RU2776905C2 - Method for self-diagnostics of mechanical and/or hydraulic state of centrifugal pump - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: present invention concerns a method for self-diagnostics of a mechanical and/or hydraulic state of a centrifugal pump, in particular a circulation pump. In this case, a pump control device contains a mathematical model of an engine to determine mechanical power of the pump and the actual speed of the pump rotation. A working point module is also provided to assess this working point of the pump based on the pump rotation speed and mechanical power of the pump. Moreover, for self-diagnostics of the pump, mechanical power of the pump determined using the engine model for the given pump rotation speed is compared with the calculated mechanical power of the pump, and this calculated mechanical power of the pump is determined by inverting the working point module for a certain pump rotation speed.

EFFECT: obtaining a method for self-diagnostics of a mechanical and/or hydraulic state of a centrifugal pump.

11 cl, 6 dwg

Description

The present invention relates to a method for self-diagnosis of the hydraulic and/or mechanical condition of a centrifugal pump, in particular a circulation pump.

Modern energy-saving centrifugal pumps are equipped with frequency converters and means of speed control in order to adjust the speed and, therefore, the power of the pump, if necessary. In order to control, respectively, determine the required set speed, the pump control needs information about the current operating point (flow Q and head H of the pump) of the pump. To save operating costs, modern centrifugal pumps are manufactured, however, without individual flow sensors and/or pressure sensors. Instead, the pump controller, using the duty point module, must estimate the current duty point based on the mechanical characteristics of the pump and the speed used. These inputs are obtained using a mathematical motor model that is redundant for the pump to run on the pump control processor.

The quality of the result of the evaluation of the operating point modulus depends, inter alia, on the reference values or parameters stored in the pump memory, which are determined on a structurally identical reference pump and stored in the pump controller. Since reference values are usually only created randomly in batch production for selected instances, they can be too inaccurate for certain pump instances due to manufacturing tolerances. In such a case, subsequent optimization of these reference values during initial commissioning is desirable, as well as during subsequent operation. Further, wear phenomena can also lead to erroneous results.

In the international publication WO 2008/138 520 A1, a method for monitoring the health of an engine condition is disclosed, in which the current operating point of the engine is evaluated in relation to a limited operating range of the engine, and when this operating range is left, a malfunction is stated, and this limited operating range is formed by operating points of the engine.

US 2010/0300220 A1 presents yet another way to control a circulation pump.

The object of the present invention is therefore to provide the pump controller with a self-diagnostic function of this kind, which can detect errors in the duty point estimation and therefore detect wear phenomena in advance or undertake subsequent parameter optimization.

This problem is solved by means of a method with features of independent claim 1. Preferred variants of the method are the subject of dependent claims.

Thus, a method is provided for diagnosing the mechanical and/or hydraulic condition of a centrifugal pump. This method according to the invention has been developed primarily for circulation pumps, however, the main aspect of the present invention can be applied without limitation to centrifugal pumps in an open hydraulic circuit.

For the sake of simplicity, in what follows we always refer to a circulation pump, and the above considerations are also valid for centrifugal pumps in an open circuit.

Said method is intended for a centrifugal pump, in particular a circulation pump, in which a pump control device with an implemented motor model is provided for determining the mechanical power of the pump and the reached pump speed. Further, the pump controller includes an operating point module for estimating the operating point of the pump based on the pump speed and the mechanical power of the pump. The duty point module is typically used in the pump master software.

According to the invention, it is proposed, in order to diagnose the mechanical and/or hydraulic condition of the pump, using an engine model for a given pump speed, to determine the mechanical power of the pump and compare it with the calculated mechanical power of the pump, which is determined by inversely performed evaluation of the operating point of the specified operating point modulus based on set pump speed.

Ultimately, this uses a conventional motor model of the pump controller, which, in the operating mode of the pump, determines the mechanical power of the pump based on the realizable actual speed and gives the result. Further, the operating point module provided for evaluating this operating point, i. e. is used inappropriately to estimate the available pump flow and therefore the pump head, in order to determine the rated mechanical power of the pump from a certain speed using this operating point module. By comparing with the output mechanical power of the pump of the specified engine model, which corresponds to the actual power of the pump, the accuracy of the operating point modulus for estimating this operating point can be evaluated.

