Multi-stage variable frequency air conditioning system operation control method and system

Abstract

The application discloses a kind of multistage variable frequency air conditioning system operation control method and system, this includes: for each air conditioning unit in multistage variable frequency air conditioning system Set minimum operating frequency;Adopt real-time air temperature and preset target temperature comparison, and according to comparison result, the working frequency of air conditioning unit is regulated;For any two air conditioning units adjacent to each other, judge whether the current working frequency of front stage unit is greater than minimum operating frequency, if not, then, judge whether the output frequency of rear stage unit is greater than X% of rated frequency, if yes, then control front stage unit to run at minimum operating frequency, if not, then control front stage unit to gradually reduce load according to preset time period, until shutdown;Based on the above operation control method, not only can avoid system shock caused by frequent start-stop of front stage unit, but also can limit the unloading rate of front stage unit, even under the environmental conditions of season alternation, two-stage unit can also be smoothly connected.

Description

Technical Field

[0001] This invention relates to the field of multi-stage joint operation air conditioning control technology, and in particular to a method and system for operating control of a multi-stage variable frequency air conditioning system. Background Technology

[0002] In the application of fresh air low-temperature dehumidification air conditioning systems, multi-stage variable frequency direct expansion refrigeration systems are typically used for staged processing, relaying dehumidification and cooling of ambient air. Currently, variable frequency compressors cannot achieve full-range output from 0% to 100%. To ensure reliable oil return to the compressor, operating frequencies below 20% (the minimum limit) are generally not permitted. To improve system reliability, when the compressor operating frequency is below 20%, it is usually forced to increase the frequency periodically to ensure sufficient lubrication in the compressor oil sump. However, when the external ambient temperature is at the critical point of the set target outlet air temperature, the compressor operating frequency is usually required to be sufficiently low to ensure a smooth system transition. This obviously conflicts with the compressor's operating state. Thus, during transitional seasons, when the ambient temperature is near the critical point (near the preset target outlet air temperature), the upstream refrigeration system will experience severe fluctuations, causing adjacent downstream refrigeration systems to affect each other. This leads to frequent compressor start-stops, causing severe fluctuations in the heat exchanger surface temperature. Repeated low-temperature cycles will cause the downstream heat exchanger to freeze, resulting in low-pressure failure and eventual collapse. Summary of the Invention

[0003] The purpose of this invention is to provide a method and system for controlling the operation of a multi-stage variable frequency air conditioning system to avoid system oscillations caused by frequent start-stop of the upstream air conditioning unit.

[0004] To achieve the above objectives, this invention discloses a method for controlling the operation of a multi-stage variable frequency air conditioning system, comprising:

[0005] A minimum operating frequency is set for each air conditioning unit in the multi-stage variable frequency air conditioning system, and the minimum operating frequency is greater than the minimum limit frequency allowed for that air conditioning unit.

[0006] Detect the real-time outlet air temperature of the air conditioning unit;

[0007] The real-time outlet air temperature is compared with the preset target temperature, and the operating frequency of the air conditioning unit is adjusted according to the comparison result.

[0008] For any two adjacent air conditioning units, determine whether the current operating frequency of the upstream unit is greater than the minimum operating frequency. If not, then...

[0009] Determine whether the output frequency of the downstream unit is greater than X% of the rated frequency, where X ≥ 50. If yes, control the upstream unit to operate at the minimum operating frequency. If no, control the upstream unit to gradually reduce load according to a preset time period until it stops.

[0010] Preferably, the heat exchange medium in the multiple air conditioning units has different specific enthalpy variation ranges, and the specific enthalpy variation ranges of the upstream unit and the downstream unit in two adjacent air conditioning units overlap.

[0011] Preferably, during the process of controlling the upstream unit to gradually reduce load until shutdown, the downstream unit is controlled to load synchronously.

[0012] Ideally, 50 ≤ X ≤ 85.

