CN117490295A - Starting control method for head compressor of centrifugal water chilling unit - Google Patents

Abstract

The invention belongs to the technical field of heat exchange, and particularly provides a starting control method of a first compressor of a centrifugal water chilling unit. The problem that the first compressor of the existing centrifugal water chilling unit is easy to generate surge phenomenon in the starting stage is solved. For this purpose, the centrifugal chiller of the present invention includes a plurality of bypass branches, a refrigerant circulation circuit, and a plurality of centrifugal compressors, condensers, throttle members and evaporators disposed on the refrigerant circulation circuit, the bypass branches are disposed so as to be capable of introducing refrigerant in the condensers into the evaporators, and electronic expansion valves are disposed on the bypass branches to control on-off states of the bypass branches, and the control method of the present invention includes: under the condition that the first centrifugal compressor is ready to be started, acquiring a system pressure ratio corresponding to the centrifugal compressor; and selectively starting the centrifugal compressor after opening the electronic expansion valve corresponding to the centrifugal compressor according to the system pressure ratio corresponding to the centrifugal compressor, so that the running stability of the unit is effectively ensured.

Description

Starting control method for head compressor of centrifugal water chilling unit

Technical Field

The invention belongs to the technical field of heat exchange, and particularly provides a starting control method of a first compressor of a centrifugal water chilling unit.

Background

With the continuous development of heat exchange technology, the types of water chilling units are more and more; among them, centrifugal chiller units are attracting attention because of their small vibration and high reliability. The basic working principle of the magnetic suspension centrifugal compressor serving as a core element of the centrifugal water chilling unit is that an impeller rotating at a high speed is utilized to do work on gas, and mechanical energy is added to the gas to raise the pressure and increase the speed of the gas, so that the gas obtains pressure energy and speed energy. However, since surge is an inherent characteristic of a speed type centrifugal compressor, a water chiller employing the centrifugal compressor inevitably tends to generate a surge phenomenon, which tends to deteriorate system stability, increase operation noise, and even damage a compressor impeller. Based on this, how to avoid the surge phenomenon generated by the centrifugal compressor while taking advantage of the centrifugal chiller becomes a problem to be solved in the art.

Specifically, the mechanism of formation of the surge phenomenon is divided into the following two cases: in the low-load operation of the compressor, when the flow rate of the refrigerant is smaller than a certain value, the refrigerant flow in a flow channel of the compressor is easy to deteriorate, at the moment, the impeller cannot effectively improve the pressure of the gas, so that the outlet pressure of the compressor is reduced, but the pressure of a pipe network of the whole system is not correspondingly reduced instantaneously, mainly because the pressure of a condenser cannot be correspondingly reduced instantaneously, the air flow is reversed from the condenser to the compressor, the refrigerant is stopped until the condensing pressure is lower than the outlet pressure of the compressor, and then the discharge capacity of the compressor is increased, and the compressor is restored to normal operation; in practice, the total load of the compressor under such conditions is very small, which limits the displacement of the compressor, the displacement of the compressor is slowly reduced, the gas is reversely flowed, and thus, the periodic airflow oscillation phenomenon is generated in the system, and the surge phenomenon is further caused. And in the high-load operation of the compressor, when the condensing pressure is higher and the lift of the compressor is smaller than the pressure difference between the condenser and the evaporator, the gas in the condenser flows back, so that the surge phenomenon is generated. For a water chilling unit adopting a magnetic suspension variable frequency centrifugal compressor, the generation time of the surge phenomenon is mainly concentrated in a low-load operation stage, a high-pressure ratio starting stage and a high-pressure ratio operation stage. For the generation of the surge phenomenon, many existing water chilling units are also configured with corresponding structures or control methods to avoid the surge phenomenon.

Further, the anti-surge measures of the existing centrifugal water chilling unit are mainly divided into the following two types: one of the problems is solved from the compressor side, which is mainly achieved by adjusting the rotation speed or the opening degree of the inlet guide vanes, so that the operation curve of the compressor is far away from the surge line and operates in a stable area. Although the compressor has an anti-surge design, in the actual operation process, the severe working condition outside the stable operation area of the compressor is always met, and under the working condition, the surge phenomenon still occurs. In addition, design optimization from the compressor side is not possible for non-compressor manufacturers, so an anti-surge design must still be added from the system side. The other is from the system side, which is mainly to increase the hot gas bypass between the evaporator and the condenser, and then to make the high pressure gas or liquid in the condenser enter the evaporator through the bypass valve, so as to reduce the pressure of the condenser, simultaneously to increase the pressure of the evaporator, and to reduce the pressure head of the compressor, simultaneously to increase the flow rate of the compressor, so as to improve the working condition to prevent surge. Because the hot gas bypass pipeline is not kept in a normally open state, but is opened only when a surge phenomenon occurs, a valve is needed to be used for switching control, in the prior art, an electromagnetic valve is used as a control valve of the hot gas bypass pipeline to control the on-off state of the pipeline, the switching action time of the electromagnetic valve is short, the pressure between the evaporator and the condenser is relatively large, the electromagnetic valve easily generates a water hammer effect in the switching process, and the electromagnetic valve and the pipeline are impacted, so that the vibration phenomenon is generated, and the service life of the electromagnetic valve is further reduced. In addition, in the continuous surge phase, the frequent switching of the electromagnetic valve can cause the pressure ratio between the evaporator and the condenser to fluctuate greatly, thereby seriously affecting the stability of the system operation. In particular, in a large centrifugal chiller in which a plurality of centrifugal compressors are arranged, when the first centrifugal compressor of the chiller starts, a surge phenomenon is also a very likely occurrence timing.

Accordingly, there is a need in the art for a new method of starting control of the initial compressor of a centrifugal chiller to address the above-mentioned problems.

Disclosure of Invention

The invention aims to solve the technical problem that the first compressor of the existing centrifugal water chilling unit is easy to generate surge phenomenon in the starting stage.

The invention provides a starting control method of a first compressor of a centrifugal water chilling unit, the centrifugal water chilling unit comprises a plurality of bypass branches, a refrigerant circulation loop, a plurality of centrifugal compressors, a condenser, a throttling component and an evaporator, wherein the plurality of centrifugal compressors, the condenser, the throttling component and the evaporator are arranged on the refrigerant circulation loop, the bypass branches and the centrifugal compressors are correspondingly arranged, the bypass branches are arranged to be capable of introducing refrigerant in the condenser into the evaporator, and an electronic expansion valve is arranged on the bypass branches to control the on-off state of the bypass branches, and the starting control method of the first compressor comprises the following steps:

under the condition that the first centrifugal compressor is ready to be started, acquiring a system pressure ratio corresponding to the centrifugal compressor;

and selectively starting the centrifugal compressor after opening the electronic expansion valve corresponding to the centrifugal compressor according to the system pressure ratio corresponding to the centrifugal compressor.

