Centrifugal compressor train and control method thereof

Abstract

The application discloses a control method of a centrifugal compressor unit, including a load operation and an unload operation. The unload operation includes reducing the operation opening of the suction guide vane, and when a first opening threshold is reached but the actual load is still greater than the target load, the opening of the air supplement valve is first reduced to a closed state, and then the operation opening of the suction guide vane is continuously reduced. The load operation includes increasing the operation opening of the suction guide vane, and when a second opening threshold is reached but the actual load is still less than the target load, the opening of the air supplement valve is first increased to a fully open state, and then the operation opening of the suction guide vane is continuously increased. According to the operation parameters and the set parameters of the centrifugal compressor unit, the control method reasonably closes or opens the air supplement valve, can help the centrifugal compressor unit to unload to a smaller load, maintains or even improves the operation efficiency of the unit, and enables the centrifugal compressor to operate in a more stable working condition.

Description

Technical Field

[0001] This application relates to the field of air conditioning units, and in particular to a centrifugal compressor unit and its control method. Background Technology

[0002] A centrifugal compressor unit includes a centrifugal compressor, a condenser, a throttling valve, and an evaporator, which are connected in sequence to form a refrigerant circulation system for external cooling or heating. In the refrigeration system, the refrigerant is compressed into a high-temperature, high-pressure refrigerant gas by the centrifugal compressor. The high-temperature, high-pressure refrigerant gas discharged from the centrifugal compressor releases heat in the condenser, is liquefied, and condenses into a high-pressure refrigerant liquid. The high-pressure refrigerant liquid flows into the throttling valve, which reduces its pressure to a low-pressure refrigerant liquid. The low-pressure refrigerant liquid absorbs heat in the evaporator, is vaporized, and evaporates to obtain a low-pressure refrigerant gas. Finally, the low-pressure refrigerant gas re-enters the centrifugal compressor, completing the refrigerant cycle. Some refrigeration systems also include an economizer, which separates the gas and liquid phases of the refrigerant after throttling by the upstream throttling valve. The gaseous refrigerant returns to the centrifugal compressor for compression, while the liquid refrigerant is throttled again by the downstream throttling valve and then enters the evaporator to evaporate.

[0003] Centrifugal compressors typically consist of components such as suction guide vanes, multi-stage compressor impellers, and a motor. Refrigerant is drawn in by the suction guide vanes and then enters the multi-stage compressor impellers. Driven by the motor, the impellers rotate to compress the refrigerant into a high-temperature, high-pressure refrigerant gas. The opening degree of the suction guide vanes affects the flow rate of refrigerant entering the centrifugal compressor, thus affecting the unit's load. The operating frequency of the centrifugal compressor motor affects the rotational speed of the compressor impellers and the compression ratio of the refrigerant, which also affects the unit's load. Summary of the Invention

[0004] This application provides a control method for a centrifugal compressor unit in a first aspect. The centrifugal compressor unit includes a centrifugal compressor, a condenser, an economizer, an evaporator, and a make-up air valve. The centrifugal compressor has suction guide vanes. The control method includes: acquiring the actual load of the centrifugal compressor unit; comparing the magnitude of the actual load and a target load of the centrifugal compressor unit; and adjusting the actual load based on the magnitude of the actual load and the target load until the actual load of the centrifugal compressor unit reaches the target load. The adjustment of the actual load includes loading and unloading operations, and the unloading operation includes reducing... The operating opening of the intake guide vane includes the following: when the operating opening of the intake guide vane reaches a first opening threshold but the actual load is still greater than the target load, the opening of the air supply valve is first reduced to the closed state. If a load reduction operation is still required, the operating opening of the intake guide vane is further reduced. The loading operation includes increasing the operating opening of the intake guide vane. When the operating opening of the intake guide vane reaches a second opening threshold but the actual load is still less than the target load, the opening of the air supply valve is first increased to the fully open state. If a loading operation is still required, the operating opening of the intake guide vane is further increased.

[0005] According to the first aspect above, the control method of the centrifugal compressor unit further includes: obtaining the minimum opening degree of the suction guide vane; setting a first opening degree threshold and a second opening degree threshold, wherein the second opening degree threshold is greater than the first opening degree threshold, and the first opening degree threshold is greater than the minimum opening degree.

