Anti-surge control method for centrifugal water chiller

Abstract

This invention belongs to the field of heat exchange technology, specifically providing a surge prevention control method for centrifugal chillers. It aims to solve the problem of surge phenomena easily occurring in the compressors of existing centrifugal chillers during high-pressure operation. To this end, the centrifugal chiller of this invention includes multiple bypass branches, a refrigerant circulation loop, and multiple centrifugal compressors, condensers, throttling components, and evaporators installed on the refrigerant circulation loop. The bypass branches are configured to introduce refrigerant from the condenser into the evaporator, and an electronic expansion valve is installed on the bypass branches to control their on / off state. The surge prevention control method of this invention includes: acquiring the current speed of the centrifugal compressor during operation; selectively opening the electronic expansion valve based on the current speed of the centrifugal compressor to effectively prevent surge phenomena during operation, thereby effectively ensuring the stability of the unit during operation.

Description

Technical Field

[0001] This invention belongs to the field of heat exchange technology, specifically providing a method for anti-surge control of centrifugal chiller units. Background Technology

[0002] With the continuous development of heat exchange technology, the types of chiller units are also increasing; among them, centrifugal chiller units have attracted much attention due to their advantages such as low vibration and high reliability. The magnetic levitation centrifugal compressor, as the core component of a centrifugal chiller unit, works by using a high-speed rotating impeller to perform work on the gas, transferring mechanical energy to the gas, increasing its pressure and velocity, thus giving the gas pressure energy and velocity energy. However, because surge is an inherent characteristic of velocity-type centrifugal compressors, chiller units using centrifugal compressors are inevitably prone to surge. Surge can easily disrupt system stability, increase operating noise, and even damage the compressor impeller. Therefore, while leveraging the advantages of centrifugal chiller units, how to avoid surge in centrifugal compressors has become an urgent problem to be solved in this field.

[0003] Specifically, the formation mechanism of surge can be divided into the following two situations: One is during low-load compressor operation. When the refrigerant flow rate is less than a certain value, refrigerant flow deteriorates in the compressor's flow path. At this time, the impeller cannot effectively increase the gas pressure, resulting in a decrease in the compressor's outlet pressure. However, because the pressure of the entire system network does not decrease instantaneously, mainly due to the condenser pressure not decreasing instantaneously, airflow flows back from the condenser to the compressor until the condensing pressure is lower than the compressor's outlet pressure. Only then does the refrigerant backflow stop, and the compressor's displacement increases, allowing it to return to normal operation. In reality, the compressor's total load under these conditions is very small, limiting its displacement. As the compressor's displacement gradually decreases, gas backflow occurs again. This cycle repeats, creating periodic airflow oscillations in the system, leading to surge. The other situation occurs during high-load compressor operation. When the condensing pressure is high and the compressor head is less than the pressure difference between the condenser and evaporator, gas in the condenser flows back, resulting in surge. For chiller units using magnetic levitation variable frequency centrifugal compressors, surge mainly occurs during low-load operation, high-pressure start-up, and high-pressure operation. To address surge, many existing chiller units are now equipped with corresponding structures or control methods to prevent it.

[0004] Furthermore, existing anti-surge measures for centrifugal chillers mainly fall into two categories: One approach addresses the issue from the compressor side, primarily by adjusting the compressor speed or the opening of the inlet guide vanes to keep the compressor's operating curve away from the surge line and within the stable operating range. Although the compressor has anti-surge design features, in actual operation, adverse operating conditions outside the compressor's stable operating range will inevitably be encountered, and surge will still occur under these conditions. Additionally, for non-compressor manufacturers, design optimization from the compressor side is not feasible; therefore, anti-surge design must be added from the system side. The other approach addresses the issue from the system side, mainly by adding a hot gas bypass between the evaporator and condenser. This bypass valve allows high-pressure gas or liquid from the condenser to enter the evaporator, thereby reducing the condenser pressure while increasing the evaporator pressure, lowering the compressor head, and increasing the compressor flow rate, thus improving operating conditions and preventing surge. Since the hot gas bypass line is not always open, but only opens when surge occurs, a valve is needed for on / off control. Current technology uses solenoid valves as control valves for the hot gas bypass line to control its on / off state. However, the solenoid valve has a short on / off time, and given the high pressure ratio between the evaporator and condenser, the solenoid valve is prone to water hammer during operation, impacting the valve and the pipeline, causing vibration and reducing its lifespan. Furthermore, during sustained surge, the frequent on / off of the solenoid valve causes significant fluctuations in the pressure ratio between the evaporator and condenser, severely affecting system stability. In particular, for large centrifugal chillers with multiple centrifugal compressors, the compressors operating at high pressure ratios are also a prime time for surge.

[0005] Accordingly, there is a need in the field for a new anti-surge control method for centrifugal chillers to solve the above problems. Summary of the Invention

[0006] The present invention aims to solve the above-mentioned technical problem, namely, to solve the problem that the compressor of the existing centrifugal chiller unit is prone to surge during the high pressure ratio operation stage.

[0007] This invention provides a surge prevention control method for a centrifugal chiller unit. The centrifugal chiller unit includes a bypass branch, a refrigerant circulation loop, and a centrifugal compressor, condenser, throttling component, and evaporator disposed on the refrigerant circulation loop. The bypass branch is configured to introduce refrigerant from the condenser into the evaporator, and an electronic expansion valve is provided on the bypass branch to control the on / off state of the bypass branch. The surge prevention control method includes:

[0008] During the operation of the centrifugal compressor, the current rotational speed of the centrifugal compressor is obtained;

[0009] The electronic expansion valve is selectively opened based on the current speed of the centrifugal compressor.

