Heat pump water heater and control method thereof

Abstract

The application belongs to the technical field of heat pumps, and particularly relates to a heat pump water heater and a control method thereof, which are used for solving the technical problem of pipeline leakage, and the control method comprises the following steps: accepting a start-up instruction; determining a target valve step number in a second preset time length after a first preset time length of operation according to an initial opening degree of a throttling device; when the target valve step number is greater than 0, adjusting the opening degree of the throttling device at a first preset period in the second preset time length according to a current discharge temperature of a compressor and the target valve step number; and adjusting the opening degree of the throttling device at a second preset period after the first preset period of adjustment of the opening degree of the throttling device is completed until the second preset time length is ended; wherein the first preset period is greater than the second preset period. The application can reduce the risk of pipeline leakage and improve safety and reliability.

Description

Technical Field

[0001] This application relates to the field of heat pump technology, and in particular to a heat pump water heater and its control method. Background Technology

[0002] Heat pump technology is a new energy-saving technology that has attracted worldwide attention. A heat pump water heater utilizes the reverse Carnot cycle to transfer heat from a low-temperature object to high-temperature water using a refrigerant. The internal structure of a heat pump water heater mainly includes a compressor, condenser, throttling device, and evaporator. The throttling device is used to change the throttling cross-section or throttling length to control the flow rate of the refrigerant.

[0003] In related technologies, throttling devices typically employ electronic expansion valves and capillary tubes. Electronic expansion valves offer a wider adjustment range and superior energy efficiency and stability. Specifically, during the initial startup phase of a heat pump water heater, the initial opening of the electronic expansion valve is determined by detecting parameters such as water temperature, ambient temperature, and compressor frequency, and maintained for a fixed duration. Once the fixed duration of adjustment is met, superheat control is initiated, adjusting according to the valve adjustment steps required during normal operation of the heat pump water heater.

[0004] However, heat pump water heaters experience increased vibration during startup, posing a risk of pipe leaks and resulting in low safety and reliability. Summary of the Invention

[0005] This application provides a heat pump water heater and its control method, which can reduce the vibration of the heat pump water heater during the start-up phase, reduce the risk of pipeline leakage, and improve the safety and reliability of the heat pump water heater during operation.

[0006] To achieve the above objectives, this application provides the following technical solution:

[0007] In a first aspect, embodiments of this application provide a control method for a heat pump water heater, including:

[0008] Upon receiving the start-up command, after running for a first preset duration based on the initial opening of the throttling device, determine the target valve control step number for entering the second preset duration;

[0009] When the target valve adjustment step number is greater than 0, the opening degree of the throttling device is adjusted within the second preset time period and the first preset cycle according to the current exhaust temperature of the compressor and the target valve adjustment step number.

[0010] The opening of the throttling device is adjusted at a first preset period until the second preset duration ends, and then the opening of the throttling device is adjusted at a second preset period; wherein the first preset period is longer than the second preset period.

[0011] In some optional embodiments, when the target valve adjustment step number is greater than 0, adjusting the opening of the throttling device within a second preset time period at a first preset cycle based on the current discharge temperature of the compressor and the target valve adjustment step number specifically includes:

[0012] Determine whether the current exhaust temperature of the compressor is greater than the first preset exhaust temperature;

[0013] If so, the opening of the throttling device is adjusted within a first preset period of time according to the target valve adjustment step number.

[0014] If not, then based on the current exhaust temperature of the compressor within the stated temperature range, the target valve adjustment step number is indeed corrected, and the opening of the throttling device is adjusted within a first preset cycle for a second preset time period based on the corrected target valve adjustment step number.

[0015] In some optional embodiments, determining the number of correction target valve adjustment steps based on the temperature range of the current discharge temperature of the compressor specifically includes:

[0016] The correction value of the throttling device is determined based on the temperature range in which the current exhaust temperature of the compressor falls.

[0017] The corrected target valve control step number is determined based on the sum of the target valve control step number and the correction value.

[0018] In some optional embodiments, determining the correction value of the throttling device based on the temperature range of the compressor's current exhaust temperature specifically includes:

[0019] If the current exhaust temperature of the compressor is less than or equal to a first preset temperature and greater than a second preset temperature, then the correction value is determined to be a first preset threshold, wherein the first preset threshold is less than 0.

