A hot fluorine thawing control method, system and variable frequency refrigeration unit

Abstract

The application relates to the technical field of energy-saving control of refrigeration equipment, and discloses a hot fluorine defrosting control method, a system and a variable-frequency refrigeration unit. The method judges defrosting conditions according to the temperature in a warehouse, the humidity in the warehouse and the refrigeration time length of the unit; when the defrosting conditions are met, the compressor is controlled to run at a switching frequency of a four-way valve and switch the four-way valve, the optimal defrosting running frequency is determined according to the ambient temperature and the temperature in the warehouse, and the defrosting running and segmented low-pressure limited frequency are implemented in combination with the allowable running frequency range of the compressor and the suction pressure; after the coil temperature reaches the defrosting exit condition, the drip mode is entered, the running frequency of the compressor is adjusted according to the coil temperature, the compressor is kept running and switched to the refrigeration direction after the preset drip running time length is reached. The application can improve the defrosting working condition adaptability and running stability of the energy-saving type refrigeration equipment, and reduce the defrosting energy consumption and the start-stop times of the compressor.

Description

Technical Field

[0001] This invention belongs to the field of high-efficiency and energy-saving refrigeration equipment control technology, and more specifically, relates to a hot fluorine defrosting control method, system and variable frequency refrigeration unit. Background Technology

[0002] Refrigeration units are commonly used temperature control devices in low-temperature storage environments such as cold storage facilities. During refrigeration operation, when the surface temperature of the heat exchanger inside the storage facility is low and the humidity is high, moisture in the air easily condenses on the surface of the heat exchanger, forming a frost layer. As the frost layer thickens, the heat exchange efficiency of the heat exchanger decreases, potentially affecting the refrigeration capacity and operational efficiency of the refrigeration unit. Therefore, to improve the operating efficiency of energy-efficient refrigeration equipment, it is necessary to defrost the heat exchanger inside the storage facility in a timely manner.

[0003] Existing refrigeration units typically use timed defrosting or determine defrosting based on a single parameter such as coil temperature. This makes it difficult to comprehensively assess the frosting status of the heat exchangers inside the refrigeration unit, considering factors such as the internal temperature, humidity, compressor operating frequency, and unit refrigeration operation duration. When the set defrosting interval or judgment conditions do not match the actual operating conditions, premature or insufficient defrosting can easily occur, leading to unnecessary defrosting energy consumption or affecting the heat exchange performance of the heat exchangers inside the refrigeration unit.

[0004] Furthermore, during hot refrigerant defrosting, ambient temperature, internal temperature, and refrigerant circulation status all affect the appropriate operating frequency of the compressor. Using a fixed defrosting frequency may result in a mismatch between the compressor's operating frequency and the actual defrosting load. If the compressor's operating frequency is not limited in time when the suction pressure decreases, it may affect the stability of refrigerant circulation and defrosting operation. Inappropriate dripping time and compressor operating frequency after defrosting may also affect the discharge of defrost water and increase the number of compressor start-stop cycles and internal temperature fluctuations during the transition from defrosting to refrigeration.

[0005] Therefore, how to determine the defrosting demand based on the actual operating conditions of the refrigeration unit, and coordinate and control the defrosting operation frequency, low-pressure frequency limiting, dripping operation, and the switching from defrosting to refrigeration state, in order to improve the defrosting operation stability of high-efficiency and energy-saving refrigeration equipment and reduce defrosting energy consumption, is a technical problem that needs to be solved. Summary of the Invention

[0006] To address the problems in existing technologies, such as the limited range of defrosting condition assessments, mismatch between defrosting frequency and actual operating conditions, excessively low suction pressure during defrosting, and unreasonable control over dripping operation and state switching after defrosting, this invention provides a hot-flecked defrosting control method, system, and variable frequency refrigeration unit. By combining the temperature and humidity inside the refrigeration unit, the unit's refrigeration time, ambient temperature, coil temperature, and suction pressure, this invention coordinates and controls the defrosting condition assessment, defrosting frequency, segmented low-pressure frequency limiting, dripping operation, and the transition from defrosting to refrigeration state.

[0007] The present invention adopts the following technical solution.

[0008] A first aspect of the present invention provides a hot refrigerant defrosting control method applied to a variable frequency refrigeration unit, the variable frequency refrigeration unit including a compressor, a four-way valve and a suction pressure sensor, the hot refrigerant defrosting control method comprising: The system acquires the temperature inside the storage room, the humidity inside the storage room, the ambient temperature, the coil temperature, the operating frequency of the compressor, and the suction pressure detected by the suction pressure sensor, and calculates the unit's cooling time based on the operating frequency of the compressor. Based on the temperature inside the cold storage, the humidity inside the cold storage, and the cooling time of the unit, determine whether the variable frequency refrigeration unit meets the defrosting conditions; When the variable frequency refrigeration unit meets the defrosting conditions, the compressor is controlled to operate at the switching frequency of the four-way valve. After the compressor operates at the switching frequency of the four-way valve, the four-way valve is controlled to switch to the defrosting direction. The optimal defrosting operating frequency is determined according to the ambient temperature and the temperature inside the refrigeration unit. Based on the optimal defrosting operating frequency and the allowable operating frequency range of the compressor, the compressor is controlled to perform defrosting operation. During the defrosting operation, the compressor is subjected to segmented low-pressure frequency limiting control based on the suction pressure; When the coil temperature is higher than the defrost exit temperature threshold, the variable frequency refrigeration unit is controlled to enter the dripping mode, the compressor is controlled to run at the dripping frequency, and the operating frequency of the compressor is adjusted according to the coil temperature. When the dripping mode runs for a duration equal to or exceeding the preset dripping duration, the compressor maintains its current operating frequency before the dripping mode ends, and the four-way valve is switched to the refrigeration direction. When the temperature inside the refrigeration chamber is greater than or equal to the sum of the preset refrigeration temperature setting and the temperature control accuracy, the variable frequency refrigeration unit is controlled to continue refrigeration operation. When the temperature inside the refrigeration chamber is less than the sum of the refrigeration temperature setting and the temperature control accuracy, the variable frequency refrigeration unit is controlled to enter a shutdown standby state.

[0009] Preferably, the step of calculating the unit's cooling time duration based on the compressor's operating frequency, and determining whether the variable frequency refrigeration unit meets the defrosting conditions based on the warehouse temperature, the warehouse humidity, and the unit's cooling time duration, includes: Establish the correspondence between temperature range, humidity range, minimum operating frequency of compressor cooling, and cooling time duration threshold in advance; When the temperature inside the refrigeration unit is higher than the preset defrosting temperature limit, it is determined that the variable frequency refrigeration unit does not meet the defrosting conditions. When the temperature inside the storage room is not higher than the preset defrost temperature upper limit, the corresponding minimum operating frequency of the compressor and the threshold of the refrigeration time are selected from the correspondence based on the temperature range of the temperature inside the storage room and the humidity range of the humidity inside the storage room. When the operating frequency of the compressor is greater than the minimum operating frequency for cooling, the running time of the compressor is accumulated to obtain the cooling time of the unit. When the operating frequency of the compressor is not greater than the minimum operating frequency of the compressor for cooling, the accumulation of the cooling time of the unit is paused, and the accumulated cooling time of the unit is retained. When the cooling time of the unit exceeds the cooling time threshold, the variable frequency cooling unit is determined to meet the defrosting condition.

[0010] Preferably, determining the optimal defrosting frequency based on the ambient temperature and the temperature inside the storage chamber includes: The product of the ambient temperature and the ambient temperature compensation coefficient is determined as the ambient temperature compensation term, and the product of the warehouse temperature and the warehouse temperature compensation coefficient is determined as the warehouse temperature compensation term. The optimal defrosting operating frequency is obtained by subtracting the ambient temperature compensation term and the warehouse temperature compensation term from the defrosting baseline operating frequency.

[0011] The step of controlling the compressor to perform defrost operation based on the optimal defrost operating frequency and the compressor's allowable operating frequency range includes: When the optimal defrosting operating frequency is higher than the maximum allowable operating frequency of the compressor, the compressor is controlled to perform defrosting operation at the maximum allowable operating frequency; When the optimal defrosting operating frequency is lower than the minimum allowable operating frequency of the compressor, the compressor is controlled to perform defrosting operation at the minimum allowable operating frequency; When the optimal defrosting operating frequency is within the allowable operating frequency range of the compressor, the compressor is controlled to perform defrosting operation according to the optimal defrosting operating frequency.

[0012] Preferably, the step of performing segmented low-pressure frequency limiting control on the compressor based on the suction pressure includes: A first pressure threshold, a second pressure threshold, and a third pressure threshold are set, wherein the first pressure threshold is greater than the second pressure threshold, and the second pressure threshold is greater than the third pressure threshold. A first frequency threshold, a second frequency threshold, and a third frequency threshold are set, wherein the first frequency threshold is greater than the second frequency threshold, and the second frequency threshold is greater than the third frequency threshold; When the suction pressure is less than the first pressure threshold and greater than or equal to the second pressure threshold, the maximum operating frequency of the compressor is limited to not exceeding the first frequency threshold. When the suction pressure is less than the second pressure threshold and greater than or equal to the third pressure threshold, the maximum operating frequency of the compressor is limited to not exceeding the second frequency threshold. When the suction pressure is less than the third pressure threshold, the maximum operating frequency of the compressor is limited to not exceeding the third frequency threshold.

[0013] The segmented low-pressure frequency limiting control has a higher priority than the control of the compressor based on the optimal defrosting operating frequency; when the optimal defrosting operating frequency is higher than the frequency threshold corresponding to the current pressure range of the suction pressure, the corresponding frequency threshold is used as the target operating frequency of the compressor.

