Cavitation detection system

Abstract

The invention provides a cavitation detection system which is used for detecting the net positive suction head of a pump. The cavitation detection system comprises a frequency converter, a pressure gauge group, a flow estimation unit, a selector and a cavitation detection unit. The frequency converter is configured to control a motor of the pump based on the rotation information to drive the pump to operate. The pressure gauge group is configured to obtain pressure information of the pump. The flow estimation unit comprises a plurality of estimation modules which are respectively used for executing different flow estimation schemes to obtain flow information related to the pump. The selector is connected with the flow estimation unit and is configured to select one of the estimation modules so as to obtain the flow information corresponding to the selected estimation module. The cavitation detection unit is configured to calculate the net positive suction head of the pump based on the rotation information, the pressure information and the flow information so as to detect the cavitation state of the pump.

Description

Technical Field

[0001] The present application relates to the technical field of pump testing, and in particular to a pump cavitation detection system. Background Art

[0002] When cavitation occurs in a pump, it will affect the normal operation of the pump and cause many serious consequences, such as vibration and noise from the pump body, accelerated damage to metal materials, shortened service life, and reduced flow and head of the pump. In severe cases, the pump may even be cut off and cannot operate normally. In order to avoid cavitation, cavitation detection must be performed when the pump is running to estimate the current cavitation margin of the system, and the cavitation detection technology needs to be implemented based on the current pipeline flow. However, in the prior art, the current pipeline flow is obtained by installing a flow meter in the system. For small fluid supply systems, the installation of a flow meter will significantly increase costs, making it difficult for users to accept and reducing the market competitiveness of the product.

[0003] In view of this, it is necessary to provide a cavitation detection system to solve the above technical problems. Summary of the invention

[0004] In order to solve the above-mentioned problems of the prior art, the purpose of the present application is to provide a cavitation detection system, which can realize the flow estimation of the pump without installing a flow meter, thereby reducing the manufacturing cost of the overall system.

[0005] The present application provides a cavitation detection system for detecting the cavitation margin of a pump, the cavitation detection system comprising: a frequency converter, a pressure gauge group, a flow estimation unit, a selector and a cavitation detection unit. The frequency converter is electrically connected to a motor of the pump and is configured to control the motor based on a rotation information to drive the pump to operate. The pressure gauge group is configured to obtain a pressure information of the pump. The flow estimation unit is electrically connected to the frequency converter and the pressure gauge group and is configured to obtain the rotation information and the pressure information, wherein the flow estimation unit comprises a plurality of estimation modules, the estimation modules are respectively used to execute different flow estimation schemes, and each of the estimation modules is configured to execute the corresponding flow estimation scheme based on the rotation information and / or the pressure information to obtain a flow information related to the pump. The selector is connected to the flow estimation unit and is configured to select one of the estimation modules based on the rotation information, the pressure information and a state information of the pump to obtain the flow information corresponding to the selected estimation module. The cavitation detection unit is electrically connected to the frequency converter, the pressure gauge group and the selector, and is configured to calculate the cavitation margin of the pump based on the rotation information, the pressure information and the flow information to detect the cavitation state of the pump.

[0006] In some embodiments, the selector is disposed between the flow estimation unit and the cavitation detection unit, and the flow estimation unit controls the selector to enable or disable the estimation modules.

[0007] In some embodiments, the estimation modules include a flow-lift estimation unit configured to obtain the corresponding flow information according to lift information.

[0008] In some embodiments, the flow head estimation unit is configured to obtain a height difference of the pressure gauge group and obtain a pressure difference according to the pressure information, and the flow head estimation unit obtains an actual head according to the height difference and the pressure difference.

[0009] In some embodiments, the rotation information includes a rotation speed information, and the flow head estimation unit is further configured to obtain a rated head according to the actual head and the rotation speed information, and obtain the flow corresponding to the rated head based on a first lookup table to obtain the flow information.

[0010] In some embodiments, the first lookup table is based on a relationship table between flow rate and head established at rated speed.

[0011] In some embodiments, the pressure gauge group includes a first pressure gauge and a second pressure gauge; the first pressure gauge is arranged at an inlet of the pump, configured to obtain an inlet pressure of the pump; and the second pressure gauge is arranged at an outlet of the pump, configured to obtain an outlet pressure of the pump, wherein the flow head estimation unit obtains the pressure difference according to the inlet pressure and the outlet pressure, and obtains the height difference according to the height information of the first pressure gauge and the second pressure gauge.

[0012] In some embodiments, the estimation modules include a flow rate power estimation unit configured to obtain the corresponding flow rate information according to the rotation information.

[0013] In some embodiments, the rotation information includes a speed information and a torque information, the flow power estimation unit is configured to obtain an actual shaft power based on the speed information and the torque information, and to obtain a rated shaft power based on the actual shaft power, and the flow power estimation unit is also configured to obtain the flow corresponding to the rated shaft power based on a second lookup table and thereby obtain the flow information.