[0020] In some optional embodiments, determining the correction value of the throttling device based on the temperature range of the compressor's current exhaust temperature specifically includes:

[0021] If the current exhaust temperature of the compressor is less than or equal to the second preset temperature and greater than the third preset temperature, then the correction value is determined to be the second preset threshold; wherein the second preset threshold is less than the first preset threshold.

[0022] In some optional embodiments, determining the correction value of the throttling device based on the temperature range of the current exhaust temperature of the compressor specifically includes:

[0023] If the current exhaust temperature of the compressor is less than or equal to a third preset temperature, then the correction value is determined to be a third preset threshold; wherein the third preset threshold is less than a second preset threshold.

[0024] In some optional embodiments, the third preset threshold is -3.

[0025] In some optional embodiments, determining the target valve adjustment steps of the throttling device after operating for a first preset time according to the initial opening during the start-up phase specifically includes:

[0026] Upon receiving the power-on command, determine the initial opening degree of the throttling device, and run for a first preset duration based on the initial opening degree;

[0027] After running for a first preset time based on the initial opening, the actual suction superheat of the compressor is determined;

[0028] The target valve adjustment step number is determined based on the difference between the actual intake superheat and the target intake superheat.

[0029] In some optional implementations, determining the actual suction superheat of the compressor specifically includes:

[0030] Obtain the suction temperature and evaporation temperature of the compressor;

[0031] The actual intake superheat of the compressor is determined based on the difference between the intake temperature and the evaporation temperature.

[0032] In some optional implementations, determining the initial opening degree of the throttling device specifically includes:

[0033] Obtain ambient temperature, water temperature, and compressor frequency;

[0034] The initial opening degree of the throttling device is determined based on the ambient temperature, the water temperature, and the compressor frequency.

[0035] Those skilled in the art will understand that the control method for a heat pump water heater provided in the embodiments of this application includes: receiving a start-up command, running for a first preset duration according to the initial opening of the throttling device, and then determining the target valve adjustment step number for entering a second preset duration;

[0036] When the target valve adjustment step number is greater than 0, the opening of the throttling device is adjusted within a first preset cycle within a second preset time period, based on the current exhaust temperature of the compressor and the target valve adjustment step number. The opening of the throttling device is adjusted within the first preset cycle until the end of the second preset time period, and then the opening of the throttling device is adjusted within the second preset cycle. The first preset cycle is longer than the second preset cycle. This technical solution reduces vibration during the start-up phase of the heat pump water heater, thereby reducing the risk of pipe leakage and improving the safety and reliability of the heat pump water heater during operation.

[0037] Secondly, this application provides a heat pump water heater, comprising: a compressor, a first heat exchanger, a throttling device, and a second heat exchanger connected in sequence. The first heat exchanger is connected to the exhaust port of the compressor, and the second heat exchanger is connected to the intake port of the compressor. When the heat pump water heater is turned on, the heat pump water heater adjusts the opening degree of the throttling device using the control method provided in the first aspect.

[0038] The heat pump water heater provided in this application has the same technical effects as the above embodiments, and will not be described again here.

[0039] In addition to the technical problems solved by the embodiments of this application, the technical features constituting the technical solutions, and the beneficial effects brought about by the technical features of these technical solutions described above, other technical problems that can be solved by the heat pump water heater and its control method provided by the embodiments of this application, other technical features included in the technical solutions, and the beneficial effects brought about by these technical features will be further explained in detail in the specific implementation. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 A flowchart illustrating the control method for a heat pump water heater provided in this application embodiment;

[0042] Figure 2 This is a schematic diagram of the structure of a heat pump water heater provided in an embodiment of this application. Detailed Implementation

[0043] In related technologies, throttling devices typically employ electronic expansion valves and capillary tubes. Electronic expansion valves offer a wider adjustment range and superior energy efficiency and stability. When a heat pump water heater is first started, the initial opening of the electronic expansion valve is determined by detecting parameters such as water temperature, ambient temperature, and compressor frequency, and maintained for a fixed duration. Once the duration condition is met, conventional superheat control is initiated, allowing the electronic expansion valve to adjust its opening during normal operation. However, because the refrigerant system is transitioning from an unsteady state to a steady state upon startup, the electronic expansion valve typically opens rapidly initially and then gradually closes during normal operation. This rapid opening at startup causes a rapid increase in refrigerant circulation, followed by a gradual closing during normal operation. This significant fluctuation in refrigerant flow rate can increase compressor vibration, leading to increased pipe system vibration and a higher risk of leaks, resulting in low safety and reliability.

