Adjustable magnetic field

Abstract

A system 100 for adjustable magnetic field in an electrical machine, comprises a first part 120 comprising induction coils 122, and a second part 130 comprising means for setting up a magnetic field 1

Description

The invention relates to adjustable magnetic fields in general and more specifically a system and a method for adjusting magnetic fields in electrical machines, such as generators and motors. State of the art is reflected in electrical machines, wherein interaction with moving magnetic field gives rise to transformation between mechanical and electrical energy. According to the abstract, WO2016080889 discloses an electrical machine comprising a rotor, a stator, a rotor power supply, at least one sensor and a rotor magnetization control arrangement. The rotor has rotor windings for controlling magnetization of rotor magnetic poles. The sensor is arranged to measure a parameter associated with a relative force between the stator and the rotor. The rotor magnetization control arrangement is communicationally connected to the sensor for receiving a signal representing the measured parameter. The rotor magnetic poles are divided into at least two groups. The rotor magnetization control arrangement is arranged for controlling the magnetization of the groups individually by providing a respective individually controllable rotor current. According to the abstract, WO2018160122 discloses an electrical synchronous machine comprising a rotor with rotor field windings and a stator with stator windings as well as a rotor power supply and a stator power supply. The rotor power supply is arranged to supply rotor field current for causing a magnetization of rotor magnetic poles. The stator power supply is arranged to supply alternating stator current for causing a rotating stator magnetic field. The electrical synchronous machine further comprises at least one sensor, arranged to measure a quantity that is dependent on a relative angle between the rotor and the rotating stator magnetic field. The electrical synchronous machine further comprises a rotor magnetization control arrangement, arranged for repeatedly varying amplitude and / or direction of the rotor current as a response to a change of the measured quantity. According to the abstract, WO2023027622 discloses a magnetic flux control system for controlling the magnetic flux in an electrical machine with concentrated windings has at least one magnetic balancing power supply, at least one balancing-current controller and electrical connections configured to permit the connection of the balancing-current controller(s) over a segment of the concentrated windings. The balancing power supply provides galvanic isolation. The magnetic balancing system has further at least one sensor configured to measure a parameter associated with a magnetic flux, a force, a position, vibrations, voltages, and / or currents. The balancing-current controller(s) is(are) connected to the sensor(s) and is(are) powered by the balancing power supply(supplies). The balancingcurrent controller is configured to control an output current in dependence of a signal representing the measured parameter of the sensor(s). A winding excitation arrangement, an electrical machine and a method for balancing are also disclosed. Prior art involves vibrations in the air gap between rotor and stator. This causes several problems. First of all this causes noise and vibrations. There is therefore a need for a method and a system to overcome the above mentioned problems. Therefore, a main objective of the present invention is to provide a system and a method for adjusting magnetic fields in electrical machines, in order to reduce or eliminate noise and / or vibrations. The objective is achieved according to the invention by an apparatus for adjusting magnetic fields in electrical machines as defined in the preamble of claim 1, having the features of the characterising portion of claim 1, and a method apparatus for adjusting magnetic fields in electrical machines as defined in the preamble of claim 8, having the features of the characterising portion of claim 8. A number of non-exhaustive embodiments, variants or alternatives of the invention are defined by the dependent claims. The present invention attains the above-described objective by a plurality of electromagnets for modulating the magnetic field applied to induction coils. In a first aspect, a system for adjustable magnetic field in an electrical machine is provided, comprising: a first part comprising induction coils; a second part comprising means for setting up a magnetic field applied to the induction coils; wherein the first and second parts are separated by a gap and rotatable with respect to each other; wherein the second part further comprises a plurality of electromagnets for modulating the magnetic field applied to the induction coils; and means for regulating the electromagnets in order to cancel vibration modes across the gap. In the case where the means for setting up a magnetic field is at least one primary electromagnet, the present solution allows for fine control of the magnetic field using electromagnets powered by a lower powered circuit, and avoid having to adjust the current in the larger power circuits controlling the currents in the primary electromagnets by superimposing a current in the individual primary electromagnets of the poles. In one embodiment the electromagnets are positioned across a surface facing the gap. In an alternative embodiment the electromagnets are positioned perpendicular to a surface facing the gap. In one embodiment the electromagnets are provided with a pole shoe. In one embodiment the means for setting up a magnetic field is a permanent magnet. This can be iron or a rare earth metal based magnet. In this embodiment the magnets cannot easily be adjusted, in which case the electromagnets provide the means for adjusting the magnetic field. In one embodiment the first part surrounds the second part. In one embodiment the second part surrounds the first part. In a second aspect, method for operating a system for adjustable magnetic field in an electrical machine is provided, wherein the plurality of electromagnets are modulated using an angular position of the first part with respect to the second part as a parameter. In one embodiment the plurality of electromagnets are modulated using a predetermined model from a simulation. This is beneficial when operating in conditions that are well characterised in advance, and provides simplicity. In one embodiment the plurality of electromagnets are modulated using measurements of vibration modes across the gap. Here the actual vibrations are measured and characterised, and then countered by energising the electromagnets accordingly. In one embodiment the method additionally takes power produced by the system as a parameter. In one embodiment each of the plurality of electromagnets are individually modulated. The present invention comprises a technological advantage over known systems and methods by use of an adjustable magnetic field. The present invention provides several further advantageous effects: • It makes it possible to reduce noise and vibration: Vibrations in the airgap can cause noise and vibration in the generator, which can be unpleasant and even harmful to the environment. Active cancellation can help to reduce these vibrations, which can improve the