[0014] In some embodiments, the second lookup table is based on a relationship table between flow rate and shaft work established at rated speed.

[0015] In some embodiments, the estimation modules include a hybrid estimation unit, configured to obtain a corresponding first flow information based on a head information and a corresponding second flow information based on the rotation information, and also configured to compare the first flow information and the second flow information with a preset flow to determine to use the first flow information or the second flow information as the flow information.

[0016] In some embodiments, when the first flow information and the second flow information are greater than the preset flow, the estimation modules use the first flow information as the flow information, and when the first flow information and the second flow information are less than the preset flow, the estimation modules use the second flow information as the flow information.

[0017] In some embodiments, the rotation information includes rotation speed information, and the estimation modules include a flow system curve estimation unit configured to obtain the flow information from the rotation speed information based on a relationship curve.

[0018] In some embodiments, the rotation information includes torque information, the relationship curve is a shaft power flow correspondence curve, and the flow system curve estimation unit obtains a shaft power information based on the speed information and the torque information, and obtains the flow corresponding to the shaft power information based on the shaft power flow correspondence curve, thereby obtaining the flow information.

[0019] In some embodiments, the shaft power flow rate corresponding curve is a curve established by obtaining flow rates at different rotation speeds through a flow meter.

[0020] In some embodiments, the relationship curve is a pressure-flow correspondence curve, and the flow system curve estimation unit obtains the flow corresponding to the pressure information based on the pressure-flow correspondence curve, thereby obtaining the flow information.

[0021] In some embodiments, the pressure gauge group includes: a first pressure gauge and a second pressure gauge. The first pressure gauge is disposed at an inlet of the pump and configured to obtain an inlet pressure of the pump. The second pressure gauge is disposed at an outlet of the pump and configured to obtain an outlet pressure of the pump. The flow system curve estimation unit obtains the pressure difference according to the inlet pressure and the outlet pressure, and obtains the flow corresponding to the pressure difference based on the pressure-flow correspondence curve as the flow information.

[0022] In some embodiments, the pressure-flow curve is a curve established by obtaining flow rates under different pressure differences through a flow meter.

[0023] In some embodiments, the cavitation detection unit is configured to obtain an actual cavitation margin based on the flow information, and the cavitation detection unit is further configured to obtain an effective cavitation margin based on the pressure information, the flow information, the current atmospheric pressure and the saturated air pressure, and the cavitation detection unit is further configured to obtain the cavitation state of the pump based on the actual cavitation margin and the effective cavitation margin.

[0024] In some embodiments, the cavitation detection system further includes an alarm unit connected to the cavitation detection unit, and the alarm unit is configured to issue an alarm message based on the cavitation state of the pump.

[0025] Compared to the prior art, the present application provides a cavitation detection system, which executes corresponding flow estimation schemes through the estimation modules of the flow estimation unit to obtain flow information related to the pump, without the need to set up a fixed flow meter in the cavitation detection system, thereby reducing manufacturing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A schematic diagram showing a cavitation detection system according to an embodiment of the present application;

[0027] Figure 2 A block diagram showing a control system of an embodiment of the present application;

[0028] Figure 3A A block diagram showing a flow head estimation unit according to an embodiment of the present application;

[0029] Figure 3B A flow chart showing a flow head estimation scheme of an embodiment of the present application;

[0030] Figure 4A A block diagram showing a flow power estimation unit according to an embodiment of the present application;

[0031] Figure 4B A flow chart showing a flow power estimation scheme of an embodiment of the present application;

[0032] Figure 5A A block diagram showing a hybrid estimation unit according to an embodiment of the present application;

[0033] Figure 5B A flow chart showing a hybrid estimation scheme of an embodiment of the present application;

[0034] Fig. 6A A block diagram showing a flow system curve estimation unit according to an embodiment of the present application;

[0035] Figure 6B A flow chart showing a flow system curve estimation solution of a first example of the present application;

[0036] Figure 6CA flow chart showing a flow system curve estimation solution of a second example of the present application.

[0037] Description of reference numerals:

[0038] 10…Cavitation detection system

[0039] 11…Inverter

[0040] 12…Controller

[0041] 121…Processor

[0042] 122…Memory

[0043] 123…Control System

[0044] 124…Database

[0045] 20…Pump

[0046] 21…Motor

[0047] 31…Flow estimation unit

[0048] 311…First estimation module

[0049] 312…Second estimation module

[0050] 313…Third estimation module

[0051] 314…Fourth estimation module

[0052] 32…Selector

[0053] 33…Cavitation detection unit

[0054] 34…Alarm unit

[0055] P1…First pressure gauge

[0056] P2…Second pressure gauge

[0057] Z1, Z2…Height

[0058] S31~S36, S41~S45, S51~S54, S61~S64, S71~S74...steps DETAILED DESCRIPTION

[0059] In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the preferred embodiments of the present application will be specifically cited below and described in detail in conjunction with the accompanying drawings of the specification as follows.

