Heat pump system with defrosting control function

Abstract

The invention relates to a heat pump system with defrosting control, which comprises the following steps: judging whether to update a PWM (Pulse Width Modulation) reference value according to a set rule in real time by adopting a defrosting interval period and the rotating speed of a direct-current fan according to the correlation between the PWM reference value corresponding to the environment temperature and the direct-current fan gear wind speed and the frosting rate and the frosting thickness of the system; whether the system enters defrosting or not is judged on the basis of the environment temperature, the relation between the difference value of the PWM value of the direct-current fan of the heat pump system and the corresponding PWM reference value and a set difference threshold value; and more accurate, efficient and reliable defrosting judgment is realized.

Description

Technical Field

[0001] The invention relates to the field of heat pump system control, and in particular to a heat pump system with defrosting control. Background Art

[0002] The heat pump system is an efficient and environmentally friendly energy utilization technology. Its core working principle is the reverse Carnot cycle. It transfers the heat energy in the low-temperature heat source to the high-temperature environment by consuming a small amount of electricity or other energy to achieve the purpose of heating or cooling. The heat pump system absorbs the low-temperature heat energy in the air with very little electricity, converts it into high-temperature heat energy after compression by the compressor, and then transmits it to the place that needs heating or cooling. It is highly favored by consumers and users and has been widely used for refrigeration and hot water supply in hotels, schools, hospitals, saunas, beauty salons, swimming pools, laundries and other places.

[0003] The current defrosting methods of variable frequency heat pumps are mainly based on timed defrosting or defrosting set according to the difference between the ambient temperature and the coil temperature of the heat pump system. For areas or seasons where the outdoor ambient temperature varies greatly, this fixed parameter setting method often cannot meet the actual defrosting needs, resulting in frequent defrosting, frost without defrosting, and frost-free defrosting, which reduces the energy consumption of the system and leads to poor heating or cooling experience for users. Summary of the invention

[0004] Based on this, an object of the present invention is to provide a heat pump system with defrost control.

[0005] A heat pump system with defrost control includes a compressor, a four-way valve, a water-side heat exchanger, an electronic expansion valve, an air-side heat exchanger connected in sequence through a refrigerant circulation pipeline, and a DC fan arranged on one side of the air-side heat exchanger, a temperature detection module, and a controller electrically and / or communicatively connected to the four-way valve, the temperature detection module and the DC fan. The controller performs defrost judgment of the heat pump system in the following manner:

[0006] S20 obtains the current ambient temperature

[0007] If the current ambient temperature Less than or equal to the first ambient temperature defrost threshold Or the current ambient temperature Greater than the first ambient temperature defrost threshold And less than or equal to the second ambient temperature defrost threshold If the defrost judgment of the previous defrost cycle is a DC fan defrost judgment, then step S30 is executed;

[0008] S30 obtains the current defrosting interval time t t , DC fan speed F i t and speed External coil temperature

[0009]

[0010] If the defrost interval time t t Shorter than the set minimum defrost interval And it is greater than the set DC fan defrost monitoring time And the current DC fan speed In gear position wind speed F i t Corresponding set speed Within the fluctuation range, or the defrost interval time t t Greater than or equal to the minimum defrost interval And it is less than the set maximum defrost interval And the current external coil temperature Less than the second disk temperature defrost threshold Then execute step S40;

[0011] S40 performs defrosting judgment on the DC fan and obtains the current PWM value of the DC fan t ; According to the current gear wind speed F i t Find the corresponding PWM reference value Calculating PWM reference value and the current PWM value PWM t The difference between the current moment PWM difference ΔPWM is obtained. t ; Determine the current PWM difference ΔPWM t Is the absolute value of greater than the preset PWM difference threshold ΔPWM TD :

[0012] If yes, the control system enters defrosting;

[0013] If no, continue monitoring;

[0014] Among them, the first ring temperature defrost threshold <Second ambient temperature defrost threshold DC fan defrost monitoring time <Minimum defrost interval time <Maximum defrost interval time

[0015] Furthermore, in step S40, the wind speed F i Corresponding PWM reference value Obtained through:

[0016] SA1 obtains the power-on status of the system:

[0017] If the system is powered on for the first time, execute step SA2;

[0018] If the system is not powered on for the first time, get the current ambient temperature