[0010] In the preferred embodiment of the above anti-surge control method, the step of "selectively opening the electronic expansion valve according to the current speed of the centrifugal compressor" specifically includes:

[0011] The current speed of the centrifugal compressor is compared with the preset speed;

[0012] If the current speed of the centrifugal compressor is less than or equal to the preset speed, the electronic expansion valve is opened.

[0013] In the preferred embodiment of the above anti-surge control method, the step of "opening the electronic expansion valve" specifically includes:

[0014] The electronic expansion valve is opened to a preset opening degree.

[0015] In a preferred embodiment of the above-mentioned anti-surge control method, when the opening of the electronic expansion valve is maintained at the preset opening for a preset duration, the anti-surge control method further includes:

[0016] Obtain the current speed of the centrifugal compressor again;

[0017] Based on the current rotational speed of the centrifugal compressor obtained again, the opening of the electronic expansion valve is selectively increased.

[0018] In the preferred embodiment of the above anti-surge control method, the step of "selectively increasing the opening of the electronic expansion valve based on the current rotational speed of the centrifugal compressor obtained again" specifically includes:

[0019] If the current speed of the centrifugal compressor is still less than or equal to the preset speed, the opening of the electronic expansion valve is increased.

[0020] In the preferred embodiment of the above anti-surge control method, the step of "increasing the opening of the electronic expansion valve" specifically includes:

[0021] Increase the opening degree of the electronic expansion valve by a preset amount.

[0022] In the preferred embodiment of the above-mentioned anti-surge control method, when the opening degree of the electronic expansion valve has increased to the maximum opening degree, the anti-surge control method further includes:

[0023] The current rotational speed of the centrifugal compressor is obtained again;

[0024] If the current speed of the centrifugal compressor is once again greater than the preset speed, the electronic expansion valve is closed.

[0025] In the preferred embodiment of the above anti-surge control method, the preset amplitude is 5%.

[0026] In the preferred embodiment of the above-mentioned anti-surge control method, the anti-surge control method further includes:

[0027] If the current speed of the centrifugal compressor is obtained again and is greater than the preset speed, the electronic expansion valve is closed.

[0028] In the preferred embodiment of the above anti-surge control method, the preset speed is equal to the surge speed multiplied by the correction coefficient;

[0029] The correction coefficient is greater than 1 and less than 2.

[0030] With the above technical solution adopted, the centrifugal chiller unit of the present invention includes multiple bypass branches, a refrigerant circulation loop, and multiple centrifugal compressors, condensers, throttling components, and evaporators arranged on the refrigerant circulation loop. The multiple bypass branches and the multiple centrifugal compressors are arranged in a corresponding manner. The bypass branches are configured to introduce refrigerant from the condenser into the evaporator, and an electronic expansion valve is provided on the bypass branches to control the on / off state of the bypass branches. The anti-surge control method of the present invention includes: during the operation of the centrifugal compressor, obtaining the current speed of the centrifugal compressor; and selectively opening the electronic expansion valve according to the current speed of the centrifugal compressor. This invention utilizes an electronic expansion valve installed on the bypass branch to control the connection status of the bypass branch according to different operating conditions. Specifically, the electronic expansion valve is selectively opened to connect the corresponding bypass branch based on the rotational speed of the centrifugal compressor during operation. This effectively avoids water hammer and large pressure fluctuations, thereby ensuring the operational stability of the centrifugal chiller unit, protecting the centrifugal compressor from damage, extending its service life, and ensuring its reliability. Attached Figure Description

[0031] The preferred embodiments of the present invention are described below with reference to the accompanying drawings, in which:

[0032] Figure 1 This is a flowchart of the main steps of the anti-surge control method of the present invention;

[0033] Figure 2 This is a flowchart illustrating the specific steps of the first preferred embodiment of the present invention;

[0034] Figure 3 This is a flowchart illustrating the specific steps of the second preferred embodiment of the present invention;

[0035] Figure 4 This is a flowchart illustrating the specific steps of the third preferred embodiment of the present invention. Detailed Implementation

[0036] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the invention and are not intended to limit the scope of protection of the invention. Those skilled in the art can make adjustments as needed to adapt to specific applications. For example, the present invention does not impose any restrictions on the specific type of the centrifugal chiller unit, as long as the centrifugal chiller unit is equipped with a centrifugal compressor and a corresponding bypass branch. Changes to the specific structure do not depart from the basic principles of the present invention and should fall within the scope of protection of the present invention.

[0037] It should be noted that in the description of this preferred embodiment, the terms "inner" and "outer," etc., indicating the direction or positional relationship, are based on the direction or positional relationship shown in the drawings. This is only for the convenience of description and does not indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of the present invention.

[0038] Furthermore, it should be noted that in the description of this invention, unless otherwise explicitly specified and limited, the term "connected" should be interpreted broadly. For example, it can refer to a direct connection, an indirect connection through an intermediate medium, or a connection within two elements. Moreover, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances. Additionally, although the steps of the control method of this invention are described in a specific order in this application, this order is not restrictive. Those skilled in the art can perform the steps in different orders without departing from the basic principles of this invention.

