Control method for defrosting and inhibiting frosting and heat pump system

Abstract

The invention belongs to the technical field of heat pumps, and discloses a control method for defrosting and inhibiting frosting and a heat pump system. The control method for defrosting and restraining frosting comprises the steps that S1, whether the heat pump system enters a defrosting mode or not is judged according to the coil pipe temperature Te, the environment temperature T1 and the accumulated operation time t of a compressor; if yes, executing the step S2; if not, executing the step S3; s2, whether the return water temperature Tin reaches the preset temperature T2 or not is judged, and if Tin is larger than or equal to T2, the four-way valve conducts reversing defrosting, and the opening degree of the first electronic expansion valve is adjusted; if Tin is smaller than T2, the first electronic expansion valve is closed, the second electronic expansion valve is opened, and the opening degree of the second electronic expansion valve is adjusted so that bypass defrosting can be conducted; and S3, entering a heating mode. According to the control method for defrosting and inhibiting frosting, when the heat pump system is controlled to normally heat, after heating and heat supply meet the target set temperature, frosting prevention of the fin heat exchanger is carried out in advance; and the plate heat exchanger is prevented from frost damage during defrosting, and normal operation of the plate heat exchanger is guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of heat pumps, and in particular to a defrosting and frosting suppression control method and a heat pump system. Background Art

[0002] Currently, in the field of air-source heat pump heating, due to the low ambient temperature in the environment where it is used, frosting occurs on the outer surface of the heat exchanger, thus affecting the use of the heat exchanger. At present, many heating heat pump systems use a four-way valve to reverse the defrosting control or defrost by means of hot gas bypass. When using the four-way valve to reverse defrosting, the following defects exist: during the process of reversing defrosting by the four-way valve, the return water temperature on the user side will decrease, resulting in a poor user experience on the user side and affecting heating. Moreover, when the return water temperature is low, the plate heat exchanger serves as an evaporator, and the refrigerant absorbs heat from the water. Due to the low water temperature, the evaporation temperature of the system is low, and it is easy to freeze and damage the plate heat exchanger, posing a risk. When using hot gas bypass defrosting, the following defects exist: regardless of whether the return water temperature is high or low, hot gas bypass defrosting is adopted, which will cause the operating energy efficiency of the entire heat pump system to become low.

[0003] Therefore, there is an urgent need for a defrosting and frosting suppression control method and a heat pump system to solve the above technical problems. Summary of the Invention

[0004] The purpose of the present invention is to provide a defrosting and frosting suppression control method and a heat pump system, which can control the heat pump system to prevent frosting of the fin heat exchanger in advance after the heating and heating meet the target set temperature during normal heating, and prevent the plate heat exchanger from being frozen during defrosting, ensuring the normal operation of the plate heat exchanger.

[0005] To achieve this purpose, the present invention adopts the following technical solutions:

[0006] A defrosting and frosting suppression control method is applied to a heat pump system. The heat pump system includes a compressor, a plate heat exchanger, a fin heat exchanger, a four-way valve, a first electronic expansion valve, and a second electronic expansion valve. The refrigerant side of the plate heat exchanger is heat exchange-connected to the heating water circuit, and the refrigerant side of the fin heat exchanger is heat exchange-connected to the air; the compressor, the four-way valve, the plate heat exchanger, the first electronic expansion valve, and the fin heat exchanger are connected in series to form a main circulation loop; the compressor, the second electronic expansion valve, the fin heat exchanger, and the four-way valve are connected in series to form a bypass circulation loop; the defrosting and frosting suppression control method includes the steps:

[0007] S1. According to the coil temperature T e , the ambient temperature T1, and the cumulative operation time t of the compressor, determine whether the heat pump system enters the defrosting mode; if so, execute step S2; if not, execute step S3;

[0008] S2. Determine the return water temperature T in Whether it reaches the preset temperature T2. If T in ≥T2, the four-way valve changes direction for defrosting and adjusts the opening degree of the first electronic expansion valve; if T in <T2, close the first electronic expansion valve, open the second electronic expansion valve and adjust the opening degree of the second electronic expansion valve to perform bypass defrosting;

[0009] S3. Enter the heating mode.