In the above preferred technical solution of the starting control method of the first compressor, the step of selectively restarting the centrifugal compressor after opening the electronic expansion valve corresponding to the centrifugal compressor according to the system pressure ratio corresponding to the centrifugal compressor specifically includes:

comparing the system pressure ratio corresponding to the centrifugal compressor with a preset starting pressure ratio;

and selectively starting the centrifugal compressor after starting the electronic expansion valve corresponding to the centrifugal compressor according to the comparison result of the system pressure ratio corresponding to the centrifugal compressor and the preset starting pressure ratio.

In the above preferred technical solution of the first compressor start control method, the step of selectively restarting the centrifugal compressor after starting the electronic expansion valve according to a comparison result of the system pressure ratio corresponding to the centrifugal compressor and the preset start pressure ratio includes:

and if the system pressure ratio corresponding to the centrifugal compressor is larger than the preset starting pressure ratio, starting the centrifugal compressor after starting the electronic expansion valve corresponding to the centrifugal compressor.

In the above preferred technical solution of the starting control method of the first compressor, the step of restarting the centrifugal compressor after opening the electronic expansion valve corresponding to the centrifugal compressor specifically includes:

Opening an electronic expansion valve corresponding to the centrifugal compressor to a preset opening degree;

detecting the corresponding system pressure ratio of the centrifugal compressor again after the preset time length;

and selectively restarting the centrifugal compressor after adjusting the opening degree of the electronic expansion valve corresponding to the centrifugal compressor according to the re-detected system pressure ratio corresponding to the centrifugal compressor.

In the above preferred technical solution of the first compressor start control method, the step of "selectively restarting the centrifugal compressor after adjusting the opening of the electronic expansion valve corresponding to the centrifugal compressor according to the redetected system pressure ratio corresponding to the centrifugal compressor" specifically includes:

and if the detected system pressure ratio corresponding to the centrifugal compressor is still larger than the preset starting pressure ratio, starting the centrifugal compressor after increasing the opening of the electronic expansion valve corresponding to the centrifugal compressor.

In a preferred technical solution of the above-mentioned initial stage compressor start-up control method, the step of restarting the centrifugal compressor after increasing the opening of the electronic expansion valve corresponding to the centrifugal compressor specifically includes:

Intermittently increasing the opening degree of the electronic expansion valve corresponding to the centrifugal compressor until the system pressure ratio corresponding to the centrifugal compressor is smaller than or equal to the preset starting pressure ratio, and restarting the centrifugal compressor.

In the above preferred technical solution of the first compressor start control method, after the centrifugal compressor starts to start, the first compressor start control method further includes:

acquiring the current rotating speed of the centrifugal compressor;

comparing the current rotation speed of the centrifugal compressor with a preset rotation speed;

and selectively increasing the opening of the electronic expansion valve corresponding to the centrifugal compressor to the maximum opening according to the comparison result of the current rotating speed of the centrifugal compressor and the preset rotating speed.

In the above preferred technical solution of the first compressor start control method, the step of selectively increasing the opening of the electronic expansion valve corresponding to the centrifugal compressor to the maximum opening according to the comparison result of the current rotation speed of the centrifugal compressor and the preset rotation speed specifically includes:

and if the current rotating speed of the centrifugal compressor is smaller than or equal to the preset rotating speed, increasing the opening of the electronic expansion valve corresponding to the centrifugal compressor to the maximum opening.

In the preferred technical scheme of the above initial stage compressor start control method, the initial stage compressor start control method further includes:

and if the current rotating speed of the centrifugal compressor is larger than the preset rotating speed, closing the electronic expansion valve corresponding to the centrifugal compressor after the centrifugal compressor is started.

In the above preferred technical solution of the first compressor start control method, the step of selectively restarting the centrifugal compressor after starting the electronic expansion valve corresponding to the centrifugal compressor according to the comparison result of the system pressure ratio corresponding to the centrifugal compressor and the preset start pressure ratio further includes:

and if the system pressure ratio corresponding to the centrifugal compressor is smaller than or equal to the preset starting pressure ratio, the electronic expansion valve corresponding to the centrifugal compressor is not started and the centrifugal compressor is directly started.

Under the condition that the technical scheme is adopted, the centrifugal water chilling unit comprises a plurality of bypass branches, a refrigerant circulation loop, a plurality of centrifugal compressors, a condenser, a throttling component and an evaporator, wherein the centrifugal compressors, the condenser, the throttling component and the evaporator are arranged on the refrigerant circulation loop, the bypass branches and the centrifugal compressors are correspondingly arranged, the bypass branches are arranged to be capable of introducing refrigerant in the condenser into the evaporator, and an electronic expansion valve is arranged on the bypass branches to control the on-off state of the bypass branches, and the starting control method of the first compressor comprises the following steps: under the condition that the first centrifugal compressor is ready to be started, acquiring a system pressure ratio corresponding to the centrifugal compressor; and selectively starting the centrifugal compressor after opening the electronic expansion valve corresponding to the centrifugal compressor according to the system pressure ratio corresponding to the centrifugal compressor. According to the invention, the electronic expansion valve is arranged on the bypass branch to correspondingly control the communication condition of the bypass branch according to different conditions of a starting stage, and the centrifugal compressor is selectively restarted after the electronic expansion valve corresponding to the centrifugal compressor is started according to the system pressure ratio corresponding to the centrifugal compressor started at the first stage, so that the generation of water hammer effect is effectively avoided, larger pressure fluctuation is effectively avoided, the running stability of the centrifugal water chilling unit is effectively ensured, the centrifugal compressor is protected from being damaged, the service life of the centrifugal compressor is effectively prolonged, and the reliability of the centrifugal compressor is ensured.

Drawings

Preferred embodiments of the present invention are described below with reference to the accompanying drawings, in which:

FIG. 1 is a flow chart of the main steps of the initial compressor start-up control method of the present invention;

FIG. 2 is a flowchart showing the specific steps of a first preferred embodiment of the present invention;

FIG. 3 is a flowchart of the specific steps of a second preferred embodiment of the present invention;

fig. 4 is a flowchart showing the specific steps of a third preferred embodiment of the present invention.

