Method for on-line establishment of surge line of centrifugal compressor

Abstract

The present application belongs to the technical field of centrifugal compressor control, and relates to an online establishment method of a centrifugal compressor surge line. The method comprises the following steps: S1, starting the centrifugal compressor; S2, establishing a partition; S3, detecting a centrifugal compressor surge point, judging whether a surge point in a frequency interval where the surge point is located has been recorded, if yes, eliminating a surge point in the frequency interval, and only keeping one surge point in each frequency interval; otherwise, recording Pc, Pr and of the surge point, and calculating a pressure ratio; S4, judging whether at least m frequency intervals have one surge point, if not, returning to step S3 for continuous detection; if yes, performing curve fitting using the recorded surge points to establish a surge line. The present application can detect and establish a surge line in real time during the operation of a centrifugal compressor, so as to accurately predict and prevent the occurrence of a surge phenomenon.

Description

Technical Field

[0001] This invention relates to an online method for establishing the surge line of a centrifugal compressor, belonging to the field of centrifugal compressor control technology. Background Technology

[0002] Surge in a centrifugal compressor refers to the sudden and intense vibration that sometimes occurs during the compressor's operation. The flow rate and pressure of the gas medium also fluctuate significantly, accompanied by a periodic, muffled "calling" sound, as well as a loud "whooshing" noise caused by airflow fluctuations in the pipeline network. This phenomenon is called the surge condition of a centrifugal compressor. The surge phenomenon in centrifugal compressors is caused by excessive pipeline resistance leading to extremely low flow rates in the centrifugal compressor. This causes rotational detachment within the impeller or diffuser, resulting in deteriorated flow and stall. The centrifugal compressor outlet pressure suddenly drops significantly, falling below the pressure in the pipeline. Consequently, gas in the pipeline instantly flows back into the centrifugal compressor. This backflow temporarily alleviates the problem of insufficient flow in the impeller or diffuser, improving flow and causing the centrifugal compressor outlet pressure to rise. However, due to the instantaneous drop in pipeline pressure caused by the backflow, the backflow stops, and the centrifugal compressor resumes supplying gas to the pipeline. Normal gas supply increases pipeline resistance, raising the pressure within the pipeline and reducing the flow rate again. When the flow rate becomes extremely low, the flow in the impeller or diffuser deteriorates again, causing the centrifugal compressor outlet pressure to drop suddenly and significantly once more, and gas in the pipeline flows back into the compressor again. This periodic, low-frequency, large-amplitude airflow oscillation phenomenon within the system is called surge.

[0003] When mild surge occurs, the pulsation and periodic oscillation of the airflow will cause large fluctuations in the air supply parameters (pressure, flow rate, etc.), which will significantly reduce the system stability and the operating efficiency of the centrifugal compressor. Severe surge will cause the blades to vibrate strongly, increase the noise, and may even cause friction and collision between moving and stationary parts, causing the compressor shaft to bend and deform, resulting in serious damage to the equipment.

[0004] The surge line, also known as the surge boundary line, is as follows: Figure 1 The diagram shows the line connecting the surge points of a centrifugal compressor. The compressor's operating point is required to be to the right of the surge line to avoid surge. However, the actual surge line differs from the theoretical surge line, and the deviation from the rated operating point increases with the actual surge line. Furthermore, the actual surge line is located to the right of the theoretical surge line. If the theoretical surge line is used for protection, the centrifugal compressor will experience surge when operating in region A between the theoretical and actual surge lines. Therefore, the theoretical surge line cannot be directly used for actual equipment. Currently, the methods for determining the surge line of centrifugal compressors in the market generally include the following:

[0005] 1) Reserve a 5%-20% protection margin directly based on the theoretical surge line, and use this as the actual surge line for equipment protection. Figure 1 As shown. The larger the protection margin reserved by this method, the farther the operating point of the centrifugal compressor is from the surge line, and the safer the equipment operation;

[0006] The disadvantage is that if the theoretical 5%-20% margin line is used for protection, the centrifugal compressor cannot operate in region B between the actual surge line and the theoretical 5%-20% margin line. This method narrows the operating range of the centrifugal compressor and makes the adjustable range too small. When the operating point of the equipment under partial load is not within the operating range of the centrifugal compressor, bypassing can only be done through the hot gas bypass valve, resulting in increased energy consumption.