When commissioning for the first time and correctly configuring the parameters used in the evaluation module, respectively, the reference values, the specified calculated mechanical power of the pump must correspond to the mechanical power of the pump determined by the motor model. If, instead, deviations occur, the pump controller can accordingly conclude that there is a fault within the centrifugal pump or the circulation pump.

According to a preferred embodiment, the operating point module is supplied with the pump flow and/or pump head expected for a certain pump speed to determine the calculated mechanical power. These expected pump flow and/or pump head are preferably determined using affinity laws. In particular, this is based on the statement of the law of affinity, according to which the volumetric flow behaves in proportion to the increase in the speed of rotation. In contrast, the pump head increases quadratically with the change in speed. When using these patterns for a given speed, which, in contrast to the previous speed, is a change in speed, it can be assumed that the volumetric flow and, accordingly, the pump head also change for it compared to those calculated for the previous value of the volumetric speed. supply, respectively, the pressure of the pump.

By means of this comparison, the difference between the power values is preferably determined. In the absence of a fault, this difference is zero or, accordingly, almost zero. If there are deviations, the pump may instead conclude that there is a fault.

In addition to simple fault detection, a usable specification of the specific fault type or cause of the fault is desirable. For such a case, it can be provided that, in the event of an incorrect behavior for a number of deviating values of the desired speed, said method is repeated. The corresponding comparison results can then be interpreted,

respectively, obtained values of the difference between the power values, so that, for example, using mathematical relationships between the individual values of the difference and the corresponding speed values, it is possible to more accurately determine the type of fault. In this case, we can assume that the mechanical power loss depends quadratically on the rotational speed. If such a mathematical relationship between the difference values and the speed values is detected, then the mechanical wear fraction can be identified as the main cause of this incorrect behavior. Other mathematical dependencies may indicate, for example, a hydraulic failure, among other things, for example, lime deposits in the slotted tube of the pump drive.

The operating point modulus used to estimate this operating point is usually also based on affinity laws. However, in order to be able to apply these regularities, it is absolutely necessary to pre-calculate the proportion of the mechanical power of the pump that characterizes the mechanical power of losses, since this proportion does not obey known regularities. For this, a corresponding corrected power value is usually used, which is taken into account in the mechanical power delivered by the pump, in particular subtracted from it, before the duty point is estimated. As a result, the correctness and accuracy of this corrected value is of great importance for the quality of the operating point estimate, i.e. how accurately this corrected value reflects the actual mechanical power loss inside the pump. The more precisely this parameter is determined, the more accurate the final estimate of the operating point will be.

However, it is this parameter that can be used in the future so that after the occurrence of a malfunction, it is possible to additionally specify the type of malfunction. At the same time, said corrected power value is systematically varied for a different speed setpoint during the repetition of the method. In particular, by systematically changing the corrected power value, an attempt is made to find a new uniform corrected value, which gives the same, respectively almost zero, for all given speeds. If this is the case, then it can be assumed that the corrected power value used during the first commissioning of the pump was not erroneous, so that this certain necessary change in the corrected power value is a sign of mechanical wear inside the pump. Correction of the specified corrected power value, in particular an increase in the value, is a clear sign of increasing wear inside the pump. An increase in the modulo value is also an indicator of an increase in mechanical wear.

If, on the other hand, no suitable corrected power value can be determined, then a mechanical cause is less likely, and this can be interpreted as an indication of a hydraulic failure. Often, lime deposits in the slotted tube of the pump drive motor lead to incorrect behavior, which is due to non-mechanical faults.

It is possible that said method is carried out during the first commissioning of the centrifugal pump or circulation pump, or alternatively at a later point in time in the operating mode of the pump. When the pump is first put into operation, this method according to the invention can be used to optimize some parameters for estimating the operating point, for example the above-mentioned corrected power value. To optimize the operating point estimate by correcting the corrected power value, for example, an iterative optimization method can be used. Alternatively or additionally, for continuous editing of the corrected power value, according to quadratic optimization, for example, a non-stationary extended Kalman filter can be used.

When the method is carried out on-line, a mechanical or hydraulic defect in the pump can instead be inferred by this method and this is communicated to the user visually and/or acoustically. It is particularly advantageous if a warning is given to the user shortly before a possible defect in the pump or, accordingly, failure of the pump. It is also possible that the pump continuously reports its status to the user and warns him shortly before failure.