Detailed Description

Preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are merely for explaining the technical principles of the present invention, and are not intended to limit the scope of the present invention. Those skilled in the art can adapt it as desired to suit a particular application. For example, the present invention does not limit the specific type of the centrifugal chiller, as long as the centrifugal chiller is provided with a centrifugal compressor and a corresponding bypass branch. Changes in the specific structure may be made without departing from the basic principles of the invention and should be considered as falling within the scope of the invention.

It should be noted that, in the description of the preferred embodiment, terms such as "inner", "outer", and the like, refer to directions or positional relationships based on the directions or positional relationships shown in the drawings, which are merely for convenience of description, and do not indicate or imply that the apparatus or elements must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the invention.

In addition, it should be noted that, in the description of the present invention, unless explicitly stated and limited otherwise, the term "connected" should be interpreted broadly, for example, as being directly connected, indirectly connected through an intermediate medium, or communicating between two members. Also, the terms "first," "second," "third," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance. The specific meaning of the above terms in the present invention can be understood by those skilled in the art according to the specific circumstances. In addition, although the various steps of the control method of the present invention are described in a particular order in this application, these orders are not limiting and one skilled in the art may perform the steps in a different order without departing from the basic principles of the invention.

Specifically, in the invention, the centrifugal water chilling unit comprises a refrigerant circulation loop, a plurality of centrifugal compressors, a condenser, a throttling component and an evaporator, wherein the centrifugal compressors, the condenser, the throttling component and the evaporator are arranged on the refrigerant circulation loop, the refrigerant circulates through the refrigerant circulation loop, and when the unit operates, the refrigerant continuously exchanges heat between the evaporator and the condenser through the refrigerant circulation loop, so that the heat exchange effect is achieved. Of course, the invention does not limit the setting mode of the specific structure of the centrifugal water chilling unit, and the person skilled in the art can set the water chilling unit according to the actual use requirement; for example, a plurality of centrifugal compressors may be arranged in parallel, and the number of the condensers and the evaporators is one, that is, the plurality of centrifugal compressors share one set of condenser and evaporator; for another example, the number of the condensers and the evaporators may be plural, and the centrifugal compressors are the same as the centrifugal compressors, and the plural centrifugal compressors are connected to the respective condensers and evaporators, that is, each centrifugal compressor is correspondingly configured with a set of a condenser and an evaporator; for another example, the number of the condensers may be plural, the number of the condensers may be the same as the number of the centrifugal compressors, and the number of the evaporators may be one, that is, the plural centrifugal compressors and the plural condensers are arranged in one-to-one correspondence and share the same evaporator, which is not limitative, and the control method of the present invention may be used as long as the centrifugal chiller is provided with plural centrifugal compressors. Such changes as to the specific application object do not change the basic principle of the invention, and belong to the protection scope of the invention.

Further, the centrifugal chiller further comprises a plurality of bypass branches, the number of the bypass branches is the same as the number of the centrifugal compressors, and the specific number is not limited, so that the centrifugal chiller can be set by a person skilled in the art according to actual use requirements. The bypass branch is arranged to be capable of leading refrigerant in the condenser into the evaporator, namely one end of the bypass branch is communicated with the condenser, the other end of the bypass branch is communicated with the evaporator, and the bypass branch is not limited in specific connection position, can be directly connected with the body, can also be connected with an outlet of the condenser or an inlet of the evaporator, and is provided with an electronic expansion valve to control the on-off state of the bypass branch. It will be understood that the bypass branch corresponding to a certain centrifugal compressor is obviously used for communicating the condenser and the evaporator corresponding to the centrifugal compressor, of course, the corresponding condenser and evaporator can be dedicated to the centrifugal compressor or shared with other centrifugal compressors, as long as the bypass branch can realize corresponding communication, and based on the connection mode, each centrifugal compressor can form a system with the evaporator and the condenser corresponding to the centrifugal compressor, namely, the centrifugal chiller unit has several systems corresponding to several centrifugal compressors, and the system pressure ratio in the invention also refers to the pressure ratio of the system corresponding to a certain specific centrifugal compressor.

In addition, the centrifugal chiller further comprises a controller, wherein the controller can acquire the pressure ratio of each system of the centrifugal chiller, can acquire the rotating speed of the centrifugal compressor, and can control the running state of the centrifugal chiller, such as the opening and closing state and specific opening degree of the electronic expansion valve, the load shedding of the compressor and the like. It can be understood by those skilled in the art that the present invention does not limit the specific structure and model of the controller, and the controller may be an original controller of the centrifugal chiller, or may be a controller separately provided for executing the control method of the present invention, and those skilled in the art may set the structure and model of the controller according to actual use requirements.

Referring first to fig. 1, a flowchart of main steps of a start control method of a head compressor according to the present invention is shown. As shown in fig. 1, based on the centrifugal chiller set described in the above embodiment, the start control method of the head compressor of the present invention mainly includes the following steps:

s1: under the condition that the first centrifugal compressor is ready to be started, acquiring a system pressure ratio corresponding to the centrifugal compressor;

S2: and selectively starting the centrifugal compressor after opening the electronic expansion valve corresponding to the centrifugal compressor according to the system pressure ratio corresponding to the centrifugal compressor.

Further, in step S1, when the first centrifugal compressor in the centrifugal chiller is ready to be started, that is, when the centrifugal chiller is ready to be started, a system pressure ratio corresponding to the centrifugal compressor, that is, a pressure ratio of a system corresponding to the first started centrifugal compressor, specifically, a ratio of an absolute pressure of a condenser to an evaporator, which is set corresponding to the first started centrifugal compressor, is obtained. It can be understood that in the control method of the present invention, in the start-up stage of the centrifugal chiller, the controller controls one of the centrifugal compressors to start first, and then selectively controls the other centrifugal compressors to start.

Next, in step S2, the controller selectively restarts the centrifugal compressor after opening the electronic expansion valve corresponding to the centrifugal compressor according to the system pressure ratio corresponding to the centrifugal compressor. Specifically, based on the system pressure ratio corresponding to the centrifugal compressor to be started first obtained in the step S1, the centrifugal compressor is selectively started after the electronic expansion valve corresponding to the centrifugal compressor is started, namely, the bypass branch corresponding to the centrifugal compressor to be started first is selectively communicated according to the requirement, and then the centrifugal compressor is controlled to be started, so that larger pressure ratio fluctuation is effectively avoided, and the running stability of the unit is ensured. It should be noted that, the present invention does not limit the specific control manner, so long as the present invention is capable of starting the centrifugal compressor after selectively starting the electronic expansion valve provided on the bypass branch corresponding to the centrifugal compressor according to the system pressure ratio corresponding to the centrifugal compressor to be started at first.