[0014] Preferably, the segmented low-voltage frequency limiting control further includes low-voltage frequency limiting recovery control, which includes: When the suction pressure rises from less than the third pressure threshold to greater than or equal to the third pressure threshold and less than the second pressure threshold, and remains within the corresponding pressure range for a preset recovery time, the limit of the compressor's maximum operating frequency is adjusted from the third frequency threshold to the second frequency threshold. When the intake pressure rises to a level greater than or equal to the second pressure threshold and less than the first pressure threshold, and remains within the corresponding pressure range for the preset recovery time, the limit of the compressor's maximum operating frequency is adjusted to the first frequency threshold. When the inhalation pressure rises to a level greater than or equal to the first pressure threshold and remains within a pressure range greater than or equal to the first pressure threshold for a preset recovery time, the segmented low-pressure frequency limiting control is released.

[0015] Preferably, the variable frequency refrigeration unit further includes an electronic expansion valve, a cooler, and a condenser. Controlling the variable frequency refrigeration unit to enter the dripping mode, controlling the compressor to operate at the dripping frequency, and adjusting the compressor's operating frequency according to the coil temperature includes: The four-way valve is controlled to maintain the defrosting direction, the opening of the electronic expansion valve is adjusted according to the suction superheat of the variable frequency refrigeration unit, the air cooler is controlled to remain closed, and the condenser fan is controlled to run at its maximum speed. Control the compressor to operate at the dripping frequency; When the coil temperature remains higher than the sum of the defrost exit temperature threshold and the temperature compensation value for a preset judgment period, the frequency reduction target frequency is determined based on the difference between the dripping operation frequency and the preset frequency reduction value. When the target frequency for frequency reduction is not lower than the minimum allowable operating frequency of the compressor, the compressor is controlled to operate at the target frequency for frequency reduction. When the target frequency for frequency reduction is lower than the minimum allowable operating frequency of the compressor, the compressor is controlled to operate at the minimum allowable operating frequency.

[0016] Preferably, when the running time of the dripping mode reaches the preset dripping running time, controlling the four-way valve to switch to the cooling direction while the compressor is continuously running includes: The duration of the dripping mode is accumulated from the time the variable frequency chiller unit enters the dripping mode. When the running time of the dripping mode reaches or exceeds the preset dripping running time, the compressor maintains the current operating frequency before the end of the dripping mode, and controls the four-way valve to switch from the defrosting direction to the cooling direction.

[0017] A second aspect of the present invention provides a hot fluorine defrosting control system for implementing any of the above-mentioned hot fluorine defrosting control methods. The hot fluorine defrosting control system includes a parameter acquisition and timing module, a defrosting judgment module, a defrosting operation control module, a low-pressure frequency limiting control module, a dripping control module, and a state switching module.

[0018] The parameter acquisition and timing module is used to acquire the temperature inside the storage room, the humidity inside the storage room, the ambient temperature, the coil temperature, the operating frequency of the compressor, and the suction pressure detected by the suction pressure sensor, and to calculate the cooling time of the unit based on the operating frequency of the compressor.

[0019] The defrosting judgment module is used to determine whether the variable frequency refrigeration unit meets the defrosting conditions based on the temperature inside the refrigeration room, the humidity inside the refrigeration room, and the refrigeration time of the unit.

[0020] The defrosting operation control module is used to control the compressor to operate at a frequency switching of a four-way valve when the variable frequency refrigeration unit meets the defrosting conditions, and to control the four-way valve to switch to the defrosting direction after the compressor operates at the frequency switching of the four-way valve; to determine the optimal defrosting operation frequency according to the ambient temperature and the temperature inside the refrigeration unit, and to control the compressor to perform defrosting operation based on the optimal defrosting operation frequency and the allowable operating frequency range of the compressor.

[0021] The low-pressure frequency limiting control module is used to perform segmented low-pressure frequency limiting control on the compressor according to the suction pressure during the defrosting operation.

[0022] The dripping control module is used to control the variable frequency refrigeration unit to enter dripping mode when the coil temperature is higher than the defrost exit temperature threshold, control the compressor to run at a dripping frequency, and adjust the operating frequency of the compressor according to the coil temperature.

[0023] The state switching module is used to maintain the compressor's current operating frequency before the end of the dripping mode when the dripping mode operation time reaches or exceeds the preset dripping operation time, and to control the four-way valve to switch to the refrigeration direction; when the temperature inside the refrigeration chamber is greater than or equal to the sum of the preset refrigeration temperature setting temperature and the temperature control accuracy, the variable frequency refrigeration unit is controlled to continue refrigeration operation; when the temperature inside the refrigeration chamber is less than the sum of the refrigeration temperature setting temperature and the temperature control accuracy, the variable frequency refrigeration unit is controlled to enter the shutdown standby state.

[0024] A third aspect of the present invention provides a variable frequency refrigeration unit, including a compressor, an oil separator, a four-way valve, a condenser, an electronic expansion valve, a cooler, a vapor-liquid separator, a suction pressure sensor, a condenser fan, an ambient temperature sensor, a storage temperature and humidity sensor, a coil temperature detection device, and the aforementioned hot refrigerant defrosting control system.

[0025] The compressor is a variable frequency compressor.

[0026] The hot-fluorine defrosting control system is connected to the compressor, the four-way valve, the electronic expansion valve, the air cooler, and the condenser, and is used to output control commands to the compressor, the four-way valve, the electronic expansion valve, the air cooler, and the condenser.

[0027] The hot fluorine defrosting control system is also connected to the suction pressure sensor, the ambient temperature sensor, the storage temperature and humidity sensor, and the coil temperature detection device to obtain suction pressure, ambient temperature, storage temperature, storage humidity, and coil temperature.

[0028] Preferably, the compressor's exhaust port is connected to the four-way valve via the oil separator, the four-way valve is connected to the condenser, the air cooler, and the vapor-liquid separator respectively, the condenser is connected to the air cooler via the electronic expansion valve, and the vapor-liquid separator is connected to the compressor's intake port.

[0029] The suction pressure sensor is installed on the suction line between the vapor-liquid separator and the compressor.

[0030] The ambient temperature sensor is located on the side of the condenser fan and is used to detect the ambient temperature.

[0031] The temperature and humidity sensor is located on the return air side of the air cooler and is used to detect the temperature and humidity inside the warehouse.

[0032] The coil temperature detection device is used to detect the coil temperature of the air cooler.

[0033] Compared with the prior art, the beneficial effects of the present invention include at least the following: 1. It should be noted that this invention determines defrosting conditions by combining the temperature and humidity inside the refrigeration unit and the refrigeration time duration, and coordinates the defrosting operation frequency, segmented low-pressure frequency limiting, dripping operation, and the switching from defrosting to refrigeration state. This solves the problem that the control of each stage in the existing hot refrigerant defrosting process is fragmented and difficult to adapt to actual operating conditions. It realizes continuous control of the entire hot refrigerant defrosting process of the variable frequency refrigeration unit, and improves the adaptability and operational stability of the defrosting control.

[0034] 2. It should be noted that this invention establishes a correspondence between temperature range, humidity range, minimum compressor cooling time operation frequency, and cooling time duration threshold, and accumulates the unit's cooling time duration only when the compressor operating frequency is greater than the corresponding minimum compressor cooling time operation frequency. This solves the problem of premature or insufficient defrosting when using only a fixed time or a single temperature parameter to determine defrosting demand, and enables the determination of defrosting timing by combining the temperature and humidity inside the cold storage and the actual operating status of the compressor.

[0035] 3. It should be noted that this invention compensates for the defrosting reference operating frequency based on the ambient temperature and the temperature inside the storage chamber, and limits the optimal defrosting operating frequency according to the allowable operating frequency range of the compressor. This solves the problems of mismatch between the compressor operating frequency and the actual defrosting load when using a fixed defrosting operating frequency, and the calculated frequency may exceed the compressor's executable range. It achieves adaptive adjustment of the defrosting operating frequency based on the operating conditions, which is beneficial to improving defrosting efficiency and reducing unnecessary defrosting energy consumption.

[0036] 4. It should be noted that this invention limits the compressor’s maximum operating frequency in segments according to the different pressure ranges of the suction pressure, and prioritizes segmented low-pressure frequency limiting control over the optimal defrosting operating frequency control. This solves the problem that the compressor may still operate at a high frequency when the suction pressure decreases during the defrosting process, and realizes graded frequency limiting control for low suction pressure conditions. This can reduce the risk of the suction pressure continuing to decrease and triggering compressor protection, and improve the stability of defrosting operation.

[0037] 5. It should be noted that the present invention solves the problem that the compressor still maintains a low frequency limit for a long time after the suction pressure recovers and that short-term fluctuations in suction pressure may cause frequent changes in the frequency limit state. This is achieved by adjusting the maximum operating frequency limit of the compressor or releasing the segmented low-pressure frequency limit control after the suction pressure recovers to the corresponding pressure range and continues to reach the preset recovery time.

[0038] 6. It should be noted that this invention solves the problem of lack of coordinated adjustment of refrigerant flow, fan status and compressor operating frequency during the dripping stage by keeping the four-way valve in the defrosting direction in dripping mode, adjusting the opening of the electronic expansion valve according to the suction superheat, controlling the evaporator to shut down and the condenser to run at maximum speed, and reducing the compressor operating frequency according to the coil temperature. This achieves control over the heat exchange intensity and heat input during the dripping stage, provides suitable operating conditions for defrosting water discharge, and reduces the energy consumption generated by the continuous high-frequency operation of the compressor.

