METHOD FOR DETERMINING A SYNCHRONOUS SPEED

Description

[0001] The present invention relates to a method for determining the synchronous speed of an electric machine in a machine driven by the electric machine. The invention further relates to a processing device, a system, and a computer program.

[0002] When operating a pump system, particularly a centrifugal pump system consisting of a pump and the electric motor driving it, especially an asynchronous motor, it is often necessary to determine its operating point. The operating point of a turbomachine, especially a centrifugal pump, on its flow-head characteristic curve (QH curve), is characterized in particular by its flow rate, also referred to as delivery rate. There are various ways to determine this. It can be determined by measuring the flow rate or by measuring the pressure. In the latter case, the pressure difference between the discharge and suction sides of the pump is usually measured. The delivery head is estimated as the quotient of the pressure difference, density, and acceleration due to gravity. With water as the pumped fluid, a pressure difference of 1 bar corresponds to a delivery head of approximately 10 meters.Furthermore, the operating point of a centrifugal pump is determined by an electrical measurement, whereby the delivered motor power is calculated from a current and voltage measurement, taking into account the efficiency of the motor.

[0003] From DE 10 2009 022 107 A1 and EP 2 433 010 B1, a device and a method are known for determining the operating point of a driven machine and / or an asynchronous motor driving it. The method and device disclosed therein can be applied to unregulated or mains-powered asynchronous machines, since in these cases the synchronous speed of the electric machine is known. The synchronous speed can be calculated, for example, by multiplying the mains frequency by the number of pole pairs. However, determining the operating point of the driven machine is problematic if it is driven by a speed-controlled asynchronous machine, and thus the synchronous speed is unknown.

[0004] DE 10 2017 213 131 A1 discloses the control of an actuator by detecting a noise emission and / or vibration emission by means of at least one acoustic sensor while the actuator is operated at a predefined operating point, and changing the operating point of the actuator if the noise emission and / or vibration is in a predefined undesirable range.

[0005] DE 10 2006 008 048 A1 discloses a motor speed detection device for detecting the rotational speed of a rotor of an induction motor, wherein the rotor is driven to rotate by excitation of a stator of the motor by means of an alternating current signal, with a control device that inserts a harmonic component of a frequency into the alternating current signal which is higher than the excitation frequency of the alternating current signal, and a filter circuit that extracts from an alternating current signal a frequency component which lies within the extraction frequency band which has been set by the filter circuit.

[0006] It is therefore an object of the present invention to at least partially solve the problems described above. In particular, it is an object of the present invention to propose an improved method for determining a synchronous speed and / or to extend the application of a known method for determining the operating point without using electrical measured variables for speed-controlled asynchronous machines.

[0007] The foregoing problem is solved by a method having the features of claim 1, a processing device having the features of claim 12, a system having the features of claim 13, and a computer program having the features of claim 15. Further features and details of the invention will become apparent from the respective dependent claims, the description, and the drawings.

[0008] The problem is solved by a method for determining a synchronous speed of an electric machine, in particular a speed-controlled asynchronous machine and / or synchronous machine and / or rotating electric machine and / or an electric motor, in particular an asynchronous motor, in a working machine driven by the electric machine, in particular a pump arrangement.

[0009] Advantageously, an (electrical) control device such as a frequency converter can be provided for speed control of the electrical machine, in particular an asynchronous machine.

[0010] Furthermore, the following process steps can be carried out, preferably one after the other in the specified order or in any order, whereby individual and / or all steps can also be repeated: Initiating and / or carrying out the acquisition of at least one (in particular mechanical) measured variable in the electric machine and / or the driven machine, preferably to obtain acquisition information specific to a rotational sound of the electric machine and / or the driven machine and / or to the synchronous speed, in particular in the form of noise information and / or a time course of the measured variable; carrying out a signal analysis, in particular frequency analysis, of the acquisition information to obtain a spectrum, in particular frequency spectrum, of the acquisition information; carrying out a selection of at least one region in the spectrum, in particular at least one frequency range in the frequency spectrum, preferably on the basis of a (in particular previously known and / or manually entered) clock frequency of the control device.where, alternatively or additionally, the selection of several different ranges can also be based on at least one multiple of the clock frequency and / or different multiples of the clock frequency; performing a detection of at least one peak value in the (respective, selected) range, in particular frequency range, in order to determine at least one or exactly two or at least two frequencies specific to the synchronous speed (in this respective range), wherein the frequency(ies) can each be a frequency of a harmonic, i.e., in particular frequencies which are excited by harmonics of the control device; performing the determination of the synchronous speed based on the at least one determined frequency.