Firstly, when a certain centrifugal compressor is controlled to be started, judging whether the centrifugal compressor is a compressor started at the head of a centrifugal water chilling unit or not, namely, before the centrifugal compressor is started, judging whether other centrifugal compressors exist in the unit or not; based on this judgment, if the centrifugal compressor is a compressor started by the head of the centrifugal chiller, the following control method in the first preferred embodiment is executed; and, if the centrifugal compressor is not the compressor of which the head of the centrifugal chiller is turned on, the following control method in the second preferred embodiment is performed. In addition, if a certain centrifugal compressor is already in a steady operation stage during its operation, the following control method in the third preferred embodiment is performed. Based on the control mode, the centrifugal water chilling unit can effectively avoid larger pressure ratio fluctuation no matter what operation stage the centrifugal water chilling unit is in, and further improves the operation stability of the unit to the greatest extent. It should be noted that, if a centrifugal chiller has only one centrifugal compressor, the control method in the first preferred embodiment of the present invention may be executed, that is, the control method in the first preferred embodiment may be executed directly when the centrifugal chiller is started; in addition, if a certain centrifugal chiller is started, a plurality of centrifugal compressors are all started at the same time, and the control method in the first preferred embodiment of the invention is also applicable; all such changes in the specific application form do not depart from the basic principles of the invention and are intended to be within the scope of the invention.

Reference is next made to fig. 2, which is a flowchart showing the specific steps of a first preferred embodiment of the present invention. As shown in fig. 2, based on the centrifugal chiller set described in the above preferred embodiment, the first preferred embodiment of the control method of the present invention specifically includes the following steps:

s101: under the condition that the first centrifugal compressor is ready to be started, acquiring a system pressure ratio corresponding to the centrifugal compressor;

s102: judging whether the system pressure ratio is larger than a preset starting pressure ratio or not; if yes, step S103 is performed; if not, executing step S104;

s103: opening an electronic expansion valve corresponding to the first centrifugal compressor to a preset opening degree;

s104: normally starting the first centrifugal compressor;

s105: detecting the corresponding system pressure ratio of the centrifugal compressor again after the preset time length;

s106: judging whether the re-acquired system pressure ratio is still larger than a preset starting pressure ratio or not; if yes, step S107 is performed; if not, executing step S110;

s107: judging whether the opening of the electronic expansion valve is the maximum opening; if yes, step S109 is executed; if not, executing step S108;

s108: increasing the opening of an electronic expansion valve corresponding to the centrifugal compressor;

S109: the first centrifugal compressor is not started;

s110: starting a first centrifugal compressor;

s111: acquiring the current rotating speed of the centrifugal compressor;

s112: judging whether the current rotating speed is larger than a preset rotating speed or not; if yes, step S115 is performed; if not, then step S113 is performed;

s113: judging whether the opening of the electronic expansion valve is the maximum opening; if yes, step S115 is performed; if not, then step S114 is performed;

s114: increasing the opening of the electronic expansion valve corresponding to the first centrifugal compressor to the maximum opening;

s115: judging whether the centrifugal compressor is started or not; if yes, go to step S116; if not, executing the step S111 again after the preset waiting time is passed;

s116: and closing the electronic expansion valve corresponding to the centrifugal compressor.

Further, in step S101, when the first centrifugal compressor in the centrifugal chiller is ready to be started, that is, when the centrifugal chiller is ready to be started, a system pressure ratio corresponding to the centrifugal compressor, that is, a pressure ratio of a system corresponding to the first started centrifugal compressor, specifically, a ratio of an absolute pressure of a condenser to an evaporator, which is set corresponding to the first started centrifugal compressor, is obtained. It will be appreciated that as a possible way, the absolute pressure may be obtained by summing the gauge pressure measured by a pressure sensor provided on the heat exchanger and a pressure correction value (preferably 103 kPa). In addition, it should be noted that the present invention does not limit which compressor the first centrifugal compressor is started for, and those skilled in the art can set the compressor according to the actual use requirement.

Then, based on the pressure ratio obtained in the step S101, the controller can compare the system pressure ratio corresponding to the centrifugal compressor to be started at the beginning with a preset starting pressure ratio; of course, the invention does not limit the specific value of the preset starting pressure ratio, and as long as the system pressure ratio is larger than the preset starting pressure ratio, the invention can indicate that the system pressure ratio is higher and the surge is easy to generate; and selectively starting the centrifugal compressor after starting the electronic expansion valve corresponding to the centrifugal compressor according to the comparison result of the system pressure ratio corresponding to the centrifugal compressor which needs to be started by the first stage and the preset starting pressure ratio. It should be noted that, the present invention does not limit the specific control manner, so long as the present invention is capable of selectively starting the centrifugal compressor after opening the electronic expansion valve disposed on the bypass branch corresponding to the centrifugal compressor according to the comparison result of the system pressure ratio corresponding to the centrifugal compressor to be started at the beginning and the preset starting pressure ratio.

Specifically, in step S102, it is determined whether the system pressure ratio corresponding to the centrifugal compressor is greater than the preset starting pressure ratio, so that the centrifugal compressor is selectively started after the electronic expansion valve corresponding to the centrifugal compressor is opened, that is, after the bypass branch corresponding to the centrifugal compressor to be started is selectively connected with the first stage according to the requirement, the centrifugal compressor is controlled to be started, so that larger pressure ratio fluctuation is effectively avoided, and stability of unit operation is ensured.

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 is indicated that the unit has a surge risk, and in this case, step S103 is executed, that is, the controller controls the electronic expansion valve corresponding to the centrifugal compressor that needs to be started to a preset opening degree, so as to effectively reduce the system pressure, and further reduce the surge risk. Of course, it should be further noted that the specific value of the preset opening is not limited in the present invention, and a person skilled in the art can set the preset opening according to the actual use requirement, so long as the pressure ratio of the system corresponding to the centrifugal compressor can be reduced. If the system pressure ratio corresponding to the centrifugal compressor is smaller than or equal to the preset starting pressure ratio, it is indicated that the unit has no surge risk, and step S104 is performed under the condition that the centrifugal compressor to be started at the head is started normally, in other words, the centrifugal compressor can be controlled to be started directly without controlling the electronic expansion valve corresponding to the centrifugal compressor to be started at the head to be started, so that the heat exchange speed is effectively ensured.

