A high-pressure unloading control method for a variable frequency heat pump air conditioning unit

Abstract

This invention discloses a high-pressure unloading control method for a variable frequency heat pump air conditioning unit, relating to the field of rail transit air conditioning. The method includes a high-pressure unloading entry process and a high-pressure unloading exit process. The high-pressure unloading entry process includes: when the air conditioning system controller detects that the high-pressure change rate reaches a certain threshold within a specific period, the compressor is frequency-reduced and load-reduced to prevent triggering of the high-pressure switch tripping. The high-pressure unloading exit process includes: when the air conditioning system controller detects that the high-pressure has decreased to a certain threshold and remains so for a certain period, the heating system exits unloading, and the compressor can increase its frequency according to the load status, switching to normal control. This achieves the goal of eliminating the need for long-term low-frequency operation of the variable frequency compressor, ensuring oil return safety, improving reliability, maintaining uninterrupted operation of the air conditioning unit for extended periods, reducing downtime caused by high-pressure protection lockout, significantly improving passenger comfort, reducing maintenance caused by high-pressure fault lockout, and saving costs.

Description

Technical Field

[0001] This invention relates to the field of rail transit air conditioning, and more specifically to a high-pressure unloading control method for a variable frequency heat pump air conditioning unit. Background Technology

[0002] In response to the trend of energy conservation and environmental protection, more and more rail vehicles are beginning to use heat pump air conditioning systems, especially in southern regions where winter outdoor temperatures range from -10℃ to 15℃. The trend of using variable frequency heat pump air conditioning to replace traditional electric heating in rail vehicles during winter is becoming increasingly apparent. When the outdoor temperature is below 0℃, the compressor needs to operate at a higher frequency to ensure appropriate heating capacity and meet indoor comfort requirements. When the outdoor temperature is above 10℃, and the target indoor temperature is set 8℃ or more higher than the actual return air temperature, the air conditioning system usually needs to operate at its highest heating level. In this case, the compressor operates at a high frequency, resulting in high heat output and good ambient temperature comfort, but it is prone to triggering high-pressure alarms. If the compressor is started and continuously run at a lower frequency for a long time, heating will be slow, and it is easy to cause insufficient oil return to the compressor, resulting in irreversible damage and affecting its service life.

[0003] Compressors that start at low frequency can briefly increase their frequency for oil return. However, since most of the refrigerant in a heat pump system is concentrated inside the outdoor heat exchanger, the heat exchange area is very small. When the outdoor temperature is high, increasing the compressor frequency for a brief oil return can easily trigger a high-pressure alarm. Therefore, it is necessary to anticipate and unload the high pressure caused by the above factors in advance.

[0004] Therefore, it is necessary to provide a high-pressure unloading control method for variable frequency heat pump air conditioning units to solve the above problems. Summary of the Invention

[0005] To achieve the above objectives, the present invention provides the following technical solution: a high-pressure unloading control method for a variable frequency heat pump air conditioning unit, comprising:

[0006] High-pressure unloading entry process and high-pressure unloading exit process;

[0007] The high-pressure unloading process includes: when the air conditioning system controller detects that the high-pressure change rate reaches a certain threshold within a specific period, it reduces the frequency and load of the compressor to prevent the high-pressure switch from tripping.

[0008] The high-pressure unloading and exit process includes: when the air conditioning system controller detects that the high pressure has dropped to a certain threshold and remains so for a certain period of time, the heating system exits unloading, and the compressor can increase its frequency according to the load status and switch to normal control.

