Anti-surge control method for centrifugal compressor unit and air conditioning equipment

Abstract

The application discloses a centrifugal compressor unit anti-surge control method and air conditioning equipment using the anti-surge control method. The anti-surge control method determines the current anti-surge mode according to the real-time pressure ratio of the unit. When the real-time pressure ratio is greater than or equal to the pressure ratio setting value, the surge line anti-surge mode is entered. When the real-time pressure ratio is less than the pressure ratio setting value, the guide vane negative pre-whirl anti-surge mode is entered. The application combines the widened centrifugal unit operation frequency range and the modulated impeller guide vane pre-whirl angle, so that the anti-surge characteristics of the unit are stronger when the unit is operated under variable working conditions.

Description

Technical Field

[0001] This invention relates to the field of air conditioning technology, and in particular to an anti-surge control method for centrifugal compressor units and an air conditioning device using the anti-surge control method. Background Technology

[0002] Centrifugal compressors have specific design ranges, including flow rate and suction / discharge conditions. However, actual operation may deviate from these design conditions. For example, when the customer's required load decreases, the compressor operates under partial load. The gas flow rate in the compressor's internal flow channels decreases significantly, the axial velocity of the airflow decreases, and the angle of attack increases. At this point, the airflow is directed towards the working surface of the blades, resulting in rotational separation rather than on the working surface. For blade structures with diffusers, rotational separation first occurs in the diffuser. When the flow rate decreases to a critical value, the separation becomes severe and rapidly expands, forming a sudden stall. This disrupts the normal gas flow, and the compressor outlet pressure drops significantly. Because the condenser has a large volume and is not very responsive, its pressure exceeds the compressor outlet pressure, causing gas backflow and significant airflow pulsations, or even gas recirculation. This phenomenon is called surge, an inherent characteristic of centrifugal compressors. Surge can severely damage the compressor structure. For example, during surge, the unit experiences severe vibrations, causing significant damage to bearings, impellers, and other components. Simultaneously, the operating current fluctuates during surge, easily damaging the motor and frequency converter.

[0003] To broaden the safe operating range of compressors, existing anti-surge methods rely on two main approaches. One is through compressor structural design, most commonly using a regulator at the impeller outlet. This regulator adjusts the impeller outlet width according to the unit's operating conditions. When the flow rate decreases, the impeller outlet width is reduced, decreasing the diffuser's flow area and thus increasing the airflow velocity at the impeller outlet, mitigating airflow instability and preventing surge. This structure effectively broadens the compressor's operating range. However, while this anti-surge measure is effective, the regulator requires a motor and a mechanical transmission system, resulting in a complex structure that complicates manufacturing and maintenance. Another approach involves measuring the surge line during production to keep the unit operating above it. However, since the surge line is derived from data fitting, under conditions of low pressure ratio (deviating from the design conditions), the motor operating frequency may deviate significantly from the required frequency, leading to anti-surge failure. Summary of the Invention

[0004] This invention proposes an anti-surge control method for centrifugal compressor units and an air conditioning device using the anti-surge control method, in order to solve the surge problem in the prior art caused by low gas flow inside the compressor due to low load.

[0005] The anti-surge control method for centrifugal compressor units proposed in this invention determines the current anti-surge mode based on the real-time pressure ratio of the unit. When the real-time pressure ratio is greater than or equal to the pressure ratio set value, the unit enters the surge line anti-surge mode and opens the hot gas bypass when the unit's operating frequency is less than the minimum frequency value. When the real-time pressure ratio is less than the pressure ratio set value, the unit enters the guide vane negative pre-rotation anti-surge mode and increases the flow rate by modulating the pre-rotation angle of the impeller guide vanes.

[0006] After entering surge line anti-surge mode, perform the following steps:

[0007] Calculate the minimum frequency value required under the current pressure ratio, and determine whether the current operating frequency value of the unit is greater than or equal to the minimum frequency value. If yes, maintain the current operating frequency unchanged; otherwise, activate the system hot gas bypass and enter the protection mode.

[0008] After entering the guide vane negative pre-spin anti-surge mode, perform the following steps on the second-stage impeller:

[0009] First, the negative pre-spin modulation of the first-stage guide vane is set to a, and the negative pre-spin modulation of the second-stage guide vane is set to b;

[0010] In one embodiment, the value of a is 0° and the value of b is -10°.

[0011] Then, based on the comparison between the detected number of current fluctuations and the fluctuation set value, the impeller guide vanes are subjected to graded negative pre-swirl modulation.

[0012] When the negative pre-swirl modulation of the impeller guide vane reaches its maximum level, and the number of detected current fluctuations is still greater than the fluctuation set value, the system hot gas bypass is activated, and the system enters protection mode.