[0039] Specifically, in this invention, the centrifugal chiller unit includes a refrigerant circulation loop and multiple centrifugal compressors, condensers, throttling components, and evaporators disposed on the refrigerant circulation loop. The refrigerant circulates through the refrigerant circulation loop. When the unit is running, the refrigerant continuously exchanges heat between the evaporator and the condenser through the refrigerant circulation loop, thereby achieving the effect of heat exchange. Of course, this invention does not impose any restrictions on the specific structural arrangement of the centrifugal chiller unit. Those skilled in the art can set it according to actual usage requirements. For example, multiple centrifugal compressors can be arranged in parallel, with one condenser and one evaporator each, meaning multiple centrifugal compressors share a single set of condensers and evaporators. Alternatively, the number of condensers and evaporators can also be multiple, the same as the number of centrifugal compressors, with each centrifugal compressor connected to a corresponding condenser and evaporator, meaning each centrifugal compressor has its own set of condensers and evaporators. Yet another example is that the number of condensers can be multiple, the same as the number of centrifugal compressors, while the number of evaporators is one, meaning multiple centrifugal compressors and multiple condensers are arranged in a one-to-one correspondence and share the same evaporator. Of course, these are not limiting; as long as the centrifugal chiller unit is equipped with multiple centrifugal compressors, the control method of this invention can be used. Such changes in specific application do not alter the basic principles of this invention and fall within the scope of protection of this invention.

[0040] Furthermore, the centrifugal chiller unit also includes multiple bypass branches. The number of bypass branches is the same as the number of centrifugal compressors. Of course, the specific number is not limited, and those skilled in the art can set it according to actual usage requirements. The bypass branches and the centrifugal compressors are arranged correspondingly. The bypass branches are configured to introduce refrigerant from the condenser into the evaporator. That is, one end of the bypass branch is connected to the condenser, and the other end is connected to the evaporator. Of course, the specific connection position is not limited; it can be directly connected to the main body, or it can be connected to the outlet of the condenser or the inlet of the evaporator. Furthermore, an electronic expansion valve is provided on the bypass branch to control the on / off state of the bypass branch. It is understood that the bypass branch corresponding to a certain centrifugal compressor is obviously used to connect the condenser and evaporator corresponding to that centrifugal compressor. Of course, the corresponding condenser and evaporator can be dedicated to that centrifugal compressor or shared with other centrifugal compressors, as long as the bypass branch can achieve corresponding connection. Based on the above connection method, each centrifugal compressor can form a system with its corresponding evaporator and condenser. That is, the centrifugal chiller unit has as many systems as there are centrifugal compressors. The system pressure ratio in this invention also refers to the pressure ratio of the system corresponding to a certain centrifugal compressor.

[0041] In addition, the centrifugal chiller unit also includes a controller. The controller can acquire the pressure ratio of each system within the centrifugal chiller unit, as well as the rotational speed of the centrifugal compressor. Furthermore, the controller can control the operating status of the centrifugal chiller unit, such as controlling the opening and closing status and specific opening degree of the electronic expansion valve, and controlling the compressor load reduction. Those skilled in the art will understand that the present invention does not impose any limitations on the specific structure and model of the controller, and the controller can be the original controller of the centrifugal chiller unit, or it can be a controller separately set up to execute the control method of the present invention. Those skilled in the art can customize the structure and model of the controller according to actual usage requirements.

[0042] First refer to Figure 1 This diagram is a flowchart of the main steps of the first compressor start-up control method of the present invention. Figure 1 As shown, based on the centrifugal chiller unit described in the above embodiments, the first compressor start-up control method of the present invention mainly includes the following steps:

[0043] S1: During the operation of the centrifugal compressor, obtain the current speed of the centrifugal compressor;

[0044] S2: Selectively open the electronic expansion valve based on the current speed of the centrifugal compressor.

[0045] Furthermore, in step S1, during the operation of the centrifugal compressor, the current speed of the centrifugal compressor is obtained; it is understood that the centrifugal compressor here can be either the first centrifugal compressor to start in the unit or a centrifugal compressor that starts later in the unit. This is not restrictive, as long as it is a centrifugal compressor in a stable operating state.

[0046] Next, in step S2, the controller selectively opens the electronic expansion valve according to the current speed of the centrifugal compressor. It should be understood that the electronic expansion valve mentioned here is the electronic expansion valve on the bypass branch corresponding to the centrifugal compressor. Of course, it should also be noted that this invention does not impose any restrictions on its specific control method; as long as the electronic expansion valve is selectively opened according to the current speed of the centrifugal compressor, it should fall within the protection scope of this invention.

[0047] First, when controlling the start-up of a centrifugal compressor, it is first determined whether this centrifugal compressor is the first compressor to be started in the centrifugal chiller unit, that is, whether any other centrifugal compressors in the unit have already been started before this centrifugal compressor is started. Based on this determination, if the centrifugal compressor is the first compressor to be started in the centrifugal chiller unit, the control method in the first preferred embodiment below is executed; and if the centrifugal compressor is not the first compressor to be started in the centrifugal chiller unit, the control method in the second preferred embodiment below is executed. Furthermore, if a centrifugal compressor is already in a stable operating phase, the control method in the third preferred embodiment below is executed during its operation. Based on the above control methods, the centrifugal chiller unit of the present invention can effectively avoid large pressure ratio fluctuations regardless of the operating phase, thereby maximizing the operational stability of the unit. It should be noted that if a centrifugal chiller unit has only one centrifugal compressor, the control method in the first preferred embodiment of the present invention can also be executed, that is, the control method in the first preferred embodiment can be directly executed when it is turned on; and if multiple centrifugal compressors of a centrifugal chiller unit start simultaneously when it is turned on, the control method in the first preferred embodiment of the present invention is also applicable; these changes in specific application methods do not deviate from the basic principles of the present invention and should fall within the protection scope of the present invention.

[0048] See next Figure 2 This figure is a flowchart illustrating the specific steps of the first preferred embodiment of the present invention. Figure 2 As shown, based on the centrifugal chiller unit described in the above preferred embodiment, the first preferred embodiment of the control method of the present invention specifically includes the following steps:

[0049] S101: When the first centrifugal compressor is about to start, obtain the system pressure ratio corresponding to the centrifugal compressor;

[0050] S102: Determine whether the system voltage ratio is greater than the preset startup voltage ratio; if yes, proceed to step S103; if no, proceed to step S104.

