Air conditioning system and defrosting control method thereof

Abstract

The present application relates to an air conditioning system, which sets the judgment of the operation frequency of the unit before defrosting, increases the compressor stop action; during defrosting, the fine adjustment of the opening of the electronic expansion valve is carried out according to the comparison of the compression ratio of the high pressure and the low pressure; through the oil return confirmation before the defrosting of the unit, the risk of liquid impact on the unit caused by the switching of the four-way valve is reduced; through the fine adjustment of the electronic expansion valve during the defrosting of the unit, the demand of controlling the refrigerant variable flow of the unit is achieved; the two work together, which can effectively solve the problem of oil shortage of the unit during the defrosting process, better protect the operation of the unit, and provide the reliability of the defrosting of the unit.

Description

Technical Field

[0001] This invention relates to the field of air conditioning, and more particularly to an air conditioning system and its defrosting control method. Background Technology

[0002] In variable frequency air conditioning systems for low-temperature heating, the issue of compressor oil return needs special attention, especially when the compressor is operating at low frequency. In such cases, the oil return problem will exacerbate the oil shortage during defrosting.

[0003] In existing variable frequency air conditioning systems, common defrosting solutions primarily adjust the compressor's operating frequency, the four-way valve's port switching, and the electronic expansion valve's opening using the following methods:

[0004] During defrosting, the compressor drops from its current frequency to the default low frequency of 30Hz, then increases to the default defrosting frequency of 70Hz. Once defrosting is complete, the compressor stops and directly switches to heating mode. The four-way valve switches its port 30 seconds after the compressor frequency drops to the four-way valve switching frequency (default 30Hz). After defrosting, the valve switches its port again after the compressor frequency drops to the four-way valve switching frequency (default 30Hz). During defrosting, the main valve of the electronic expansion valve maintains a fixed opening (default 450P) for defrosting control. In summary, the combined actions of all components complete the entire defrosting command.

[0005] This type of defrosting method has the following problems: 1) It does not determine the operating status of the unit before defrosting. If the unit is running at a low frequency before defrosting, it will cause oil shortage during defrosting; 2) During defrosting, the electronic expansion valve is always kept at a fixed opening, which does not meet the flow control of the unit under such variable operating conditions, and is very likely to cause liquid or oil return problems.

[0006] In response to these problems, the following defrosting solution is proposed. Summary of the Invention

[0007] Therefore, the purpose of this invention is to provide an air conditioning system whose defrosting method can ensure the reliability of the unit during defrosting and avoid compressor liquid or oil return problems.

[0008] An air conditioning system includes a compressor, a four-way valve, a condenser, an electronic expansion valve, an evaporator, and a pressure monitoring module, all connected via refrigerant piping; and a controller electrically and / or communicatively connected to the compressor, the electronic expansion valve, the four-way valve, and the pressure monitoring module. The controller regulates the compressor, the four-way valve, and the electronic expansion valve for defrosting control using the following method:

[0009] Upon receiving the defrost command, the controller obtains the compressor's operating frequency before initiating the defrost process.

[0010] If the operating frequency is greater than the preset defrost threshold frequency, the compressor will be stopped for a second period of time. During the stop, the opening of the electronic expansion valve will be adjusted to the maximum opening.

[0011] If the operating frequency is less than or equal to the defrost threshold frequency, the opening of the electronic expansion valve is controlled according to the frequency-opening linear adjustment table to raise the unit frequency to the defrost threshold frequency, and the unit is controlled to run at the defrost threshold frequency for the first time period before the above shutdown operation is performed.

[0012] After the shutdown control ends, start the compressor, and control the electronic expansion valve to adjust the initial opening to the minimum defrost opening, and then continuously adjust the opening of the electronic expansion valve according to the adjustment rate ΔK; after the compressor starts for the third time period, control the four-way valve port to switch.

[0013] Enter defrost mode, control the compressor to operate at the defrost frequency, and obtain the compressor's high-pressure pressure in real time:

[0014] If the high-pressure is less than the preset high-pressure threshold, the low-pressure of the compressor is further obtained, and the compression ratio R is calculated based on the high-pressure and low-pressure. H / L The compression ratio is compared with a preset compression threshold ratio, and the fine-tuning of electron expansion is controlled based on the comparison result.

