Anti-surge control method for air-suspension variable-frequency centrifugal water chilling unit

Abstract

The invention provides an anti-surge control method for an air-suspension variable-frequency centrifugal water chilling unit, and the anti-surge control method is realized by an air-suspension variable-frequency centrifugal water chilling unit system. The air-suspension variable-frequency centrifugal water chilling unit system comprises an evaporator, a compressor, a condenser, a first-stage throttling valve, an economizer, a second-stage throttling valve, a hot air bypass valve and an exhaust pressure sensor, the exhaust pressure sensor is further installed at an exhaust port of the compressor, and the hot air bypass valve is further arranged between the evaporator and the condenser. The evaporator and the condenser are further communicated with the compressor, and the economizer is communicated to the evaporator and the condenser through the second-stage throttling valve and the first-stage throttling valve. The air-suspension variable-frequency centrifugal water chilling unit has the beneficial effect that the problem that a compressor bearing, a sealing system, a motor and a frequency converter are damaged due to surge, stall and the like of the compressor in the operation process of the air-suspension variable-frequency centrifugal water chilling unit can be solved.

Description

Technical Field

[0001] The present invention belongs to the field of chiller control, and particularly relates to an anti-surge control method for a magnetic levitation variable frequency centrifugal chiller. Background Art

[0002] The magnetic levitation variable frequency centrifugal chiller uses a hydrodynamic magnetic levitation centrifugal refrigeration compressor. Surge is a common fault phenomenon during the operation of the compressor. Compressor surge is caused by a reduction in gas flow or pressure changes, resulting in periodic oscillations in the internal air flow of the compressor. Surge is an inherent characteristic of centrifugal compressors. When compressor surge occurs, periodic oscillations occur in the internal air flow of the compressor, accompanied by harsh mechanical noise, leading to strong vibrations of working components. In severe cases, it may cause permanent damage to the compressor bearings and sealing system. At the same time, the operating current of the compressor also fluctuates during the surge process, which is likely to damage the motor and frequency converter.

[0003] In order to prevent compressor surge, the existing anti-surge method is to make the unit operate above the surge line. However, since the surge line is fitted from test data, when the deviation between the operating speed of the compressor and the actual required speed is large under low-load conditions, the anti-surge failure will occur. Summary of the Invention

[0004] In view of this, the present invention aims to propose an anti-surge control method for a magnetic levitation variable frequency centrifugal chiller to solve the problems of damage to the compressor bearings, sealing system, motor, and frequency converter caused by compressor surge and stall during the operation of the magnetic levitation variable frequency centrifugal chiller.

[0005] To achieve the above object, the technical solution of the present invention is realized as follows:

[0006] An anti-surge control method for a magnetic levitation variable frequency centrifugal chiller, the anti-surge control method is implemented by a magnetic levitation variable frequency centrifugal chiller system. The magnetic levitation variable frequency centrifugal chiller system includes an evaporator, a compressor, a condenser, a primary throttle valve, an economizer, a secondary throttle valve, a hot gas bypass valve, and an exhaust pressure sensor. An exhaust pressure sensor is also installed at the compressor exhaust port. A hot gas bypass valve is also configured between the evaporator and the condenser. The evaporator and the condenser are both connected to the compressor. The economizer is respectively connected to the evaporator and the condenser through the secondary throttle valve and the primary throttle valve;

[0007] The anti-surge control method includes surge detection, continuous surge protection, and surge fault handling. The surge detection includes:

[0008] After the compressor runs, the controller detects compressor surge by monitoring the discharge pressure collected by the discharge pressure sensor at the compressor outlet and the compressor current fed back by the frequency converter. When the compressor surges, the discharge pressure and the compressor current will show periodic fluctuations;

[0009] The judgment basis for surge detection is as follows:

[0010] For discharge surge, if the discharge pressure change rate ≥ the discharge surge detection value and the discharge pressure change rate ≤ - the discharge surge detection value occur once within one discharge surge detection period, it is determined as one discharge surge; where the discharge pressure change rate = the discharge pressure change value / the discharge pressure detection time;

[0011] For current surge, the current at the start of each current surge detection period is used as the reference current. The current change value is the current at the end of each current surge detection period - the reference current. If the current change value ≥ the reference current × the current surge detection value and the current change ≤ - the reference current × the current surge detection value occur once within one current surge detection period, it is determined as one current surge;

[0012] For continuous surge, the controller starts timing from the time point when surge is judged. Within the surge detection period, if the cumulative number of discharge surges or the cumulative number of current surges ≥ the continuous surge detection value, it is determined as continuous surge.

