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

Abstract

The invention provides an air-suspension variable-frequency centrifugal water chilling unit starting control method, which is realized by an air-suspension variable-frequency centrifugal water chilling unit system, and the air-suspension variable-frequency centrifugal water chilling unit system comprises a system main path cycle, a compressor air supply cycle, a motor cooling cycle and a frequency converter cooling cycle. The method has the beneficial effects that the problem that a compressor bearing and a sealing system are damaged due to surge, stall, suction liquid carrying, current overload and the like in the starting process of the compressor 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 in particular relates to a starting control method for an air suspension variable frequency centrifugal chiller. Background Art

[0002] The air suspension variable frequency centrifugal chiller uses a hydrodynamic air suspension centrifugal refrigeration compressor. The compressor adopts hydrodynamic air floating bearing technology, relying on the high-speed rotation of the rotor to form an air film, without the need for lubricating oil and a gas supply system, enabling the compressor shaft to float in the air, reducing the efficiency loss, vibration, and noise generated by mechanical friction. Therefore, the compressor bearing, as a key component for the stable operation of the compressor, plays a crucial role.

[0003] The operation process of the compressor is divided into three stages: start-up, normal operation, and shutdown. During the start-up stage, the compressor accelerates from zero speed to the suspension speed, and the compressor shaft enters the suspended state. During the normal operation stage, the compressor adjusts its operating speed according to different load requirements. During operation, there is no direct physical contact between the main shaft of the compressor and the bearing. During the shutdown stage, the shaft freely stops from the suspended operation state until it completely stops.

[0004] Before starting the air suspension variable frequency centrifugal chiller, it should be ensured that all interlock conditions of the system are met, such as the chilled water temperature meeting the start-up conditions, the chilled and cooling water flows both meeting the specified flow rates, and the unit being fault-free, etc. During the compressor start-up process, if it is the first start-up or a long time after shutdown and then start-up, there is no pressure difference between the condenser and the evaporator, and the compressor can start and operate at the preset start-up speed; if it is restarted shortly after shutdown during operation, due to the pressure difference existing between the condenser and the evaporator itself, the suction pressure in the evaporator is low and the condensation pressure of the condenser is high. If starting at the preset start-up speed again, the compressor is prone to surge, stall, and other fault phenomena due to low speed, and problems such as liquid carryover during suction, excessive operating power, and current overload may occur if the compressor speed is too high, causing permanent damage to the compressor bearing and sealing system. Summary of the Invention

[0005] In view of this, the present invention aims to propose a starting control method for an air suspension variable frequency centrifugal chiller to solve the problems of surge, stall, liquid carryover during suction, current overload, etc. during the start-up process of the compressor of the air suspension variable frequency centrifugal chiller, and the damage to the compressor bearing and sealing system.

[0006] To achieve the above object, the technical solution of the present invention is realized as follows:

[0007] A starting control method for an air suspension variable frequency centrifugal chiller, which is implemented by the air suspension variable frequency centrifugal chiller system. The air suspension variable frequency centrifugal chiller system includes a system main circuit circulation, a compressor gas replenishment circulation, a motor cooling circulation, and a frequency converter cooling circulation;

[0008] The system main circuit circulation includes an evaporator, a compressor, a condenser, a primary throttle valve, an economizer, a secondary throttle valve, and a hot gas bypass valve;

[0009] The compressor gas replenishment circulation includes an economizer, a gas replenishment solenoid valve, and a compressor;

[0010] The motor cooling circulation includes a condenser, a motor cooling solenoid valve, a compressor, and an evaporator;

[0011] The frequency converter cooling circulation includes a condenser, a frequency converter cooling solenoid valve, a frequency converter, and an evaporator;

[0012] The evaporator and the condenser are connected through a hot gas bypass valve. The economizer is connected to the evaporator and the condenser through a secondary throttle valve and a primary throttle valve respectively. The economizer is also connected to the compressor through a gas replenishment solenoid valve. The compressor is connected to the evaporator and the condenser respectively. A motor cooling solenoid valve is also installed between the compressor and the condenser. The condenser is sequentially connected to the evaporator through a frequency converter cooling solenoid valve and a frequency converter;

[0013] The starting control method includes the following steps:

[0014] When a compressor start command is received, immediately open the motor cooling solenoid valve, the frequency converter cooling solenoid valve, and the gas replenishment solenoid valve, open the IGV of the compressor, and then delay to judge whether the position opening of the IGV is fully open. If the position opening of the IGV is within 100% ± a preset deviation range, it is determined that the IGV is fully open. If the position opening of the IGV is not fully open, a fault alarm is processed;

[0015] If the position opening of the IGV is fully open, open the hot gas bypass valve, and delay to judge whether the position opening of the hot gas bypass valve is fully open. If the position opening of the hot gas bypass valve is within 100% ± a preset deviation range, it is determined that the hot gas bypass valve is fully open;

[0016] If the position opening of the hot gas bypass valve does not reach fully open, a fault alarm is given; if the position opening of the hot gas bypass valve is already fully open, a pre-start judgment starting speed calculation is performed.

