Method for detecting cavitation and / or air bubbling or air inflow in hydraulic system

Abstract

The invention relates to a method for detecting cavities and / or air bubbles or air inflow in a hydraulic system comprising at least one electromotively driven pump for conveying a liquid conveying medium, the method comprises the following steps: detecting at least one operating parameter of the drive motor, which influences the torque of the pump drive, determining a variance of the detected operating parameter for a defined observation time period, and if the determined variance value exceeds a defined threshold value, starting the pump drive when the determined variance value exceeds the defined threshold value. Cavities and / or air bubbles or air inflow in the hydraulic system are detected.

Description

Technical Field

[0001] The present invention relates to a method for detecting cavitation and / or air bubbling or air inflow in a hydraulic system, the hydraulic system including at least one electric motor driven pump for conveying a liquid transport medium within the hydraulic system. Background Technology

[0002] Modern pumps are increasingly equipped with a wide range of functions for monitoring the current pump operation, as well as more advanced functions for monitoring the entire hydraulic system. Therefore, it is essential to efficiently and as quickly as possible identify any potential anomalies in the pump or within the hydraulic system, so that alarm messages can be generated or countermeasures can be taken when necessary.

[0003] One possible anomaly is the presence of cavitation, which may occur in the impeller region of a centrifugal pump. Cavitation refers to the formation and disintegration of steam-filled cavities in the pumped medium, which can cause high-frequency impacts at the pump impeller. The persistent presence of cavitation can lead to mechanical damage to the pump, especially the impeller, making early identification crucial for remedial action. Air bubbling, or air entering the hydraulic system, can also cause impacts at the impeller and lead to mechanical damage.

[0004] The occurrence of cavitation in hydraulic systems, especially closed hydraulic systems, is primarily driven by pressure drops at the pump's suction inlet. In this context, it is suggested that the detected cavitation could also indicate potential negative pressure in the pump's suction area, ultimately enabling the identification of leaks within closed systems. Summary of the Invention

[0005] The objective of this invention is to enable the reliable and efficient detection of the aforementioned anomalies using a novel method.

[0006] This task is accomplished by a method according to the features of claim 1. Advantageous embodiments of this method are the subject of the dependent claims.

[0007] According to the present invention, during pump operation, suitable operating parameters of an electric motor-driven pump are continuously or periodically detected within the hydraulic system. The operating parameter to be detected is either a characteristic of the torque of the pump drive unit, or at least has a decisive correlation with or influence on the torque produced by the pump drive unit.

[0008] For the detected operating parameters, the possible variance of the operating parameters is then calculated within a defined observation period. In other words, the degree of possible signal fluctuation or noise of the detected operating parameters is determined by variance determination. The calculated variance value is used as an indicator of the presence of pump cavitation and / or air bubbling / air inflow into the hydraulic system. Because the high-frequency impact caused by cavitation (due to negative pressure or bubbling air) leads to a variance in the resultant torque and thus results in enhanced and deterministic signal fluctuations, a variance value exceeding a defined threshold can be evaluated as indicating the presence of cavitation or air bubbling / air inflow.

[0009] The duration of the observation period used to determine the variance can be in the range of 1 to 10 minutes, preferably in the range of 1 to 5 minutes, and particularly preferably in the range of 1 to 2 minutes.

[0010] One possible operating parameter for determining its variance could be, for example, the torque itself. It is also conceivable to measure or calculate electrical parameters of the drive motor that are characterizing the synthesized motor torque. Therefore, the current component that forms the motor torque, such as the q-axis component i of the stator current, can be particularly conceivable as operating parameters (e.g., the consumed motor power and / or motor current). q .

[0011] The operating parameter is monitored over a defined time period, and its variance is determined using statistical methods. By comparing it to a defined threshold or reference value, it can be assessed whether the calculated variance falls within the normal range or deviates from it, indicating an increased dispersion of the operating parameter. Increased dispersion indicates anomalies in pump operation, particularly caused by cavitation and / or air bubbling / air inflow in a closed loop. The corresponding operating parameter can be either directly measured or derived from other parameters and estimated based on the measured parameters using a motor model.

