Compensation device for reducing one or more harmonic oscillations in an electric machine
Patent Information
- Application Number
- EP2023786183
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-11-10
- Filing Date
- 2023-09-20
- Publication Date
- 2025-09-17
AI Technical Summary
Electrical machines experience undesirable harmonics in their magnetic fields, leading to losses and noise, which are difficult to predict and mitigate post-design, often requiring complex mechanical solutions or heavy, stiff constructions to meet noise limit values.
A compensation device connected to the electrical machine generates an electrical signal, measured by sensors at the machine's terminals, to counteract harmonics in the voltage or current, using a microprocessor-controlled energy source that can be integrated with the power converter, allowing for phase-aligned and amplitude-controlled signals to reduce or eliminate harmonics.
This approach effectively reduces losses and noise by targeting specific harmonics, allowing for efficient operation with minimal adjustment effort, and can be easily retrofitted into existing electric drives, meeting stringent noise and loss requirements while simplifying the design and control of electric drives.
Smart Images
Figure 1.1
Abstract
Description
[0001] Description
[0002] Compensation device for reducing one or more harmonics in an electrical machine
[0003] The invention relates to a compensation device for an electrical machine. Furthermore, the invention relates to an electrical drive comprising such a compensation device and an electrical machine. The invention further relates to a method for controlling or regulating such a compensation device or such an electrical drive.
[0004] In addition to the torque-generating fundamental wave, the magnetic field in an electrical machine often exhibits additional harmonics. These harmonics generate undesirable side effects, such as losses or forces that can excite vibrations. These vibrations generate airborne and / or structure-borne noise, which is subject to specific limits specific to the application. Compliance with these limits can be a considerable technical challenge.
[0005] The electrical machine is often supplied with electrical energy by a power converter. The power converter often acts as the final control element for controlling or regulating the electrical machine, for example, in terms of speed or torque. The power converter generates harmonics in its output voltage and current, which cause harmonics in the magnetic field. Motors and generators are examples of electrical machines.
[0006] Since it is often difficult to accurately predict the vibration and noise levels resulting from partially parasitic field waves, only complex mechanical mitigation measures, such as special damping elements, are possible after the electrical machine or drive has been designed and manufactured. Another remedy is a mechanical structure that is as rigid and therefore as heavy as possible.
[0007] The term "harmonic" refers to a frequency that is higher than the first frequency used to power the electrical machine. The harmonic is not necessarily a multiple of the first frequency.
[0008] The supply voltage refers to the voltage with which the electrical machine is supplied, i.e., fed electrically. Characteristic parameters are the amplitude and the frequency, with the frequency being referred to as the first frequency or fundamental frequency.
[0009] The invention is based on the object of improving an electric drive.
[0010] This object is achieved by a compensation device for an electrical machine, wherein the compensation device has an energy source, wherein the energy source is designed to generate an electrical signal, in particular a voltage or a current, which counteracts the harmonic as a function of measured values from a sensor for determining at least one harmonic. This object is further achieved by an electric drive having such a compensation device, an electrical machine and a sensor for determining at least one harmonic, in particular a harmonic of the current or the voltage, at connection terminals of the electrical machine, wherein the compensation device is connected to the connection terminals of the electrical machine.This object is further achieved by a method for controlling or regulating such a compensation device or such an electric drive, wherein at least one harmonic is determined at the connection terminals of the electric machine, wherein by means of the compensation device an electrical signal, in particular a voltage or a current, is generated which counteracts the harmonic at the connection terminals of the electric machine.
[0011] Further advantageous embodiments of the invention are specified in the dependent claims.
[0012] The invention is based, among other things, on the finding that the harmonic situation and the associated losses and noise in an electrical machine can be improved by connecting a compensation device to the electrical machine or integrating it into the electrical drive. This makes it possible to avoid harmonics that arise by preventing the formation of the harmonic, for example, due to a harmonic in the voltage and / or current at the connection terminals of the electrical machine.
[0013] A sensor in the compensation device measures the harmonics at the terminals of the electrical machine. Harmonics of the current and / or voltage can be measured at the terminals. These provide information about the harmonics of the magnetic field in the electrical machine, which not only generates losses but also noise.
[0014] It has been shown that by reducing at least one harmonic of current and / or voltage the losses and at the same time the noise of the electrical machine can be reduced. By means of the compensation device an electrical signal, for example a voltage or a current, is coupled into the electrical drive which is phased in such a way that this signal counteracts the harmonic measured by the sensor. It has also been shown that by deliberately impressing a current in the form of a current harmonic with a defined phase position and amplitude or a voltage in the form of a voltage harmonic with a defined phase position and amplitude additional force waves can be excited or generated.The phase and amplitude of these additional force waves are controlled or regulated in such a way that they counteract existing force waves, thus compensating for them or at least reducing them. This approach is particularly advantageous for force waves with an atomic number of 0.