[0011] This has the advantage that the synchronous speed can be determined even without access to electrical measurements of the driven machine, in particular the electric machine and / or the control device, and / or without knowledge of the control parameters of the control device. The control parameters are, for example, a set speed and / or a control variable, or similar, which are used for speed control. Furthermore, in a speed-controlled electric machine or asynchronous machine, the synchronous speed can deviate from the rated speed and, for example, always be slightly above the rated speed. The rotating magnetic field in an asynchronous machine induces voltages and currents in the rotor windings only when the rotor rotates asynchronously with the rotating magnetic field. The difference in speed between the rotating field and the rotor relative to the rotating field speed, i.e., the synchronous speed, is called slip.

[0012] It is possible to perform the selection, detection, and determination steps of the synchronous speed for different regions within the spectrum, encompassing the clock frequency and / or multiples thereof and / or different multiples thereof. For example, at least two or at least three different regions within the spectrum can be selected based on the clock frequency and / or multiples thereof and / or different multiples thereof. Each region can therefore encompass a different multiple of the clock frequency or even the clock frequency itself. Within each region, the peak values ​​can be detected to determine the frequencies specific to the synchronous speed. A value for the synchronous speed can then be determined for each region based on the frequencies identified within it.The determined values ​​can also be used together to determine the synchronous speed, thereby increasing accuracy. Therefore, performing the selection based on the clock frequency also includes performing the selection based on at least one multiple of the clock frequency.

[0013] Advantageously, the synchronous speed is determined by measuring at least one such quantity that occurs merely as a side effect of the operation of the electric or driven machine, yet nevertheless provides information about the synchronous speed. This can be sound (e.g., structure-borne or airborne sound pressure), so that the quantity can also be understood as noise emitted by the electric or driven machine. The quantity can provide information about the synchronous speed. This information can also result from an effect of the operation that is generally considered disruptive, such as the noise characteristics of the control device. Furthermore, the information can be specific to the rotational sound of the electric and / or driven machine, e.g.,...The noise is caused by periodic alternating forces in the electric motor and / or driven machine. The acquisition of the measured quantity serves to make this information accessible for processing. This can be achieved by converting the measured quantity into the acquisition information, for example, using a sound transducer and / or an analog-to-digital conversion.

[0014] The control device can include at least one power electronic switch for speed control of the electric or asynchronous machine, particularly in the form of controlled bridges. This switch can be, for example, a power transistor, preferably a metal-oxide-semiconductor field-effect transistor (MOSFET), junction field-effect transistor (JFET), insulated-gate bipolar transistor (IGBT), or IGC thyristors. Furthermore, the control device can generate a variable output voltage by means of pulse-width modulation (PWM). In this way, the magnitude of the resulting output voltage and its frequency can be controlled within wide limits.

[0015] It is possible that the acquisition information is specific to the rotational noise and / or the synchronous speed because the acquisition information results from noise generated by the electric machine and / or driven machine. Specifically, when using a PWM clock frequency in the audible range for the control device, disturbing noises can occur. These are caused, for example, by mechanical vibrations of the stator. Increasing the clock frequency can reduce this effect, but it can also increase the power loss of the frequency converter. According to the invention, however, the noise generation can also be used to determine the synchronous speed of the electric machine based on the noise generation. The noise generated by the electric machine can, for example, be acquired as acquisition information for processing (i.e., for further process steps such as signal analysis, etc.).The data can be made available to determine the synchronous speed through processing. This can take advantage of the effect that the synchronous speed influences these noises, particularly through amplitude modulation of the rotational frequency of the control device. Therefore, the frequencies determined by detecting at least one peak value can also be specific to the synchronous speed.

[0016] It is also conceivable that at least one windowing of the frequency spectrum is performed to select at least one frequency range. Here, a window width and / or a window position can be defined for the windowing (i.e., the window) such that, by subsequently detecting at least one peak value, or at least two, or exactly two peak values ​​in the respective frequency range, only (one or more) frequencies within the frequency range that are specific to the synchronous speed are determined. As described above, the synchronous speed can be deduced from the acquired information. In particular, the synchronous speed has an effect on the spectrum of the acquired information. For example, in a PWM, characteristic oscillations are excited for the synchronous speed, the frequencies of which occur around the clock frequency or multiples of the clock frequency of the control device.The distance of these frequencies from the clock frequency or its multiples can depend on the synchronous rotational speed. The window parameters window width and / or window position can then be set such that the at least one frequency range resulting from the at least one windowing includes these frequencies, while excluding other similarly strong or stronger frequencies in the frequency spectrum. This has the advantage that only these frequencies are determined during the subsequent peak detection. The specific setting of the window parameters to achieve this desired function can be carried out, for example, by manual adjustment in the manner of a calibration before the method according to the invention is used.

