Heat pump unit with oil blockage prevention function

Abstract

The embodiment of the invention relates to a heat pump unit with an oil blockage prevention function. The heat pump unit comprises a refrigerant circulation loop, a heating module, a first temperature sensor, a second temperature sensor and a controller. The controller is configured to obtain the shutdown duration of the compressor under the condition that a starting signal for the compressor is detected, obtain the environment temperature detected by the first temperature sensor and determine the oil blockage risk grade according to the shutdown duration and the environment temperature; under the condition that the oil blockage risk grade is larger than a preset threshold value, the current pressure of the heat pump unit is determined; the target oil temperature is calculated according to the refrigerant saturation temperature of the current pressure; according to the target oil temperature and the current oil temperature detected by a second temperature sensor, target preheating duration is calculated; and the heating module is controlled to at least run for the target preheating duration so as to heat lubricating oil in the compressor. The heat pump unit can ensure that a refrigerant is fully separated from lubricating oil, can prevent the condition of oil blockage in the compressor, and prevents the compressor from being damaged.

Description

A heat pump unit with anti-oil-clogging function Technical Field

[0001] This application relates to the field of electrical technology, specifically to a heat pump unit with an anti-oil-clogging function. Background Technology

[0002] With increasing global demands for environmental protection and energy efficiency, air-source heat pump units using natural and environmentally friendly refrigerants (such as R290 propane) are gradually replacing traditional Freon refrigerants due to their zero ozone depletion potential and extremely low global warming potential. However, R290 has extremely high miscibility with compressor lubricating oil. When the heat pump unit starts up, it produces a large amount of foamy oil-refrigerant mixture. This mixture easily accumulates in low-temperature areas during circulation within the heat pump unit, forming oil blockages. This leads to poor refrigerant circulation, abnormal pressure, and reduced heating capacity within the heat pump unit. In severe cases, it can even trigger a protective shutdown of the heat pump unit or damage to the compressor. Summary of the Invention

[0003] This application discloses a heat pump unit with anti-oil blockage function, which can fully heat the lubricating oil in the compressor, ensure that the refrigerant and lubricating oil in the compressor are fully separated, prevent oil blockage in the compressor, and avoid compressor damage.

[0004] This application discloses a heat pump unit with anti-oil-clogging function, comprising: a refrigerant circulation loop including a compressor, an outdoor heat exchanger, an electronic expansion valve, and an indoor heat exchanger connected in sequence, wherein the refrigerant circulation loop is configured to circulate refrigerant; the compressor is filled with lubricating oil for lubricating the moving parts of the compressor; a heating module is disposed at the bottom of the compressor and is configured to heat the lubricating oil inside the compressor; a first temperature sensor is configured to detect the outdoor ambient temperature where the heat pump unit is located; and a second temperature sensor is disposed inside the compressor and is configured to detect the lubricating oil inside the compressor. The controller is configured to: upon detecting a start signal for the compressor, acquire the compressor's shutdown duration and the ambient temperature detected by the first temperature sensor, and determine the oil blockage risk level based on the shutdown duration and the ambient temperature; if the oil blockage risk level is greater than a preset threshold, determine the current pressure of the heat pump unit; calculate the target oil temperature based on the refrigerant saturation temperature corresponding to the current pressure; calculate the target preheating time based on the target oil temperature and the current oil temperature detected by the second temperature sensor; and control the heating module to run for at least the target preheating time to heat the lubricating oil in the compressor.

[0005] In this embodiment, by assessing the risk level of oil blockage based on ambient temperature and compressor downtime before starting the compressor, and dynamically calculating the required preheating time, sufficient heating of the lubricating oil inside the compressor can be achieved, ensuring complete separation of the refrigerant and lubricating oil. This fundamentally reduces the risk of refrigerant violently boiling and carrying oil during startup, thereby preventing oil blockage inside the compressor and avoiding compressor damage. Furthermore, accurate calculation of the preheating time can also avoid the high energy consumption problem of excessively long heating time, improving the startup reliability and startup success rate of the heat pump unit.

[0006] As an optional implementation, determining the oil blockage risk level based on the downtime and the ambient temperature includes: determining the current oil blockage risk level based on risk assessment rules, according to the ambient temperature and the downtime; the oil blockage risk level includes a first risk level, a second risk level, and a third risk level, wherein the probability of oil blockage risk corresponding to the third risk level is greater than the probability of oil blockage risk corresponding to the second risk level, and the probability of oil blockage risk corresponding to the second risk level is greater than the probability of oil blockage risk corresponding to the first risk level; the oil blockage risk level being greater than a preset threshold includes: the current oil blockage risk level being either the second risk level or the third risk level.

[0007] In this embodiment of the application, by classifying the oil blockage risk into multiple levels, a refined assessment of the oil blockage risk is achieved. By combining different ambient temperatures and downtime, the risk of oil blockage can be more accurately reflected as ambient temperature and downtime accumulate, providing a more accurate basis for the subsequent calculation of preheating time.

[0008] As an optional implementation, the risk assessment rules include: when the ambient temperature is less than a first temperature threshold and the downtime is greater than or equal to a first duration threshold, the oil blockage risk level is the third risk level; when the ambient temperature is less than the first temperature threshold and the downtime is less than the first duration threshold, or when the ambient temperature is greater than or equal to the first temperature threshold and less than a second temperature threshold, and the downtime is greater than or equal to the second duration threshold, the oil blockage risk level is the second risk level; the second temperature threshold is greater than the first temperature threshold; the second duration threshold is greater than the first duration threshold; when the ambient temperature is greater than the second temperature threshold, or when the ambient temperature is greater than or equal to the first temperature threshold and less than the second temperature threshold, and the downtime is less than the second duration threshold, the oil blockage risk level is the first risk level.

[0009] In this application embodiment, the quantitative relationship between the first temperature threshold, the second temperature threshold, the first duration threshold, and the second duration threshold is clearly defined, and a clear assessment rule for oil blockage risk is constructed, making the assessment of oil blockage risk more concrete. This reflects the principle that the lower the ambient temperature and the longer the downtime, the higher the oil blockage risk, thus achieving an accurate judgment of the current oil blockage risk.

[0010] As an optional implementation, the step of calculating the target oil temperature based on the refrigerant saturation temperature corresponding to the current pressure includes: compensating the reference temperature according to the time coefficient corresponding to the current oil blockage risk level to obtain the compensated reference temperature; the time coefficient corresponding to the second risk level is less than the time coefficient corresponding to the third risk level; and taking the sum of the compensated reference temperature and the refrigerant saturation temperature corresponding to the current pressure as the target oil temperature.

[0011] In this embodiment of the application, the risk level of oil blockage is quantified into a time coefficient, and the target oil temperature is calculated based on the influence of the time coefficient. The higher the risk level (such as the third risk level), the higher the corresponding target oil temperature, so as to ensure more complete oil-coolant separation under more severe operating conditions. At the same time, the target oil temperature is lower when the risk level is lower, avoiding unnecessary overheating, and further optimizing the energy efficiency and reliability balance of the entire heat pump unit.

[0012] As an optional implementation, the step of calculating the target preheating time based on the target oil temperature and the current oil temperature detected by the second temperature sensor includes: determining the target preheating time based on the difference between the target oil temperature and the current oil temperature detected by the second temperature sensor, and the heating coefficient of the heating module.

[0013] In this embodiment, the difference between the target oil temperature and the current oil temperature is used as the core for calculating the target preheating time. This allows the target preheating time to be adaptively adjusted according to the actual current oil temperature of the compressor at startup, achieving accurate calculation of the target preheating time. When the current oil temperature is close to the target oil temperature, the target preheating time is shorter to avoid energy waste; when the current oil temperature is lower, the target preheating time is longer to ensure sufficient heating. This not only ensures the reliability of the preheating effect but also minimizes unnecessary energy consumption.

[0014] As an optional implementation, the heat pump unit further includes an oil level sensor disposed inside the compressor. The oil level sensor is configured to detect the actual oil level of the lubricating oil inside the compressor. The controller is further configured to: start the compressor after the heating module finishes heating, and control the compressor to operate at a first operating frequency; the first operating frequency is less than the rated frequency of the compressor; acquire the current actual oil level detected by the oil level sensor; and when the current actual oil level is lower than the safe oil level threshold corresponding to the compressor, maintain or reduce the operating frequency of the compressor until the current actual oil level detected by the oil level sensor is higher than or equal to the safe oil level threshold.

[0015] In this embodiment, after preheating, the compressor is controlled to run at a lower first operating frequency, and the current actual oil level of the compressor is continuously monitored. When the current actual oil level is found to be lower than the safety threshold, the operating frequency is maintained or further reduced to reduce the internal disturbance of the compressor, providing more stable conditions for lubricating oil return and oil level recovery. This avoids problems such as sudden drop in oil level and increased oil carryover that may be caused by directly starting the compressor at high frequency, ensuring that the compressor smoothly transitions to normal operation under the premise of sufficient lubricating oil, and improving the safety and reliability of the start-up process.

[0016] As an optional implementation, the controller is further configured to: when the duration for which the current actual oil level detected by the oil level sensor is higher than or equal to the safe oil level threshold is greater than or equal to a first duration threshold, control the operating frequency of the compressor to gradually increase to a second operating frequency, wherein the second operating frequency is greater than or equal to the rated frequency of the compressor.

[0017] In this embodiment of the application, by using the duration of the current actual oil level being greater than or equal to a first duration threshold as a prerequisite for increasing the compressor frequency, the interference of instantaneous changes in oil level can be avoided, ensuring sufficient lubricating oil return and guaranteeing the stability of the startup process.

[0018] As an optional implementation, the heat pump unit further includes an oil level sensor disposed inside the compressor. The oil level sensor is configured to detect the actual oil level of the lubricating oil inside the compressor. The controller is further configured to: determine the duration of low-frequency operation of the compressor at a frequency less than or equal to a first frequency threshold during compressor operation; the first frequency threshold is less than the rated frequency of the compressor; if the duration of low-frequency operation is greater than a second duration threshold, detect the operating parameters of the compressor and / or obtain the current actual oil level detected by the oil level sensor; if the operating parameters and / or the current actual oil level meet preset oil return conditions, adjust the operating frequency of the compressor to allow the lubricating oil to flow back to the compressor.