[0044] To address the aforementioned technical problems, this application provides a heat pump water heater and its control method. By adding a buffer zone between the initial opening stage and the normal operation stage of the throttling device, the opening adjustment of the throttling device during startup can be made smoother, reducing fluctuations and thus reducing the impact of refrigerant circulation flow changes on pipeline system vibration, thereby reducing the risk of pipeline leakage and improving safety and reliability.

[0045] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0046] Example 1

[0047] Figure 1 A flowchart illustrating the control method for a heat pump water heater provided in this application embodiment. See also... Figure 1 As shown in the embodiment of this application, the control method for a heat pump water heater includes the following steps:

[0048] Step S101: Receive the start command, run for a first preset time according to the initial opening of the throttling device, and then determine the target valve control step number to enter the second preset time.

[0049] The throttling device includes, but is not limited to, structures such as electronic expansion valves. In this application, an example is given where the throttling device includes an electronic expansion valve. Those skilled in the art will understand that the throttling device may also include only structures such as electronic expansion valves.

[0050] Optionally, the initial opening degree can be determined based on parameters such as ambient temperature, water temperature, and compressor frequency. When a start-up command is received, the throttling device opens to the initial opening degree and runs for a first preset duration. In this embodiment, the first preset duration can be represented by T1.

[0051] It should be noted that the first preset duration is a fixed duration. The first preset duration can be set in advance by the throttling device at the factory; or it can be customized by the user according to their needs. This application does not impose any specific restrictions on this.

[0052] After running for the first preset time based on the initial opening, the actual suction superheat of the compressor is determined.

[0053] Taking the properties of water and steam as an example, superheat refers to the degree to which the steam temperature exceeds the saturation temperature at the corresponding pressure. In this application, the superheat control of the throttling device includes intake superheat control, exhaust superheat control, and control of both intake and exhaust superheat. In this application, the method of adjusting the opening of the throttling device during the start-up phase is illustrated using intake superheat control as an example.

[0054] Optionally, determine the actual suction superheat of the compressor, specifically including:

[0055] Obtain the compressor's suction temperature and evaporation temperature; determine the compressor's actual suction superheat based on the difference between the suction temperature and the evaporation temperature.

[0056] In some embodiments, the compressor’s suction temperature and evaporation temperature can be detected by a temperature sensor or other detection device, and the difference between the suction temperature and the evaporation temperature can be calculated. This difference is the compressor’s actual suction superheat.

[0057] The target number of valve control steps is determined based on the difference between the actual intake superheat and the target intake superheat.

[0058] The target intake superheat can be controlled based on the type of refrigerant controller used and its adjustment value.

[0059] It is understandable that the target valve control step number is the difference between the actual intake superheat and the target intake superheat.

[0060] The target valve control steps can be calculated using the following formula:

[0061] △P=(To-Te)-△t1 (1)

[0062] Where △P is the target valve control step number; To is the suction temperature; Te is the steam temperature; and △t1 is the target suction superheat.

[0063] The target intake superheat can be determined by referring to relevant technologies, which will not be elaborated here.

[0064] Determine whether the difference between the actual intake superheat and the target superheat is greater than 0.

[0065] If the difference between the actual intake superheat and the target superheat is not greater than 0 (i.e., the difference is less than or equal to 0), then the target valve adjustment step number is the actual calculated difference. For example, if the calculated difference is 0, -1, or -2, then the target valve adjustment step number will adjust the opening of the throttling device according to the calculated difference.

[0066] Understandably, based on the current actual opening degree of the throttling device and the target valve control step, the target opening degree of the throttling device for the next operation can be calculated. The calculation formula is as follows:

[0067] P i+1 =P i +△P (2)

[0068] Among them, P i+1 P is the target opening degree of the throttling device for the next operation. i This represents the current actual opening degree of the throttling device.

[0069] It is understandable that the next opening size of the throttling device is the sum of the current actual opening size of the throttling device and the target valve control step.

[0070] Step S102: When the target valve adjustment step number is greater than 0, adjust the opening of the throttling device within the second preset time period and the first preset cycle according to the current exhaust temperature of the compressor and the target valve adjustment step number.

[0071] Specifically, when the target valve control step number is greater than 0, it is determined whether the current exhaust temperature of the compressor is greater than the first preset exhaust temperature.

