Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D29/00—Details, component parts, or accessories
  • F04D29/66—Combating cavitation, whirls, noise, vibration or the like; Balancing
  • F04D29/669—Combating cavitation, whirls, noise, vibration or the like; Balancing especially adapted for liquid pumps
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D15/00—Control, e.g. regulation, of pumps, pumping installations or systems
  • F04D15/0066—Control, e.g. regulation, of pumps, pumping installations or systems by changing the speed, e.g. of the driving engine
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D15/00—Control, e.g. regulation, of pumps, pumping installations or systems
  • F04D15/0088—Testing machines

Definitions

• the invention relates to a method for avoiding or reducing mechanical vibrations during operation of a pump, in particular a centrifugal pump.
• the causes of vibrations can be varied.
• the cause can be externally excited vibrations, e.g. due to the rotation of the pump impeller, or free vibrations due to the natural frequencies of the built-in pump.
• Solid pumps are centrifugal pumps for the transport of fluids with highly abrasive solid parts, for example slag, coal or ore in mining.
• the pumping medium can also contain stones or other rigid elements which, when the pump is in operation, can generate shocks when they hit the pump structure, which lead to the free vibrations of the pump being excited. This ef fect occurs increasingly with pumps for the sewage sector.
• a particularly unfavorable case is when the rotational frequency of the impeller, ie the set pump speed, falls to the natural frequency of the built-in pump or corresponds to an integer multiple of the natural frequency. In this case resonance oscillations occur, ie the two causes of oscillation reinforce each other. It is similarly problematic when the set rotational frequency of the impeller coincides with the pipe resonance of the conveyor system.
• FIG. shows the frequency response of a ready-to-use centrifugal pump.
• the natural frequencies at which the system oscillates freely have the frequency values fi, f2, f3.
• the frequency response i.e. the position of the natural frequencies fi, f2, f3 depends on the specific pump structure, the selected installation position, the materials used and the bearings installed. If the rotational frequency of the pump wheel set by means of the frequency converter is identical to, or if instead it is an integer multiple of one of the natural frequencies fi, f2, f3 shown, the system is excited by the separately excited rotation of the impeller and an increased resonance oscillation of the pump occurs. If the rotational frequency of the impeller is instead in the range of one of the anti-resonances afi, af2 shown here, this effect is minimal and there is no or only a very small oscillation.
• the idea of the present application builds on the above knowledge and proposes a method that reduces the risk of possible vibrations, in particular resonances, to a minimum by taking specific measures during the pump operation.
• a frequency converter to change the speed of the pump is decisive for the execution of the procedure.
• a frequency converter is integrated into the pump, attached to the pump housing or installed separately from the pump.
• the solution according to the invention of the present application consists in varying the speed of a pump with a frequency converter by a pump control during the pump operation in such a way that mechanical vibrations of the pump are reduced as optimally as possible.
• Another core aspect of the invention is that the pump independently identifies its natural frequencies during operation by means of suitable signal evaluation in order to be able to optimally adapt the set pump speed based on this knowledge.
• the pump therefore does not need information about its frequency response that has already been generated and stored in the pump, but can instead determine this independently during operation.
• the pump records a signal during pump operation, which characterizes a pump operating parameter that is influenced by mechanical vibrations that occur.
• the recorded signal is then examined by the pump for the presence of any vibrations, in particular resonance vibrations. Such a vibration is subsequently reduced by changing the speed accordingly.
• the frequency spectrum of the recorded signal is therefore considered. It is advantageous if the signal is first transformed into its frequency spectrum by means of transformation, in particular by means of Fast Fourier Transformation, in order to identify the corresponding frequency values and associated amplitudes of signal oscillations occurring.
• the motor current or currents of the pump drive proves to be a suitable operating signal for identifying any vibrations.
• the current values are already available to the frequency converter used, so that no further sensors are required becomes. Since mechanical vibrations in the pump system are also reflected in the motor windings of the pump drive due to magnetic induction and accordingly in the current of the motor, the motor consequently acts as an effective sensor that is available at all times. Mechanical vibrations of the pump system can then be identified with sufficient accuracy by means of a corresponding current analysis. This possibility exists regardless of the type of motor used for the electric pump drive.
