Control method of centrifugal compressor and air conditioning system

Abstract

The application provides a centrifugal compressor control method and an air conditioning system. The centrifugal compressor control method comprises the following steps: S100, when the inlet opening degree of the centrifugal compressor is lower than a first preset value, the driving motor of the centrifugal compressor is turned off; or S200, when the inlet opening degree of the centrifugal compressor is not lower than the first preset value, the following operations are performed according to a preset sequence: reducing the inlet opening degree of the centrifugal compressor and increasing the rotating speed of the centrifugal compressor. According to the scheme, the centrifugal compressor control method provides higher reliability, longer service life and lower noise for the air conditioning system.

Description

Technical Field

[0001] This application relates to the field of air conditioning, and more specifically, to a control method for a centrifugal compressor in an air conditioning system. Background Technology

[0002] Currently, refrigeration systems and related equipment are widely used in various temperature control fields, including residential air conditioning, commercial air conditioning, cold chain transportation, and cryogenic storage. For applications with low evaporation temperatures and high cooling capacity requirements, such as freezing and refrigeration, and low-temperature environment laboratories, large-scale refrigeration equipment is typically required. Centrifugal compressors are commonly used power source components in large refrigeration systems. They are used to compress the gaseous refrigerant within the system, converting it from a low-pressure state to a high-pressure state, and subsequently participating in condensation, throttling, and evaporation processes.

[0003] However, for existing refrigeration systems using centrifugal compressors, the robustness of the compressor's components faces significant challenges. For example, when the system stops operating and the centrifugal compressor's drive motor shuts off, the disappearance of the large pressure differential provided by the compressor can cause refrigerant in the condenser to flow back into the compressor, leading to compressor reversal, generating loud noise, and impacting the compressor's rotor bearings. Another example is a system where, upon shutdown, the centrifugal compressor first reduces the drive motor speed and then closes the compressor inlet guide vanes. In this case, the compressor may experience surge. Summary of the Invention

[0004] This application aims to provide a control method for a centrifugal compressor and an air conditioning system to at least partially solve or alleviate the problems existing in the prior art.

[0005] To achieve at least one objective of this application, according to one aspect of this application, a control method for a centrifugal compressor is provided, comprising: S100, when the inlet opening of the centrifugal compressor is lower than a first preset value, shutting off the drive motor of the centrifugal compressor; or S200, when the inlet opening of the centrifugal compressor is not lower than the first preset value, performing the following operations in a preset sequence: reducing the inlet opening of the centrifugal compressor and increasing the rotational speed of the centrifugal compressor.

[0006] In addition to one or more of the features mentioned above, or as an alternative, in another embodiment, step S200 includes: S210, when the inlet opening of the centrifugal compressor is not lower than a first preset value and is lower than a second preset value, the preset sequence is: increasing the rotational speed of the centrifugal compressor, and then or simultaneously reducing the inlet opening of the centrifugal compressor to the first preset value; or S220, when the inlet opening of the centrifugal compressor is not lower than the second preset value, the preset sequence is: first reducing the inlet opening of the centrifugal compressor to the second preset value, and then executing S210.

[0007] In addition to one or more of the features described above, or as an alternative, in another embodiment, the first preset value is 10% of the full opening of the entrance; and / or the second preset value is 30% of the full opening of the entrance.

[0008] In addition to one or more of the features described above, or as an alternative, in another embodiment, the speed of the centrifugal compressor is controlled by adjusting the output power of the drive motor of the centrifugal compressor.

[0009] In addition to one or more of the features described above, or as an alternative, in another embodiment, the output current is adjusted to 60%-65% of the full load current to control the output power of the drive motor of the centrifugal compressor.

[0010] In addition to one or more of the features described above, or as an alternative, in another embodiment, the inlet opening of the centrifugal compressor is adjusted by adjusting the inlet guide vanes of the centrifugal compressor.

[0011] In addition to one or more of the features described above, or as an alternative, in another embodiment, the operation of increasing the speed of the centrifugal compressor in step S200 includes: dynamically reducing the acceleration that increases the speed of the centrifugal compressor to 0 as the inlet opening of the centrifugal compressor decreases.