[0019] In this embodiment of the application, when the cumulative low-frequency operation time exceeds the second duration threshold, a comprehensive judgment is made by combining the compressor's operating parameters and real-time oil level. If the oil return condition is met, the compressor frequency is actively adjusted to drive the retained lubricating oil back to the compressor. This can prevent the risk of chronic oil blockage and oil shortage caused by long-term low-frequency operation, thereby improving the stability and reliability of the compressor under partial load or long-term operation conditions.

[0020] As an optional implementation, the compressor's operating parameters include the compressor's discharge superheat and / or the compressor's cumulative operating time; the oil return conditions include at least one of the following: the cumulative operating time is greater than a third duration threshold, the third duration threshold is greater than a second duration threshold; the duration for which the compressor's discharge superheat is less than a first superheat threshold is greater than a fourth duration threshold; the current actual oil level is lower than a target oil level threshold; the target oil level threshold is greater than the compressor's corresponding safe oil level threshold.

[0021] In this embodiment, by combining the cumulative running time, exhaust superheat and the current actual oil level, the adaptability to complex operating conditions is enhanced, ensuring that the lubricating oil can be returned to the compressor in a timely manner under different operating conditions, thereby maintaining the oil balance of the compressor, preventing performance degradation or insufficient lubrication of the compressor due to uneven oil distribution, and improving the overall reliability and robustness of the heat pump unit under long-term, variable operating conditions.

[0022] As an optional implementation, adjusting the operating frequency of the compressor includes: increasing the operating frequency of the compressor to a third operating frequency, and controlling the opening of the electronic expansion valve to increase to a preset target opening, until a second condition is met; the third operating frequency is greater than the rated frequency of the compressor; when the second condition is met, reducing the operating frequency of the compressor to the operating frequency before the increase, and controlling the opening of the electronic expansion valve to adjust to the opening before the increase; wherein, the second condition includes one or more of the following: the duration of the compressor operating at the third operating frequency is greater than the oil return duration threshold; the current actual oil level detected by the oil level sensor is higher than or equal to the target oil level threshold; the exhaust superheat of the compressor is less than a second superheat threshold; the second superheat threshold is less than the first superheat threshold.

[0023] In this embodiment, during oil return, a coordinated strategy of increasing the compressor's operating frequency and the opening of the electronic expansion valve is employed to enhance the circulation power and flow rate of the circulation loop, thereby driving the lubricating oil in the pipeline back to the compressor. Simultaneously, the oil return operation is terminated when the oil return duration threshold is reached, the oil level returns to the target oil level threshold, or the exhaust superheat is too low (posing a risk of liquid slugging). This prevents damage to the compressor due to excessive oil return or liquid return, thus ensuring the safety of the entire heat pump unit. Attached Figure Description

[0024] Figure 1 is a structural block diagram of a heat pump unit in one embodiment; Figure 2 is a structural block diagram of a heat pump unit in one embodiment; Figure 3 is a control flowchart of a controller in one embodiment; Figure 4 is a control flowchart of a controller in another embodiment; Figure 5 is a structural block diagram of a heat pump unit in one embodiment; Figure 6 is a control flowchart of a controller in one embodiment; Figure 7 is a control flowchart of a controller in another embodiment; Figure 8 is a schematic diagram of the connection of components within a heat pump unit in one embodiment; Figure 9 is a control flowchart of a controller in one embodiment; Figure 10 is a flowchart of a control method for a heat pump unit in one embodiment. Detailed Implementation

[0025] 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, and 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.

[0026] It should be noted that the terms "comprising" and "having," and any variations thereof, in the embodiments and accompanying drawings of this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or devices.

[0027] It is understood that the terms "first," "second," etc., used in this application may be used to describe various elements herein, but these elements are not limited by these terms. These terms are only used to distinguish one element from another. For example, without departing from the scope of this application, a first temperature sensor may be referred to as a second temperature sensor, and similarly, a second temperature sensor may be referred to as a first temperature sensor. However, the first temperature sensor and the second temperature sensor detect different objects; the first temperature sensor detects the ambient temperature of the outdoor environment, while the second temperature sensor detects the oil temperature of the lubricating oil inside the compressor.

[0028] Figure 1 is a structural block diagram of a heat pump unit in one embodiment. As shown in Figure 1, the heat pump unit 100 may include an outdoor unit 101 and an indoor unit 102. The outdoor unit 101 is typically installed outdoors for heat exchange with the outdoor environment. The indoor unit 102 is typically installed indoors and may be in the form of a wall-mounted unit, a floor-standing unit, etc. The indoor unit 102 and the outdoor unit 101 can be connected via gas pipes and liquid pipes. Optionally, the outdoor unit 101 can have various implementation forms, such as the outdoor unit of a wall-mounted heat pump unit or the outdoor unit of a floor-standing air conditioner.

[0029] For example, Figure 2 is a structural block diagram of a heat pump unit in one embodiment. As shown in Figure 2, the outdoor unit 101 includes a compressor 111, an outdoor heat exchanger 112, an electronic expansion valve 113, and an outdoor fan, etc. The outdoor heat exchanger 112 is used to exchange heat with outdoor air through refrigerant; the compressor 111 is used to compress the refrigerant from a low-pressure state to a high-pressure state and drive the refrigerant to circulate in the refrigerant circulation loop 110; the electronic expansion valve 113 is used to regulate the flow rate of refrigerant in the refrigerant circulation loop 110, and can also throttle and reduce the pressure of the refrigerant to make it a gas-liquid two-phase mixture (a mixture of liquid and gaseous refrigerant), such as a mist, which helps the refrigerant to evaporate; the outdoor fan is used to drive the outdoor air to flow and enhance the heat exchange effect of the outdoor heat exchanger 112. The indoor unit 102 may include an indoor heat exchanger 114, etc.; the indoor heat exchanger 114 is used to exchange heat with a medium through refrigerant.

[0030] Specifically, as shown in Figure 2, when the heat pump unit 100 operates in a low-temperature environment, it needs to heat the indoor environment. At this time, the indoor heat exchanger 114 works as a condenser, releasing heat; the outdoor heat exchanger 112 works as an evaporator, absorbing heat. The refrigerant is compressed by the compressor 111 into a high-temperature, high-pressure gaseous state; it flows into the indoor heat exchanger 114 to release heat and condense into a liquid state (or a gas-liquid mixture); then it flows into the outdoor heat exchanger 112 to absorb heat and evaporate into a gaseous state; finally, it is transferred back to the compressor 111 to complete a complete refrigerant circulation loop 110, thereby achieving the heating of the indoor environment.

[0031] Optionally, the compressor 111 may include a crankcase, which is typically connected to or integrally formed with the lower housing of the compressor 111, creating a sealed oil reservoir for holding lubricating oil. This lubricating oil is pumped through internal oil passages (such as oil holes, oil grooves, or centrifugal oil-throwing structures) during compressor 111 operation to the surfaces of moving parts such as cylinders, pistons, crankshafts, and bearings, forming an oil film. This film serves to lubricate, reduce friction and wear, assist in sealing cylinder clearances, and remove some heat from the moving parts. During compressor 111 shutdown, the lubricating oil is primarily stored at the bottom of the crankcase; when the compressor 111 restarts and reaches a certain speed, the lubrication system re-establishes circulation, returning the lubricating oil to its respective lubrication points.

[0032] Furthermore, during the operation of the heat pump unit 100, a small amount of lubricating oil typically enters the refrigerant circulation loop 110 along with the refrigerant. This lubricating oil, carried by the refrigerant, flows through components such as the indoor heat exchanger 114, electronic expansion valve 113, and outdoor heat exchanger 112, and gradually returns to the compressor 111 during the circulation process. Under normal operation, the distribution of lubricating oil within the heat pump unit 100 is in a dynamic equilibrium state. However, when using refrigerants such as R290, which are highly miscible with lubricating oil, if the heat pump unit is in a low-temperature environment where it is not running (especially during winter heating shutdowns), a large amount of refrigerant will continue to dissolve in the compressor's lubricating oil over the downtime, leading to an increase in the oil level in the compressor and a decrease in the viscosity of the lubricating oil.

[0033] When the heat pump unit restarts, the internal pressure of the compressor drops sharply. The refrigerant dissolved in the lubricating oil escapes rapidly and boils violently, producing a large amount of foamy oil-refrigerant mixture. On the one hand, when the foamy mixture leaves the compressor, a large amount of lubricating oil is carried out of the crankcase in the form of foam, which disrupts the original oil balance. This causes the moving parts inside the compressor to wear or even seize due to instantaneous lack of oil. On the other hand, the foamy mixture enters the refrigerant circulation loop and is prone to accumulate in low-temperature parts such as the outdoor heat exchanger and electronic expansion valve during the circulation process, forming oil blockage. This leads to poor refrigerant circulation, abnormal pressure of the heat pump unit, and reduced heating capacity. In severe cases, it may even trigger the protective shutdown of the heat pump unit or damage the compressor.

[0034] In related technologies, to address the risk of oil blockage, a common approach is to install a crankcase heating belt at the bottom of the compressor to continuously heat the lubricating oil during heat pump unit shutdown, thereby reducing the refrigerant's solubility. However, this heating method has significant limitations. Firstly, the continuous heating of the heating belt requires prolonged power supply, resulting in high energy consumption. Secondly, the heating intensity and duration are unstable, and the generated heat may be insufficient to achieve adequate separation of the lubricating oil and refrigerant, thus failing to prevent oil blockage. Therefore, traditional heating methods cannot adequately prevent the risk of oil blockage.

[0035] This application discloses a heat pump unit with anti-oil blockage function, which can fully heat the lubricating oil in the compressor, ensure that the refrigerant and lubricating oil in the compressor are fully separated, prevent oil blockage in the compressor, and avoid compressor damage.