[0013] This invention also discloses a multi-stage variable frequency air conditioning system operation control system, wherein each air conditioning unit in the multi-stage variable frequency air conditioning system is provided with a minimum operating frequency, the minimum operating frequency being greater than the minimum allowable limit frequency of the air conditioning unit, and the operation control system includes:

[0014] A temperature detection module is used to detect the real-time outlet air temperature of the air conditioning unit;

[0015] The comparison module is used to compare the real-time outlet air temperature with the preset target temperature.

[0016] A control module is used to control the operating frequency of the air conditioning unit based on feedback from the comparison module;

[0017] The first judgment module is used to determine whether the current operating frequency of the upstream unit in any two adjacent air conditioning units is greater than the minimum operating frequency.

[0018] The second judgment module is used to determine whether the output frequency of the downstream unit is greater than X% of the rated frequency when the judgment result of the first judgment module is negative, and X≥50.

[0019] An execution module is configured to control the upstream unit to operate at the minimum operating frequency when the judgment result of the second judgment module is yes, and to control the upstream unit to gradually reduce the load according to a preset time period until it stops when the judgment result of the second judgment module is no.

[0020] Preferably, the heat exchange medium in the multiple air conditioning units has different specific enthalpy variation ranges, and the specific enthalpy variation ranges of the upstream unit and the downstream unit in two adjacent air conditioning units overlap.

[0021] Preferably, during the process of controlling the upstream unit to gradually reduce its load to shutdown, the execution module controls the downstream unit to load synchronously.

[0022] Ideally, 50 ≤ X ≤ 85.

[0023] This invention also discloses a multi-stage variable frequency air conditioning system operation control system, which includes:

[0024] One or more processors;

[0025] Memory;

[0026] and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, the programs including instructions for performing the multi-stage variable frequency air conditioning system operation control method as described above.

[0027] The present invention also discloses a computer-readable storage medium comprising a computer program that can be executed by a processor to perform the multi-stage variable frequency air conditioning system operation control method as described above.

[0028] Compared with the prior art, the above-mentioned technical solution of the present invention sets the minimum operating frequency of each air conditioning unit in the multi-stage variable frequency air conditioning system to be greater than the minimum allowable limit frequency of the air conditioning unit, thereby avoiding the air conditioning unit from automatically increasing the frequency according to the time period after reducing the frequency to the minimum limit frequency; when the current stage unit is working at the minimum operating frequency, only when the output frequency of the adjacent downstream unit is lower than the preset value (such as 80% of the rated frequency), the current upstream unit is gradually unloaded according to the preset time period without depending on the current environmental conditions, until it stops. Thus, not only can the system oscillation caused by the frequent start and stop of the upstream unit be avoided, but also the unloading rate of the upstream unit can be limited, so that the two stages of units can be smoothly connected even under the environmental conditions of seasonal changes, so as to achieve the purpose of high-precision control of multi-stage air conditioning units throughout the year. Attached Figure Description

[0029] Figure 1 This is a flowchart of the operation control method in an embodiment of the present invention. Detailed Implementation

[0030] To illustrate the technical content, structural features, objectives, and effects of the present invention in detail, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0031] This embodiment discloses a method for controlling the operation of a multi-stage variable frequency air conditioning system. This system is used for fresh air cooling and dehumidification, but can also be used in other applications. In this embodiment, the multi-stage variable frequency air conditioning system includes multiple cascaded air conditioning units. These units cool and dehumidify the air in a relay manner. For example, in a three-stage variable frequency air conditioning system including a primary unit, a secondary unit, and a final unit, the output airflow of the primary unit becomes the input airflow of the secondary unit, and the output airflow of the secondary unit becomes the input airflow of the final unit. Based on this, as... Figure 1 The operation control method in this embodiment includes:

[0032] S1: Set a minimum operating frequency a for each air conditioning unit in the multi-stage variable frequency air conditioning system. The minimum operating frequency is greater than the minimum limit frequency b allowed by the air conditioning unit. In this embodiment, the minimum operating frequency a and the minimum limit frequency b both represent the working state of the compressor in the air conditioning unit. a is 35% of the rated power of the air conditioning unit compressor and b is 20% of the rated power of the air conditioning unit compressor.

