CN211089269U

CN211089269U - Generator with secondary coil

Info

Publication number: CN211089269U
Application number: CN201922190697.4U
Authority: CN
Inventors: 卡布·瓦尔特·马吉尔
Original assignee: Kmn Trust Performance Temporary Trusteeship
Current assignee: Kmn Trust Performance Temporary Trusteeship
Priority date: 2018-12-07
Filing date: 2019-12-06
Publication date: 2020-07-24
Anticipated expiration: 2029-12-06
Also published as: BR202019025617U2; PH22019001588U1; JP3225166U; DE202019106776U1

Abstract

A generator is disclosed having a secondary coil, the generator comprising a rotor having a magnet arrangement configured to provide armature coils to a primary field stator, the rotor being rotatable about the stator such that a primary magnetic field induces a current in the armature coils. The generator further comprises a secondary winding provided around or outside the stator, the secondary winding being configured to generate a secondary magnetic field, the secondary magnetic field interacting with and increasing or enhancing the primary magnetic field, the switching means being configured to switch at least one of the strength or polarity of the magnetic field of the secondary winding based on the position of the rotor relative to the secondary winding.

Description

Generator with secondary coil

Technical Field

The present disclosure relates to electric machines, and more particularly to a generator that generates its magnetic field in a rotating part of the generator.

Background

In a conventional electric machine, such as a generator, a magnetic field is generated by a rotor by supplying a DC current to a field coil wound around the rotor. In a particular type of generator, the field coils are supplied with current via a brush and slip ring system when the rotor rotates. The field coil may be subjected to a large centrifugal force due to the rotation of the rotor. To fix the field coils, they are generally coated in resin and placed in coil slots on the rotor body.

The number of turns of the rotor coil is related to the strength of the magnets, while the amount of induced electromotive force in the stator coil is limited by the size of the rotor cavity. In summary, the use of a rotor as a source of magnetic flux in a generator is feasible, but there are practical limitations, namely the need for a brush and slip ring system, the need for stationary field coils to withstand centrifugal forces, and finally, the physical space within the rotor cavity in turn limits the size and strength of the magnets.

The applicant has noted that efforts have been made to control or influence the excitation coil by including a secondary coil.

US4887020 (self-compensating brushless alternator) discloses a secondary stator coil whose function is to generate electric power which is then fed back to the rotor coil. US9912206 (electric motor with damping device) discloses a secondary stator coil whose function is to generate a damping torque on the rotor by means of its own magnetic field generated by an induced current flowing through it. In both cases, a current is induced in the secondary coil to play a role.

US7545056 (saturation control of an electric machine) and US20040239202 (architecture of an electric machine) both describe generators comprising a secondary coil in the stator, which is supplied with a DC current. The generators described in these patents are all permanent magnet generators. A limitation of permanent magnet generators is that their output voltage can only be controlled by the speed of the machine. These patents relate to increasing the controllability of the output of a permanent magnet generator. This is achieved by introducing a secondary control winding within the stator of the machine. The magnetic field generated by the control winding is magnetically isolated from the magnetic field generated by the permanent magnets in the rotor. The effect of the magnetic field of the control winding is to change the saturation level of the stator material. Changing the saturation level changes the resistance of the magnetic circuit and thus affects the output voltage induced by the power winding. This approach has some control over the output produced by the permanent magnet motor, although it is inefficient because it requires additional power to saturate the return path, thereby reducing the output power. Generally, the more input power that is input to the machine, the less net output power that is produced.

Applicants desire an improved generator. The applicant proposes to achieve such an improved generator by providing a secondary coil configured differently from the prior art disclosures known to the applicant.

SUMMERY OF THE UTILITY MODEL

Accordingly, the present disclosure provides a generator comprising:

a rotor having a magnet arrangement configured to provide a primary magnetic field; and

a stator having armature coils about which the rotor is rotatable such that the primary magnetic field induces a current in the armature coils,

wherein the generator further comprises:

a secondary winding provided around or outside the stator, the secondary winding configured to generate a secondary magnetic field that interacts with and increases or enhances the primary magnetic field; and

a switching device configured to switch at least one of a strength or a polarity of a magnetic field of the secondary winding based on a position of the rotor relative to the secondary winding.