[0072] The first preset exhaust temperature can be an exhaust temperature value that has been set according to user needs.

[0073] If the current exhaust temperature of the compressor is greater than the first preset exhaust temperature, the opening of the throttling device is adjusted within the second preset time period according to the target valve adjustment step number and the first preset cycle.

[0074] If the current exhaust temperature of the compressor is less than or equal to the first preset exhaust temperature, then the number of correction target valve adjustment steps is determined according to the temperature range of the current exhaust temperature of the compressor, and the opening of the throttling device is adjusted according to the preset cycle within the second preset time period based on the number of correction target valve adjustment steps.

[0075] The second preset duration is the transition period from the first preset duration of operation during the start-up phase to the normal operation phase of the heat pump water heater. This allows the throttling device to form a transition range from its initial opening to its normal operating opening. In this way, the opening of the throttling device can smoothly transition from its initial opening to its normal adjustment opening within the second preset duration, making the opening adjustment of the throttling device smoother and reducing fluctuations. This reduces the impact of refrigerant flow changes on the vibration of the pipeline system, thereby reducing the risk of pipeline leakage.

[0076] Specifically, when the target valve adjustment step number is greater than 0, and the current exhaust temperature of the compressor is also greater than the first preset exhaust temperature, the opening of the throttling device is adjusted according to the target valve adjustment step number, and the opening of the throttling device is cyclically adjusted within a second preset time period according to a first preset cycle. For example, the second preset time period is 10 minutes and the first preset cycle is 120 seconds. In this way, the opening of the throttling device is adjusted according to the target valve adjustment step number, with a time interval of 120 seconds between two adjacent adjustments. Thus, the opening adjustment of the throttling device is periodically adjusted until the second preset time period ends.

[0077] When the target valve adjustment step number is greater than 0 and the current discharge temperature of the compressor is less than or equal to the first preset discharge temperature, the target valve adjustment step number is determined according to the temperature range of the current discharge temperature of the compressor. This allows the throttling device to adjust its opening according to a preset cycle within a second preset time period based on the target valve adjustment step number, so as to avoid the throttling device opening being too large.

[0078] It is understandable that the target valve control step number is the sum of the target valve control step number and the correction value, and the correction value is related to the temperature range of the current exhaust temperature of the compressor. That is, the correction value of the throttling device can be determined based on the temperature range of the current exhaust temperature of the compressor.

[0079] The formula for calculating the number of steps for correcting the target valve control is as follows:

[0080] △P 1 =△P+△t2 (3)

[0081] Among them, △P 1 The target valve control step number is corrected, and Δt2 is the correction value.

[0082] For example, if the current exhaust temperature of the compressor is less than or equal to the first preset exhaust temperature and greater than the second preset exhaust temperature, then the correction value is determined to be the first preset threshold, wherein the first preset threshold is less than 0, for example, the first preset threshold is -1.

[0083] It should be noted that the correction value can also be adjusted according to different evaporation temperatures and other conditions, which will not be elaborated here.

[0084] For example, the correction value is adjusted differently based on the exhaust temperature.

[0085] Specifically, if the current exhaust temperature of the compressor is less than or equal to the second preset temperature but greater than the third preset temperature, then the correction value is determined to be the second preset threshold, where the second preset threshold is less than the first preset threshold, for example, the second preset threshold is -2.

[0086] If the current exhaust temperature of the compressor is less than or equal to the third preset temperature, then the correction value is determined to be the third preset threshold, where the third preset threshold is less than the second preset threshold, for example, the third preset threshold is -3.

[0087] It should be noted that when the corrected △P 1 When the value is less than 0, △P 1 The value is 0. For example, if the target valve control step count ΔP before correction is 1, and the correction value Δt2 is -2, then the target valve control step count ΔP after correction is 0. 1 The value is 1 + (-2) = -1. Since -1 < 0, the corrected target valve control step number ΔP 1 The value is 0.

[0088] Understandably, after determining the target valve adjustment step number, the throttling device adjusts the opening of the throttling device within the second preset time period according to the target valve adjustment step number, and performs cyclic adjustment at a preset period, for example, the preset period is 120s, until the second preset time period ends.

[0089] Understandably, during the second preset operating period, the opening of the throttling device is adjusted differently according to different exhaust temperatures. For example, no adjustment is made when the exhaust temperature is high, and an adjustment is made when the exhaust temperature is low. In this way, the amount of refrigerant circulating during the start-up phase can be controlled, so that the opening adjustment of the throttling device is more stable, the heat pump water heater is more stable during operation, avoids the risk of pipeline leakage, and improves the safety and reliability of the heat pump water heater during operation.