[0060] Please refer to Figure 1, which shows a schematic diagram of a cavitation detection system according to an embodiment of the present application. The cavitation detection system 10 is connected to a pump 20 and a motor 21. The motor 21 is connected to the pump 20 to drive the pump 20 to operate. The cavitation detection system 10 is used to detect the cavitation margin of the pump 20.

[0061] like Figure 1 As shown, the pump 20 includes an inlet and an outlet. It should be understood that when the pump 20 is running, the liquid pressure decreases along the inlet of the pump 20 to the impeller inlet. Usually, the pressure at the impeller inlet is relatively low. However, when the pressure there is reduced to the saturated vapor pressure at the corresponding temperature, part of the liquid will be vaporized to form a large number of bubbles. After these bubbles enter the impeller with the liquid, the pressure of the liquid outside is higher than the vaporization pressure inside the bubbles due to the increase in pressure, and the bubbles condense and collapse again to form holes. The surrounding liquid rushes to the hole at a high speed, causing the liquid to collide with each other, causing the local pressure to increase suddenly. If these bubbles collapse near the impeller wall, the liquid will continuously hit the metal surface of the impeller in a high-frequency and high-pressure manner, causing the metal surface to peel due to impact fatigue. Furthermore, when the liquid condenses from the gas phase to the liquid phase, a large amount of heat will be released, causing electrochemical corrosion to the metal, accelerating the rate of damage by metal stripping. The above-mentioned combined phenomenon of mechanical fracturing and electrochemical corrosion damage of the metal materials of the pump body and impeller 20 caused by the generation and condensation of bubbles is called cavitation. In order to avoid the occurrence of cavitation, cavitation detection must be performed when the pump 20 is running to estimate the current cavitation margin of the system, wherein the cavitation detection technology needs to be implemented based on the current pipeline flow. However, in the prior art, the current pipeline flow is obtained by installing a flow meter in the system. For small fluid supply systems, the installation of a flow meter will significantly increase the cost. In order to avoid the higher manufacturing cost caused by the installation of a flow meter, the present application realizes the flow estimation of the pump 20 through the cavitation detection system 10 without the installation of a flow meter, as described below.

[0062] like Figure 1As shown, the cavitation detection system 10 includes a frequency converter 11, a pressure gauge group and a controller 12. The frequency converter 11 is electrically connected to the motor 21 controlling the pump 20, and is configured to control the motor 21 based on the rotation information to drive the pump 20 to operate, wherein the rotation information includes the speed information and the torque information. The pressure gauge group is configured to obtain the pressure information of the pump 20. Specifically, the pressure gauge group includes a first pressure gauge P1 and a second pressure gauge P2, wherein the first pressure gauge P1 is arranged at the inlet of the pump 20, and is configured to obtain the inlet pressure of the pump 20, and the second pressure gauge P2 is arranged at the outlet of the pump 20, and is configured to obtain the outlet pressure of the pump 20. The controller 12 is electrically connected to the frequency converter 11 and the pressure gauge group, and includes a processor 121, a memory 122, a control system 123 and a database 124. The memory 122 is configured to store computer programs, and the operations related to cavitation detection can be compiled into computer programs and stored in the memory 122. The processor 121 reads the computer programs stored in the memory 122 and runs programs corresponding to these computer programs so that the control system 123 performs operations related to cavitation detection. The database 124 is configured to store information related to cavitation detection. In practical applications, the controller 12 is, for example, a programmable logic controller (PLC), an industrial computer, a tablet computer, a smart phone, etc.

[0063] In the present embodiment, the processor 121 is generally configured to control the overall operation of the cavitation detection system 10. The processor 121 includes one or more processors to execute instructions and perform actions in all or part of the steps in the cavitation detection process. In addition, the processor 121 includes one or more modules that facilitate the interaction between the processor 121 and other components. For example, the processor 121 includes a communication module to facilitate the interaction between the communication component and the processor 121. The memory 122 is configured to store various types of data to support the operation of the cavitation detection system 10. Such data, for example, includes instructions for any application or method operating on the cavitation detection system 10. The memory 122 can be implemented using any type of volatile or non-volatile memory device or a combination thereof. The cavitation detection system 10 may also include one or more of the following components: a circuit board, a power supply circuit, etc. The power supply circuit supplies power to various components of the cavitation detection system 10. The power supply circuit may include a power management system, one or more power supplies, and any other components associated with the generation, management, and distribution of power for the cavitation detection system 10. In an exemplary embodiment, the cavitation detection system 10 may be implemented by an independent terminal device or an integrated controller, microcontroller, or other electronic component.

[0064] Please refer to Figure 1 and Figure 2 , Figure 2A block diagram of a control system according to an embodiment of the present application is shown. The control system 123 includes a flow estimation unit 31 , a selector 32 , a cavitation detection unit 33 and an alarm unit 34 .