[0006] According to the first aspect above, the first opening threshold and the second opening threshold are set as follows: the centrifugal compressor unit has a first state and a second state with the same operating conditions, and the actual load and operating efficiency of the centrifugal compressor unit are the same in the first state and the second state; wherein, when the centrifugal compressor unit is in the first state, the air supply valve is in the open state, and the operating opening of the suction guide vane reaches the first opening threshold; when the centrifugal compressor unit is in the second state, the air supply valve is in the closed state, and the operating opening of the suction guide vane reaches the second opening threshold.

[0007] According to the first aspect above, the first opening threshold is the minimum opening plus 0 to 20%; and / or the second opening threshold is the minimum opening plus 20 to 50%.

[0008] According to the first aspect above, when the operating opening of the intake guide vane is less than the minimum opening, the operating opening of the intake guide vane is increased to the minimum opening.

[0009] According to the first aspect above, obtaining the minimum opening of the intake guide vane includes: obtaining the intake pressure and the exhaust pressure; and dynamically calculating the minimum opening of the intake guide vane based on the intake pressure and the exhaust pressure.

[0010] According to the first aspect above, the control method for the centrifugal compressor unit further includes: acquiring the operating frequency of the centrifugal compressor; acquiring the suction pressure and the discharge pressure; dynamically calculating the surge frequency of the centrifugal compressor based on the suction pressure, the discharge pressure, and the operating opening of the suction guide vane; and increasing the operating frequency of the centrifugal compressor to the surge frequency when the operating frequency of the centrifugal compressor is less than the surge frequency.

[0011] According to the first aspect above, determining whether to perform a loading or unloading operation based on the acquired operating parameters and target load includes: acquiring the actual outlet water temperature, which reflects the actual load; acquiring the target outlet water temperature, which reflects the target load; comparing the actual outlet water temperature and the target outlet water temperature, and performing a loading operation when the actual outlet water temperature is greater than the target outlet water temperature, and performing a unloading operation when the actual outlet water temperature is less than the target outlet water temperature.

[0012] According to the first aspect above, the centrifugal compressor unit further includes a bypass line and a bypass valve, the bypass line being controllably connected between the condenser and the evaporator via the bypass valve; the loading operation further includes: before increasing the operating opening of the suction guide vane, reducing the opening of the bypass valve until the opening is 0; and / or the unloading operation further includes: after reducing the operating opening of the suction guide vane to the minimum opening, increasing the opening of the bypass valve until the opening is 100%.

[0013] According to the first aspect above, the loading operation further includes: increasing the operating frequency of the centrifugal compressor after the operating opening of the suction guide vane is increased to 100%; the unloading operation further includes: reducing the operating frequency of the centrifugal compressor before reducing the operating opening of the suction guide vane.

[0014] According to the first aspect above, the air replenishment valve is a switching valve or a regulating valve.

[0015] In a second aspect, this application also provides a centrifugal compressor unit, the centrifugal compressor unit comprising: a centrifugal compressor, a condenser, an economizer, an evaporator, a make-up air valve, and a controller, the centrifugal compressor having suction guide vanes, and the controller controlling the centrifugal compressor unit according to the control method of the centrifugal compressor unit described in any one of the first aspects. Attached Figure Description

[0016] Figure 1This is a schematic block diagram of a centrifugal compressor unit according to this application;

[0017] Figure 2A for Figure 1 The block diagram of the controller in the diagram;

[0018] Figure 2B for Figure 2A A block diagram of the input interface in the diagram;

[0019] Figure 2C for Figure 2A The block diagram of the output interface in the document;

[0020] Figure 3A A flowchart of the control method for the centrifugal compressor according to this application;

[0021] Figure 3B for Figure 3A A flowchart of the steps for obtaining and setting various operating and setting parameters of the unit;

[0022] Figure 3C for Figure 3A The flowchart of the steps to adjust Q1 to reach Q0;

[0023] Figure 4A for Figure 3C A flowchart of the loading operation in the process;

[0024] Figure 4B for Figure 3C The flowchart of the unloading operation in the process;

[0025] Figure 5 The graph shows the relationship between the actual load and operating efficiency of the centrifugal compressor unit 110 under a certain operating condition. Detailed Implementation

[0026] Various specific embodiments of the present invention will now be described with reference to the accompanying drawings, which form part of this specification. It should be understood that although terms indicating direction, such as "front," "rear," "upper," "lower," "left," "right," "top," and "bottom," are used herein to describe various exemplary structural parts and elements, their use is merely for ease of description and is based on the exemplary orientations shown in the accompanying drawings. Since the embodiments disclosed herein can be arranged in different orientations, these terms indicating direction are illustrative only and should not be considered limiting.