[0012] As an alternative to the aforementioned operating parameters, the actual pump speed can also be detected and analyzed. The actual speed can be measured using a speed sensor, or alternatively estimated using a motor model. In pump control devices with speed regulators, cavitation or air bubbling / air inflow can be triggering factors for speed fluctuations, making cavitation detection possible by detecting the motor speed and, in particular, determining the speed variance.

[0013] The occurrence and extent of cavitation can be influenced by external factors. In this context, it is meaningful to use dynamic thresholds adapted to external conditions for variance comparison. Generally, it is recommended to use adaptive thresholds that depend on the current operating mode and / or the current pump operating point. Specifically, this adaptive threshold can depend on the current system pressure in the hydraulic equipment and / or the current operating pump speed and / or the current actual temperature of the conveyed medium. It is precisely the medium temperature that has a significant impact on cavitation formation, as the probability of cavitation increases with the temperature of the conveyed medium.

[0014] Particularly advantageous is the determination of the average value of the operating parameters, or the average value of parameters derived from the operating parameters, in parallel with the determination of the variance. Here, a moving average calculation is preferred, which thus determines the average value over a continuously sliding time window. For example, the electrical power consumption of the motor is derived from the operating parameters (especially the motor current) and the actual speed of the motor. By observing the average value, especially the power consumption, possible power drops in the pump can be detected, which are characterizing, for example, possible pressure losses in the equipment (e.g., those caused by leaks within the system). However, since power drops can also be triggered by regular load changes, a reliable distinction can be made between power drops triggered solely by load changes and power drops caused by leaks by monitoring a combination of the average and variance values.

[0015] For example, a decrease in power is detected when the average value undergoes a change in a specific difference (especially a jump).

[0016] Therefore, if the system detects a power drop along with an increase in the variance of the detected operating parameters, it can be inferred that pressure loss is accompanied by cavitation, which is a compelling indication of a possible leak in the hydraulic system.

[0017] To avoid potential misjudgments and to verify leaks, it is advisable to temporarily pre-set an adjusted target speed for the pump's motor regulator, allowing the motor to operate temporarily at its current limit, provided it is not already operating at its current limit during normal operation. This further optimizes the accuracy and reliability of variance detection. Therefore, with the temporarily adjusted speed, the operating parameters are re-tested and the variance determined. If, under this operating condition, the dispersion of the operating parameters increases again and exceeds a threshold, then normal load changes can be ruled out, and leaks in the system should be verified instead.

[0018] For example, the target speed of the speed regulator of the motor control device is adjusted or increased to operate at the current limit during a defined time interval, especially during a period of 1-5 minutes, especially during a period of 1-4 minutes, and preferably during a period of about 3 minutes.

[0019] As explained above, the hydraulic system is preferably a closed system.

[0020] In addition to the method according to the invention, the invention also relates to a pump, preferably a centrifugal pump, particularly preferably a heating circulation pump, for example for a solar thermal system, having a pump control device or pump regulating device configured to perform the method according to the invention. The pump control device or pump regulating device may be a frequency converter. For this pump, the same advantages and characteristics as previously explained by means of the method according to the invention are obtained. For this reason, repeated descriptions can be omitted. The pump control device or pump monitoring device may be an integral part of the pump; however, alternatively, it may be configured as an external module.

[0021] Finally, the present invention relates to a hydraulic system comprising at least one pump that circulates a transport medium in a closed loop, and a pump control device or pump monitoring device configured to perform the method according to the invention. The pump control device or pump monitoring device may be an integral part of the pump; however, alternatively, it may be configured as an external module that communicates only with the integral pump control device and retrieves necessary operating parameters for analysis from the pump control device. Attached Figure Description

[0022] The other advantages and features of the method will now be explained in more detail with the aid of the embodiments shown in the accompanying drawings.

[0023] Figure 1 A simplified illustration of a hydraulic system according to the present invention is shown. Figure 2 A flowchart of a method for leak identification according to the present invention is shown, and Figure 3 The detected current component i of the stator current of the pump drive unit is shown. q An example time chart. Detailed Implementation

[0024] The present invention is based on the understanding that cavitation and / or air bubbling / air inflow can cause high-frequency and severe impacts at the pump impeller, which in turn can cause strong signal fluctuations in current measurement and in speed regulation downstream of the pump. These signal fluctuations can be detected by a novel logic according to the present invention in motor regulation, thereby reliably identifying cavitation.