[0017] Furthermore, it is conceivable that the control device is designed as a frequency converter. Alternatively or additionally, the at least one frequency range can be selected around the clock frequency and / or at least a multiple of the clock frequency, preferably having the clock frequency or the multiple of the clock frequency as its center frequency. Thus, during the selection process, at least one window for selecting the at least one frequency range is placed centrally around the clock frequency and / or the at least one multiple of the clock frequency. In this way, frequencies can be selected that occur at a distance from this clock frequency and / or multiples of the clock frequency, where this distance can depend on the synchronous speed. In other words, one or more windowing operations can be performed during the selection process, each resulting in a frequency range around the clock frequency and / or a multiple thereof.

[0018] Furthermore, it is optionally provided that the selection process includes the following steps: Defining (at least) a window width based on a predefined expected synchronous speed, defining (at least) a window position based on the clock frequency, in particular at the clock frequency and / or at least a multiple of the clock frequency, e.g. at the position of the clock frequency or multiples of the clock frequency, such that the clock frequency or multiples of the clock frequency form the center frequency for the frequency range, performing at least one windowing of the frequency spectrum in each case to select the frequency range as a range around the clock frequency or the multiples of the clock frequency with the defined window width and window position.

[0019] This approach allows for the selection of only the relevant frequencies that can be used to determine the synchronous speed. The aforementioned selection steps can be repeated for different window positions, preferably defined by the clock frequency and / or multiples thereof. In other words, the windowing can be performed multiple times for different frequency ranges, and several frequency ranges around the clock frequency and / or different multiples thereof can be selected. For each selected frequency range, a value for the synchronous speed can advantageously be estimated based on the frequencies determined within it, in order to determine the synchronous speed using these values.

[0020] Furthermore, it is conceivable that the clock frequency lies in the range of 1 kHz to 20 kHz, preferably 2 kHz to 16 kHz, preferably 4 kHz to 12 kHz. Accordingly, the range within which the frequency range is selected can be narrowed down.

[0021] Furthermore, it is optionally provided that the mechanical measurement differs from an electrical measurement of the electric machine and / or the control device, and is preferably acquired independently of a control parameter of the control device. This allows the method according to the invention to be carried out even without direct access to the control device and / or the electric machine, e.g., simply by acquiring the measurement such as sound pressure or the like.

[0022] Preferably, the mechanical measurement quantity may include at least one of the following measurement quantities: a pressure, a differential pressure, a force, a vibration, a structure-borne sound, an airborne sound.

[0023] This enables the inventive method to be carried out without direct contact with the electrical machine and / or working machine, e.g. by means of a processing device according to the invention, e.g. in the form of a mobile measuring device.

[0024] It is also conceivable, optionally, that the frequency range window width is defined such that exactly two, or at least two, peak values ​​are detected during subsequent detection. At each of these peak values, one of the frequencies specific to the synchronous speed can be determined, and the synchronous speed is then calculated based on the frequency difference between the determined frequencies. This enables a reliable determination of the synchronous speed.

[0025] Another possibility is to stipulate that the frequency range window width is at least twice or at least four times the expected synchronous frequency (according to the synchronous speed). This makes it possible to reliably limit the range of relevant frequencies. The window width can, for example, be a maximum of two, three, four, or six times the expected synchronous speed.

[0026] The invention also relates to a processing device, e.g., a measuring device, which is also designed for processing, in particular data processing. It is provided that the processing device includes means for carrying out the steps of a method according to the invention. Thus, the processing device according to the invention offers the same advantages as those described in detail with reference to a method according to the invention.

[0027] A system is provided, featuring: a working machine, in particular a pump arrangement, an electric machine, in particular a speed-controlled asynchronous machine, in particular of the working machine, for driving the working machine, preferably to generate a rotary movement in the working machine for conveying a medium to be conveyed, a control device of the working machine and in particular of the electric machine, preferably for speed control of the electric machine, in particular to set a current speed of the rotary movement, a processing device according to the invention.

[0028] Furthermore, it may be provided within the scope of the invention that the working machine is designed as a pump arrangement, in particular a centrifugal pump arrangement, and / or that the processing device is designed separately from the working machine, in particular in the form of a mobile device.

[0029] The invention also relates to a computer program, in particular a computer program product, comprising instructions which, when executed by a processing device according to the invention, cause the processing device to execute a method according to the invention. The computer program according to the invention thus offers the same advantages as those described in detail with reference to a method according to the invention. For the execution of the computer program, the processing device can have a processor which reads the computer program from a non-volatile memory of the processing device.