[0019] Such as ambient temperature Less than or equal to the sampling ambient temperature threshold Then get the gear wind speed F of the DC fan i and PWM value PWM i , the PWM value PWM i Set to gear wind speed F i Corresponding PWM reference value and store;

[0020] SA2 obtains the current external coil temperature of the system Ambient temperature

[0021] If the external coil temperature Greater than the first disk temperature defrost threshold T1 target And the ambient temperature Less than or equal to the sampling ambient temperature threshold Then get the gear wind speed F of the DC fan i and PWM value PWM i , the PWM value PWM i Set to gear wind speed F i Corresponding PWM reference value and store;

[0022] If the external coil temperature Less than or equal to the first disk temperature defrost threshold T1 target If the duration is greater than or equal to 3 minutes, the control system enters defrosting. After the defrosting is completed and the fan is restarted, the gear wind speed F of the DC fan is obtained. i and PWM value PWM i , the PWM value PWM i Set to gear wind speed F i Corresponding PWM reference value and store.

[0023] Furthermore, the PWM reference value in step S40 Update according to the running situation. The update method is as follows:

[0024] SC1 obtains the current defrost interval T of the system t :

[0025] If the defrost interval period T t Less than the set PWM value acquisition cycle threshold Then continue to obtain the next defrost interval period T t+1 ;

[0026] If the defrost interval period T t Greater than or equal to the set PWM acquisition cycle threshold Get the DC fan's gear speed F i and DC fan speed

[0027] Such as DC fan speed In gear position wind speed F i Corresponding set speed If it is within the fluctuation range, execute SC2;

[0028] If it is other situations and lasts for 4 minutes, the control system will enter defrosting, restart the fan after defrosting is completed, and continue to obtain the DC fan PWM value;

[0029] SC2 collects the DC fan PWM value for a period of time at a certain collection frequency and calculates the average value of the DC fan PWM value

[0030] If the average Less than or equal to the stored reference value Then the average value As the new baseline Execute step SC3;

[0031] If the average Less than the stored reference value and is greater than the stored reference value The average value Add 10%*C1 as the new reference value Step SC3 is performed, wherein

[0032]

[0033] If the average Greater than or equal to the stored reference value The stored reference value is not updated.

[0034]

[0035] SC3 determines the new reference value Is it within the allowed initial baseline value? Within the fluctuation range:

[0036] If the new baseline belong The new baseline value As a benchmark Update and store;

[0037] If it is other cases, the reference value is not updated this time, and the control system enters defrosting, restarts the fan after defrosting is completed, and then continues to obtain the DC fan PWM value;

[0038] Wherein, C1 represents the first constant, and C2 represents the second constant.

[0039] Further, S50 controls the four-way valve working valve port reversal and obtains the defrosting duration t' and the external coil temperature

[0040] If the defrost duration t` is greater than or equal to the set defrost time Then the DC fan reference value corresponding to all gear wind speeds stored is adjusted down by 10%*C1 as the new reference value Storage, and exit defrosting, control the reversal of the working valve port of the four-way valve; among them,

[0041] If the defrost duration t` is less than the set defrost time And the external coil temperature Greater than or equal to the first defrost exit temperature threshold Then the defrosting is stopped and the working valve port of the four-way valve is controlled to be reversed;

[0042] If the defrost duration t` is less than the set defrost time And the external coil temperature Greater than or equal to the second defrost exit temperature threshold And less than the first defrost exit temperature threshold If the duration is greater than 10s, the defrosting is terminated and the four-way valve is controlled to switch the working valve port; the first defrosting exit temperature threshold Greater than the second defrost exit temperature threshold

[0043]

[0044] In other cases, defrost control is continued;

[0045] The C1 satisfies: C1=α*50%; wherein α represents the defrosting coefficient of the DC fan.

[0046] Furthermore, before step S20, the following logical judgment is also included:

[0047] S10 obtains the system power-on status:

[0048] If it is not the first power-on, execute step S20;

[0049] If it is the first time to power on, get the current external coil temperature of the system

[0050] The external coil temperature Less than or equal to the first disk temperature defrost threshold If the situation lasts for the first time period t1, the control system enters defrosting and updates the DC fan reference value after exiting defrosting.

[0051] If it is other cases, determine the current external coil temperature Whether the timed defrosting conditions are met:

[0052] If it is satisfied, the control system will enter timed defrosting;

[0053] If not satisfied, execute step S30.