[0013] A current ripple difference ΔI is defined as a current fluctuation when it is greater than the ripple setting value.

[0014] Preferably, the impeller guide vanes are subjected to three-stage negative pre-spin modulation. In the first-stage negative pre-spin modulation, the first-stage guide vane is negatively pre-spin modulated to a1 and the second-stage guide vane is negatively pre-spin modulated to b1. In the second-stage negative pre-spin modulation, the first-stage guide vane is negatively pre-spin modulated to a2 and the second-stage guide vane is negatively pre-spin modulated to b2. In the third-stage negative pre-spin modulation, the first-stage guide vane is negatively pre-spin modulated to a3 and the second-stage guide vane is negatively pre-spin modulated to b3.

[0015] In one embodiment, the value of a1 is -10°, the value of b1 is -20°, the value of a2 is 0°, the value of b2 is -20°, the value of a3 is -10°, and the value of b3 is -20°.

[0016] When the number of current fluctuations detected is greater than the fluctuation set value, a first-level negative pre-spin modulation is performed; when the number of current fluctuations detected after the first-level negative pre-spin modulation is less than or equal to the fluctuation set value, a second-level negative pre-spin modulation is performed; when the number of current fluctuations detected after the second-level negative pre-spin modulation is greater than the fluctuation set value, a third-level negative pre-spin modulation is performed.

[0017] Preferably, after entering the guide vane negative pre-rotation anti-surge mode, the single impeller guide vane is subjected to two-stage negative pre-rotation modulation. First, the guide vane negative pre-rotation is modulated to a1; if the number of detected current fluctuations is greater than the fluctuation set value, the impeller guide vane negative pre-rotation is modulated to a2; when the number of detected current fluctuations is still greater than the fluctuation set value, the system hot gas bypass is activated, and the system enters the protection mode.

[0018] In one embodiment, the value of a1 is -10° and the value of a2 is -20°.

[0019] The present invention also proposes a centrifugal compressor air conditioning device, wherein the compressor adopts the above-mentioned anti-surge control method.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] This invention combines widening the operating frequency range of the centrifuge unit with modulating the pre-rotation angle of the impeller guide vanes, making the unit more resistant to surge when operating under varying conditions. Attached Figure Description

[0022] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments, wherein:

[0023] Figure 1 This is a cross-sectional schematic diagram of a single-stage centrifugal compressor;

[0024] Figure 2 This is a schematic diagram showing the guide vane angle without pre-rotation;

[0025] Figure 3 This is a schematic diagram of the guide vane at a negative pre-rotation angle;

[0026] Figure 4 This is a diagram of a refrigeration system with a centrifugal compressor unit;

[0027] Figure 5 This is a flowchart of the control method of the present invention. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the following specific embodiments are only used to explain the invention and do not constitute a limitation thereof.

[0029] Figure 1This is a cross-sectional schematic diagram of a single-stage centrifugal compressor. The centrifugal compressor includes an impeller 11, guide vanes 12, a guide vane motor 13 for driving the guide vanes to rotate, a motor 14 for driving the impeller to rotate, and a speed-changing gear 15.

[0030] The purpose of installing guide vanes at the impeller inlet is to adjust the flow rate by creating pre-swirl at their angle. Pre-swirl is positive when the direction is the same as the impeller's rotation, and negative when it's opposite. Positive pre-swirl reduces flow rate, while negative pre-swirl increases it. The performance of the compression stage differs at different pre-swirl angles.

[0031] Figure 2 This is a schematic diagram showing the guide vane angle without pre-rotation.

[0032] Figure 3 This is a schematic diagram of the guide vane angle pre-rotation by -10 degrees.

[0033] Figure 4 This is a system diagram of a centrifugal chiller unit, including: a dual-impeller centrifugal compressor 1, a condenser 2, a throttling device 3, and an evaporator 4. A bypass 5 is provided between the high-pressure outlet discharge pipe and the low-pressure suction pipe of the centrifugal compressor, and a control valve 6 is installed on the bypass 5. During operation, low-temperature, low-pressure refrigerant gas enters the compressor and is compressed into high-temperature, high-pressure gas. Then, it is cooled into high-pressure, medium-temperature liquid in the condenser, then passes through the throttling device to become low-temperature, low-pressure liquid again. Finally, it absorbs heat in the evaporator to become low-temperature, low-pressure gas again, and then returns to the compressor for recirculation.

[0034] The anti-surge control method proposed in this invention increases the pressure and flow of the centrifugal compressor by combining the widening of the operating frequency range of the centrifugal unit with the modulation of the pre-rotation angle of the impeller inlet guide vanes, thereby widening the compressor's operating range and increasing its anti-surge characteristics under low load.