[0027] Figure 1 This is a schematic block diagram of the centrifugal compressor unit 110 of this application, used to illustrate the structure of the centrifugal compressor unit 110. Figure 1As shown, the centrifugal compressor unit 110 includes a centrifugal compressor 100, a condenser 101, a first-stage throttling valve 104, an economizer 103, a make-up gas valve 106, a second-stage throttling valve 105, and an evaporator 102. The high-temperature, high-pressure gaseous refrigerant discharged from the centrifugal compressor 100 enters the condenser 101, releases heat to the outside, condenses into liquid refrigerant, and then passes through the first-stage throttling valve 104 to become a medium-pressure two-phase refrigerant before entering the economizer 103. In the economizer 103, the medium-pressure two-phase refrigerant undergoes gas-liquid separation. The gaseous refrigerant returns controllably to the centrifugal compressor 100 through the make-up gas valve 106, while the liquid refrigerant flows out of the economizer 103 to the second-stage throttling valve 105. Then, the liquid refrigerant is throttled into a low-pressure two-phase refrigerant by the secondary throttling valve 105 and enters the evaporator 102. The low-pressure two-phase refrigerant absorbs heat from the chilled water flowing through the evaporator 102 and evaporates into a gaseous refrigerant. Finally, it returns to the centrifugal compressor 100, completing the refrigerant circulation.

[0028] In this embodiment, the centrifugal compressor 100 includes an intake guide vane 108, an impeller 111, and a motor 109. The intake guide vane 108 is located between the outlet of the evaporator 102 and the inlet of the impeller 111, and is used to control the flow rate of the gaseous refrigerant drawn into the centrifugal compressor 100, thereby regulating the load of the centrifugal compressor unit. In this embodiment, the intake guide vane 108 controls the flow rate of the refrigerant drawn into the centrifugal compressor 100 by adjusting its operating opening. The impeller 111 is used to increase the temperature and pressure of the gaseous refrigerant drawn into the centrifugal compressor 100. In this embodiment, the impeller 111 of the centrifugal compressor 100 includes two stages of impellers, and the gaseous refrigerant drawn into the centrifugal compressor 100 by the intake guide vane 108 flows through the two stages of impellers in sequence. The gaseous refrigerant from the economizer 103 is connected between the two stages of impellers of the centrifugal compressor 100 through a make-up valve 106. The motor 109 drives the impeller 111 to rotate and adjusts the speed of the impeller 111, thereby also adjusting the load of the centrifugal compressor unit 110. In this application, the motor 109 is a variable frequency motor, and its operating frequency is adjusted by a frequency converter. The operating frequency of the motor 109 is the operating frequency of the centrifugal compressor 100.

[0029] The centrifugal compressor unit 110 also includes a bypass line 112, which is controllably connected to the condenser 101 and the evaporator 102 via a bypass valve 107. The load on the centrifugal compressor unit 110 can also be adjusted by controlling the opening degree of the bypass valve 107. In various embodiments of this application, the gas supply valve 106 and the bypass valve 107 can be either on / off valves or regulating valves.

[0030] In this embodiment, the load of the centrifugal compressor unit 110 is reflected by the outlet water temperature of the evaporator 102. During the flow of chilled water through the evaporator 102, it exchanges heat with the refrigerant in the evaporator 102, releasing heat to the refrigerant and thus lowering its temperature. Therefore, the outlet water temperature of the chilled water in the evaporator 102 reflects the heat absorbed by the refrigerant, which in turn reflects the load of the centrifugal compressor unit 110.

[0031] The centrifugal compressor unit 110 also includes a controller 120. The controller 120 is used to control the actual load of the centrifugal compressor unit 110 so that the actual load is consistent with the target load. In this embodiment, the actual load of the centrifugal compressor unit 110 is related to the operating opening degree of the suction guide vane 108, the operating frequency of the motor 109, the opening degree of the bypass valve 107, and the opening degree of the make-up air valve 106.