[0065] In this embodiment, the flow estimation unit 31 is electrically connected to the frequency converter 11 and the pressure gauge group, and is configured to obtain rotation information and pressure information. Figure 2 As shown, the flow estimation unit 31 includes a plurality of estimation modules. For example, in the present embodiment, the flow estimation unit 31 includes four estimation modules, such as a first estimation module 311, a second estimation module 312, a third estimation module 313 and a fourth estimation module 314, but the present application is not limited thereto. In some embodiments, the flow estimation unit 31 optionally includes two or three of the above four estimation modules 311-314. In some embodiments, the flow estimation unit 31 optionally includes more than four estimation modules. These estimation modules 311-314 are respectively used to execute different flow estimation schemes. Each estimation module configuration 311-314 is to execute a corresponding flow estimation scheme based on rotation information and / or pressure information to obtain flow information related to the pump 20.

[0066] Optionally, the first estimation module 311 includes a flow head estimation unit configured to execute a flow head estimation scheme, and then obtain corresponding flow information according to the head information. Figure 3A and Figure 3B , Figure 3A A block diagram showing a flow head estimation unit according to an embodiment of the present application, and Figure 3B The flow chart of the flow head estimation scheme of the embodiment of the present application is shown. The specific implementation of the flow head estimation scheme is as follows.

[0067] like Figure 3A and Figure 3B As shown, first, in step S31, the flow head estimation unit is configured to obtain the height difference of the pressure gauge group. Figure 1 As shown, the height of the first pressure gauge P1 is Z1, and the height of the second pressure gauge P2 is Z2, wherein the height difference is Z2-Z1. Optionally, the heights Z1 and Z2 can be obtained by a distance sensor and pre-written into the database 124 of the controller 12.

[0068] like Figure 3A and Figure 3B As shown, in step S32, the flow head estimation unit is configured to obtain the gauge pressure of the above-mentioned pressure gauge group, such as obtaining the gauge pressure of the first pressure gauge P1 and the gauge pressure of the second pressure gauge P2.

[0069] like Figure 3A As shown, the flow head estimation unit includes an actual head calculation module. Figure 3BAs shown, in step S33, the actual head calculation module of the flow head estimation unit is configured to obtain the pressure difference according to the pressure information, and to obtain the actual head according to the height difference and pressure difference of the pressure gauge group. In this embodiment, the calculation formula of the actual head is: H Act =H Lif t+H Sense +H Velocity , where H Act is the actual head of the system, H Lift is the height difference of the pressure gauge group, H Sense is the pressure difference between the two ends, and H Velocity As mentioned above, the height of the first pressure gauge P1 is Z1, and the height of the second pressure gauge P2 is Z2, where H Lif t=Z2-Z1.

[0070] In this embodiment, H Sense The calculation formula is: Where P M1 is the gauge pressure of the first pressure gauge P1, P M2 is the gauge pressure of the second pressure gauge P2, ρ is the liquid density, and g is the gravitational acceleration.

[0071] In this embodiment, H Velocity The calculation formula is: V outlet is the flow rate at the outlet of the pump 20, and V inlet is the flow rate at the outlet of the pump 20. It should be understood that V outlet With V inlet The dynamic pressure is related to the cross-sectional area of ​​the outlet and inlet diameters. When the two diameters are the same, the dynamic pressure is 0. In addition, in the present application, the dynamic pressure is preset to 0 during the first iterative operation. Moreover, after obtaining the numerical value of the actual head, the flow information can be estimated (described in detail later). The calculated flow value is divided by the cross-sectional area of ​​the outlet and inlet diameters, respectively, to obtain the flow rate of the outlet and inlet. The obtained value can be brought into the next iterative operation to obtain the dynamic pressure during the iterative operation. Optionally, the outlet and inlet diameters of the pump 20 can be obtained by a distance sensor and written into the database 124 of the controller 12 in advance.

[0072] like Figure 3A As shown, the flow head estimation unit includes a rated head conversion module. Figure 3B As shown, in step S34, after obtaining the actual head, the rated head conversion module of the flow head estimation unit is further configured to obtain the rated head according to the actual head and the speed information of the motor 21 controlled by the inverter 11, wherein the speed information is the actual speed of the motor.

[0073] In this embodiment, the calculation formula for the rated lift is: Among them, H Rated is the rated head, N Rated is the rated speed of the motor 21, N Act is the actual speed of the motor 21. "Rated" refers to the factory preset / theoretical performance value of the pump 20, which can be obtained from a performance curve diagram related to the pump 20 provided by the manufacturer, and the performance curve can be stored in the database 124 of the controller 12 in the form of a lookup table or the like. In this embodiment, the rated speed of the motor 21 can be found by the frequency of the inverter 11.

[0074] like Figure 3A As shown, the flow head estimation unit includes a rated flow search module. Figure 3B As shown, in step S35, after obtaining the actual head, the flow head estimation unit is further configured to obtain the rated flow corresponding to the rated head at the rated speed based on the first lookup table. It should be noted that the first lookup table is a relationship table between the flow and the head established at the rated speed. Optionally, the first lookup table is stored in the database 124 of the controller 12.