[0051] S103: Open the electronic expansion valve corresponding to the first centrifugal compressor to the preset opening degree;

[0052] S104: Normal start-up of the first centrifugal compressor;

[0053] S105: After a preset time, the system pressure ratio corresponding to the centrifugal compressor is checked again;

[0054] S106: Determine whether the system voltage ratio obtained again is still greater than the preset startup voltage ratio; if yes, proceed to step S107; if no, proceed to step S110.

[0055] S107: Determine whether the opening degree of the electronic expansion valve is the maximum opening degree; if yes, proceed to step S109; if no, proceed to step S108.

[0056] S108: Increase the opening degree of the electronic expansion valve corresponding to the centrifugal compressor;

[0057] S109: Do not start the first centrifugal compressor;

[0058] S110: Start the first centrifugal compressor;

[0059] S111: Obtain the current speed of the centrifugal compressor;

[0060] S112: Determine whether the current speed is greater than the preset speed; if yes, proceed to step S115; if no, proceed to step S113.

[0061] S113: Determine whether the opening degree of the electronic expansion valve is the maximum opening degree; if yes, proceed to step S115; if no, proceed to step S114.

[0062] S114: Increase the opening of the electronic expansion valve corresponding to the first centrifugal compressor to the maximum opening.

[0063] S115: Determine whether the centrifugal compressor has finished starting; if yes, proceed to step S116; if no, proceed to step S111 again after a preset waiting time.

[0064] S116: Close the electronic expansion valve corresponding to the centrifugal compressor.

[0065] Further, in step S101, when the first centrifugal compressor in the centrifugal chiller unit is about to start, that is, when the centrifugal chiller unit is about to start, the system pressure ratio corresponding to the centrifugal compressor is obtained, that is, the system pressure ratio corresponding to the first started centrifugal compressor, specifically the ratio of the absolute pressure of the condenser and the evaporator corresponding to the first started centrifugal compressor. It is understood that, as a feasible method, the absolute pressure can be obtained by summing the gauge pressure measured by the pressure sensor installed on the heat exchanger and the pressure correction value (preferably 103 kPa). Furthermore, it should be noted that the present invention does not impose any restrictions on which specific centrifugal compressor is the first to be started; those skilled in the art can set it according to actual usage requirements.

[0066] Next, based on the pressure ratio obtained in step S101, the controller can compare the system pressure ratio corresponding to the first centrifugal compressor to be started with a preset starting pressure ratio. Of course, this invention does not impose any restrictions on the specific value of the preset starting pressure ratio; as long as the system pressure ratio is greater than the preset starting pressure ratio, it indicates that the system pressure ratio is high and prone to surge. Furthermore, based on the comparison result between the system pressure ratio corresponding to the first centrifugal compressor to be started and the preset starting pressure ratio, the controller selectively starts the centrifugal compressor after opening the electronic expansion valve corresponding to that centrifugal compressor. It should be noted that this invention does not impose any restrictions on its specific control method; as long as the centrifugal compressor is started selectively after opening the electronic expansion valve on the bypass branch corresponding to that centrifugal compressor based on the comparison result between the system pressure ratio corresponding to the first centrifugal compressor to be started and the preset starting pressure ratio, it falls within the protection scope of this invention.

[0067] Specifically, in step S102, it is determined whether the system pressure ratio corresponding to the centrifugal compressor is greater than the preset start-up pressure ratio, so that the centrifugal compressor can be selectively started after the electronic expansion valve corresponding to the centrifugal compressor is opened. That is, according to the needs, the bypass branch corresponding to the first centrifugal compressor that needs to be started is selectively connected, and then the centrifugal compressor is controlled to start, so as to effectively avoid large pressure ratio fluctuations and ensure the stability of unit operation.

[0068] Based on the judgment result of step S102, if the system pressure ratio corresponding to the centrifugal compressor is greater than the preset starting pressure ratio, it indicates that the unit has a surge risk. In this case, step S103 is executed, that is, the controller controls the electronic expansion valve corresponding to the first centrifugal compressor to be started to open to a preset opening degree, so as to effectively reduce the system pressure drop and thus reduce the surge risk. Of course, it should also be noted that the present invention does not impose any restrictions on the specific value of the preset opening degree. Those skilled in the art can set it according to actual usage needs, as long as it can reduce the system pressure ratio corresponding to the centrifugal compressor. If the system pressure ratio corresponding to the centrifugal compressor is less than or equal to the preset starting pressure ratio, it indicates that the unit does not have a surge risk. In this case, step S104 is executed, that is, the first centrifugal compressor to be started can be started normally. In other words, it is not necessary to control the opening of the electronic expansion valve corresponding to the first centrifugal compressor to be started to directly control the centrifugal compressor to start, so as to effectively ensure the heat exchange rate.

[0069] Next, in step S105, after a preset time, the system pressure ratio corresponding to the centrifugal compressor is detected again to determine the start-up timing of the first compressor. It should be noted that those skilled in the art need to set the specific value of the preset time according to actual usage requirements. The specific value can be determined according to the opening speed of the electronic expansion valve, preferably set to less than 3 minutes.

[0070] Based on the result obtained in step S105, the controller can selectively restart the centrifugal compressor after adjusting the opening of the electronic expansion valve corresponding to the centrifugal compressor, according to the system pressure ratio corresponding to the centrifugal compressor detected again. Specifically, in step S106, it is determined whether the system pressure ratio corresponding to the centrifugal compressor obtained again is still greater than the preset start-up pressure ratio, so as to selectively restart the centrifugal compressor after increasing the opening of the electronic expansion valve corresponding to the centrifugal compressor.