[0039] 7. It should be noted that this invention starts accumulating the running time of the dripping mode when the self-converting frequency refrigeration unit enters the dripping mode, and after the running time reaches or exceeds the preset dripping running time, it maintains the current operating frequency of the compressor before the end of the dripping mode and switches the four-way valve. This solves the problems of the lack of a clear starting point for dripping operation and the need to stop the compressor during the transition from defrosting to refrigeration. It realizes dripping operation according to the preset time and non-stop switching from defrosting mode to refrigeration mode, reducing the number of compressor shutdowns and restarts and temperature fluctuations in the refrigeration unit.

[0040] 8. It should be noted that this invention solves the problem of scattered control functions and lack of coordination between control logics in each stage of hot fluorine defrosting by setting a parameter acquisition and timing module, a defrosting judgment module, a defrosting operation control module, a low-pressure frequency limiting control module, a dripping control module, and a state switching module. It realizes the modular configuration of defrosting demand judgment, defrosting frequency control, low-pressure frequency limiting, dripping control, and state switching functions, and improves the control coordination of the hot fluorine defrosting control system.

[0041] 9. It should be noted that by connecting the hot fluorine defrosting control system to the compressor, four-way valve, electronic expansion valve, air cooler, condenser fan, and various detection components, this invention solves the problem of unclear correspondence between the objects of operating parameter acquisition and the objects of defrosting control command execution. It realizes centralized acquisition of suction pressure, ambient temperature, temperature and humidity inside the storage room, and coil temperature, as well as coordinated control of compressor operating frequency, four-way valve direction, electronic expansion valve opening, and fan operating status, providing a unit structure foundation for implementing the hot fluorine defrosting control method.

[0042] 10. It should be noted that this invention solves the problem of refrigerant flow switching between refrigeration and hot defrosting operations in variable frequency refrigeration units by forming a refrigerant circulation loop with the compressor, oil separator, four-way valve, condenser, electronic expansion valve, air cooler, and vapor-liquid separator, and by switching the refrigerant flow direction through the four-way valve. This enables the same refrigerant circulation loop to switch between refrigeration and defrosting modes. At the same time, by setting the suction pressure sensor, ambient temperature sensor, storage temperature and humidity sensor, and coil temperature detection device in the corresponding detection positions, it is possible to obtain detection data reflecting the unit's suction pressure, environmental conditions, storage environment, and coil status, providing a data basis for defrosting condition judgment, defrosting operation frequency adjustment, and operation mode switching. Attached Figure Description

[0043] Figure 1 This is a schematic flowchart of the thermal defrosting control method of the present invention.

[0044] Figure 2 This is a system schematic diagram of the variable frequency refrigeration unit of the present invention, wherein 1 is a compressor, 2 is an oil separator, 3 is a four-way valve, 4 is a condenser, 5 is an electronic expansion valve, 6 is a fan, 7 is a vapor-liquid separator, and 8 is a suction pressure sensor. Detailed Implementation

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

[0046] In the description of this invention, unless otherwise explicitly specified and limited, the terms "connection," "connection," etc., should be interpreted broadly. For example, they can refer to a fixed connection or a detachable connection; a direct connection or an indirect connection via intermediate components; a mechanical connection, an electrical connection, or a communication connection. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0047] Example 1 This embodiment provides a hot refrigerant defrosting control method applied to a variable frequency refrigeration unit. The variable frequency refrigeration unit includes a compressor 1, a four-way valve 3, and a suction pressure sensor 8. Figure 1 As shown, the thermal defrosting control method includes the following steps.

[0048] Step 1: Obtain the temperature inside the storage room, humidity inside the storage room, ambient temperature, coil temperature, operating frequency of compressor 1, and suction pressure detected by suction pressure sensor 8, and calculate the unit's cooling time based on the operating frequency of compressor 1.

[0049] Specifically, during the refrigeration operation of the variable frequency refrigeration unit, the following parameters are continuously acquired: the temperature Tin inside the refrigeration chamber, the humidity ψin inside the refrigeration chamber, the ambient temperature Tout, the coil temperature Tpg, the operating frequency F(n) of the compressor 1, and the suction pressure Psu detected by the suction pressure sensor 8.

[0050] Preferably, the temperature Tin and humidity ψin inside the storage are detected by a storage temperature and humidity sensor installed on the return air side of the evaporator 6, the ambient temperature Tout is detected by an ambient temperature sensor installed on the condenser fan side, the coil temperature Tpg is detected by a coil temperature detection device, and the suction pressure Psu is detected by a suction pressure sensor 8.

[0051] More preferably, the unit cooling time tc is the cumulative running time when the operating frequency F(n) of compressor 1 is greater than the minimum cooling time operating frequency F(js) of compressor 1 within the current cooling operation cycle.

[0052] When the operating frequency F(n) of compressor 1 is greater than the minimum operating frequency F(js) for compressor cooling, the running time of compressor 1 is accumulated. When the operating frequency F(n) of compressor 1 is not greater than the minimum operating frequency F(js) for compressor cooling, the accumulation of the unit cooling time tc is paused, and the already accumulated unit cooling time tc is retained. When the operating frequency F(n) of compressor 1 is again greater than the minimum operating frequency F(js) for compressor cooling, the accumulation continues based on the already accumulated unit cooling time tc.

[0053] The minimum operating frequency F(js) of the compressor refrigeration is determined based on the temperature range of the temperature Tin inside the warehouse and the humidity range of the humidity ψin inside the warehouse.

[0054] Step 2: Determine whether the variable frequency refrigeration unit meets the defrosting conditions based on the temperature and humidity inside the warehouse and the refrigeration time of the unit.

[0055] Preferably, a correspondence is established in advance between temperature range, humidity range, minimum operating frequency F(js) of compressor cooling, and cooling time duration threshold.

[0056] When the temperature inside the refrigeration unit, Tin, is higher than the preset defrosting temperature limit, the variable frequency refrigeration unit is determined not to meet the defrosting conditions.

[0057] When the temperature Tin inside the storage room is not higher than the preset defrost temperature upper limit, the corresponding minimum compressor refrigeration timing operation frequency F(js) and refrigeration timing duration threshold are selected from the corresponding relationship based on the temperature range where the temperature Tin inside the storage room is located and the humidity range where the humidity ψin inside the storage room is located.

[0058] When the operating frequency F(n) of compressor 1 is greater than the selected minimum operating frequency F(js) for compressor cooling, the running time of compressor 1 is accumulated to obtain the unit cooling time tc. When the unit cooling time tc is greater than the selected cooling time threshold, the variable frequency refrigeration unit is determined to meet the defrosting condition.

[0059] For example, the preset defrost temperature upper limit can be 10℃, and the correspondence between the temperature range, humidity range, minimum compressor cooling timer operating frequency F(js), and cooling timer duration threshold can be set according to the following table: Table 1. Defrosting Parameters for Different Temperature and Humidity Ranges in the Storage Room

[0060] For example, when 0℃ < Tin ≤ 10℃ and ψin < 80%, the selected minimum operating frequency F(js) for compressor refrigeration is 50Hz, and the refrigeration time threshold is 3h. When compressor 1 runs at an operating frequency greater than 50Hz for more than 3 hours, the variable frequency refrigeration unit is determined to meet the defrosting conditions.

[0061] When 0℃<Tin≤10℃ and ψin≥90%, the minimum operating frequency F(js) for compressor refrigeration is selected as 40Hz, and the refrigeration time threshold is 1h. When compressor 1 runs at a frequency greater than 40Hz for more than 1 hour, the variable frequency refrigeration unit is deemed to meet the defrosting conditions.

[0062] Specifically, when the humidity inside the warehouse is high, the evaporator frosts relatively quickly, so a relatively short cooling time threshold can be set; when the temperature or humidity inside the warehouse is low, different minimum compressor cooling time operating frequencies F(js) and cooling time thresholds can be set according to the corresponding operating conditions.

[0063] It should be noted that this invention solves the problem of over-defrosting or under-defrosting when defrosting demand is judged solely based on a fixed time or a single temperature by pre-establishing the correspondence between the temperature range, humidity range, minimum timing operation frequency of the compressor, and the threshold for the duration of the defrosting time. It also accumulates the operating time when the compressor operating frequency is higher than the corresponding minimum timing operation frequency. This invention enables indirect judgment of the degree of evaporator frost formation and accurate identification of the defrosting timing.

[0064] Step 3: When the variable frequency refrigeration unit meets the defrosting conditions, control the compressor 1 to switch the operating frequency using the four-way valve, and control the four-way valve 3 to switch to the defrosting direction; determine the optimal defrosting operating frequency based on the ambient temperature and the temperature inside the refrigeration unit, and control the compressor 1 to perform defrosting operation based on the optimal defrosting operating frequency and the allowable operating frequency range of the compressor 1.

[0065] Specifically, when the variable frequency refrigeration unit meets the defrosting conditions, the operating frequency of compressor 1 is adjusted to the four-way valve switching operating frequency F(qh), and compressor 1 is controlled to continuously operate at the four-way valve switching operating frequency F(qh) for a preset stable switching time. After the preset stable switching time is reached, the four-way valve 3 is controlled to switch from the refrigeration direction to the defrosting direction.

[0066] Preferably, the four-way valve switching operating frequency F(qh) is the operating frequency used by the compressor 1 before the four-way valve 3 switches to the defrosting direction, and its value range is 30Hz to 40Hz. The preset switching stabilization time is 30s, so that the high and low pressure difference of the variable frequency refrigeration unit is within the range suitable for the switching of the four-way valve 3.