[0090] Step S103: Adjust the opening of the throttling device with the first preset period until the second preset duration ends, and then adjust the opening of the throttling device with the second preset period; wherein the first preset period is greater than the second preset period.

[0091] Understandably, after running for the second preset time, the refrigerant in the heat pump water heater transitions from an unsteady state to a steady state, and the heat pump water heater enters a stable operating phase. The opening adjustment cycle of the throttling device is then adjusted so that the opening adjustment of the throttling device cycles according to the second preset cycle. For example, if the second preset cycle is 90 seconds, the opening adjustment cycle of the throttling device can be changed from 120 seconds to 90 seconds. This shortens the opening adjustment cycle of the throttling device and improves the sensitivity of the throttling device when adjusting the flow rate.

[0092] Understandably, the adjustment cycle of the throttling device within the second preset time period is longer than the adjustment cycle during normal operation. This avoids the problem of the throttling device opening too wide due to delayed execution when adjusting the opening within the second preset time period. In addition, by making different corrections to the target valve step number based on conditions such as exhaust temperature within the second preset time period, the smoothness of the throttling device's opening adjustment can be increased, fluctuations can be reduced, and the impact of changes in refrigerant flow on pipeline system vibration can be reduced, thereby reducing the risk of pipeline leakage and improving operational safety and reliability.

[0093] Example 2

[0094] Figure 2 A schematic diagram of the structure of a heat pump water heater provided in an embodiment of this application. See also... Figure 2 As shown in the embodiment of this application, a heat pump water heater 100 is also provided, including: a compressor 110, a first heat exchanger 120, a throttling device 130 and a second heat exchanger 140 connected in sequence. The first heat exchanger 120 is connected to the exhaust port of the compressor 110, and the second heat exchanger 140 is connected to the intake port of the compressor 110. When the heat pump water heater 100 is turned on, the heat pump water heater 100 adjusts the opening degree of the throttling device 130 using the control method in the above embodiment.

[0095] The control method of the heat pump water heater 100 has been described in detail in the above embodiments and will not be repeated here.

[0096] Optionally, the first heat exchanger 120 can be an outdoor unit, and the second heat exchanger 140 can be an indoor unit. During heating, the second heat exchanger 140 acts as a condenser, and the first heat exchanger 120 acts as an evaporator. Furthermore, it is understood that the control method described above for a heat pump water heater can also be applied to other devices with similar structures and operating principles to the heat pump water heater 100, such as devices equipped with electronic expansion valves, which can then be used for both cooling and heating. In this case, when the device similar to the heat pump water heater 100 is used for cooling, the first heat exchanger 120 acts as a condenser, and the second heat exchanger 140 acts as an evaporator.

[0097] When the heat pump water heater 100 is operating for heating, the exhaust port of the compressor 110 is connected to the second heat exchanger 140. The high-temperature and high-pressure refrigerant gas discharged by the compressor 110 is cooled by the second heat exchanger 140 to form a medium-temperature and high-pressure liquid refrigerant. In this way, the second heat exchanger 140 can release heat to the water to be heated in the heat pump water heater 100 to increase the water temperature. The medium-temperature and high-pressure liquid refrigerant is throttled and depressurized by the throttling device 130 to form a low-temperature and low-pressure gas-liquid mixture, which then enters the first heat exchanger 120. The first heat exchanger 120 absorbs heat from the air or circulating water to vaporize the low-temperature and low-pressure gas-liquid mixture, turning it into refrigerant gas, which then returns to the compressor 110 for further compression and continues to circulate for heating.

[0098] Optionally, the heat pump water heater 100 also includes a control valve 150. For example, the control valve 150 is a four-way valve. The compressor 110 is connected to the first heat exchanger 120 and the second heat exchanger 140 respectively through the control valve 150, and the connection of the heating circuit or other circuits is realized through the control valve 150.