[0015] If the high pressure is greater than or equal to the high pressure threshold pressure, the defrosting mode will be exited, the electronic expansion valve will be controlled to maintain the current opening, and after the compressor frequency drops to the defrosting frequency and runs for the fourth time period, the four-way valve will be controlled to switch the valve port and enter the normal heating mode control.

[0016] Compared with existing technologies, the air conditioning system proposed in this application, based on the above-mentioned optimized control logic, can effectively solve the problem of oil return caused by the low-frequency operation of the compressor before defrosting, which exacerbates the oil shortage problem during the defrosting process. Specifically, it confirms the oil return of the unit before defrosting by judging the unit's operating frequency; it reduces the risk of liquid slugging caused by the switching of the four-way valve by stopping the compressor before defrosting; and it finely adjusts the opening of the electronic expansion valve based on the comparison of the compression ratio of the high-pressure and low-pressure pressures during defrosting to control the variable refrigerant flow requirements of the unit, better match defrosting, better protect the operation of the unit, and improve the reliability of the unit's defrosting.

[0017] Furthermore, the regulating rate ΔK of the electronic expansion valve satisfies:

[0018] ΔK=(K CS -K MIN-CS ) / F CS

[0019] In the formula, ΔK is the opening adjustment rate of the electronic expansion valve in each valve adjustment cycle; KCS K represents the defrost opening degree of the electronic expansion valve. MIN-CS F represents the minimum defrost opening of the electronic expansion valve. CS This is the preset compressor defrosting frequency.

[0020] Furthermore, the compression ratio is compared with a preset compression threshold ratio, and the fine-tuning of electronic expansion is controlled based on the comparison result, specifically including:

[0021] If the compression ratio R H / L The compression ratio R is less than or equal to the first compression threshold. H Va / lu L e-1 And for 10 seconds, the opening of the electronic expansion valve is reduced by a slight adjustment K in the current valve adjustment cycle;

[0022] If the compression ratio R H / L Greater than the first compression threshold R H Va / lu L e-1 And less than the second compression threshold ratio R H Va / lu L e-2 And for 20 seconds, the opening of the electronic expansion valve remains unchanged;

[0023] If the compression ratio R H / L Greater than or equal to the second compression threshold ratio R H Va / lu L e-2 And for 20 seconds, the opening degree of the electronic expansion valve is increased by a slight adjustment K in the current valve adjustment cycle, but does not exceed the defrost opening degree K of the electronic expansion valve. CS .

[0024] Furthermore, the compression ratio R H / L satisfy:

[0025] R H / L =(P H +1) / (P L +1)

[0026] In the formula: P H For high pressure, P L It is a low pressure.

[0027] Based on the above-mentioned air conditioning system, the present invention provides a defrosting control method for an air conditioning system.

[0028] S10 receives a defrost command and, before entering defrost mode, obtains the compressor's operating frequency and determines whether the compressor's operating frequency is greater than the preset defrost threshold frequency.

[0029] If so, proceed to step S20;

[0030] If not, control the opening of the electronic expansion valve according to the frequency-opening linear adjustment table to raise the unit frequency to the preset defrost threshold frequency, and control the unit to run at the defrost threshold frequency for a first time period before executing step S20.

[0031] S20 controls the compressor to stop for the second time period, during which the opening of the electronic expansion valve is adjusted to the maximum opening.

[0032] After the S30 shutdown control ends, the compressor is started. The initial opening of the electronic expansion valve is adjusted to the minimum defrosting opening, and then the opening of the electronic expansion valve is continuously adjusted according to the adjustment rate ΔK. After the third time period of compressor startup, the four-way valve port is switched.

[0033] S40 enters defrost mode, controlling the compressor to operate at the defrost frequency, acquiring the compressor's high-pressure pressure in real time, and determining whether the high-pressure pressure is greater than or equal to the preset high-pressure threshold pressure.