The magnet arrangement of the rotor may be in the form of an electromagnet or a permanent magnet with an excitation coil.

Thus, the secondary coil may be configured to increase or enhance the current induced in the armature coil from around or outside the stator, in other words, not from inside the stator which may house the rotor. This may result in a higher current induction (and hence generation) without increasing or even reducing the complexity of the rotor. Reduced rotor complexity may come at the expense of the power required to drive the secondary winding to generate the secondary magnetic field.

The generator may be configured to supply a current, e.g. a DC (direct current) current, to the secondary coil. The current may be provided or controlled by a switching device.

The applicant believes that the technical advantage of the present disclosure over the prior art disclosures mentioned in the background is that there is no magnetic linkage between the magnetic field of the rotor and the magnetic field generated elsewhere, for example in the secondary stator coils. The present disclosure aims to improve this by ensuring that the secondary magnetic field (or flux) generated by the secondary coil outside the rotor increases the output of the generator consistently and constructively, for example, by increasing the flux generated by the rotor.

In other words, the present disclosure proposes the idea of moving a portion (or even a large portion) of the flux production away from the rotor, but instead generating flux outside the rotor, for example in or by the stator, in the return path, even outside the machine. The fields (primary and secondary) generated from two different sources (excitation and secondary) may have a constructive role.

The generation of magnetic flux outside the rotor may have many advantages, for example inside and outside the stator instead of inside the rotor, i.e. the stator is stationary, and therefore a lossy brush and slip ring system may not be needed, nor the centrifugal forces can be counteracted. The stator is located outside the rotor, and therefore, the space or size limitations of the secondary stator coil may be small, unlike the space limitations placed on the rotor coil. Other advantages are that the requirement for cooling is less complex and easier to repair and maintain than a rotor as a source of magnetic field. This reduces the volume and space required in the rotor inside the machine by increasing the magnetic field generated outside the rotor.

The switching device may be configured to provide a switching algorithm according to the rotor position.

The secondary coil may be provided at one or more of the following locations:

an inner portion of the stator;

an outer portion of the stator; and/or

Completely outside the stator.

When a magnetic field is generated outside the stator, a high permeability material may be used to link and direct the secondary magnetic field to the stator. The high permeability material may comprise mu metal, pure iron or a superalloy.

Drawings

The disclosure will now be further described, by way of example, with reference to the accompanying drawings.

In the drawings:

figure 1 shows a schematic cross-sectional view of a simplified conventional two-pole generator;

fig. 2 shows a schematic cross-sectional view of a generator according to an example embodiment of the present disclosure;

FIG. 3 shows a schematic diagram of the switching of the secondary coils according to the rotor position in the generator of FIG. 2;

FIG. 4 shows a graphical view of a plot of secondary coil current as a function of rotor position in the generator of FIG. 2;

FIG. 5 is a graphical view of a smooth step function plot of secondary coil current versus rotor position in the generator of FIG. 2;

FIG. 6 shows a schematic cross-sectional view of an alternative embodiment of a generator according to the present disclosure;

FIG. 7 shows a schematic diagram of secondary coil switching according to the rotor position of the generator of FIG. 2;

FIG. 8 shows a schematic diagram of another embodiment of a generator according to the present disclosure having two external electromagnets for a four pole generator;

FIG. 9 shows a schematic view of another embodiment of a generator according to the present disclosure, wherein both north poles are connected to the stator;

FIG. 10 shows a schematic view of another embodiment of a generator according to the present disclosure, wherein two south poles and a central north pole are connected to the stator;

FIG. 11 shows a schematic diagram of another embodiment of a generator according to the present disclosure, wherein the secondary coil includes two north poles and two south poles;

FIG. 12 shows a schematic view of another embodiment of a generator according to the present disclosure, with two north poles and no south pole linked to the stator; and

fig. 13 shows a schematic view of another embodiment of a generator according to the present disclosure, where two north and two south poles with magnetic barriers for large external magnet surface area coverage are linked to the stator.