[0033] S2: Detects the real-time air outlet temperature of the air conditioning unit;

[0034] S3: The real-time outlet air temperature is compared with the preset target temperature, and the operating frequency of the air conditioning unit is adjusted according to the comparison result.

[0035] S4: For any two adjacent air conditioning units, determine whether the current operating frequency c of the upstream unit is greater than the minimum operating frequency a. If yes, execute S5; otherwise, execute S6.

[0036] S5: This controls the operating frequency c of the upstream unit;

[0037] S6: Determine whether the output frequency d of the downstream unit is greater than X% of the rated frequency, X≥50. If yes, proceed to S7; otherwise, proceed to S8.

[0038] S7: Control the upstream unit to operate at the lowest operating frequency a. That is, force the upstream unit to maintain the lowest operating frequency a. The compressor of the upstream unit will no longer unload according to the actual energy demand. This will cause the outlet air temperature of the upstream unit to gradually exceed the set target outlet air temperature. Then, due to the deviation of the air intake state, the compressor of the downstream unit will also start to unload at a reduced frequency according to the energy demand.

[0039] S8: Controls the upstream unit to gradually reduce load according to a preset time period until it stops. When the output frequency d of the downstream unit drops to X% of the rated frequency, it indicates that the current environmental conditions have changed significantly, causing the operating frequency of the downstream unit to drop sharply. Therefore, the upstream unit can be shut down to avoid frequent start-ups and shutdowns.

[0040] Furthermore, the heat exchange media within multiple air conditioning units each have different specific enthalpy variation ranges, and the specific enthalpy variation ranges of the upstream and downstream units in two adjacent air conditioning units overlap. In this embodiment, the specific enthalpy variation period is constituted by the specific enthalpy of the heat exchange media at the air inlet and the specific enthalpy at the exhaust outlet of the air conditioning unit. For example, for an air conditioning system composed of two-stage air conditioning units, the specific enthalpy at the inlet of the primary air conditioning unit is 120, and the specific enthalpy at the exhaust outlet is 60, then the specific enthalpy variation range of the primary air conditioning unit is [60, 120]. The specific enthalpy at the inlet of the secondary air conditioning unit is 65, and the specific enthalpy at the exhaust outlet of the secondary air conditioning unit is 30, then the specific enthalpy variation range of the secondary air conditioning unit is [30, 65]. Therefore, the specific enthalpy variation ranges of the primary and secondary air conditioning units overlap [60, 65].

[0041] Furthermore, 50 ≤ X ≤ 85. Preferably, in this embodiment, X is 80.

[0042] In addition, to further ensure a smooth transition between upstream and downstream units, the downstream units are controlled to load synchronously during the process of gradually reducing the load on the upstream units until they stop.

[0043] The above operation control method will be explained in detail below using a two-stage air conditioning system, which includes a front-stage unit and a rear-stage unit, as an example.

[0044] By using temperature sensors installed on the evaporator outlet side, the real-time outlet air temperature of the two air conditioning units is detected in real time. The real-time outlet air temperature is compared with the corresponding target outlet air temperature, and the operation of the two air conditioning units is controlled based on the comparison result.

[0045] When the transitional season arrives, environmental conditions change drastically, and the upstream unit gradually unloads according to actual energy demand. When the compressor operating frequency of the upstream unit unloads to point a, the compressor will no longer unload according to actual energy demand. This will cause the outlet air temperature of the upstream unit to gradually fall below the target outlet air temperature. Due to the deviation in the air intake state, the compressor of the downstream unit will also begin to unload according to energy demand. When the compressor of the downstream unit unloads to below 80%, the upstream unit will then be gradually and forcibly unloaded in a cyclical manner (e.g., once every 1 minute) until the upstream unit is completely shut down. Similarly, when there are three-stage air conditioning units, the secondary units execute the corresponding shutdown procedures according to the operating frequency of the final stage unit, which will not be elaborated further here.