[0067] Specifically, during the switching of the four-way valve 3, the air cooler 6, the condenser fan, and the electronic expansion valve 5 do not perform any additional adjustment actions.

[0068] After the four-way valve 3 is switched to the defrosting direction, the heat exchanger inside the air cooler 6 acts as the condensing side, and the outdoor condenser 4 acts as the evaporating side. The high-temperature refrigerant flows through the heat exchanger inside the air cooler 6 to melt the frost layer on its surface.

[0069] Preferably, the optimal defrosting operating frequency F(de) is determined based on the ambient temperature Tout and the internal temperature Tin, including: The product of ambient temperature Tout and ambient temperature compensation coefficient C1 is determined as the ambient temperature compensation term, and the product of indoor temperature Tin and indoor temperature compensation coefficient C2 is determined as the indoor temperature compensation term. The optimal defrost operating frequency F(de) is obtained by subtracting the ambient temperature compensation term and the warehouse temperature compensation term from the defrost baseline operating frequency F(de1), i.e.: F(de)=F(de1)-C1×Tout-C2×Tin.

[0070] Where F(de1) is the defrosting reference operating frequency in Hz; C1 is the ambient temperature compensation coefficient, and C2 is the storage temperature compensation coefficient. The units of C1 and C2 are both Hz / ℃, so that the units of the ambient temperature compensation item and the storage temperature compensation item are both Hz.

[0071] Preferably, the defrosting reference operating frequency F(de1) is determined based on the performance characteristics of compressor 1 and the test results, and its value range is 40Hz to 60Hz.

[0072] Preferably, the ambient temperature compensation coefficient C1 and the warehouse temperature compensation coefficient C2 are determined based on the test results of different models, and the values ​​of C1 and C2 are both in the range of 0.1Hz / ℃~0.3Hz / ℃.

[0073] For example, the defrosting reference operating frequency F(de1) can be the compressor defrosting operating frequency determined under a preset reference operating condition. For instance, the preset reference operating condition can be the condition where both the ambient temperature Tout and the internal temperature Tin are 0°C.

[0074] Specifically, during the defrosting operation, the higher the temperature Tin inside the storage room, the lower the heat required for defrosting, and the lower the defrosting operation frequency required by compressor 1; the higher the ambient temperature Tout, the faster the outdoor heat exchanger absorbs heat, and the lower the defrosting operation frequency required by compressor 1.

[0075] More preferably, based on the optimal defrosting operating frequency F(de) and the allowable operating frequency range of compressor 1, the compressor 1 is controlled to perform defrosting operation, including: When the optimal defrosting operating frequency F(de) is higher than the maximum allowable operating frequency of compressor 1, compressor 1 is controlled to perform defrosting operation at the maximum allowable operating frequency; When the optimal defrosting operating frequency F(de) is lower than the minimum allowable operating frequency of compressor 1, compressor 1 is controlled to perform defrosting operation according to the minimum allowable operating frequency; When the optimal defrosting operating frequency F(de) is within the allowable operating frequency range of compressor 1, compressor 1 is controlled to perform defrosting operation according to the optimal defrosting operating frequency F(de).

[0076] It should be noted that this invention compensates for the defrosting reference operating frequency based on the ambient temperature and the temperature inside the defrost to determine the optimal defrosting operating frequency that is suitable for the current operating conditions. It also limits the actual defrosting operating frequency based on the allowable operating frequency range of the compressor. This solves the problem of mismatch between the compressor operating frequency and the actual defrosting load when a fixed defrosting frequency is used, and achieves improved defrosting efficiency and reduced defrosting energy consumption while ensuring that the compressor operating frequency is executable.

[0077] Step 4: During the defrosting process, the compressor 1 is subjected to segmented low-pressure frequency limiting control based on the suction pressure.

[0078] Preferably, a first pressure threshold P1, a second pressure threshold P2 and a third pressure threshold P3 are set, and P1 > P2 > P3; a first frequency threshold F(1), a second frequency threshold F(2) and a third frequency threshold F(3) are set, and F(1) > F(2) > F(3).

[0079] Specifically, when P2≤Psu<P1, the maximum operating frequency of compressor 1 is limited to not exceed the first frequency threshold F(1); When P3≤Psu<P2, the maximum operating frequency of compressor 1 is limited to not exceed the second frequency threshold F(2); When Psu < P3, the maximum operating frequency of compressor 1 is limited to not exceed the third frequency threshold F(3).

[0080] For example, the first pressure threshold P1 can be 0.4 MPa, the second pressure threshold P2 can be 0.3 MPa, and the third pressure threshold P3 can be 0.2 MPa; the first frequency threshold F(1) can be 50 Hz, the second frequency threshold F(2) can be 40 Hz, and the third frequency threshold F(3) can be 30 Hz.

[0081] More preferably, the segmented low-pressure frequency limiting control has a higher priority than the control of compressor 1 based on the optimal defrost operating frequency F(de). When the optimal defrost operating frequency F(de) is higher than the frequency threshold corresponding to the current suction pressure range, the frequency threshold is used as the maximum operating frequency limit of compressor 1.

[0082] Specifically, when the segmented low-pressure frequency limiting control is not triggered, compressor 1 operates at the defrosting target frequency determined in step 3.

[0083] When segmented low-pressure frequency limiting control is triggered, the defrosting target frequency determined in step 3 is compared with the frequency threshold corresponding to the current pressure range of the suction pressure Psu. When the defrosting target frequency is not higher than the corresponding frequency threshold, the compressor 1 still operates according to the defrosting target frequency; when the defrosting target frequency is higher than the corresponding frequency threshold, the compressor 1 operates according to the corresponding frequency threshold.

[0084] It should be noted that this invention achieves graded frequency limiting control for low suction pressure conditions by progressively limiting the maximum operating frequency of compressor 1 according to different pressure ranges of suction pressure. This reduces the risk of further decrease in suction pressure, abnormal defrosting operation, and triggering compressor protection, thereby improving the operational stability of the hot refrigerant defrosting process.

[0085] More preferably, the segmented low-voltage frequency limiting control further includes low-voltage frequency limiting recovery control.

[0086] Specifically, when the suction pressure Psu rises from less than the third pressure threshold P3 to P3≤Psu<P2 and remains in this pressure range for a preset recovery time t1, the limit of the highest operating frequency of compressor 1 is adjusted from the third frequency threshold F(3) to the second frequency threshold F(2).

[0087] When the suction pressure Psu rises further to P2≤Psu<P1 and remains in this pressure range for a preset recovery time t1, the limit of the highest operating frequency of compressor 1 is adjusted to the first frequency threshold F(1).

[0088] When the suction pressure Psu rises to Psu≥P1 and remains within the pressure range of Psu≥P1 for a preset recovery time t1, the segmented low-pressure frequency limiting control is released, allowing compressor 1 to resume defrosting operation at the frequency determined in step 3.

[0089] Preferably, the preset recovery time t1 ranges from 3s to 30s.

[0090] More preferably, when the suction pressure Psu is lower than the third pressure threshold P3, and the compressor 1 operates at a limited frequency according to the third frequency threshold F(3), and the suction pressure Psu still has not recovered, a low pressure alarm message is output.

[0091] When the suction pressure Psu further decreases below the preset low-pressure protection value, the low-pressure protection control of the variable frequency refrigeration unit is triggered. The preset low-pressure protection value is lower than the third pressure threshold P3. The low-pressure protection action and the low-pressure protection release or reset method are executed according to the protection control strategy preset by the variable frequency refrigeration unit.

[0092] It should be noted that this invention solves the problem of frequent switching of frequency limiting levels caused by short-term fluctuations in suction pressure by gradually increasing the maximum operating frequency limit of the compressor or releasing the segmented low-pressure frequency limiting control after the suction pressure recovers to the corresponding pressure range and continues to reach the preset recovery time. This achieves a smooth recovery of the compressor's operating frequency and improves the stability of defrosting operation control.

[0093] Step 5: When the coil temperature is higher than the defrost exit temperature threshold, control the variable frequency refrigeration unit to enter the dripping mode, control compressor 1 to run at the dripping frequency, and adjust the operating frequency of compressor 1 according to the coil temperature.

[0094] Specifically, during defrosting operation, the coil temperature Tpg is monitored in real time. When Tpg > Tdt, the inverter chiller unit is determined to have met the defrosting exit condition, and the inverter chiller unit is controlled to enter dripping mode. Here, Tdt is the defrosting exit temperature threshold.

[0095] Preferably, after the variable frequency refrigeration unit enters the dripping mode, the four-way valve 3 is controlled to maintain the defrosting direction, the opening of the electronic expansion valve 5 is adjusted according to the suction superheat of the variable frequency refrigeration unit, the air cooler 6 is controlled to remain closed, and the condenser fan is controlled to run at its maximum speed. More preferably, the opening of the electronic expansion valve 5 is dynamically adjusted using a proportional-integral-derivative control method according to the suction superheat.

[0096] Specifically, after entering dripping mode, compressor 1 is controlled to operate at a dripping frequency F(ds). The dripping frequency F(ds) is determined based on the model of the variable frequency refrigeration unit and the test results.

[0097] For example, the dripping frequency F(ds) ranges from 20Hz to 40Hz.

[0098] When compressor 1 operates at a dripping frequency F(ds), the discharge temperature and discharge pressure of compressor 1 decrease, and the temperature of the gaseous refrigerant entering the corresponding heat exchanger of the air cooler 6 decreases accordingly, thereby reducing the heat exchange intensity on the surface of the heat exchanger.

[0099] Preferably, the coil temperature Tpg is continuously monitored in drip mode, and the operating frequency of compressor 1 is adjusted according to the coil temperature Tpg.