In addition to the method according to the invention, the invention also relates to a centrifugal pump, in particular a circulation pump having a variable speed pump drive and a pump controller for carrying out the method according to the invention. Accordingly, said centrifugal pump, in particular the circulation pump, has the same advantages and properties as have already been discussed in connection with the method of the invention mentioned above. For this reason, they are not described here again.

Other advantages and details of the present invention will be presented below in connection with the exemplary embodiment shown in the drawings. These drawings show the following.

Fig. 1: two diagram examples for possible pump characteristic curves;

Fig. 2: another diagram with different power characteristic curves;

Fig. 3: block diagram for showing the operating point unit for operating point estimation;

Fig. 4: block diagram for explaining the individual steps for the specified embodiment of the method according to the invention,

Fig. 5: diagram to explain the relationship between rotation speed and mechanical power loss, and

Fig. 6: diagrams of FIG. 1 to explain the method for determining the appropriate pump head depending on the mechanical power of the pump.

The centrifugal pump according to the invention in the form of a circulation pump is equipped with a frequency converter and a speed control device. In order for the pump controller to be able to adjust the speed as needed, it needs information about the current operating point (flow rate Q and head H of the pump). These values are evaluated using the operating point module implemented in the software, i.e. this actual duty point is evaluated from mechanical power and speed. Both parameters are given by the mathematical model of the engine, which is redundant for the pump to work on the processor.

The duty point is estimated using affinity laws, taking into account the stored characteristic curves, as well as a corrected value for the mechanical power loss of the pump. These affinity laws are well known in the literature and state that the power, volumetric flow and head of the pump behave as follows when changing the speed:

Further, in the pump control device, the specified dependences of mechanical power and volume flow, as well as pump head and volume flow at nominal speed, are stored in the form of characteristic curves. Diagram a) for the rated speed n _N shows the relationship between the volumetric flow and the mechanical power P _mech that the engine produces. Diagram b) shows the relationship between pump head and volume flow at nominal speed n _N .

The mechanical power P _mech corresponds to the sum of the hydraulic power P _hydr, the power of hydraulic losses P _hydr.losses , and the power of mechanical losses P _{mech. losses} . On FIG. 2 separately shows the power curves depending on the volume flow.

It is known that the hydraulic power of the pump P _hydr , as well as the power of hydraulic losses P _hydr.losses of the pump quite accurately follow the laws of affinity. The power of mechanical losses P mechanical _{losses of the} pump, on the contrary, does not follow these laws, however, it can be taken as independent of the volumetric flow and approximately proportional to the square of the rotational speed. In this regard, one can compare the diagram in Fig. 5, where pump speed is opposed to mechanical loss power. First, the actual measurement curve of the circulating pump under test is shown, as well as the corresponding quadratic interpolation. Mathematically, this dependence can be represented as follows:

Mechanical losses, although relatively low, must, however, be calculated before applying the laws of affinity, since this small fraction due to the third power (see Equation 3) would greatly distort the result. To prevent this, said relationship between the speed n and the mechanical loss P _mechanical loss is stored in the pump.

On FIG. Figure 3 shows the full process of estimating the duty point using the duty point module located inside the pump.

The input values are the speed values n current provided by the motor controller _. and mechanical power R _mech . In area a) of this Fig. 3 mechanical losses P _mech.losses are subtracted from the motor power P mech by means of the corrected value _{Pcorr ,} and due to this, the application of the laws of affinity is possible.

In area b), this power, on the basis of the laws of affinity, is transformed to the normalized power P _n , which would take place when the speed is increased to the nominal speed n _N . With this normalized power P _N , on the basis of the stored characteristic curve P/Q (Fig. 1a), the normalized volumetric flow _Qn norm can be derived, which would be established with a normalized power P _N and nominal speed

Q _norms in area c) are transformed back to the currently available speed n current by means of affinity laws _. . Thus, the calculated volumetric flow Q calculated is _obtained. In areas d) and e), equivalent to areas b) and c), the design head of the pump H _{calc is determined.} . This process is illustrated again in Fig. 6 with diagrams contrasted with the diagram in FIG. 1. First (FIG. 6a) using the diagram in FIG. 1a) determines the normalized volumetric flow Q _n suitable for the normalized power P _n . In the next step, for the normalized volume flow Q _n from diagram 1b), the normalized pump head H _N is read. If the pump has a pressure transducer, the calculated and measured pump head can be summed up by combining data from systems with multiple sensors (Multisensor Datenfusion) and thus the duty point estimate can be improved.