[0075] like Figure 3A As shown, the flow head estimation unit includes an actual flow calculation module. Figure 3B As shown, in step S36, after obtaining the rated flow, the flow head estimation unit is further configured to calculate the actual flow according to the rated flow. The calculation formula of the actual flow is: Where Q Act is the actual flow rate, and Q Rated In this embodiment, the flow information of the pump obtained when executing the flow head estimation scheme includes the rated flow and the actual flow.

[0076] like Figure 3A As shown, after obtaining the flow information of the current iterative calculation, the flow information can be input into the actual head calculation module to bring the flow information into the next iterative calculation to obtain the dynamic pressure during the iterative calculation.

[0077] Optionally, the second estimation module 312 includes a flow power estimation unit configured to execute a flow power estimation scheme, thereby obtaining corresponding flow information according to the rotation information. Figure 4A and Figure 4B , Figure 4A A block diagram showing a flow power estimation unit according to an embodiment of the present application, and Figure 4B The flowchart of the flow power estimation solution of the embodiment of the present application is shown. The specific implementation of the flow power estimation solution is as follows.

[0078] like Figure 4A and Figure 4BAs shown, first, in step S41, the flow power estimation unit is configured to obtain rotation information from the inverter 11, wherein the rotation information includes rotation speed information and torque information.

[0079] like Figure 4A As shown in FIG. 1 , the flow head estimation unit includes a shaft power calculation and conversion module. Figure 4B As shown, in step S42, the shaft work calculation module of the flow power estimation unit is configured to calculate the actual shaft work according to the speed information and the torque information, wherein the speed information and the torque information are the actual speed and the actual torque of the motor respectively. The actual shaft work is obtained according to the known shaft work calculation formula, which will not be described in detail here.

[0080] like Figure 4B As shown, in step S43, the shaft power calculation module of the flow power estimation unit is further configured to obtain the rated shaft power according to the actual shaft power. In this embodiment, the calculation formula of the rated shaft power is: Where P Rated is the rated shaft power and P Act is the actual shaft work, N Rated is the rated speed of the motor 21, N Act is the actual rotation speed of the motor 21.

[0081] like Figure 4A As shown, the flow power estimation unit includes a rated flow search module. Figure 4B As shown, in step S44, after obtaining the rated shaft power, the flow power estimation unit is further configured to obtain the rated flow corresponding to the rated shaft power at the rated speed based on the second lookup table. The second lookup table is a relationship table between the flow and the shaft power established at the rated speed. Optionally, the second lookup table is stored in the database 124 of the controller 12.

[0082] like Figure 4A As shown, the flow power estimation unit includes an actual flow calculation module. Figure 4B As shown, in step S45, after obtaining the rated flow, the flow power estimation unit is further configured to calculate the actual flow according to the rated flow. The calculation formula of the actual flow is: Where Q Act is the actual flow rate, and Q Rated In this embodiment, the flow information of the pump obtained when executing the flow head estimation scheme includes the rated flow and the actual flow.

[0083] Optionally, the third estimation module 313 includes a hybrid estimation unit configured to execute a hybrid estimation scheme, thereby determining whether to obtain the flow information of the pump according to the head information or the rotation information. Figure 5A and Figure 5B , Figure 5AA block diagram showing a hybrid estimation unit according to an embodiment of the present application, and Figure 5B A flow chart showing a hybrid estimation scheme of an embodiment of the present application. In this embodiment, the rotation information includes speed information and torque information, which can be obtained through the frequency converter 11. The specific implementation of the hybrid estimation scheme is as follows.

[0084] like Figure 5A and Figure 5B As shown, first, in step S51, the hybrid estimation unit is configured to obtain corresponding first flow information according to the head information, wherein the method for obtaining the first flow information can be implemented by executing the flow head estimation scheme according to the above-mentioned flow head estimation unit, which is not elaborated here.

[0085] like Figure 5A and Figure 5B As shown, secondly, in step S52, the hybrid estimation unit is further configured to obtain corresponding second flow information according to the rotation information, wherein the method for obtaining the second flow information can be implemented according to the above-mentioned flow power estimation unit executing the flow power estimation scheme, which is not described in detail here. It should be understood that the order of step S51 and step S52 can be interchanged, and is not limited to this.

[0086] like Figure 5A As shown in FIG. 1 , the hybrid estimation unit also includes a comparison module. Figure 5B As shown, in step S53, after obtaining the first flow information and the second flow information, the comparison module of the hybrid estimation unit is further configured to compare the first flow information and the second flow information with a preset flow.

[0087] like Figure 5B As shown, in step S54, it is determined whether to output the first flow information or the second flow information as the flow information of the pump according to the comparison result. Specifically, when the first flow information and the second flow information are greater than the preset flow, the hybrid estimation unit uses the first flow information as the flow information of the pump. On the other hand, when the first flow information and the second flow information are less than the preset flow, the hybrid estimation unit uses the second flow information as the flow information of the pump.