Next, in step S105, after a preset period of time, detecting the system pressure ratio corresponding to the centrifugal compressor again, so as to determine the start timing of the first compressor again; it should be noted that, a person skilled in the art needs to set the specific value of the preset duration according to the actual use requirement, where the specific value may be determined according to the opening speed of the electronic expansion valve, and is preferably set to be less than 3 minutes.

Based on the result of the step S105, the controller may selectively restart the centrifugal compressor after adjusting the opening degree 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 starting pressure ratio, so that the centrifugal compressor is selectively started after increasing the opening degree of the electronic expansion valve corresponding to the centrifugal compressor.

Based on the determination result in step S106, if the system pressure ratio corresponding to the centrifugal compressor detected again is still greater than the preset starting pressure ratio, starting the centrifugal compressor after increasing the opening of the electronic expansion valve corresponding to the centrifugal compressor. Specifically, step S107 is executed first, i.e. it is first determined whether the opening degree of the electronic expansion valve is already the maximum opening degree. If the current opening degree of the electronic expansion valve is not the maximum opening degree, the step S108 is continued, i.e. the opening degree of the electronic expansion valve is increased, after which the step S105 is executed again. It should be noted that, the present invention does not limit the increase value of the opening of the electronic expansion valve, and those skilled in the art can set the opening value of the electronic expansion valve according to the actual use requirement, preferably to 5% of the maximum opening of the electronic expansion valve. Meanwhile, if the current opening degree of the electronic expansion valve is already the maximum opening degree, step S109 is performed, i.e., the centrifugal compressor is not started, i.e., the centrifugal chiller is not started, so as to prevent damage of the chiller due to an excessive pressure ratio.

Based on the determination result of step S106, if the system pressure ratio corresponding to the centrifugal compressor detected again is smaller than or equal to the preset starting pressure ratio, step S110 is executed, that is, the centrifugal compressor that needs to be started by the head station is started. It will be appreciated that it is not possible for each compressor to reach a steady state operation immediately after start-up, and it is generally necessary to go through a start-up phase before normal operation can begin. In the start-up phase, step S111 is performed, i.e. the current rotational speed of the centrifugal compressor is obtained. Next, in step S112, it is determined whether the current rotational speed of the centrifugal compressor is greater than the preset rotational speed, so as to further determine the magnitude of the surge risk of the centrifugal compressor. It should be noted that the specific value of the preset rotating speed is not limited in the invention, and the preset rotating speed can be set by a person skilled in the art according to actual use requirements; as a preferred value mode, the preset rotation speed is equal to the surge rotation speed multiplied by the correction coefficient; wherein the surge rotational speed is measured according to a test, and the correction coefficient is greater than 1 and less than 2.

Based on the judgment result of step S112, if the current rotation speed of the centrifugal compressor is greater than the preset rotation speed, step S115 is executed; if the current rotational speed of the centrifugal compressor is less than or equal to the preset rotational speed, step S113 is performed. Specifically, in step S113, it is first determined whether the opening degree of the electronic expansion valve has been the maximum opening degree; if the current opening degree of the electronic expansion valve is not the maximum opening degree, step S114 is performed, that is, the opening degree of the electronic expansion valve corresponding to the centrifugal compressor that needs to be opened at the head is increased to the maximum opening degree, and then step S115 is performed.

Specifically, in step S115, the controller determines whether the first centrifugal compressor to be started has been started, i.e. has entered a stage of steady operation, and of course, the present invention does not limit its specific determination criteria, and may determine the rotational speed or the power change condition.

Based on the judgment result of the step S115, if the centrifugal compressor to be started at the head stage is not started yet, after the preset waiting time period elapses, the step S111 is executed again, so as to effectively judge the opening and closing time of the electronic expansion valve; it should be noted that, the present invention does not limit the specific value of the preset waiting time, and a person skilled in the art can set the value according to the actual use requirement; preferably, the preset waiting time period is set to 15S, so as to effectively ensure the judging efficiency thereof. If the centrifugal compressor to be started at the head stage is already started, step S116 is directly executed, namely, the electronic expansion valve corresponding to the centrifugal compressor to be started at the head stage is directly closed, so that the normal heat exchange of the unit is effectively ensured.

Referring next to fig. 3, a flowchart of the specific steps of a second preferred embodiment of the present invention is shown. As shown in fig. 3, based on the centrifugal chiller set described in the above preferred embodiment, the second preferred embodiment of the control method of the present invention specifically includes the following steps:

S201: acquiring the starting requirements of the rest centrifugal compressors in a stop state under the condition that at least one centrifugal compressor is already in an operating state;

s202: if the centrifugal compressor in the stop state has a starting requirement, the centrifugal compressor in the running state is unloaded to a preset load;

s203: after the load shedding of the centrifugal compressor in the running state is completed, acquiring a system pressure ratio corresponding to the centrifugal compressor with a starting requirement;

s204: judging whether the system pressure ratio is larger than a preset starting pressure ratio or not; if yes, step S205 is performed; if not, executing step S206;

s205: opening an electronic expansion valve corresponding to the centrifugal compressor to a preset opening degree;

s206: normally starting the centrifugal compressor;

s207: detecting the corresponding system pressure ratio of the centrifugal compressor again after the preset time length;

s208: judging whether the re-acquired system pressure ratio is still larger than a preset starting pressure ratio or not; if yes, go to step S209; if not, executing step S212;

s209: judging whether the opening of the electronic expansion valve is the maximum opening; if yes, go to step S210; if not, executing step S211;

S210: not starting the centrifugal compressor;

s211: increasing the opening of an electronic expansion valve corresponding to the centrifugal compressor;

s212: starting the centrifugal compressor;

s213: acquiring the current rotating speed of the centrifugal compressor;

s214: judging whether the current rotating speed is larger than a preset rotating speed or not; if yes, go to step S217; if not, then step S215 is performed;

s215: judging whether the opening of the electronic expansion valve is the maximum opening; if yes, go to step S217; if not, then step S216 is performed;

s216: increasing the opening of the electronic expansion valve corresponding to the centrifugal compressor to the maximum opening;

s217: judging whether the centrifugal compressor is started or not; if yes, go to step S218; if not, executing step S213 again after the preset waiting time;

s218: and closing the electronic expansion valve corresponding to the centrifugal compressor.