[0099] This application provides a heat pump water heater and its control method. The control method includes receiving a start-up command, running the throttling device for a first preset time based on its initial opening, and then determining a target valve adjustment step number for a second preset time. When the target valve adjustment step number is greater than 0, adjusting the opening of the throttling device at a first preset cycle within the second preset time based on the compressor's current exhaust temperature and the target valve adjustment step number; adjusting the opening of the throttling device at the first preset cycle until the second preset time ends, and then adjusting the opening of the throttling device at a second preset cycle; wherein the first preset cycle is longer than the second preset cycle. This technical solution reduces vibration during the start-up phase of the heat pump water heater, thereby reducing the risk of pipe leakage and improving the safety and reliability of the heat pump water heater during operation.

[0100] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art will understand the specific meaning of the above terms in this application based on the specific circumstances.

[0101] The terms "first" and "second" used in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented, for example, in orders other than those illustrated or described herein.

[0102] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A control method of a heat pump water heater, characterized by, The method comprises the following steps: receiving a start-up instruction, and determining a target valve step number for a second preset time period after a first preset time period of operation according to an initial opening degree of a throttling device; when the target valve step number is greater than 0, adjusting the opening degree of the throttling device at a first preset period within the second preset time period according to the current exhaust temperature of the compressor and the target valve step number; adjusting the opening degree of the throttling device at a second preset period after the first preset period of adjustment of the opening degree of the throttling device ends; wherein the first preset period is greater than the second preset period.

2. The control method of the heat pump hot-water supply unit according to claim 1, wherein The step of adjusting the opening degree of the throttling device at the first preset period within the second preset time period according to the current exhaust temperature of the compressor and the target valve step number when the target valve step number is greater than 0 specifically comprises: determining whether the current exhaust temperature of the compressor is greater than a first preset exhaust temperature; if yes, adjusting the opening degree of the throttling device at the first preset period within the second preset time period according to the target valve step number; if no, determining a corrected target valve step number according to the temperature range in which the current exhaust temperature of the compressor is located, and adjusting the opening degree of the throttling device at the first preset period within the second preset time period according to the corrected target valve step number.

3. The control method of the heat pump hot-water supply unit according to claim 2, wherein The step of determining the corrected target valve step number according to the temperature range in which the current exhaust temperature of the compressor is located specifically comprises: determining a correction value of the throttling device according to the temperature range in which the current exhaust temperature of the compressor is located; determining the corrected target valve step number according to the sum of the target valve step number and the correction value.

4. The control method of a heat pump hot-water supply unit according to claim 3, wherein The step of determining the correction value of the throttling device according to the temperature range in which the current exhaust temperature of the compressor is located specifically comprises: if the current exhaust temperature of the compressor is less than or equal to a first preset temperature and greater than a second preset temperature, determining the correction value as a first preset threshold value, wherein the first preset threshold value is less than 0.

5. The control method of a heat pump hot-water supply unit according to claim 3, wherein The step of determining the correction value of the throttling device according to the temperature range in which the current exhaust temperature of the compressor is located specifically comprises: if the current exhaust temperature of the compressor is less than or equal to the second preset temperature and greater than a third preset temperature, determining the correction value as a second preset threshold value; wherein the second preset threshold value is less than the first preset threshold value.

6. The control method of a heat pump water heater according to claim 3, wherein The step of determining the correction value of the throttling device according to the temperature range in which the current exhaust temperature of the compressor is located specifically comprises: if the current exhaust temperature of the compressor is less than or equal to the third preset temperature, determining the correction value as a third preset threshold value; wherein the third preset threshold value is less than the second preset threshold value.

7. The control method of a heat pump hot-water supply unit according to claim 6, wherein The third preset threshold value is -3.

8. The control method of a heat pump hot-water device according to any one of claims 1 to 7, characterized by, The step of determining the target valve step number for the second preset time period specifically comprises: determining an actual suction superheat degree of the compressor after the first preset time period of operation according to the initial opening degree; determining the target valve step number according to the difference between the actual suction superheat degree and a target suction superheat degree.

9. The control method of a heat pump hot-water supply unit according to claim 8, wherein The step of determining the actual suction superheat degree of the compressor specifically comprises: obtaining a suction temperature and an evaporation temperature of the compressor; A difference between the suction temperature and the evaporation temperature is determined to be an actual suction superheat of the compressor.

10. A heat pump water heater, characterized by, Comprise: A compressor, a first heat exchanger, a throttling device and a second heat exchanger connected in sequence, the first heat exchanger being connected with a discharge port of the compressor, the second heat exchanger being connected with a suction port of the compressor; when the heat pump water heater is started, the heat pump water heater adjusts the opening of the throttling device by using the control method in any one of claims 1-9.

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