[0035] The anti-surge control method proposed in this invention sets the unit surge into two modes: one is the surge line anti-surge mode, and the other is the guide vane negative pre-rotation anti-surge mode. When the detected real-time pressure ratio is greater than or equal to the pressure ratio set value, the surge line anti-surge mode is entered; when the real-time pressure ratio is less than the pressure ratio set value, the guide vane negative pre-rotation anti-surge mode is entered.

[0036] After entering surge line anti-surge mode, perform the following steps:

[0037] Calculate the minimum frequency value required under the current pressure ratio, and determine whether the current operating frequency value of the unit is greater than or equal to the minimum frequency value. If yes, maintain the current operating frequency unchanged; otherwise, activate the system hot gas bypass and enter the protection mode.

[0038] For a two-stage impeller centrifugal compressor, after entering the guide vane anti-surge mode, the impeller guide vanes are subjected to graded negative pre-swirl modulation based on the comparison results of the detected current fluctuation number and the fluctuation set value.

[0039] For single-stage impeller centrifugal compressors, after entering the guide vane anti-surge mode, a two-stage negative pre-swirl modulation is adopted.

[0040] Figure 5 This is a control flowchart of an embodiment of the present invention, including the following steps:

[0041] The controller of the air conditioning equipment monitors the compressor's pressure ratio (the ratio of the outlet pressure of the second-stage impeller to the suction pressure of the first-stage impeller) in real time. It compares the real-time monitored pressure ratio with the pressure ratio set value. When the real-time pressure ratio is greater than or equal to the pressure ratio set value, it enters the surge line anti-surge mode; when the real-time pressure ratio is less than the pressure ratio set value, it enters the guide vane negative pre-rotation anti-surge mode.

[0042] After entering the surge line anti-surge mode, perform the following steps: calculate the minimum required frequency under the current pressure ratio and compare it with the unit's operating frequency. If the unit's operating frequency is lower than the minimum required frequency under the current pressure ratio, the unit will open the hot gas bypass and enter the protection mode; if it is higher than the minimum frequency under the current pressure ratio, the unit will operate normally.

[0043] After entering the guide vane negative pre-rotation anti-surge mode, the first-stage guide vane negative pre-rotation is first modulated to a, and the second-stage guide vane negative pre-rotation is modulated to b. In this embodiment, a is 0° and b is -10°. Then, the motor current value driving the impeller is detected. If the current pulsation difference (the difference between the peak and valley values ​​of the motor current) exceeds the fluctuation setting value, it is recorded as 1 current fluctuation. When the current fluctuation number does not exceed the fluctuation setting value, the unit operates normally. If the current fluctuation number exceeds the fluctuation setting value, it enters the staged guide vane negative pre-rotation modulation. In this embodiment, the modulation is performed in three stages. In the first-stage guide vane negative pre-rotation debugging, the first-stage guide vane negative pre-rotation is modulated to a1 (e.g., -10°), and the second-stage guide vane negative pre-rotation is modulated to b1 (e.g., -20°). Then, the number of motor current fluctuations is detected. When the number of motor current fluctuations does not exceed the fluctuation setting value, the unit will continue to find the optimal guide vane opening matching value through the number of current fluctuations, that is, to perform the second-stage modulation and continue to change the guide vane negative pre-rotation angle. In this embodiment, during the second-stage guide vane negative pre-rotation adjustment, the first-stage guide vane is negatively pre-rotated to a2 (e.g., 0°), and the second-stage guide vane is negatively pre-rotated to b2 (e.g., -20°). If the number of current fluctuations is less than or equal to the fluctuation set value when the first-stage guide vane is negatively pre-rotated to 0° and the second-stage guide vane is negatively pre-rotated to -20°, the unit operates normally; otherwise, the third-stage negative pre-rotation modulation is performed, with the first-stage guide vane negatively pre-rotated to a3 (e.g., -10°) and the second-stage guide vane negatively pre-rotated to b3 (e.g., -20°). If the number of current fluctuations still exceeds the fluctuation set value at this time, it is determined to be a surge mode, and the unit opens the hot gas bypass and enters the protection mode.

[0044] The guide vane negative pre-spin angle and modulation level described above can be changed according to the actual unit and experimental data, and are not limited to the values ​​in the above embodiments.

[0045] The control method proposed in this invention is applicable to a double-cantilever refrigeration compressor with two guide vane adjustment mechanisms. The motor shaft of this type of compressor extends to both ends, with an impeller at each end. Compared with units that simply set up anti-surge lines, this anti-surge control method broadens the frequency range of the unit's operation and enhances the compressor's anti-surge characteristics under low load.