[0013] Furthermore, in the continuous surge protection stage, after the controller detects that the compressor enters continuous surge, it is necessary to avoid surge according to the continuous surge protection measures. The continuous surge protection measures are as follows:

[0014] a. If the IGV position opening is not fully open, open the IGV; the IGV is determined to be fully open when the position opening of the IGV is within the range of 100% ± the preset deviation;

[0015] b. Increase the compressor speed by the surge avoidance speed increase value based on the current speed;

[0016] The controller starts timing from the completion of the first compressor speed increase and judges whether surge occurs again within the non - surge detection period;

[0017] If no surge occurs again, the unit resumes normal speed control; if surge occurs again, first judge whether the compressor speed is the maximum speed value;

[0018] If the compressor speed is not the maximum speed value, continue to increase the compressor speed until the compressor no longer surges and resumes normal speed control;

[0019] If the compressor has reached the maximum speed value, the compressor will enter the protection mode;

[0020] In the compressor protection mode, the hot gas bypass valve is opened and the surge detection is continued within the surge failure detection cycle;

[0021] If surge does not occur again within the surge non-establishment period, the hot gas bypass valve is closed and the unit resumes normal speed control.

[0022] Furthermore, for surge fault processing, the controller starts timing from the completion of the first compressor speed increase, and detects whether surge occurs again within the surge non-establishment detection period;

[0023] If surge occurs again, the surge times during the protection process will be accumulated and counted. When the accumulated surge times during the protection process exceed the maximum surge protection times, the compressor will perform an emergency shutdown and issue a surge fault alarm.

[0024] Furthermore, the exhaust surge detection period is 5s, the exhaust surge detection value is 10kpa / s, and the exhaust pressure detection time is 1s.

[0025] Furthermore, the current surge detection period is set to 10s, and the current surge detection value is set to 15%.

[0026] Furthermore, the surge detection period is set to 30 seconds, and the continuous surge detection value is set to 3 times.

[0027] Furthermore, an IGV is installed on the air intake of the compressor.

[0028] Furthermore, the compressor is driven by a frequency converter, and the frequency converter realizes data exchange with the controller through RS-485 communication protocol.

[0029] Furthermore, the controller directly adjusts the IGV opening through the IGV control signal, and collects the exhaust pressure sensor and IGV position feedback on the compressor; the controller also adjusts the opening of the hot gas bypass valve through the hot gas bypass valve control signal, and obtains the position feedback of the hot gas bypass valve.

[0030] Compared with the prior art, the anti-surge control method of an air-suspended variable frequency centrifugal chiller described in the present invention has the following advantages:

[0031] The invention discloses an anti-surge control method for an air-suspended variable-frequency centrifugal chiller. The invention can solve the problem of damage to the compressor bearings, sealing system, motor and frequency converter caused by surge and stall of the compressor during the operation of the air-suspended variable-frequency centrifugal chiller. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0033] Figure 1 Schematic diagram of the air suspension variable frequency centrifugal chiller system according to an embodiment of the present invention;

[0034] Figure 2 Schematic diagram of the control principle of the air suspension variable frequency centrifugal chiller system according to an embodiment of the present invention;

[0035] Figure 3 Schematic diagram of the surge prevention control method according to an embodiment of the present invention;

[0036] Figure 4 Schematic diagram of the implementation process of the surge prevention control method according to an embodiment of the present invention;

[0037] Figure 5 Top view schematic diagram of the air suspension variable frequency centrifugal chiller system according to an embodiment of the present invention;

[0038] Figure 6 Front view schematic diagram of the air suspension variable frequency centrifugal chiller system according to an embodiment of the present invention.

[0039] Explanation of reference numerals:

[0040] 1, evaporator; 2, compressor; 3, condenser; 4, primary throttle valve; 5, economizer; 6, secondary throttle valve; 7, hot gas bypass valve; 8, exhaust pressure sensor. Detailed implementation manners

[0041] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0042] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first", "second", etc. can explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, the meaning of "a plurality" is two or more.

[0043] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "installation", "connection", and "coupling" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0044] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0045] As Figures 1 to 6 shown, a surge prevention control method for an air suspension variable frequency centrifugal chiller is provided. The surge prevention control method is implemented by an air suspension variable frequency centrifugal chiller system, which mainly includes an evaporator 1, a compressor 2, a condenser 3, a primary throttle valve 4, an economizer 5, a secondary throttle valve 6, a hot gas bypass valve 7, and an exhaust pressure sensor 8. Among them, an intake regulating mechanism (IGV) is provided at the suction port of the compressor. A high-pressure pressure sensor (exhaust pressure sensor 8) is also installed at the exhaust port of the compressor 2. An energy regulating valve (hot gas bypass valve 7) is also configured between the evaporator 1 and the condenser 3. Both the evaporator 1 and the condenser 3 are also connected to the compressor 2. The economizer 5 is respectively connected to the evaporator 1 and the condenser 3 through the secondary throttle valve 6 and the primary throttle valve 4.