[0054] Compared with the prior art, the heat pump system provided by the present invention uses the defrost interval period and the DC fan speed to determine in real time whether to update the PWM reference value according to the set rules, based on the correlation between the ambient temperature, the PWM reference value corresponding to the DC fan gear speed, and the system frosting rate and frosting thickness; and determines whether the system has entered defrosting based on the relationship between the ambient temperature, the PWM value of the DC fan of the heat pump system and the corresponding PWM reference value and the set difference threshold, thereby achieving more accurate, efficient and reliable defrosting judgment.

[0055] For better understanding and implementation, the present invention is described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 A schematic diagram of the system structure of an embodiment of the present invention;

[0057] Figure 2 is a flow chart of a control method according to an embodiment of the present invention;

[0058] Figure 3 for Figure 2 Defrost judgment flow chart in. DETAILED DESCRIPTION

[0059] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention.

[0060] In order to solve the problem that the existing heat pump system cannot meet the scientific defrosting requirements of the heat pump system in areas or seasons with large changes in outdoor ambient temperature when defrosting by setting fixed parameters such as fixed defrosting interval time and fixed temperature difference between ambient temperature and coil temperature, frequent defrosting, no defrosting, and no frost defrosting often occur, which reduces the energy consumption of the system and leads to poor heating or cooling experience for users; after research and debugging, the present invention proposes a heat pump system with defrosting control. According to the correlation between the PWM value change of the DC fan and the system frosting rate and frosting thickness, the heat pump system monitors the PWM value change of the DC fan in real time, reasonably updates the reference value of the PWM value, and comprehensively detects the changes in indoor and outdoor temperature and humidity, so as to achieve more accurate, efficient and reliable defrosting control.

[0061] For specific implementation, please refer to Figure 1 The heat pump system with defrost control proposed by the present invention comprises a compressor 10, a four-way valve 20, a water-side heat exchanger 30, an electronic expansion valve 40, an air-side heat exchanger 50, and a DC fan 60 arranged on the side of the air-side heat exchanger 50, a temperature detection module 70, a controller (not shown), and other auxiliary pipes connected by a refrigerant pipeline. The controller is electrically connected or communicatively connected with the compressor 10, the electronic expansion valve 40, the DC fan 60 and the temperature detection module 70.

[0062] The temperature detection module 70 includes a first temperature sensor 71 and a second temperature sensor 72. The first temperature sensor 71 is disposed on the outer coil of the air side heat exchanger 50, and is used to collect the temperature signal of the outer coil and convert the outer coil temperature into a value. The second temperature sensor 72 is used to collect the ambient temperature. And the ambient temperature The second temperature sensor 72 can be arranged on the outside of the air-side heat exchanger 50 or on the casing of the heat pump system, which is not limited in the present application.

[0063] The controller receives the PWM value of the DC fan 60 and the temperature signal collected by the temperature detection module 70, and judges the defrosting of the system according to the stored calculation and judgment program, and controls the four-way valve to perform valve conversion to enter defrosting control.

[0064] For details, please refer to Figure 2 The controller of the heat pump system of the present invention performs defrost judgment and defrost control of the system through the following method.

[0065] S10 obtains the system power-on status:

[0066] If it is not the first power-on, execute step S20;

[0067] If it is the first time to power on, get the current external coil temperature of the system

[0068] The external coil temperature Less than or equal to the first disk temperature defrost threshold If the situation lasts for the first time period t1, the control system enters defrosting and updates the DC fan reference value after exiting defrosting.

[0069] If it is other cases, determine the current external coil temperature Whether the timed defrosting conditions are met:

[0070] If satisfied, the control system enters timed defrosting;

[0071] If not satisfied, execute step S30.

[0072] In specific implementation, the first disk temperature defrosting threshold The setting range is -8℃~-6℃, preferably -7℃.

[0073] The first time period t1 is set in a range of 2 minutes to 4 minutes, preferably 3 minutes.

[0074] The timed defrosting conditions are:

[0075] Current external coil temperature Greater than the first disk temperature defrost threshold And less than the second disk temperature defrost threshold And, the current defrost interval time t t Greater than or equal to the set minimum defrost interval

[0076] The second disk temperature defrost threshold The setting range is -4 to -2°C, preferably -3°C.

[0077] The minimum defrost interval duration Set to 45min.