[0012] To achieve at least one objective of this application, according to another aspect of this application, an air conditioning system is provided, comprising: a centrifugal compressor for compressing refrigerant within the air conditioning system; an opening sensor for acquiring the inlet opening of the centrifugal compressor; and a controller configured to perform the following operations based on the inlet opening of the centrifugal compressor acquired by the opening sensor: when the inlet opening of the centrifugal compressor is lower than a first preset value, shutting off the drive motor of the centrifugal compressor; or when the inlet opening of the centrifugal compressor is not lower than the first preset value, performing the following operations in a preset sequence: decreasing the inlet opening of the centrifugal compressor and increasing the rotational speed of the centrifugal compressor.

[0013] In addition to one or more of the features described above, or as an alternative, in another embodiment, the controller is further configured to perform the following preset sequence when the inlet opening of the centrifugal compressor is not lower than a first preset value and is lower than a second preset value: increasing the rotational speed of the centrifugal compressor, and then or simultaneously decreasing the inlet opening of the centrifugal compressor to the first preset value; or when the inlet opening of the centrifugal compressor is not lower than the second preset value, the preset sequence is: first decreasing the inlet opening of the centrifugal compressor to the second preset value, then increasing the rotational speed of the centrifugal compressor, and then or simultaneously decreasing the inlet opening of the centrifugal compressor to the first preset value.

[0014] In addition to one or more of the features described above, or as an alternative, in another embodiment, the first preset value is 10% of the full opening of the entrance; and / or the second preset value is 30% of the full opening of the entrance.

[0015] In addition to one or more of the features described above, or as an alternative, in another embodiment, the controller is also configured to adjust the output power of the drive motor of the centrifugal compressor to control the rotational speed of the centrifugal compressor.

[0016] In addition to one or more of the features described above, or as an alternative, in another embodiment, the controller is also configured to adjust the output current to 60%-65% of the full load current to regulate the output power of the drive motor of the centrifugal compressor.

[0017] In addition to one or more of the features described above, or as an alternative, in another embodiment, the centrifugal compressor further includes an inlet guide vane; wherein the controller is further configured to perform: adjusting the inlet opening of the centrifugal compressor by adjusting the inlet guide vane.

[0018] In addition to one or more of the features described above, or as an alternative, in another embodiment, the controller is further configured to: dynamically reduce the acceleration of increasing the speed of the centrifugal compressor to 0 as the inlet opening of the centrifugal compressor decreases during the process of increasing the speed of the centrifugal compressor.

[0019] According to the centrifugal compressor control method of this application, the inlet opening of the centrifugal compressor is graded, and the drive motor of the centrifugal compressor is directly shut off only at a lower opening. At this time, due to the lower opening, the refrigerant backflow generated by the condenser is limited, thus preventing the compressor from violently reversing or generating severe vibration and noise. Furthermore, when the inlet opening of the centrifugal compressor is large, both backflow and surge problems are avoided by adjusting the inlet opening to a smaller degree and increasing the speed of the centrifugal compressor. Therefore, air conditioning systems using this method have higher reliability, longer lifespan, and lower noise. Attached Figure Description

[0020] Figure 1 This is a schematic diagram showing the parameter changes during the shutdown process of an air conditioning system, resulting from an embodiment of the centrifugal compressor control method of this application. Detailed Implementation

[0021] The present application will now be described in detail with reference to exemplary embodiments shown in the accompanying drawings. However, it should be understood that the present application may be implemented in many different forms and should not be construed as limited to the embodiments set forth herein. These embodiments are provided herein to make the disclosure of the present application more complete and exhaustive, and to fully convey the concept of the present application to those skilled in the art.

[0022] Furthermore, for any single technical feature described or implied in the embodiments mentioned herein, or any single technical feature shown or implied in the various figures, this application still allows for any combination or deletion of these technical features (or their equivalents) without any technical obstacle, thereby obtaining more other embodiments of this application that may not be directly mentioned herein.

[0023] Furthermore, the term "surge envelope" mentioned in the text is a fitted curve used to assess compressor surge risk based on several parameters associated with compressor surge. For example, combining... Figure 1 As shown in the figure, curves B and C are the "surge envelope". The horizontal axis in the figure represents the change of the surge envelope with the inlet guide vane opening, while the vertical axis represents several key parameters affecting surge, such as the surge pressure ratio, which is the ratio of the measured refrigerant pressure in the condenser to the measured refrigerant pressure in the evaporator; and the surge temperature difference, which is the difference between the saturation temperature in the condenser and the saturation temperature in the evaporator. The aforementioned parameters measure surge from different perspectives and can therefore be used to fit the surge envelope.