[0088] Optionally, the fourth estimation module 314 includes a flow system curve estimation unit configured to execute a flow system curve estimation scheme, thereby obtaining the flow information of the pump according to the rotation information based on the relationship curve. Fig. 6A , which shows a block diagram of a flow system curve estimation unit of an embodiment of the present application. In this embodiment, the rotation information includes speed information and torque information, which can be obtained through the frequency converter 11. The specific implementation of the flow system curve estimation solution includes the following two examples.

[0089] First example:

[0090] Please refer to Fig. 6A and Figure 6B , Figure 6B The flowchart of the flow system curve estimation scheme of the first example of the present application is shown. First, in step S61, a detachable flow meter is installed at the outlet of the pump. At this time, it is necessary to ensure that the pipeline of the system is in normal operation mode.

[0091] like Fig. 6A As shown, the flow system curve estimation unit includes a relationship curve establishment module. Figure 6B As shown, in step S62, the relationship curve establishment module of the flow system curve estimation unit is configured to establish a shaft work flow correspondence curve, and use it as a relationship curve. For example, first, the pump is operated at a speed of 50%, and the current output torque and speed are obtained through the frequency converter 11 to calculate the shaft work. After the shaft work is calculated, the shaft work and flow at 50% speed are recorded. Subsequently, the pump is operated at a speed of 100%, and the current output torque and speed are obtained through the frequency converter 11 to calculate the shaft work. After the shaft work is calculated, the shaft work and flow at 100% speed are recorded. The above-mentioned shaft work flow correspondence curve can be obtained by curve simulation of the recorded data.

[0092] like Figure 6B As shown, in step S63, after the relationship curve is obtained, the flow meter is removed. Optionally, the shaft work flow corresponding curve can be stored in the database 124 of the controller 12 in the form of a lookup table or the like.

[0093] like Fig. 6A As shown, the flow system curve estimation unit includes a search module. Figure 6B As shown, in step S64, after obtaining the shaft power flow corresponding curve, the search module of the flow system curve estimation unit is also configured to obtain shaft power information according to the actual rotational speed, and obtain the flow corresponding to the shaft power information based on the shaft power flow corresponding curve, thereby obtaining the flow information of the current system.

[0094] Second example:

[0095] Please refer to Fig. 6A and Figure 6B , Figure 6C The flowchart of the flow system curve estimation scheme of the second example of the present application is shown. First, in step S71, a detachable flow meter is installed at the outlet of the pump. At this time, it is necessary to ensure that the pipeline of the system is in normal operation mode.

[0096] like Fig. 6A As shown, the flow system curve estimation unit includes a relationship curve establishment module. Figure 6CAs shown, in step S72, the relationship curve establishment module of the flow system curve estimation unit is configured to establish a pressure-flow correspondence curve and use it as a relationship curve. For example, first, the pump is operated at a speed of 50%, and the pressure difference and flow rate at the speed of 50% are recorded. Subsequently, the pump is operated at a speed of 100%, and the pressure difference and flow rate at the speed of 100% are recorded. The recorded data can be simulated by curves to obtain the above-mentioned pressure-flow correspondence curve.

[0097] like Figure 6C As shown, in step S73, after the relationship curve is obtained, the flow meter is removed. Optionally, the pressure-flow correspondence curve can be stored in the database 124 of the controller 12 in the form of a lookup table or the like.

[0098] like Fig. 6A As shown, the flow system curve estimation unit includes a search module. Figure 6C As shown, in step S74, after obtaining the pressure-flow correspondence curve, the search module of the flow system curve estimation unit is further configured to obtain the flow corresponding to the pressure information based on the pressure-flow correspondence curve, wherein the pressure information is the pressure difference. That is, in this example, the flow system curve estimation unit obtains the pressure difference based on the inlet pressure and the outlet pressure, and obtains the flow corresponding to the pressure difference based on the pressure-flow correspondence curve, and then uses it as the flow information of the system.

[0099] It should be understood that, from the above two examples, the flow meter will be removed after the relationship curve is established. In subsequent use, the cavitation detection system 10 can obtain flow information without the need for a flow meter. Therefore, the use of the above flow system curve estimation solution will not result in the disadvantage of high cost caused by setting up a fixed flow meter.

[0100] As can be seen from the above, the present application uses the estimation modules 311-314 of the flow estimation unit 31 to execute the corresponding flow estimation scheme to obtain flow information related to the pump 20, without setting a fixed flow meter in the cavitation detection system 10, thereby reducing manufacturing costs.