[0078] S20 obtains the current ambient temperature

[0079] If the current ambient temperature Less than or equal to the first ambient temperature defrost threshold Then execute step S30;

[0080] If the current ambient temperature Greater than the first ambient temperature defrost threshold And less than or equal to the second ambient temperature defrost threshold Then obtain the defrost judgment of the previous defrost cycle:

[0081] If the defrost judgment of the previous defrost cycle is a DC fan defrost judgment, step S30 is executed;

[0082] If the defrost of the previous defrost cycle is judged as the external coil temperature Judge, then according to the current external coil temperature Determine whether the timed defrost conditions are met, if so, the control system enters the timed defrost mode;

[0083] If the current ambient temperature Greater than the second ambient temperature defrost threshold Then continue monitoring.

[0084] In specific implementation, the first ambient temperature defrosting threshold Set to 10℃; the second ambient temperature defrost threshold Set to 14°C.

[0085] Furthermore, when there are several DC fans, if one of them is abnormal or has a fault, the external coil temperature at the current moment is used. Determine whether the system has entered timed defrost.

[0086] S30 obtains the current defrosting interval time t t , DC fan speed F i t and speed External coil temperature

[0087]

[0088] If the defrost interval time t t Shorter than the set minimum defrost interval And it is greater than the DC fan defrost monitoring time Right now Then further determine the current DC fan speed Is the wind speed F at the current gear? i t Corresponding set speed Within the fluctuation range, that is, whether

[0089] If yes, Then execute step S40;

[0090] If no, If the duration is greater than or equal to 4 minutes, the control system enters the defrosting execution S50; if the defrosting interval time t t Greater than or equal to the minimum defrost interval And it is less than the set maximum defrost interval And the current external coil temperature Less than the second disk temperature defrost threshold Right now and Then execute step S40;

[0091] If the defrost interval time t t Greater than the maximum defrost interval Right now Then the control system enters the defrosting execution S50;

[0092] For other situations, continue to monitor.

[0093] In specific implementation, the defrosting interval time t t Refers to the time period from the current running time to the end of the previous defrost after the system enters the working mode.

[0094] The maximum defrost interval duration The setting range is 5.5h to 6.5h, preferably 6.0h.

[0095] The minimum defrost interval duration The setting range is 40min to 50min, preferably 45min.

[0096] The DC fan defrost monitoring time The setting range is 9min to 11min, preferably 10min.

[0097] S40 performs defrosting judgment on the DC fan and obtains the current PWM value of the DC fan t ; According to the current gear wind speed F i t Find the corresponding PWM reference value The PWM reference value Update based on operating conditions; calculate PWM reference value and the current PWM value PWM t The difference between the current moment PWM difference ΔPWM is obtained. t ; Determine the current PWM difference ΔPWM t Is the absolute value of greater than the preset PWM difference threshold ΔPWM TD :

[0098] If yes, the control system enters defrosting execution S50;

[0099] If no, continue monitoring.

[0100] In specific implementation, the sampling of the DC fan PWM value meets the following requirements:

[0101] (1) When sampling, the wind speed F of the DC fan is at the gear speed F i Within the allowed fluctuation range, that is, F∈(F i ±10RPM); Example: The sampling range of the wind speed at gear position 720RPM is between 710RPM and 730RPM.

[0102] (2) The sampling period is 1 minute;

[0103] (3) The sampling frequency is 60 times / min.

[0104] The PWM difference threshold ΔPWM TD The setting range is 490 to 510, preferably 500.

[0105] The gear wind speed F of the DC fan i Including (F1, F2, ..., F9), that is, F1 to F9, corresponding to different PWM reference values Right now And the benchmark value can be updated in real time according to the operating conditions and operating environment.

[0106] The wind speed F i Corresponding PWM reference value Obtained through:

[0107] SA1 obtains the power-on status of the system:

[0108] If the system is powered on for the first time, execute step SA2;

[0109] If the system is not powered on for the first time, get the current ambient temperature

[0110] Such as ambient temperature Greater than the set sampling ambient temperature threshold Then continue to obtain the ambient temperature at the next moment

[0111] Such as ambient temperature Less than or equal to the sampling ambient temperature threshold Then get the gear wind speed F of the DC fan i and PWM value PWM i , the PWM value PWM i Set to gear wind speed F i Corresponding PWM reference value and store.