[0032] To acquire various parameters of the centrifugal compressor unit 110, the centrifugal compressor unit 110 also includes a chilled water outlet temperature sensor 126, a suction pressure sensor 127, a discharge pressure sensor 128, and a suction guide vane opening controller 125. The chilled water outlet temperature sensor 126 is installed on the outlet pipe of the evaporator 102. The suction pressure sensor 127 is installed on the pipe between the evaporator 102 and the centrifugal compressor 100, and the discharge pressure sensor 128 is installed on the pipe between the centrifugal compressor 100 and the condenser 101. The suction guide vane opening controller 125 is connected to the suction guide vane 108 of the centrifugal compressor 100 and is used to detect and control the operating opening of the suction guide vane 108.

[0033] Those skilled in the art will understand that during the operation of the centrifugal compressor unit 110, it is also necessary to ensure that the operating opening of the suction guide vane 108 is always not less than its minimum opening, and that the operating frequency of the centrifugal compressor 100 is always not less than its surge frequency, in order to avoid the centrifugal compressor 100 from experiencing surge, which would have an adverse effect on the unit.

[0034] In this application, the controller 120 controls the operating opening of the suction guide vane 108, the operating frequency of the motor 109, the opening of the bypass valve 107, and the opening of the make-up air valve 106 based on these parameters and according to a certain control method, so as to adjust the actual outlet temperature of the chilled water to be consistent with the target outlet temperature, that is, to make the actual load of the centrifugal compressor unit 110 consistent with the target load.

[0035] Figures 2A-2C A block diagram of the controller 120 is shown. Figure 2A The overall structure of the controller 120 is shown. Figure 2B The input structure block diagram is shown. Figure 2C The output structure block diagram is shown. For example... Figure 2AAs shown, the controller 120 includes a bus 241, a processor 242, an input interface 243, an output interface 244, and a memory 245 containing a control program 246. The various components of the controller 120, including the processor 242, input interface 243, output interface 244, and memory 245, are communicatively connected to the bus 241, enabling the processor 242 to control the operation of the input interface 243, output interface 244, and memory 245. Specifically, the memory 245 stores programs, instructions, and data, while the processor 242 reads programs, instructions, and data from the memory 245 and can write data to the memory 245. By executing the programs and instructions read from the memory 245, the processor 242 controls the operation of the input interface 243 and output interface 244.

[0036] like Figure 2B and Figure 2C As shown, input interface 243 is communicatively connected to motor 109, intake guide vane opening controller 125, chilled water outlet temperature sensor 126, intake pressure sensor 127, and exhaust pressure sensor 128 via connection 247 to receive data such as pressure and / or temperature parameters from the sensors, and / or operating frequency of motor 109 and / or operating opening of intake guide vanes, and stores this data in memory 245. Output interface 244 is communicatively connected to make-up air valve 106, bypass valve 107, motor 109, and intake guide vane opening controller 125 via connection 248. By executing control program 246 in memory 245, controller 120 controls make-up air valve 106, bypass valve 107, motor 109, and intake guide vane opening controller 125 according to certain steps.

[0037] Figures 3A-3C The control flow of the centrifugal compressor unit 110 is shown. For example... Figure 3A As shown, the unit starts operating at step 330, and then step 331 is executed.

[0038] In step 331, the controller 120 acquires various operating parameters of the centrifugal compressor unit 110 and manually set parameters, and then executes step 332.

[0039] In step 332, the controller 120 obtains the relationship between the actual load Q1 and the target load Q0 by comparing the relationship between the actual outlet temperature of the chilled water and the target outlet temperature of the chilled water, and then executes step 333.

[0040] At step 333, controller 120 determines whether the actual load Q1 is equal to the target load Q0. If the actual load Q1 is equal to the target load Q0, it returns to before step 331 and continues executing step 331. If the actual load Q1 is not equal to the target load Q0, it executes step 334.

[0041] In step 334, the controller 120 adjusts the actual load Q1 of the centrifugal compressor unit 110 until the actual load Q1 reaches the target load Q0, that is, the actual outlet water temperature of the chilled water is consistent with the target outlet water temperature. Then step 335 is executed.

[0042] In step 335, the controller 120 determines whether the centrifugal compressor unit 110 has stopped. If so, it executes step 336, and the centrifugal compressor unit 110 stops running. Otherwise, it returns to the state before step 331 and continues executing step 331.