[0034] If not, then execute S50;

[0035] If yes, then execute S60;

[0036] S50 obtains the low-pressure pressure of the compressor and calculates the compression ratio R based on the high-pressure and low-pressure pressures. H / L and the compression ratio R H / L It is compared with a preset compression threshold ratio, and the electronic expansion is fine-tuned based on the comparison result;

[0037] S60 exits defrost mode, controls the electronic expansion valve to maintain the current opening, and after the compressor frequency drops to the defrost frequency and runs for four hours, controls the four-way valve to switch the valve port and enter normal heating mode control.

[0038] Furthermore, step S50, which controls the fine-tuning of electronic expansion based on the comparison result, specifically includes:

[0039] If the compression ratio R H / L The compression ratio R is less than or equal to the first compression threshold. H Va / lu L e-1And for 10 seconds, the opening of the electronic expansion valve is reduced by a slight adjustment K in the current valve adjustment cycle;

[0040] If the compression ratio R H / L Greater than the first compression threshold R H Va / lu L e-1 And less than the second compression threshold ratio R H Va / lu L e-2 And for 20 seconds, the opening of the electronic expansion valve remains unchanged;

[0041] If the compression ratio R H / L Greater than or equal to the second compression threshold ratio R H Va / lu L e-2 And for 20 seconds, the opening degree of the electronic expansion valve is increased by a slight adjustment K in the current valve adjustment cycle, but does not exceed the defrost opening degree K of the electronic expansion valve. CS .

[0042] Further, step S40 is S`40:

[0043] S`40 enters defrost mode, controlling the compressor to operate at the defrost frequency and acquiring the compressor's high-pressure pressure in real time to determine whether the high-pressure pressure is greater than or equal to the preset fan start-up threshold pressure.

[0044] If not, then execute S50;

[0045] If so, further determine whether the high-pressure is greater than or equal to the preset high-pressure threshold pressure:

[0046] If not, adjust the opening of the electronic expansion valve to the defrost opening of the electronic expansion valve, start the fan and control the fan to run at low speed, and continuously judge whether the high pressure is greater than or equal to the preset high pressure threshold pressure.

[0047] If so, then execute S60.

[0048] To better understand and implement this invention, the following detailed description is provided in conjunction with the accompanying drawings. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the air conditioning system of the present invention;

[0050] Figure 2This is a schematic flowchart of the defrosting control method for the air conditioning system of the present invention;

[0051] Figure 3 This is a schematic flowchart of the defrosting control method with fan control for the air conditioning system of the present invention;

[0052] Figure 4 This is a schematic diagram of the defrosting control with fan control in the air conditioning system of the present invention. Detailed Implementation

[0053] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings of the embodiments of the present invention.

[0054] To address the problem of low-frequency compressor operation before defrosting, which leads to oil return issues and exacerbates oil shortage during defrosting, this invention proposes an air conditioning system that includes an improved defrosting control method.

[0055] For specific implementation details, please refer to [link / reference]. Figure 1 The air conditioning system proposed in this invention includes a compressor 10, a four-way valve 20, a condenser 30, an electronic expansion valve 40, an evaporator 50, a fan 60, a pressure monitoring module 70, a controller (not shown), and other auxiliary pipes. The compressor 10, four-way valve 20, condenser 30, electronic expansion valve 40, and evaporator 50 are sequentially connected via refrigerant piping. The controller is electrically and / or communicatively connected to the compressor 10, four-way valve 20, electronic expansion valve 40, fan 60, and pressure monitoring module 70.

[0056] The pressure monitoring module 70 includes a first pressure sensor 71 and a second pressure sensor 72. The first pressure sensor 71 is located at the discharge end of the compressor 10 and is used to measure the high-pressure P of the refrigerant. H The pressure signal is transmitted to the controller. The second pressure sensor 72 is located at the return gas end of the compressor 10 and is used to measure the low-pressure P of the refrigerant. L It then transmits the pressure signal to the controller.