[0071] Based on the judgment result of step S106, if the system pressure ratio corresponding to the centrifugal compressor is still greater than the preset starting pressure ratio, the centrifugal compressor is started again after increasing the opening of the electronic expansion valve corresponding to the centrifugal compressor. Specifically, step S107 is executed first, that is, it is determined whether the opening of the electronic expansion valve is already at its maximum. If the current opening of the electronic expansion valve is not yet at its maximum, step S108 is executed, that is, the opening of the electronic expansion valve is increased, and then step S105 is executed again. It should be noted that the present invention does not impose any limit on the increase value of the opening of the electronic expansion valve. Those skilled in the art can set it according to actual usage needs, preferably set to 5% of the maximum opening of the electronic expansion valve. At the same time, if the current opening of the electronic expansion valve is already at its maximum, step S109 is executed, that is, the centrifugal compressor is not started, that is, the centrifugal chiller unit is not started, in order to prevent the unit from being damaged due to excessive pressure ratio.

[0072] Based on the judgment result of step S106, if the system pressure ratio corresponding to the centrifugal compressor detected again is less than or equal to the preset start-up pressure ratio, then step S110 is executed, that is, the first centrifugal compressor to be started is started. It is understood that each compressor cannot directly reach a stable operating stage after being started; it usually needs to go through a start-up stage before it can start normal operation. During the start-up stage, step S111 is executed, that is, the current speed of the centrifugal compressor is obtained. Next, in step S112, it is determined whether the current speed of the centrifugal compressor is greater than the preset speed, in order to further determine the surge risk of the centrifugal compressor. It should be noted that the present invention does not impose any restrictions on the specific value of the preset speed; those skilled in the art can set it according to actual usage requirements. As a preferred value, the preset speed is equal to the surge speed multiplied by a correction coefficient; wherein, the surge speed is measured experimentally, and the correction coefficient is greater than 1 and less than 2.

[0073] Based on the judgment result of step S112, if the current speed of the centrifugal compressor is greater than the preset speed, then step S115 is executed; if the current speed of the centrifugal compressor is less than or equal to the preset speed, then step S113 is executed. Specifically, in step S113, it is first determined whether the opening degree of the electronic expansion valve is already at its maximum opening degree; if the current opening degree of the electronic expansion valve is not yet at its maximum opening degree, then step S114 is executed, that is, the opening degree of the electronic expansion valve corresponding to the first centrifugal compressor to be turned on is increased to its maximum opening degree, and then step S115 is executed.

[0074] Specifically, in step S115, the controller determines whether the first centrifugal compressor to be started has been started, that is, whether it has entered a stable operation stage. Of course, the present invention does not impose any restrictions on its specific judgment criteria. It can be judged by its rotational speed or by its power change.

[0075] Based on the judgment result of step S115, if the first centrifugal compressor to be started has not yet completed startup, step S111 is executed again after the preset waiting time to effectively determine the opening and closing timing of the electronic expansion valve. It should be noted that this invention does not impose any restrictions on the specific value of the preset waiting time; those skilled in the art can set it according to actual usage requirements. Preferably, the preset waiting time is set to 15 seconds to effectively ensure its judgment efficiency. If the first centrifugal compressor to be started has already started, step S116 is executed directly, that is, the electronic expansion valve corresponding to the first centrifugal compressor to be started is directly closed to effectively ensure the normal heat exchange of the unit.

[0076] See next Figure 3 This figure is a flowchart illustrating the specific steps of the second preferred embodiment of the present invention. Figure 3 As shown, based on the centrifugal chiller unit described in the above preferred embodiment, the second preferred embodiment of the control method of the present invention specifically includes the following steps:

[0077] S201: If at least one centrifugal compressor is already in operation, obtain the start-up requirements of the remaining centrifugal compressors that are in a stopped state;

[0078] S202: If a centrifugal compressor that is in a stopped state has a start-up requirement, reduce the load of the centrifugal compressor that is in operation to a preset load.

[0079] S203: After the centrifugal compressor in operation has completed unloading, obtain the system pressure ratio corresponding to the centrifugal compressor that needs to start.

[0080] S204: Determine whether the system voltage ratio is greater than the preset startup voltage ratio; if yes, proceed to step S205; if no, proceed to step S206.

[0081] S205: Opens the electronic expansion valve corresponding to the centrifugal compressor to the preset opening degree;

[0082] S206: Normal start-up of centrifugal compressor;

[0083] S207: After a preset time, the system pressure ratio corresponding to the centrifugal compressor is checked again;

[0084] S208: Determine whether the system voltage ratio obtained again is still greater than the preset startup voltage ratio; if yes, proceed to step S209; if no, proceed to step S212.

[0085] S209: Determine whether the opening degree of the electronic expansion valve is the maximum opening degree; if yes, proceed to step S210; if no, proceed to step S211.

[0086] S210: Do not start the centrifugal compressor;

[0087] S211: Increase the opening degree of the electronic expansion valve corresponding to the centrifugal compressor;

[0088] S212: Start the centrifugal compressor;

[0089] S213: Obtain the current speed of the centrifugal compressor;

[0090] S214: Determine whether the current speed is greater than the preset speed; if yes, proceed to step S217; if no, proceed to step S215.

[0091] S215: Determine whether the opening degree of the electronic expansion valve is the maximum opening degree; if yes, proceed to step S217; if no, proceed to step S216.

[0092] S216: Increase the opening degree of the electronic expansion valve corresponding to the centrifugal compressor to the maximum opening degree;

[0093] S217: Determine whether the centrifugal compressor has finished starting; if yes, proceed to step S218; if no, proceed to step S213 again after a preset waiting time.

[0094] S218: Close the electronic expansion valve corresponding to the centrifugal compressor.

