] When Tao < T1, the ambient temperature is low, which is conducive to the heat release of the low-temperature stage condenser 13. Therefore, the low-temperature stage compressor 11 is started first. During the heat exchange process between the low-temperature stage condenser 13 and the ambient air, due to the limited heat exchange capacity of the ambient air and the absence of the high-temperature stage compressor 12, the high-temperature stage evaporator cannot actively absorb heat from the low-temperature stage condenser through the intermediate plate heat exchanger 13. At this time, the low-temperature stage condensing temperature will continue to rise. To prevent the low-temperature stage condensing temperature from becoming too high and exceeding the set maximum low-temperature stage condensing temperature Td2, which would cause a high-pressure alarm, the third temperature sensor is controlled to obtain the low-temperature stage condensing temperature Td_L and compare it with the third preset temperature Td2. When Td_L ≥ Td2, the high-temperature stage compressor 12 is started. The high-temperature stage evaporator 13 absorbs the heat from the low-temperature stage condenser 13 through evaporation, and also provides heat for the high-temperature stage evaporator 13 to evaporate, thereby ensuring the normal operation of the high-temperature stage heating system and the low-temperature stage heating system.

[0077] The following reference Figure 1 , Figure 2 , Figure 7 A fourth embodiment of the control method for a cascade heat pump unit 1 of the present invention will be described. Among them, Figure 7 This is a flowchart of a fourth embodiment of the control method for a cascade heat pump unit 1 according to the present invention.

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

[0079] S4. Start-up conditions for the compressors that start after the start-up sequence of the low-temperature compressor 11 and the high-temperature compressor 12 is set.

[0080] Step S4 further includes:

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

[0082] S405. Compare the magnitudes of Ts_H and 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 evaporator side through the intermediate plate heat exchanger 13, and the high-temperature stage evaporation temperature will passively and gradually increase. In order to prevent the high-temperature stage evaporation temperature from being too high and exceeding the maximum high-temperature stage evaporation temperature Tmax, which would lead to a low-pressure over-temperature alarm, the above-mentioned implementation method is proposed. When the above-mentioned implementation method is adopted, during the process of the high-temperature stage evaporation temperature gradually increasing, the second temperature sensor is controlled to obtain the high-temperature stage evaporation temperature Ts_H, and the magnitude of Ts_H and the fourth preset temperature Ts2 (Ts2 = Tmax - 5℃) 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 effect of the high-temperature stage evaporator 13, thereby avoiding the high-temperature stage evaporation temperature from being too high and leading to a low-pressure over-temperature alarm. Furthermore, those skilled in the art will understand that setting the condition for starting the high-temperature stage compressor 12 to have a high-temperature stage evaporation temperature greater than or equal to the high-temperature stage maximum evaporation temperature Tmax-5°C is intended to enable the high-temperature stage compressor 12 to start and begin cooling earlier, thus preventing the high-temperature stage evaporation temperature from rising above the high-temperature stage maximum evaporation temperature and thereby avoiding damage to the plate heat exchanger 13 and the high-temperature stage compressor 12.

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

[0086] S407. If the high-temperature compressor (12) has not started after time t2 after the low-temperature compressor (11) has been started, then the high-temperature compressor (12) shall be started.

[0087] Although the aforementioned start-up conditions for starting the high-temperature compressor (12) after starting the low-temperature compressor (11) were mentioned, these are protective conditions set to avoid adverse consequences. Based on this, this embodiment is proposed to ensure the normal operation of the cascade heat pump unit (1). If the high-temperature compressor (12) has not started after time t2 since the low-temperature compressor (12) was started, then the high-temperature compressor (12) is started. In this way, the components of the cascade heat pump unit (1) can be started and used normally without damage, avoiding the situation where the high-temperature compressor (12) does not start after the low-temperature compressor (11) is started.