[0101] Furthermore, if Figure 2 As shown, the selector 32 is connected between the flow estimation unit 31 and the cavitation detection unit 33, wherein the flow estimation unit 31 controls the selector 32 to enable or disable the estimation modules. Specifically, the controller 12 can control the selector 32 to select one of the estimation modules 311-314 according to a preset condition, such as Figure 2As shown, or in different embodiments, a combination of at least one or more estimation modules is selected to obtain the flow information corresponding to the selected estimation modules 311-314. The preset conditions include the rotation information of the motor, the pressure information, the preset flow rate, the state information of the pump, etc., wherein the state information of the pump is related to the back-end use condition. For example, the execution strategy of the selector 32 may include when the pump 20 is in operation and the back-end use condition remains unchanged, such as the operating conditions such as the fixed amount of liquid used and the valve of the liquid is kept normally open, the selector 32 preferably selects to use the fourth estimation module 314 including the flow system curve estimation unit.

[0102] In addition, in some embodiments, the controller 12 may be connected to a human-machine interface (such as a display). In addition, the estimation modules 311 to 314 of the flow estimation unit 31 of the present application are presented in the form of menus or buttons in the human-machine interface, so that the user can select which estimation module to use to obtain flow information.

[0103] like Figure 2 As shown, the cavitation detection unit 33 is electrically connected to the inverter 11, the pressure gauge group and the selector 32, and is configured to calculate the cavitation margin of the pump 20 based on the rotation information, the pressure information and the flow information to detect the cavitation state of the pump 20. The cavitation state detection method is specifically as follows.

[0104] First, the cavitation detection unit 33 obtains the flow information (including the actual flow and the rated flow) calculated by the estimation module selected above. The rated flow refers to the estimated flow at the rated speed.

[0105] Subsequently, the cavitation detection unit 33 finds the rated cavitation margin at the rated speed through the rated flow rate, and calculates the actual cavitation margin through the rated cavitation margin. For example, the rated cavitation margin is found through a flow rate and cavitation margin table, wherein the flow rate and cavitation margin table can be stored in the database 124 of the controller 12.

[0106] In this embodiment, the calculation formula of the actual NPSH is: NPSHr Act is the actual NPSH, and NPSHr Rated is the rated NPSH.

[0107] Secondly, the cavitation detection unit 33 is further configured to obtain an effective cavitation margin according to the pressure information, the flow information, the current atmospheric pressure and the saturated pressure.

[0108] In this embodiment, the calculation formula of the effective NPSH is: NPSH Ais the effective net positive suction head. Pa is the atmospheric pressure, which can be obtained by setting a pressure sensor (not shown in the figure) near the pump 20. Ps is the pressure at the inlet of the pump 20, i.e., the gauge pressure of the first pressure gauge P1. Pvpa is the saturated vapor pressure, which is related to the ambient temperature of the system. The ambient temperature can be obtained by setting a thermometer (not shown in the figure) near the pump 20, and then the saturated vapor pressure of the liquid can be determined.

[0109] Furthermore, the cavitation detection unit 33 is also configured to obtain the cavitation state of the pump 20 based on the actual net positive suction head and the effective net positive suction head. When the effective net positive suction head is greater than the actual net positive suction head, it indicates that no cavitation phenomenon occurs. On the other hand, when the effective net positive suction head is less than the actual net positive suction head, it indicates that a cavitation phenomenon occurs.

[0110] As Figure 2 shown, the alarm unit 34 is connected to the cavitation detection unit 33. The alarm unit 34 is configured to issue alarm information based on the cavitation state of the pump 20 to indicate to the user whether the pump 20 is currently cavitating.

[0111] Compared with the prior art, the present application provides a cavitation detection system, which executes corresponding flow rate estimation schemes through these estimation modules of the flow rate estimation unit, and the flow rate estimation unit controls the selector to select these estimation modules to obtain the flow rate value corresponding to the selected estimation module, so as to obtain flow rate information related to the pump, without the need to set a fixed flow meter in the cavitation detection system, thereby reducing the manufacturing cost.

[0112] The above are only the preferred embodiments of the present application. It should be noted that for those skilled in the art, without departing from the principle of the present application, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present application.

Claims

1. A cavitation detection system for detecting the cavitation head of a pump. It is characterized in that The cavitation detection system includes: a frequency converter electrically connected to a motor of the pump and configured to control the motor based on rotation information to drive the pump to operate; A pressure gauge set, configured to obtain a pressure information of the pump; a flow estimation unit, electrically connected to the frequency converter and the pressure gauge group, and configured to obtain the rotation information and the pressure information, wherein the flow estimation unit includes a plurality of estimation modules, the estimation modules are respectively used to execute different flow estimation schemes, and each of the estimation modules is configured to execute the corresponding flow estimation scheme based on the rotation information and / or the pressure information to obtain a flow information related to the pump; a selector connected to the flow estimation unit and configured to select one of the estimation modules according to the rotation information, the pressure information and a state information of the pump to obtain the flow information corresponding to the selected estimation module; and A cavitation detection unit is electrically connected to the frequency converter, the pressure gauge group and the selector, and is configured to calculate the cavitation margin of the pump based on the rotation information, the pressure information and the flow information to detect the cavitation state of the pump.

2. The cavitation detection system according to claim 1, It is characterized in that The selector is disposed between the flow estimation unit and the cavitation detection unit, and the flow estimation unit controls the selector to enable or disable the estimation modules.

