Method for Preventing Vibration in Pumps

Abstract

A method for preventing or reducing mechanical vibrations of a pump, in particular a centrifugal pump, during pump operation is provided. A pump controller detects at least one signal of a pump operation parameter and identifies signal fluctuations in order to detect mechanical vibrations occurring in the pump. The pump controller controls the frequency converter to modify the pump speed in order to reduce a detected pump vibration.

Claims

1-12. (canceled)

13. A method for preventing or reducing mechanical vibrations of a pump having a frequency converter and a pump controller, comprising the steps of: detecting with the pump controller at least one signal of a pump operating parameter; analyzing with the pump controller the at least one signal to identify signal oscillations characteristic of mechanical vibrations of the pump; and changing the pump revolution rate by the pump controller controlling the frequency converter to reduce the mechanical vibrations of the pump.

14. The method as claimed in claim 13, wherein the step of analyzing the at least one signal includes calculation of a frequency spectrum of the at least one signal by Fast Fourier Transformation.

15. The method as claimed in claim 14, wherein at least one signal of the at least one signal corresponds to a motor current of a pump drive.

16. The method as claimed in claim 14, wherein at least one signal of the at least one signal corresponds to a hydraulic final pressure of the pump, and the hydraulic final pressure is determined by one of both of a pressure sensor and an estimate of an operating point of the pump.

17. The method as claimed in claim 14, wherein the step of changing the pump revolution rate includes iteratively varying pump revolution rate to identify a pump revolution rate at which an amplitude of the frequency spectrum is at a minimum.

18. The method as claimed in claim 17, wherein the pump revolution rate is iteratively varied within a predefined tolerance range.

19. The method as claimed in claim 17, wherein the pump revolution rate is iteratively varied to identify at least one anti-resonance of the pump, and the step of changing the pump revolution rate includes operating the pump at the at least one antiresonance of the pump.

20. The method according to claim 17, wherein the pump revolution rate is varied by one or both of an interval halving method and an optimization method.

21. The method according to claim 17, wherein the pump revolution rate is varied by one or more of an active set method, a Newton method, and a genetic algorithm.

22. The method as claimed in claim 14, further comprising the steps of: storing the calculated frequency spectrum, comparing subsequently calculated frequency spectrums to identify frequency spectrum changes corresponding to changes in pump resonance vibrations.

23. The method as claimed in claim 22, further comprising the step of: outputting a signal in the event of an identified change in pump resonance vibrations indicating one of both of pump wear and damage to the pump structure.

24. A pump arrangement, comprising: a pump; a frequency converter; and a pump controller, wherein the pump controller is configured to receive at least one signal of a pump operating parameter, analyze the at least one signal to identify signal oscillations characteristic of mechanical vibrations of the pump, and control the frequency converter to change the pump revolution rate to reduce the mechanical vibrations of the pump.

25. The pump arrangement as claimed in claim 24, wherein the pump is a centrifugal pump.

26. The pump arrangement as claimed in claim 25, wherein the centrifugal pump is a waste water pump, solids pump or supply pump.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1: shows a possible frequency response of an installed and operational centrifugal pump,

[0026] FIG. 2: shows a time diagram of a periodic signal and

[0027] FIG. 3: shows the calculated frequency spectrum of the time signal from FIG. 2.

DETAILED DESCRIPTION

[0028] The invention according to the present application describes a method for the targeted prevention of undesirable vibration amplifications in the resonant case during the operation of a pump, in particular a solids pump, a waste water pump or another supply pump, by means of a frequency converter. The foundation for the targeted prevention of these resonant vibrations is that such resonance cases must initially be detected by the pump controller, but preferably without having to retrofit the pump with a special sensor system such as accelerometers. However, there is nothing to prevent fitting the pump with additional sensors, for example accelerometers, which may increase the accuracy of the method if necessary.

[0029] Since the mechanical vibrations are a consequence of the interaction between the structure and the force of the motor, these mechanical vibrations can also be seen as a superposition in the drive currents of the pump current of the pump drive. Since the intensity of the individual superimposed vibrations is of interest here, the evaluation of the motor currents is carried out by analyzing the frequency spectrum of the recorded motor signal, which the pump controller obtains by executing the Fast Fourier Transformation (FFT).