[0010] Optionally, in step S1, the judgment conditions for the defrosting mode of the heat pump system include:

[0011] T e ≤ -3°C and last for 1 minute; and,

[0012] T1 - T e ≥ 10°C and last for 1 minute; and,

[0013] t ≥ 45 minutes.

[0014] Optionally, when the heating mode in step S3 is running, according to the return water temperature T in or the return water temperature rising rate T3, judge whether it meets the opening condition for entering the anti - frosting mode. If so, open the second electronic expansion valve and adjust the opening degree of the second electronic expansion valve. If not, maintain the heating mode.

[0015] Optionally, the judgment conditions for the opening of the anti - frosting mode include:

[0016] T1 ≥ T4 - ΔT; or,

[0017] T3 ≥ 1°C / min;

[0018] Wherein, the above - mentioned T4 is the target temperature on the user's heating use side; the above - mentioned ΔT is the bypass start hysteresis.

[0019] Optionally, in step S3, the anti - frosting mode also has a closing condition. If the closing condition is met, close the second electronic expansion valve. The judgment conditions for the closing of the anti - frosting mode include:

[0020] T1 < T4 - ΔT; and,

[0021] T3 < 1°C / min;

[0022] Wherein, the above - mentioned T4 is the target temperature on the user's heating use side; the above - mentioned ΔT is the bypass start hysteresis.

[0023] Optionally, in steps S2 and S3, the adjustment method for the actual opening degree P n of the second electronic expansion valve includes:

[0024] P n = P n-1 + [KP * (T Dn - T et ) + KD * (T Dn - T Dn-1) ;

[0025] Wherein, P n-1 is the opening degree of the above-mentioned second electronic expansion valve in the previous cycle; KP is the proportionality coefficient, generally 2; KD is the differential coefficient, generally 1; T et is the target exhaust temperature of the above-mentioned compressor, and T Dn is the actual exhaust temperature of the above-mentioned compressor; T Dn-1 is the exhaust temperature of the above-mentioned compressor in the previous cycle.

[0026] Optionally, the above-mentioned target exhaust temperature satisfies: T et = A - B * T e + C * T c ;

[0027] Wherein, A, B, and C are all coefficients, A = 15, B = -1, C = 1.5, and T c = outlet water temperature + 4°C.

[0028] Optionally, the initial opening degree of the above-mentioned second electronic expansion valve satisfies: EXV0 = 2 * K1 + K2 * T e - K3 * T in , 60P ≤ EXV0 ≤ 480P;

[0029] Wherein, K1, K2, and K3 are all coefficients, K1 = 120, K2 = 4, and K3 = 2.

[0030] Optionally, the above-mentioned second electronic expansion valve is adjusted with a preset time T exv as the period, and T exv = 15s.

[0031] The purpose of the present invention is to provide a heat pump system, which uses the defrosting and frost formation inhibition control method described in any of the above solutions, and can, during normal heating, perform anti-frosting of the fin heat exchanger in advance after the heating and heating meet the target set temperature, and prevent the plate heat exchanger from freezing during defrosting, ensuring the normal operation of the plate heat exchanger.

[0032] Advantages of the present invention:

[0033] The present invention provides a defrosting and frost formation inhibition control method and a heat pump system. When defrosting the fin heat exchanger, it can determine whether the heat in the heating water circuit meets the user's needs according to the return water temperature in the heating water circuit. If it meets, i.e., Tin ≥ T2, the four-way valve is reversed for defrosting. At this time, the fin heat exchanger is the condenser, and the plate heat exchanger is the evaporator to defrost the fin heat exchanger. If the return water temperature is low, i.e., T in < T2, the bypass circulation loop can be opened and the main circulation loop can be closed, so that the high-temperature and high-pressure refrigerant from the compressor directly acts on the fin heat exchanger to achieve better defrosting of the fins. At the same time, it avoids the situation that the evaporation temperature is too low during the four-way valve reversing defrosting and damages the plate heat exchanger, and also avoids the problem that the overall energy efficiency of the heat pump system becomes low due to long-term use of the bypass defrosting method under large differences in return water temperature, improving the reliability and service life of the heat pump system. Moreover, after the bypass circulation loop is opened, the flow rate of the bypass circulation loop is controlled by adjusting the opening of the second electronic expansion valve, which is more convenient for defrosting fin heat exchangers at different temperatures. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a schematic structural diagram of the heat pump system provided by the specific embodiment of the present invention in the heating mode;