[0015] It has proven advantageous to determine precisely one harmonic using the sensor and to compensate for it or at least reduce it using the electrical signal. This requires only minimal adjustment effort and the compensation device can be operated in a particularly small and efficient manner. Furthermore, it has been shown that both the losses and the noise behavior can be significantly improved with just one harmonic. This means that the compensation or reduction of further harmonics can be dispensed with in favor of a small and efficiently operated compensation device. However, it is also possible to determine several harmonics and to eliminate or reduce them with the help of the compensation device.This makes it possible to meet even particularly stringent requirements regarding the loss or noise performance of an electrical machine or an entire electrical drive. In this case, too, the compensation device can be easily and cost-effectively designed for a specific number of harmonics. Furthermore, it is possible to utilize design reserves for the compensation of additional harmonics.
[0016] Such a compensation device advantageously has microprocessor-controlled electronics that provide the desired electrical signal at the appropriate signal strength. This device is arranged either in series with the connection terminals of the electrical machine, so that the compensation device acts as an additional voltage source, or in parallel with the connection terminals of the electrical machine, so that the compensation device works as a current source. In principle, inductive coupling of the signal is recommended. Bandpass filters, similar to those used in power line communication, can be used to decouple the fundamental oscillation.
[0017] The compensation device also offers the advantage of being retrofittable into existing electric drives. In other words, the compensation device is easy to retrofit.
[0018] In an advantageous embodiment of the invention, the compensation device has a filter, in particular a bandpass filter. For the coupling of the harmonic with the aid of the electrical signal, it has proven advantageous if the energy source for the coupling does not also have to generate the fundamental or possibly further harmonics in order to couple in the electrical signal of the harmonic. The need to generate the fundamental arises partly from the fact that an exchange of currents with the fundamental is to be prevented. This is also possible using a filter in the compensation device, which reliably prevents the formation of fundamental currents between the compensation device and the electrical machine. On the one hand, this increases the control reserve of the compensation device because the fundamental is not generated by the compensation device.Secondly, control becomes simpler, since not only is the fundamental oscillation generated, but it also needs to be switched on in phase. By using a filter, these measures are eliminated. At the same time, the requirements for the electrical performance of the electrical components of the compensation device and for the control system are reduced. Furthermore, the control reserve, i.e., the ability to counteract disturbances, is increased.
[0019] In a further advantageous embodiment of the invention, the energy source is designed as a power converter, wherein the power converter is connectable to an electrical machine, wherein the power converter is set up to generate a supply voltage with a first frequency for feeding the electrical machine. In other words, the power converter and compensation device form a unit. The power converter not only makes the electrical energy available by means of a supply voltage with the first frequency, but the signal generated by the compensation device is superimposed on the supply voltage, for example as a voltage, also referred to as compensation voltage, and counteracts a harmonic in voltage and / or current. The advantage is that with just one component, i.e.With the power converter, the electrical machine can be supplied with electrical energy by generating the supply voltage, and harmonics can be reduced or even eliminated using the compensation voltage. Thus, no additional actuator is required for the compensation device; instead, an existing power converter can be used.
[0020] In a further advantageous embodiment of the invention, the power converter is designed as a DC link converter, wherein the power converter is configured to provide a voltage, in particular the compensation voltage, as a signal, which is superimposed on the supply voltage. With a DC link converter, comparatively high frequencies can be generated at its output voltage compared to a direct converter. Furthermore, operation causes significantly fewer harmonics than with a direct converter. The DC link converter is therefore particularly suitable for generating a superposition of the supply voltage and the compensation voltage. The frequency of the compensation voltage can also be selected to be significantly higher, for example at 25 times the frequency of the supply voltage.This large usable frequency spectrum makes it possible to eliminate a large number of harmonics, in particular two or more harmonics of different frequencies.
[0021] In a further advantageous embodiment of the invention, the energy source is designed as a voltage source and is arranged in a series circuit with the connection terminals of the electrical machine. In the series circuit, the voltage of the energy supply and the compensation device add up to a total voltage which is present at the terminals of the electrical machine. By introducing a voltage through the compensation device, a harmonic in the voltage of the energy supply can be counteracted. The corresponding harmonic which is contained in the voltage of the energy supply and causes the harmonic in the electrical machine, for example due to a switching frequency of a feeding power converter, is compensated by the compensation device in such a way that this harmonic is in the form of a voltage with the opposite sign, i.e.with a phase shift of 180°, generated by the compensation device. Due to the series connection, this generated voltage is superimposed on the harmonic of the power supply, so that this harmonic is no longer present at the connection terminals of the electrical machine. The voltage of the compensation device can be coupled in, for example, directly or via a transformer.