[0043] like Figure 3B As shown, in step 331, acquiring various operating parameters and manually set parameters of the centrifugal compressor unit 110 includes steps 341, 342, 343, 344, and 345. Depending on the specific unit settings and calculation methods, most of these parameters can be acquired simultaneously or in a certain order.

[0044] In step 341, the controller 120 acquires the minimum opening IGV of the intake guide vane. min In this embodiment, the minimum opening degree IGV of the intake guide vane is... min The minimum opening of the intake guide vane (IGV) is dynamically calculated based on the intake and exhaust pressures obtained from the controller 120. min This indicates the non-surge region of the centrifugal compressor 100, specifically the operating opening (IGV) of the intake guide vanes. run Greater than IGV min When the motor frequency is not less than the surge frequency, the centrifugal compressor 100 will not experience surge.

[0045] In step 342, the operating opening (IGV) of the intake guide vane is obtained. run .

[0046] In step 343, a first opening threshold IGV1 and a second opening threshold IGV2 are set for the intake guide vane. Both the first opening threshold IGV1 and the second opening threshold IGV2 are greater than the minimum opening IGV of the intake guide vane. min Furthermore, the second opening threshold IGV2 is greater than the first opening threshold IGV1. In this application, the first opening threshold IGV1 and the second opening threshold IGV2 can be manually set by the operator or calculated based on data stored in the controller 120. An example of calculating the first opening threshold IGV1 and the second opening threshold IGV2 will be provided in conjunction with... Figure 5 describe.

[0047] In step 344, the surge frequency of the centrifugal compressor is obtained. In this embodiment, the surge frequency of the centrifugal compressor is based on the intake pressure and exhaust pressure obtained by the controller 120, as well as the operating opening degree (IGV) of the intake guide vanes. run It was obtained through dynamic calculation.

[0048] In step 345, the actual load Q1 and target load Q0 of the centrifugal compressor unit are obtained. In this embodiment, the controller obtains the actual outlet temperature of the chilled water, which reflects the actual load Q1. The controller also obtains the target outlet temperature of the chilled water, which reflects the target load Q0.

[0049] like Figure 3C As shown, in step 334, the controller adjusts the actual load Q1 of the centrifugal compressor unit 110 until the actual load Q1 reaches the target load Q0, that is, the actual outlet water temperature of the chilled water is consistent with the target outlet water temperature, including the following steps:

[0050] After executing step 333 and determining that Q1 is not equal to Q0, step 346 is executed. In step 346, the controller determines whether Q1 is greater than Q0. If Q1 is greater than Q0, that is, the actual outlet water temperature is less than the target outlet water temperature, then the unloading operation in step 348 is performed; if Q1 is less than Q0, that is, the actual outlet water temperature is greater than the target outlet water temperature, then the loading operation in step 347 is performed.

[0051] Once Q1 is adjusted to reach Q0, return to step 335.

[0052] Those skilled in the art will understand that, during the adjustment process in step 334, in order to ensure the normal operation of the centrifugal compressor 100, it is also necessary to monitor the operating opening of the suction guide vane and the operating frequency of the centrifugal compressor in real time. When the operating opening of the suction guide vane is IGV... run Less than minimum opening IGV min When this is the case, increase the operating opening of the intake guide vane (IGV). run To minimum opening IGV min Furthermore, when the operating frequency of the centrifugal compressor is lower than the surge frequency, the operating frequency of the centrifugal compressor is increased to the surge frequency.

[0053] Figure 4A and Figure 4B The document further illustrates the specific processes for loading and unloading operations. Figure 4A The loading operation flow of step 347 is shown. Figure 4B The unloading operation process of step 348 is shown.

[0054] like Figure 4AAs shown, during the loading operation, step 451 is executed first to reduce the opening of the bypass valve, and then step 452 is executed.

[0055] In step 452, the controller determines whether the opening degree of the bypass valve is 0, that is, when the bypass valve is closed, but Q1 is still less than Q0. If yes, proceed to step 453. If no, complete the loading operation when Q1 and Q0 are the same, and proceed to step 335.

[0056] In step 453, the operating opening of the intake guide vane (IGV) is increased. run Then proceed to step 454.

[0057] In step 454, the controller determines the operating opening degree (IGV) of the intake guide vane. run Does the second opening threshold IGV2 have been reached, but Q1 is still less than Q0? If yes, proceed to step 455. If no, complete the loading operation when Q1 matches Q0, and proceed to step 335.