[0035] Figure 2 is a schematic structural diagram of the heat pump system provided by the specific embodiment of the present invention in the anti-frost mode;

[0036] Figure 3 is a schematic structural diagram of the heat pump system provided by the specific embodiment of the present invention in the four-way valve heat exchange defrosting mode;

[0037] Figure 4 is a schematic structural diagram of the heat pump system provided by the specific embodiment of the present invention in the hot gas bypass defrosting mode.

[0038] In the figure:

[0039] 1. Compressor; 2. Plate heat exchanger; 3. Fin heat exchanger; 4. Four-way valve; 5. First electronic expansion valve; 6. Second electronic expansion valve; 7. Coil temperature detector; 8. Return water temperature detector; 9. Outlet water temperature detector; 10. Exhaust gas temperature detector; 11. Suction gas temperature detector;

[0040] 101. Main circulation loop; 102. Bypass circulation loop; 103. Heating water circuit. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] The present invention will be further described in detail below with reference to the drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the present invention, rather than limiting the present invention. In addition, it should be noted that for the convenience of description, only parts related to the present invention are shown in the drawings, rather than all the structures.

[0042] In the description of the present invention, unless otherwise clearly defined and limited, the terms "connected", "connected to", and "fixed" shall be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be directly connected, or indirectly connected through an intermediate medium, and may be the communication inside two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0043] In the present invention, unless otherwise clearly defined and limited, the first feature being "above" or "below" the second feature may include the direct contact between the first and second features, or may include the situation where the first and second features are not in direct contact but in contact through other features between them. Moreover, the first feature being "above", "above and to the upper side", and "on the upper surface" of the second feature includes that the first feature is directly above and obliquely above the second feature, or merely indicates that the horizontal height of the first feature is higher than that of the second feature. The first feature being "below", "below and to the lower side", and "on the lower surface" of the second feature includes that the first feature is directly below and obliquely below the second feature, or merely indicates that the horizontal height of the first feature is lower than that of the second feature.

[0044] In the description of this embodiment, the orientation or positional relationships such as "upper", "lower", "left", "right", etc. are based on the orientation or positional relationships shown in the drawings, and are only for the convenience of description and simplifying the operation, rather than indicating or implying that the device or component referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention. In addition, the terms "first" and "second" are only used for distinction in description and have no special meanings.

[0045] The following refers to Figures 1 to 4 to introduce the defrosting and frost formation inhibition control method and heat pump system provided by the present invention.

[0046] This embodiment provides a heat pump system for heating. When heating normally, after the heating meets the target set temperature, it can prevent frost formation on the fin heat exchanger 3 in advance, and prevent the plate heat exchanger 2 from being frozen during defrosting, ensuring the normal operation of the plate heat exchanger 2.

[0047] Please refer to Figures 1 to 4 , specifically, the heat pump system includes a compressor 1, a plate heat exchanger 2, a fin heat exchanger 3, a four-way valve 4, a first electronic expansion valve 5, and a second electronic expansion valve 6. The refrigerant side of the plate heat exchanger 2 is heat exchange-connected to the heating water circuit 103, and the refrigerant side of the fin heat exchanger 3 is heat exchange-connected to the air; the compressor 1, the four-way valve 4, the plate heat exchanger 2, the first electronic expansion valve 5, and the fin heat exchanger 3 are connected in series to form a main circulation loop 101; the compressor 1, the second electronic expansion valve 6, the fin heat exchanger 3, and the four-way valve 4 are connected in series to form a bypass circulation loop 102.