[0030] The solution according to the invention can be used to carry out the method described in EP 2 433 010 B1 and / or to operate the device described therein for determining the operating point. Specifically, the method and / or the processing device according to the invention can be used to determine the synchronous speed (hereinafter also referred to as synchronous speed) for this purpose. Reference is therefore made to the aforementioned patent document and also to the associated application (WO 2010 / 133425), the contents of which are hereby incorporated into this application. An advantage of the present invention is that the scope of application of the aforementioned patent can thus be extended to speed-controlled asynchronous machines.

[0031] For example, it may be possible to use the determined synchronous speed to determine an operating point of the driven machine. Thus, the method according to the invention, based on the determination of the synchronous speed, can also be used to determine the operating point of the driven machine or the electric machine driving the driven machine. The driven machine can, for example, be driven by the speed-controlled asynchronous machine (as the electric machine), for which determining the synchronous speed is conventionally impossible or only technically complex. The operating point can be characterized by the power consumed by the driven machine and / or its delivery rate.

[0032] For example, it is conceivable that the following steps are carried out to determine the operating point based on the synchronous speed and a different current speed of the driven machine: Determining a rotational tone frequency linearly proportional to the rotational tone of the driven machine and / or electrical machine from the frequency spectrum, determining the current rotational speed of the driven machine based on the determined rotational tone frequency, determining a speed-torque characteristic curve of the electrical machine, e.g. at least based on given motor parameters such as rated power and / or rated speed and / or synchronous speed, determining a power input from the driven machine based on the determined current speed and the speed-torque characteristic curve, whereby the operating point is characterized by the power input.

[0033] To acquire at least one measured quantity, one or more sensors can be used, which acquire the measured quantity as an operating-point-dependent quantity of the driven machine. The measured values ​​determined in this way can be evaluated and / or stored during operation of the driven machine using a method according to the invention. Furthermore, the invention may provide that the operating point is determined without the use of electrical measured quantities from the driving asynchronous motor. For this purpose, a frequency linearly proportional to the rotational noise of the driven machine and / or electrical machine (rotational noise frequency) can be determined from a mechanical measured quantity such as pressure, differential pressure, force, vibration, structure-borne sound, or airborne sound by means of signal analysis, in particular frequency analysis.From this, the rotational speed of the drive machine can be determined, and the operating point can be determined from the slip-related rotational speed-torque relationship of the asynchronous motor. Furthermore, the power input of the driven machine can be determined by the following steps (the electrical machine will subsequently be referred to as the motor): Determination of the motor's speed-torque characteristic, in particular through specified motor parameters such as rated power and rated speed, optionally synchronous speed, pull-out torque, pull-out speed or pull-out slip. Determination of the motor's input power or torque from the determined input speed (i.e., the current speed) and the motor's speed-torque characteristic.

[0034] In the case of a pump, particularly a centrifugal pump, used as a working machine, it may be possible to determine the pump's flow rate from its drive speed. Only mechanical parameters are then measured at the pump. The drive or shaft speed of the pump can be determined from the measured rotational frequency. This offers a significant cost advantage compared to directly measuring the flow rate, for example, using ultrasonic or magnetic-inductive flow measurement technology. The effort and costs are also minimized compared to determining the flow rate based on electrical power measurement.

[0035] The processing device according to the invention can be arranged on the pump, on its drive motor or in its vicinity and / or be integrated with the pump or its drive motor.

[0036] The processing device according to the invention can further determine the delivery rate of the pump, in particular centrifugal pump, from the power input or shaft power determined from the drive speed or shaft speed.

[0037] It has proven advantageous for the processing device according to the invention to determine the delivery rate of the pump, in particular centrifugal pump, from parameters of the motor that describe a speed-torque characteristic of the motor, as well as from parameters of the pump that describe a flow rate-power characteristic, and the drive speed or shaft speed.

[0038] It can also be provided that the processing device according to the invention determines the delivery rate of the pump, in particular a centrifugal pump, directly from a characteristic curve that represents the load-dependent change in speed versus the delivery rate of the pump. Such a characteristic curve can be determined through test runs and stored in the data memory so that it can be retrieved during operation of the centrifugal pump. Here, however, the speed-torque relationship of the asynchronous motor is used, which leads to a change in speed across the flow rate range. From this, the operating point, characterized by the power consumed by the driven machine and / or its delivery rate, can be determined particularly easily.

[0039] The data storage device of the processing unit according to the invention can store motor parameters describing the speed-torque relationship of the asynchronous motor and / or other technological data of the machine assembly. This data can be accessed during operation of the machine to determine the operating point. Acquisition of electrical measurements by the processing unit is not necessary. The processing unit can determine the operating point of the machine from a single measurement signal, for example, a pressure sensor signal.

[0040] It can also be provided that the processing device according to the invention has at least one connection for a pressure sensor and determines the drive speed or shaft speed from measured values ​​of a connected pressure sensor in order to determine the operating point of the machine. Pressure sensors for detecting static pressures are also capable of detecting dynamic pressure fluctuations. Such pressure sensors are already fitted to many pumps, in particular to detect their ultimate pressure.