[0022] In a further advantageous embodiment of the invention, the energy source is designed as a current source and is arranged in a parallel circuit with the connection terminals of the electrical machine. In the parallel circuit, the currents of the energy supply and the compensation device add up to a total current which flows into the electrical machine via the connection terminals. This current can therefore also be referred to as the current at the electrical connection terminals. By introducing a current through the compensation device, a harmonic in the current of the energy supply can be counteracted. The corresponding harmonic from the energy supply, which flows as current into the electrical machine, for example due to a switching frequency of a feeding power converter, is compensated by the compensation device in such a way that this harmonic is in the form of a current with the opposite sign, i.e.with a phase shift of 180°, generated by the compensation device. Due to the parallel connection, this generated current is superimposed on the harmonic of the power supply, so that this harmonic is no longer present at the terminals of the electrical machine.
[0023] In a further advantageous embodiment of the invention, the energy source is connected to the connection terminals of the electrical machine via an inductive coupling, in particular via a transformer. With the help of the inductive coupling, currents and voltages can be easily coupled into the electrical machine or generally into the electrical drive. The existing currents and voltages can be adjusted using a transformer as an inductive coupling element, so that the compensation device can be operated at a favorable operating point. Good utilization of the semiconductors with regard to blocking voltage and current carrying capacity is also possible. Furthermore, the inductive coupling reliably prevents earth currents that could disrupt the function of the drive. Coupling via an inductive coupling therefore enables reliable and efficient operation.
[0024] In a further advantageous embodiment of the invention, the electric drive comprises a power converter, the connection terminals of the electric machine being connected to the power converter. In many applications, the electric machine is fed by a power converter. With the help of the power converter, the electric machine can be regulated or controlled in terms of speed and torque. This enables the widespread use of such drives in many applications. However, the power converter also generates harmonics, in particular harmonics in the current and / or voltage of the motor, which can lead to losses and noise. With the help of the compensation device, an electric drive with good controllability and adjustability can be realized which also has a high dynamic response.The disadvantage of the harmonics generated by the converter and the associated losses and noise can be eliminated with the help of the compensation device. This allows a converter-fed, low-loss, low-noise electric drive to be realized in a particularly simple and cost-effective manner.
[0025] Especially when the electric drive and thus the power converter are designed for high-power operation, especially for power greater than 1 MW, the harmonic distortion is high due to low reactances. This leads to significant losses and perceptible noise, which can be easily eliminated by the compensation device. The sensor of the compensation device is capable of detecting small amplitudes and their phase position with sufficient accuracy and reliability, even at high operating currents.
[0026] In a further advantageous embodiment of the invention, a harmonic with 25 times the frequency of the fundamental oscillation is determined and reduced by an electrical signal from the compensation device. It has been shown that such a frequency is perceived as particularly disturbing and thus the elimination of this noise is particularly advantageous. To compensate for this force wave with the spatial atomic number 0 and an angular frequency of 24di, an additional oscillation with w2=25di can be impressed, for example. The phase position must then be adjusted so that the harmonic is canceled out by antiphase.
[0027] In a further advantageous embodiment of the invention for controlling or regulating an electric drive with a power converter, the harmonic is determined in the range of the switching frequency and / or in the range of a multiple of the switching frequency of the power converter. The switching frequency range of a feeding power converter is usually the significant portion of the existing harmonic that generates losses and noise. This eliminates the need to search for the relevant frequency range. The sensor only determines harmonics with frequencies in the range of the switching frequency or in the range of a multiple of the switching frequency. The range defines the range resulting from the switching frequency or a multiple minus the fundamental frequency up to the switching frequency or a multiple plus the fundamental frequency.This allows for particularly simple harmonic determination, as the frequency range to be analyzed is selected to be correspondingly small. This simplifies the evaluation and determination of the harmonic to be compensated. Thus, compensation can be achieved with particularly low computational effort, even with a simple control device.
[0028] In a further advantageous embodiment of the invention, the harmonic is determined in the range between the first frequency and the switching frequency. In this range, a DC link converter in particular can compensate for harmonics in a particularly simple manner without generating further harmonics. Harmonics often arise in a certain frequency range due to the geometry of the electrical machine. It is advantageous to provide a power converter for feeding this electrical machine whose switching frequency is above the resulting harmonics. It has proven particularly advantageous if the switching frequency is greater than 25 times the maximum first frequency, since this arrangement allows a power converter to be manufactured inexpensively and at the same time the power converter can be used for feeding as well as compensating for harmonics.