[0048] For the heat pump system in this embodiment, please refer to Figure 1 , when in the heating mode, the fin heat exchanger 3 in the main circulation loop 101 serves as the evaporator, and the plate heat exchanger 2 serves as the condenser, thus enabling heat supply to the heating water circuit 103. Please refer to Figure 2 , during the operation of the heating mode, if the temperature of the heating water circuit 103 is relatively high or the heating rate of the heating water circuit 103 is relatively high, at this time, the bypass circulation loop 102 can be opened by opening the second electronic expansion valve 6 to supply heat to the fin heat exchanger 3, effectively suppressing frosting of the fin heat exchanger 3. And in the defrosting mode, the heat of the heating water circuit 103 can be determined whether it meets the user's demand according to the return water temperature on the heating water circuit 103. Please refer to Figure 3 , if it is satisfied, the four-way valve 4 is reversed for defrosting. At this time, the fin heat exchanger 3 is the condenser, and the plate heat exchanger 2 is the evaporator; please refer to Figure 4 , and if the return water temperature is relatively low, the bypass circulation loop 102 can be opened and the main circulation loop 101 can be closed. In this way, the high-temperature and high-pressure refrigerant coming out of the compressor 1 can directly act on the fin heat exchanger 3 to achieve better defrosting of the fins. At the same time, it also avoids the situation that the plate heat exchanger 2 is frozen due to too low evaporation temperature when the four-way valve 4 is reversed for defrosting, and also avoids the problem that the overall operation energy efficiency of the heat pump system becomes low due to long-term use in the case of large differences in return water temperature when using the bypass defrosting method, improving the reliability and service life of the heat pump system. And, the bypass circulation loop 102 adopts the second electronic expansion valve 6 to realize the control of the flow rate of the bypass circulation loop 102, which is more convenient for anti-frosting and defrosting of the fin heat exchanger 3 at different temperatures.

[0049] Specifically, the four-way valve 4 includes a first port, a second port, a third port, and a fourth port. The first port is connected to the outlet of the compressor 1, the second port is connected to the outlet of the fin heat exchanger 3, the third port is connected to the inlet of the compressor 1, and the fourth port is connected to the outlet of the plate heat exchanger 2. Through the matching connection between the various ports in the four-way valve 4, the heating circulation of the main circulation loop 101, the reverse circulation during defrosting, and the circulation of the bypass circulation loop 102 can be realized.

[0050] In order to detect the temperatures of each structure of the heat pump system, so that the operators can timely obtain the corresponding temperature information.

[0051] The heat pump system in this embodiment further includes a coil temperature detector 7, which is connected to the coil of the fin heat exchanger 3 and is used to detect the coil temperature of the fin heat exchanger 3 to judge whether the fin heat exchanger 3 will frost.

[0052] Specifically, the heat pump system further includes a return water temperature detector 8 connected to the return water side of the heating water circuit 103 for detecting the return water temperature of the heating water circuit 103, so as to understand the actual operating temperature of the heating water circuit 103.

[0053] More specifically, the heat pump system further includes a water outlet temperature detector 9 connected to the water outlet side of the heating water circuit 103 for detecting the water outlet temperature of the heating water circuit 103, so as to understand the hot water temperature supplied to the heating water circuit 103. The situation of the heating water circuit 103 is jointly obtained by both the return water temperature detector 8 and the water outlet temperature detector 9, and corresponding control is performed.

[0054] In this embodiment, the heat pump system further includes an exhaust gas temperature detector 10 connected to the outlet of the compressor 1 for detecting the exhaust gas temperature of the compressor 1, so as to understand the exhaust gas temperature of the compressor 1, ensure the normal operation of the equipment, and also facilitate the operator to perform corresponding control on the refrigerant circulation circuit through the exhaust gas temperature of the compressor 1.