[0057] The controller further includes a storage unit and a processing unit. The storage unit is used to store a preset compressor defrost threshold frequency F. C V S alue Compressor defrosting frequency F CS Compressor defrosting frequency F HS Compression threshold ratio R H Va / lu L e Fan start-up threshold pressure PF Value High pressure threshold pressure P H Value Frequency-opening linear correspondence adjustment table; and at each time acquisition point, the first pressure sensor 71 acquires the high pressure P. H t The second pressure sensor 72 collects the low pressure P. L t The system includes programs for controlling the start / stop, frequency increase / decrease, and rotation of the compressor 10; the valve port rotation of the four-way valve 20; the opening adjustment of the electronic expansion valve 40; and the start / stop and speed adjustment of the fan. The processing unit is used to calculate the opening adjustment rate ΔK of the electronic expansion valve and the unit compression ratio R. H / L And to execute various judgment procedures.

[0058] Please see Figure 2 The controller controls the defrosting operation of the air conditioning system by combining control of the compressor operating frequency, the four-way valve port switching, and the opening of the electronic expansion valve. Specifically, before defrosting, the controller determines the unit's operating frequency and adds a compressor shutdown action; during defrosting, it fine-tunes the opening of the electronic expansion valve based on a comparison of the compression ratio of the high-pressure and low-pressure pressures; by confirming the oil return before defrosting, it reduces the risk of liquid slugging caused by the four-way valve switching; and by fine-tuning the electronic expansion valve during defrosting, it controls the variable refrigerant flow requirements of the unit. These two mechanisms work together to effectively solve the problem of oil shortage during defrosting, better protect the unit's operation, and improve the reliability of defrosting. The specific steps include:

[0059] S10 receives a defrost command and, before entering defrost mode, obtains the compressor's operating frequency F and determines whether the compressor's operating frequency F is greater than the preset defrost threshold frequency F. C V S alue :

[0060] If so, proceed to step S20;

[0061] If not, the opening of the electronic expansion valve and auxiliary electronic expansion valve is controlled according to the frequency-opening linear adjustment table to raise the unit frequency to the preset defrosting threshold frequency F. C V S alue And control the unit at the preset defrosting threshold frequency F C V S alue After the first time period t1, step S20 is executed.

[0062] Specifically, the operating frequency F of the compressor is the average frequency value within 3 minutes before the defrost command is issued.

[0063] The preset defrosting threshold frequency F C V S alue It is 60Hz.

[0064] The frequency-opening linear correspondence adjustment table is preset by the system and is based on experimental values ​​obtained from different power levels and models.

[0065] After the first time period, t1 is set to 3 minutes.

[0066] S20 controls the compressor to stop during the second time period t2, during which the electronic expansion valve opening is adjusted to the maximum opening K. MAX .

[0067] The maximum opening degree K of the electronic expansion valve MAX It is 480P.

[0068] The second time period t2 is set to 50s to 60s.

[0069] S30 stops the machine and starts the compressor. The electronic expansion valve's initial opening is adjusted to the minimum defrosting opening K. MIN-CS Then, continuously adjust the opening of the electronic expansion valve by adjusting the rate ΔK; after the compressor starts, control the switching of the four-way valve port after the third time period t3.

[0070] The opening adjustment rate ΔK of the electronic expansion valve satisfies:

[0071] ΔK=(K CS -K MIN-CS ) / F CS

[0072] In the formula, ΔK is the opening adjustment rate of the electronic expansion valve in each valve adjustment cycle, where the valve adjustment cycle is determined according to different models, and a valve adjustment cycle of 5s is recommended; K CS The defrost opening of the electronic expansion valve is 430P; K MIN-CS The minimum defrost opening of the electronic expansion valve is 240P; F CS This is the preset compressor defrosting frequency, which is 80Hz.

[0073] The third time period t3 is set to 30s.

[0074] S40 enters defrost mode, controlling the compressor at defrost frequency F. CS It operates under these conditions and acquires the compressor's high-pressure P in real time. H And determine the high pressure P HIs it greater than or equal to the preset high-pressure threshold pressure P? H Value :

[0075] If not, then execute S50;

[0076] If yes, then execute S60.

[0077] The high voltage threshold P H Value It is 4.2 MPa.

[0078] S50 obtains the low-pressure P of the compressor. L According to the high pressure P H and low pressure P L Calculate the compression ratio R H / L and the compression ratio R H / L Compared to the preset compression threshold R H Va / lu L e The comparisons are made, and the fine-tuning of electronic expansion is controlled based on the comparison results.