[0112] SA2 obtains the current external coil temperature of the system

[0113] If the external coil temperature Greater than the first disk temperature defrost threshold T1 target , then further obtain the current ambient temperature

[0114] Such as ambient temperature Greater than the sampling ambient temperature threshold Then continue to obtain the external coil temperature at the next moment

[0115] Such as ambient temperature Less than or equal to the sampling ambient temperature threshold Then get the gear wind speed F of the DC fan i and PWM value PWM i , the PWM value PWM i Set to gear wind speed F i Corresponding PWM reference value and store;

[0116] If the external coil temperature Less than or equal to the first disk temperature defrost threshold T1 target If the duration is greater than or equal to 3 minutes, the control system will immediately enter defrosting. After the defrosting is completed and the DC fan is restarted, the gear wind speed F of the DC fan is obtained. i and PWM value PWM i , the PWM value PWM i Set to gear wind speed F i Corresponding PWM reference value and store.

[0117] This method is used to ensure that the PWM reference value of the DC fan is obtained in a frost-free state.

[0118] In specific implementation, the sampling ambient temperature threshold The setting range is 7 to 9°C, preferably 8°C.

[0119] The PWM reference value Update according to the running situation. The specific update method is as follows:

[0120] SC1 obtains the current defrost interval T of the system t :

[0121] If the defrost interval period T t Less than the set PWM value acquisition cycle threshold Then continue to obtain the next defrost interval period T t+1 ;

[0122] If the defrost interval period T t Greater than or equal to the set PWM acquisition cycle threshold Get the DC fan's gear speed F i and DC fan speed R t :

[0123] For example, the DC fan speed R t In gear position wind speed F i Corresponding set speed Within the fluctuation range, that is Then execute SC2;

[0124] If it is other situation and it lasts for 4 minutes, the control system will enter defrosting, restart the fan after defrosting is completed, and continue to obtain the DC fan PWM value.

[0125] SC2 collects the DC fan PWM value for a period of time at a certain collection frequency and calculates the average value of the collected DC fan PWM value

[0126] If the average Less than or equal to the stored reference value The average value As the new baseline Execute step SC3;

[0127] If the average Less than the stored reference value and is greater than the stored reference value The average value Add 10%*C1 as the new reference value Step SC3 is performed, wherein

[0128]

[0129] If the average Greater than or equal to the stored reference value The stored reference value is not updated.

[0130]

[0131] In a specific implementation, the first constant C1=α*50%, wherein α represents the defrosting coefficient of the DC fan.

[0132] SC3 determines the new reference value Is it within the allowed initial baseline value? Within the fluctuation range:

[0133] If the new baseline belong The new baseline value As a benchmark Update and store;

[0134] If it is other cases, the reference value is not updated this time, and the control system enters defrosting, and after the defrosting is completed and the fan is restarted, the DC fan PWM value is continuously obtained.

[0135] In a specific implementation, the second constant C2=α*150%.

[0136] The PWM reference value corresponding to the DC fan gear speed may be updated once after N defrosting cycles.

[0137] S50 controls the reversal of the four-way valve working port and obtains the defrost duration t` and the temperature of the external coil

[0138] If the defrost duration t` is greater than the set defrost time Then execute step S60;

[0139] If the defrost duration t` is less than the set defrost time And the external coil temperature Greater than or equal to the first defrost exit temperature threshold Then, the defrosting is exited, the working valve port of the four-way valve is controlled to be reversed and step S20 is executed;

[0140] If the defrost duration t` is less than the set defrost time And the external coil temperature Greater than or equal to the second defrost exit temperature threshold And less than the first defrost exit temperature threshold If the duration is greater than 10 seconds, the defrosting is terminated, the working valve port of the four-way valve is controlled to be reversed and step S20 is executed;

[0141] In other cases, defrost control is continued.

[0142] In specific implementation, the defrosting time The setting range is 8min~10min.

[0143] The first defrost exit temperature threshold The setting range is 24-26°C, preferably 25°C. The second defrost exit temperature threshold The setting range is 14-16°C, preferably 15°C.