[0055] Further, the heat pump system further includes a suction temperature detector 11 connected to the inlet of the compressor 1 for detecting the suction temperature of the compressor 1, so as to understand the suction temperature of the compressor 1, ensure the normal operation of the equipment, and also facilitate the operator to perform corresponding control on the refrigerant circulation circuit through the suction temperature and the exhaust gas temperature of the compressor 1.

[0056] Optionally, the above-mentioned coil temperature detector 7, return water temperature detector 8, water outlet temperature detector 9, exhaust gas temperature detector 10 and suction temperature detector 11 all adopt temperature sensors, so as to detect the temperature at the corresponding position.

[0057] This embodiment also provides a defrosting and frost formation suppression control method, which is applied to the above-mentioned heat pump system to control the heat pump system to perform anti-frosting of the fin heat exchanger 3 in advance after the heating and heating meet the target set temperature during normal heating, and avoid freezing the plate heat exchanger 2 due to the four-way valve 4 reversing for defrosting during defrosting.

[0058] Please refer to Figures 1 to 4 , specifically, the defrosting and frost formation suppression control method is applied to the heat pump system, and the defrosting and frost formation suppression control method includes the steps:

[0059] S1. According to the coil temperature T e , ambient temperature T1 and the cumulative operation time t of the compressor 1, determine whether the heat pump system enters the defrosting mode; if so, execute step S2; if not, execute step S3;

[0060] S2. Determine whether the return water temperature T in reaches the preset temperature T2. If T in≥T2, the four-way valve 4 changes direction for defrosting and adjusts the opening degree of the first electronic expansion valve 5; if T in <T2, close the first electronic expansion valve 5, open the second electronic expansion valve 6 and adjust the opening degree of the second electronic expansion valve 6 to perform bypass defrosting;

[0061] S3. Enter the heating mode.

[0062] In the defrosting and frost formation inhibition control method in this embodiment, when defrosting the fin heat exchanger 3, it is possible to determine whether the heat in the heating water circuit 103 meets the user's requirements according to the return water temperature on the heating water circuit 103. If it meets, that is, T in ≥T2, then defrosting is carried out by changing the direction of the four-way valve 4. At this time, the fin heat exchanger 3 is the condenser and the plate heat exchanger 2 is the evaporator to defrost the fin heat exchanger 3; if the return water temperature is low, that is, T in <T2, then by opening the bypass circulation circuit 102 and closing the main circulation circuit 101, the high-temperature and high-pressure refrigerant coming out of the compressor 1 can directly act on the fin heat exchanger 3, so as to achieve better defrosting effect on the fins. At the same time, it also avoids the situation that the evaporation temperature is too low when the four-way valve 4 changes direction for defrosting and damages the plate heat exchanger 2, and also avoids the problem that the overall operation energy efficiency of the heat pump system becomes low due to long-term use of the bypass defrosting method under large differences in return water temperature, improving the reliability and service life of the heat pump system. And, after the bypass circulation circuit 102 is opened, the opening degree of the second electronic expansion valve 6 is adjusted to control the flow rate of the bypass circulation circuit 102, which is more convenient for defrosting the fin heat exchanger 3 at different temperatures.

[0063] Specifically, in step S1, the judgment conditions for the defrosting mode of the heat pump system include: T e ≤ -3°C and last for 1 minute; and T1 - T e ≥ 10°C and last for 1 minute; and t ≥ 45 minutes. When the above three conditions are met, the defrosting mode can be entered.

[0064] Among them, T e can be obtained from the temperature value measured by the coil temperature detector 7, and T1 is obtained from the temperature detector in the environment.

[0065] Furthermore, in step S2, T in can be obtained from the temperature value measured by the return water temperature detector 8, and T2 is the lowest temperature on the user's heating use side, generally 20°C.