[0088] Furthermore, regarding the priorities of steps S41-S43, S44-S46, and S7 mentioned above, as well as the priorities of steps S401-S403, S404-S406, and S407, those skilled in the art will understand that steps S41-S43 and S44-S46 have higher priorities than step S7, and steps S41-S43 and S44-S46 can be judged simultaneously. Similarly, steps S401-S403 and S404-S406 have higher priorities than step S407, and steps S401-S403 and S404-S406 can be judged simultaneously. Of course, those skilled in the art can also adjust the priorities of the above steps according to the needs of actual use, and these changes do not exceed the protection scope of this invention.

[0089] It should be noted that the above embodiments are merely used to illustrate the principles of the present invention and are not intended to limit the scope of protection of the present invention. Without departing from the principles of the present invention, those skilled in the art can adjust the above structure so that the present invention can be applied to more specific application scenarios.

[0090] Those skilled in the art will understand that the aforementioned cascade heat pump unit 1 also includes other known structures, such as processors, controllers, and memories. These memories include, but are not limited to, random access memory (RAM), flash memory, read-only memory (ROM), programmable read-only memory (PROM), volatile memory, non-volatile memory, serial memory, parallel memory, or registers. Processors include, but are not limited to, CPLD / FPGA, DSP, ARM processors, and MIPS processors. To avoid unnecessarily obscuring the embodiments of this disclosure, these known structures are not shown in the accompanying drawings.

[0091] Furthermore, the present invention also provides a control device for a cascade heat pump unit 1, the control device including a processor and a memory storing program instructions, the processor being configured to execute the control method for the cascade heat pump unit 1 according to any of 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 acquiring ambient temperature, a second temperature sensor capable of acquiring high-temperature stage evaporation temperature, a third temperature sensor capable of acquiring low-temperature stage condensation temperature, and the control device for the cascade heat pump unit 1 described above.

[0093] Furthermore, the present invention also provides a readable storage medium storing a plurality of program codes adapted for loading and running by a processor to perform the control method for air conditioning refrigerant diversion according to any of the above-described technical claims.

[0094] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles 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 such changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A control method for a cascade heat pump unit (1), characterized in that, The control method of the cascade heat pump unit (1) comprises: controlling which of the low-temperature stage compressor (11) and the high-temperature stage compressor (12) is started first according to the ambient temperature; determining the starting condition of the compressor started later based on the starting sequence of the low-temperature stage compressor (11) and the high-temperature stage compressor (12); the step of "controlling which of the low-temperature stage compressor (11) and the high-temperature stage compressor (12) is started first according to the ambient temperature" further comprises: when Tao≥T1, starting the high-temperature stage compressor (12) first and then starting the low-temperature stage compressor (11); when Tao wherein Tao is the ambient temperature and T1 is a preset value of the ambient temperature.

2. The control method for a cascade heat pump unit (1) according to claim 1, characterized in that, The cascade heat pump unit (1) further comprises a high-temperature stage evaporator (13), and the step of "determining the starting condition of the compressor started later based on the starting sequence of the low-temperature stage compressor (11) and the high-temperature stage 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 a first preset temperature.

3. The control method for a cascade heat pump unit (1) according to claim 1, 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 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 a second preset temperature.

4. The control method for a cascade heat pump unit (1) according to claim 1, characterized in that, The control method further comprises: if the low-temperature stage compressor (11) has not been started after the high-temperature stage compressor (12) has been started for a time t1, starting the low-temperature stage compressor (11).

5. The control method for a cascade heat pump unit (1) according to claim 1, 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 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 a third preset temperature.

6. The control method for a cascade heat pump unit (1) according to claim 5, characterized in that, The cascade heat pump unit (1) further comprises a high-temperature stage evaporator (13), and the step of "determining the starting condition of the compressor started later based on the starting sequence of the low-temperature stage compressor (11) and the high-temperature stage 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 a fourth preset temperature.

7. The control method for a cascade heat pump unit (1) according to claim 1, characterized in that, The control method further comprises: if the high-temperature stage compressor (12) has not been started after the low-temperature stage compressor (11) has been started for a time t2, starting the high-temperature stage compressor (12).

8. 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 evaporating temperature, a third temperature sensor capable of acquiring a low-temperature stage condensing temperature, and is capable of executing the control method for the cascade heat pump unit (1) according to any one of claims 1-7.

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