[0058] In step 455, the opening of the air supply valve is increased, and then step 456 is executed.

[0059] In step 456, the controller determines whether the air supply valve is fully open (100% opening), but Q1 is still less than Q0. If so, proceed to step 457. If not, complete the loading operation when Q1 equals Q0, and proceed to step 335.

[0060] In step 457, the operating opening of the intake guide vane (IGV) is further increased. run Then proceed to step 458.

[0061] In step 458, the controller determines the operating opening degree (IGV) of the intake guide vane. run Does it reach 100%, but Q1 is still less than Q0? If yes, continue to step 459. If no, complete the loading operation when Q1 and Q0 are the same, and proceed to step 335.

[0062] In step 459, the operating frequency of the centrifugal compressor is increased, that is, the operating frequency of the centrifugal compressor motor is increased until Q1 and Q0 are consistent, and the loading operation is completed, and step 335 is executed.

[0063] like Figure 4B As shown, during the unloading operation, step 461 is executed first to reduce the operating frequency of the centrifugal compressor, that is, to reduce the operating frequency of the centrifugal compressor motor, and then step 462 is executed.

[0064] In step 462, the controller determines whether the operating frequency of the centrifugal compressor has reached the surge frequency, but Q1 is still greater than Q0. If so, proceed to step 463. If not, complete the loading operation when Q1 and Q0 are equal, and proceed to step 335.

[0065] In step 463, the operating opening IGV of the intake guide vane is reduced. run Then proceed to step 464.

[0066] In step 464, the controller determines the operating opening degree (IGV) of the intake guide vane. run Does the first opening threshold IGV1 have been reached, but Q1 is still greater than Q0? If so, proceed to step 465. If not, complete the loading operation when Q1 and Q0 are equal, and proceed to step 335.

[0067] In step 465, the opening of the air supply valve is reduced, and then step 466 is executed.

[0068] In step 466, the controller determines whether the air supply valve is fully closed, i.e., the opening is 0, but Q1 is still greater than Q0. If yes, proceed to step 467. If no, complete the loading operation when Q1 and Q0 are the same, and proceed to step 335.

[0069] In step 467, the operating opening (IGV) of the intake guide vane is further reduced. run Then proceed to step 468.

[0070] In step 468, the controller determines the operating opening degree (IGV) of the intake guide vane. run Has the minimum opening IGV been reached? min However, Q1 is still greater than Q0. If so, proceed to step 469. If not, complete the loading operation when Q1 and Q0 are the same, and proceed to step 335.

[0071] In step 469, the opening of the bypass valve is increased until Q1 and Q0 are consistent, thus completing the unloading operation and proceeding to step 335.

[0072] Therefore, in this application, during load reduction operation, when the operating opening of the suction guide vane has not yet decreased to its minimum opening but has reached the first threshold opening, the opening of the make-up air valve is first adjusted to be completely closed before the operating opening of the suction guide vane is further reduced. Closing the make-up air valve before the suction guide vane reaches its minimum opening prevents the suction guide vane from frequently reaching its minimum opening, and the operating frequency of the centrifugal compressor does not frequently increase due to the increase in surge frequency, thus helping the centrifugal compressor operate within a safer and more reliable range. Furthermore, this control method can also help the unit reduce its load to a lower level without surging.

[0073] Furthermore, during the loading operation of this application, when the operating opening of the intake guide vane has not yet increased to its maximum opening but has reached the second threshold opening, the opening of the air supply valve is first adjusted to be fully open before the operating opening of the intake guide vane is further increased. Increasing the operating opening of the intake guide vane before adjusting the opening and closing of the air supply valve can avoid frequent opening and closing of the air supply valve.

[0074] Figure 5 A graph showing the relationship between the actual load and operating efficiency of centrifugal compressor unit 110 under a certain operating condition is provided to illustrate an example of calculating the first opening threshold IGV1 and the second opening threshold IGV2. Figure 5 As shown, under the same operating conditions, line 581 illustrates the relationship between the load (i.e., cooling capacity) of the centrifugal compressor unit 110 and the system operating efficiency (COP) when the make-up air valve 106 is open. Line 582 illustrates the relationship between the load (i.e., cooling capacity) of the centrifugal compressor unit 110 and the system operating efficiency (COP) when the make-up air valve 106 is closed.