[0066] Furthermore, when the heating mode is running in step S3, according to the return water temperature T inOr the rising rate of the return water temperature T3 is used to determine whether to enter the anti-frost mode. If so, the second electronic expansion valve 6 is opened and the opening degree of the second electronic expansion valve 6 is adjusted. If not, the heating mode is maintained. That is, during the operation of the heating mode, if the temperature of the heating water circuit 103 is relatively high or the rising rate of the heating water circuit 103 is relatively high, at this time, the bypass circulation circuit 102 can be conducted by opening the second electronic expansion valve 6 to supply heat to the fin heat exchanger 3, effectively preventing the fin heat exchanger 3 from frosting. Thus, preparations are made in advance before frosting, effectively reducing the amount of frosting, thereby reducing the defrosting time and the difficulty of defrosting.

[0067] Specifically, the method for determining whether to enter the anti-frost mode includes: T1≥T4-ΔT; or T3≥1°C / min; where T4 is the target temperature on the user's heating side; ΔT is the bypass start-backlash. Meeting either of them can enter the anti-frost mode.

[0068] Among them, ΔT is generally defaulted to 3°C, that is, after the bypass circulation circuit 102 is opened, the temperature change value in the heating water circuit 103 is generally 3°C.

[0069] Specifically, in step S3, the anti-frost mode also has a closing condition. If the closing condition is met, the second electronic expansion valve 6 is closed. The determination conditions for closing the anti-frost mode include: T1<T4-ΔT; and T3<1°C / min; when both are met at the same time, the anti-frost mode can be closed.

[0070] Further, in steps S2 and S3, the method for adjusting the actual opening degree Pn of the second electronic expansion valve 6 includes: P n =P n-1 +[KP*(T Dn -T et )+KD(T Dn -T Dn-1) ; where P n-1 is the opening degree of the second electronic expansion valve 6 in the previous cycle; KP is the proportionality coefficient, generally 2; KD is the differential coefficient, generally 1; T et is the target exhaust temperature of the compressor 1, T Dn is the actual exhaust temperature of the compressor 1; T Dn-1 is the exhaust temperature of the compressor 1 in the previous cycle. That is, the actual opening degree of the second electronic expansion valve 6 can be adjusted each time through the exhaust temperature of the compressor 1, so as to better defrost and not waste energy.

[0071] Among them, T Dn and T Dn-1 are both measured by the exhaust temperature detection component 10.

[0072] Specifically, the target exhaust temperature satisfies: T et =A-B*Te +C*T c ; where A, B, and C are all coefficients, A = 15, B = -1, C = 1.5, and T c = the outlet water temperature + 4°C. Thus, the specific temperature value of the target exhaust gas temperature can be obtained. Among them, the outlet water temperature can be measured by the outlet water temperature detector 9.

[0073] Specifically, the initial opening degree of the second electronic expansion valve 6 satisfies: EXV0 = 2*K1 + K2*T e -K3*T in , 60P ≤ EXV0 ≤ 480P; where K1, K2, and K3 are all coefficients, K1 = 120, K2 = 4, K3 = 2. In order to calculate the actual opening degree from the initial opening degree of the second electronic expansion valve 6, and at the same time, the range value of the opening degree of the second electronic expansion valve 6 as described above also needs to be satisfied.

[0074] Specifically, the second electronic expansion valve 6 is adjusted with a preset time T exv as the period, and T exv = 15s. That is, it operates in a cycle, and the opening degree of the second electronic expansion valve 6 is adjusted accordingly after each cycle to ensure the reliability of the operation of the heat pump system.