[0030] This procedure can be briefly illustrated based on the representations of the FIGS. 2, 3. FIG. 2 shows a time diagram of a recorded signal, which was generated here for the sake of simplicity by a superposition of three sinusoidal signals with different frequencies. By applying the FFT, the time signal can now be decomposed into its harmonic components, and it results in the frequency amplitude spectrum represented in FIG. 3, from which, as expected, the individual frequencies of the sinusoidal signals can be read out.

[0031] Due to the FFT of the motor currents, the pump can therefore detect mechanical vibrations which are reflected in the recorded motor current. In the following step, the pump or the pump controller then seeks to set the pump revolution rate so that the resulting rotational frequency of the impeller does not fall on a natural frequency of the pump or a multiple of such a natural frequency. For this purpose, the revolution rate is initially varied and in a further step a spectrum analysis of the currently recorded motor current is again performed at a changed revolution rate. If the amplitude of the occurring current oscillation has become smaller, this is an indication that the mechanical vibration could be successfully reduced by the revolution rate variation. The method is now carried out iteratively to achieve as small an amplitude value of the occurring fluctuations in the current signal as possible. Finding the ideal revolution rate can in principle be carried out according to two scenarios:

Scenario 1: The Required Rotational Frequency is Subject to Fixed Requirements.

[0032] According to scenario 1, the rotational frequency may only have a certain value. This may have energy-related reasons or the intended purpose requires a certain (fixed) revolution rate. In this case, the pump operator defines a tolerance value in the pump controller by which the circulating frequency may deviate maximally from the setpoint, for example ±3 Hz. The pump controller then varies the revolution rate within the allowable tolerance range and iteratively finds out the revolution rate at which the vibration amplitude is minimal. Often even very small variations are sufficient to depart from the natural frequency of the system and thus to minimize the occurring mechanical vibrations.

Scenario 2: There are No Special Requirements for the Rotational Frequency.

[0033] If there are no process-side requirements for the rotational frequency, the pump controller can change the pump revolution rate at will. This allows a targeted search for an anti-resonance and setting the final operating revolution rate of the pump to this anti-resonance. The easiest way (and thus the one with the lowest memory and process requirements) to determine the appropriate revolution rate (antiresonance) from the available revolution rate range is based on bisection. Mathematical optimization methods are faster and more effective, such as the “active-set method” or the “Newton method”. A global optimum can also be reliably determined by means of a genetic algorithm.

[0034] Alternatively or in addition to the motor currents, the signal of the final pressure of the pump can also be examined, in that similarly to the motor current here too the frequency spectrum is analyzed and evaluated for corresponding resonance frequencies by means of Fast Fourier Transformation. The final pressure can be calculated, for example, with a pressure sensor of the pump or else by means of operating point estimation.

[0035] To increase the signal quality, both signals (final pressure and motor current) can also be merged by means of sensor data fusion. If this is not possible, current and pressure signals can also be evaluated individually. For the sensor fusion, for example the individual signal values can be evaluated as shown above and then merged by means of weighting. It is also conceivable to define ranges of interest in which the individual results of the separately evaluated signals can be weighted differently. For example, the result of the evaluation of the motor currents for frequency ranges between 10 and 200 Hz is used, while the result of the final pressure evaluation for higher frequencies is taken into account.

[0036] A particular advantage of the method presented here is that the pump itself can find its natural frequencies and therefore no mathematical process model, which would be complex to develop, is required. The main application of the method presented here is the prevention or reduction of vibrations to reduce wear and noise during pump operation. In addition, the process can also provide a contribution to wear and damage monitoring and can warn the user in case of damage.

Wear Monitoring

[0037] With the presented method, the frequency response of the built-in pump is permanently monitored. However, as mentioned above, this depends on the construction of the pump, the installation position, the materials and the bearings. Therefore a change in the frequency response is in any case an indication that one or more of these variables have changed, for example due to wear and tear. This information can then be used for wear monitoring, for example in combination with the solution from DE 10 2018 200 651, to which express reference is made at this point. A combination of these two approaches makes it possible to evaluate the wear condition more precisely.

Warning of Damage

[0038] In contrast to wear, which leads to a very slow change in frequency response, pump damage would change the frequency response abruptly and significantly. Damage can be, among many other things, a bearing or impeller break. Due to the rapid change of the frequency response, the pump controller can reliably separate wear and tear and damage and in the event of damage can issue a warning to the operator.