[0036] As shown in Figure 2, in one embodiment, a heat pump unit 100 with anti-oil blockage function is provided. The heat pump unit 100 includes one or more of the following components: refrigerant circulation loop 110, heating module 120, first temperature sensor 131, second temperature sensor 132, and controller 140.

[0037] The refrigerant circulation loop 110 may include a compressor 111, an outdoor heat exchanger 112, an electronic expansion valve 113, and an indoor heat exchanger 114 connected in sequence.

[0038] In the heat pump unit 100, each component can be connected through refrigerant pipes, so that the refrigerant circulates within the heat pump unit 100 through each component, forming a complete cooling or heating cycle loop to realize the cooling or heating function of the heat pump unit 100.

[0039] In some embodiments, the heat pump unit 100 may also include necessary components such as a four-way valve (not shown in Figure 2) to ensure the integrity and functionality of the heat pump unit 100. The four-way valve can be used to change the direction of refrigerant flow.

[0040] The refrigerant circulation loop 110 is configured to circulate the refrigerant in order to achieve the cooling or heating function of the heat pump unit 100.

[0041] Specifically, compressor 111 can compress refrigerant from a low-temperature, low-pressure state to a high-temperature, high-pressure state. After compression, compressor 111 outputs the high-temperature, high-pressure refrigerant through its exhaust port, providing power for refrigerant circulation to drive the refrigerant to circulate within the heat pump unit 100, thereby achieving effective heat transfer and exchange. The exhaust port refers to the channel interface on compressor 111 used to discharge the compressed, high-temperature, high-pressure refrigerant. The exhaust port of compressor 111 can be connected to the outdoor heat exchanger 112 and the indoor heat exchanger 114 via a four-way valve.

[0042] In some embodiments, the compressor 111 may also include an air inlet. The low-temperature, low-pressure gaseous refrigerant, after passing through other components in the heat pump unit 100, enters the compressor 111 through the air inlet. Under the action of the compressor 111, it begins to be compressed, gradually increasing its pressure and temperature to obtain a high-temperature, high-pressure refrigerant.

[0043] Specifically, when the heat pump unit 100 is in heating mode, it needs to heat the indoor environment. The refrigerant is compressed by the compressor 111 and becomes a high-temperature and high-pressure gas. It flows into the indoor heat exchanger 114 to release heat and condense into a liquid (or a gas-liquid mixture). Then it flows into the outdoor heat exchanger 112 through the electronic expansion valve 113 to absorb heat and evaporate into a gas. Finally, it is transferred to the compressor 111 to complete the refrigerant cycle, thereby achieving the heating of the indoor environment.

[0044] In some embodiments, the opening degree of the electronic expansion valve 113 affects the refrigerant flow rate in the refrigerant circulation loop 110, thereby affecting the suction state and current discharge temperature of the compressor 111. When the first opening degree increases, the refrigerant flow rate in the refrigerant circulation loop 110 increases, which helps to reduce the current discharge temperature; when the first opening degree decreases, the refrigerant flow rate in the refrigerant circulation loop 110 decreases, which can increase the suction superheat of the compressor 111, thereby reducing the risk of liquid slugging and improving operational reliability.

[0045] The compressor 111 is filled with lubricating oil, which is used to lubricate the moving parts of the compressor 111.

[0046] During the operation of the heat pump unit 100, a small amount of lubricating oil enters the refrigerant circulation loop 110 along with the refrigerant. After flowing through various heat exchangers and the electronic expansion valve, it eventually returns to the compressor 111 with the refrigerant. This oil circulation mechanism can maintain the long-term lubrication of the compressor 111, but excessive lubricating oil entering the refrigerant circulation loop 110 will increase the risk of oil blockage in the loop. Therefore, in oil blockage prevention control, it is necessary to control the amount of lubricating oil entering the refrigerant circulation loop 110.

[0047] In some embodiments, increasing the opening of the electronic expansion valve 113 can increase the refrigerant flow rate and velocity, enhancing circulation power, thereby helping to promote the flow of lubricating oil in the pipeline and its return to the compressor 111. Conversely, if the opening is too small, the circulation capacity weakens, and lubricating oil is prone to stagnation and accumulation in low-temperature and low-pressure parts such as heat exchangers and electronic expansion valve 113, increasing the risk of oil blockage. Therefore, in oil blockage prevention control, the oil recovery effect can be enhanced by adjusting the opening of the electronic expansion valve 113.

[0048] The heating module 120, located at the bottom of the compressor 111, is configured to heat the lubricating oil inside the compressor 111 to raise the temperature of the lubricating oil before the heat pump unit 100 starts, reduce the solubility of the refrigerant in the oil, promote the separation of the lubricating oil and the refrigerant, thereby preventing the risk of oil blockage during the low-temperature start-up phase.

[0049] In some embodiments, during the shutdown of the compressor 111, the lubricating oil is mainly stored at the bottom of the crankcase, which is connected to or integrally formed with the lower housing of the compressor 111. Therefore, the heating module 120 may also be located at the bottom of the crankcase or in the lower area of ​​the outer wall of the crankcase to directly heat the lubricating oil in the oil storage area, thereby improving heating efficiency and reducing heat loss.

[0050] Specifically, the heating module 120 can be a crankcase heating belt. The crankcase heating belt can be tightly wrapped or attached to the outer surface of the crankcase of the compressor 111, and heat is conducted to the lubricating oil inside the crankcase through electric current heating, thereby heating the lubricating oil.

[0051] The first temperature sensor 131 is configured to detect the outdoor ambient temperature where the heat pump unit 100 is located.

[0052] Optionally, the first temperature sensor 131 is located in the outdoor unit 101 in a well-ventilated position away from the coil of the outdoor heat exchanger 112 (e.g., near the air inlet of the outdoor unit or outside the electrical control box) to avoid direct radiation or airflow interference from the coil temperature of the outdoor heat exchanger 112 during operation, thereby enabling more accurate acquisition of the outdoor ambient temperature of the outdoor heat exchanger 112.

[0053] Optionally, after the heat pump unit 100 stops, the internal temperature of the compressor in the outdoor unit 101 gradually approaches the ambient temperature. As the ambient temperature decreases, the solubility of the refrigerant in the lubricating oil increases, causing the lubricating oil viscosity to decrease and the oil to become thinner. This not only affects lubrication performance but also makes it easier for the lubricating oil to form a foam mixture with the refrigerant. Furthermore, in low-temperature environments, the system pressure difference during heat pump unit startup is greater, which can more easily lead to violent boiling of the lubricating oil, causing more lubricating oil to foam and be carried into the refrigerant circulation loop 110, thereby increasing the risk of oil blockage. Therefore, the oil blockage prevention operation during shutdown and startup needs to assess the risk of oil blockage based on the outdoor ambient temperature to ensure the reliable operation of the compressor 111.

[0054] Optionally, the first temperature sensor 131 may be a temperature sensor with high precision, fast response and long-term stability, such as a thermistor or thermocouple, which can accurately measure the corresponding temperature value.

[0055] The second temperature sensor 132 is located inside the compressor 111 and is configured to detect the oil temperature of the lubricating oil inside the compressor 111.

[0056] The temperature of the lubricating oil directly reflects the state of the lubricating oil inside the compressor 111. In low-temperature shutdown environments, a large amount of refrigerant dissolves in the lubricating oil, and changes in oil temperature affect the solubility of the refrigerant in the lubricating oil; the higher the oil temperature, the lower the solubility of the refrigerant. Therefore, the controller 140 can accurately determine the degree of refrigerant dissolution in the lubricating oil by collecting the oil temperature in real time, thereby judging the degree of separation between the lubricating oil and the refrigerant and identifying the risk of oil blockage. Simultaneously, the oil temperature can also be used to assess the operating status of the compressor 111. Abnormal oil temperatures (such as excessively high or rapidly rising temperatures) may indicate potential faults in the compressor 111, such as poor lubrication, increased friction, or abnormal refrigerant circulation. Collecting the oil temperature helps to promptly detect and address these potential faults, ensuring the normal operation of the compressor 111.

[0057] Optionally, the second temperature sensor 132 can be a platinum resistance or thermistor temperature sensor. These types of sensors have good temperature measurement stability, high accuracy, and strong vibration resistance, making them suitable for installation in the compressor's internal oil passages or crankcase walls to indirectly or directly detect the temperature of the lubricating oil.

[0058] Alternatively, the second temperature sensor 132 may also be a special temperature sensor with a metal sheath or an oil-resistant and corrosion-resistant package to adapt to the oil-immersed, high-pressure, and vibration environment inside the compressor.

[0059] Optionally, the aforementioned temperature sensor can be configured to collect the corresponding temperature according to a preset temperature detection cycle. For example, the first temperature sensor 131 can collect the outdoor ambient temperature once every minute, every few minutes, or for longer periods. By periodically collecting the input temperature, continuous temperature change data can be obtained, thereby avoiding the randomness of temperature anomalies and balancing the real-time requirements of the control system with the data processing burden.

[0060] As shown in Figure 3, the controller 140 is configured to perform the following steps 310 to 350.

[0061] Step 310: When a start signal for the compressor is detected, the corresponding shutdown duration of the compressor is obtained, and the ambient temperature detected by the first temperature sensor is obtained. The oil blockage risk level is determined based on the shutdown duration and the ambient temperature.

[0062] In some embodiments, when the compressor 111 is in a stopped state and the heat pump unit is powered normally, the user can trigger a heating / cooling start command via a remote control, wired controller, smart terminal or unit control panel, or an internal start command generated by the heat pump unit 100 according to a preset program (such as timed start). These heating / cooling start commands and internal start commands can be regarded as start commands for the compressor 111, which are used to trigger the controller 140 to execute the oil blockage prevention control process.

[0063] The compressor's downtime refers to the time interval elapsed from the last time the compressor 111 stopped operating to the current time when a start signal is detected. This downtime can be recorded and stored by a real-time clock module or timer inside the controller 140. The timer starts every time the compressor 111 stops and continues until the next start signal is detected, at which point it is read and used for subsequent risk assessment.