[0024] The following will first describe an embodiment of the air conditioning system of this application. This air conditioning system may include conventional refrigeration components such as a compressor, condenser, throttling element, and evaporator to achieve basic functions such as cooling and heating by compressing the refrigerant, causing the refrigerant to condense and dissipate heat, causing the refrigerant to expand and throttle, and causing the refrigerant to evaporate and absorb heat. It may also include functional components such as an economizer, gas-liquid separator, and four-way valve to additionally perform improved functions such as enthalpy increase, separation, and reversing. For the air conditioning system described in the embodiment, the compressor should be selected as a centrifugal compressor, and it should be equipped with an opening sensor for acquiring parameters for control applications and a controller for implementing control logic. The opening sensor can be used to acquire the inlet opening of the centrifugal compressor; and the controller can be configured to execute a control method for the centrifugal compressor based on the inlet opening of the centrifugal compressor acquired by the opening sensor.

[0025] Specifically, the implemented control method includes the following steps: Step S100 involves shutting off the drive motor of the centrifugal compressor when the inlet opening of the centrifugal compressor is lower than a first preset value. At this time, because the inlet opening of the centrifugal compressor is small, the refrigerant backflow generated by the condenser is limited, thus preventing the rotor of the centrifugal compressor from violently reversing or generating severe vibration and noise. Alternatively, Step S200 involves performing the following operations in a preset sequence when the inlet opening of the centrifugal compressor is not lower than the first preset value: reducing the inlet opening of the centrifugal compressor and increasing the speed of the centrifugal compressor. At this time, because the inlet opening of the centrifugal compressor is large, the backflow problem can be avoided by reducing the inlet opening, and the surge problem can be avoided by increasing the speed of the centrifugal compressor.

[0026] In this arrangement, the air conditioning system in the aforementioned embodiments, by employing the control method of the centrifugal compressor, classifies the inlet opening of the centrifugal compressor and provides different shutdown steps based on different inlet opening degrees. This achieves a smooth shutdown of the centrifugal compressor while reducing backflow, lowering noise, and preventing rotor bearing damage. Therefore, the air conditioning system using this method also has higher reliability, longer lifespan, and provides a better user experience.

[0027] Regarding the air conditioning system mentioned in this application, those skilled in the art should understand that it does not narrowly refer to air conditioners used in buildings that have indoor cooling / heating units and outdoor heat exchange units. Rather, it should be understood as a type of thermal system that achieves air conditioning function, driven by various power sources (e.g., electricity), and achieves heat exchange with the air at the location to be conditioned through the phase change of the refrigerant within the system. For example, when this air conditioning system is used in building HVAC, it may be a refrigeration system with cooling function only, or it may be a heat pump system with both cooling and heating capabilities. Similarly, when this air conditioning system is used in the cold chain field, it may be a transport refrigeration system, or it may be a refrigeration / freezing system. However, regardless of the specific form of the air conditioning system, a centrifugal compressor must be present for the centrifugal compressor control method described in this application to be applicable.

[0028] The following will illustrate further modifications to the control method of the centrifugal compressor and corresponding changes to the structural layout of the air conditioning system through exemplary description, in order to further improve its efficiency, reliability, or for other improvements.

[0029] For example, as a refinement of the control process in step S200, the inlet opening range of the centrifugal compressor is further subdivided into not lower than a first preset value and not lower than a second preset value, and the following subdivided control steps are made based on the subdivided inlet opening range. Specifically, S210 involves operations when the inlet opening of the centrifugal compressor is not lower than the first preset value and lower than the second preset value. In this case, the preset sequence of control operations mentioned in the previous embodiment is as follows: first, the speed of the centrifugal compressor is increased based on the surge envelope. Since the inlet opening of the centrifugal compressor remains constant while the speed increases, the surge threshold value corresponding to the surge envelope also increases, thus making it less likely for a surge problem to occur. Then, the inlet opening of the centrifugal compressor is reduced to the first preset value. At this time, as the inlet opening of the centrifugal compressor decreases, the degree of refrigerant backflow generated by the condenser is limited, thus preventing the rotor of the centrifugal compressor from violently reversing or generating severe vibration and noise. At the same time, since the surge envelope that forms the surge threshold has increased as the rotational speed increases, the surge threshold will not be reached even after the inlet opening of the centrifugal compressor is reduced, thus avoiding surge problems from beginning to end.