[0144] S60 adjusts the stored DC fan reference values ​​corresponding to all gear wind speeds down by 10%*C1 as the new reference value Store, and exit defrosting, control the four-way valve working valve port to switch and execute step S20; wherein,

[0145] Compared with the prior art, the heat pump system with a defrost control mode of the present invention uses the defrost interval period and the DC fan speed to determine in real time whether to update the PWM reference value according to the set rules, based on the correlation between the ambient temperature, the PWM reference value corresponding to the DC fan gear speed and the system frosting rate and frosting thickness; and determines whether the system has entered defrost based on the relationship between the ambient temperature, the PWM value of the DC fan of the heat pump system and the corresponding PWM reference value and the set difference threshold, thereby achieving more accurate, efficient and reliable defrost judgment.

[0146] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the embodiments of the present application. The singular forms of "a", "said" and "the" used in the embodiments of the present application and the claims are also intended to include plural forms, unless the context clearly indicates other meanings. It should also be understood that, unless otherwise specified, "multiple" and "several" refer to two or more; "and / or" refers to and includes any or all possible combinations of one or more associated listed items; "first", "second", "third", etc. are only used to distinguish, rather than to describe a specific order or sequence, and cannot be understood as indicating or implying relative importance. When the above description relates to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. In the description of the present application, for those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances.

[0147] The above-mentioned embodiments only express several implementation methods of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, and the present invention is also intended to include these modifications and modifications.

Claims

1. A heat pump system with defrost control, comprising a compressor, a four-way valve, a water-side heat exchanger, an electronic expansion valve, an air-side heat exchanger connected in sequence through a refrigerant circulation pipeline, and a DC fan arranged on one side of the air-side heat exchanger, and a temperature detection module, and a controller electrically and / or communicatively connected to the four-way valve, the temperature detection module and the DC fan, characterized in that: The controller makes defrost judgment on the heat pump system in the following ways: S20 obtains the current ambient temperature If the current ambient temperature Less than or equal to the first ambient temperature defrost threshold Or the current ambient temperature Greater than the first ambient temperature defrost threshold And less than or equal to the second ambient temperature defrost threshold If the defrost judgment of the previous defrost cycle is a DC fan defrost judgment, then step S30 is executed; S30 obtains the current defrosting interval time t t , DC fan speed F i t and speed External coil temperature If the defrost interval time t t Shorter than the set minimum defrost interval And it is greater than the set DC fan defrost monitoring time And the current DC fan speed In gear position wind speed F i t Corresponding set speed Within the fluctuation range, or the defrost interval time t t Greater than or equal to the minimum defrost interval And it is less than the set maximum defrost interval And the current external coil temperature Less than the second disk temperature defrost threshold Then execute step S40; S40 performs defrosting judgment on the DC fan and obtains the current PWM value of the DC fan t ; According to the current gear wind speed F i t Find the corresponding PWM reference value Calculating PWM reference value and the current PWM value PWM t The difference between the current moment PWM difference ΔPWM is obtained. t ; Determine the current PWM difference ΔPWM t Is the absolute value of greater than the preset PWM difference threshold ΔPWM TD : If yes, the control system enters defrosting; If no, continue monitoring; Among them, the first ring temperature defrost threshold <Second ambient temperature defrost threshold DC fan defrost monitoring time <Minimum defrost interval time <Maximum defrost interval time 2. The heat pump system according to claim 1, characterized in that: In step S40, the wind speed F in the middle position i Corresponding PWM reference value Obtained through: SA1 obtains the power-on status of the system: If the system is powered on for the first time, execute step SA2; If the system is not powered on for the first time, get the current ambient temperature Such as ambient temperature Less than or equal to the sampling ambient temperature threshold Then get the gear wind speed F of the DC fan i and PWM value PWM i , the PWM value PWM i Set to gear wind speed F i Corresponding PWM reference value and store; SA2 obtains the current external coil temperature of the system Ambient temperature If the external coil temperature Greater than the first disk temperature defrost threshold T1 target And the ambient temperature Less than or equal to the sampling ambient temperature threshold Then get the gear wind speed F of the DC fan i and PWM value PWM i , the PWM value PWM i Set to gear wind speed F i Corresponding PWM reference value and store; If the external coil temperature Less than or equal to the first disk temperature defrost threshold T1 target If the duration is greater than or equal to 3 minutes, the control system enters defrosting. After the defrosting is completed and the fan is restarted, the gear wind speed F of the DC fan is obtained. i and PWM value PWM i , the PWM value PWM i Set to gear wind speed F i Corresponding PWM reference value and store.