[0100] Specifically, when the coil temperature Tpg remains higher than the sum of the defrost exit temperature threshold Tdt and the temperature compensation value C3 for a preset judgment period, the operating frequency of compressor 1 is adjusted to the difference between the dripping operating frequency F(ds) and the preset frequency reduction value C4, that is: F(n) = F(ds) - C4 Where F(n) is the adjusted compressor operating frequency, C3 is the temperature compensation value, and C4 is the preset frequency reduction value.

[0101] When the compressor operating frequency F(n) calculated according to F(n)=F(ds)-C4 is not lower than the minimum allowable operating frequency of compressor 1, compressor 1 is controlled to operate at the calculated compressor operating frequency F(n); when the calculated compressor operating frequency F(n) is lower than the minimum allowable operating frequency of compressor 1, compressor 1 is controlled to operate at the minimum allowable operating frequency.

[0102] During the coil temperature judgment process, the preset frequency reduction value C4 is subtracted from the dripping operating frequency F(ds) each time. The preset frequency reduction value C4 is not continuously subtracted from the previous frequency reduction result to avoid the compressor operating frequency decreasing one after another.

[0103] In this embodiment, after the frequency reduction control is triggered, the compressor 1 continues to operate at the reduced operating frequency until the dripping mode ends.

[0104] For example, the temperature compensation value C3 ranges from 1℃ to 10℃, and the preset frequency reduction value C4 ranges from 5Hz to 10Hz.

[0105] Preferably, the preset judgment time is determined according to the model of the variable frequency refrigeration unit, the temperature inside the refrigeration unit or the ambient temperature, and its value ranges from 3s to 30s, preferably 10s.

[0106] It should be noted that the present invention controls the compressor 1 to operate at a dripping frequency after defrosting ends, and further reduces the operating frequency of the compressor 1 when the coil temperature remains high. This achieves the regulation of the heat exchange intensity and heat input of the coil during the dripping stage, which can provide suitable temperature conditions for defrosting water discharge, reduce the risk of re-icing at the water receiving pan or chassis, and reduce the energy consumption generated by the compressor's continuous high-frequency operation.

[0107] Step 6: When the running time of the dripping mode reaches the preset dripping running time, while the compressor 1 continues to run, control the four-way valve 3 to switch to the refrigeration direction; control the variable frequency refrigeration unit to continue refrigeration operation or enter the shutdown standby state according to the temperature inside the warehouse.

[0108] Specifically, the running time of the dripping mode is accumulated from the moment the variable frequency chiller unit enters the dripping mode.

[0109] During the operation of the dripping mode, when the operating frequency of compressor 1 is adjusted, the running time of the dripping mode continues to accumulate, and the timing will not restart when compressor 1 is adjusted from the dripping operating frequency F(ds) to the reduced operating frequency.

[0110] When the running time of the dripping mode reaches or exceeds the preset dripping running time t(ds), the compressor 1 maintains the current operating frequency before the end of the dripping mode, and controls the four-way valve 3 to switch from the defrosting direction to the refrigeration direction, so that the variable frequency refrigeration unit exits the dripping mode and resumes the refrigeration operation logic.

[0111] Wherein, when no further frequency reduction control is triggered, the current operating frequency is the dripping operating frequency F(ds); when further frequency reduction control has been triggered, the current operating frequency is the frequency after frequency reduction determined according to the aforementioned minimum operating frequency limit.

[0112] Preferably, the preset dripping time t(ds) is determined based on the model of the variable frequency refrigeration unit, the temperature inside the refrigeration unit, the ambient temperature, and the structure of the evaporator.

[0113] For example, the preset dripping time t(ds) ranges from 1 min to 10 min.

[0114] After the four-way valve 3 switches to the refrigeration direction, it controls the variable frequency refrigeration unit to continue refrigeration operation or enter the shutdown standby state based on the real-time internal temperature Tin, the set internal temperature Ts, and the temperature control accuracy ΔT.

[0115] Specifically, when Tin≥Ts+ΔT, it indicates that the cold storage still has refrigeration demand, and the variable frequency refrigeration unit is controlled to continue refrigeration operation.

[0116] When Tin < Ts + ΔT, it indicates that the temperature inside the refrigeration unit has reached the set control range, and the variable frequency refrigeration unit is controlled to enter the shutdown standby state.

[0117] In this embodiment, after completing one defrost operation and exiting the dripping mode, the unit cooling time tc used for judging the defrost conditions is reset to zero.

[0118] When the variable frequency chiller unit continues to run in cooling mode, the unit's cooling time tc for the next defrost cycle is recalculated from the moment the four-way valve 3 switches to the cooling direction and resumes cooling operation. When the variable frequency chiller unit enters the standby state, the unit's cooling time tc for the next defrost cycle is recalculated from the moment the variable frequency chiller unit starts running in cooling mode.

[0119] For example, the temperature control accuracy ΔT can be 1℃.

[0120] It should be noted that this invention starts accumulating the running time of the dripping mode when the self-converting frequency refrigeration unit enters the dripping mode, and maintains the compressor operation and switches the four-way valve after reaching the preset dripping running time. This solves the problems of insufficient defrosting water due to too short a dripping time or heat and energy waste due to too long a dripping time. It achieves accurate control of the dripping time and non-stop switching from defrosting mode to refrigeration mode, reducing the number of compressor shutdowns and restarts and temperature fluctuations inside the refrigeration unit.

[0121] Example 2 This embodiment provides a hot-fluid defrosting control system for implementing the hot-fluid defrosting control method described in Embodiment 1. The hot-fluid defrosting control system includes a parameter acquisition and timing module, a defrosting judgment module, a defrosting operation control module, a low-pressure frequency limiting control module, a dripping water control module, and a state switching module.

[0122] The parameter acquisition and timing module is used to acquire the internal temperature Tin, internal humidity ψin, ambient temperature Tout, coil temperature Tpg, operating frequency F(n) of compressor 1, and suction pressure Psu detected by suction pressure sensor 8, and to calculate the unit cooling time tc based on the operating frequency F(n) of compressor 1.

[0123] Preferably, the parameter acquisition and timing module receives the storage temperature Tin and storage humidity ψin detected by the storage temperature and humidity sensor, the ambient temperature Tout detected by the ambient temperature sensor, the coil temperature Tpg detected by the coil temperature detection device, and the suction pressure Psu detected by the suction pressure sensor 8.

[0124] More preferably, when the operating frequency F(n) of compressor 1 is greater than the minimum timing operating frequency F(js) of compressor refrigeration, the parameter acquisition and timing module accumulates the running time of compressor 1 to obtain the unit refrigeration timing duration tc.

[0125] When the operating frequency F(n) of compressor 1 is not greater than the minimum operating frequency F(js) of compressor cooling, the parameter acquisition and timing module pauses the accumulation of unit cooling time tc and retains the already accumulated unit cooling time tc.

[0126] The defrosting judgment module is used to determine whether the variable frequency refrigeration unit meets the defrosting conditions based on the temperature Tin inside the refrigeration unit, the humidity ψin inside the refrigeration unit, and the refrigeration time tc of the unit.

[0127] Preferably, the defrost judgment module pre-stores the correspondence between temperature range, humidity range, minimum compressor cooling timing operation frequency F(js), and cooling timing duration threshold.

[0128] Specifically, when the temperature Tin inside the refrigeration unit is higher than the preset defrosting temperature limit, the defrosting judgment module determines that the variable frequency refrigeration unit does not meet the defrosting conditions.

[0129] When the temperature Tin inside the storage room is not higher than the preset defrost temperature upper limit, the defrost judgment module selects the corresponding minimum compressor refrigeration timing operation frequency F(js) and refrigeration timing duration threshold from the corresponding relationship based on the temperature range where the temperature Tin inside the storage room is located and the humidity range where the humidity ψin inside the storage room is located.

[0130] When the unit's cooling time duration tc is greater than the cooling time duration threshold, the defrosting judgment module determines that the variable frequency refrigeration unit meets the defrosting conditions and sends the corresponding defrosting trigger signal to the defrosting operation control module.

[0131] The defrosting operation control module controls the compressor 1 to continuously operate at the four-way valve switching frequency F(qh) for a preset stable switching time, and after reaching the preset stable switching time, controls the four-way valve 3 to switch to the defrosting direction.

[0132] Preferably, the defrosting operation control module controls the compressor 1 to continuously operate at the four-way valve switching frequency F(qh) for a preset stable switching time, so that the high and low pressure difference of the variable frequency refrigeration unit is within a range suitable for the switching of the four-way valve 3.

[0133] More preferably, the defrosting operation control module determines the optimal defrosting operation frequency F(de) based on the ambient temperature Tout and the temperature Tin inside the storage room.

[0134] Specifically, the defrosting operation control module determines the ambient temperature compensation term by multiplying the ambient temperature Tout by the ambient temperature compensation coefficient C1, and determines the internal temperature compensation term by multiplying the internal temperature Tin by the internal temperature compensation coefficient C2, and determines the optimal defrosting operation frequency F(de) according to the following formula: F(de)=F(de1)-C1×Tout-C2×Tin.

[0135] Where F(de1) is the defrosting reference operating frequency, in Hz; C1 is the ambient temperature compensation coefficient, and C2 is the storage temperature compensation coefficient. The units of C1 and C2 are both Hz / ℃.

[0136] The defrosting operation control module is also used to control the compressor 1 to perform defrosting operation based on the optimal defrosting operation frequency F(de) and the allowable operating frequency range of the compressor 1.

[0137] When the optimal defrosting operating frequency F(de) is higher than the maximum allowable operating frequency of compressor 1, the defrosting operation control module controls compressor 1 to perform defrosting operation according to the maximum allowable operating frequency.