[0007] 2) Various advanced intelligent algorithms, such as neural networks and genetic algorithms. This method is applicable to two situations:

[0008] A. Standardized products: Before a standard product leaves the factory, a large number of experiments are required to obtain a massive amount of experimental data. Then, regression analysis is performed on various models. This method can achieve relatively accurate surge prevention for the product and maximize the operating range of the centrifugal compressor.

[0009] B. The control system connects to the centrifugal compressor equipment or project on the cloud platform through an IoT gateway. This method can achieve accurate prediction and protection of the equipment throughout its entire life cycle using advanced intelligent algorithms, and maximize the operating range and operating efficiency.

[0010] The drawback is that for non-standard products and projects based on data confidentiality, where devices are not allowed to connect to the cloud platform, the intelligent algorithm cannot be used.

[0011] 3) Test on the test bench before leaving the factory, measure several or a dozen surge points, and then use data regression software such as Excel to regress the surge line equation. Then input the equation into the PLC for surge line protection. This method can regress the surge line more accurately.

[0012] shortcoming:

[0013] A. When there are a large number of surge points to measure, it will consume a lot of manpower and resources;

[0014] B. When the number of surge points measured is small, the surge line is inaccurate;

[0015] C. Factory test data cannot fully simulate the actual situation, making model updates difficult;

[0016] D. If the factory test values ​​are inaccurate, it will affect the operation of the equipment throughout its entire life cycle;

[0017] E. In Excel software, many trendline regression models have poor accuracy and cannot intuitively display the model residuals, making model selection inconvenient.

[0018] F. The high cost of setting up the test bench system and the long testing time result in increased product costs and extended delivery time. Summary of the Invention

[0019] The purpose of this invention is to provide a new technical solution to improve or solve the technical problems existing in the prior art as described above.

[0020] The technical solution provided by this invention is as follows: An online method for establishing a surge line in a centrifugal compressor, comprising a centrifugal compressor system, wherein the centrifugal compressor system includes a centrifugal compressor, and the online method for establishing the surge line includes the following steps:

[0021] S1. Start the centrifugal compressor;

[0022] S2. Establish partitions, divide the operating frequency range of the centrifugal compressor into G frequency intervals, and divide the operating pressure ratio range into G pressure ratio intervals, with the G frequency intervals and G pressure ratio intervals corresponding one-to-one.

[0023] S3. Detect the surge point of the centrifugal compressor;

[0024] S4. Determine if a surge point has already been recorded within the frequency range containing the surge point. If so, remove one surge point from the frequency range, keeping only one surge point per frequency range; otherwise, record the surge point. and , This refers to the discharge pressure of the centrifugal compressor. This refers to the suction pressure of the centrifugal compressor. Calculate the pressure ratio for the frequency. ;

[0025] S5. Determine if there is a surge point in at least m frequency intervals. If not, return to step S3 to continue the detection; if enough, use the recorded surge points to perform curve fitting and establish a surge line.

[0026] The technical solution provided by this invention has the following beneficial effects compared with the prior art: This invention can detect surge points in real time during the operation of a centrifugal compressor, and obtain surge points for establishing surge lines through a partitioned acquisition method, realizing the online establishment function of surge lines, thereby accurately predicting surge and preventing its occurrence. By using this online establishment method, the centrifugal compressor can operate more stably and the operating condition range of the centrifugal compressor can be broadened. This invention can not only improve the efficiency and performance of centrifugal compressors, but also extend their service life. Moreover, since this online establishment method can be tested and verified during actual operation, it can save factories money and time investment in testing and experimentation, thereby improving production efficiency.