overall performance and reliability of the generator. • It makes it possible to by the elimination of the vibrations to allow for a slimmer design envelope of stator and rotor, thus enabling a more lean design using less material and being more cost effective. • It makes it possible to increase efficiency: Vibrations in the airgap can also cause losses in the generator, which can reduce its efficiency. Active cancellation can help to reduce these losses, which can improve the efficiency of the generator. • It makes it possible to extend lifetime: Vibrations in the airgap can also cause wear and tear on the generator, which can shorten its lifetime. Active cancellation can help to reduce this wear and tear, which can extend the lifetime of the generator. The above and further features of the invention are set forth with particularity in the appended claims and together with advantages thereof will become clearer from consideration of the following detailed description of an [exemplary] embodiment of the invention given with reference to the accompanying drawings. The invention will be further described below in connection with exemplary embodiments which are schematically shown in the drawings, wherein: Fig. 1 shows and embodiment of the invention with electromagnets around an outer periphery outside permanent magnets, Fig. 2 shows an alternative with electromagnets around an inner periphery, Fig. 3 shows an alternative with surface mounted electromagnets, and Fig. 4 shows a variation of the embodiment of Fig. 3 with pole shows added. The following reference numbers and signs refer to the drawings: 100 The system, electrical machine 102 Gap 120 First part 122 Induction coils 130 Second part 132 Means for setting up a magnetic field 134 Electromagnets 135 Pole shoe 136 Ferromagnetic steel 138 Non-magnetic material, support Various aspects of the disclosure are described more fully hereinafter with reference to the accompanying drawings. This disclosure may, however, be embodied in many different forms and should not be construed as limited to any specific structure or function presented throughout this disclosure. Rather, these aspects are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Based on the teachings herein one skilled in the art should appreciate that the scope of the disclosure is intended to cover any aspect of the disclosure disclosed herein, whether implemented independently of or combined with any other aspect of the disclosure. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth herein. In addition, the scope of the disclosure is intended to cover such an apparatus or method which is practiced using other structure, functionality, or structure and functionality in addition to or other than the various aspects of the disclosure set forth herein. It should be understood that any aspect of the disclosure disclosed herein may be embodied by one or more elements of a claim. The inventor has realised that irregularities in the magnetic field in the gap between a rotor and a stator in an electrical machine, such as a generator, will give rise to vibrations and noise. These irregularities in the magnetic field can be adjusted with an adjustable magnetic field. This can be achieved using electromagnets, typically provided in close proximity to the means for setting up the magnetic field. This can take on two primary solutions, here illustrated in practical examples of reduction to practice that can be generalised. In a first solution, the rotor is configured as an iron core parallel with the permanent magnets. The latter are provided with a field winding that can either “short out” parts of the flux from the permanent magnet so that the flux from the pole in the rotor to the stator is reduced and thus reducing the force for that pole, or by adding a current increasing the force between that pole and the stator. In this way one can control the force between every pole and the stator using a small current in the added field windings. In a second solution one may instead of working on the rotor, chose to strengthen the flux from the stator to the rotor. This also strengthens the flux in the airgap which in turn increases the force in the airgap. This can be achieved by feeding a small superimposed current to the windings in the stator, individually controlled for each pole, typically two or three phases. This is more complex since the stator windings builds up the voltage of the generator. In an example, the entire voltage is 48,000 V, with 500 V for each of the 96 poles. In this example, pole 10 will start at 5,000 V and end at 5,500 V above ground potential. So to provide an extra 500 V to this pole to add to the current, it has to be above the 5,000 V potential, or fed in at a floating potential of 5,000 V. This required means for feeding in to a floating potential, and can be means such as inductive feeding for substantially each pole. The advantage in this solution is that one does not have to modify the rotor or feed a rotating rotor. Fig. 1 shows and embodiment of the invention with electromagnets around an outer periphery outside permanent magnets. The system comprises an electrical machine 100, which in turn comprises a first 120 and second 130 part, separated by a gap 102. Typically the inner part is the rotor, and the outer part is the stator. In the present example, the first inner part 120 comprises induction coils 122. The second, outer part 130 comprises means for setting up a magnetic field 132. This can be coils or permanent magnets. In the exemplary embodiments shown, permanent magnets are used. Separating the means for setting up a magnetic field 132 is ferromagnetic steel 136. There are also structural parts 138 for support, made of non-magnetic material, here shown as a ring 138. The second, outer part 130 further comprises a plurality of electromagnets 134 for modulating the magnetic field applied to the induction coils. In this embodiment, the magnets are provided in a transversal orientation. The system also comprises means for regulating the electromagnets in order to cancel vibration modes across the gap 102. In the shown embodiment, the electromagnets are provided laterally to each permanent magnet. Fig. 2 shows an alternative with electromagnets around an inner periphery. Fig. 3 shows an alternative with surface mounted electromagnets 134, where the electromagnets 134 are provided in a radial orientation. Fig. 4 shows a variation of the embodiment of Fig. 3 with pole shoes 135 added. The embodiment of the apparatus according to the invention shown in Fig. 1 places the electromagnets on an outside, which makes it easier to cool the ohmic heating from the current flowing in the electromagnets. In practice the gap will be an airgap, though one may also use other gases or vacuum for specialised applications. A number of variations on the above can be envisaged. For instance while the embodiments relate to a generator, the technology can equally well be applied to motors. Also, while Figs. 3 and 4 show the electromagnets on the outside, one can also have embodiments where the electromagnets are facing inwards. While the embodiments shown relate to electromagnets provided on or near the stator, one may also provide electromagnets on or near the rotor. The invention according to the application finds use in electrical machines, especially generators, where it is desirable to cancel vibration modes across an air gap.