[0041] The parameters necessary for carrying out the individual process steps can be stored or stored in a data storage device of the processing device according to the invention and are thus available for carrying out the individual process steps.

[0042] Further advantages, features, and details of the invention will become apparent from the following description, in which exemplary embodiments of the invention are described in detail with reference to the drawings. The features mentioned in the claims and in the description can each be essential to the invention individually or in any combination. The drawings show: Fig. 1 a schematic representation for visualizing a method according to the invention, Fig. 2 a schematic representation of parts of a system according to the invention, Fig. 3 a schematic representation of a windowing of the frequency spectrum for selecting the frequency range, Fig. 4 a schematic representation of a detection of peak values ​​in the frequency range, Fig. 5 a schematic representation of a frequency spectrum of a stator voltage, Fig. 6 a schematic partial representation of the frequency spectrum of the stator voltage, Fig. 7 a schematic representation of a frequency spectrum of a noise, Fig. 8 a schematic partial representation of the frequency spectrum of the noise.

[0043] In the following figures, identical reference numerals are used for the same technical features even for different embodiments.

[0044] In Figure 1A method according to the invention for determining a synchronous speed n0 of an electric machine 2, specifically and by way of example in the form of a speed-controlled asynchronous machine 2, for a working machine 1 driven by the asynchronous machine 2, is schematically visualized with the associated method steps. As in Figure 2As shown, a control device 3 for speed control of the asynchronous machine 2 can be provided. The control device 3 can, together with the driven machine 1 and / or the processing device 10 according to the invention, be part of a system according to the invention. Furthermore, the asynchronous machine 2 and the control device 3 can be part of the driven machine 1, whereas the processing device 10 can be designed as a mobile device separate from the driven machine 1. A computer program according to the invention can be stored non-volatilely in a memory 15 of the processing device 10 in order to be executed by a processor of the processing device 10 (not explicitly shown) to carry out the process steps of a method according to the invention.

[0045] According to a first step of a method according to the invention, the acquisition of at least one mechanical measurement variable 101 can be initiated at the working machine 1 and / or electrical machine 2 in order to obtain acquisition information 200 specific to a rotational sound of the working machine 1 and / or electrical machine 2. For this purpose, sensors such as pressure sensors and / or at least one microphone can be used at the working machine 1 and / or electrical machine 2. Subsequently, the acquisition information 200 can be further processed, wherein the following process steps are provided for this processing: Performing a frequency analysis 102 such as a Fourier transform of the acquisition information 200 to obtain a frequency spectrum 210 of the acquisition information 200, performing a selection 103 of at least one frequency range 220 in the frequency spectrum 210 based on a clock frequency fT (i.e., possibly also based on at least one multiple of the clock frequency fT) of the control device 3, performing a detection 104 of at least one peak value 230 or at least or exactly two peak values ​​230 in the (respective) frequency range 220 to determine at least one frequency f1, f2 specific for the synchronous speed n0, performing the determination 105 of the synchronous speed n0 based on the at least one determined frequency f1, f2.

[0046] The objective of determining the synchronous speed n0 can be to establish an operating point for the driven machine 1. To determine the speed of the electric machine 2, particularly the asynchronous machine, of the driven machine 1, a first step is to ascertain the current synchronous speed n0 of the electric machine 2. In the method according to the invention, it may be possible to determine the current synchronous speed by analyzing a frequency spectrum generated by the driven machine 1 and / or electric machine 2.

[0047] The magnetically excited acoustic noises in electrical machines 2 can have various causes, such as stator and rotor utilization, stator and rotor saturation, coupling between fundamental wave air gap fields (which arises from the inverter-induced fundamental and harmonic current feed), the type of inverter feed, etc. A problem can arise when determining the current synchronous speed n0 because the electrical machine 2 is unknown, and therefore both the stator and rotor utilization and the stator and rotor saturation are unknown. Thus, it is advantageous to evaluate the vibrational forces in the air gap resulting from the coupling between the fundamental wave rotating fields generated by the inverter-induced fundamental and harmonic currents in order to determine the synchronous speed n0. The harmonics can be determined by the type of inverter feed.The method according to the invention can be suitable for determining the synchronous speed n0 of an electric machine 2 which uses the asynchronous pulse width modulation (PWM) subharmonic method with a symmetrical triangular carrier signal.