[0079] The specific fine-tuning method is as follows:

[0080] If the compression ratio R H / L The compression ratio R is less than or equal to the first compression threshold. H Va / lu L e-1 And for 10 seconds, control the opening degree K of the electronic expansion valve. t In the current valve adjustment cycle, slightly reduce the valve opening by K;

[0081] If the compression ratio R H / L Greater than the first compression threshold R H Va / lu L e-1 And less than the second compression threshold ratio R H Va / lu L e-2 And for 20 seconds, control the opening degree K of the electronic expansion valve. t Remain unchanged;

[0082] If the compression ratio R H / L Greater than or equal to the second compression threshold ratio R H Va / lu L e-2 And for 20 seconds, control the opening degree K of the electronic expansion valve. t Increase the valve opening by one fine adjustment degree K during the current valve adjustment cycle, but do not exceed the defrost opening degree K of the electronic expansion valve. CS .

[0083] The compression ratio R H / L satisfy:

[0084] R H / L =(P H +1) / (P L +1)

[0085] In the formula: P H For high pressure, P L It is a low pressure.

[0086] The first compression threshold ratio R H Va / lu L e-1 The value is 2; the second compression threshold ratio R H Va / lu L e-2 The value is 3.

[0087] The valve adjustment cycle is 5 seconds.

[0088] The value range of the fine-tuning opening K is 15 to 25P.

[0089] The compressor increases its frequency to the defrost frequency F at a rate of 1 Hz / s. CS 80Hz.

[0090] Combining steps S30 to S50, the main valve opening range during defrosting is the minimum defrosting opening K. MIN-CS To defrost opening K CS Specifically, the range is 240P to 430P.

[0091] S60 exits defrost mode, controlling the electronic expansion valve to maintain its current opening, until the compressor frequency drops to the defrost frequency F. HS Then, during the fourth time period t4, the four-way valve is controlled to switch the valve port and enter the normal heating mode control.

[0092] The defrosting frequency F HS The recommended defrosting frequency F depends on the specific model. HS Set to 30Hz.

[0093] The fourth time period t4 is 5 seconds.

[0094] Please see Figure 3 , Figure 4 In another embodiment, the control of the fan is also included. Specifically, the above step S40 is modified to S`40.

[0095] S`40 enters defrost mode, controlling the compressor at defrost frequency F CS It operates under these conditions and acquires the compressor's high-pressure P in real time. H Determine the high pressure P H Is it greater than or equal to the preset fan start-up threshold pressure P? F Value :

[0096] If not, then execute S50;

[0097] If so, further determine the high-pressure P. H Is it greater than or equal to the preset high-pressure threshold pressure P? H Value :

[0098] If not, adjust the opening of the electronic expansion valve to the defrost opening K of the electronic expansion valve. CS Start the fan and control it to run at low speed, while continuously monitoring the high pressure P. H Is it greater than or equal to the preset high-pressure threshold pressure P? H Value ;

[0099] If so, then execute S60.

[0100] The fan start-up threshold pressure P F Value Set to 3.6MPa.

[0101] The fan operates at a speed of 300 rpm to 400 rpm at low speed.

[0102] Adding fan detection and control can enhance the unit's high-pressure protection of the compressor during defrosting.

[0103] The air conditioning system described in this application, based on the above-mentioned optimized control logic design, can better handle problems that conventional logic cannot solve. By setting a pre-defrost judgment of the unit's operating frequency, oil return before defrosting is confirmed; by stopping the compressor before defrosting, the risk of liquid slugging caused by the four-way valve switching can be reduced; during defrosting, the opening of the electronic expansion valve is adjusted according to the compression ratio to control the unit's refrigerant flow requirements and better match defrosting. Through the above optimized control scheme, the compressor oil and liquid return problems during unit defrosting can be solved.

[0104] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and the present invention also intends to include these modifications and variations.