Further, in step S201, in the case where at least one centrifugal compressor is already in an operating state, of course, the number of specific compressors in the operating state is not limited, and the start-up requirements of the remaining centrifugal compressors in a stopped state (hereinafter, referred to as hysteresis centrifugal compressors) are obtained. It should be noted that the present invention does not limit the starting conditions of the rest of the lag centrifugal compressors, and those skilled in the art can set the starting conditions according to the actual use requirements. Next, in step S202, if there is a start-up demand for the centrifugal compressor in the stopped state, the centrifugal compressor in the running state is offloaded; of course, the particular amount and manner of load shedding is not limiting. It can be appreciated that since the compressor is already in the running state in the unit, the pressure ratio in the unit must be high, so that before the lagging centrifugal compressor is started, the centrifugal compressor in the running state is controlled in advance to carry out load shedding, so that the pressure ratio in the unit is effectively reduced, and the surge risk can be effectively avoided.

Further, in step S203, after the load shedding of the centrifugal compressor in the running state is completed, a system pressure ratio corresponding to the centrifugal compressor with a start requirement, that is, a pressure ratio of a system corresponding to the lagging centrifugal compressor, specifically, an absolute pressure ratio of a condenser to an evaporator corresponding to the lagging centrifugal compressor is obtained. It should be noted that the present invention does not limit the specific opening conditions and opening sequence of each centrifugal compressor, and those skilled in the art can set the conditions according to the actual use requirements. Then, based on the data obtained in step S203, the controller can selectively restart the centrifugal compressor after opening the electronic expansion valve corresponding to the centrifugal compressor according to the system pressure ratio corresponding to the centrifugal compressor with the start requirement, that is, selectively connect the bypass branch corresponding to the lagging centrifugal compressor according to the requirement, and then control the centrifugal compressor to be started, so as to effectively avoid larger pressure ratio fluctuation and ensure the stability of unit operation. It should be noted that the present invention does not limit the specific control manner, so long as the present invention is within the scope of protection of the present invention, if the electronic expansion valve provided on the bypass branch corresponding to the centrifugal compressor is selectively opened according to the system pressure ratio corresponding to the lagged centrifugal compressor, and then the centrifugal compressor is started.

Specifically, in step S204, it is determined whether the system pressure ratio corresponding to the lagged centrifugal compressor is greater than the preset starting pressure ratio, so that the centrifugal compressor is selectively started after the electronic expansion valve corresponding to the centrifugal compressor is opened, that is, the lagged centrifugal compressor is selectively connected with the bypass branch corresponding to the lagged centrifugal compressor according to the requirement, and then the lagged centrifugal compressor is controlled to be opened, so that larger pressure ratio fluctuation is effectively avoided, and the running stability of the unit is ensured.

Based on the determination result in step S204, if the system pressure ratio corresponding to the centrifugal compressor is greater than the preset starting pressure ratio, it is indicated that the unit has a surge risk, and in this case, step S205 is executed, that is, the controller controls the electronic expansion valve corresponding to the lagged centrifugal compressor to open to a preset opening degree, so as to effectively reduce the system pressure, and further reduce the surge risk. It should be noted that, the present invention does not limit the specific value of the preset opening, and a person skilled in the art can set the preset opening according to the actual use requirement, so long as the pressure ratio of the system corresponding to the centrifugal compressor can be reduced. If the system pressure ratio corresponding to the centrifugal compressor is smaller than or equal to the preset starting pressure ratio, it is indicated that the unit has no surge risk, in this case, step S206 is performed, that is, the delayed centrifugal compressor to be started is started normally, in other words, the centrifugal compressor can be controlled to be started directly without controlling the electronic expansion valve corresponding to the centrifugal compressor to be started, so as to effectively ensure the heat exchange speed.

Next, in step S207, after a preset period of time, detecting the system pressure ratio corresponding to the centrifugal compressor again, so as to determine the start timing of the lagging centrifugal compressor again; it should be noted that, a person skilled in the art needs to set the specific value of the preset duration according to the actual use requirement, where the specific value may be determined according to the opening speed of the electronic expansion valve, and is preferably set to be less than 3 minutes.

Based on the result of the step S207, the controller can selectively restart the centrifugal compressor after adjusting the opening degree 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 that the centrifugal compressor is selectively started after increasing the opening degree of the electronic expansion valve corresponding to the centrifugal compressor.

Based on the determination result in step S208, if the system pressure ratio corresponding to the centrifugal compressor detected again is still greater than the preset starting pressure ratio, the centrifugal compressor is started after increasing the opening of the electronic expansion valve corresponding to the centrifugal compressor. Specifically, step S209 is executed first, i.e. it is first determined whether the opening degree of the electronic expansion valve is already the maximum opening degree. If the current opening degree of the electronic expansion valve is not the maximum opening degree, the step S211 is continued, i.e. the opening degree of the electronic expansion valve is increased, after which the step S207 is executed again. It should be noted that, the present invention does not limit the increase value of the opening of the electronic expansion valve, and those skilled in the art can set the opening value of the electronic expansion valve according to the actual use requirement, preferably to 5% of the maximum opening of the electronic expansion valve. Meanwhile, if the current opening degree of the electronic expansion valve is already the maximum opening degree, step S210 is performed, i.e., the system corresponding to the centrifugal compressor is not started, i.e., the lagging centrifugal compressor is not started, so as to prevent the system from being damaged due to an excessive pressure ratio.

Based on the determination result in step S208, if the system pressure ratio corresponding to the centrifugal compressor detected again is less than or equal to the preset starting pressure ratio, step S212 is executed, that is, the delayed centrifugal compressor that needs to be started is started. It will be appreciated that it is not possible for each compressor to reach a steady state operation immediately after start-up, and it is generally necessary to go through a start-up phase before normal operation can begin. In the start-up phase, step S213 is performed, i.e. the current rotational speed of the centrifugal compressor is obtained. Next, in step S214, it is determined whether the current rotational speed of the centrifugal compressor is greater than the preset rotational speed, so as to further determine the magnitude of the surge risk of the centrifugal compressor. It should be noted that the specific value of the preset rotating speed is not limited in the invention, and the preset rotating speed can be set by a person skilled in the art according to actual use requirements; as a preferred value mode, the preset rotation speed is equal to the surge rotation speed multiplied by the correction coefficient; wherein the surge rotational speed is measured according to a test, and the correction coefficient is greater than 1 and less than 2.

Based on the result of the determination in step S214, if the current rotation speed of the centrifugal compressor is greater than the preset rotation speed, step S217 is performed; if the current rotational speed of the centrifugal compressor is less than or equal to the preset rotational speed, step S215 is performed. Specifically, in step S215, it is first determined whether the opening degree of the electronic expansion valve has been the maximum opening degree; if the current opening degree of the electronic expansion valve is not the maximum opening degree, step S216 is performed, that is, the opening degree of the electronic expansion valve corresponding to the delayed centrifugal compressor that needs to be opened is increased to the maximum opening degree, and then step S217 is performed.