[0027] Based on the above technical solution, the present invention can be further improved as follows.

[0028] Furthermore, it also includes S6, the actual operating pressure ratio of the centrifugal compressor during operation. and frequency If the corresponding operating point is to the right of the surge line, the centrifugal compressor will operate normally; if it is to the left, the operating frequency of the centrifugal compressor will be increased.

[0029] The advantage of adopting the above-mentioned further solutions is that surge can be avoided.

[0030] Furthermore, in step S5, when the number of recorded surge points is less than m, the zone where the surge point is located is protected by operating condition protection, and the protection method is as follows:

[0031] Let the pressure ratio at the surge point be... , frequency is The pressure ratio range where the surge point is located is Lower limit of protection frequency range , The width of the frequency range; the upper limit of the protected frequency range. When the actual operating pressure ratio of the centrifugal compressor is The protection frequency of the centrifugal compressor Where η represents the deviation. That is, when the actual working pressure ratio is... The minimum operating frequency of a centrifugal compressor should not be lower than H, otherwise surge will easily occur.

[0032] Further, in step S5, the surge line is established by curve fitting using the recorded surge points as follows: the least squares method is used to perform nonlinear equation regression to establish the surge line equation. The nonlinear equation is assumed to be expressible by a polynomial, as shown in equation (1):

[0033] (1)

[0034] Then, based on the principle of least squares, the coefficients are calculated. Make error Minimum, error The calculation formula is as shown in equation (2):

[0035] (2)

[0036] in: The dependent variable represents the minimum operating frequency value;

[0037] is the independent variable, representing the pressure ratio;

[0038] It is a function;

[0039] These are the polynomial coefficients;

[0040] m is the number of surge points;

[0041] n is the highest order of the polynomial;

[0042] Indicates which data point is being analyzed;

[0043] The nonlinear regression problem is transformed into an extremum problem. Equation (2) is then applied to... Taking the partial derivative and setting it to 0, we get equation (3):

[0044]

[0045]

[0046]

[0047]

[0048] Arrange equation (3) to obtain the matrix form as shown in equation (4):

[0049] (4)

[0050] Further simplified to equation (5):

[0051] (5)

[0052] in:

[0053] , ,

[0054] At the same time, it can be found Since it is a symmetric positive definite matrix, according to the Cholesky decomposition method, we can obtain equation (6):

[0055] (6)

[0056] in:

[0057]

[0058] in Representative matrix The value in the nth row and nth column;

[0059] From equations (5) and (6), we obtain equation (7):

[0060] (7)

[0061] Then calculate the matrix. inverse matrix sum matrix inverse matrix Thus, we obtain equation (8).

[0062] (8)

[0063] The final coefficients are obtained The value of .

[0064] Furthermore, It is a positive integer less than or equal to 6.

[0065] Furthermore, in step S3, the centrifugal compressor system also includes a frequency converter for controlling the operation of the centrifugal compressor and a pipeline network connected to the centrifugal compressor; the centrifugal compressor includes an inlet guide vane, the pipeline network is provided with a bypass valve, and also includes a frequency converter input power detection device; the method for detecting the surge point of the centrifugal compressor is as follows;

[0066] S31. Continuously measure the input power of the frequency converter within a set period using the frequency converter input power detection device. ,in The input power of the inverter is calculated as a positive integer greater than or equal to 1. If the absolute value of the standard deviation s within one cycle is less than or equal to the surge judgment setpoint Q, the input power of the inverter is continuously monitored. If the absolute value of the standard deviation s within one cycle is greater than the surge judgment setpoint Q, the process continues to execute S32.

[0067] S32. Determine if the issue is caused by changes in active load. If not, proceed to S33. If so, continue execution.

[0068] S32.1 Determine whether the change is caused by a change in the set frequency. If so, execute S31 after the frequency change response time TF. If not, continue to execute S32.2.