[0064] Because the dissolution of refrigerant in lubricating oil is a cumulative process over time, in low-temperature environments, the longer the shutdown period, the more refrigerant typically dissolves in the lubricating oil. This increases the risk of violent refrigerant boiling and oil blockage upon startup. Therefore, shutdown duration is a key parameter for quantifying oil blockage risk and can distinguish the risk differences between short and long shutdowns.

[0065] In some embodiments, since the solubility of refrigerant in lubricating oil is not only related to time but also affected by ambient temperature, the lower the ambient temperature of the outdoor environment, the higher the solubility of refrigerant in lubricating oil. Therefore, in order to further reflect the amount of refrigerant dissolved in lubricating oil, the compressor shutdown time can be combined with the ambient temperature of the outdoor environment to jointly assess the risk of oil blockage, which can make the assessment results more comprehensive and accurate.

[0066] For example, the risk of oil blockage increases when the downtime is long and the ambient temperature is low; while the risk of oil blockage is relatively low when the downtime is short and the ambient temperature is high.

[0067] Since the risk of oil blockage essentially stems from the continuous dissolution of refrigerant in lubricating oil at low temperatures, this dissolution process is influenced by both ambient temperature and dissolution time (which can be the duration of compressor shutdown). Ambient temperature determines the strength and rate of refrigerant-lubricating oil miscibility: the lower the ambient temperature, the higher the solubility of refrigerant in lubricating oil, and the greater the pressure difference during low-temperature startup, the more likely refrigerant boiling will occur. The compressor shutdown duration reflects the cumulative effect of the dissolution process; the longer the shutdown duration, the longer the dissolution time between refrigerant and lubricating oil, resulting in a greater accumulation of refrigerant dissolved in the lubricating oil, and a higher probability of boiling and oil carryover during startup. Therefore, combining the shutdown duration of compressor 111 with the ambient temperature of the outdoor environment allows for a more accurate assessment of the oil blockage risk level.

[0068] Step 320: If the oil blockage risk level is greater than the preset threshold, determine the current pressure corresponding to the heat pump unit.

[0069] An oil blockage risk level greater than the preset threshold means that, based on the current outdoor ambient temperature of the heat pump unit 100 and the downtime of the compressor 111, the risk of oil blockage when starting the compressor 111 under the current operating conditions has exceeded the acceptable low-risk range. At this time, directly starting the compressor 111 is likely to cause oil blockage, and oil blockage prevention intervention is required.

[0070] Alternatively, the current pressure of the heat pump unit 100 may refer to the evaporation pressure.

[0071] Under low-temperature heating conditions, the outdoor heat exchanger 112 operates as an evaporator. During its operation, it absorbs heat from the environment, causing the ambient temperature to decrease. Given the already low ambient temperature, the saturation temperature (evaporation temperature) corresponding to the evaporation pressure of the evaporator directly reflects the temperature level on the low-temperature side of the heat pump unit. The lower the evaporation temperature, the lower the oil temperature in the evaporator and return gas pipeline. This makes the lubricating oil more viscous and less fluid due to the low temperature, making the refrigerant more easily dissolve in the lubricating oil. Therefore, when the controller 140 determines that the risk level of oil blockage under the current operating conditions is high, it can obtain the current pressure corresponding to the heat pump unit 100 to calculate the target oil temperature. This allows for more targeted setting of the preheating intensity, ensuring that the preheated oil temperature is sufficient to maintain good fluidity on the low-temperature side and promote oil-refrigerant separation, thereby preventing oil blockage at its source.

[0072] Step 330: Calculate the target oil temperature based on the refrigerant saturation temperature corresponding to the current pressure.

[0073] The refrigerant saturation temperature corresponding to the current pressure refers to the phase change temperature at which the refrigerant changes from a liquid to a gaseous state (boiling) or from a gaseous state to a liquid state (condensation) under the current system pressure. For example, if the current pressure is the evaporation pressure, then the corresponding saturation temperature is the evaporation temperature.

[0074] Specifically, the controller 140 can determine the refrigerant saturation temperature corresponding to the current pressure based on the refrigerant property table; or, it can calculate the refrigerant saturation temperature corresponding to the current pressure based on the refrigerant state equation. The refrigerant property table is a discrete data table that reflects the correspondence between the refrigerant saturation temperature and pressure of a specific refrigerant. The refrigerant state equation is a state equation that describes the thermodynamic properties of the refrigerant and is used to convert pressure into saturated refrigerant temperature.

[0075] The solubility of refrigerant in lubricating oil decreases as the oil temperature increases. When the oil temperature is higher than the refrigerant saturation temperature, the refrigerant dissolved in the oil tends to precipitate out of the lubricating oil, thus separating the lubricating oil from the refrigerant. Conversely, if the oil temperature is close to or lower than the refrigerant saturation temperature, the refrigerant is more likely to remain in the lubricating oil.

[0076] Optionally, to ensure sufficient separation of lubricating oil and refrigerant before startup, controller 140 can heat the lubricating oil to a level higher than the refrigerant saturation temperature under the current operating conditions. Therefore, the target oil temperature can be higher than the refrigerant saturation temperature corresponding to the current pressure.

[0077] For example, controlling the temperature to 140°C can be based on the saturation temperature corresponding to the current pressure, plus a temperature difference compensation value, to determine a target oil temperature that effectively promotes the separation of lubricating oil and refrigerant without overheating. The temperature compensation value can include basic compensation and risk compensation; basic compensation refers to the minimum temperature rise required to cover the preset low-temperature operating conditions; risk compensation refers to additional temperature rise compensation dynamically adjusted based on the oil blockage risk determined by ambient temperature and downtime. A higher oil blockage risk level indicates a greater accumulation of dissolved refrigerant or more severe environmental conditions, requiring a stronger separation driving force, and therefore, the corresponding risk compensation also increases.

[0078] Step 340: Calculate the target preheating time based on the target oil temperature and the current oil temperature detected by the second temperature sensor.

[0079] In some embodiments, the controller 140 may determine the target preheating time based on the difference between the target oil temperature and the current oil temperature detected by the second temperature sensor, and the heating coefficient of the heating module 120.

[0080] The heating coefficient of the heating module 120 represents the temperature at which the heating module 120 can raise the temperature of the lubricating oil per unit time.

[0081] Optionally, the heating coefficient can be calculated using parameters such as the rated frequency of the heating module 120, the heat transfer efficiency of the installation location, and the specific heat capacity and mass of the lubricating oil.

[0082] The difference between the target oil temperature and the current oil temperature reflects the temperature rise required to reach the target oil temperature. The larger the difference between the target oil temperature and the current oil temperature, the greater the heat required, and the longer the calculated target preheating time; conversely, the smaller the difference between the target oil temperature and the current oil temperature, the less heat required, and the shorter the calculated target preheating time.

[0083] Specifically, the controller 140 can use the ratio of the difference between the target oil temperature and the current oil temperature detected by the second temperature sensor to the heating coefficient of the heating module 120 as the target preheating time. For example, the controller 140 can calculate the target preheating time using formula (1). .

[0084] (1); where, Target oil temperature; The current oil temperature is detected by the second temperature sensor; k is the heating coefficient of the heating module 120 (unit: ℃ / min).

[0085] Optionally, the heating coefficient k can be dynamically corrected based on the current ambient temperature and / or lubricating oil condition to improve calculation accuracy. For example, at extremely low ambient temperatures, the actual effective heating coefficient may decrease due to increased heat dissipation; in this case, k compensated for by the ambient temperature can be used to calculate the target preheating time.

[0086] Optionally, to avoid calculation errors or ensure minimum preheating effect, upper and lower limits for the target preheating time can be set. For example, when the calculated target preheating time is less than the minimum preheating time (e.g., 30 seconds), the target preheating time is controlled to the minimum preheating time; when the calculated target preheating time is greater than the maximum preheating time (e.g., 30 minutes), the target preheating time is controlled to the maximum preheating time, and an error prompt is triggered to inform the user that the current compressor lubricating oil is abnormal.

[0087] Step 350: Control the heating module to run for at least the target preheating time to heat the lubricating oil in the compressor.

[0088] Optionally, to ensure the separation effect of refrigerant and lubricating oil, during the heating process of the heating module 120 heating the lubricating oil, the controller 140 continuously determines the new current pressure corresponding to the heat pump unit 100, calculates the new target oil temperature based on the refrigerant saturation temperature corresponding to the new current pressure, and calculates the new target preheating time based on the new target oil temperature and the new current oil temperature detected by the second temperature sensor 132. It then determines whether the actual heating time of the heating module 120 is greater than or equal to the new target preheating time. If the actual heating time is less than the new target preheating time, the controller controls the heating module 120 to continue heating. If the actual heating time is greater than or equal to the new target preheating time, the controller controls the heating module 120 to stop heating and starts the compressor 111.

[0089] Optionally, to ensure effective separation of the refrigerant and lubricating oil, the controller 140 can monitor the oil temperature in real time via the second temperature sensor 132 during the heating process of the lubricating oil by the heating module 120. If the current oil temperature has reached or exceeded the target oil temperature before the end of the target preheating time, the controller 140 can control the heating module 120 to terminate heating in advance to improve energy efficiency; if the current oil temperature is still lower than the target oil temperature after the target preheating time has been reached, the controller 140 can appropriately extend the heating time until the oil temperature reaches the target value or the maximum safe heating time.

[0090] In this embodiment, by assessing the risk of oil blockage based on the ambient temperature and the downtime of the compressor 111 before starting the compressor 111, and dynamically calculating the required preheating time, sufficient heating of the lubricating oil inside the compressor 111 can be achieved, ensuring that the refrigerant and lubricating oil are fully separated. This reduces the risk of the refrigerant violently boiling and carrying oil during startup, thereby preventing oil blockage in the compressor and avoiding compressor damage. Furthermore, accurate calculation of the preheating time can also avoid the high energy consumption problem of excessive heating time, improving the startup reliability and startup success rate of the heat pump unit 100.