[0095] Further, in step S201, when at least one centrifugal compressor is already running (the specific number of running compressors is not limited), the starting requirements of the remaining centrifugal compressors that are in a stopped state (hereinafter referred to as delayed centrifugal compressors) are obtained. It should be noted that this invention does not impose any restrictions on the starting conditions of the remaining delayed centrifugal compressors; those skilled in the art can set them according to actual usage requirements. Next, in step S202, if there is a starting requirement for a stopped centrifugal compressor, the running centrifugal compressors are unloaded; of course, the specific amount and method of unloading are not limiting. It is understood that since some compressors in the unit are already running, the pressure ratio in the unit is certainly high. Therefore, controlling the running centrifugal compressors to unload before the delayed centrifugal compressors start effectively reduces the pressure ratio in the unit and can effectively avoid the risk of surge.

[0096] Further, in step S203, after the centrifugal compressor in operation has finished unloading, the system pressure ratio corresponding to the centrifugal compressor with startup requirements is obtained, that is, the system pressure ratio corresponding to the lagging centrifugal compressor, specifically the ratio of the absolute pressure of the condenser and evaporator corresponding to the lagging centrifugal compressor. It should be noted that this invention does not impose any restrictions on the specific starting conditions and sequence of each centrifugal compressor; those skilled in the art can set these according to actual usage requirements. Next, based on the data obtained in step S203, the controller can selectively start the centrifugal compressor after opening the electronic expansion valve corresponding to the centrifugal compressor with startup requirements, that is, selectively connect the bypass branch corresponding to the lagging centrifugal compressor according to requirements, and then control the centrifugal compressor to start, so as to effectively avoid large pressure ratio fluctuations and ensure the stability of unit operation. It should be noted that this invention does not impose any restrictions on its specific control method. As long as the centrifugal compressor is started selectively by opening the electronic expansion valve set on the bypass branch corresponding to the centrifugal compressor according to the system pressure ratio corresponding to the lagging centrifugal compressor, it falls within the protection scope of this invention.

[0097] Specifically, in step S204, it is determined whether the system pressure ratio corresponding to the lagging centrifugal compressor is greater than the preset starting pressure ratio, so that the centrifugal compressor can be selectively started after the electronic expansion valve corresponding to the centrifugal compressor is opened. That is, the bypass branch corresponding to the lagging centrifugal compressor is selectively connected according to the needs, and then the lagging centrifugal compressor is controlled to start, so as to effectively avoid large pressure ratio fluctuations and ensure the stability of unit operation.

[0098] Based on the judgment result of step S204, if the system pressure ratio corresponding to the centrifugal compressor is greater than the preset starting pressure ratio, it indicates that the unit has a surge risk. In this case, step S205 is executed, that is, the controller controls the electronic expansion valve corresponding to the lagging centrifugal compressor to open to a preset opening degree, so as to effectively reduce the system pressure drop and thus reduce the surge risk. It should be noted that the present invention does not impose any restrictions on the specific value of the preset opening degree. Those skilled in the art can set it according to actual usage needs, as long as it can reduce the system pressure ratio corresponding to the centrifugal compressor. If the system pressure ratio corresponding to the centrifugal compressor is less than or equal to the preset starting pressure ratio, it indicates that the unit does not have a surge risk. In this case, step S206 is executed, that is, the lagging centrifugal compressor that needs to be started can be started normally. In other words, it is not necessary to control the opening of the electronic expansion valve corresponding to the centrifugal compressor that needs to be started to directly control the centrifugal compressor to start, so as to effectively ensure the heat exchange rate.

[0099] Next, in step S207, after a preset time, the system pressure ratio corresponding to the centrifugal compressor is detected again in order to determine the start-up timing of the lagging centrifugal compressor again. It should be noted that those skilled in the art need to set the specific value of the preset time according to actual usage requirements. The specific value can be determined according to the opening speed of the electronic expansion valve, preferably set to less than 3 minutes.

[0100] Based on the results obtained in step S207, the controller can selectively restart the centrifugal compressor after adjusting the opening of the electronic expansion valve corresponding to the centrifugal compressor, according to the system pressure ratio corresponding to the centrifugal compressor detected again. Specifically, in step S208, it is determined whether the system pressure ratio corresponding to the centrifugal compressor obtained again is still greater than the preset starting pressure ratio, so as to selectively restart the centrifugal compressor after increasing the opening of the electronic expansion valve corresponding to the centrifugal compressor.

[0101] Based on the judgment result of step S208, if the system pressure ratio corresponding to the centrifugal compressor is still greater than the preset starting pressure ratio, the centrifugal compressor is started again after increasing the opening of the electronic expansion valve corresponding to the centrifugal compressor. Specifically, step S209 is executed first, that is, it is determined whether the opening of the electronic expansion valve is already at its maximum. If the current opening of the electronic expansion valve is not yet at its maximum, step S211 is executed again, that is, the opening of the electronic expansion valve is increased, and then step S207 is executed again. It should be noted that the present invention does not impose any limit on the increase value of the opening of the electronic expansion valve. Those skilled in the art can set it according to actual usage requirements, preferably set to 5% of the maximum opening of the electronic expansion valve. At the same time, if the current opening of the electronic expansion valve is already at its maximum, step S210 is executed, that is, the centrifugal compressor is not started, that is, the system corresponding to the lagging centrifugal compressor is not started, so as to prevent the system from being damaged due to excessive pressure ratio.