[0048] In Figure 5 Figure 1 shows an exemplary frequency spectrum of a stator voltage of the electric machine 2 for an exemplary clock frequency fT of 4 kHz. The frequencies relevant for the method according to the invention are highlighted by a dashed rectangle, and in Figure 6The image is shown enlarged. It can be seen that the characteristic frequency sidebands result around multiples of the clock frequency fT, e.g., 2*fT = 8 kHz, 3*fT = 12 kHz, etc. (highlighted by a dashed rectangle in Figure 6). The dashed rectangles around the clock frequency fT, or its multiples, can also represent possible windowing windows. The amplitudes of the respective frequency bands also depend on the modulation index. The frequency sidebands of the current and voltage can be calculated using the clock frequency fT and the fundamental frequency fS as follows: f k = n 1 ⋅ f T ± n 2 ⋅ f S .

[0049] If n If 1 is an odd integer, then n 2 an even integer, and if n If 1 is an even integer, then n 2 is an odd integer. For example, fk = f T ± 2 · f S ; f T ± 4 · f S ; ... 2 · f T ± fs ; 2 · f T ± 3 · f S ; 2 · f T ± 5 · fs ; ... 3 · f T ± 2 · fs ; 3 · f T ± 4 · f S ; 3 · f T ± 6 · f S ; ... etc.

[0050] In Figure 7 An exemplary frequency spectrum 210 of a noise from the working machine 1 operated on a speed-controlled asynchronous machine 2 is shown. The dashed rectangle indicates the frequencies relevant to the method according to the invention, which are excited by the harmonics of the frequency converter. An enlarged representation of these frequencies is shown schematically in Figure 8 shown.

[0051] Similar to the stator current and stator voltage (see Figure 5 and 6 Characteristic frequency sidebands also result in the noise of the working or electrical machine 2. These frequency sidebands are in Figure 8Highlighted by dashed rectangles, these frequencies are also multiples of the clock frequency fT (here, for example, 4 kHz). However, these noise frequencies are shifted from the frequencies of the harmonics (due to the interaction between the fundamental frequency and the fundamental frequencies of the harmonics) by the fundamental frequency fS. The frequency sidebands of the noise can therefore be calculated using the clock frequency fT and the fundamental frequency fS as follows: f k = m 1 ⋅ f T ± m 2 ⋅ f S .

[0052] If m If 1 is an odd integer, then m 2 an odd integer, and if m If 1 is an even integer, then m 2 is an even integer. For example, fk = f T ± f S ; f T ± 3 · f S ; ...2 · f T ± 2 · f S ; 2 · f T ± 4 · fs; 2 · f T ± 6 · f S ; ...3 · f T ± 5 · f S ; 3· f T ± 7 · f S; 3 · f T ± 9· f S ; ...etc. .

[0053] The current fundamental frequency fS of the asynchronous machine can be determined, for example, from two determined harmonics of the noise signal. f k =1 = f 1 = f T + f S and f k =2 = f 2 = f T - f S determine: f S = f k = 1 − f k = 2 2 = f T + f S − f T − f S 2 = f S .

[0054] The synchronous speed n0 is still obtained from the fundamental oscillation frequency fS divided by the number of pole pairs p of the asynchronous machine 2: n 0 = f S p

[0055] Once the synchronous speed n0 is known, the method disclosed in EP 2 433 010 B1 can advantageously be applied to determine the operating point of the driven machine 1. Furthermore, the accuracy can be increased by analyzing or comparing the frequencies in several frequency windows.

[0056] To determine the harmonics, this can be done in the Figure 7 and 8 The displayed frequency spectrum is evaluated using windowing and peak detection. As shown in Figure 3 As shown, optionally, performing selection 103 can include windowing the frequency spectrum 210. For this purpose, a - in Figure 4 The window width fb, which is marked, is determined based on a predefined expected synchronous speed n0. The minimum window width, which must be considered around the clock frequency and / or a multiple of the clock frequency of the control device 3, in particular a frequency converter 3, can be determined by ±2 · maximum expected fundamental frequencyThe window position can then be determined based on the clock frequency fT. In the example shown, the window position corresponds to the clock frequency fT, so the clock frequency can be considered the center frequency of the frequency range 220. Alternatively or additionally, at least one windowing can be performed in which the window position corresponds to a multiple of the clock frequency fT, so that the multiple of the clock frequency fT can be considered the center frequency of the frequency range 220. This range can then be selected, i.e., a windowing of the frequency spectrum 210 can be performed to select 103 of the frequency range 220 as a range around the clock frequency fT with the defined window width fb and window position. Specifically, this can be done (e.g.,(through test series) the window width fb and the window position for the windowing are determined in such a way that, by the subsequent detection 104 of at least one peak value 230 or at least or exactly two peak values ​​230 in the frequency range 220, only such frequencies f1, f2 of the frequency range 220 are determined which are specific for the synchronous speed n0 (see . Figure 4 To detect the peak values ​​230, for example, the amplitudes of the frequencies in the frequency range 220 can be compared with a threshold value in order to select the frequencies f1, f2, which exceed this threshold and are specific to the synchronous speed n0. In other words, the amplitudes A can be considered as peak values ​​230 that exceed the threshold value.