[0017] Furthermore, the air suspension variable frequency centrifugal chiller system further includes a control panel and a frequency conversion cabinet, and a control panel and a frequency conversion cabinet are respectively installed on one side of the evaporator and the condenser.

[0018] Furthermore, an IGV is installed on the compressor.

[0019] Further, the preset deviation range is 1%.

[0020] Further, in the startup control method, by detecting the evaporator outlet water temperature T1 and the condenser outlet water temperature T2 of the system, the evaporation temperature Te and the condensation temperature Tc of the system are calculated;

[0021] wherein, Te = T1 - T3;

[0022] Tc = T2 + T4;

[0023] wherein, T3 is the evaporation temperature correction value, and its value is 1.0°C; T4 is the condensation temperature correction value, and its value is 1.5°C.

[0024] Further, in the startup control method, according to the condensation temperature, the evaporation temperature and the refrigerant type, the corresponding saturated condensation pressure Pc and saturated evaporation pressure Pe are obtained by looking up the table through the control program, and the pressure ratio X of the system is calculated using the saturated condensation pressure and the saturated evaporation pressure;

[0025] wherein,

[0026] wherein, Pa is the atmospheric pressure, and its value is 1.01 bar;

[0027] The calculated pressure ratio is limited within the range of 1 to the preset pressure ratio upper limit, and the calculated pressure ratio is substituted into the compressor lower limit speed calculation formula to calculate the predicted startup speed Y,

[0028] Y = (1 + K) × (AX 3 + BX 2 + CX + D);

[0029] wherein, the preset pressure ratio upper limit value is 2.2; K is the surge margin, and its value is 1%; A is the lower limit speed cubic coefficient, and its value is 1.03096; B is the lower limit speed quadratic coefficient, and its value is -8.67321; C is the lower limit speed linear coefficient, and its value is 27.4864; D is the lower limit speed constant term coefficient, and its value is -15.2056.

[0030] Compared with the prior art, the startup control method of the air suspension variable frequency centrifugal chiller described in the present invention has the following advantages:

[0031] For the startup control method of the air suspension variable frequency centrifugal chiller described in the present invention, the present invention can solve the problems of damage to the compressor bearings and sealing system caused by surging, stalling, liquid carry - over during suction, and current overload during the startup process of the compressor of the air suspension variable frequency centrifugal chiller. Description of the Drawings

[0032] The accompanying drawings, which form a part of the present invention, are used to provide a further understanding of the present invention. The schematic 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 drawings:

[0033] Figure 1 It is a schematic diagram of the principle of the air suspension variable frequency centrifugal chiller system according to the embodiment of the present invention;

[0034] Figure 2 It is a schematic diagram of the start control method according to the embodiment of the present invention;

[0035] Figure 3 It is a schematic diagram of the relationship between the starting speed and pressure ratio of the compressor according to the embodiment of the present invention;

[0036] Figure 4 It is a side view schematic diagram of the air suspension variable frequency centrifugal chiller system according to the embodiment of the present invention;

[0037] Figure 5 It is a front view schematic diagram of the air suspension variable frequency centrifugal chiller system according to the embodiment of the present invention;

[0038] Figure 6 It is a top view schematic diagram of the air suspension variable frequency centrifugal chiller system according to the embodiment of the present invention.

[0039] Description of reference numerals:

[0040] 1. Evaporator; 2. Compressor; 3. Condenser; 4. First throttle valve; 5. Economizer; 6. Second throttle valve; 7. Hot gas bypass valve; 8. Frequency converter; 9. Frequency converter cooling solenoid valve; 10. Motor cooling solenoid valve; 11. Gas supplement solenoid valve; 12. Control panel; 13. Frequency conversion cabinet. Detailed embodiments

[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 relationships indicated by the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. are based on the orientation or positional relationships shown in the drawings. These are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it 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 specifying the quantity of the indicated technical features. Thus, features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise stated, 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 limited, the terms "installed", "connected", "coupled" 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 directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood through specific situations.