[0046] The present invention provides a control schematic diagram of an air suspension variable frequency centrifugal chiller as Figure 2 , the compressor 2 is driven by a frequency converter to operate. The controller realizes data interaction with the frequency converter through the RS-485 communication protocol to adjust the speed of the compressor 2 and receive feedback information such as the operating status, parameters, and compressor current of the frequency converter in real time. At the same time, the controller directly adjusts the opening of the IGV through the IGV control signal and collects the exhaust pressure sensor 8 on the compressor 2 and the position feedback of the IGV. In addition, the controller also adjusts the opening of the hot gas bypass valve 7 through the hot gas bypass valve 7 control signal and obtains the position feedback of the hot gas bypass valve 7.

[0047] The present invention provides a surge prevention control method for an air suspension compressor as Figure 3 , which mainly includes three parts: surge detection, continuous surge protection, and surge fault handling.

[0048] Surge detection: After the compressor 2 operates, the controller detects the compressor surge by monitoring the exhaust pressure collected by the exhaust pressure sensor 8 at the compressor outlet and the compressor current fed back by the frequency converter. When the compressor surges, the exhaust pressure and the compressor current will show periodic fluctuations. The specific determination basis is as follows:

[0049] Exhaust surge: If the exhaust pressure change rate ≥ the exhaust surge detection value and the exhaust pressure change rate ≤ - the exhaust surge detection value occur once within an exhaust surge detection period, it is determined as one exhaust surge. Among them, the exhaust pressure change rate = the exhaust pressure change value / the exhaust pressure detection time. In this embodiment, the exhaust surge detection period is 5 s, the exhaust surge detection value is 10 kPa / s, and the exhaust pressure detection time is 1 s;

[0050] Current surge: Take the current at the start of each current surge detection period as the reference current. The current change value is the current at the end of each current surge detection period - the reference current. If the current change value ≥ the reference current × the current surge detection value and the current change ≤ - the reference current × the current surge detection value occur once within a current surge detection period, it is determined as one current surge. In this embodiment, the current surge detection period is 10 s, and the current surge detection value is 15%.

[0051] Continuous surge: The controller starts timing from the time point when a surge (exhaust surge or current surge) is determined. If the cumulative number of exhaust surges or the cumulative number of current surges ≥ the continuous surge detection value within the surge detection period, it is determined as continuous surge. In this embodiment, the surge detection period is 30 s, and the continuous surge detection value is 3 times. This value can avoid misjudging occasional surges and ensure timely protection when the compressor 2 has continuous surges.

[0052] During the continuous surge protection stage, after the controller detects that the compressor enters continuous surge, it is necessary to avoid surges according to the continuous surge protection measures as Figure 4 . The specific continuous surge protection measures are as follows:

[0053] a. If the position opening of the intake air regulating mechanism (IGV) is not fully open, open the intake air regulating mechanism; if the position opening of the IGV is within the range of 100% ± the preset deviation, it is determined that the IGV is fully open.

[0054] b. Increase the compressor 2 speed by the surge avoidance speed increase value based on the current speed. In this embodiment, the surge avoidance speed increase value is 0.5%.

[0055] The controller starts timing from the completion of the first compressor speed increase, and determines whether surge occurs again within the surge non-occurrence detection period. If no surge occurs again, the unit resumes normal speed control; if surge occurs again, it first determines whether the compressor speed is the maximum speed value. If the compressor speed is not the maximum speed value, the compressor speed increase continues until surge no longer occurs in Compressor 2 and normal speed control is resumed; if Compressor 2 has reached the maximum speed value, Compressor 2 will enter the protection mode. In the compressor protection mode, the hot gas bypass valve 7 is opened, and surge detection within the surge non-occurrence detection period continues. If no surge occurs again within the surge non-occurrence period, the hot gas bypass valve 7 is closed, and the unit resumes normal speed control. In this embodiment, the surge non-occurrence detection period is set to 30 s, and the maximum speed value is set to 16,500 rpm.

[0056] For a surge fault, the controller starts timing from the completion of the first compressor speed increase, and detects whether a second surge occurs within the surge non-occurrence detection period. If a second surge occurs, the number of surges during the protection process is cumulatively counted. When the cumulative number of surges during the protection process exceeds the maximum value of the surge protection times, the compressor performs an emergency shutdown and issues a "surge fault" alarm. In this embodiment, the surge non-occurrence detection period is set to 30 s, and the maximum value of the surge protection times is set to 3 times.