[0057] The current synchronous speed n0 of the electric machine 2 can thus be determined by examining the frequency spectrum 210 in ranges around multiples of the clock frequency fT. Possible clock frequencies could be, for example, 2 kHz, 4 kHz, 6 kHz, 8 kHz, 10 kHz, 12 kHz, 14 kHz, or 16 kHz.

[0058] According to Figures 3 and 4 Can a window width fb of the frequency range 220 be defined such that, during the subsequent detection 104, exactly or at least two peak values ​​230 are detected in order to determine one of the frequencies f1, f2 specific to the synchronous speed n0 at each of the peak values ​​230? These frequencies can be... f k =1 and f k The harmonics are treated as described above. Based on the frequency difference between the determined frequencies f1 and f2, the synchronous speed n0 can then be determined, for example, as described above.

[0059] In Figure 4 The frequency range around fT = 4 kHz is shown as an example. The characteristic harmonics are excited by the control device. It is evident that characteristic peak values ​​230 are present both above and below fT = 4 kHz. Several peaks are found in the considered frequency range 220, of which the one closest to the clock frequency is considered further. The current synchronous speed n0 of the electric machine 2 can be calculated from the frequencies f1 and f2 of these two nearest peak values ​​230.

[0060] Once the synchronous speed nSince 0 is known, the method from EP 2 433 010 B1 can be further applied to determine the operating point of the driven machine. To determine the current slip s of the asynchronous machine, the current speed n and the synchronous speed n 0 of the electric machine 2 can be used: s = n o − n n 0

[0061] The current rotational speed n can be determined using conventional methods from the frequency spectrum of the detection information 200 shown in Figure 3, in particular a noise.

[0062] Furthermore, the following steps can be carried out to determine the operating point based on the synchronous speed n0 and a different current speed of the working machine 1: Determine a rotational tone frequency linearly proportional to the rotational tone of the driven machine 1 from the frequency spectrum 210, determine the current speed of the driven machine 1 based on the determined rotational tone frequency, determine a speed-torque characteristic curve of the asynchronous machine 2 at least based on given motor parameters such as rated power and rated speed and the synchronous speed n0, determine a power input of the driven machine 1 from the determined current speed and the speed-torque characteristic curve, whereby the operating point is characterized by the power input.

[0063] Necessary parameters for determining the speed-torque characteristic (nM characteristic) of the asynchronous machine 2 can also be derived from the nameplate data of the asynchronous machine 2; for example, the rated or nominal torque MN results from the quotient of the rated power of the asynchronous machine 2 (P 2N ) and the rated speed (n N ) to M N = P 2 N ω N = P 2 N 2 πn N

[0064] Given the known pull-out torque MK and / or pull-out slip sK of the asynchronous machine 2, the Kloss equation is used. M M k = 2 s s k + s k s The speed-torque characteristic curve, nM characteristic curve of the asynchronous machine 2, is shown. The slip s of the asynchronous machine 2 is also shown. s = n o − n n 0 The resulting nM characteristic curve is as follows: M n = 2 M k n 0 − n n 0 − n k + n 0 − n k n 0 − n with the tipping speed nk n k = n 0 ⋅ 1 − M k M N n 0 − n N n 0 2 − n 0 − n N n 0 2 + M k M N n 0 − n N n 0

[0065] In this way, the working machine 1 can be reliably characterized on the basis of the nM characteristic curve, whereby the necessary synchronous rotational speed is determined by means of the method according to the invention. Reference symbol list

[0066] 1. Working machine 2. Asynchronous machine, asynchronous motor 3. Control device, frequency converter 10 Processing device 15 Storage 101 Acquisition 102 Frequency analysis, Fourier analysis 103 Selection, windowing 104 Detection, peak detection 105 Determination, calculation 200 Acquisition information 210 Frequency spectrum 220Frequency range 230Peak, peak fFrequency fTClockfrequency fbWindowwidth f1First determined frequency f2Second determined frequency n0Synchronous speed, synchronous speed AAmplitude

Claims

1. Method for determining a synchronous speed (n0) of an electric machine (2), in particular a speed-regulated asynchronous machine (2), in a work machine (1) driven by the electric machine (2), wherein a regulating device (3) is provided for speed regulation of the electric machine (2), wherein the following steps are carried out: - initiating a detection (101) of at least one mechanical measured variable in the electric machine (2) and / or the driven work machine (1) to obtain an item of detection information (200) specific for a rotational sound of the electric machine (2) and / or the driven work machine (1), - carrying out a frequency analysis (102) of the detection information (200) to obtain a frequency spectrum (210) of the detection information (200), characterized by the following steps: - carrying out a selection (103) of at least one frequency range (220) in the frequency spectrum (210) on the basis of a clock frequency (fT) of the regulating device (3), - carrying out a recognition (104) of at least one peak value (230) in the frequency range (220) to ascertain at least one frequency (f1, f2) specific for the synchronous speed (n0), - carrying out the determination (105) of the synchronous speed (n0) on the basis of the at least one ascertained frequency (f1, f2).