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

[0045] As Figures 1 to 6 shown, a starting control method for an air suspension variable frequency centrifugal chiller is provided. The starting control method is implemented by an air suspension variable frequency centrifugal chiller system. The main circuit circulation of the system 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, etc. and their connecting pipelines; the compressor air supplement circulation mainly includes an economizer 5, an air supplement solenoid valve 11, a compressor 2, etc. and their connecting pipelines; the motor cooling circulation mainly includes a condenser 3, a motor cooling solenoid valve 10, a compressor 2, an evaporator 1, etc. and their connecting pipelines; the frequency converter cooling circulation mainly includes a condenser 3, a frequency converter cooling solenoid valve 9, a frequency converter 8, an evaporator 1, etc. and their connecting pipelines. Among them, the compressor 2 is equipped with an intake regulating mechanism (IGV), and a control panel 12 and a frequency conversion cabinet 13 are also included. The control panel 12 and the frequency conversion cabinet 13 are respectively installed on one side of the evaporator 1 and the condenser 3.

[0046] As Figure 2 shown, the present invention provides a starting control method for an air suspension variable frequency centrifugal chiller, including the following steps:

[0047] After receiving the start instruction of the compressor 2, immediately open the motor cooling solenoid valve 10, the frequency converter cooling solenoid valve 9, and the gas replenishing solenoid valve 11, open the intake regulating mechanism of the compressor 2, and then delay to judge whether the IGV position opening is fully open. If the IGV position opening is within the range of 100% ± the preset deviation, it is determined that the IGV is fully open. If the IGV position opening is not fully open, perform a fault alarm; if the IGV position opening is fully open, open the hot gas bypass valve 7, and delay to judge whether the position opening of the hot gas bypass valve 7 is fully open. If the position opening of the hot gas bypass valve 7 is within the range of 100% ± the preset deviation, it is determined that the hot gas bypass valve 7 is fully open; if the position opening of the hot gas bypass valve 7 does not reach full open, perform a fault alarm; if the position opening of the hot gas bypass valve 7 is already fully open, perform a pre-start judgment to calculate the starting speed.

[0048] In this embodiment, the preset deviation range is 1%, and this value can effectively avoid the problem of judgment failure caused by sensor signals or acquisition channel errors.

[0049] By detecting the evaporator outlet water temperature T1 and the condenser outlet water temperature T2 of the system, calculate the evaporation temperature Te and the condensation temperature Tc of the system.

[0050] Te = T1 - T3;

[0051] Tc = T2 + T4;

[0052] In this embodiment, T3 is the evaporation temperature correction value, with a value of 1.0 °C; T4 is the condensation temperature correction value, with a value of 1.5 °C; the actual evaporation temperature of the unit is lower than the evaporator outlet water temperature, and the actual condensation temperature is higher than the condenser outlet water temperature. Through this correction value, the evaporation temperature Te and the condensation temperature Tc calculated are closer to the actual values.

[0053] According to the condensation temperature, evaporation temperature, and refrigerant type, look up the corresponding saturated condensation pressure Pc and saturated evaporation pressure Pe through the control program, and calculate the pressure ratio X of the system using the saturated condensation pressure and saturated evaporation pressure.

[0054]

[0055] In this embodiment, Pa is the atmospheric pressure, with a value of 1.01 bar.

[0056] Limit the calculated pressure ratio within the range of 1 to the preset pressure ratio upper limit, substitute the calculated pressure ratio into the compressor lower limit speed calculation formula to calculate the pre-start judgment speed Y,

[0057] Y = (1 + K) × (AX 3 + BX 2 + CX + D);

[0058] In this embodiment, the preset upper limit of the pressure ratio is set to 2.2; K is the surge margin, with a value of 1%; A is the coefficient of the cube of the lower limit speed, with a value of 1.03096; B is the coefficient of the square of the lower limit speed, with a value of -8.67321; C is the coefficient of the first power of the lower limit speed, with a value of 27.4864; D is the constant term coefficient of the lower limit speed, with a value of -15.2056.

[0059] The relationship between the starting speed and the pressure ratio of the compressor is as Figure 3 . If it is predicted that the starting speed is greater than the preset starting speed, the starting speed of the compressor is taken as the predicted starting speed for starting. If the predicted starting speed is less than or equal to the preset starting speed, the starting speed of the compressor is taken as the preset starting speed for starting. After a specified time delay after the compressor starts, the hot gas bypass valve is fully closed, and the compressor starts and enters normal speed control.

[0060] The present invention can solve the problems of damage to the compressor bearings and sealing system caused by surge, stall, liquid entrainment in suction, current overload, etc. during the starting process of the compressor of an air suspension variable frequency centrifugal chiller.