[0075] Obviously, the above-mentioned embodiments of the present invention are merely examples for clearly explaining the present invention, rather than limiting the implementation manners of the present invention. For those of ordinary skill in the art, various obvious changes, re-adjustments, and substitutions can be made without departing from the protection scope of the present invention. It is not necessary and impossible to enumerate all the implementation manners here. Any modifications, equivalent substitutions, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A method for controlling defrosting and inhibiting frost, characterized in that: The invention is applied to a heat pump system, the heat pump system comprising a compressor (1), a plate heat exchanger (2), a fin heat exchanger (3), a four-way valve (4), a first electronic expansion valve (5) and a second electronic expansion valve (6); the refrigerant side of the plate heat exchanger (2) is connected to a heating water circuit (103) for heat exchange, and the refrigerant side of the fin heat exchanger (3) is connected to air for heat exchange; the compressor (1), the four-way valve (4), the plate heat exchanger (2), the first electronic expansion valve (5) and the fin heat exchanger (3) are connected in sequence to form a main circulation loop (101); the compressor (1), the second electronic expansion valve (6), the fin heat exchanger (3) and the four-way valve (4) are connected in sequence to form a bypass circulation loop (102); the defrosting and frosting suppression control method comprises the following steps: S1, according to the coil temperature T e , the ambient temperature T1 and the accumulated running time t of the compressor (1), determining whether the heat pump system enters the defrosting mode; if so, executing step S2; if not, executing step S3; S2. Determine the return water temperature T in Whether the preset temperature T2 is reached, if T in ≥T2, the four-way valve (4) is switched to defrost and adjust the opening of the first electronic expansion valve (5); if T in <T2, closing the first electronic expansion valve (5), opening the second electronic expansion valve (6) and adjusting the opening degree of the second electronic expansion valve (6) to perform bypass defrosting; S3. Enter heating mode.

2. The defrosting and frost suppression control method according to claim 1, characterized in that: In step S1, the judgment conditions of the heat pump system defrost mode include: T e ≤ -3°C for 1 minute; and, T1-T e ≥10°C for 1 minute; and, t ≥ 45 minutes.

3. The defrosting and frost suppression control method according to claim 1, characterized in that: When the heating mode in step S3 is running, according to the return water temperature T in Or the return water temperature rise rate T3, judge whether the opening condition for entering the anti-frost mode is met, if so, open the second electronic expansion valve (6) and adjust the opening degree of the second electronic expansion valve (6), if not, maintain the heating mode.

4. The defrosting and frost suppression control method according to claim 3, characterized in that: The conditions for determining whether to start the anti-frost mode include: T1 ≥ T4 - ΔT; or, T3 ≥ 1℃ / min; Wherein, T4 is the target temperature of the user's heating usage side; ΔT is the bypass start-up hysteresis.

5. The defrosting and frost suppression control method according to claim 3, characterized in that: In step S3, the anti-frost mode further has a closing condition. If the closing condition is met, the second electronic expansion valve (6) is closed. The closing condition of the anti-frost mode is judged to include: T1<T4-ΔT;and, T3<1℃ / min; Wherein, T4 is the target temperature of the user's heating usage side; ΔT is the bypass start-up hysteresis.

6. The defrosting and frost suppression control method according to claim 3, characterized in that: In step S2 and step S3, the actual opening degree P of the second electronic expansion valve (6) is n The adjustment methods include: P n =P n-1 +[KP*(T Dn -T et )+KD(T Dn -T Dn-1) ]; Among them, P n-1 is the opening degree of the second electronic expansion valve (6) in the previous cycle; KP is the proportional coefficient, which is generally 2; KD is the differential coefficient, which is generally 1; T et is the target exhaust temperature of the compressor (1), T Dn is the actual exhaust temperature of the compressor (1); T Dn-1 is the exhaust temperature of the compressor (1) in the previous cycle.

7. The defrosting and frost suppression control method according to claim 6, characterized in that: The target exhaust temperature satisfies: T et =AB*T e +C*T c ; Among them, A, B and C are coefficients, A = 15, B = -1, C = 1.5, T c =Water outlet temperature + 4℃.

8. The defrosting and frost suppression control method according to claim 6, characterized in that: The initial opening degree of the second electronic expansion valve (6) satisfies: EXV0 = 2*K1+K2*T e -K3*T in , 60P≤EXV0≤480P; Among them, K1, K2 and K3 are coefficients, K1=120, K2=4, K3=2.

9. The defrosting and frost suppression control method according to claim 1, characterized in that: The second electronic expansion valve (6) is closed at a preset time T exv To adjust the cycle, T exv =15s.

10. A heat pump system, characterized in that: Use the defrosting and frost suppression control method as described in any one of claims 1 to 9.

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