Claims

1. An air conditioning system, comprising a compressor, a four-way valve, a condenser, an electronic expansion valve, an evaporator, and a pressure monitoring module, all connected via refrigerant piping, and a controller electrically and / or communicatively connected to the compressor, the electronic expansion valve, the four-way valve, and the pressure monitoring module, characterized in that, The controller regulates the compressor, four-way valve, and electronic expansion valve for defrosting control using the following method: Upon receiving the defrost command, the controller obtains the compressor's operating frequency before initiating the defrost process. If the operating frequency is greater than the preset defrost threshold frequency, the compressor will be stopped for a second period of time. During the stop, the opening of the electronic expansion valve will be adjusted to the maximum opening. If the operating frequency is less than or equal to the defrost threshold frequency, the opening of the electronic expansion valve is controlled according to the frequency-opening linear adjustment table to raise the unit frequency to the defrost threshold frequency, and the unit is controlled to run at the defrost threshold frequency for the first time period before the above shutdown operation is performed. After the shutdown control ends, start the compressor, adjust the initial opening of the electronic expansion valve to the minimum defrost opening, and then continuously adjust the opening of the electronic expansion valve according to the adjustment rate ΔK. After the compressor starts for the third time period, the control valve switches the four-way valve port. Enter defrost mode, control the compressor to operate at the defrost frequency, and obtain the compressor's high-pressure pressure in real time: If the high-pressure is less than the preset high-pressure threshold, the low-pressure of the compressor is further obtained, and the compression ratio R is calculated based on the high-pressure and low-pressure. H / L The compression ratio is compared with a preset compression threshold ratio, and the fine-tuning of electron expansion is controlled based on the comparison result. If the high pressure is greater than or equal to the high pressure threshold pressure, the defrosting mode will be exited, the electronic expansion valve will be controlled to maintain the current opening, and after the compressor frequency drops to the defrosting frequency and runs for the fourth time period, the four-way valve will be controlled to switch the valve port and enter the normal heating mode control.

2. The air conditioning system according to claim 1, characterized in that, The regulating rate ΔK of the electronic expansion valve satisfies: ΔK=(K CS -K MIN-CS ) / F CS In the formula, ΔK is the opening adjustment rate of the electronic expansion valve in each valve adjustment cycle; K CS K represents the defrost opening degree of the electronic expansion valve. MIN-CS This is the minimum defrost opening of the electronic expansion valve; F CS This is the preset compressor defrosting frequency.

3. The air conditioning system according to claim 1 or 2, characterized in that, The compression ratio is compared with a preset compression threshold ratio, and the fine-tuning of electron expansion is controlled based on the comparison result, specifically including: If the compression ratio R H / L The compression ratio R is less than or equal to the first compression threshold. H Va / lu L e-1 And for 10 seconds, the opening of the electronic expansion valve is reduced by a slight adjustment K in the current valve adjustment cycle; If the compression ratio R H / L Greater than the first compression threshold R H Va / lu L e-1 And less than the second compression threshold ratio R H Va / lu L e-2 And for 20 seconds, the opening of the electronic expansion valve remains unchanged; If the compression ratio R H / L Greater than or equal to the second compression threshold ratio R H Va / lu L e-2 And for 20 seconds, the opening degree of the electronic expansion valve is increased by a slight adjustment K in the current valve adjustment cycle, but does not exceed the defrost opening degree K of the electronic expansion valve. CS .

4. The air conditioning system according to claim 3, characterized in that, The compression ratio R H / L satisfy: R H / L =(P H +1) / (P L +1) In the formula: P H For high pressure, P L It is a low pressure.

5. The air conditioning system according to any one of claims 1, 2, and 4, characterized in that, It also includes a fan, which is electrically and / or communicatively connected to the controller; before judging the high pressure of the compressor and the high pressure threshold pressure, the high pressure of the compressor and the fan start-up threshold pressure of the fan are first judged: If the high-pressure is lower than the fan start-up threshold pressure, then the low-pressure of the compressor is further obtained, and the compression ratio R is calculated based on the high-pressure and low-pressure. H / L The compression ratio is compared with a preset compression threshold ratio, and the fine-tuning of electron expansion is controlled based on the comparison result. If the high pressure is greater than or equal to the fan start-up threshold pressure, but less than the high pressure threshold pressure, the opening of the electronic expansion valve is adjusted to the defrost opening of the electronic expansion valve, the fan is started and controlled to run at low speed, and the high pressure is continuously checked to see if it is greater than or equal to the high pressure threshold pressure.