[0061] 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 starting control method for an air suspension variable frequency centrifugal chiller, characterized in that: The start-up control method is implemented by an air suspension variable frequency centrifugal chiller system, which includes a main system loop, a compressor gas replenishment loop, a motor cooling loop, and a frequency converter cooling loop; The main system loop includes an evaporator (1), a compressor (2), a condenser (3), a primary throttle valve (4), an economizer (5), a secondary throttle valve (6), and a hot gas bypass valve (7); The compressor gas replenishment loop includes an economizer (5), a gas replenishment solenoid valve (11), and a compressor (2); The motor cooling loop includes a condenser (3), a motor cooling solenoid valve (10), a compressor (2), and an evaporator (1); The frequency converter cooling loop includes a condenser (3), a frequency converter (8) cooling solenoid valve, a frequency converter (8), and an evaporator (1); The evaporator (1) and the condenser (3) are connected through a hot gas bypass valve (7). The economizer (5) is connected to the evaporator (1) and the condenser (3) through a secondary throttle valve (6) and a primary throttle valve (4) respectively. The economizer (5) is also connected to the compressor (2) through a gas replenishment solenoid valve (11). The compressor (2) is connected to the evaporator (1) and the condenser (3) respectively. A motor cooling solenoid valve (10) is also installed between the compressor (2) and the condenser (3). The condenser (3) is also connected to the evaporator (1) through a frequency converter (8) cooling solenoid valve and a frequency converter (8) in sequence; The start-up control method includes the following steps: After receiving the start command of the compressor (2), immediately open the motor cooling solenoid valve (10), the frequency converter (8) cooling solenoid valve, and the gas replenishment solenoid valve (11), open the IGV of the compressor (2), and then delay to judge whether the position opening of the IGV is fully open. If the position opening of the IGV is within the range of 100% ± a preset deviation, it is determined that the IGV is fully open. If the position opening of the IGV is not fully open, a fault alarm is processed; If the position opening of the IGV is fully open, open the hot gas bypass valve (7), and delay to judge whether the position opening of the hot gas bypass valve (7) is fully open. If the position opening of the hot gas bypass valve (7) is within the range of 100% ± a preset deviation, it is determined that the hot gas bypass valve (7) is fully open; If the position opening of the hot gas bypass valve (7) does not reach full open, a fault alarm is given; if the position opening of the hot gas bypass valve (7) is already fully open, a pre-start prediction start speed calculation is performed.

2. The start-up control method of an air suspension variable frequency centrifugal chiller according to claim 1, characterized in that: The air suspension variable frequency centrifugal chiller system also includes a control panel (12) and a frequency conversion cabinet (13). A control panel (12) and a frequency conversion cabinet (13) are respectively installed on one side of the evaporator (1) and the condenser (3).

3. A starting control method for an air suspension variable frequency centrifugal chiller according to claim 1, characterized in that: An IGV is installed on the compressor (2).

4. A starting control method for an air suspension variable frequency centrifugal chiller according to claim 1, characterized in that: The preset deviation range is 1%.

5. A starting control method for an air suspension variable frequency centrifugal chiller according to claim 1, characterized in that: In the start-up control method, by detecting the evaporator outlet water temperature T1 and the condenser outlet water temperature T2 of the system, the evaporation temperature Te and the condensation temperature Tc of the system are calculated; where Te = T1 - T3; Tc = T2 + T4; where T3 is the evaporation temperature correction value, with a value of 1.0 °C; T4 is the condensation temperature correction value, with a value of 1.5 °C.

6. The start-up control method of an air suspension variable frequency centrifugal chiller according to claim 1, characterized in that: In the startup control method, the corresponding saturated condensing pressure Pc and saturated evaporation pressure Pe are obtained by looking up a table through a control program according to the condensing temperature, evaporation temperature, and refrigerant type, and the pressure ratio X of the system is calculated using the saturated condensing pressure and saturated evaporation pressure; Among them, where Pa is the atmospheric pressure, with a value of 1.01 bar; The calculated pressure ratio is restricted within the range of 1 to the preset upper limit of the pressure ratio, and the calculated pressure ratio is substituted into the compressor lower limit speed calculation formula to calculate the predicted startup speed Y, Y = (1 + K)×(AX 3 + BX 2 + CX + D); where the preset upper limit of the pressure ratio is 2.2; K is the surge margin, with a value of 1%; A is the coefficient of the cube of the lower limit speed, with a value of 1.03096; B is the coefficient of the square of the lower limit speed, with a value of -8.67321; C is the coefficient of the first power of the lower limit speed, with a value of 27.4864; D is the constant term coefficient of the lower limit speed, with a value of -15.2056.

Images