[0091] In some embodiments, as shown in FIG4, controller 140 is configured to perform steps 402 to 418.

[0092] Step 402: When a start signal for the compressor is detected, the corresponding shutdown duration of the compressor is obtained, and the ambient temperature detected by the first temperature sensor is obtained.

[0093] The relevant description of step 402 can be found in the relevant description of step 310 in the above embodiments, and will not be repeated here.

[0094] Step 404: Based on the risk assessment rules, determine the current oil blockage risk level according to the ambient temperature and downtime.

[0095] In some embodiments, the oil blockage risk level includes a first risk level, a second risk level, and a third risk level. The probability of oil blockage risk corresponding to the third risk level is greater than the probability of oil blockage risk corresponding to the second risk level; the probability of oil blockage risk corresponding to the second risk level is greater than the probability of oil blockage risk corresponding to the first risk level.

[0096] For example, the first risk level can be low risk, the second risk level can be medium risk, and the third risk level can be high risk.

[0097] Optionally, the oil blockage risk level may include multiple risk levels. Based on the principle that the lower the ambient temperature and the longer the downtime, the higher the risk of oil blockage, the ambient temperature and downtime are divided into different ranges and corresponding to different risk levels.

[0098] In some embodiments, the risk assessment rules include the following three.

[0099] 1. When the ambient temperature is less than the first temperature threshold and the downtime is greater than or equal to the first duration threshold, the oil blockage risk level is the third risk level.

[0100] The first temperature threshold can be set to a low temperature value, such as 10°C, to identify the critical ambient temperature at which low temperatures are prone to clogging.

[0101] The first duration threshold can be set as the threshold for short-term shutdown, that is, if the shutdown duration is less than the second duration threshold, it means that the heat pump unit will be shut down for a short time, such as 12 hours, which is used to identify the shutdown duration required to achieve significant cumulative dissolution at low temperatures.

[0102] If the ambient temperature is less than the first temperature threshold and the shutdown time is greater than or equal to the first duration threshold, it means that the heat pump unit 100 is in a low-temperature environment and is not in a short-term shutdown condition. At this time, the amount of refrigerant dissolved and accumulated in the lubricating oil is already very high. Starting the compressor 111 will cause the greatest risk of oil blockage. Therefore, this condition is considered to be the highest risk level (third risk level).

[0103] 2. When the ambient temperature is less than the first temperature threshold and the downtime is less than the first duration threshold, or when the ambient temperature is greater than or equal to the first temperature threshold and less than the second temperature threshold, and the downtime is greater than or equal to the second duration threshold, the oil blockage risk level is the second risk level.

[0104] The second temperature threshold is greater than the first temperature threshold, for example, 20°C. The second temperature threshold is used to delineate the boundary between medium and low risk.

[0105] The second duration threshold can be set as a threshold for long-term shutdown. That is, if the shutdown duration is greater than or equal to the second duration threshold, it means that the heat pump unit will be shut down for an extended period of time, such as 24 hours. The second duration threshold is greater than the first duration threshold.

[0106] If the ambient temperature is less than the first temperature threshold and the downtime is less than the first duration threshold, it means that the heat pump unit 100 is in a low-temperature environment but is shut down for a short time. At this time, although the ambient temperature is low, the downtime is short, the amount of refrigerant dissolution and accumulation is limited, and the risk of oil blockage is increased but still controllable. Therefore, this condition is defined as medium risk level (second risk level).

[0107] If the ambient temperature is greater than or equal to the first temperature threshold and less than the second temperature threshold, and the shutdown duration is greater than or equal to the second duration threshold, it means that the heat pump unit 100 is in a condition of prolonged shutdown but the ambient temperature is not too low. At this time, although the long shutdown time may cause the dissolution rate to reach a significant level, the ambient temperature is moderate and the refrigerant solubility decreases. Therefore, this condition is also defined as a medium-risk level (second risk level).

[0108] 3. When the ambient temperature is greater than the second temperature threshold, or when the ambient temperature is greater than or equal to the first temperature threshold and less than the second temperature threshold, and the downtime is less than the second duration threshold, the oil blockage risk level is the first risk level.

[0109] If the ambient temperature is greater than the second temperature threshold, it means that the heat pump unit 100 is in a relatively high ambient temperature condition. At this time, the solubility of the refrigerant in the lubricating oil is low, and the risk of oil blockage is small. Therefore, this condition is defined as a low-risk level (first risk level).

[0110] If the ambient temperature is greater than or equal to the first temperature threshold and less than the second temperature threshold, and the downtime is less than the second downtime threshold, it means that the heat pump unit 100 is in a condition where the ambient temperature is moderate and the downtime is short. The cumulative effect of refrigerant dissolution is not obvious and the risk of oil blockage is small. Therefore, this condition is defined as a low-risk level (first risk level).

[0111] Step 406: Determine whether the current oil blockage risk level is greater than the preset threshold; if not, proceed to step 408; if yes, proceed to step 410.

[0112] Oil blockage risk levels exceeding preset thresholds include: the current oil blockage risk level being either the second or third risk level.

[0113] The current oil blockage risk level is level two or three, which means that the current oil blockage risk is relatively serious and cannot be ignored. Anti-blockage intervention (heating the lubricating oil) is required.

[0114] In this embodiment of the application, by clearly defining the quantitative relationship between the first temperature threshold, the second temperature threshold, the first duration threshold, and the second duration threshold, a clear rule for assessing oil blockage risk is constructed, making the risk assessment more concrete and reflecting the principle that the lower the ambient temperature and the longer the downtime, the higher the risk of oil blockage, thus achieving an accurate judgment of the current oil blockage risk.

[0115] Step 408: In response to the start signal for the compressor, control the compressor to start.

[0116] In some embodiments, if the current oil blockage risk level is not greater than a preset threshold, it means that the current oil blockage risk level is the first risk level. Therefore, the current oil blockage risk is considered to be small and within the acceptable range of the heat pump unit 100. The controller 140 can confirm that there is no need to intervene to prevent oil blockage. In response to the start signal for the compressor 111, the controller controls the compressor 111 to start directly and enter normal operation.

[0117] Step 410: Determine the current pressure corresponding to the heat pump unit.

[0118] In some embodiments, if the current oil blockage risk level is greater than a preset threshold, it means that the current oil blockage risk level is the second or third risk level. The current oil blockage risk is relatively serious and cannot be ignored. Therefore, the controller 140 can confirm that oil blockage prevention intervention is needed, and then determine the current pressure corresponding to the heat pump unit 100 to calculate the target oil temperature.

[0119] Step 412: Based on the time coefficient corresponding to the current oil blockage risk level, compensate the reference temperature to obtain the compensated reference temperature.

[0120] The time coefficient corresponding to the current oil blockage risk level is used to quantify the differences in target oil temperature requirements for different oil blockage risk levels.

[0121] A reference temperature represents the basic temperature rise above the refrigerant saturation temperature required for oil refrigerant separation without additional risk compensation. For example, a reference temperature could be 15°C.

[0122] Because the amount of refrigerant dissolved in the lubricating oil and the difficulty of separation vary under different oil blockage risk levels, the higher the oil blockage risk, the more refrigerant is dissolved in the lubricating oil, the more difficult the separation, and the more powerful the preheating (higher target oil temperature) is required to ensure effective separation. Therefore, the time coefficient corresponding to the second risk level is smaller than that corresponding to the third risk level, in order to obtain a higher compensation value when calculating the target oil temperature (for example, the time coefficient corresponding to the second risk level (medium risk) can be set to 4 minutes; the time coefficient corresponding to the third risk level (high risk) can be set to 8 minutes). Furthermore, by compensating the reference temperature with different time coefficients, the target oil temperature and the risk level can be linked, so that the target temperature calculated subsequently can more effectively separate the lubricating oil and the refrigerant.

[0123] In some embodiments, the controller 140 can multiply the time coefficient corresponding to the current oil blockage risk level by a preset parameter to obtain a risk compensation amount; then, it adds this risk compensation amount to a reference temperature to obtain the compensated reference temperature. The preset parameter is a fixed coefficient used to calibrate the risk compensation intensity, which can characterize the additional temperature rise requirement corresponding to each unit time coefficient increment. For example, when the preset parameter is 5 and the time coefficient corresponding to the current oil blockage risk level is 4, the risk compensation amount of the controller 140 for the reference temperature can be 5 × 4 = 20.

[0124] Step 414: The sum of the compensated reference temperature and the refrigerant saturation temperature corresponding to the current pressure is taken as the target oil temperature.

[0125] Specifically, the controller 140 can obtain the target oil temperature by multiplying the time coefficient corresponding to the current oil blockage risk level by the preset parameter, adding the reference temperature, and adding the refrigerant saturation temperature corresponding to the current pressure. For example, the controller 140 can calculate the target oil temperature using formula (2). .

[0126] (2); where, is the refrigerant saturation temperature corresponding to the current pressure; a is the reference temperature; b is the preset parameter; R is the time coefficient corresponding to the current oil blockage risk level.

[0127] By quantifying the risk level of oil blockage into a time coefficient and calculating the impact of the time coefficient on the target oil temperature, the higher the risk level (such as the third risk level), the higher the corresponding target oil temperature. This ensures more complete oil-coolant separation under harsher operating conditions, while lower target oil temperatures are achieved under lower risk levels to avoid unnecessary overheating and further optimize the energy efficiency and reliability balance of the entire heat pump unit.

[0128] Step 416: Calculate the target preheating time based on the target oil temperature and the current oil temperature detected by the second temperature sensor.

[0129] Step 418: Control the heating module to run for at least the target preheating time to heat the lubricating oil in the compressor.

[0130] The relevant descriptions of steps 416 to 418 can be found in the relevant descriptions of steps 340 to 350 in the above embodiments, and will not be repeated here.

[0131] In this embodiment, by classifying the oil blockage risk into multiple levels, a refined assessment of the oil blockage risk is achieved. By combining different ambient temperatures and downtime, the risk of oil blockage can be more accurately reflected as temperature and duration accumulate, providing a more precise basis for subsequent preheating control and further optimizing the balance between energy consumption and anti-blockage effect.