[0069] S32.2 Determine whether the change is caused by the inlet guide vane opening. If so, execute S31 after the inlet guide vane response time TR. If not, execute S32.3.

[0070] S32.3 is caused by a change in the opening degree of the bypass valve. S31 will be executed after the bypass valve response time Tb.

[0071] S33. Determine whether the power fluctuation is caused by passive load changes: When the load increases, a correlation coefficient r ≥ 0.8 indicates a positive high correlation, while when the load decreases, a correlation coefficient r ≤ -0.8 indicates a negative high correlation. When the absolute value of the power standard deviation s within a cycle is greater than the surge judgment setpoint Q, and the correlation coefficient r first shows a negative high correlation and then a positive high correlation, then it is determined that the centrifugal compressor has experienced a surge, the surge point is recorded, and S31 continues to be executed; when the absolute value of the standard deviation s is greater than the surge judgment setpoint Q, and the correlation coefficient does not show a negative high correlation followed by a positive high correlation, then it is considered to be caused by passive load changes, and S31 continues to be executed.

[0072] The beneficial effect of adopting the above-mentioned further scheme is that it can determine whether the centrifugal compressor has surged by using the standard deviation and correlation coefficient of the change in the inverter input power. However, since changes in active load and passive load can also cause changes in the power standard deviation and correlation coefficient, in order to avoid system misjudgment, the characteristics of changes in active load and passive load are analyzed and eliminated in the surge change judgment to ensure the accuracy of surge judgment.

[0073] Furthermore, in step S2, the operating frequency of the centrifugal compressor is divided into G frequency intervals of equal width. Attached Figure Description

[0074] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0075] Figure 1 This is a surge curve diagram for a centrifugal compressor.

[0076] Figure 2 This is a flowchart of the online method for establishing the surge line of a centrifugal compressor according to the present invention;

[0077] Figure 3 This is a diagram of the centrifugal compressor surge detection method of the present invention; Detailed Implementation

[0078] The principles and features of the present invention are described below with reference to examples. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0079] like Figure 2 As shown, an online method for establishing a surge line in a centrifugal compressor includes a centrifugal compressor system, wherein the centrifugal compressor system includes a centrifugal compressor, and the online method for establishing the surge line includes the following steps:

[0080] S1. Start the centrifugal compressor;

[0081] S2. Establish zones to divide the operating frequency range of the centrifugal compressor. The operating voltage ratio range is divided into several frequency intervals. Each pressure ratio range The frequency ranges and Each pressure ratio interval corresponds one-to-one, and surge point data is obtained by partitioning; in this embodiment, the operating frequency range of the centrifugal compressor is divided into equal widths. One frequency range;

[0082] For example, the theoretical maximum pressure ratios corresponding to the frequencies of 266.7Hz and 366.7Hz of a centrifugal compressor are 1.83 and 3.07, respectively. The pressure ratio range is divided into 10 zones: [1.83, 1.954], (1.954, 2.078], (2.078, 2.202], (2.202, 2.326], (2.326, 2.45], (2.45, 2.574], (2.574, 2.698], (2.698, 2.822], (2.822, 2.946], and (2.946, 3.07]. At the same time, the 266.7Hz to 366.7Hz range is divided into 10 frequency zones corresponding to the pressure ratio range, with each zone having a frequency range of 10Hz. Only one surge point is retained in each zone.

[0083] S3. Detect the surge point of the centrifugal compressor;

[0084] S4. Determine if a surge point has already been recorded within the frequency range containing the surge point. If so, remove one surge point from the frequency range, keeping only one surge point per frequency range; otherwise, record the surge point. and , This refers to the discharge pressure of the centrifugal compressor. This refers to the suction pressure of the centrifugal compressor. Calculate the pressure ratio for the frequency. ;

[0085] More specifically, continuous monitoring of the centrifugal compressor during operation. , and , The discharge pressure of the centrifugal compressor is used to determine whether the centrifugal compressor is experiencing surge. If no surge occurs, the detection continues. If surge occurs, it is determined whether a surge point has already been recorded within the frequency range containing the surge point. If so, one surge point within that frequency range is removed, and only one surge point is retained per frequency range. Otherwise, the surge point is recorded. and ;

[0086] S5. Determine if there is a surge point in at least m frequency intervals. If not, return to step S3 to continue the detection; if enough, perform curve fitting to establish a surge line.