[0025] Furthermore, this method can reliably identify leaks or drops in system pressure within a closed hydraulic system, especially under high-temperature media.

[0026] Figure 1 A possible structure of such a hydraulic system is schematically illustrated. A closed hydraulic circuit 1 is shown, such as a conventional heating circuit for a residential building to be heated. Possible consumers within the heating circuit are simplified and labeled with reference numeral 2, and the installed circulation pump is labeled with reference numeral 10. An electric motor 11, especially a synchronous motor, and particularly preferably a permanent magnet motor, is used to drive the pump 10, which is implemented as a centrifugal pump. This motor is controlled with high energy efficiency by means of a frequency converter 12 and a speed regulator implemented in the controller of the frequency converter.

[0027] exist Figure 2 The diagram shows a flowchart depicting the steps of a method for leak identification in a closed loop. The entire method is implemented in the pump control unit or the frequency converter 12 that forms part of the pump 2; however, in principle, the method can also be performed outside the pump, and one or more required operating parameters are instead communicated from the pump 2 to the external unit for performing the method.

[0028] exist Figure 2 In box 15 of the diagram, the operating parameters are first determined. Here, in the inverter of the motor regulating device, the motor current consumed by motor 11 is determined by three-phase current measurement. Using the motor model 20 stored in the microprocessor, the q-axis component i of the stator current can be calculated based on the measurement results. q (t), the q-axis component is causally related to the motor torque. Current component i q (t) and the target value i of the integral current regulator q_set (t) are provided together to box 30 for variance calculation.

[0029] Then, in box 30, the target value i can be calculated using statistical methods. q_set The dispersion around (t). As the current component i q The observation period for (t) is typically set at intervals of 1 to 2 minutes. The calculated variance is then compared in box 40 to an adaptively adjustable threshold, where exceeding the threshold indicates the presence of cavitation or air bubbling / air inflow, and the method continues in boxes 70 or 80. If the threshold is not exceeded, it is assumed that there is no anomaly and the pump continues operating normally with continuous current measurements in box 15.

[0030] If, in addition to the hole effect, this method should also be used to identify negative pressure scenarios or leaks in closed loops, then the detection 50, necessary in parallel with the determination of variance and the reduction of power, is meaningful. To this end, the current electrical power consumption of the pump motor 11 is determined, and the average value is calculated over a finite time window (box 51). For this purpose, box 51, in addition to the current motor current i qIn addition, the estimated rotational speed n of the motor is obtained from motor model 20 for calculating electrical power consumption. This time window is sliding, allowing for continuous updates of the power value. Then, in box 52, it is checked whether a drastic change in the average value has occurred, specifically whether the power consumption has decreased below a certain minimum. If such a power decrease exists and the variance calculated in parallel in box 30 is above a threshold, then cavitation or air bubbling / air inflow is currently considered to occur in the suction area of ​​pump 10, resulting from a pre-pressure loss. For verification, a pre-pressure loss guessing test is performed in box 80.

[0031] Otherwise, if a power decrease is detected but the calculated variance does not exceed a threshold, it is assumed that the power decrease is caused only by normal load changes and that there is no pressure loss due to leakage. The method then returns to the current measurement in box 15.

[0032] The guessing test in box 80 is used to verify cavitation or potential leakage. For the guessing test, the target speed in the speed regulator of pump 10 is temporarily set for a short period (e.g., about 3-5 minutes) to cause the motor to operate at its current limit. This measure further amplifies the signal fluctuations caused by air bubbling / air inflow or cavitation, and thus allows for more accurate and reliable detection. Higher current intensity results in a larger current variance, and this verification method is used to validate the detection.

[0033] If the variance exceeds the threshold again in the pre-pressure loss guessing test 80, the guess of cavitation and leakage in the system can be confirmed, and a corresponding alarm message 100 can be generated. In principle, it can be assumed that the variance increases again when operating at the current limit.