• An alternative or additional operating parameter for determining the frequency response of the pump is, for example, the pump pressure, in particular the final pressure of the pump.
• the final pressure of the pump can be determined, for example, by means of an existing pressure sensor and transformed into its frequency spectrum by means of signal transformations, in particular Fast Fourier transformation.
• a suitable sensor does not necessarily have to be kept ready for signal acquisition.
• the existing pump pressure can be determined by calculation, for example by means of operating point estimation. A possible method for this is disclosed in DE102018200651, the content of which is fully included at this point.
• the method can be carried out iteratively with a varying pump speed, for example to identify that pump speed at which the amplitude of an identified oscillation is as minimal as possible. So after the speed change has taken place, the pump again analyzes the frequency spectrum of the repeatedly recorded signal and checks whether the variation in speed has led to a decrease in the corresponding amplitude.
• the iterative execution of the method steps can provide an arbitrary or accidental or a controlled speed change. If the amplitude increases, for example, the speed change that occurred between two iterations is reversed, otherwise retained. It is also conceivable to run through a certain speed range completely and then to set the speed with the lowest amplitude for the pump operation.
• suitable methods and algorithms can be used to identify a local or global amplitude minimum with the associated speed.
• An interval halving method and / or an optimization method such as an active set method and / or Newton method, are conceivable in order to determine the appropriate speed as quickly as possible, which leads to an amplitude minimum.
• a genetic algorithm is also conceivable, which is comparatively slow, but enables a global minimum of the frequency response to be identified.
• the setting of the speed or its variation during the process iterations also depends on the operating conditions, for example, specified by the pump operator. It is conceivable, for example, that the pump operator specifies a constant pump speed or only a small tolerance range for speed changes. During the process iterations, a speed variation then only takes place within the previously defined tolerance range. In such a case, an iterative method execution is usually sufficient, in which all or at least some of the permitted speeds are run in order to determine the corresponding amplitude minimum for this range.
• the method can not only serve to reduce occurring vibrations, but the determination of the frequency response according to the invention is also suitable for pump monitoring in order to be able to detect wear or any damage to the pump mechanics at an early stage.
• a key aspect of the invention is to determine the frequency response of the pump. This essentially depends on the pump design, its installation position, the materials used and the bearing components installed. A change in one of these factors, for example due to wear or material damage, leads to a change in the frequency response of the pump.
• the pump therefore preferably saves the determined frequency response and monitors it for frequency shifts in the relevant frequencies identified by continuous repetitive measurements. If such a frequency deviation is recognized, this is an indication of wear and tear or pump damage.
• the pump can then generate a corresponding warning message or take appropriate action.
• the degree of change can also be included.
• the present invention also relates to a pump, preferably a centrifugal pump, particularly preferably a waste water or solids or supply pump, with an internal or external frequency converter and an internal or external pump control for carrying out the method according to the invention.
• a pump preferably a centrifugal pump, particularly preferably a waste water or solids or supply pump, with an internal or external frequency converter and an internal or external pump control for carrying out the method according to the invention.
• the application proposes the use according to the invention of a pump, in particular a centrifugal pump as a waste water pump, solids pump or supply pump.
• a pump in particular a centrifugal pump as a waste water pump, solids pump or supply pump.
• the inventive minimization of occurring me- Mechanical vibrations are of particular importance in sewage or solids pumps, so that the application of the method according to the invention with such types of pumps has far-reaching advantages.
• Fig. 1 a possible frequency response of an installed and operational centrifugal pump
• Fig. 2 a timing diagram of a periodic signal
• the invention according to the present application describes a method to specifically avoid undesirable vibration amplifications in the case of resonance when operating a pump, in particular a solid, sewage or other supply pump by means of a frequency converter.
• the basis for the targeted avoidance of these resonance vibrations is that such cases of resonance must first be recognized by the pump control, but if possible without having to retrofit the pump with special sensors such as acceleration sensors.
• acceleration sensors there is nothing against equipping the pump with additional sensors, for example acceleration sensors, whereby the accuracy of the method can be increased if necessary.