[0087] The online method for establishing the surge line of the centrifugal compressor also includes S5, which involves determining the actual pressure ratio of the centrifugal compressor during operation. and frequency If the corresponding operating point is to the right of the surge line, the centrifugal compressor will operate normally; if it is to the left, the operating frequency of the centrifugal compressor will be increased.

[0088] In step S5, when the number of recorded surge points is less than m, the zone containing the surge point is protected by operating condition protection. The protection method is as follows:

[0089] Let the pressure ratio at the surge point be... , frequency is The pressure ratio range where the surge point is located is The protection frequency range is Lower limit of protection frequency range , The width of the frequency range; the upper limit of the protected frequency range. When the actual operating pressure ratio of the centrifugal compressor is The protection frequency of the centrifugal compressor Where η represents the deviation. That is, when the actual working pressure ratio is... The minimum operating frequency of a centrifugal compressor should not be lower than H, otherwise surge will easily occur.

[0090] For example: the pressure ratio at the surge point is =2.01, frequency is Hz, the pressure ratio range where the surge point is located is Lower limit of protection frequency range The width of the frequency range is 10Hz; the upper limit of the protection frequency range. When the actual operating pressure ratio of the centrifugal compressor is The protection frequency of the centrifugal compressor ,in, This indicates a deviation. That is, when the actual working pressure ratio is... The minimum operating frequency of a centrifugal compressor should not be lower than H, otherwise surge will easily occur.

[0091] In step S5, the least squares method is used to perform nonlinear equation regression to obtain the surge line equation. The equation regression method is as follows:

[0092] Suppose that the nonlinear equation can be expressed by a polynomial, as in equation (1):

[0093] (1)

[0094] Then, based on the principle of least squares, the coefficients are calculated. Make error Minimum, error The calculation formula is as shown in equation (2):

[0095] (2)

[0096] Where: y is the dependent variable, representing the minimum operating frequency value;

[0097] is the independent variable, representing the pressure ratio;

[0098] It is a function;

[0099] These are the polynomial coefficients;

[0100] m is the number of surge points;

[0101] n is the highest order of the polynomial;

[0102] Indicates which data point is being analyzed;

[0103] The nonlinear regression problem is transformed into an extremum problem. Equation (2) is then applied to... Taking the partial derivative and setting it to 0, we get equation (3):

[0104]

[0105]

[0106]

[0107]

[0108] Arrange equation (3) to obtain the matrix form as shown in equation (4):

[0109] (4)

[0110] Further simplified to equation (5):

[0111] (5)

[0112] in:

[0113] , ,

[0114] At the same time, it can be found Since it is a symmetric positive definite matrix, according to the Cholesky decomposition method, we can obtain equation (6):

[0115] (6)

[0116] in:

[0117]

[0118] in Representative matrix The value in the nth row and nth column;

[0119] From equations (5) and (6), we obtain equation (7):

[0120] (7)

[0121] Then calculate the matrix. inverse matrix sum matrix inverse matrix Thus, we obtain equation (8).

[0122] (8)

[0123] The final coefficients are obtained The value of .

[0124] Determination of the value: Since different devices have different surge properties, the order of the optimal regression equation may also be different. Considering the PLC's computing power and the accuracy of Lreal data, this method will... The maximum value is set to 6, therefore nonlinear regression needs to start from... The optimal order solution is obtained by finding the solution.

[0125] when The corresponding coefficients can be calculated at each time. Values, and substitute the coefficients into ) 2 Find the smallest one. The value corresponding to the value of n The value is the coefficient of the final surge line. This is the highest order of the surge line.