Claims

1. A system (100) for adjustable magnetic field (104) in an electrical machine, comprising:a first part (120) comprising induction coils (122);a second part (130) comprising means for setting up a magnetic field (132) applied to the induction coils (122);wherein the first (120) and second (130) parts are separated by a gap (102) and rotatable with respect to each other;characterised in that the second part (130) further comprises a plurality of electromagnets (134) for modulating the magnetic field applied to the induction coils; and means for regulating the electromagnets in order to cancel vibration modes across the gap.

2. The system according to claim 1, wherein the electromagnets (134) are positioned across a surface facing the gap.

3. The system according to claim 1, wherein the electromagnets (134) are positioned perpendicular to a surface facing the gap.

4. The system according to claim 3, wherein the electromagnets (134) are provided with a pole shoe.

5. The system according to one of claims 1 - 4, wherein the means for setting up a magnetic field (132) is a permanent magnet.

6. The system according to one of claims 1-5, wherein the first part surrounds the second part.

7. The system according to one of claims 1 - 5, wherein the second part surrounds the first part.

8. A method for operating a system according to claim 1, wherein the plurality of electromagnets are modulated using an angular position of the first part with respect to the second part as a parameter.

9. The method according to claim 8, wherein the plurality of electromagnets are modulated using a predetermined model from a simulation.

10. The method according to claim 8, wherein the plurality of electromagnets are5 modulated using measurements of vibration modes across the gap.

11. The method according to one of claim 9 or 10, wherein the method additionally takes power produced by the system as a parameter.10 12. The method according to one of claims 9 - 11, wherein each of the plurality ofelectromagnets are individually modulated.10

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