[0132] In some embodiments, as shown in FIG5, the heat pump unit 100 may further include an oil level sensor 150. The oil level sensor 150 is disposed inside the compressor 111.

[0133] The oil level sensor 150 is configured to detect the actual oil level of the lubricating oil in the compressor 111.

[0134] In some embodiments, as shown in FIG6, the controller 140 may execute steps 602 to 610.

[0135] Step 602: After the heating module finishes heating, start the compressor and control the compressor to run at the first operating frequency.

[0136] The first operating frequency is less than the compressor's rated frequency.

[0137] After the heating module 120 finishes heating the lubricating oil, although the lubricating oil has been heated, the separation process between the refrigerant and the lubricating oil, as well as the reflux distribution of the lubricating oil within the heat pump unit 100, still require a certain amount of time to stabilize. If the compressor 111 is started directly at a higher rated frequency, a large pressure difference and flow shock will quickly form inside the compressor 111, which may violently agitate and carry out the incompletely separated oil-refrigerant mixture, exacerbating the risk of oil flooding. At the same time, the suction and discharge pulsation of the compressor 111 is enhanced under high-frequency operation, which is not conducive to the smooth reflux of lubricating oil back to the compressor. Therefore, the compressor 140 is controlled to start at a lower initial operating frequency to promote the smooth recovery of the oil level and further separation of the oil and refrigerant.

[0138] Step 604: Obtain the current actual oil level detected by the oil level sensor.

[0139] The oil level in compressor 111 can directly assess the actual oil content inside the compressor. If the current actual oil level is lower than the safe oil level threshold, it indicates that the lubricating oil is not flowing back sufficiently. If the operating frequency of the compressor is increased rashly at this time, it may lead to insufficient lubrication of the moving parts inside compressor 111, causing accelerated wear, abnormal temperature rise, or even seizure.

[0140] Step 606: Determine whether the current actual oil level is lower than the corresponding safe oil level threshold of the compressor; if yes, proceed to step 608; if no, proceed to step 610.

[0141] The safe oil level threshold is a preset minimum oil level limit required to ensure that all moving parts of the compressor 111 are adequately lubricated.

[0142] Step 608: Maintain or reduce the operating frequency of the compressor until the current actual oil level detected by the oil level sensor is higher than or equal to the safe oil level threshold.

[0143] If the current actual oil level is lower than the safe oil level threshold corresponding to compressor 111, it means that the lubricating oil has not fully returned to compressor 111, or that a large amount of oil is still retained in the refrigerant circulation loop 110 in the form of foam. If the operating frequency of compressor 111 is increased at this time, it may exacerbate the risk of oil shortage. Therefore, when the current actual oil level is lower than the safe oil level threshold corresponding to compressor 111, controller 140 maintains or reduces the operating frequency of compressor 111 to reduce internal system disturbances and refrigerant flow rate, creating more favorable conditions for the natural return or gravity settling of lubricating oil. Only when the current actual oil level detected by oil level sensor 150 is higher than or equal to the safe oil level threshold will the operating frequency of compressor 111 be gradually increased to ensure lubrication safety.

[0144] Step 610: Gradually increase the operating frequency of the compressor to the second operating frequency.

[0145] When the current actual oil level is higher than or equal to the safe oil level threshold corresponding to compressor 111, it means that the lubricating oil has basically returned sufficiently, and the basic lubrication is guaranteed.

[0146] Specifically, if the duration for which the actual oil level detected by the oil level sensor 150 is higher than or equal to the safe oil level threshold is greater than or equal to a first duration threshold, the operating frequency of the compressor 111 is gradually increased to a second operating frequency, which is greater than or equal to the compressor's rated frequency. The setting of the first duration threshold avoids misjudgments due to instantaneous fluctuations or brief recovery of the oil level, ensuring the oil level remains in a safe state and thus guaranteeing the stability and reliability of the frequency increase process.

[0147] In some embodiments, after the heating module finishes heating, while starting the compressor 111, the controller 140 can control the electronic expansion valve 113 to open to its minimum opening degree to initially open the refrigerant circulation loop 110, but limit the initial refrigerant flow rate to avoid liquid carryover in the compressor 111 or drastic fluctuations in the oil level due to excessive flow. Furthermore, when the current actual oil level is higher than or equal to the safe oil level threshold corresponding to the compressor 111, the controller 140 gradually increases the opening degree of the electronic expansion valve 113 while gradually increasing the operating frequency of the compressor 111 to a second operating frequency, to match the gradually increasing refrigerant flow demand and maintain the stability and energy efficiency of the heat pump unit 100.

[0148] In some embodiments, to further enhance the safety of the compressor 111 startup process, during the startup process of the compressor 111, the controller 140 continuously monitors the exhaust superheat and / or the current actual oil level of the compressor 111; if there is a drastic abnormality in the exhaust superheat and / or the current actual oil level (e.g., the rate of decrease of exhaust superheat is greater than the rate threshold or the exhaust superheat decreases to a preset minimum superheat), the controller 140 controls the compressor 111 to pause startup or controls the compressor 111 to reduce its frequency, so as to prevent serious faults such as liquid slugging and oil shortage, and to achieve protection during the startup process.

[0149] In this embodiment, after preheating, the compressor is controlled to operate at a lower first operating frequency, and the current actual oil level of the compressor is continuously monitored. If the current actual oil level is found to be lower than a safety threshold, the operating frequency is maintained or further reduced to mitigate internal disturbances in the compressor. This creates more stable conditions for lubricating oil return and oil level recovery, avoiding problems such as sudden drops in oil level and increased oil carryover that may occur when directly starting the compressor at high frequency. This fundamentally ensures that the compressor smoothly transitions to normal operation with sufficient lubricating oil, improving the safety and reliability of the startup process. Furthermore, by using a duration greater than or equal to the first duration threshold as a prerequisite for increasing the compressor frequency, interference from instantaneous changes in oil level can be avoided, ensuring sufficient lubricating oil return and guaranteeing the stability of the startup process.

[0150] In some embodiments, as shown in FIG7, the controller 140 may execute steps 702 to 712.

[0151] Step 702: During compressor operation, determine the low-frequency running time when the compressor operates at a frequency less than or equal to the first frequency threshold.

[0152] The first frequency threshold is less than the compressor's rated frequency.

[0153] During the operation of compressor 111, if compressor 111 operates at a frequency less than or equal to a first frequency threshold, it means that compressor 111 is operating under partial or low load. In this state, the refrigerant circulation is relatively weak, the refrigerant flow rate is low, and lubricating oil is more likely to gradually stagnate and accumulate in low-temperature areas of the pipeline (especially the evaporator) due to gravity or viscosity. Long-term operation may lead to an imbalance in the system's oil distribution, creating a potential risk of oil blockage. Therefore, controller 140 determines whether there is a significant risk of oil blockage during compressor 111 operation by determining the duration of low-frequency operation at a frequency less than or equal to the first frequency threshold.

[0154] Step 704: Determine whether the low-frequency running time is greater than the second duration threshold; if not, proceed to step 706; if yes, proceed to step 708.

[0155] Since the migration and retention of lubricating oil in pipelines is a cumulative process over time, short periods of low-frequency operation will not immediately lead to serious oil distribution problems. Therefore, setting a second duration threshold can identify periods of sustained low-load operation, at which point the risk of lubricating oil retention has significantly increased. It is necessary to further determine whether active intervention in oil return is required (whether there is a significant risk of oil blockage), thus avoiding frequent or premature oil return actions that could interfere with the normal operation of the heat pump unit.

[0156] Step 706: Control the compressor to continue running.

[0157] In some embodiments, if the low-frequency running time of the compressor 111 at an operating frequency less than or equal to a first frequency threshold is less than or equal to a second duration threshold, and the lubricating oil retention is considered to be within an acceptable range and there is no risk of oil blockage, then the controller 140 can control the compressor 111 to continue operating normally without initiating the oil return operation.

[0158] In some embodiments, if the low-frequency operating time exceeds the second duration threshold, but the operating parameters and / or the current actual oil level do not meet the preset oil return conditions, it means that the overall operating status of the heat pump unit 100 is still within the normal range, and the risk of oil blockage caused by the low-frequency operation of the compressor 111 is still within the acceptable range. In this case, the controller 140 can control the compressor 111 to continue operating to avoid unnecessary oil return actions.

[0159] Step 708: Detect the compressor's operating parameters and / or obtain the current actual oil level detected by the oil level sensor.

[0160] In some embodiments, a low-frequency operating time exceeding a second duration threshold indicates that the heat pump unit 100 is in a stage where the risk of serious oil blockage due to lubricating oil retention needs to be monitored. Therefore, when the low-frequency operating time exceeds the second duration threshold, the controller 140 can detect the operating parameters of the compressor 111 and / or obtain the current actual oil level detected by the oil level sensor 150 to further assess whether the overall operating status of the heat pump unit 100 truly requires the oil return operation, avoiding false triggering based solely on the single condition of operating time.

[0161] Optionally, the operating parameters of compressor 111 include the discharge superheat of compressor 111 and / or the cumulative operating time of compressor 111.

[0162] The discharge superheat of compressor 111 refers to the difference between the discharge temperature and the evaporation temperature of compressor 111. The cumulative running time of compressor 111 refers to the total continuous running time of compressor 111 since this start-up (or since the end of the last oil return operation).

[0163] Optionally, the controller 140 can detect the exhaust temperature by a temperature sensor located at the exhaust port of the compressor 111, and detect the evaporation temperature by a temperature sensor located in the evaporator (in heating mode, the evaporator is an outdoor heat exchanger) pipeline, and then subtract the two to obtain the exhaust superheat.

[0164] Step 710: Determine whether the operating parameters and / or the current actual oil level meet the preset oil return conditions; if yes, proceed to step 712; if no, proceed to step 706.