[0126] like Figure 3 As shown, in step S3, the centrifugal compressor system further includes a frequency converter for controlling the operation of the centrifugal compressor and a pipeline network connected to the centrifugal compressor; the centrifugal compressor includes an inlet guide vane, the pipeline network is provided with a bypass valve, and also includes a frequency converter input power detection device. The method for detecting the surge point of the centrifugal compressor is as follows;

[0127] S31. Continuously measure the input power of the frequency converter within a set period using an input power detection device. ,in Find the standard deviation of the power change for any positive integer greater than or equal to 1. If the standard deviation over a period of time The absolute value is less than or equal to the surge judgment setting value. Then continue to detect the input power of the frequency converter. If the standard deviation within one cycle is... The absolute value is greater than the surge judgment setting value. If so, continue executing S32;

[0128] S32. Determine if the issue is caused by changes in the active load. Changes in the active load include changes in the inverter frequency, the inlet guide vane opening, and the bypass valve opening. If not, proceed to S33; otherwise, continue execution.

[0129] S32.1 Determine if the change is caused by a change in the set frequency. If so, wait for the frequency change response time. Then, if S31 is executed and the frequency is increasing, the response time for the frequency change will be... To speed up host response time, If the frequency is decreasing, the response time to the frequency change is... For host deceleration response time, ,in, This is the maximum frequency of the inverter. To speed up the process, For deceleration time, For the increase in frequency, The frequency decrease is [amount], and the duration of the power feedback fluctuation caused by the frequency change is [duration]. If the issue is not caused by a change in the set frequency, then continue executing S32.2.

[0130] S32.2 Determine if the change is caused by a change in the inlet guide vane opening. If so, wait for the inlet guide vane response time. Then execute S31, inlet guide vane response time , For the full stroke time of the inlet guide vane, The change in inlet guide vane opening is [value], and the duration of the power feedback fluctuation caused by the change in inlet guide vane opening is [value]. If not, then execute S32.3;

[0131] S32.3 is caused by changes in the bypass valve opening; wait for the bypass valve to respond. S31 is executed subsequently; bypass valve response time , This refers to the full stroke time of the bypass valve. The change in bypass valve opening is the duration of the power feedback fluctuation caused by the change in bypass valve opening. .

[0132] It should be noted that since changes in the frequency of the inverter, the opening of the inlet guide vane, and the opening of the bypass valve can also cause power feedback fluctuations, when the system experiences the above-mentioned active load changes, power feedback detection should be performed after a certain response time to determine whether surge has occurred, so as to avoid false alarms from the equipment.

[0133] S33. Determine whether the power fluctuation is caused by passive load changes: When the load increases, a correlation coefficient r ≥ 0.8 indicates a positive high correlation, while when the load decreases, a correlation coefficient r ≤ -0.8 indicates a negative high correlation. When a centrifugal compressor experiences surge, the inverter's input power will change periodically. If the absolute value of the power standard deviation s within one cycle is greater than the surge judgment setting value Q, and the correlation coefficient r first shows a negative high correlation and then a positive high correlation, then it is determined that the centrifugal compressor has experienced a surge. Record the inverter's frequency and the ratio of the centrifugal compressor's suction pressure to discharge pressure during the surge, and continue executing S31. If the absolute value of the standard deviation s is greater than the surge judgment setting value Q, and the correlation coefficient does not show a negative high correlation followed by a positive high correlation, then it is considered to be caused by passive load changes, and continue executing S31.

[0134] During surge, the power characteristics of the inverter fluctuate periodically, with the periodicity and power standard deviation varying with the severity of the surge. Mild surges have longer surge cycles and smaller power standard deviations, while severe surges have shorter surge cycles and larger power standard deviations. Therefore, the surge intensity judgment in this invention is determined by the standard deviation and the surge cycle. A strong correlation coefficient that is initially negative and then positive indicates surge. If this pattern is not observed, it is considered to be caused by passive load. Passive load-induced surges may only show a positive or negative correlation coefficient, and the correlation coefficient may not reach 0.8. Therefore, the standard deviation will be greater than the set value. As long as the initial negative-then-positive pattern is not observed, it is considered to be caused by passive load changes.