Specifically, in step S217, the controller determines whether the delayed centrifugal compressor to be started has been started, i.e. has entered a stage of steady operation, and of course, the present invention does not limit its specific determination criteria, and may determine the rotational speed or the power change condition.

Based on the judgment result of the step S217, if the delayed centrifugal compressor to be started is not started, after the preset waiting time period elapses, the step S213 is executed again, so as to effectively judge the opening and closing time of the electronic expansion valve; it should be noted that, the present invention does not limit the specific value of the preset waiting time, and a person skilled in the art can set the value according to the actual use requirement; preferably, the preset waiting time period is set to 15S, so as to effectively ensure the judging efficiency thereof. If the delayed centrifugal compressor to be started is already started, step S218 is directly performed, i.e., the electronic expansion valve corresponding to the delayed centrifugal compressor to be started is directly closed, so as to effectively ensure the normal heat exchange of the unit.

Referring next to fig. 4, a flowchart of the specific steps of a third preferred embodiment of the present invention is shown. As shown in fig. 4, based on the centrifugal chiller set described in the above preferred embodiment, a third preferred embodiment of the control method of the present invention specifically includes the following steps:

S301: acquiring the current rotating speed of the centrifugal compressor in the running process of the centrifugal compressor;

s302: if the current rotating speed of the centrifugal compressor is smaller than or equal to the preset rotating speed, the electronic expansion valve is opened to a preset opening degree;

s303: when the time length of maintaining the opening of the electronic expansion valve at the preset opening reaches the preset time length, acquiring the current rotating speed of the centrifugal compressor again;

s304: judging whether the current rotation speed obtained again is still smaller than or equal to the preset rotation speed; if yes, go to step S306; if not, then step S305 is performed;

s305: closing the electronic expansion valve;

s306: judging whether the opening of the electronic expansion valve is the maximum opening; if yes, executing step S303 again after the first preset waiting time period; if not, then step S307 is performed;

s307: the opening degree of the electronic expansion valve is increased by a preset magnitude, and step S303 is performed again after the second preset waiting period elapses.

Further, in step S301, during operation of the centrifugal compressor, a current rotational speed of the centrifugal compressor is obtained; it is to be understood that the centrifugal compressor may be either a first-start centrifugal compressor in the unit or a later-start centrifugal compressor in the unit, and this is not limitative, as long as it is a centrifugal compressor in a steady operation state.

Next, based on the data acquired in step S301, the controller selectively opens the electronic expansion valve according to the current rotation speed of the centrifugal compressor, and it is understood that the electronic expansion valve herein is an electronic expansion valve on a bypass branch provided correspondingly to the centrifugal compressor. Of course, it should be noted that the present invention is not limited in any way to the specific control manner, and it is within the scope of the present invention to selectively open the electronic expansion valve according to the current rotation speed of the centrifugal compressor.

Specifically, the controller can compare the current rotation speed of the centrifugal compressor with the preset rotation speed so as to effectively judge the risk of the centrifugal compressor for generating a surge phenomenon according to a comparison result, and then selectively open an electronic expansion valve corresponding to the centrifugal compressor according to the risk; it should be noted that the specific value of the preset rotating speed is not limited in the invention, and the preset rotating speed can be set by a person skilled in the art according to actual use requirements; as a preferred value mode, the preset rotation speed is equal to the surge rotation speed multiplied by the correction coefficient; the surge rotating speed is measured according to a surge test, and the correction coefficient is larger than 1 and smaller than 2.

Specifically, in step S302, if the current rotation speed of the centrifugal compressor is less than or equal to the preset rotation speed, the electronic expansion valve is opened to the preset opening degree, so as to effectively communicate with a bypass branch correspondingly arranged in the centrifugal compressor, and further effectively balance the pressure between the evaporator and the condenser correspondingly arranged in the centrifugal compressor, so as to play a role in reducing the pressure ratio, so that the actual rotation speed line of the centrifugal compressor can be always far away from the surge rotation speed line, and the surge phenomenon is avoided to the greatest extent.

It should be noted that, the present invention does not limit the specific value of the preset opening, and a person skilled in the art can set the preset opening according to the actual use requirement, so long as the pressure ratio of the system corresponding to the centrifugal compressor can be reduced.

Next, in step S303, when the duration in which the opening degree of the electronic expansion valve is maintained at the preset opening degree reaches the preset duration, acquiring the current rotation speed of the centrifugal compressor again; it should be noted that, a person skilled in the art needs to set the specific value of the preset duration according to the actual use requirement, and preferably, the specific value is set to be less than 3 minutes.

Based on the result of the step S303, the controller may selectively close the electronic expansion valve after adjusting the opening of the electronic expansion valve corresponding to the centrifugal compressor according to the re-acquired current rotation speed of the centrifugal compressor. Specifically, in step S304, it is determined whether the current rotational speed of the centrifugal compressor obtained again is still less than or equal to the preset rotational speed, so that the electronic expansion valve is closed after the opening degree of the electronic expansion valve corresponding to the centrifugal compressor is selectively increased.

Based on the determination result of step S304, if the detected current rotation speed of the centrifugal compressor is still less than or equal to the preset rotation speed, determining the time for closing the electronic expansion valve after increasing the opening of the electronic expansion valve corresponding to the centrifugal compressor. Specifically, step S306 is performed first, that is, whether the opening degree of the electronic expansion valve is already the maximum opening degree. If the current opening of the electronic expansion valve is the maximum opening, after the first preset waiting time is passed, step S303 is executed again, that is, the current rotation speed of the centrifugal compressor is obtained again, so that the next judgment can be performed in time, and further, the normal operation of the unit can be restored in time after the surge risk is eliminated. It should be noted that, the specific value of the first preset waiting duration is not limited in the present invention, and preferably, the first preset waiting duration is set to 30S, so as to fully ensure the eliminating effect of the surge risk. If the current opening of the electronic expansion valve is not the maximum opening, step S307 is performed, i.e., the opening of the electronic expansion valve is increased by a preset magnitude; it should be noted that, the specific value of the preset amplitude is not limited in the present invention, and a person skilled in the art can set the preset amplitude according to the actual use requirement, preferably, the preset amplitude is set to be 5% of the maximum opening of the electronic expansion valve. After step S307 is performed, step S105 is performed again. After the second preset waiting period, step S303 is executed again, that is, the current rotation speed of the centrifugal compressor is obtained again, so as to perform the next judgment in time. It should be noted that, the specific value of the second preset waiting duration is not limited in the present invention, and preferably, the second preset waiting duration is set to 15S, so as to ensure that the normal operation of the unit is restored in time.