[0165] In some embodiments, the oil return conditions include at least one of the following: the cumulative runtime is greater than a third duration threshold, the third duration threshold is greater than a second duration threshold; the duration for which the exhaust superheat of compressor 111 is less than a first superheat threshold is greater than a fourth duration threshold; the current actual oil level is lower than a target oil level threshold; and the target oil level threshold is greater than the safe oil level threshold corresponding to compressor 111.

[0166] Among these, a cumulative runtime exceeding the third duration threshold ensures that the heat pump unit 100 can periodically perform oil level readjustment, guaranteeing the lubricating oil level in the compressor 111, even under conditions without significant abnormalities. For example, the third duration threshold could be 2 hours.

[0167] If the duration for which the discharge superheat of compressor 111 is less than the first superheat threshold is greater than the fourth duration threshold, it means that the discharge superheat of compressor 111 is consistently low. A consistently low discharge superheat may indicate that the liquid return demand of compressor 111 is increased or that the evaporator heat exchange is poor (low temperature), which may lead to lubricating oil retention and requires intervention by oil return operation.

[0168] The current actual oil level is lower than the target oil level threshold, and the target oil level threshold is greater than the safe oil level threshold corresponding to compressor 111. This directly indicates that although the oil level in compressor 111 is not low enough to immediately endanger lubrication safety, the oil distribution in compressor 111 has begun to deviate from the ideal state, and oil return replenishment is required.

[0169] Specifically, the target oil level threshold can be 90% of the normal oil level (i.e., 10% lower than the normal oil level). The normal oil level refers to the ideal range or center value of the internal lubricating oil level of the compressor 111 when it is running stably under rated operating conditions.

[0170] Step 712: Adjust the operating frequency of the compressor.

[0171] If the operating parameters and / or the current actual oil level meet the preset oil return conditions, it means that there is a risk of unbalanced oil distribution, lubricating oil retention or lack of oil. In this case, the controller 140 adjusts the operating frequency of the compressor 111 to enhance the system circulation power and force the lubricating oil in the pipeline to flow back to the compressor 111 to restore the oil balance of the compressor.

[0172] In some embodiments, the controller 140 may increase the operating frequency of the compressor to a third operating frequency and control the opening of the electronic expansion valve to increase to a preset target opening until a second condition is met; the third operating frequency is greater than the rated frequency of the compressor; when the second condition is met, the operating frequency of the compressor is reduced to the operating frequency before the increase, and the opening of the electronic expansion valve is adjusted to the opening before the increase; wherein, the second condition includes one or more of the following: the duration of the compressor operating at the third operating frequency is greater than the oil return duration threshold; the current actual oil level detected by the oil level sensor is higher than or equal to the target oil level threshold; the discharge superheat of the compressor is less than the second superheat threshold; the second superheat threshold is less than the first superheat threshold.

[0173] During oil return, a synergistic strategy of increasing the compressor's operating frequency and the opening of the electronic expansion valve is employed to enhance the circulation power and flow rate of the circulation loop, thereby driving the lubricating oil in the pipeline back to the compressor. Simultaneously, the oil return operation terminates when a preset duration is reached, the oil level returns to the threshold, or the discharge is excessively low (posing a risk of liquid slugging). This ensures sufficient oil return while preventing compressor damage due to excessive oil return or liquid return, thus improving oil balance maintenance capabilities while guaranteeing the safety of the entire oil return process.

[0174] In this embodiment, by combining the cumulative running time, exhaust superheat and the current actual oil level, the adaptability to complex operating conditions and potential faults is enhanced, ensuring that the oil return operation can be started in a timely manner under different abnormal scenarios, thereby maintaining the oil balance of the compressor, preventing performance degradation or insufficient lubrication of the compressor due to uneven oil distribution, and improving the overall reliability and robustness of the heat pump unit under long-term, variable operating conditions.

[0175] In some embodiments, the connection relationship of the various components in the heat pump unit 100 can be as shown in Figure 8. Specifically, the heat pump unit 100 includes a compressor 111, an outdoor heat exchanger 112, an electronic expansion valve 113, an indoor heat exchanger 114, a heating module 120, a first temperature sensor 131, a second temperature sensor 132, an oil level sensor 150, and a four-way valve 160.

[0176] Specifically, as shown in Figure 9, the controller 140 is configured to perform the following steps 901 to 940.

[0177] As shown in Figure 9, when the heat pump unit 100 is in a low-temperature shutdown state and heating is required, the controller 140, upon detecting a start signal for the compressor 111 (used to start the heating mode of the heat pump unit 100), obtains the corresponding shutdown duration of the compressor 111 and the ambient temperature detected by the first temperature sensor 131. Based on risk assessment rules, the controller determines the oil blockage risk, etc., according to the ambient temperature and shutdown duration. Specifically, when the ambient temperature < the first temperature threshold A and the shutdown duration ≥ the first duration threshold a, the controller 140 confirms the current oil blockage risk level as high risk (third risk level); when the ambient temperature < A and the shutdown duration < a, or when A ≤ the ambient temperature < the second temperature threshold B and the shutdown duration ≥ the second duration threshold b, the controller 140 confirms the current oil blockage risk level as medium risk (second risk level); when the ambient temperature > B, or when A ≤ the ambient temperature < B and the shutdown duration < b, the controller 140 confirms the current oil blockage risk level as low risk (first risk level).

[0178] When the current oil blockage risk level is low, the controller 140 can directly respond to the start signal for the compressor 111 and control the compressor 111 to start. However, when the current oil blockage risk level is medium or high, the controller 140 needs to perform an anti-oil blockage operation. The controller 140 determines the current pressure corresponding to the heat pump unit 100 and obtains the target oil temperature using the formula (time coefficient corresponding to the current oil blockage risk level × preset parameter + reference temperature) + refrigerant saturation temperature corresponding to the current pressure = target oil temperature. The controller 140 obtains the current oil temperature of the lubricating oil in the compressor 111 through the second temperature sensor 132 and obtains the target preheating time using the formula (target oil temperature - current oil temperature) / heating coefficient = target preheating time. The controller 140 controls the heating module 120 to run for at least the target preheating time to heat the lubricating oil in the compressor 111, and after the heating module 120 finishes heating, it controls the compressor 111 to start.

[0179] When the compressor 111 is first started, the compressor 111 is controlled to run at a first operating frequency, and the current actual oil level detected by the oil level sensor 150 is obtained. If the current actual oil level is not lower than the safe oil level threshold, the operating frequency of the compressor 111 is directly controlled to gradually increase to the second operating frequency. If the current actual oil level is lower than the safe oil level threshold, the controller 140 maintains or reduces the operating frequency of the compressor 111 until the current actual oil level detected by the oil level sensor 150 is higher than or equal to the safe oil level threshold, and then the operating frequency of the compressor 111 is controlled to gradually increase to the second operating frequency.

[0180] During the operation of compressor 111, controller 140 determines the low-frequency running duration of compressor 111 at a frequency less than or equal to a first frequency threshold; when the low-frequency running duration is less than or equal to a second duration threshold, controller 140 controls compressor 111 to continue running without performing oil return operation; when the low-frequency running duration is greater than the second duration threshold, controller 140 detects the cumulative running duration of compressor 111 and / or discharge superheat and / or current actual oil level; when the operating parameters of compressor 111 and / or the current actual oil level do not meet the oil return conditions (the cumulative running duration is less than or equal to a third duration threshold, and the duration for which the discharge superheat of compressor 111 is less than or equal to a first superheat threshold is less than or equal to a fourth duration threshold, and the current actual oil level is higher than...), If the operating parameters of the compressor 111 and / or the current actual oil level meet the oil return conditions, the controller 140 increases the operating frequency of the compressor 111 to the third operating frequency and controls the opening of the electronic expansion valve 113 to increase to the preset target opening, so that the lubricating oil flows back to the compressor 111, until the second condition is met (the duration of the compressor running at the third operating frequency is greater than the oil return duration threshold, or the current actual oil level detected by the oil level sensor is higher than or equal to the target oil level threshold, or the exhaust superheat of the compressor is less than the second superheat threshold), then the operating frequency of the compressor is reduced to the operating frequency before the increase, and the opening of the electronic expansion valve is adjusted to the opening before the increase.

[0181] As shown in Figure 10, in one embodiment, a control method for a heat pump unit with anti-oil-clogging function is provided, which can be applied to the aforementioned heat pump unit 100. The method may include steps 1010 to 1050.

[0182] Step 1010: When a start signal for the compressor is detected, the corresponding shutdown duration of the compressor is obtained, and the ambient temperature detected by the first temperature sensor is obtained. The oil blockage risk level is determined based on the shutdown duration and the ambient temperature.

[0183] Step 1020: If the oil blockage risk level is greater than the preset threshold, determine the current pressure corresponding to the heat pump unit.

[0184] Step 1030: Calculate the target oil temperature based on the refrigerant saturation temperature corresponding to the current pressure.

[0185] Step 1040: Calculate the target preheating time based on the target oil temperature and the current oil temperature detected by the second temperature sensor.

[0186] Step 1050: Control the heating module to run for at least the target preheating time to heat the lubricating oil in the compressor.

[0187] In some embodiments, step 1010 may further include: the heat pump unit may determine the current oil blockage risk level based on risk assessment rules, according to ambient temperature and downtime; wherein the oil blockage risk level includes a first risk level, a second risk level and a third risk level, the probability of oil blockage risk corresponding to the third risk level is greater than the probability of oil blockage risk corresponding to the second risk level, and the probability of oil blockage risk corresponding to the second risk level is greater than the probability of oil blockage risk corresponding to the first risk level.

[0188] Optionally, the oil blockage risk level is greater than a preset threshold, including: the current oil blockage risk level is the second risk level or the third risk level.

[0189] In some embodiments, the risk assessment rules include: when the ambient temperature is less than a first temperature threshold and the downtime is greater than or equal to a first duration threshold, the oil blockage risk level is the third risk level; when the ambient temperature is less than the first temperature threshold and the downtime is less than the first duration threshold, or when the ambient temperature is greater than or equal to the first temperature threshold and less than a second temperature threshold, and the downtime is greater than or equal to the second duration threshold, the oil blockage risk level is the second risk level; the second temperature threshold is greater than the first temperature threshold; the second duration threshold is greater than the first duration threshold; when the ambient temperature is greater than the second temperature threshold, or when the ambient temperature is greater than or equal to the first temperature threshold and less than the second temperature threshold, and the downtime is less than the second duration threshold, the oil blockage risk level is the first risk level.