[0057] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A surge prevention control method for an air suspension variable frequency centrifugal chiller, characterized in that: The anti-surge control method is implemented by an air suspension variable frequency centrifugal chiller system, which includes an evaporator (1), a compressor (2), a condenser (3), a primary throttle valve (4), an economizer (5), a secondary throttle valve (6), a hot gas bypass valve (7), and an exhaust pressure sensor (8). An exhaust pressure sensor (8) is also installed at the exhaust port of the compressor (2). A hot gas bypass valve (7) is also configured between the evaporator (1) and the condenser (3). The evaporator (1) and the condenser (3) are both connected to the compressor (2). The economizer (5) is respectively connected to the evaporator (1) and the condenser (3) through the secondary throttle valve (6) and the primary throttle valve (4); The anti-surge control method includes surge detection, continuous surge protection, and surge fault handling. The surge detection includes: After the compressor (2) runs, the controller detects the surge of the compressor (2) by monitoring the exhaust pressure collected by the exhaust pressure sensor (8) at the outlet of the compressor (2) and the current of the compressor (2) fed back by the frequency converter. When the compressor (2) surges, the exhaust pressure and the current of the compressor (2) will show periodic fluctuations; The judgment basis for surge detection is as follows: Exhaust surge: If the exhaust pressure change rate ≥ the exhaust surge detection value and the exhaust pressure change rate ≤ - the exhaust surge detection value occur once within an exhaust surge detection cycle, it is determined as one exhaust surge; where the exhaust pressure change rate = exhaust pressure change value / exhaust pressure detection time; Current surge: The current at the start of each current surge detection cycle is used as the reference current. The current change value is the current at the end of each current surge detection cycle - the reference current. If the current change value ≥ the reference current × the current surge detection value and the current change ≤ - the reference current × the current surge detection value occur once within a current surge detection cycle, it is determined as one current surge; Continuous surge: The controller starts timing from the time point when it is judged as a surge. During the surge detection cycle, if the cumulative number of exhaust surges or the cumulative number of current surges ≥ the continuous surge detection value, it is determined as continuous surge.

2. A surge prevention control method for an air suspension variable frequency centrifugal chiller according to claim 1, characterized in that: In the continuous surge protection stage, after the controller detects that the compressor (2) enters continuous surge, it is necessary to avoid surge according to the continuous surge protection measures. The continuous surge protection measures are as follows: a. If the IGV position opening is not fully open, open the IGV; the IGV is determined to be fully open when the position opening of the IGV is within the range of 100% ± the preset deviation; b. Increase the compressor (2) speed by the surge avoidance speed increase value based on the current speed; The controller starts timing from the completion of the first compressor (2) speed increase and judges whether a surge occurs again during the non-surge detection cycle; If no surge occurs again, the unit resumes normal speed control; If a surge occurs again, first judge whether the compressor (2) speed is the maximum speed value; If the compressor (2) speed is not the maximum speed value, continue to increase the compressor (2) speed until the compressor (2) no longer surges and resumes normal speed control; If the compressor (2) has reached the maximum speed value, the compressor (2) will enter the protection mode; In the compressor (2) protection mode, open the hot gas bypass valve (7), and continue to perform surge detection during the non - surge detection cycle. If no surge occurs again during the non - surge cycle, close the hot gas bypass valve (7), and the unit resumes normal speed control.

3. A surge prevention control method for an air suspension variable frequency centrifugal chiller according to claim 1, characterized in that: For surge fault handling, the controller starts timing from the completion of the first increase in the compressor (2) speed, and detects whether a surge occurs again during the non - surge detection cycle. If a surge occurs again, the number of surges during the protection process is cumulatively counted. When the cumulative number of surges during the protection process exceeds the maximum value of the surge protection times, the compressor (2) performs an emergency shutdown and issues a surge fault alarm.

4. A surge prevention control method for an air suspension variable frequency centrifugal chiller according to claim 1, characterized in that: The exhaust surge detection cycle is set to 5 s, the exhaust surge detection value is set to 10 kPa / s, and the exhaust pressure detection time is set to 1 s.

5. A surge prevention control method for an air suspension variable frequency centrifugal chiller according to claim 1, characterized in that: The current surge detection cycle is set to 10 s, and the current surge detection value is set to 15%.

6. A surge prevention control method for an air suspension variable frequency centrifugal chiller according to claim 1, characterized in that: The surge detection cycle is set to 30 s, and the continuous surge detection value is set to 3 times.

7. A surge prevention control method for an air suspension variable frequency centrifugal chiller according to claim 1, characterized in that: An IGV is installed at the suction port of the compressor (2).

8. A surge prevention control method for an air suspension variable frequency centrifugal chiller according to claim 1, characterized in that: The compressor (2) is driven by a frequency converter, and the frequency converter realizes data interaction with the controller through the RS - 485 communication protocol.

9. A surge prevention control method for an air suspension variable frequency centrifugal chiller according to claim 8, characterized in that: The controller directly adjusts the opening of the IGV through the IGV control signal, and collects the exhaust pressure sensor (8) on the compressor (2) and the IGV position feedback; the controller also adjusts the opening of the hot gas bypass valve (7) through the hot gas bypass valve (7) control signal, and obtains the position feedback of the hot gas bypass valve (7).

Images