[0138] When the optimal defrosting operating frequency F(de) is lower than the minimum allowable operating frequency of compressor 1, the defrosting operation control module controls compressor 1 to perform defrosting operation according to the minimum allowable operating frequency.

[0139] When the optimal defrosting operating frequency F(de) is within the allowable operating frequency range of compressor 1, the defrosting operation control module controls compressor 1 to perform defrosting operation according to the optimal defrosting operating frequency F(de).

[0140] The low-pressure frequency limiting control module is used to perform segmented low-pressure frequency limiting control on compressor 1 according to the suction pressure Psu during defrosting operation.

[0141] Preferably, the low-pressure frequency limiting control module is preset with a first pressure threshold P1, a second pressure threshold P2 and a third pressure threshold P3, and P1 > P2 > P3; it is also preset with a first frequency threshold F(1), a second frequency threshold F(2) and a third frequency threshold F(3), and F(1) > F(2) > F(3).

[0142] Specifically, when P2≤Psu<P1, the low-pressure frequency limiting control module limits the maximum operating frequency of compressor 1 to no higher than the first frequency threshold F(1).

[0143] When P3≤Psu<P2, the low-pressure frequency limiting control module limits the highest operating frequency of compressor 1 to no higher than the second frequency threshold F(2).

[0144] When Psu < P3, the low-pressure frequency limiting control module limits the highest operating frequency of compressor 1 to no higher than the third frequency threshold F(3).

[0145] More preferably, the control priority of the low-pressure frequency limiting control module is higher than the control implemented by the defrost operation control module based on the optimal defrost operation frequency F(de). When the optimal defrost operation frequency F(de) is higher than the frequency threshold corresponding to the current pressure range, the frequency threshold is used as the maximum operating frequency limit of compressor 1.

[0146] More preferably, the low-voltage frequency limiting control module is also used to implement low-voltage frequency limiting recovery control.

[0147] When the suction pressure Psu rises from less than the third pressure threshold P3 to P3≤Psu<P2 and remains in this pressure range for a preset recovery time t1, the low-pressure frequency limiting control module adjusts the limit of the highest operating frequency of compressor 1 from the third frequency threshold F(3) to the second frequency threshold F(2).

[0148] When the suction pressure Psu further rises to P2≤Psu<P1 and remains in this pressure range for a preset recovery time t1, the low-pressure frequency limiting control module adjusts the limit of the highest operating frequency of compressor 1 to the first frequency threshold F(1).

[0149] When the inhalation pressure Psu rises to Psu≥P1 and remains within the pressure range of Psu≥P1 for a preset recovery time t1, the low-pressure frequency limiting control module releases the segmented low-pressure frequency limiting control.

[0150] Optionally, the low-pressure frequency limiting control module is also used to output low-pressure alarm information when the suction pressure Psu has not recovered after the compressor 1 operates at the third frequency threshold F (3), and to trigger the low-pressure protection control preset in the variable frequency refrigeration unit when the suction pressure Psu is further reduced to below the preset low-pressure protection value.

[0151] When the segmented low-pressure frequency limiting control is triggered, the low-pressure frequency limiting control module compares the defrosting target frequency determined by the defrosting operation control module with the frequency threshold corresponding to the current pressure range of the suction pressure Psu, and uses the smaller of the two values ​​as the target operating frequency of the compressor 1.

[0152] The dripping control module is used to control the variable frequency refrigeration unit to enter the dripping mode when the coil temperature Tpg is higher than the defrost exit temperature threshold Tdt, control the compressor 1 to run at the dripping operating frequency F(ds), and adjust the operating frequency of the compressor 1 according to the coil temperature Tpg.

[0153] Preferably, after the variable frequency refrigeration unit enters the dripping mode, the dripping control module controls the four-way valve 3 to maintain the defrosting direction, adjusts the opening of the electronic expansion valve 5 according to the suction superheat of the variable frequency refrigeration unit, controls the air cooler 6 to remain closed, and controls the condenser fan to run at its maximum speed.

[0154] More preferably, the drip control module dynamically adjusts the opening of the electronic expansion valve 5 according to the intake superheat using a proportional-integral-derivative control method.

[0155] Specifically, when the coil temperature Tpg remains higher than the sum of the defrost exit temperature threshold Tdt and the temperature compensation value C3 for a preset judgment period, the dripping control module determines the target frequency for frequency reduction based on the difference between the dripping operating frequency F(ds) and the preset frequency reduction value C4. When the target frequency for frequency reduction is not lower than the minimum allowable operating frequency of compressor 1, compressor 1 is controlled to operate at the target frequency for frequency reduction; when the target frequency for frequency reduction is lower than the minimum allowable operating frequency of compressor 1, compressor 1 is controlled to operate at the minimum allowable operating frequency.

[0156] The state switching module is used to maintain the current operating frequency of the compressor 1 before the end of the dripping mode when the running time of the dripping mode reaches or exceeds the preset dripping running time, and to control the four-way valve 3 to switch to the refrigeration direction.

[0157] Preferably, the state switching module starts accumulating the running time of the dripping mode when the variable frequency refrigeration unit enters the dripping mode; when the dripping control module adjusts the operating frequency of the compressor 1, it does not reset the running time of the dripping mode.

[0158] When the running time of the dripping mode reaches the preset dripping running time t(ds), the state switching module maintains the operation of the compressor 1 and controls the four-way valve 3 to switch from the defrosting direction to the cooling direction.

[0159] After the four-way valve 3 switches to the refrigeration direction, when the temperature Tin inside the refrigeration chamber is greater than or equal to the sum of the set temperature Ts and the temperature control accuracy ΔT, the state switching module controls the variable frequency refrigeration unit to continue refrigeration operation.

[0160] When the temperature inside the refrigeration unit Tin is less than the sum of the set temperature Ts and the temperature control accuracy ΔT, the state switching module controls the variable frequency refrigeration unit to enter a shutdown standby state.

[0161] The parameter acquisition and timing module is also used to reset the unit cooling time tc used for this defrosting condition judgment to zero after the variable frequency chiller unit completes one defrosting operation and exits the dripping mode, and to recalculate the unit cooling time tc when the next cooling operation of the variable frequency chiller unit begins.

[0162] The parameter acquisition and timing module, defrosting judgment module, defrosting operation control module, low-pressure frequency limiting control module, dripping control module, and state switching module can be configured separately or combined according to the actual control program architecture. The modules interact with each other through the detection of parameters, timing results, judgment results, and control commands.

[0163] It should be noted that this invention, by setting a parameter acquisition and timing module, a defrosting judgment module, a defrosting operation control module, a low-pressure frequency limiting control module, a dripping control module, and a state switching module, allows defrosting demand judgment, optimal defrosting frequency calculation, low-pressure frequency limiting, dripping temperature control, and operation mode switching to be executed by corresponding functional modules. This solves the problems of dispersed defrosting control functions and lack of coordination between control logics in traditional defrosting systems, realizes modular control of the entire hot-fluorine defrosting process, and improves the operational reliability and control efficiency of the control system.

[0164] Example 3 This embodiment provides a variable frequency refrigeration unit. For example... Figure 2 As shown, the variable frequency refrigeration unit includes a compressor 1, an oil separator 2, a four-way valve 3, a condenser 4, an electronic expansion valve 5, a cooler 6, a vapor-liquid separator 7, a suction pressure sensor 8, a condenser fan, an ambient temperature sensor, a storage temperature and humidity sensor, a coil temperature detection device, and the hot fluorine defrosting control system described in the aforementioned system embodiment.

[0165] Compressor 1 is a variable frequency compressor, which can change its operating frequency according to the frequency control command output by the hot fluorine defrosting control system.

[0166] The hot-air defrosting control system is connected to compressor 1, four-way valve 3, electronic expansion valve 5, air cooler 6 and condenser fan respectively, and is used to output corresponding control commands to compressor 1, four-way valve 3, electronic expansion valve 5, air cooler 6 and condenser fan.

[0167] Specifically, the hot-air defrosting control system outputs frequency control commands to compressor 1, reversing control commands to four-way valve 3, opening control commands to electronic expansion valve 5, and start / stop or speed control commands to evaporator 6 and condenser fan.

[0168] The hot fluorine defrosting control system is also connected to the suction pressure sensor 8, the ambient temperature sensor, the warehouse temperature and humidity sensor, and the coil temperature detection device to obtain suction pressure Psu, ambient temperature Tout, warehouse temperature Tin, warehouse humidity ψin, and coil temperature Tpg.

[0169] Preferably, the suction pressure sensor 8 is used to detect the suction pressure Psu of the compressor 1.

[0170] The ambient temperature sensor is used to detect the ambient temperature Tout of the environment where the condenser 4 is located.

[0171] The temperature and humidity sensor is used to detect the temperature Tin and humidity ψin inside the cold storage where the air cooler 6 is located.

[0172] The coil temperature detection device is used to detect the coil temperature Tpg of the air cooler 6.

[0173] During the normal cooling operation of the variable frequency refrigeration unit, the hot fluorine defrosting control system acquires the temperature Tin inside the refrigeration chamber, the humidity ψin inside the refrigeration chamber, the ambient temperature Tout, the coil temperature Tpg, the suction pressure Psu, and the operating frequency F(n) of compressor 1, and calculates the cooling time tc of the unit based on the operating frequency F(n) of compressor 1.