[0135] Furthermore, when the load remains constant, it will not cause changes in the power standard deviation and correlation coefficient, thus avoiding false surge predictions. The speed of active load adjustment is determined by the setter and may be very fast, adjusting every few seconds or tens of seconds; however, passive load fluctuations in the system will not be as frequent.

[0136] The formula for calculating the standard deviation s is as follows:

[0137]

[0138] in, Here is the number of samples, and the sample mean is: , This is a power sample.

[0139] The formula for calculating the correlation coefficient r is as follows:

[0140]

[0141] in, for The time sample corresponding to the power sample, and .

[0142] The correlation coefficient changes from -1 to +1, when This indicates that the two variables are positively correlated, meaning that the larger the value of one variable is, the larger the value of the other variable will also be. This indicates that the two variables are negatively correlated, meaning that the larger the value of one variable is, the smaller the value of the other variable will be. The larger the absolute value of the coefficient, the stronger the correlation between the two variables. It is generally believed that... There is a significant correlation. Highly correlated The correlation is moderate. Low correlation The relationship is extremely weak; it is considered unrelated.

[0143] The standard deviation and correlation coefficient of the inverter input power change are used to determine whether a centrifugal compressor has experienced surge. However, since changes in active and passive loads can also cause changes in the power standard deviation and correlation coefficient, in order to avoid system misjudgment, the characteristics of active and passive load changes are analyzed and eliminated in the surge change judgment to ensure the accuracy of surge judgment.

[0144] This invention enables real-time detection and establishment of surge lines during the operation of centrifugal compressors, thereby accurately predicting and preventing surge phenomena. By using this online establishment method, centrifugal compressors can operate more stably and their operating range can be broadened. This not only improves the efficiency and performance of centrifugal compressors but also extends their service life. Furthermore, since this online establishment method can be tested and verified during actual operation, it saves factories money and time on testing and experimentation, thus improving production efficiency.

[0145] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for online establishment of a surge line in a centrifugal compressor, comprising a centrifugal compressor system, wherein the centrifugal compressor system includes a centrifugal compressor, characterized in that, The online method for establishing surge lines includes the following steps: S1. Start the centrifugal compressor; S2. Establish partitions, dividing the operating frequency range of the centrifugal compressor into... The operating voltage ratio range is divided into several frequency intervals. Each pressure ratio range The frequency ranges and Each of the aforementioned pressure ratio ranges corresponds one-to-one; S3. Detect the surge point of the centrifugal compressor; S4. Determine if a surge point has already been recorded within the frequency range containing the surge point. If so, remove one surge point from the frequency range, keeping only one surge point in each frequency range; otherwise, record the surge point. , and , This refers to the discharge pressure of the centrifugal compressor. This refers to the suction pressure of the centrifugal compressor. Calculate the pressure ratio for the frequency. ; S5, Determine at least Each frequency range has a surge point. If not enough, return to step S3 to continue the detection; if enough, use the recorded surge points to perform curve fitting and establish a surge line. In step S3, the centrifugal compressor system further includes a frequency converter for controlling the operation of the centrifugal compressor and a pipeline network connected to the centrifugal compressor; the centrifugal compressor includes an inlet guide vane, the pipeline network is provided with a bypass valve, and the system also includes a frequency converter input power detection device. The surge point detection method of the centrifugal compressor is as follows; S31. Continuously measure the input power of the frequency converter within a set period using the frequency converter input power detection device. ,in The input power of the inverter is calculated as a positive integer greater than or equal to 1. If the absolute value of the standard deviation s within one cycle is less than or equal to the surge judgment setpoint Q, the input power of the inverter is continuously monitored. If the absolute value of the standard deviation s within one cycle is greater than the surge judgment setpoint Q, the process continues to execute S32. S32. Determine if the issue is caused by changes in active load. If not, proceed to S33. If so, continue execution. S32.1 Determine whether the change is caused by a change in the set frequency. If so, execute S31 after the frequency change response time TF. If not, continue to execute S32.