[0034] Figure 3 The calculated current component i that forms the torque is shown. q The time curve of (t). In the time interval of 0-100 seconds, component i... q The current intensity at (t) is 5A, where the signal curve exhibits slight measurement fluctuations. At 100 seconds, a significant power drop occurs, and the average current intensity suddenly drops to approximately 3.75A, caused by a pressure drop in the system from 4 bar to 2 bar. Subsequently, significantly stronger signal fluctuations in the current component appear, and the calculated current variance, if necessary, exceeds a predetermined threshold, allowing the inference of a leakage in the system that not only forces the power drop but also simultaneously causes holes and corresponding current signal fluctuations.

[0035] At the 200-second mark, a further power decrease occurs due to the system pressure dropping from 2 Bar to 0.5 Bar. As a result, the current variance also increases significantly again at this point.

[0036] Using the described method, possible leaks in a closed hydraulic system can be reliably inferred, which is confirmed by the decrease in pump motor power and the appearance of excessive current signal fluctuations.

[0037] Since the operating parameters used for monitoring the logic are already being monitored in most regulating modules used in pump drives, this method can be implemented without additional hardware and extensive reconfiguration of the pump regulator, thus providing cost-effective protection for existing pump systems.

Claims

1. A method for detecting cavitation and / or air bubbling, or air inflow, within a hydraulic system (1), said hydraulic system comprising at least one electrically driven pump (10) for conveying a liquid transport medium, said method comprising the following steps: - Detect at least one operating parameter of the drive motor (11) that affects the torque of the pump drive unit (11), - Determine the variance of the detected operating parameters within a defined observation period. - When the determined variance value exceeds the defined threshold, cavitation and / or air bubbling or air inflow in the hydraulic system (1) is detected.

2. The method according to claim 1, characterized in that, The operating parameters are the motor torque and / or the electrical power consumed by the motor (11) and / or the motor current, especially the current component i that forms the motor torque. q .

3. The method according to claim 1, characterized in that, The operating parameters are the actual speed of the pump (10) or the motor (11), and especially the estimated actual speed.

4. The method according to any one of the preceding claims, characterized in that, The defined threshold used for comparison with the determined variance is selected based on the operating mode and / or operating point, especially based on the current system pressure and / or the speed of the pump (10) and / or the temperature of the conveyed medium.

5. The method according to any one of the preceding claims, characterized in that, In parallel with the determination of variance, the average value of the operating parameters or the average value of parameters derived from the operating parameters is calculated.

6. The method according to claim 5, characterized in that, The average value is formed within a defined time period or determined within a sliding time window.

7. The method according to any one of claims 5 or 6, characterized in that, The pump's power drop can be identified using the average value, especially when the average value undergoes a change of a specific difference.

8. The method according to any one of the preceding claims, characterized in that, When a power drop and cavitation and / or air bubbling or air inflow have been detected, especially when the variance exceeds the threshold and the average shows a jump in the difference, a leak in system (1) is identified.

9. The method according to any one of the preceding claims, characterized in that, When the defined threshold is exceeded and / or when a power drop is detected, the pump motor (11) is operated at the current limit, in particular by adjusting or increasing the target speed of the speed regulator of the motor control device (12), wherein operation at the current limit is preferably performed within a time interval of 1 to 5 minutes, especially about 3 minutes.

10. The method according to claim 9, characterized in that, During operation of the pump (10) at the current limit, the variance value is recalculated in order to verify the pre-pressure loss of the pump (10) or the negative pressure in the suction area of ​​the pump (10).

11. The method according to claim 10, characterized in that, During operation at the current limit, the determined variance value is compared with the previously determined variance value, and in particular, the pre-pressure loss is determined when the variance value obtained during operation at the current limit is larger.

12. The method according to any one of the preceding claims, characterized in that, The predetermined duration for determining the variance is in the range of 1 to 10 minutes, preferably in the range of 1 to 5 minutes, and particularly preferably in the range of 1 to 2 minutes.

13. The method according to any one of the preceding claims, characterized in that, The hydraulic system (1) is a closed system.

14. A pump (10, 11), preferably a centrifugal pump, particularly preferably a heating circulation pump, having a pump control / regulation device (12) configured to perform the method according to any one of the preceding claims.

15. A hydraulic system (1) comprising at least one pump (10, 11) that circulates a transport medium in a closed loop and a pump control / monitoring device (12) configured to perform the method according to any one of claims 1 to 14.

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