[0174] When the hot-fluid defrosting control system determines that the variable frequency refrigeration unit meets the defrosting conditions based on the temperature Tin inside the refrigeration chamber, the humidity ψin inside the refrigeration chamber, and the refrigeration time tc of the unit, the hot-fluid defrosting control system controls the compressor 1 to continuously run at the preset switching stable time by switching the operating frequency F(qh) with the four-way valve. After the preset switching stable time is reached, the control system controls the four-way valve 3 to switch the refrigerant flow direction so that the variable frequency refrigeration unit enters the defrosting operation.

[0175] During the defrosting operation, the hot fluorine defrosting control system determines the optimal defrosting operating frequency F(de) based on the ambient temperature Tout and the temperature Tin inside the storage room, and controls the operation of compressor 1 based on the optimal defrosting operating frequency F(de) and the allowable operating frequency range of compressor 1.

[0176] Meanwhile, the hot-air defrosting control system performs segmented low-pressure frequency limiting control on the highest operating frequency of compressor 1 based on the pressure range of the suction pressure Psu.

[0177] When the defrosting target frequency determined based on the ambient temperature Tout and the internal temperature Tin is higher than the frequency threshold corresponding to the current pressure range of the suction pressure Psu, the hot fluorine defrosting control system controls the compressor 1 to operate according to the frequency threshold; when the defrosting target frequency is not higher than the corresponding frequency threshold, the hot fluorine defrosting control system controls the compressor 1 to operate according to the defrosting target frequency.

[0178] When the coil temperature Tpg is higher than the defrost exit temperature threshold Tdt, the hot-fluid defrost control system controls the variable frequency refrigeration unit to enter the dripping mode and controls the compressor 1 to run at the dripping operating frequency F(ds).

[0179] In drip mode, the hot refrigerant defrosting control system further adjusts the operating frequency of compressor 1 according to the coil temperature Tpg in order to regulate the temperature of the heat exchanger and chassis corresponding to the air cooler 6.

[0180] When the running time of the dripping mode reaches or exceeds the preset dripping running time t(ds), the hot-fluorine defrosting control system maintains the current operating frequency of compressor 1 before the end of the dripping mode, and controls the four-way valve 3 to switch from the defrosting direction to the refrigeration direction, so that the variable frequency refrigeration unit exits the dripping mode and resumes refrigeration operation.

[0181] When no further frequency reduction control is triggered in drip mode, the current operating frequency of compressor 1 before the end of drip mode is the drip operating frequency F(ds); when further frequency reduction control has been triggered, the current operating frequency of compressor 1 before the end of drip mode is the frequency after frequency reduction determined according to the drip operating frequency F(ds), the preset frequency reduction value C4, and the minimum allowable operating frequency of compressor 1.

[0182] After the four-way valve 3 switches to the refrigeration direction, when the temperature inside the refrigeration unit Tin is greater than or equal to the sum of the set temperature Ts and the temperature control accuracy ΔT, the hot fluorine defrosting control system controls the variable frequency refrigeration unit to continue refrigeration operation; when the temperature inside the refrigeration unit Tin is less than the sum of the set temperature Ts and the temperature control accuracy ΔT, the hot fluorine defrosting control system controls the variable frequency refrigeration unit to enter the shutdown standby state.

[0183] It should be noted that this invention solves the problem of lack of overall coordination between detection parameters and defrosting control actions in conventional refrigeration units by setting up a hot fluorine defrosting control system in the variable frequency refrigeration unit and connecting the hot fluorine defrosting control system with various detection and execution components. It realizes coordinated control of compressor frequency, four-way valve direction, electronic expansion valve opening and fan operating status, thereby improving the defrosting efficiency, operational stability and energy saving effect of the variable frequency refrigeration unit.

[0184] Furthermore, the exhaust port of compressor 1 is connected to four-way valve 3 via oil separator 2. Four-way valve 3 is connected to condenser 4, air cooler 6 and vapor-liquid separator 7 respectively. Condenser 4 is connected to air cooler 6 via electronic expansion valve 5. Vapor-liquid separator 7 is connected to suction port of compressor 1.

[0185] The suction pressure sensor 8 is installed on the suction line between the vapor-liquid separator 7 and the compressor 1. The ambient temperature sensor is installed on the condenser fan side to detect the ambient temperature Tout.

[0186] The temperature and humidity sensor is located on the return air side of the air cooler 6 to detect the temperature Tin and humidity ψin inside the warehouse.

[0187] The coil temperature detection device is used to detect the coil temperature Tpg of the air cooler 6.

[0188] In refrigeration operation, the four-way valve 3 causes the refrigerant discharged from the compressor 1 to flow sequentially to the condenser 4, the electronic expansion valve 5, and the air cooler 6, and then return to the compressor 1 via the vapor-liquid separator 7.

[0189] During defrosting operation, the four-way valve 3 switches the flow direction of the refrigerant, causing the high-temperature refrigerant discharged from the compressor 1 to flow to the heat exchanger inside the air cooler 6, using the heat released by the refrigerant to melt the frost layer on the surface of the heat exchanger inside the air cooler.

[0190] Oil separator 2 is used to separate the refrigerant and lubricating oil discharged from compressor 1. Vapor-liquid separator 7 is used to separate the refrigerant into vapor and liquid phases entering the suction side of compressor 1, reducing the risk of liquid refrigerant entering compressor 1.

[0191] The suction pressure sensor 8 is installed on the suction side of the compressor 1 and can detect the suction pressure Psu before entering the compressor 1, thereby providing a detection basis for segmented low-pressure frequency limiting control.

[0192] An ambient temperature sensor is installed on the condenser fan side to obtain the ambient temperature Tout corresponding to the outdoor heat exchange environment; a cold storage temperature and humidity sensor is installed on the return air side of the evaporator 6 to obtain the internal temperature Tin and internal humidity ψin, which can characterize the internal environment of the cold storage; a coil temperature detection device is used to detect the coil temperature Tpg of the evaporator 6, which can provide a detection basis for defrosting exit judgment and frequency adjustment in dripping mode.

[0193] It should be noted that this invention forms a circulating loop with switchable refrigerant flow by sequentially connecting the compressor, oil separator, four-way valve, condenser, electronic expansion valve, air cooler, and vapor-liquid separator. Corresponding operating parameters are obtained at the compressor suction side, condenser fan side, air cooler return side, and air cooler coil. This solves the problem of insufficient data for detecting the operating status during defrosting control, realizes reliable switching between refrigeration operation and hot refrigerant defrosting operation, and provides a parameter basis for defrosting timing judgment, defrosting frequency control, low-pressure frequency limiting, and dripping control.

[0194] This disclosure can be a system, method, and / or computer program product. A computer program product may include a computer-readable storage medium having computer-readable program instructions loaded thereon for causing a processor to implement various aspects of this disclosure.

[0195] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A hot-frozen refrigerant defrosting control method, applied to a variable frequency refrigeration unit, the variable frequency refrigeration unit comprising a compressor (1), a four-way valve (3), and a suction pressure sensor (8), characterized in that, include: The unit obtains the temperature inside the storage room, humidity inside the storage room, ambient temperature, coil temperature, operating frequency of the compressor (1) and suction pressure detected by the suction pressure sensor (8), and calculates the unit's cooling time based on the operating frequency of the compressor (1). Based on the temperature inside the cold storage, the humidity inside the cold storage, and the cooling time of the unit, determine whether the variable frequency refrigeration unit meets the defrosting conditions; When the variable frequency refrigeration unit meets the defrosting conditions, the compressor (1) is controlled to operate at the four-way valve switching frequency. After the compressor (1) operates at the four-way valve switching frequency, the four-way valve (3) is controlled to switch to the defrosting direction. The optimal defrosting operating frequency is determined according to the ambient temperature and the temperature inside the refrigeration unit. Based on the optimal defrosting operating frequency and the allowable operating frequency range of the compressor (1), the compressor (1) is controlled to perform defrosting operation. During the defrosting operation, the compressor (1) is subjected to segmented low-pressure frequency limiting control according to the suction pressure; When the temperature of the coil is higher than the defrost exit temperature threshold, the variable frequency refrigeration unit is controlled to enter the dripping mode, the compressor (1) is controlled to run at the dripping frequency, and the operating frequency of the compressor (1) is adjusted according to the temperature of the coil. When the running time of the dripping mode reaches or exceeds the preset dripping running time, the compressor (1) maintains the current operating frequency before the end of the dripping mode and controls the four-way valve (3) to switch to the refrigeration direction; when the temperature inside the refrigeration chamber is greater than or equal to the sum of the preset refrigeration chamber temperature setting temperature and the temperature control accuracy, the variable frequency refrigeration unit is controlled to continue refrigeration operation; when the temperature inside the refrigeration chamber is less than the sum of the refrigeration chamber temperature setting temperature and the temperature control accuracy, the variable frequency refrigeration unit is controlled to enter the shutdown standby state.

2. The thermal defrosting control method according to claim 1, characterized in that: The step of calculating the unit's cooling time based on the compressor's (1) operating frequency, and determining whether the variable frequency refrigeration unit meets the defrosting conditions based on the temperature inside the refrigeration unit, the humidity inside the refrigeration unit, and the unit's cooling time, includes: Establish the correspondence between temperature range, humidity range, minimum operating frequency of compressor cooling, and cooling time duration threshold in advance; When the temperature inside the refrigeration unit is higher than the preset defrosting temperature limit, it is determined that the variable frequency refrigeration unit does not meet the defrosting conditions. When the temperature inside the storage room is not higher than the preset defrost temperature upper limit, the corresponding minimum operating frequency of the compressor and the threshold of the refrigeration time are selected from the correspondence based on the temperature range of the temperature inside the storage room and the humidity range of the humidity inside the storage room. When the operating frequency of the compressor (1) is greater than the minimum operating frequency of the compressor for refrigeration, the running time of the compressor (1) is accumulated to obtain the refrigeration time of the unit; When the operating frequency of the compressor (1) is not greater than the minimum operating frequency of the compressor for refrigeration, the accumulation of the refrigeration time of the unit is paused, and the accumulated refrigeration time of the unit is retained. When the cooling time of the unit exceeds the cooling time threshold, the variable frequency cooling unit is determined to meet the defrosting condition.