2. Method according to Claim 1, characterized in that at least one windowing of the frequency spectrum (210) is carried out to select (103) the at least one frequency range (220), wherein in each case a window width (fb) and a window position for the windowing are defined in such a way that by the subsequent recognition (104) of the at least one peak value (230) in the respective frequency range (220), only those frequencies (f1, f2) of the frequency range (220) are ascertained which are specific for the synchronous speed (n0).

3. Method according to Claim 1 or 2, characterized in that the regulating device (3) is designed as a frequency converter (3), wherein the at least one frequency range (220) is selected around the clock frequency (fT) and / or around at least one multiple of the clock frequency (fT) and in particular has the clock frequency (fT) and / or the multiple of the clock frequency (fT) as the centre frequency.

4. Method according to Claim 3, characterized in that carrying out the selection (103) comprises the following steps: - defining a window width (fb) on the basis of a predefined expected synchronous speed (n0), - defining at least one window position on the basis of the clock frequency (fT), in particular at the clock frequency (fT) and / or the multiple of the clock frequency (fT), - carrying out a windowing of the frequency spectrum (210) to select (103) the frequency range (220) as a range around the clock frequency (fT) and / or around the multiple of the clock frequency (fT) using the defined window width (fb) and window position, wherein the steps for carrying out the selection are carried out repeatedly for different window positions.

5. Method according to one of Claims 3 or 4, characterized in that the clock frequency (fT) is in the range from 1 kHz to 20 kHz, preferably 2 kHz to 16 kHz, preferably 4 kHz to 12 kHz.

6. Method according to any one of the preceding claims, characterized in that the mechanical measured variable differs from an electrical measured variable of the electric machine (2) and / or the regulating device (3) and is preferably detected independently of a regulating parameter of the regulating device (3).

7. Method according to any one of the preceding claims, characterized in that the mechanical measured variable comprises at least one of the following measured variables: - a pressure, - a differential pressure, - a force, - a vibration, - a structure-borne sound, - an airborne sound.

8. Method according to any one of the preceding claims, characterized in that a window width (fb) of the frequency range (220) is defined in such a way that upon the subsequent recognition (104), precisely or at least two peak values (230) are recognized, in order to ascertain one of the frequencies (f1, f2) specific for the synchronous speed (n0) at each one of the peak values (230), wherein the synchronous speed (n0) is determined on the basis of a frequency difference of the ascertained frequencies (f1, f2).

9. Method according to any one of the preceding claims, characterized in that the window width (fb) of the frequency range (220) is at least 1.5 times or at least two times a synchronous frequency to be expected.

10. Method according to any one of the preceding claims, characterized in that the determined synchronous speed (n0) is used to determine an operating point of the work machine (1).

11. Method according to Claim 10, characterized in that the following steps are carried out to determine the operating point on the basis of the synchronous speed (n0) and a present speed of the work machine (1) deviating therefrom: - ascertaining a rotational sound frequency linearly proportional to the rotational sound of the electric machine (2) and / or the work machine (1) from the frequency spectrum (210), - determining the present speed of the work machine (1) on the basis of the ascertained rotational sound frequency, - determining a speed-torque characteristic curve of the electric machine (2) at least on the basis of predetermined motor parameters such as rated power and rated speed and the synchronous speed (n0), - determining a power consumed by the work machine (1) from the ascertained present speed and the speed-torque characteristic curve, wherein the operating point is characterized by the consumed power.

12. Processing device (10) for data processing, comprising means for executing the steps of a method according to any one of Claims 1 to 11.

13. System, comprising: - a work machine (1), - an electric machine (2) of the work machine (1) for driving the work machine (1), - a regulating device (3) of the work machine (1) for speed regulation of the electric machine (2), - a processing device (10) according to Claim 12.

14. System according to Claim 13, characterized in that the work machine (1) is designed as a pump assembly, in particular a centrifugal pump assembly, and the processing device (10) is embodied separately from the work machine (1), in particular in the form of a mobile device.

15. Computer program, comprising commands which, upon the execution of the computer program by a processing device (10) according to Claim 12, prompt it to carry out a method according to any one of Claims 1 to 11.