This method of estimating the operating point is possible according to the mechanical power P _mech and the rotational speed n _current. determine the volume flow Q _calc. and pump head H _calc. However, this only works if the stored characteristic curves as well as the stored corrected power values _Pcorr exactly correspond to reality. In practice, however, there may be deviations between the stored data and the actual behavior of the pump. The reasons for this may be the following.

- due to mechanical wear, as well as lime deposits in the slotted pipe, the friction properties change over time. This leads to the fact that the corrected power values P _corr are no longer correct.

- due to deposits in the pump, as well as due to the expansion of the slot gap (Spaltaufweitung), the hydraulic characteristic of the pump changes. This means that the stored Q/H and Q/P characteristic curves no longer correspond to reality.

- due to tolerances, the specified corrected power values as well as the stored characteristic curves differ from pump to pump. Since only one pump is measured and this data is stored in all pumps of this series, these stored data are only conditionally correct.

Due to these limitations, deviations of up to 15% are possible when estimating the operating point. The present invention describes a method by which deviations between the actual behavior of the pump and the stored corrected values of the power _Pcorr and, accordingly, the coefficient α in a closed water circuit can be detected. This method is based on the fact that the pump briefly changes its speed during operation. The resulting affinity operating point changes can be calculated from the previous operating point and can also be estimated from the mechanical power _Pmech of the engine. By comparing the two determined operating points, a conclusion can be drawn about the quality of the corrected power values _Pcorr stored in the pump, respectively the factor α.

This rating is only valid if the system characteristic remains constant during speed changes. In a heating circuit, this means that the thermostatic valves do not have to be adjusted. Since this change in speed occurs very quickly and only in a very short time period, it is assumed that the specified prerequisite is fulfilled.

This method is divided into four steps and will be explained with reference to FIG. 4. Stage 1 (initial situation) is considered first. The pump is still in normal operation; the operating mode "detection of the state of wear" is not yet enabled. The engine reaches the set speed n ₀ . It is assumed that the set and actual speeds are identical. The operating point evaluation determines the currently available pump head (N _cal.,0 ) as well as the flow rate (Q _cal.,0 ).

When the pump is switched on in the "detection of the state of wear" mode, then these currently available values for n ₀ , Q _{calculated, 0} and H _{calculated, 0 are stored} . Next, step 2 (preparation for changing the speed) is considered. The pump is now checked to see what would happen if the actual speed po changed by the amount k without actually changing the speed. Based on the laws of affinity (see equations 1 and 2) it is expected that in this case the established volumetric flow Q is _expected. changes by the value k (Q _expected. =kQ current _{, 0} ).

Accordingly, the pump head would change by the value of k ² (N _expect. =k ² - N _{current., 0} ).

Using the inverse duty point estimate, said pump calculates the expected mechanical power P _expected from these values. This is the value of the expected power P _expected. is remembered. In the next step (step 3: change the rotational speed), the pump increases the actual rotational speed n ₀ by actually the value k and obtains the currently available mechanical power ( _Pmech,1 ) from the motor model. This power value is memorized. Step 4 is the interpretation. Were determined two power values P _mech , u P _expected. related to one operating point. The value of P _{is expected.} was calculated by means of affinity laws for another operating point. The value of P _mex,1 was determined from the actual corresponding operating point. If the corrected power values P _corr and α stored in the pump are accurate, then the difference between both power values (P _mex,1 and P _expected. ) is zero (P _defect = 0). If P _defect is not equal to zero, then the stored power correction is erroneous. The reason is either that the frictional properties have changed due to mechanical wear, or there is a non-mechanical influence, for example, a slotted pipe has also been added due to lime deposits.

In order to be able to separate these two actions, the described steps 1-4 are carried out repeatedly using different values of k.