[0009] Furthermore, as a preferred embodiment, the variable frequency heat pump air conditioning unit includes:

[0010] Compressor, four-way reversing valve, indoor heat exchanger, indoor fan, dryer filter, sight glass, electronic expansion valve, outdoor heat exchanger, outdoor fan, gas-liquid separator, low-pressure switch, low-pressure sensor, high-pressure switch, high-pressure sensor;

[0011] The compressor is connected to the four-way reversing valve, which is connected to the indoor heat exchanger. One side of the indoor heat exchanger is connected to the indoor fan, and the other side is connected to the dryer filter. The dryer filter is connected in sequence to the sight glass and the electronic expansion valve. The electronic expansion valve is connected to the outdoor heat exchanger. The outdoor heat exchanger is connected to the outdoor fan on one side and the gas-liquid separator on the other side. The gas-liquid separator is connected to the compressor. The low-pressure switch and low-pressure sensor are installed on the connecting pipeline between the compressor and the gas-liquid separator. The high-pressure switch and high-pressure sensor are connected on the connecting pipeline between the compressor and the four-way reversing valve.

[0012] Furthermore, as a preferred approach, the cause of the high-pressure alarm can be determined by combining the high-pressure value and the return air temperature change rate within a specific period, and the heating system can be unloaded in advance by predicting the high-pressure change rate within a specific period.

[0013] Furthermore, as a preferred option, the high-pressure unloading method should not interfere with high-pressure alarms caused by other harmful factors triggered by normal control, and should only unload high-pressure alarms caused by excessively high ambient temperature or load changes in advance.

[0014] Furthermore, as a preferred embodiment, when the variable frequency heat pump air conditioning unit is running at full heat, the high pressure unloading can be performed multiple times in a cycle without triggering the high pressure switch 13 to cut off the operation of the compressor 1, and only the operating frequency of the compressor 1 is adjusted.

[0015] Furthermore, as a preferred option, it is necessary to set the upper limit threshold for the air conditioning unit to enter high-pressure unloading, the lower limit threshold for exiting high-pressure unloading, and the sampling period for detecting return air temperature and high-pressure pressure, based on the characteristics of different refrigerants; and after the end of each sampling period, calculate the rate of change of return air temperature and the rate of change of high-pressure pressure within the period.

[0016] Furthermore, as a preferred option, the steps are as follows:

[0017] S1: The heat pump starts running, and the relevant controller collects relevant data at certain intervals;

[0018] S2: Determine whether the rate of change of indoor temperature within this cycle is greater than or equal to the preset value. If the relevant rate of change is greater than or equal to the preset value, proceed to the next judgment step. If it is less than the preset value, switch to normal control operation.

[0019] S3: Determine whether the high pressure of this cycle is less than or equal to 50% of the upper pressure threshold. If it is less than or equal to 50% of the upper pressure threshold, proceed to the next determination step. If it is greater than 50% of the upper pressure threshold, switch to normal control operation.

[0020] S4: Determine whether the high pressure of this cycle is less than or equal to the upper pressure threshold. If it is less than or equal to the upper pressure threshold, proceed to the next determination step. If it is greater than the upper pressure threshold, switch to normal control operation.

[0021] S5: Determine whether the high pressure change rate during the cycle of step S3 is greater than a preset value. If it is greater than the preset value, switch to normal control. If it is not greater than the preset value, switch to the next determination step.

[0022] S6: Determine whether the high pressure change rate during the cycle of step S4 is less than a preset value. If it is less than the preset value, switch to normal control. If it is not less than the preset value, enter the high pressure unloading process.

[0023] S7: During high-pressure unloading, the pressure is checked periodically to see if it exceeds the lower threshold. If it exceeds the lower threshold, high-pressure unloading continues. If it does not exceed the lower threshold, high-pressure unloading stops and the system switches to normal control.

[0024] S8: Repeat the above judgment at a specific cycle until the heat pump stops running.

[0025] Compared with the prior art, the present invention provides a high-pressure unloading control method for variable frequency heat pump air conditioning units, which has the following beneficial effects:

[0026] In this embodiment of the invention, a high-pressure unloading method is applied to the air conditioning unit operating in heating mode to ensure the safe operation of the variable frequency compressor at an appropriate frequency and improve the reliability of oil return. Furthermore, by combining the high-pressure value and return air temperature change rate within a specific cycle, the cause of the high-pressure alarm is determined. The high-pressure change rate within a specific cycle is used to predict the necessity of unloading the heating system in advance, thus protecting the system and reducing the failure rate. This method does not interfere with high-pressure alarms caused by other harmful factors triggered by normal control, and allows the heating system to operate normally for a longer period, thus regulating environmental comfort. Attached Figure Description

[0027] Figure 1 This is a schematic diagram illustrating the refrigeration principle of a variable frequency heat pump air conditioning unit.