Detailed Description

The following description of the present disclosure is provided as an enabling teaching of the present disclosure. One skilled in the relevant art will recognize that many changes can be made to the embodiments described, while still obtaining the beneficial results of the present disclosure. It will also be apparent that some of the desired benefits of the present disclosure can be obtained by selecting some of the features of the present disclosure without utilizing other features. Thus, those who work in the art will recognize that modifications and adaptations to the present disclosure are possible and can even be desirable in certain circumstances and are a part of the present disclosure. Accordingly, the following description is provided as illustrative of the principles of the present disclosure and not in limitation thereof.

Referring to fig. 1, a conventional two-pole motor can be seen. A conventional machine consists of a stator 1 containing armature coils 2 and a rotor 3 containing field coils 4. The DC current is supplied to the rotor field coil 4. The direction of current through the rotor coils 4 is indicated by the intersection, which indicates current entering the page, and the index of the dots, which indicates current leaving the page. The current direction shown in the rotor field coil 4 results in a magnetic field 5 observed in the machine.

Fig. 2 shows an embodiment of the present disclosure in which the conventional design has been modified to include a secondary coil 6 in the stator. Note that the outer part of the stator 7, which serves as the return path of the machine, has been extruded radially outwards in comparison to conventional designs. This increases the size of the stator slots 8, thereby providing space and accessibility for the secondary coils 6. Pressing the return path outward also increases the accessibility of the stator armature coils 9, thereby facilitating cooling of the coils.

The secondary coil 6 is energized by an external DC current, the direction of which is also depicted by a cross and dot key (dot), where dot represents the direction of current out of the page and cross represents the direction into the page. Note that the secondary coil 6a on the left hand side of the machine has a different current direction than the coil 6b on the right hand side of the machine. This is done to ensure that the magnetic field generated by the secondary coil 6 complements the magnetic field generated by the rotor field coil 10.

The secondary coil along the centre line of the machine 6c is not supplied with any current as this will destructively interfere with the magnetic field within the machine and so there is no cross or point index. In order to constructively increase the magnetic field generated by the rotor field coil 10 in the secondary stator coil 6, it is necessary to switch the direction of the current passing through the secondary stator coil 6 according to the position of the rotor 11.

Fig. 3 shows how the current through the secondary stator coil 6 is switched depending on the rotor position. Referring to label a on fig. 3, which highlights a particular secondary stator coil, it can be seen that as the rotor moves from position 1 to position 2 to position 3, the direction of current through that coil changes from out of the page to zero and into the page. This ensures that the magnetic field generated by the secondary stator coil 6 changes direction as the rotor 11 rotates, so that it always aligns itself with the rotating magnetic field generated by the rotor field coil 9.

Fig. 4 is an example graph of the current applied to the secondary coil labeled by label a versus the rotor position in degrees in fig. 3. The purpose of fig. 4 is to show how the sign of the current indicating direction varies with rotor position. Note that this embodiment is not limited to the step-function waveform shape shown in fig. 4.

In fact, as long as the sign of the secondary coil varies according to the rotor position, many waveform shapes can be applied to the secondary coil to ensure that the magnetic field of the secondary coil constructively increases the magnetic field of the rotor. An example of an alternative waveform shape is shown in fig. 5. Here, the handover function is adjusted (rounded) to smooth the handover transition. If the rate of change of current through the solenoid is high, a large induced magnetic field is induced, causing a spike in the induced output voltage waveform. Smooth switching transitions help mitigate these spikes in the output voltage.

Fig. 6 illustrates another embodiment of the present disclosure. In this embodiment, instead of the secondary stator coil sharing the same slots as the stator armature coil as in the previous embodiments, the secondary stator coil 12 is extruded from the generator body 13. The magnetic flux is transferred to the generator body via flux bridges 14. To ensure that the flux generated by the secondary coil 12 actually passes through the air gap 15 and links with the rotor flux 16, an air gap 17 must be introduced in the stator return path.

The air gap 17 may be a magnetic flow resistance device material comprising air or a non-magnetic material. The air gap 17 ensures that the flux generated by the secondary coil 12 does not bypass the rotor and in turn forces the flux to intersect the armature winding 18, resulting in a greater induced output voltage.