[0075] At point 583, lines 581 and 582 intersect. The centrifugal compressor unit 110 has a first state and a second state with the same operating conditions. That is, in the first state and the second state, the load and COP of the centrifugal compressor unit 110 are the same. Specifically, in line 581, the make-up air valve 106 is open, and the operating opening degree of the suction guide vane 108 reaches a first opening threshold. In this embodiment, the first opening threshold is 35%. In line 582, the make-up air valve 106 is closed, and the operating opening degree of the suction guide vane 108 reaches a second opening threshold. In this embodiment, the second opening threshold is 75%. As a specific example, in this embodiment, the minimum opening degree of the suction guide vane 108 is 25%, the first opening threshold is the minimum opening degree plus 10%, and the second opening threshold is the minimum opening degree plus 50%. In other embodiments, the first opening threshold may also be the minimum opening degree plus 0-20%; the second opening threshold may also be the minimum opening degree plus 20-50%.

[0076] Therefore, if the intake guide vane reaches the first threshold opening when the make-up air valve is open, closing the make-up air valve first, and then further reducing the load by decreasing the opening of the intake guide vane, can improve the unit's COP. Furthermore, closing the make-up air valve further reduces the minimum load achievable by the centrifugal compressor unit.

[0077] Similarly, if the intake guide vane reaches the second opening threshold when the make-up air valve is closed, opening the make-up air valve first and then increasing the opening of the intake guide vane to increase the load can also improve the unit's COP.

[0078] To avoid surge in centrifugal compressors, it is generally necessary to control the operating opening of the suction guide vanes to be greater than the minimum opening. Furthermore, the operating frequency of the centrifugal compressor is increased when the suction guide vanes are close to the minimum opening. The applicant found that when adjusting the load on the centrifugal compressor unit, if the suction guide vanes are already at a small opening, continuing to close them causes the operating frequency of the centrifugal compressor to increase more rapidly, affecting the coefficient of performance (COP). This results in low operating efficiency and unstable operation of the centrifugal compressor unit.

[0079] The control method of this application reasonably closes or opens the air supply valve according to the operating parameters and set parameters of the centrifugal compressor unit. This not only helps the centrifugal compressor unit unload to a smaller load, but also maintains or even improves the operating efficiency of the unit, and enables the centrifugal compressor to operate under more stable conditions.

[0080] Furthermore, since opening and closing the air supply valve has a significant impact on the unit load, the centrifugal compressor unit of this application sets a first opening threshold and a second opening threshold for the intake guide vane, which can avoid frequently closing or opening the air supply valve.

[0081] Although this disclosure has been described in conjunction with examples of the embodiments outlined above, various alternatives, modifications, variations, improvements, and / or substantially equivalents, whether known or now or soon to be foreseen, will likely be apparent to those skilled in the art. Therefore, the examples of embodiments of this disclosure set forth above are intended to be illustrative rather than restrictive. Various changes can be made without departing from the spirit or scope of this disclosure. Therefore, this disclosure is intended to include all known or previously developed alternatives, modifications, variations, improvements, and / or substantially equivalents. The technical effects and problems described in this specification are exemplary rather than restrictive. It should be noted that the embodiments described in this specification may have other technical effects and may solve other technical problems.

Claims

1. A control method for a centrifugal compressor unit, the centrifugal compressor unit (110) comprising: A centrifugal compressor (100), a condenser (101), an economizer (103), an evaporator (102), and a make-up air valve (106), wherein the centrifugal compressor (100) has an intake guide vane (108), characterized in that: The control method includes: Obtain the actual load of the centrifugal compressor unit (110); Compare the actual load and target load of the centrifugal compressor unit (110); The actual load is adjusted based on the relationship between the actual load and the target load until the actual load of the centrifugal compressor unit (110) reaches the target load. The adjustment of the actual load includes loading and unloading operations. The unloading operation includes reducing the operating opening of the intake guide vane (108). When the operating opening of the intake guide vane (108) reaches a first opening threshold but the actual load is still greater than the target load, the opening of the supplementary air valve (106) is first reduced to the closed state. If unloading is still required, the operating opening of the intake guide vane (108) is further reduced. The loading operation includes increasing the operating opening of the intake guide vane (108). When the operating opening of the intake guide vane (108) reaches the second opening threshold but the actual load is still less than the target load, the opening of the supplementary air valve (106) is first increased to the fully open state. If the loading operation is still required, the operating opening of the intake guide vane (108) is further increased.