[0030] Similarly, the centrifugal compressor speed can be increased simultaneously while the inlet opening of the centrifugal compressor is reduced to a first preset value, based on the surge envelope. Since increasing the centrifugal compressor speed rapidly raises the corresponding surge threshold on the surge envelope, simultaneously reducing the inlet opening of the centrifugal compressor also reduces the likelihood of surge problems. Correspondingly, since the aforementioned control steps are performed simultaneously, the time required for this control process can be saved. Because the probability of surge also increases with time, this modification of the control steps also helps to avoid surge problems.

[0031] Furthermore, S220 relates to the operation when the inlet opening of the centrifugal compressor is not lower than a second preset value. In this case, the preset sequence of control operations mentioned in the previous embodiment is: first, reduce the inlet opening of the centrifugal compressor to the second preset value. During this stage, since the inlet opening of the centrifugal compressor is relatively large, and considering that the surge threshold corresponding to the surge envelope is high and generally difficult to reach, the operation of increasing the compressor speed is not performed first. Instead, the inlet opening of the centrifugal compressor is directly reduced to decrease the degree of refrigerant backflow generated by the condenser, thereby avoiding violent reverse rotation of the centrifugal compressor rotor or the generation of severe vibration and noise during this stage. Subsequently, the operation process in the embodiment of step S210 described above is executed. That is, either the centrifugal compressor speed can be increased first, followed by reducing the inlet opening of the centrifugal compressor to the first preset value; or the centrifugal compressor speed can be increased simultaneously while reducing the inlet opening of the centrifugal compressor to the first preset value. This effectively avoids the risk of the surge threshold being reached by raising the surge threshold corresponding to the surge envelope, thus reducing the likelihood of surge problems.

[0032] As an application of the aforementioned control method in a type of air conditioning system, its control parameters and control methods can be clearly defined and refined.

[0033] For example, the first preset value mentioned in the method could be a 10% inlet full opening, while the second preset value could be a 30% inlet full opening. Furthermore, the specific object controlling the inlet opening could be the inlet guide vanes of a centrifugal compressor.

[0034] For example, the speed control of a centrifugal compressor can be achieved by adjusting the output power of the compressor's drive motor. More specifically, the output power of the compressor's drive motor can be controlled by adjusting the output current to 60%-65% of the full-load current.

[0035] For example, in the aforementioned process of increasing the speed of the centrifugal compressor, to further refine this control step, the incremental change value of the speed can also be controlled. Specifically, as the opening becomes smaller and the speed increases, it becomes less prone to surge. Therefore, in this process, as the inlet opening of the centrifugal compressor decreases, the acceleration that increases the speed of the centrifugal compressor can be dynamically reduced to 0.

[0036] Regarding the aforementioned control method, as a complete closed loop for controlling the shutdown of a centrifugal compressor in an air conditioning system, in one type of operating condition, step S100 can be executed directly to complete the shutdown process; in another type of operating condition, steps S200 and S100 can be executed sequentially to complete the shutdown process. In a more specific embodiment, in one type of operating condition, steps S210 and S100 can be executed sequentially to complete the shutdown process; in another type of operating condition, steps S220, S210, and S100 can be executed sequentially to complete the shutdown process.

[0037] The following will be combined with the appendix Figure 1 An embodiment of the shutdown process of a centrifugal compressor in an air conditioning system employing the aforementioned control method is described exemplarily. Line A indicates the surge lift and opening changes of the centrifugal compressor throughout the shutdown process; curve B indicates the surge envelope at the compressor's rotational speed during the shutdown operation; and curve C indicates the surge envelope after increasing the compressor's rotational speed.

[0038] First, when the air conditioning system controller receives the shutdown command, the centrifugal compressor is at the rightmost endpoint of line A, possessing its pre-shutdown speed and inlet opening. Since this inlet opening is not lower than the second preset value, step S220 is executed, whereby the controller first controls the centrifugal compressor to reduce its inlet opening to the second preset value. Then, step S210 is executed; while reducing the centrifugal compressor's inlet opening to the first preset value, the controller begins to increase the centrifugal compressor's speed, causing the surge envelope faced by the system to change from curve B to curve C. At this point, the centrifugal compressor moves from the intersection of line A and curve B, or near that intersection, to the leftmost endpoint of line A, still located to the right of curve C, eliminating the risk of surge. Simultaneously, as the centrifugal compressor's inlet opening decreases, the refrigerant backflow from the condenser is limited, preventing violent reverse rotation of the centrifugal compressor rotor or severe vibration and noise. Then, step S100 is executed; when the centrifugal compressor's inlet opening falls below the first preset value, the centrifugal compressor's drive motor is shut off, thus completing a smooth and reliable shutdown process for the centrifugal compressor.