[0046] According to the operation control method disclosed in the above embodiments, since the minimum operating frequency of each air conditioning unit in the multi-stage variable frequency air conditioning system is set to be greater than the minimum allowable limit frequency of the air conditioning unit, the automatic frequency increase according to the time period is avoided after the air conditioning unit drops to the minimum limit frequency. When the upstream unit of two adjacent air conditioning units is operating at the minimum operating frequency, only when the output frequency of the adjacent downstream unit is lower than the preset value, the current upstream unit is gradually unloaded according to the preset time period until it stops. Therefore, not only can system oscillation caused by frequent start-stop of upstream units be avoided, but also by limiting the unloading rate of upstream units, the two-stage air conditioning units can be smoothly connected even under seasonal environmental conditions, achieving the goal of high-precision control of multi-stage air conditioning units throughout the year. In addition, since the specific enthalpy change ranges of upstream and downstream units in two adjacent air conditioning units overlap, system oscillation caused by the start-stop of upstream units can be further avoided, allowing the system to transition smoothly.

[0047] In another preferred embodiment of the present invention, a multi-stage variable frequency air conditioning system operation control system is also disclosed. Each air conditioning unit in the multi-stage variable frequency air conditioning system is equipped with a minimum operating frequency, which is greater than the minimum allowable limit frequency of the air conditioning unit. The operation control system includes:

[0048] Temperature detection module, which is used to detect the real-time outlet air temperature of the air conditioning unit;

[0049] The comparison module is used to compare the real-time outlet air temperature with the preset target temperature.

[0050] The control module is used to adjust the operating frequency of the air conditioning unit based on the feedback from the comparison module.

[0051] The first judgment module is used to determine whether the current operating frequency of the upstream unit in any two adjacent air conditioning units is greater than the minimum operating frequency.

[0052] The second judgment module is used to determine whether the output frequency of the downstream unit is greater than X% of the rated frequency when the judgment result of the first judgment module is negative, and X≥50.

[0053] The execution module is used to control the upstream unit to operate at the lowest operating frequency when the judgment result of the second judgment module is yes, and to control the upstream unit to gradually reduce the load according to the preset time period until it stops when the judgment result of the second judgment module is no.

[0054] Furthermore, the heat exchange media in multiple air conditioning units have different specific enthalpy variation ranges, and the specific enthalpy variation ranges of the upstream and downstream units in two adjacent air conditioning units overlap.

[0055] Furthermore, during the process of controlling the upstream units to gradually reduce load until shutdown, the execution module controls the downstream units to load synchronously.

[0056] It should also be noted that the working principle and process of the operation control system in this embodiment are detailed in the above-mentioned operation control method, and will not be repeated here.

[0057] This invention also discloses another multi-stage variable frequency air conditioning system operation control system, which includes one or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors. The programs include instructions for executing the multi-stage variable frequency air conditioning system operation control method described above. The processor can be a general-purpose central processing unit (CPU), a microprocessor, an application-specific integrated circuit (ASIC), or one or more integrated circuits, used to execute relevant programs to achieve the functions required by the modules in the multi-stage variable frequency air conditioning system operation control system of this application embodiment, or to execute the multi-stage variable frequency air conditioning system operation control method of this application embodiment.

[0058] This invention also discloses a computer-readable storage medium comprising a computer program that can be executed by a processor to perform the multi-stage variable frequency air conditioning system operation control method described above. The computer-readable storage medium can be any available medium accessible to a computer or a data storage device such as a server or data center that integrates one or more available media. The available medium can be read-only memory (ROM), random access memory (RAM), or magnetic media, such as floppy disks, hard disks, magnetic tapes, magnetic disks, or optical media, such as digital versatile discs (DVDs), or semiconductor media, such as solid-state disks (SSDs).