In addition, based on the determination result of step S304, if the detected current rotation speed of the centrifugal compressor is greater than the preset rotation speed, step S305 is executed, that is, the electronic expansion valve is directly closed, and the operation according to the normal operation logic of the unit is continued.

Finally, it should be noted that, the preset values in the above three preferred embodiments are irrelevant, that is, the preset values in the embodiments need to be set individually by those skilled in the art according to actual use requirements.

Based on the control scheme described in the three preferred embodiments above, the present invention can be used in three phases where surge mainly occurs: the low-load operation stage, the high-pressure ratio starting stage and the high-pressure ratio operation stage effectively avoid surging, and further the operation stability of the centrifugal water chilling unit is ensured to the greatest extent.

Thus far, the technical solution of the present invention has been described in connection with the preferred embodiments shown in the drawings, but it is easily understood by those skilled in the art that the scope of protection of the present invention is not limited to these specific embodiments. Equivalent modifications and substitutions for related technical features may be made by those skilled in the art without departing from the principles of the present invention, and such modifications and substitutions will fall within the scope of the present invention.

Claims (10)

1. The utility model provides a centrifugal chiller's first compressor start control method, its characterized in that, centrifugal chiller includes a plurality of bypass branch road, refrigerant circulation circuit and sets up a plurality of centrifugal compressors, condenser, throttle component and the evaporimeter on the refrigerant circulation circuit, a plurality of bypass branch road and a plurality of centrifugal compressor are corresponding setting up, bypass branch road sets up to can introduce the refrigerant in the condenser in the evaporimeter, and be provided with electronic expansion valve on the bypass branch road in order to control bypass branch road's break-make state, first compressor start control method includes:

under the condition that the first centrifugal compressor is ready to be started, acquiring a system pressure ratio corresponding to the centrifugal compressor;

and selectively starting the centrifugal compressor after opening the electronic expansion valve corresponding to the centrifugal compressor according to the system pressure ratio corresponding to the centrifugal compressor.

2. The initial stage compressor start-up control method according to claim 1, wherein the step of selectively restarting the centrifugal compressor after opening the electronic expansion valve corresponding to the centrifugal compressor according to the system pressure ratio corresponding to the centrifugal compressor specifically comprises:

Comparing the system pressure ratio corresponding to the centrifugal compressor with a preset starting pressure ratio;

and selectively starting the centrifugal compressor after starting the electronic expansion valve corresponding to the centrifugal compressor according to the comparison result of the system pressure ratio corresponding to the centrifugal compressor and the preset starting pressure ratio.

3. The initial stage compressor start-up control method according to claim 2, wherein the step of selectively restarting the centrifugal compressor after opening the electronic expansion valve according to a comparison result of the system pressure ratio corresponding to the centrifugal compressor and the preset start-up pressure ratio includes:

and if the system pressure ratio corresponding to the centrifugal compressor is larger than the preset starting pressure ratio, starting the centrifugal compressor after starting the electronic expansion valve corresponding to the centrifugal compressor.

4. The initial stage compressor start-up control method according to claim 3, wherein the step of restarting the centrifugal compressor after opening the electronic expansion valve corresponding to the centrifugal compressor specifically comprises:

opening an electronic expansion valve corresponding to the centrifugal compressor to a preset opening degree;

Detecting the corresponding system pressure ratio of the centrifugal compressor again after the preset time length;

and selectively restarting the centrifugal compressor after adjusting the opening degree of the electronic expansion valve corresponding to the centrifugal compressor according to the re-detected system pressure ratio corresponding to the centrifugal compressor.

5. The initial stage compressor start-up control method according to claim 4, wherein the step of selectively restarting the centrifugal compressor after adjusting the opening degree of the electronic expansion valve corresponding to the centrifugal compressor according to the re-detected system pressure ratio corresponding to the centrifugal compressor specifically comprises:

and if the detected system pressure ratio corresponding to the centrifugal compressor is still larger than the preset starting pressure ratio, starting the centrifugal compressor after increasing the opening of the electronic expansion valve corresponding to the centrifugal compressor.

6. The initial stage compressor start-up control method according to claim 5, wherein the step of restarting the centrifugal compressor after increasing the opening degree of the electronic expansion valve corresponding to the centrifugal compressor specifically comprises:

intermittently increasing the opening degree of the electronic expansion valve corresponding to the centrifugal compressor until the system pressure ratio corresponding to the centrifugal compressor is smaller than or equal to the preset starting pressure ratio, and restarting the centrifugal compressor.

7. The initial stage compressor start-up control method according to claim 6, wherein after the centrifugal compressor starts to start up, the initial stage compressor start-up control method further comprises:

acquiring the current rotating speed of the centrifugal compressor;

comparing the current rotation speed of the centrifugal compressor with a preset rotation speed;

and selectively increasing the opening of the electronic expansion valve corresponding to the centrifugal compressor to the maximum opening according to the comparison result of the current rotating speed of the centrifugal compressor and the preset rotating speed.

8. The initial stage compressor start-up control method according to claim 7, wherein the step of selectively increasing the opening degree of the electronic expansion valve corresponding to the centrifugal compressor to the maximum opening degree according to the comparison result of the current rotation speed of the centrifugal compressor and the preset rotation speed specifically comprises:

and if the current rotating speed of the centrifugal compressor is smaller than or equal to the preset rotating speed, increasing the opening of the electronic expansion valve corresponding to the centrifugal compressor to the maximum opening.

9. The initial stage compressor start-up control method according to claim 7, further comprising:

And if the current rotating speed of the centrifugal compressor is larger than the preset rotating speed, closing the electronic expansion valve corresponding to the centrifugal compressor after the centrifugal compressor is started.

10. The initial stage compressor start-up control method according to claim 2, wherein the step of selectively restarting the centrifugal compressor after opening the electronic expansion valve corresponding to the centrifugal compressor according to the comparison result of the system pressure ratio corresponding to the centrifugal compressor and the preset start-up pressure ratio further comprises:

and if the system pressure ratio corresponding to the centrifugal compressor is smaller than or equal to the preset starting pressure ratio, the electronic expansion valve corresponding to the centrifugal compressor is not started and the centrifugal compressor is directly started.