6. A defrosting control method for an air conditioning system, comprising the following steps: S10 receives a defrost command and, before entering defrost mode, obtains the compressor's operating frequency and determines whether the compressor's operating frequency is greater than the preset defrost threshold frequency. If so, proceed to step S20; If not, control the opening of the electronic expansion valve according to the frequency-opening linear adjustment table to raise the unit frequency to the preset defrost threshold frequency, and control the unit to run at the defrost threshold frequency for a first time period before executing step S20. S20 controls the compressor to stop for the second time period, during which the opening of the electronic expansion valve is adjusted to the maximum opening. After the S30 shutdown control ends, the compressor is started, and the initial opening of the electronic expansion valve is adjusted to the minimum defrosting opening. Then, the opening of the electronic expansion valve is continuously adjusted according to the adjustment rate ΔK. After the compressor starts for the third time period, the control valve switches the four-way valve port. S40 enters defrost mode, controlling the compressor to operate at the defrost frequency, acquiring the compressor's high-pressure pressure in real time, and determining whether the high-pressure pressure is greater than or equal to the preset high-pressure threshold pressure. If not, then execute S50; If yes, then execute S60; S50 obtains the low-pressure pressure of the compressor and calculates the compression ratio R based on the high-pressure and low-pressure pressures. H / L and the compression ratio R H / L It is compared with a preset compression threshold ratio, and the electronic expansion is fine-tuned based on the comparison result; S60 exits defrost mode, controls the electronic expansion valve to maintain the current opening, and after the compressor frequency drops to the defrost frequency and runs for four hours, controls the four-way valve to switch the valve port and enter normal heating mode control.

7. The defrosting control method according to claim 6, characterized in that, The adjustment rate ΔK in step S30 satisfies: ΔK=(K CS -K MIN-CS ) / F CS In the formula, ΔK is the opening adjustment rate of the electronic expansion valve in each valve adjustment cycle; K CS K represents the defrost opening degree of the electronic expansion valve. MIN-CS This is the minimum defrost opening of the electronic expansion valve; F CS This is the preset compressor defrosting frequency.

8. The defrosting control method according to claim 6 or 7, characterized in that, Step S50, which controls the fine-tuning of electronic expansion based on the comparison results, specifically includes: If the compression ratio R H / L The compression ratio R is less than or equal to the first compression threshold. H Va / lu L e-1 And for 10 seconds, the opening of the electronic expansion valve is reduced by a slight adjustment K in the current valve adjustment cycle; If the compression ratio R H / L Greater than the first compression threshold R H Va / lu L e-1 And less than the second compression threshold ratio R H Va / lu L e-2 And for 20 seconds, the opening of the electronic expansion valve remains unchanged; If the compression ratio R H / L Greater than or equal to the second compression threshold ratio R H Va / lu L e-2 And for 20 seconds, the opening degree of the electronic expansion valve is increased by a slight adjustment K in the current valve adjustment cycle, but does not exceed the defrost opening degree K of the electronic expansion valve. CS .

9. The defrosting control method according to claim 8, characterized in that, The compression ratio R H / L satisfy: R H / L =(P H +1) / (P L +1) In the formula: P H For high pressure, P L It is a low pressure.

10. The defrosting control method according to any one of claims 6, 7, and 9, characterized in that, Step S40 is S`40: S`40 enters defrost mode, controlling the compressor to operate at the defrost frequency and acquiring the compressor's high-pressure pressure in real time to determine whether the high-pressure pressure is greater than or equal to the preset fan start-up threshold pressure. If not, then execute S50; If so, further determine whether the high-pressure is greater than or equal to the preset high-pressure threshold pressure: If not, adjust the opening of the electronic expansion valve to the defrost opening of the electronic expansion valve, start the fan and control the fan to run at low speed, and continuously judge whether the high pressure is greater than or equal to the preset high pressure threshold pressure. If so, then execute S60.

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