[0029] In a further advantageous embodiment of the invention, the electrical signal represents a voltage superimposed on the supply voltage, wherein the electrical signal has the frequency of the harmonic. By implementing the energy source via the power converter, the signal can be generated simply by superimposing a voltage for compensating the harmonic, the compensation voltage, on the supply voltage. This is a particularly simple and cost-effective embodiment for using the power converter for both supply and compensation.
[0030] In a further advantageous embodiment of the invention, the harmonic is determined by means of the sensor by varying the frequency of the compensation voltage. This makes it possible to dispense with the need for an analytical method to determine the frequency of the harmonic. Instead, the effect on the harmonic can be observed using an experimental method by generating the signal with a frequency. By specifically varying the parameters amplitude, frequency and phase position of the compensation voltage, the harmonic can be eliminated as far as possible, and in some cases even completely, while utilizing the available control reserve. A particular advantage of this method is that the variables amplitude, frequency and phase position of the signal from the compensation device can be specified and varied independently of one another.In this way, any harmonic that occurs can be eliminated quickly and with little effort, since no analytical and convergent procedure is required.
[0031] In the following, the invention is described and explained in more detail with reference to the exemplary embodiments shown in the figures. Therein: FIG. 1 to FIG. 3 show exemplary embodiments of an electric drive with a proposed compensation device.
[0032] FIG 1 shows an electric drive 10. This has an electric machine 2 which is supplied with electrical energy from a power supply 7. For the control and / or regulation of the electric machine, the electric drive 10 can optionally have a power converter 11. A compensation device 1 is used to eliminate disturbing harmonics at terminals 21 of the electric machine 2 which lead to undesirable noise or electrical losses. For this purpose, the harmonics at the connection terminals 21 of the electric machine 2 are detected or determined using a sensor 4. Depending on these measured values, the energy source 3 generates an electrical signal which counteracts at least one harmonic.
[0033] In this embodiment, the harmonics are determined based on the current by means of sensor 4. This is advantageously designed as a current sensor. Alternatively, the harmonics can also be determined via the voltage using a voltage transformer between the phases or with respect to a reference potential. The measured values of sensor 4 are transmitted to the compensation device 1.
[0034] In this exemplary embodiment, the energy source 3 is designed as a voltage source 31. This is arranged in a series circuit with the connection terminals 21 of the electrical machine 2, so that the voltage of the energy supply 7 and the voltage of the compensation device 1 add up and are applied to the connection terminals 21 of the electrical machine 2.
[0035] The power converter 11 can be used to control the electric machine. It can control, regulate, and / or monitor the speed and / or torque of the electric machine 2.
[0036] In this case, the power converter 11 can simultaneously perform the function of the voltage source 31 in addition to supplying the motor with the first frequency. In other words, the power converter 11 has the voltage source 31 of the compensation device 1, with which a signal for compensating a harmonic is generated. Alternatively, a superposition of the supply voltage and the compensation voltage can be achieved by an arrangement in which the components are arranged one behind the other between the power supply 7 and the electric machine 2.
[0037] The arrangement of the sensor 4 between the compensation device 1 and the electrical machine 2 is particularly advantageous because the compensation or reduction of the harmonics can be controlled. If the sensor 4 is alternatively arranged between the energy supply 7 and the compensation device 1, the compensation or reduction of the harmonics can be controlled. In addition, the measured values of a measured value recorder for controlling the electrical machine 2 can also be used simultaneously as sensor 4 for the compensation device 1. The measured values can be transmitted directly from the measured value recorder to the compensation device 1 or from a control module of the power converter 11 to the compensation device 1.
[0038] FIG. 2 shows a further exemplary embodiment of a proposed electric drive 10 with the compensation device 1. In this exemplary embodiment too, the energy source 3 of the compensation device 1 is designed as a voltage source 31 and is arranged in series with the connection terminals 21 of the electrical machine 2. The connection of the compensation device 1 to the connection between the energy supply 7 and the electrical machine 2 is effected via an inductive coupling 33 with the aid of a transformer. To avoid repetition, reference is made to the description of FIG. 1 and to the reference symbols introduced there. In particular, the statements regarding the arrangement of the sensor 4 and the power converter 11 also apply to the arrangement of the exemplary embodiment according to FIG. 2.