[0028] Figure 2 This is a logic flowchart of a high-pressure unloading control method for a variable frequency heat pump air conditioning unit.

[0029] In the diagram: 1. Compressor; 2. Four-way reversing valve; 3. Indoor heat exchanger; 4. Indoor fan; 5. Dryer filter; 6. Sight glass; 7. Electronic expansion valve; 8. Outdoor heat exchanger; 9. Outdoor fan; 10. Gas-liquid separator; 11. Low-pressure switch; 12. Low-pressure sensor; 13. High-pressure switch; 14. High-pressure sensor. Detailed Implementation

[0030] Please see Figures 1-2 In this embodiment of the invention, a high-pressure unloading control method for a variable frequency heat pump air conditioning unit includes:

[0031] High-pressure unloading entry process and high-pressure unloading exit process;

[0032] The high-pressure unloading process includes: when the air conditioning system controller detects that the high-pressure change rate reaches a certain threshold within a specific period, it reduces the frequency and load of the compressor to prevent the high-pressure switch from tripping.

[0033] The high-pressure unloading and exit process includes: when the air conditioning system controller detects that the high pressure has dropped to a certain threshold and remains so for a certain period of time, the heating system exits unloading, and the compressor can increase its frequency according to the load status and switch to normal control.

[0034] In this embodiment, as Figure 1 The variable frequency heat pump air conditioning unit includes:

[0035] 1. Compressor; 2. Four-way reversing valve; 3. Indoor heat exchanger; 4. Indoor fan; 5. Dryer filter; 6. Sight glass; 7. Electronic expansion valve; 8. Outdoor heat exchanger; 9. Outdoor fan; 10. Gas-liquid separator; 11. Low-pressure switch; 12. Low-pressure sensor; 13. High-pressure switch; 14. High-pressure sensor.

[0036] The compressor 1 is connected to the four-way reversing valve 2, which is connected to the indoor heat exchanger 3. One side of the indoor heat exchanger 3 is connected to the indoor fan 4, and the other side is connected to the dryer filter 5. The dryer filter 5 is connected in sequence to the sight glass 6 and the electronic expansion valve 7. The electronic expansion valve 7 is connected to the outdoor heat exchanger 8. The outdoor heat exchanger 8 is connected to the outdoor fan 9 on one side and the gas-liquid separator 10 on the other side. The gas-liquid separator 10 is connected to the compressor 1. The low-pressure switch 11 and the low-pressure sensor 12 are installed on the connecting pipeline between the compressor 1 and the gas-liquid separator 10. The high-pressure switch 13 and the high-pressure sensor 14 are connected on the connecting pipeline between the compressor 1 and the four-way reversing valve 2.

[0037] In a preferred embodiment, during the heat pump heating process, the compressor 1 discharges gas into the four-way reversing valve 2, thereby allowing the gas to enter the indoor heat exchanger 3. The indoor fan 4 performs air-side heat exchange on the gas entering the indoor heat exchanger 3. The refrigerant then enters the dryer filter 5 for drying. After passing through the sight glass 6 and the electronic expansion valve 7, the relevant gas is dried again by the dryer filter 5 located after the electronic expansion valve 7 before entering the indoor heat exchanger 8. It then exchanges heat with the ambient temperature through the outdoor fan 9. Finally, the refrigerant passes through the gas-liquid separator 10 and is drawn in by the compressor 1, completing one heat cycle.

[0038] It should be noted that the low-pressure sensor 12 can detect the pressure in the pipeline connecting the gas-liquid separator 10 and the compressor 1, and control the opening and closing of the pipeline through the low-pressure switch 11; the high-pressure sensor 14 can detect the pressure in the pipeline connecting the compressor 1 and the four-way reversing valve 2, and at the same time, control the relevant connecting pipeline through the high-pressure switch 13.