3. The cavitation detection system according to claim 1, It is characterized in that The estimation modules include a flow-lift estimation unit configured to obtain the corresponding flow information according to lift information.

4. The cavitation detection system according to claim 3, It is characterized in that The flow head estimation unit is configured to obtain a height difference of the pressure gauge group and obtain a pressure difference according to the pressure information, and the flow head estimation unit obtains an actual head according to the height difference and the pressure difference.

5. The cavitation detection system according to claim 4, It is characterized in that The rotation information includes a rotation speed information, and the flow head estimation unit is further configured to obtain a rated head according to the actual head and the rotation speed information, and obtain the flow corresponding to the rated head based on a first lookup table to obtain the flow information.

6. The cavitation detection system according to claim 5, It is characterized in that The first lookup table is based on a relationship table between flow rate and head established at rated speed.

7. The cavitation detection system according to claim 4, It is characterized in that The pressure gauge set includes a first pressure gauge and a second pressure gauge; The first pressure gauge is disposed at an inlet of the pump and is configured to obtain an inlet pressure of the pump; and The second pressure gauge is disposed at an outlet of the pump and is configured to obtain an outlet pressure of the pump, wherein the flow head estimation unit obtains the pressure difference according to the inlet pressure and the outlet pressure, and obtains the height difference according to the height information of the first pressure gauge and the second pressure gauge.

8. The cavitation detection system according to claim 1, It is characterized in that The estimation modules include a flow rate power estimation unit configured to obtain the corresponding flow rate information according to the rotation information.

9. The cavitation detection system according to claim 8, It is characterized in that The rotation information includes a speed information and a torque information. The flow power estimation unit is configured to obtain an actual shaft power based on the speed information and the torque information, and to obtain a rated shaft power based on the actual shaft power. The flow power estimation unit is also configured to obtain the flow corresponding to the rated shaft power based on a second lookup table and thus obtain the flow information.

10. The cavitation detection system according to claim 9, It is characterized in that The second lookup table is based on a relationship table between flow rate and shaft work established at rated speed.

11. The cavitation detection system according to claim 1, It is characterized in that The estimation modules include a hybrid estimation unit, which is configured to obtain a corresponding first flow information according to a head information and a corresponding second flow information according to the rotation information, and is also configured to compare the first flow information and the second flow information with a preset flow to determine whether to use the first flow information or the second flow information as the flow information.

12. The cavitation detection system according to claim 11, It is characterized in that When the first flow information and the second flow information are greater than the preset flow, the estimation modules use the first flow information as the flow information, and when the first flow information and the second flow information are less than the preset flow, the estimation modules use the second flow information as the flow information.

13. The cavitation detection system according to claim 1, It is characterized in that The rotation information includes rotation speed information, and the estimation modules include a flow system curve estimation unit configured to obtain the flow information from the rotation speed information based on a relationship curve.

14. The cavitation detection system according to claim 13, It is characterized in that The rotation information includes torque information, the relationship curve is a shaft power flow corresponding curve, and the flow system curve estimation unit obtains shaft power information according to the speed information and the torque information, and obtains the flow corresponding to the shaft power information based on the shaft power flow corresponding curve, thereby obtaining the flow information.

15. The cavitation detection system according to claim 14, It is characterized in that The shaft power flow corresponding curve is a curve established by obtaining the flow at different rotation speeds through a flow meter.

16. The cavitation detection system according to claim 13, It is characterized in that The relationship curve is a pressure-flow correspondence curve, and the flow system curve estimation unit obtains the flow corresponding to the pressure information based on the pressure-flow correspondence curve, thereby obtaining the flow information.

17. The cavitation detection system according to claim 16, It is characterized in that The pressure gauge set includes: a first pressure gauge disposed at an inlet of the pump and configured to obtain an inlet pressure of the pump; and a second pressure gauge disposed at an outlet of the pump and configured to obtain an outlet pressure of the pump; The flow system curve estimation unit obtains the pressure difference according to the inlet pressure and the outlet pressure, and obtains the flow corresponding to the pressure difference based on the pressure-flow correspondence curve as the flow information.

18. The cavitation detection system according to claim 17, It is characterized in that The pressure-flow correspondence curve is a curve established by obtaining flow rates under different pressure differences through a flow meter.

19. The cavitation detection system according to claim 1, It is characterized in that The cavitation detection unit is configured to obtain an actual cavitation margin according to the flow information, and the cavitation detection unit is also configured to obtain an effective cavitation margin according to the pressure information, the flow information, the current atmospheric pressure and the saturated air pressure, and the cavitation detection unit is also configured to obtain the cavitation state of the pump according to the actual cavitation margin and the effective cavitation margin.

20. The cavitation detection system according to claim 1, It is characterized in that The cavitation detection system further includes an alarm unit connected to the cavitation detection unit, and the alarm unit is configured to issue an alarm message based on the cavitation state of the pump.

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