3. The heat pump system according to claim 1 or 2, characterized in that: The PWM reference value in step S40 Update according to the running situation. The update method is as follows: SC1 obtains the current defrost interval T of the system t : If the defrost interval period T t Less than the set PWM value acquisition cycle threshold Then continue to obtain the next defrost interval period T t+1 ; If the defrost interval period T t Greater than or equal to the set PWM acquisition cycle threshold Get the DC fan's gear speed F i and DC fan speed Such as DC fan speed In gear position wind speed F i Corresponding set speed If it is within the fluctuation range, execute SC2; If it is other situations and lasts for 4 minutes, the control system will enter defrosting, restart the fan after defrosting is completed, and continue to obtain the DC fan PWM value; SC2 collects the DC fan PWM value for a period of time at a certain collection frequency and calculates the average value of the DC fan PWM value If the average Less than or equal to the stored reference value Then the average value As the new baseline Execute step SC3; If the average Less than the stored reference value and is greater than the stored reference value Then the average value Add 10%*C1 as the new reference value Step SC3 is performed, wherein If the average Greater than or equal to the stored reference value The stored reference value is not updated. SC3 determines the new reference value Is it within the allowed initial baseline value? Within the fluctuation range: If the new baseline belong The new baseline value As a benchmark value Update and store; If it is other cases, the reference value is not updated this time, and the control system enters defrosting, restarts the fan after defrosting is completed, and then continues to obtain the DC fan PWM value; Wherein, C1 represents the first constant, and C2 represents the second constant.

4. The heat pump system according to claim 3, characterized in that: The first constant C1 satisfies: C1＝α*50％； The second constant C2 satisfies: C2＝α*150％； Wherein, α represents the defrost coefficient of the DC fan.

5. The heat pump system according to claim 4, characterized in that: The sampling of the DC fan PWM value meets the following requirements: When sampling, the wind speed F of the DC fan is at the gear speed F i Within the allowable fluctuation range, that is, F is within (F i ±10RPM); The sampling period is 1min; The sampling frequency is 60 times / min.

6. The heat pump system according to any one of claims 1, 2, 4 and 5, characterized in that: The DC fan defrost monitoring time The setting range is 9min~11min; the minimum defrost interval time The setting range is 40min~50min; the maximum defrost interval time The setting range is 5.5h~6.5h.

7. The heat pump system according to claim 6, characterized in that: The first ambient temperature defrost threshold Set to 10℃; the second ambient temperature defrost threshold Set to 14°C.

8. The heat pump system according to claim 7, characterized in that: The DC fan has a gear speed of (F1, F2, ..., F9), and the PWM reference value corresponding to each gear is 9. The heat pump system according to any one of claims 1, 2, 4, 5, 7 and 8, characterized in that: The defrosting process includes the following logic controls: S50 controls the reversal of the four-way valve working port and obtains the defrost duration t` and the temperature of the external coil If the defrost duration t` is greater than or equal to the set defrost time Then the DC fan reference value corresponding to all gear wind speeds stored is adjusted down by 10%*C1 as the new reference value Storage, and exit defrosting, control the reversal of the working valve port of the four-way valve; among them, If the defrost duration t` is less than the set defrost time And the external coil temperature Greater than or equal to the first defrost exit temperature threshold Then the defrosting is stopped and the working valve port of the four-way valve is controlled to be reversed; If the defrost duration t` is less than the set defrost time And the external coil temperature Greater than or equal to the second defrost exit temperature threshold And less than the first defrost exit temperature threshold If the duration is greater than 10s, the defrosting is terminated and the four-way valve is controlled to switch the working valve port; the first defrosting exit temperature threshold Greater than the second defrost exit temperature threshold In other cases, defrost control is continued; The C1 satisfies: C1=α*50%; wherein α represents the defrosting coefficient of the DC fan.

10. The heat pump system according to any one of claims 1, 2, 4, 5, 7, 8, and 9, characterized in that: Before step S20, the following logic judgment is also included: S10 obtains the system power-on status: If it is not the first power-on, execute step S20; If it is the first time to power on, get the current external coil temperature of the system The external coil temperature Less than or equal to the first disk temperature defrost threshold If the situation lasts for the first time period t1, the control system enters defrosting and updates the DC fan reference value after exiting defrosting. If it is other cases, determine the current external coil temperature Whether the timed defrosting conditions are met: If satisfied, the control system enters timed defrosting; If not satisfied, execute step S30.

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