[0039] In this embodiment, as Figure 2 By combining the high pressure value and return air temperature change rate within a specific period, the cause of the high pressure alarm can be determined, and the heating system can be unloaded in advance by predicting the high pressure change rate within a specific period.

[0040] In this embodiment, as Figure 2 The high-pressure unloading method must not interfere with high-pressure alarms caused by other harmful factors triggered by normal control. It should only unload high-pressure alarms caused by excessively high ambient temperature or load changes in advance.

[0041] In this embodiment, as Figure 2 When the variable frequency heat pump air conditioning unit is running at full heat, the high pressure unloading can be performed multiple times without triggering the high pressure switch 13 to cut off the operation of the compressor 1. Only the operating frequency of the compressor 1 is adjusted.

[0042] In this embodiment, as Figure 2 Based on the characteristics of different refrigerants, it is necessary to set the upper limit threshold for the air conditioning unit to enter high-pressure unloading, the lower limit threshold for exiting high-pressure unloading, and the sampling period for detecting return air temperature and high-pressure; and after the end of each sampling period, calculate the rate of change of return air temperature and the rate of change of high-pressure pressure within the period.

[0043] In this embodiment, as Figure 2 The steps are as follows:

[0044] S1: The heat pump starts running, and the relevant controller collects relevant data at certain intervals;

[0045] S2: Determine whether the rate of change of indoor temperature within this cycle is greater than or equal to the preset value. If the relevant rate of change is greater than or equal to the preset value, proceed to the next judgment step. If it is less than the preset value, switch to normal control operation.

[0046] S3: Determine whether the high pressure of this cycle is less than or equal to 50% of the upper pressure threshold. If it is less than or equal to 50% of the upper pressure threshold, proceed to the next determination step. If it is greater than 50% of the upper pressure threshold, switch to normal control operation.

[0047] S4: Determine whether the high pressure of this cycle is less than or equal to the upper pressure threshold. If it is less than or equal to the upper pressure threshold, proceed to the next determination step. If it is greater than the upper pressure threshold, switch to normal control operation.

[0048] S5: Determine whether the high pressure change rate during the cycle of step S3 is greater than a preset value. If it is greater than the preset value, switch to normal control. If it is not greater than the preset value, switch to the next determination step.

[0049] S6: Determine whether the high pressure change rate during the cycle of step S4 is less than a preset value. If it is less than the preset value, switch to normal control. If it is not less than the preset value, enter the high pressure unloading process.

[0050] S7: During high-pressure unloading, the pressure is checked periodically to see if it exceeds the lower threshold. If it exceeds the lower threshold, high-pressure unloading continues. If it does not exceed the lower threshold, high-pressure unloading stops and the system switches to normal control.

[0051] S8: Repeat the above judgment at a specific cycle until the heat pump stops running.

[0052] As a preferred embodiment, let:

[0053] P max Unloading pressure upper limit threshold;

[0054] P min : Lower limit threshold for unloading pressure;

[0055] ΔT i When the heat pump is running, a certain cycle of continuous timing begins after the variable frequency compressor rises to the target frequency or drops to the unloading frequency.

[0056] Δa i Rate of change of indoor temperature over a period of ΔT The preset values ​​are ΔA;

[0057] Δp i : Rate of change of high pressure over a period of ΔT The preset values ​​for the rate of change are ΔP1 and ΔP2, respectively.

[0058] When the heat pump is running, once the compressor's actual operating frequency reaches the target frequency, the timing cycle begins, with t1, t2, and t3 each constituting a cycle n. i (i: 1~3), the starting points of the three timing cycles are the same. Record the high pressure P at the beginning and end of each cycle. i With return air temperature value a i And the high pressure change rate Δp was calculated. i With return air temperature change rate Δa i The calculation methods are as follows: (P 末 P represents the high pressure at the end of a single cycle. 始 (where t is the high pressure at the start of a single cycle and t is the cycle time); Δ (a 末 a is the return air temperature at the end of a single cycle. 始 (where t is the return air temperature at the start of a single cycle and t is the cycle time).