[0039] FIG 3 shows a further embodiment of a proposed electric drive 10 with the compensation device 1. In this embodiment, the compensation device 1 is arranged parallel to the connection terminals 21 of the electric machine 2 and also parallel to the power supply 7. The currents of the power supply 7 or the power converter 11 are added to the currents of the compensation device to form a total current that flows through the electric machine 2. This current therefore also flows through the connection terminals 21 of the electric machine 2. A harmonic in the current from the power supply can be compensated by a current from the compensation device 1 with the same amplitude, the same frequency and a phase shift of 180°. In this embodiment, the compensation device 1 has a filter 5.This can, for example, be designed in such a way that it only allows the frequency range of the harmonic to be compensated to pass through and blocks all other frequencies, such as the fundamental frequency.
[0040] Furthermore, the power converter 11 is present in this exemplary embodiment. Alternatively, it can be omitted by connecting the electric machine 2 directly to the power supply 7. To avoid repetition, reference is made to the description of Figures 1 and 2 and to the reference symbols used therein. In particular, the statements regarding the arrangement of the sensor 4 and the power converter 11 also apply to the arrangement of the exemplary embodiment according to Figure 2.
[0041] In summary, the invention relates to a compensation device 1 for an electrical machine 2. In order to improve an electrical drive, it is proposed that the compensation device 1 has an energy source 3, wherein the energy source is designed to generate an electrical signal, in particular a voltage or a current, which counteracts the harmonic as a function of measured values from a sensor 4 for determining at least one harmonic. The invention further relates to an electrical drive 10, comprising such a compensation device 1, an electrical machine 2 and a sensor for determining at least one harmonic at connection terminals 21 of the electrical machine 2, wherein the compensation device 1 is connected to the connection terminals 21 of the electrical machine 2.Furthermore, the invention relates to a method for controlling or regulating such a compensation device 1 or such an electric drive 10, wherein at least one harmonic is determined at the connection terminals 21 of the electric machine 2, wherein by means of the compensation device 1 an electrical signal is generated which counteracts the harmonic at the connection terminals 21 of the electric machine 2.
Claims
Patent claims 1. Compensation device (1) for an electrical machine (2), wherein the compensation device (1) has an energy source (3), wherein the energy source (3) is designed to generate an electrical signal, in particular a voltage or a current, which counteracts the harmonic, as a function of measured values of a sensor (4) for determining at least one harmonic.
2. Compensation device (1) according to claim 1, wherein the compensation device (1) comprises a filter (5), in particular a bandpass filter.
3. Compensation device (1) according to one of claims 1 or 2, wherein the energy source (3) is designed as a power converter (11), wherein the power converter (11) is connectable to an electrical machine (2), wherein the power converter (11) is configured to generate a supply voltage with a first frequency for feeding the electrical machine (2).
4. Compensation device (1) according to one of claims 3, wherein the power converter (11) is designed as a DC voltage intermediate circuit converter, wherein the power converter (11) is designed to provide a voltage as a signal which is superimposed on the supply voltage.
5. Electric drive (10), comprising a compensation device (1) according to one of claims 1 to 4, an electric machine (2) and a sensor for determining at least one harmonic, in particular a harmonic of the current or the voltage, at connection terminals (21) of the electric machine (2), wherein the compensation device (1) is connected to the connection terminals (21) of the electric machine (2).
6. Electric drive (10) according to claim 5, wherein the electric drive (10) comprises a power converter (11) according to claim 3, wherein the connection terminals (21) of the electric machine (2) are connected to the power converter (11).
7. Method for controlling or regulating a compensation device (1) according to one of claims 1 to 3 or an electric drive (10) according to one of claims 4 to 6, wherein at least one harmonic, in particular a harmonic of the current and / or the voltage, is determined at the connection terminals (21) of the electrical machine (2), wherein by means of the compensation device (1) an electrical signal, in particular a voltage or a current, is generated which counteracts the harmonic at the connection terminals (21) of the electrical machine (2).
8. The method according to claim 7, wherein a harmonic having 25 times the frequency of the fundamental oscillation is determined and is reduced by an electrical signal of the compensation device (1).
9. Method according to one of claims 7 or 8, wherein the harmonic is determined in the range of a switching frequency and / or in the range of a multiple of the switching frequency of the power converter (11).
10. The method according to claim 7 or 8, wherein the harmonic is determined in the range between the first frequency and the switching frequency.
11. The method according to any one of claims 7 to 10, wherein the electrical signal represents a voltage superimposed on the supply voltage, the electrical signal having the frequency of the harmonic.
12. Method according to one of claims 7 to 11, wherein the harmonic is determined by means of the sensor (4) by varying the frequency of the compensation voltage.