• FIG. 2 shows a time diagram of a recorded signal which, for the sake of simplicity, was generated here by superimposing three sinusoidal signals with different frequencies.
• the time signal can now be broken down into its harmonic components and the result is the frequency amplitude spectrum shown in FIG. 3, from which, as expected, the individual frequencies of the sinusoidal signals can be read.
• the pump can detect mechanical vibrations that are reflected in the recorded motor current.
• the pump or the pump control then tries to set the pump speed 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.
• the speed is first varied and in a further step a spectrum analysis of the currently recorded motor current is carried out again with a changed speed. If the amplitude of the current oscillation that occurs has become smaller, this is an indication that the mechanical oscillation was successfully reduced by the speed variation.
• the method is now carried out iteratively in order to achieve the smallest possible amplitude value of the fluctuations in the current signal.
• the ideal speed can be found according to two scenarios:
• Scenario 1 The required rotational frequency is subject to fixed requirements.
• the rotational frequency may only have a certain value. This can have energetic reasons or the application requires a certain (fixed) speed.
• the pump operator defines a tolerance value in the pump control by which the rotational frequency may deviate from the setpoint, e.g. B. + 3 Hz.
• the pump control then varies the speed within the permitted tolerance range and iteratively finds the speed at which the oscillation amplitude is minimal. Often, even very small variations are sufficient here to leave the natural frequency of the system and thus to minimize the mechanical vibrations that occur.
• Scenario 2 There are no special requirements for the circulation frequency.
• the pump control can change the pump speed at will. This enables a targeted search for an anti-resonance and the setting of the final operating speed of the pump to this anti-resonance.
• the simplest way (and therefore the one with the lowest memory and process requirements) to determine the appropriate speed (anti-resonance) from the available speed range is based on bisection.
• Mathematical optimization methods such as the "Active-Set method” or the “Newton method", are faster and more effective. A global optimum can also be reliably determined using a genetic algorithm.
• the signal of the final pressure of the pump can also be examined by analyzing the frequency spectrum analogously to the motor current by means of Fast Fourier transformation and evaluating it for corresponding resonance frequencies.
• the final pressure can for example be calculated with a pressure sensor of the pump or by means of operating point estimation.
• both signals can also be merged using sensor data fusion.
• current and pressure signals can also be evaluated individually.
• the individual signal values can be evaluated as shown above and then combined by means of weighting. It is also conceivable to define frequency ranges in which the individual results of the separately evaluated signals are weighted differently. E.g. the result of the evaluation of the motor currents is used for frequency ranges between 10 and 200 Hz, while the result of the final pressure evaluation is taken into account for higher frequencies.
• a particular advantage of the method presented here is that the pump can find its own natural frequencies and therefore no mathematical process model, which would be laborious to develop, is required.
• the main application of the procedure presented here is the avoidance or reduction of vibrations, to reduce wear and noise during pump operation.
• the method can also make a contribution to wear and damage monitoring and warn the user in the event of damage. Wear monitoring
• the frequency response of the built-in pump is permanently monitored. However, as mentioned above, this depends on the design of the pump, the installation position, the materials and the bearings. A change in the frequency response is therefore always 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 also in combination with the solution from DE 10 2018 200 651, to which reference is expressly made at this point. A combination of these two approaches makes it possible to assess the state of wear more precisely.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Control Of Non-Positive-Displacement Pumps (AREA)
• Structures Of Non-Positive Displacement Pumps (AREA)
• Control Of Positive-Displacement Pumps (AREA)

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• 2019
  • 2019-04-18 DE DE102019002826.0A patent/DE102019002826A1/de active Pending
• 2020
  • 2020-04-14 US US17/594,433 patent/US20220186749A1/en active Pending
  • 2020-04-14 WO PCT/EP2020/060432 patent/WO2020212330A1/de not_active Ceased
  • 2020-04-14 JP JP2021562026A patent/JP7583742B2/ja active Active
  • 2020-04-14 CN CN202080029386.2A patent/CN113646538B/zh active Active
  • 2020-04-14 EP EP20719397.0A patent/EP3956567A1/de active Pending

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