[0059] First, it is necessary to determine the value of Δa in the above data at a certain period. i If the temperature change rate of the relevant heat pump is not fast, it means that there is no need to reduce the frequency of operation of the relevant compressor by unloading. In this case, the relevant components will return to normal operation and wait for the next cycle judgment. If the temperature change rate is greater than or equal to ΔA, the system will enter the next judgment step and decide whether to unload the relevant components based on the subsequent judgment.

[0060] Δa was confirmed to have occurred in the previous cycle. i After ≥ΔA, it is necessary to determine whether the relevant high-pressure P1 in the previous cycle is less than or equal to the preset value P. max Half of, i.e., P1≤P max ×50%, if P1>

[0061] P max If the value is ×50%, then the high pressure is too high at this time, and it is no longer caused by excessively high ambient temperature or load changes. Therefore, the relevant components switch to normal operation, thereby avoiding high pressure alarms caused by other harmful factors that interfere with normal control triggering, and wait for the next trigger judgment; if P1≤P max If the value reaches 50%, then proceed to the next judgment cycle.

[0062] After confirming P1≤P max After multiplying by 50%, it is necessary to determine whether the relevant high-pressure P1 is less than or equal to the preset value P in the next cycle. max That is, P2≤P max If P2 > P maxIf the high pressure rises too rapidly, it is no longer caused by excessively high ambient temperature or load changes. Therefore, the relevant components return to normal operation to avoid triggering high pressure alarms caused by other harmful factors that interfere with normal control, and wait for the next trigger to make a judgment; if P2≤P max If so, proceed to the next judgment cycle.

[0063] After confirming P2≤P max Then, it is determined whether Δp2 from P2 to P1 is less than or equal to the preset value ΔP1, i.e., Δp2≤ΔP1. If Δp2>ΔP1, the high pressure rises too quickly and is no longer caused by excessive ambient temperature or load changes. Therefore, the relevant components switch to normal operation to avoid high pressure alarms caused by other harmful factors that interfere with normal control triggering, and wait for the next trigger judgment. If Δp2≤ΔP1, then the next judgment cycle begins.

[0064] After determining that Δp2≤ΔP1, wait for the next cycle and test and record the relevant high pressure P3 to determine whether Δp3 from P3 to P2 is greater than or equal to the preset value ΔP2, i.e., Δp3≥ΔP2. If Δp3<ΔP2, it means that the rate of increase of the high pressure has slowed down or has begun to decrease, so no related unloading is required. If Δp3≥ΔP2, then the relevant high pressure unloading is started, and the next judgment stage is entered.

[0065] When the system is in the high-pressure unloading phase, it is necessary to periodically determine whether the relevant high-pressure is less than or equal to P. min If less than or equal to P min If the high-pressure unloading has been completed, the relevant components will return to normal operation; if it is greater than P... min This proves that the relevant high-pressure unloading objective has not yet been achieved, and the unloading process should continue.

[0066] The above process continues from the moment the heat pump is turned on until it is finished.