[0190] Optionally, step 1030 may include: compensating the reference temperature according to the time coefficient corresponding to the current oil blockage risk level to obtain the compensated reference temperature; the time coefficient corresponding to the second risk level is less than the time coefficient corresponding to the third risk level; and using the sum of the compensated reference temperature and the refrigerant saturation temperature corresponding to the current pressure as the target oil temperature.

[0191] Optionally, step 1040 may include: determining the target preheating time based on the difference between the target oil temperature and the current oil temperature detected by the second temperature sensor, and the heating coefficient of the heating module.

[0192] In some embodiments, the heat pump unit may start the compressor after the heating module finishes heating and control the compressor to operate at a first operating frequency; the first operating frequency is less than the rated frequency of the compressor; the current actual oil level detected by the oil level sensor is obtained; when the current actual oil level is lower than the corresponding safe oil level threshold of the compressor, the operating frequency of the compressor is maintained or reduced until the current actual oil level detected by the oil level sensor is higher than or equal to the safe oil level threshold.

[0193] In some embodiments, the heat pump unit may control the compressor's operating frequency to gradually increase to a second operating frequency, where the duration for which the current actual oil level detected by the oil level sensor is higher than or equal to a safe oil level threshold is greater than or equal to a first duration threshold. The second operating frequency is greater than or equal to the compressor's rated frequency.

[0194] In some embodiments, the heat pump unit may determine the low-frequency running time of the compressor during compressor operation at a frequency less than or equal to a first frequency threshold; the first frequency threshold is less than the rated frequency of the compressor; if the low-frequency running time is greater than a second duration threshold, the operating parameters of the compressor are detected and / or the current actual oil level detected by the oil level sensor is obtained; if the operating parameters and / or the current actual oil level meet the preset oil return conditions, the operating frequency of the compressor is adjusted to allow the lubricating oil to flow back to the compressor.

[0195] Optionally, the compressor's operating parameters include the compressor's discharge superheat and / or the compressor's cumulative operating time.

[0196] Optionally, the oil return conditions include at least one of the following: the cumulative runtime is greater than a third duration threshold, the third duration threshold is greater than a second duration threshold; the duration for which the compressor's exhaust superheat is less than a first superheat threshold is greater than a fourth duration threshold; the current actual oil level is lower than a target oil level threshold; and the target oil level threshold is greater than the compressor's corresponding safe oil level threshold.

[0197] In some embodiments, the heat pump unit may further increase the operating frequency of the compressor to a third operating frequency and control the opening of the electronic expansion valve to increase to a preset target opening until the second condition is met; the third operating frequency is greater than the rated frequency of the compressor; if the second condition is met, the operating frequency of the compressor is reduced to the operating frequency before the increase, and the opening of the electronic expansion valve is adjusted to the opening before the increase.

[0198] Optionally, the second condition includes one or more of the following: the duration of the compressor operating at the third operating frequency is greater than the oil return duration threshold; the current actual oil level detected by the oil level sensor is higher than or equal to the target oil level threshold; the compressor's exhaust superheat is less than the second superheat threshold; and the second superheat threshold is less than the first superheat threshold.

[0199] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0200] The foregoing has provided a detailed description of a heat pump unit with anti-oil-clogging function disclosed in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are merely for the purpose of helping to understand the method and core ideas of this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A heat pump unit with anti-oil-clogging function, characterized in that, include: The refrigerant circulation loop includes a compressor, an outdoor heat exchanger, an electronic expansion valve, and an indoor heat exchanger connected in sequence. The refrigerant circulation loop is configured to circulate refrigerant. The compressor is filled with lubricating oil, which is used to lubricate the moving parts of the compressor. A heating module is disposed at the bottom of the compressor, and the heating module is configured to heat the lubricating oil inside the compressor; a first temperature sensor is configured to detect the outdoor ambient temperature where the heat pump unit is located; A second temperature sensor is disposed inside the compressor and is configured to detect the oil temperature corresponding to the lubricating oil inside the compressor; the controller is configured to: when a start signal for the compressor is detected, acquire the shutdown duration corresponding to the compressor and acquire the ambient temperature detected by the first temperature sensor, and determine the oil blockage risk level based on the shutdown duration and the ambient temperature; If the oil blockage risk level is greater than a preset threshold, determine the current pressure corresponding to the heat pump unit; calculate the target oil temperature based on the refrigerant saturation temperature corresponding to the current pressure; calculate the target preheating time based on the target oil temperature and the current oil temperature detected by the second temperature sensor; control the heating module to run for at least the target preheating time to heat the lubricating oil in the compressor.

2. The heat pump unit according to claim 1, characterized in that, The step of determining the oil blockage risk level based on the downtime and the ambient temperature includes: determining the current oil blockage risk level based on risk assessment rules, according to the ambient temperature and the downtime; the oil blockage risk level includes a first risk level, a second risk level, and a third risk level, wherein the probability of oil blockage risk corresponding to the third risk level is greater than the probability of oil blockage risk corresponding to the second risk level, and the probability of oil blockage risk corresponding to the second risk level is greater than the probability of oil blockage risk corresponding to the first risk level; the oil blockage risk level being greater than a preset threshold includes: the current oil blockage risk level being either the second risk level or the third risk level.

3. The heat pump unit according to claim 2, characterized in that, The risk assessment rules include: when the ambient temperature is less than a first temperature threshold and the downtime is greater than or equal to a first duration threshold, the oil blockage risk level is the third risk level; when the ambient temperature is less than the first temperature threshold and the downtime is less than the first duration threshold, or when the ambient temperature is greater than or equal to the first temperature threshold and less than a second temperature threshold, and the downtime is greater than or equal to the second duration threshold, the oil blockage risk level is the second risk level; the second temperature threshold is greater than the first temperature threshold; the second duration threshold is greater than the first duration threshold; when the ambient temperature is greater than the second temperature threshold, or when the ambient temperature is greater than or equal to the first temperature threshold and less than the second temperature threshold, and the downtime is less than the second duration threshold, the oil blockage risk level is the first risk level.

4. The heat pump unit according to claim 2, characterized in that, The step of calculating the target oil temperature based on the refrigerant saturation temperature corresponding to the current pressure includes: compensating the reference temperature based on the time coefficient corresponding to the current oil blockage risk level to obtain the compensated reference temperature; the time coefficient corresponding to the second risk level is less than the time coefficient corresponding to the third risk level; and taking the sum of the compensated reference temperature and the refrigerant saturation temperature corresponding to the current pressure as the target oil temperature.

5. The heat pump unit according to claim 1, characterized in that, The step of calculating the target preheating time based on the target oil temperature and the current oil temperature detected by the second temperature sensor includes: determining the target preheating time based on the difference between the target oil temperature and the current oil temperature detected by the second temperature sensor, and the heating coefficient of the heating module.

6. The heat pump unit according to claim 1, characterized in that, The heat pump unit also includes an oil level sensor, which is located inside the compressor and configured to detect the actual oil level of the lubricating oil inside the compressor. The controller is further configured to: start the compressor after the heating module finishes heating, and control the compressor to operate at a first operating frequency; the first operating frequency is less than the rated frequency of the compressor; and acquire the current actual oil level detected by the oil level sensor. When the current actual oil level is lower than the safe oil level threshold corresponding to the compressor, the operating frequency of the compressor is maintained or reduced until the current actual oil level detected by the oil level sensor is higher than or equal to the safe oil level threshold.

7. The heat pump unit according to claim 6, characterized in that, The controller is further configured to: when the duration for which the current actual oil level detected by the oil level sensor is higher than or equal to the safe oil level threshold is greater than or equal to a first duration threshold, control the operating frequency of the compressor to gradually increase to a second operating frequency, wherein the second operating frequency is greater than or equal to the rated frequency of the compressor.

8. The heat pump unit according to claim 1, characterized in that, The heat pump unit also includes an oil level sensor, which is installed inside the compressor. The oil level sensor is configured to detect the actual oil level of the lubricating oil inside the compressor. The controller is also configured to determine the duration of low-frequency operation when the compressor operates at a frequency less than or equal to a first frequency threshold during the operation of the compressor. The first frequency threshold is less than the rated frequency of the compressor; when the low-frequency operating length is greater than the second duration threshold, the operating parameters of the compressor are detected and / or the current actual oil level detected by the oil level sensor is obtained; If the operating parameters and / or the current actual oil level meet the preset oil return conditions, the operating frequency of the compressor is adjusted so that the lubricating oil flows back to the compressor.

9. The heat pump unit according to claim 8, characterized in that, The operating parameters of the compressor include the discharge superheat of the compressor and / or the cumulative running time of the compressor; the oil return condition includes at least one of the following: the cumulative running time is greater than a third time threshold, and the third time threshold is greater than a second time threshold; The duration for which the compressor's exhaust superheat is less than the first superheat threshold is greater than the fourth duration threshold; the current actual oil level is lower than the target oil level threshold; and the target oil level threshold is greater than the safe oil level threshold corresponding to the compressor.

10. The heat pump unit according to claim 8, characterized in that, The adjustment of the compressor's operating frequency includes: increasing the compressor's operating frequency to a third operating frequency and controlling the opening of the electronic expansion valve to increase to a preset target opening until a second condition is met; the third operating frequency is greater than the compressor's rated frequency; when the second condition is met, reducing the compressor's operating frequency to the operating frequency before the increase and controlling the opening of the electronic expansion valve to adjust to the opening before the increase; wherein, the second condition includes one or more of the following: the compressor operates at the third operating frequency for a duration greater than a return oil duration threshold; the current actual oil level detected by the oil level sensor is higher than or equal to a target oil level threshold; the compressor's exhaust superheat is less than a second superheat threshold; the second superheat threshold is less than the first superheat threshold.

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