[0102] Based on the judgment result of step S208, if the system pressure ratio corresponding to the centrifugal compressor detected again is less than or equal to the preset start-up pressure ratio, then step S212 is executed, that is, the delayed centrifugal compressor that needs to be started is started. It is understood that each compressor cannot directly reach a stable operating stage after starting; it usually needs to go through a start-up stage before it can start normal operation. During the start-up stage, step S213 is executed, that is, the current speed of the centrifugal compressor is obtained. Next, in step S214, it is determined whether the current speed of the centrifugal compressor is greater than the preset speed, in order to further determine the surge risk of the centrifugal compressor. It should be noted that the present invention does not impose any restrictions on the specific value of the preset speed; those skilled in the art can set it according to actual usage requirements. As a preferred value, the preset speed is equal to the surge speed multiplied by a correction coefficient; wherein, the surge speed is measured experimentally, and the correction coefficient is greater than 1 and less than 2.

[0103] Based on the judgment result of step S214, if the current speed of the centrifugal compressor is greater than the preset speed, then step S217 is executed; if the current speed of the centrifugal compressor is less than or equal to the preset speed, then step S215 is executed. Specifically, in step S215, it is first determined whether the opening degree of the electronic expansion valve is already at its maximum opening degree; if the current opening degree of the electronic expansion valve is not yet at its maximum opening degree, then step S216 is executed, that is, the opening degree of the electronic expansion valve corresponding to the delayed centrifugal compressor that needs to be opened is increased to its maximum opening degree, and then step S217 is executed.

[0104] Specifically, in step S217, the controller determines whether the delayed centrifugal compressor that needs to be started has been started, that is, whether it has entered the stable operation stage. Of course, the present invention does not impose any restrictions on its specific judgment criteria. It can be judged by its rotational speed or by its power change.

[0105] Based on the judgment result of step S217, if the delayed centrifugal compressor to be started has not yet completed its startup, then after the preset waiting time, step S213 is executed again to effectively determine the opening and closing timing of the electronic expansion valve. It should be noted that this invention does not impose any restrictions on the specific value of the preset waiting time; those skilled in the art can set it according to actual usage requirements. Preferably, the preset waiting time is set to 15 seconds to effectively ensure its judgment efficiency. If the delayed centrifugal compressor to be started has already completed its startup, then step S218 is executed directly, that is, the electronic expansion valve corresponding to the delayed centrifugal compressor to be started is directly closed to effectively ensure the normal heat exchange of the unit.

[0106] See next Figure 4 This figure is a flowchart illustrating the specific steps of the third preferred embodiment of the present invention. Figure 4 As shown, based on the centrifugal chiller unit described in the above preferred embodiments, the third preferred embodiment of the control method of the present invention specifically includes the following steps:

[0107] S301: During the operation of the centrifugal compressor, obtain the current speed of the centrifugal compressor;

[0108] S302: If the current speed of the centrifugal compressor is less than or equal to the preset speed, the electronic expansion valve will open to the preset opening degree.

[0109] S303: When the electronic expansion valve maintains its opening at the preset opening for a preset duration, the current speed of the centrifugal compressor is obtained again.

[0110] S304: Determine whether the current rotational speed obtained again is still less than or equal to the preset rotational speed; if yes, proceed to step S306; if no, proceed to step S305.

[0111] S305: Close the electronic expansion valve;

[0112] S306: Determine whether the opening degree of the electronic expansion valve is the maximum opening degree; if yes, execute step S303 again after the first preset waiting time; if no, execute step S307.

[0113] S307: Increase the opening of the electronic expansion valve by a preset amount, and execute step S303 again after a second preset waiting time.

[0114] Furthermore, in step S301, during the operation of the centrifugal compressor, the current speed of the centrifugal compressor is obtained; it can be understood that the centrifugal compressor here can be either the first centrifugal compressor to start in the unit or a centrifugal compressor that starts later in the unit. This is not restrictive, as long as it is a centrifugal compressor in a stable operating state.

[0115] Next, based on the data obtained in step S301, the controller selectively opens the electronic expansion valve according to the current speed of the centrifugal compressor. It should be understood that the electronic expansion valve mentioned here is the electronic expansion valve on the bypass branch corresponding to the centrifugal compressor. Of course, it should also be noted that this invention does not impose any restrictions on its specific control method; as long as the electronic expansion valve is selectively opened according to the current speed of the centrifugal compressor, it should fall within the protection scope of this invention.

[0116] Specifically, the controller can compare the current speed of the centrifugal compressor with the preset speed to effectively determine the risk of surge in the centrifugal compressor based on the comparison result, and then selectively open the electronic expansion valve corresponding to the centrifugal compressor according to the risk level. It should be noted that the present invention does not impose any restrictions on the specific value of the preset speed, and those skilled in the art can set it according to actual usage requirements. As a preferred value, the preset speed is equal to the surge speed multiplied by a correction coefficient. The surge speed is measured based on a surge test, and the correction coefficient is greater than 1 and less than 2.

[0117] Specifically, in step S302, if the current speed of the centrifugal compressor is less than or equal to the preset speed, the electronic expansion valve is opened to the preset opening degree to effectively connect the bypass branch corresponding to the centrifugal compressor, thereby effectively balancing the pressure between the corresponding evaporator and condenser, reducing the pressure ratio, so that the actual speed line of the centrifugal compressor can always be far away from the surge speed line, thereby minimizing the occurrence of surge.

[0118] It should be noted that the present invention does not impose any restrictions on the specific value of the preset opening degree. Those skilled in the art can set it according to actual usage requirements, as long as it can reduce the pressure ratio of the system corresponding to the centrifugal compressor.

[0119] Next, in step S303, when the opening of the electronic expansion valve is maintained at the preset opening for a preset duration, the current speed of the centrifugal compressor is obtained again. It should be noted that those skilled in the art need to set the specific value of the preset duration according to actual usage requirements, preferably less than 3 minutes.