[0067] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A high-pressure unloading control method for a variable frequency heat pump air conditioning unit, characterized in that: include: High-pressure unloading entry process and high-pressure unloading exit process; The high-pressure unloading entry process includes: when the air conditioning system controller detects that the high-pressure change rate reaches a certain threshold within a specific period, the compressor frequency is reduced and the load is decreased to prevent the high-pressure switch from tripping; the high-pressure unloading exit process includes: when the air conditioning system controller detects that the high-pressure pressure has dropped to a certain threshold and has remained for a certain period of time, the heating system exits unloading, and the compressor can increase the frequency according to the load status and switch to normal control. The steps are as follows: S1: The heat pump starts running, and the relevant controller collects relevant data at certain intervals; S2: Determine whether the rate of change of indoor temperature within this cycle is greater than or equal to the preset value. If the relevant rate of change is greater than or equal to the preset value, proceed to the next judgment step. If it is less than the preset value, switch to normal control operation. S3: Determine whether the high pressure of this cycle is less than or equal to 50% of the upper pressure threshold. If it is less than or equal to 50% of the upper pressure threshold, proceed to the next determination step. If it is greater than 50% of the upper pressure threshold, switch to normal control operation. S4: Determine whether the high pressure of this cycle is less than or equal to the upper pressure threshold. If it is less than or equal to the upper pressure threshold, proceed to the next determination step. If it is greater than the upper pressure threshold, switch to normal control operation. S5: Determine whether the high pressure change rate during the cycle of step S3 is greater than a preset value. If it is greater than the preset value, switch to normal control. If it is not greater than the preset value, switch to the next determination step. S6: Determine whether the high pressure change rate during the cycle of step S4 is less than a preset value. If it is less than the preset value, switch to normal control. If it is not less than the preset value, enter the high pressure unloading process. S7: During high-pressure unloading, the pressure is checked periodically to see if it exceeds the lower threshold. If it exceeds the lower threshold, high-pressure unloading continues. If it does not exceed the lower threshold, high-pressure unloading stops and the system switches to normal control. S8: Repeat the above judgment at a specific cycle until the heat pump stops running.

2. The high-pressure unloading control method for a variable frequency heat pump air conditioning unit according to claim 1, characterized in that: The variable frequency heat pump air conditioning unit includes: a compressor (1), a four-way reversing valve (2), an indoor heat exchanger (3), an indoor fan (4), a dryer filter (5), a sight glass (6), an electronic expansion valve (7), an outdoor heat exchanger (8), an outdoor fan (9), a gas-liquid separator (10), a low-pressure switch (11), a low-pressure sensor (12), a high-pressure switch (13), and a high-pressure sensor (14); the compressor (1) is connected to the four-way reversing valve (2), the four-way reversing valve (2) is connected to the indoor heat exchanger (3), one side of the indoor heat exchanger (3) is connected to the indoor fan (4), and the other side is connected to the dryer filter (5). The dryer filter (5) is connected in sequence to the sight glass (6) and the electronic expansion valve (7). The electronic expansion valve (7) is connected to the outdoor heat exchanger (8). One side of the outdoor heat exchanger (8) is connected to the outdoor fan (9), and the other side is connected to the gas-liquid separator (10). The gas-liquid separator (10) is connected to the compressor (1). The low-pressure switch (11) and the low-pressure sensor (12) are installed on the connecting pipeline between the compressor (1) and the gas-liquid separator (10). The high-pressure switch (13) and the high-pressure sensor (14) are connected on the connecting pipeline between the compressor (1) and the four-way reversing valve (2).

3. The high-pressure unloading control method for a variable frequency heat pump air conditioning unit according to claim 2, characterized in that: By combining the high pressure value and return air temperature change rate within a specific period, the cause of the high pressure alarm can be determined, and the heating system can be unloaded in advance by predicting the high pressure change rate within a specific period.

4. The high-pressure unloading control method for a variable frequency heat pump air conditioning unit according to claim 1, characterized in that: The high-pressure unloading method must not interfere with high-pressure alarms caused by other harmful factors triggered by normal control. It should only unload high-pressure alarms caused by excessively high ambient temperature or load changes in advance.

5. The high-pressure unloading control method for a variable frequency heat pump air conditioning unit according to claim 3, characterized in that: When the variable frequency heat pump air conditioning unit is running at full heat, the high pressure unloading can be performed multiple times without triggering the high pressure switch (13) to cut off the operation of the compressor (1). Only the operating frequency of the compressor (1) is adjusted.

6. The high-pressure unloading control method for a variable frequency heat pump air conditioning unit according to claim 3, characterized in that: Based on the characteristics of different refrigerants, it is necessary to set the upper limit threshold for the air conditioning unit to enter high-pressure unloading, the lower limit threshold for exiting high-pressure unloading, and the sampling period for detecting return air temperature and high-pressure; and after the end of each sampling period, calculate the rate of change of return air temperature and the rate of change of high-pressure pressure within the period.

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