[0039] The above examples primarily illustrate the control method for the centrifugal compressor and the air conditioning system of this application. Although only some embodiments of this application have been described, those skilled in the art should understand that this application can be implemented in many other forms without departing from its spirit and scope. Therefore, the examples and embodiments shown are intended to be illustrative rather than restrictive, and various modifications and substitutions may be made without departing from the spirit and scope of this application as defined in the appended claims.

Claims

1. A control method for a centrifugal compressor, characterized in that, include: S100, when the inlet opening of the centrifugal compressor is lower than the first preset value, the drive motor of the centrifugal compressor is turned off; or S200, when the inlet opening of the centrifugal compressor is not lower than a first preset value, the following operations are performed in a preset sequence: reducing the inlet opening of the centrifugal compressor and increasing the rotational speed of the centrifugal compressor, wherein step S200 includes: S210, when the inlet opening of the centrifugal compressor is not lower than a first preset value and is lower than a second preset value, the preset sequence is: increase the rotational speed of the centrifugal compressor, and then, or simultaneously, decrease the inlet opening of the centrifugal compressor to the first preset value; or S220, when the inlet opening of the centrifugal compressor is not lower than the second preset value, the preset sequence is: first reduce the inlet opening of the centrifugal compressor to the second preset value, and then execute S210.

2. The control method according to claim 1, characterized in that, The first preset value is a 10% full opening of the entrance; and / or the second preset value is a 30% full opening of the entrance.

3. The control method according to claim 1, characterized in that, The speed of the centrifugal compressor is controlled by adjusting the output power of the drive motor of the centrifugal compressor.

4. The control method according to claim 3, characterized in that, The output current is adjusted to 60%-65% of the full load current to control the output power of the drive motor of the centrifugal compressor.

5. The control method according to claim 1, characterized in that, The inlet opening of the centrifugal compressor is adjusted by adjusting the inlet guide vanes.

6. The control method according to claim 1, characterized in that, The operation of increasing the rotational speed of the centrifugal compressor in step S200 includes: as the inlet opening of the centrifugal compressor decreases, the acceleration that increases the rotational speed of the centrifugal compressor is dynamically reduced to 0.

7. An air conditioning system, characterized in that, include: A centrifugal compressor used to compress the refrigerant within the air conditioning system; An opening sensor is used to acquire the inlet opening degree of the centrifugal compressor; as well as A controller is configured to perform the following operations based on the inlet opening of the centrifugal compressor obtained by the opening sensor: when the inlet opening of the centrifugal compressor is lower than a first preset value, shutting off the drive motor of the centrifugal compressor; or when the inlet opening of the centrifugal compressor is not lower than the first preset value, performing the following operations in a preset sequence: decreasing the inlet opening of the centrifugal compressor and increasing the rotational speed of the centrifugal compressor, wherein the controller is further configured to perform the following operations: when the inlet opening of the centrifugal compressor is not lower than the first preset value and is lower than a second preset value, the preset sequence is: increasing the rotational speed of the centrifugal compressor, and then or simultaneously decreasing the inlet opening of the centrifugal compressor to the first preset value; or when the inlet opening of the centrifugal compressor is not lower than the second preset value, the preset sequence is: first decreasing the inlet opening of the centrifugal compressor to the second preset value, then increasing the rotational speed of the centrifugal compressor, and then or simultaneously decreasing the inlet opening of the centrifugal compressor to the first preset value.

8. The air conditioning system according to claim 7, characterized in that, The first preset value is a 10% full opening of the entrance; and / or the second preset value is a 30% full opening of the entrance.

9. The air conditioning system according to claim 7, characterized in that, The controller is also configured to adjust the output power of the drive motor of the centrifugal compressor to control the speed of the centrifugal compressor.

10. The air conditioning system according to claim 9, characterized in that, The controller is also configured to adjust the output current to 60%-65% of the full load current to regulate the output power of the drive motor of the centrifugal compressor.

11. The air conditioning system according to claim 7, characterized in that, The centrifugal compressor further includes an inlet guide vane; wherein the controller is further configured to perform: adjusting the inlet opening of the centrifugal compressor by adjusting the inlet guide vane.

12. The air conditioning system according to claim 7, characterized in that, The controller is also configured to: during the process of increasing the speed of the centrifugal compressor, dynamically reduce the acceleration of increasing the speed of the centrifugal compressor to 0 as the inlet opening of the centrifugal compressor decreases.

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