[0120] Based on the result obtained in step S303, the controller can selectively adjust the opening of the electronic expansion valve corresponding to the centrifugal compressor and then close the electronic expansion valve according to the current speed of the centrifugal compressor obtained again. Specifically, in step S304, it is determined whether the current speed of the centrifugal compressor obtained again is still less than or equal to the preset speed, so as to selectively increase the opening of the electronic expansion valve corresponding to the centrifugal compressor and then close the electronic expansion valve.

[0121] Based on the judgment result of step S304, if the current speed of the centrifugal compressor detected again is still less than or equal to the preset speed, the timing for closing the electronic expansion valve is determined after increasing the opening degree of the electronic expansion valve corresponding to the centrifugal compressor. Specifically, step S306 is executed first, that is, whether the opening degree of the electronic expansion valve is already at its maximum. If the current opening degree of the electronic expansion valve is already at its maximum, then after the first preset waiting time, step S303 is executed again, that is, the current speed of the centrifugal compressor is obtained again, so as to make the next judgment in a timely manner, and thus restore the normal operation of the unit in a timely manner after the surge risk is eliminated. It should be noted that the present invention does not impose any restrictions on the specific value of the first preset waiting time. Preferably, the first preset waiting time is set to 30 seconds, so as to fully ensure the elimination effect of the surge risk. If the current opening of the electronic expansion valve is not yet at its maximum, step S307 is executed, that is, the opening of the electronic expansion valve is increased by a preset amount. It should be noted that the present invention does not impose any restrictions on the specific value of the preset amount; those skilled in the art can set it according to actual usage requirements. Preferably, the preset amount is set to 5% of the maximum opening of the electronic expansion valve. After executing step S307, step S105 is executed again. After the second preset waiting time, step S303 is executed again, that is, the current speed of the centrifugal compressor is obtained again for timely judgment. It should be noted that the present invention does not impose any restrictions on the specific value of the second preset waiting time. Preferably, the second preset waiting time is set to 15 seconds to ensure timely restoration of normal unit operation.

[0122] Furthermore, based on the judgment result of step S304, if the current speed of the centrifugal compressor is detected again to be greater than the preset speed, then step S305 is executed, that is, the electronic expansion valve is directly closed, and the unit continues to operate according to the normal operating logic.

[0123] Finally, it should be noted that the preset values ​​involved in the above three preferred embodiments are not related, that is, the preset values ​​in each embodiment need to be set individually by those skilled in the art according to actual usage needs.

[0124] Based on the control methods described in the three preferred embodiments above, the present invention can effectively avoid surge in the three main stages of surge: low load operation stage, high pressure ratio start-up stage, and high pressure ratio operation stage, thereby maximizing the stability of the centrifugal chiller unit.

[0125] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A method for preventing surge control in a centrifugal chiller unit, characterized in that, The centrifugal chiller unit includes a bypass branch, a refrigerant circulation loop, and a centrifugal compressor, condenser, throttling device, and evaporator installed on the refrigerant circulation loop. The bypass branch is configured to introduce refrigerant from the condenser into the evaporator, and an electronic expansion valve is installed on the bypass branch to control its on / off state. The number of centrifugal compressors is multiple. The anti-surge control method includes: When the first centrifugal compressor is about to start, obtain the system pressure ratio corresponding to the centrifugal compressor; Determine whether the system pressure ratio is greater than the preset starting pressure ratio, and adjust the opening of the electronic expansion valve according to the comparison result between the system pressure ratio and the preset starting pressure ratio; The first centrifugal compressor is started only when the system pressure ratio is less than or equal to the preset starting pressure ratio. During the operation of the centrifugal compressor, the current rotational speed of the centrifugal compressor is obtained; The electronic expansion valve is selectively opened based on the current speed of the centrifugal compressor.

2. The anti-surge control method according to claim 1, characterized in that, The step of "selectively opening the electronic expansion valve according to the current speed of the centrifugal compressor" specifically includes: The current speed of the centrifugal compressor is compared with the preset speed; If the current speed of the centrifugal compressor is less than or equal to the preset speed, the electronic expansion valve is opened.

3. The anti-surge control method according to claim 2, characterized in that, The steps of "opening the electronic expansion valve" specifically include: The electronic expansion valve is opened to a preset opening degree.

4. The anti-surge control method according to claim 3, characterized in that, When the opening of the electronic expansion valve is maintained at the preset opening for a preset duration, the anti-surge control method further includes: Obtain the current speed of the centrifugal compressor again; Based on the current rotational speed of the centrifugal compressor obtained again, the opening of the electronic expansion valve is selectively increased.

5. The anti-surge control method according to claim 4, characterized in that, The step of "selectively increasing the opening of the electronic expansion valve based on the current rotational speed of the centrifugal compressor obtained again" specifically includes: If the current speed of the centrifugal compressor is still less than or equal to the preset speed, the opening of the electronic expansion valve is increased.

6. The anti-surge control method according to claim 5, characterized in that, The specific steps of "increasing the opening of the electronic expansion valve" include: Increase the opening degree of the electronic expansion valve by a preset amount.

7. The anti-surge control method according to claim 6, characterized in that, When the opening of the electronic expansion valve has increased to its maximum opening, the anti-surge control method further includes: The current rotational speed of the centrifugal compressor is obtained again; If the current speed of the centrifugal compressor is once again greater than the preset speed, the electronic expansion valve is closed.

8. The anti-surge control method according to claim 6, characterized in that, The preset amplitude is 5%.

9. The anti-surge control method according to claim 4, characterized in that, The anti-surge control method further includes: If the current speed of the centrifugal compressor is obtained again and is greater than the preset speed, the electronic expansion valve is closed.

10. The surge control method according to any one of claims 2 to 9, characterized in that, The preset rotational speed is equal to the surge rotational speed multiplied by the correction factor; The correction coefficient is greater than 1 and less than 2.

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