2. S32.2 Determine whether the change is caused by the inlet guide vane opening. If so, execute S31 after the inlet guide vane response time TR. If not, execute S32.

3. S32.3 is caused by a change in the opening degree of the bypass valve. S31 will be executed after the bypass valve response time Tb. S33. Determine whether the power fluctuation is caused by passive load changes: When the load increases, a correlation coefficient r ≥ 0.8 indicates a positive high correlation, while when the load decreases, a correlation coefficient r ≤ -0.8 indicates a negative high correlation. When the absolute value of the power standard deviation s within a cycle is greater than the surge judgment setting value Q, and the correlation coefficient r first shows a negative high correlation and then a positive high correlation, then it is determined that the centrifugal compressor has experienced a surge, the surge point is recorded, and S31 continues to be executed; when the absolute value of the standard deviation s is greater than the surge judgment setting value Q, and the correlation coefficient does not show a negative high correlation followed by a positive high correlation, then it is considered to be caused by passive load changes, and S31 continues to be executed.

2. The online method for establishing the surge line of a centrifugal compressor according to claim 1, characterized in that, It also includes S6, the actual operating pressure ratio of the centrifugal compressor during operation. and frequency If the corresponding operating point is to the right of the surge line, the centrifugal compressor will operate normally; if it is to the left, the operating frequency of the centrifugal compressor will be increased by the frequency converter.

3. The online method for establishing the surge line of a centrifugal compressor according to claim 1, characterized in that, In step S5, when the number of recorded surge points is less than At that time, the zone where the surge point is located is protected by the following operating point protection method: Let the pressure ratio at the surge point be... The frequency is The surge point is located in the pressure ratio range (a, b], which is the lower limit of the protection frequency range. , The width of the frequency range; the upper limit of the protected frequency range. ; When the actual operating pressure ratio of the centrifugal compressor is The protection frequency of the centrifugal compressor is then... ,in, Indicates deviation.

4. The online method for establishing the surge line of a centrifugal compressor according to claim 1, characterized in that, In step S5, the surge line is established by curve fitting using the recorded surge points as follows: The least squares method is used to perform nonlinear equation regression to establish the surge line equation. The nonlinear equation is expressed by a polynomial, as shown in equation (1): （1） Then, based on the principle of least squares, the coefficients are calculated. Make error Minimum, error The calculation formula is as shown in equation (2): （2） in: The dependent variable represents the minimum operating frequency value; is the independent variable, representing the pressure ratio; It is a function; These are the polynomial coefficients; m is the number of surge points; It is the highest order of the polynomial; Indicates which data point is being analyzed; The nonlinear regression problem is transformed into an extremum problem. Equation (2) is then applied to... Taking the partial derivative and setting it to 0, we get equation (3): Arrange equation (3) to obtain the matrix form as shown in equation (4): （4） Further simplified to equation (5): （5） in: ， ， At the same time, it can be found Since it is a symmetric positive definite matrix, according to the Cholesky decomposition method, we can obtain equation (6): （6） in: in Representative matrix The value in the nth row and nth column; From equations (5) and (6), we obtain equation (7): （7） Then calculate the matrix. inverse matrix sum matrix inverse matrix Thus, we obtain equation (8). （8） The final coefficients are obtained The value of .

5. The online method for establishing the surge line of a centrifugal compressor according to claim 4, characterized in that, n is a positive integer less than or equal to 6.

6. The method for online establishment of surge lines in a centrifugal compressor according to claim 1, characterized in that, In step S2, the operating frequency of the centrifugal compressor is divided into G frequency intervals of equal width.

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