2. The control method for the centrifugal compressor unit according to claim 1, characterized in that... Also includes: Obtain the minimum opening of the intake guide vane (108); A first opening threshold and a second opening threshold are set, wherein the second opening threshold is greater than the first opening threshold, and the first opening threshold is greater than the minimum opening.

3. The control method for the centrifugal compressor unit according to claim 2, characterized in that: The first opening threshold and the second opening threshold are set as follows: The centrifugal compressor unit (110) has a first state and a second state with the same operating conditions, and the actual load and operating efficiency of the centrifugal compressor unit (110) are the same in the first state and the second state. When the centrifugal compressor unit (110) is in the first state, the air supply valve (106) is in the open state, and the operating opening degree of the suction guide vane (108) reaches the first opening degree threshold. When the centrifugal compressor unit (110) is in the second state, the air supply valve (106) is closed, and the operating opening of the suction guide vane (108) reaches the second opening threshold.

4. The control method for the centrifugal compressor unit according to claim 3, characterized in that: The first opening threshold is the minimum opening plus 0-20%; and / or The second opening threshold is the minimum opening plus 20% to 50%.

5. The control method for the centrifugal compressor unit according to claim 2, characterized in that: When the operating opening of the intake guide vane (108) is less than the minimum opening, the operating opening of the intake guide vane (108) is increased to the minimum opening.

6. The control method for the centrifugal compressor unit according to claim 2, characterized in that: The minimum opening of the intake guide vane (108) is obtained by: Obtain the inhalation pressure and exhaust pressure; The minimum opening of the intake guide vane (108) is dynamically calculated based on the intake pressure and the exhaust pressure.

7. The control method for the centrifugal compressor unit according to claim 2, characterized in that... Also includes: Obtain the operating frequency of the centrifugal compressor (100); Obtain the inhalation pressure and exhaust pressure; The surge frequency of the centrifugal compressor (100) is dynamically calculated based on the intake pressure, the exhaust pressure, and the operating opening of the intake guide vane (108); When the operating frequency of the centrifugal compressor (100) is less than the surge frequency, the operating frequency of the centrifugal compressor (100) is increased to the surge frequency.

8. The control method for a centrifugal compressor unit according to claim 1, characterized in that: Determining whether to perform a load increase or a load decrease based on the acquired operating parameters and target load includes: Obtain the actual outlet water temperature, which reflects the actual load. Obtain the target outlet water temperature, which reflects the target load. The actual outlet water temperature is compared with the target outlet water temperature. When the actual outlet water temperature is greater than the target outlet water temperature, a loading operation is required. When the actual outlet water temperature is less than the target outlet water temperature, a unloading operation is required.

9. The control method for a centrifugal compressor unit according to claim 1, characterized in that: The centrifugal compressor unit (110) also includes a bypass line (112) and a bypass valve (107), wherein the bypass line (112) is controllably connected between the condenser (101) and the evaporator (102) through the bypass valve (107); The loading operation further includes: before increasing the operating opening of the intake guide vane (108), reducing the opening of the bypass valve (107) until the opening is 0; and / or The unloading operation further includes: after reducing the operating opening of the intake guide vane (108) to the minimum opening, increasing the opening of the bypass valve (107) until the opening is 100%.

10. The control method for a centrifugal compressor unit according to claim 1, characterized in that: The loading operation further includes: increasing the operating frequency of the centrifugal compressor (100) after the operating opening of the suction guide vane (108) is increased to 100%; The unloading operation further includes reducing the operating frequency of the centrifugal compressor (100) before reducing the operating opening of the suction guide vane (108).

11. The control method for a centrifugal compressor unit according to claim 1, characterized in that: The air replenishment valve (106) is a switching valve or a regulating valve.

12. A centrifugal compressor unit, said centrifugal compressor unit (110) comprising: A centrifugal compressor (100), a condenser (101), an economizer (103), an evaporator (102), a make-up air valve (106), and a controller (120), wherein the centrifugal compressor (100) has an intake guide vane (108), characterized in that: The controller (120) controls the centrifugal compressor unit (110) according to the control method of any one of claims 1-11.

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