Knowing that the power of mechanical losses depends quadratically on the speed of rotation n, it is possible to single out the share of mechanical wear unambiguously, since the corrected power value α (equation 4) varies systematically. If due to this it is possible to reduce the value of the error P _defect to zero for all values of k, then these deviations are reduced to mechanical friction. Otherwise, this error value P _defect can be attributed to non-mechanical influences (such as lime deposits in a slotted pipe). These non-mechanical influences follow other mathematical relationships, which can also be determined by changing the multiplication factor k. The exact relationship between the limescale loss in the slotted pipe and the rotational speed must be determined by experiment.

Thanks to the present invention, the following application scenarios are thus possible. However, this is not a complete enumeration.

1. Equipment health monitoring / equipment condition monitoring

Using the proposed method, the pump can determine its own state. It can detect errors in its stored data both after commissioning and during its lifetime. An error during initial commissioning is attributed to manufacturing tolerances. The change over the service life is indicative of wear and hydraulic wear. Said pump could continuously report its status to the user and warn him shortly before failure.

2. Improved operating point estimate

The indicated pump recognizes an error in its stored data and can conditionally distinguish between hydraulic influences and mechanical wear. In this way he can optimize his own operating point estimate by correcting the stored data. This can be done by iterative parameter tuning. Alternatively, using a non-stationary extended Kalman filter, continuous tuning of the parameters according to quadratic optimization can be performed.

With the method according to the invention, the error in the stored corrected power values can be very accurately deduced. However, deviations in the stored P/Q and H/Q characteristic curves (in sensorless systems) may not be detected. However, it is known from various experiments that the predominant wear phenomena can be attributed to lime deposits in the slotted tube and, to a lesser extent, to mechanical wear. In this way, at least one relevant wear fraction can be recognized in this way and the estimate of the operating point can be partially improved accordingly.

Claims (13)

1. A method for self-diagnosis of the mechanical and/or hydraulic state of a centrifugal pump, in particular a circulation pump, wherein the pump control device contains a mathematical model of the engine for determining the mechanical power of the pump and the actual speed of the pump, and for self-diagnosis of the pump, the mechanical power of the pump, determined using the engine model for a given pump speed, compared with the calculated mechanical power of the pump, characterized in that for estimating the duty point of the pump based on the pump speed and the mechanical power of the pump, a duty point module is provided, whereby this calculated mechanical pump power is determined by the inversion of the duty point module for a given pump speed, and within the duty point module, the corrected power value is included in the indicated mechanical pump power to compensate for mechanical power losses. 2. The method according to claim 1, characterized in that the operating point module for determining the calculated mechanical power is supplied with a pump flow and/or pump head expected for a given pump speed, and these expected pump flow and/or pump head are preferably determined with using the laws of affinity. 3. A method according to any one of the preceding claims, characterized in that, by said comparison, the difference between the power values is determined, and if the difference is not equal to zero, incorrect behavior of the pump is recognized. 4. The method according to any one of paragraphs. 1 or 2, characterized in that this method is carried out repeatedly in case of incorrect behavior for different determined speed values, and by interpreting the results of the comparison, respectively, the difference values, a defect determination is undertaken. 5. The method according to claim 4, characterized in that this corrected power value systematically varies during the repetition of the method. 6. The method according to claim 5, characterized in that by systematically changing the corrected power value, attempts are made to determine a new single corrected power value that provides a difference equal to zero or close to zero for different setpoints of rotational speed. 7. The method according to claim 6, characterized in that the pump control device proceeds from increased mechanical wear of the pump if a new single corrected power value can be determined, and otherwise proceed from a non-mechanical defect, in particular from a hydraulic defect, inside the pump. 8. The method according to any one of paragraphs. 1 or 2, characterized in that this method is carried out during the first commissioning of the pump or at a later point in time in the current mode of the pump. 9. The method according to claim 8, characterized in that during the first commissioning, optimization of the operating point estimate can be undertaken by editing said corrected power value, in particular by iterative optimization and/or by using a non-stationary extended Kalman filter for continuous editing the corrected power value according to quadratic optimization. 10. The method according to claim 8, characterized in that when the method is carried out in the current mode of operation, mechanical and / or hydraulic defects of the pump are recognized and indicated to the user visually and / or acoustically, in particular, a warning is issued shortly before the pump fails. 11. A centrifugal pump, in particular a circulation pump, with a variable speed pump drive and with a pump controller for carrying out the method according to any one of the preceding claims.

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