[0059] This application also discloses a computer program product or computer program, which includes computer instructions stored in a computer-readable storage medium. The processor of an electronic device reads the computer instructions from the computer-readable storage medium and executes the computer instructions, causing the electronic device to perform the aforementioned multi-stage variable frequency air conditioning system operation control method.

[0060] The above-disclosed embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, any equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for controlling the operation of a multi-stage variable frequency air conditioning system, characterized in that, include: A minimum operating frequency is set for each air conditioning unit in a multi-stage variable frequency air conditioning system, and the minimum operating frequency is greater than the minimum allowable limit frequency of the air conditioning unit. Detect the real-time outlet air temperature of the air conditioning unit; The real-time outlet air temperature is compared with the preset target temperature, and the operating frequency of the air conditioning unit is adjusted according to the comparison result. For any two adjacent air conditioning units, determine whether the current operating frequency of the upstream unit is greater than the minimum operating frequency. If not, then... Determine whether the output frequency of the downstream unit is greater than X% of the rated frequency, where X ≥ 50. If yes, control the upstream unit to operate at the minimum operating frequency. If no, control the upstream unit to gradually reduce load according to a preset time period until it stops.

2. The multi-stage variable frequency air conditioning system operation control method according to claim 1, characterized in that, The heat exchange medium in the multiple air conditioning units has different specific enthalpy variation ranges, and the specific enthalpy variation ranges of the upstream and downstream units in two adjacent air conditioning units overlap.

3. The multi-stage variable frequency air conditioning system operation control method according to claim 1, characterized in that, During the process of controlling the upstream unit to gradually reduce load until shutdown, the downstream unit is controlled to load synchronously.

4. The multi-stage variable frequency air conditioning system operation control method according to claim 1, characterized in that, 50≤X≤85。 5. A multi-stage variable frequency air conditioning system operation control system, characterized in that, Each air conditioning unit in the multi-stage variable frequency air conditioning system is equipped with a minimum operating frequency, which is greater than the minimum allowable limit frequency of the air conditioning unit. The operation control system includes: A temperature detection module is used to detect the real-time outlet air temperature of the air conditioning unit; The comparison module is used to compare the real-time outlet air temperature with the preset target temperature. A control module is used to control the operating frequency of the air conditioning unit based on feedback from the comparison module; The first judgment module is used to determine whether the current operating frequency of the upstream unit in any two adjacent air conditioning units is greater than the minimum operating frequency. The second judgment module is used to determine whether the output frequency of the downstream unit is greater than X% of the rated frequency when the judgment result of the first judgment module is negative, and X≥50. An execution module is configured to control the upstream unit to operate at the minimum operating frequency when the judgment result of the second judgment module is yes, and to control the upstream unit to gradually reduce the load according to a preset time period until it stops when the judgment result of the second judgment module is no.

6. The multi-stage variable frequency air conditioning system operation control system according to claim 5, characterized in that, The heat exchange medium in the multiple air conditioning units has different specific enthalpy variation ranges, and the specific enthalpy variation ranges of the upstream and downstream units in two adjacent air conditioning units overlap.

7. The multi-stage variable frequency air conditioning system operation control system according to claim 5, characterized in that, During the process of controlling the upstream unit to gradually reduce load to shutdown, the execution module controls the downstream unit to load synchronously.

8. The multi-stage variable frequency air conditioning system operation control system according to claim 5, characterized in that, 50≤X≤85。 9. A multi-stage variable frequency air conditioning system operation control system, characterized in that, include: One or more processors; Memory; And one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, the programs including instructions for performing the multi-stage variable frequency air conditioning system operation control method as described in any one of claims 1 to 4.

10. A computer-readable storage medium, characterized in that, It includes a computer program that can be executed by a processor to perform the multi-stage variable frequency air conditioning system operation control method as described in any one of claims 1 to 4.

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