[0046] If the compressor uses a single impeller structure, after entering the guide vane anti-surge mode, the single impeller guide vane is modulated with two stages of negative pre-swirl. First, the guide vane negative pre-swirl is modulated to a1 (e.g., -10°); if the number of current fluctuations detected is still greater than the fluctuation set value, the impeller guide vane negative pre-swirl is modulated to a2 (e.g., -20°); if the number of current fluctuations detected after the two modulations is still greater than the fluctuation set value, the system hot gas bypass is activated, and the system enters the protection mode.

[0047] The anti-surge control method proposed in this invention combines widening the operating frequency range of the centrifuge unit with modulating the pre-rotation angle of the impeller guide vanes, making the unit more resistant to surge when operating under varying conditions.

[0048] Using the anti-surge control method proposed in this invention can make air conditioning equipment operate smoothly, reliably, and more efficiently.

[0049] The above description is merely a specific embodiment of the present invention. It should be noted that any modifications, equivalent substitutions, and variations made within the spirit and framework of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preventing surge control in a centrifugal compressor unit, characterized in that, The current anti-surge mode is determined based on the unit's real-time pressure ratio. When the real-time pressure ratio is greater than or equal to the pressure ratio set value, the surge line anti-surge mode is entered and the following steps are executed: calculate the minimum frequency value required under the current pressure ratio, determine whether the current operating frequency value of the unit is greater than or equal to the minimum frequency value, and if so, maintain the current operating frequency unchanged; If not, the system hot air bypass will be activated, and the system will enter protection mode. When the real-time pressure ratio is less than the pressure ratio set value, the guide vane negative pre-swirl anti-surge mode is entered and the following steps are performed on the second-stage impeller: First, the negative pre-swirl of the first-stage guide vane is modulated to a, and the negative pre-swirl of the second-stage guide vane is modulated to b; then, according to the comparison result of the detected current fluctuation number with the fluctuation set value, the impeller guide vane is subjected to graded negative pre-swirl modulation.

2. The anti-surge control method as described in claim 1, characterized in that, The value of a is 0°, and the value of b is -10°.

3. The anti-surge control method as described in claim 1, characterized in that, When the negative pre-swirl modulation of the impeller guide vane reaches its maximum level, and the number of detected current fluctuations is still greater than the fluctuation set value, the system hot gas bypass is activated, and the system enters protection mode.

4. The anti-surge control method as described in claim 1, characterized in that, A current ripple difference ΔI is defined as a current fluctuation when it is greater than the ripple setting value.

5. The anti-surge control method as described in claim 1, characterized in that, When the number of current fluctuations is less than or equal to the fluctuation set value, the impeller guide vane is subjected to three-stage negative pre-spin modulation. In the first stage of negative pre-spin modulation, the first-stage guide vane is negatively pre-spin modulated to a1, and the second-stage guide vane is negatively pre-spin modulated to b1. In the second-stage negative pre-spin modulation, the first-stage guide vane is negatively pre-spin-modulated as a2, and the second-stage guide vane is negatively pre-spin-modulated as b2; in the third-stage negative pre-spin modulation, the first-stage guide vane is negatively pre-spin-modulated as a3, and the second-stage guide vane is negatively pre-spin-modulated as b3.

6. The anti-surge control method as described in claim 5, characterized in that, When the number of current fluctuations detected exceeds the fluctuation set value, a first-level negative pre-spin modulation is performed.

7. The anti-surge control method as described in claim 6, characterized in that, When the number of current fluctuations detected after the first-stage negative pre-spin modulation is less than or equal to the fluctuation set value, the second-stage negative pre-spin modulation is performed.

8. The anti-surge control method as described in claim 7, characterized in that, When the number of current fluctuations detected after the second-level negative pre-spin modulation is greater than the fluctuation set value, the third-level negative pre-spin modulation is performed.

9. The anti-surge control method as described in claim 5, characterized in that, The value of a1 is -10°, the value of b1 is -20°, the value of a2 is 0°, the value of b2 is -20°, the value of a3 is -10°, and the value of b3 is -20°.

10. The anti-surge control method as described in claim 1, characterized in that, After entering the guide vane negative pre-rotation anti-surge mode, the single impeller guide vane is modulated with two levels of negative pre-rotation. First, the guide vane negative pre-rotation is modulated to a1; if the number of detected current fluctuations is greater than the fluctuation set value, the impeller guide vane negative pre-rotation is modulated to a2; if the number of detected current fluctuations is still greater than the fluctuation set value, the system hot gas bypass is activated and the system enters the protection mode.

11. The anti-surge control method as described in claim 10, characterized in that, The value of a1 is -10°, and the value of a2 is -20°.

12. A centrifugal compressor air conditioning device, characterized in that, Its compressor adopts the anti-surge control method according to any one of claims 1-11.

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