3. The thermal defrosting control method according to claim 1, characterized in that: Determining the optimal defrosting frequency based on the ambient temperature and the temperature inside the storage chamber includes: The product of the ambient temperature and the ambient temperature compensation coefficient is determined as the ambient temperature compensation term, and the product of the warehouse temperature and the warehouse temperature compensation coefficient is determined as the warehouse temperature compensation term. The optimal defrosting operating frequency is obtained by subtracting the ambient temperature compensation term and the warehouse temperature compensation term from the defrosting baseline operating frequency. The method of controlling the compressor (1) to perform defrosting operation based on the optimal defrosting operating frequency and the allowable operating frequency range of the compressor (1) includes: When the optimal defrosting operating frequency is higher than the maximum allowable operating frequency of the compressor (1), the compressor (1) is controlled to defrost at the maximum allowable operating frequency; When the optimal defrosting operating frequency is lower than the minimum allowable operating frequency of the compressor (1), the compressor (1) is controlled to defrost at the minimum allowable operating frequency; When the optimal defrosting operating frequency is within the allowable operating frequency range of the compressor (1), the compressor (1) is controlled to perform defrosting operation according to the optimal defrosting operating frequency.

4. The thermal defrosting control method according to claim 1, characterized in that: The segmented low-pressure frequency limiting control of the compressor (1) based on the suction pressure includes: A first pressure threshold, a second pressure threshold, and a third pressure threshold are set, wherein the first pressure threshold is greater than the second pressure threshold, and the second pressure threshold is greater than the third pressure threshold. A first frequency threshold, a second frequency threshold, and a third frequency threshold are set, wherein the first frequency threshold is greater than the second frequency threshold, and the second frequency threshold is greater than the third frequency threshold. When the suction pressure is less than the first pressure threshold and greater than or equal to the second pressure threshold, the maximum operating frequency of the compressor (1) is limited to not be higher than the first frequency threshold; When the suction pressure is less than the second pressure threshold and greater than or equal to the third pressure threshold, the maximum operating frequency of the compressor (1) is limited to not exceeding the second frequency threshold; When the suction pressure is less than the third pressure threshold, the maximum operating frequency of the compressor (1) is limited to not exceeding the third frequency threshold; Among them, the segmented low-pressure frequency limiting control has a higher priority than the control of the compressor (1) based on the optimal defrosting operating frequency; when the optimal defrosting operating frequency is higher than the frequency threshold corresponding to the current pressure range of the suction pressure, the corresponding frequency threshold is used as the target operating frequency of the compressor (1).

5. The thermal defrosting control method according to claim 4, characterized in that: The segmented low-voltage frequency limiting control further includes low-voltage frequency limiting recovery control, which includes: When the suction pressure rises from less than the third pressure threshold to greater than or equal to the third pressure threshold and less than the second pressure threshold, and remains in the corresponding pressure range for a preset recovery time, the limit of the highest operating frequency of the compressor (1) is adjusted from the third frequency threshold to the second frequency threshold. When the suction pressure rises to a level greater than or equal to the second pressure threshold and less than the first pressure threshold, and remains within the corresponding pressure range for the preset recovery time, the limit of the highest operating frequency of the compressor (1) is adjusted to the first frequency threshold. When the inhalation pressure rises to a level greater than or equal to the first pressure threshold and remains within a pressure range greater than or equal to the first pressure threshold for a preset recovery time, the segmented low-pressure frequency limiting control is released.

6. The thermal defrosting control method according to claim 1, characterized in that: The variable frequency refrigeration unit also includes an electronic expansion valve (5), a cooler (6), and a condenser fan; The control of the variable frequency chiller unit to enter the dripping mode, the control of the compressor (1) to operate at the dripping frequency, and the adjustment of the operating frequency of the compressor (1) according to the coil temperature include: Control the four-way valve (3) to maintain the defrosting direction, adjust the opening of the electronic expansion valve (5) according to the suction superheat of the variable frequency refrigeration unit, control the air cooler (6) to remain closed, and control the condenser fan to run at the maximum speed; Control the compressor (1) to operate at the dripping frequency; When the coil temperature remains higher than the sum of the defrost exit temperature threshold and the temperature compensation value for a preset judgment period, the frequency reduction target frequency is determined based on the difference between the dripping operation frequency and the preset frequency reduction value. When the target frequency of frequency reduction is not lower than the minimum allowable operating frequency of the compressor (1), the compressor (1) is controlled to operate at the target frequency of frequency reduction; When the target frequency of frequency reduction is lower than the minimum allowable operating frequency of the compressor (1), the compressor (1) is controlled to operate at the minimum allowable operating frequency.

7. The thermal defrosting control method according to claim 1, characterized in that: When the running time of the dripping mode reaches the preset dripping running time, controlling the four-way valve (3) to switch to the refrigeration direction while the compressor (1) continues to run includes: The duration of the dripping mode is accumulated from the time the variable frequency chiller unit enters the dripping mode. When the running time of the dripping mode reaches or exceeds the preset dripping running time, the compressor (1) maintains the current operating frequency before the end of the dripping mode, and controls the four-way valve (3) to switch from the defrosting direction to the refrigeration direction.

8. A thermal defrosting control system for implementing the thermal defrosting control method according to any one of claims 1-7, characterized in that, include: The module includes a parameter acquisition and timing module, a defrosting judgment module, a defrosting operation control module, a low-pressure frequency limiting control module, a dripping water control module, and a state switching module. The parameter acquisition and timing module is used to acquire the temperature inside the warehouse, the humidity inside the warehouse, the ambient temperature, the coil temperature, the operating frequency of the compressor (1) and the suction pressure detected by the suction pressure sensor (8), and to calculate the cooling time of the unit based on the operating frequency of the compressor (1). The defrosting judgment module is used to determine whether the variable frequency refrigeration unit meets the defrosting conditions based on the temperature inside the refrigeration room, the humidity inside the refrigeration room, and the refrigeration time of the unit. The defrosting operation control module is used to control the compressor (1) to operate at the four-way valve switching frequency when the variable frequency refrigeration unit meets the defrosting conditions, and to control the four-way valve (3) to switch to the defrosting direction after the compressor (1) operates at the four-way valve switching frequency; to determine the optimal defrosting operation frequency according to the ambient temperature and the temperature inside the refrigeration unit, and to control the compressor (1) to perform defrosting operation based on the optimal defrosting operation frequency and the allowable operating frequency range of the compressor (1); The low-pressure frequency limiting control module is used to perform segmented low-pressure frequency limiting control on the compressor (1) according to the suction pressure during the defrosting operation. The dripping control module is used to control the variable frequency refrigeration unit to enter the dripping mode when the coil temperature is higher than the defrost exit temperature threshold, control the compressor (1) to run at the dripping frequency, and adjust the operating frequency of the compressor (1) according to the coil temperature. The state switching module is used to maintain the current operating frequency of the compressor (1) before the end of the dripping mode when the running time of the dripping mode reaches or exceeds the preset dripping running time, and to control the four-way valve (3) to switch to the refrigeration direction; when the temperature inside the refrigeration chamber is greater than or equal to the sum of the preset refrigeration temperature setting temperature and the temperature control accuracy, the variable frequency refrigeration unit is controlled to continue refrigeration operation; when the temperature inside the refrigeration chamber is less than the sum of the refrigeration temperature setting temperature and the temperature control accuracy, the variable frequency refrigeration unit is controlled to enter the shutdown standby state.

9. A variable frequency refrigeration unit, characterized in that, Includes a compressor (1), an oil separator (2), a four-way valve (3), a condenser (4), an electronic expansion valve (5), a cooler (6), a vapor-liquid separator (7), a suction pressure sensor (8), a condenser fan, an ambient temperature sensor, a storage temperature and humidity sensor, a coil temperature detection device, and the hot fluorine defrosting control system as described in claim 8. The compressor (1) is a variable frequency compressor; The hot fluorine defrosting control system is connected to the compressor (1), the four-way valve (3), the electronic expansion valve (5), the air cooler (6) and the condenser respectively, and is used to output control commands to the compressor (1), the four-way valve (3), the electronic expansion valve (5), the air cooler (6) and the condenser. The hot fluorine defrosting control system is also connected to the suction pressure sensor (8), the ambient temperature sensor, the warehouse temperature and humidity sensor and the coil temperature detection device, respectively, to obtain suction pressure, ambient temperature, warehouse temperature, warehouse humidity and coil temperature.

10. A variable frequency chiller unit according to claim 9, characterized in that: The exhaust port of the compressor (1) is connected to the four-way valve (3) via the oil separator (2). The four-way valve (3) is connected to the condenser (4), the air cooler (6) and the vapor-liquid separator (7) respectively. The condenser (4) is connected to the air cooler (6) via the electronic expansion valve (5). The vapor-liquid separator (7) is connected to the suction port of the compressor (1). The suction pressure sensor (8) is installed on the suction line between the vapor-liquid separator (7) and the compressor (1); The ambient temperature sensor is located on the side of the condenser fan and is used to detect the ambient temperature; The temperature and humidity sensor is located on the return air side of the air cooler (6) and is used to detect the temperature and humidity inside the warehouse. The coil temperature detection device is used to detect the coil temperature of the air cooler (6).

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