The advantage of this embodiment is that the secondary stator coil 12 has its own magnetic support structure 19, which magnetic support structure 19 is physically removed from the structure of the generator 13. This makes it easy to cool the secondary coil 12 and easy to maintain, since the generator does not have to be shut down when maintaining the secondary coil. In order for the secondary coil to constructively increase the magnetic flux generated by the rotor 16, a switching algorithm similar to the previous embodiment must be used.

Fig. 7 shows how the current direction in the secondary stator coil 12, depicted by the dot and cross indices, remains the same from position 1 to 3, but changes as the rotor 16 passes through the 90 ° position, as can be seen by comparing

positions

3 and 4. To ensure that the flux generated by the secondary coil is consistent with the flux generated by the rotor 16, a change in the direction of the current in the secondary coil 12 is necessary. As the rotor 16 changes direction, its magnetic flux also changes, so the direction of the magnetic flux of the secondary coil 12 needs to be changed to ensure that they coincide with each other.

The generators of fig. 2-3 have secondary windings arranged circumferentially around the stator. The stator may act as a back-iron (back-iron) to provide a return path for the magnetic field/flux. However, in fig. 6 to 13, the secondary winding is provided outside the stator and spaced apart from the stator. An arm or core of magnetically permeable material is then included to provide a return path from the secondary winding to the stator so that the secondary magnetic field can interact with the rotor.

When there are two north poles feeding the magnetic field into the return path, some embodiments will have a greater magnetic field strength generated outside the rotor, while other embodiments will generate a greater magnetic field in the rotor to promote flux flow to the rotor. If there are two north poles feeding a magnetic field into the return path, the electromagnet will have two coils with different current directions, so that two north poles are formed at both ends and a south pole in the middle, and the magnetic field inside the magnet will flow/point in all directions to the north poles. In contrast to the above, two south poles at both ends are connected to a north pole in the return path and one north pole in the middle is connected to a south pole in the return path, to which return path both south pole fields will flow.

Some embodiments are generators with more poles, for example 8 pole generators, where the four north poles of the external electromagnet are connected to the four south poles of the generator. The magnetic field generated outside the machine must be axial and enter the return path along the magnetically permeable material. The path of the magnetic field generated from outside the machine must be as short as possible in order for the machine to reach an optimum operating state.

In order to make the travelling magnetic field path shorter, the electromagnetic coil must optimally end up very close to the return path, so that the magnetic field does not have a long travelling path. In order to direct the flux into the rotor and avoid flux short-circuiting, the return path will have a plurality of air gaps, as shown in fig. 7, in this case two air gaps. For a four-pole machine, there will be four air gaps. The number of poles will match the number of air gap points.

Clause and subclause

1. A generator causes some magnetic field to be generated outside the rotor by electronic control that changes the direction of the current relative to the rotor position to the secondary coil and electromagnet to change its polarity, thereby adding magnetic field constructively and constantly into the magnetic circuit through the return path.

2. The generator of clause 1, wherein the secondary coil that generates the secondary magnetic field is located in an outer region of the stator, wherein the stator is an outer member that surrounds the rotor.

3. The generator of clause 1, wherein the secondary coil for generating the secondary magnetic field is located in an interior region of the stator, wherein the stator is an interior member surrounding the rotor.

4. The generator according to clause 1, wherein the (electromagnet) secondary coil for generating the secondary magnetic field is located outside the electrical machine.

5. The generator of clause 4, wherein when the machine has X number of poles, the return path will have X reluctance devices containing air gaps, which is the return path, two air gaps for a two pole machine and four air gaps for a four pole machine.

6. A four pole generator according to clause 5 wherein there are two external electromagnets with two north pole ends connected to the two south poles of the motor.

7. A four pole generator according to clause 5 wherein there are two electromagnets with four north pole ends connected to the two south poles of the motor.

8. A multi-pole generator, the north pole of the external electromagnet feeds the magnetic field into the south pole of the generator.

9. The generator of clause 4, wherein the magnetic field generated outside the rotor is greater than the magnetic field generated in the rotor electromagnets to increase the strength of the magnetic field flowing into the windings.

10. The generator of clause 4, wherein the external electromagnets have magnetic barriers between the electromagnets, wherein the surface contact area with the return path covers a larger surface area on the return path.

11. The generator of clause 4, wherein the magnetic field is directed by a high permeability material comprising a mu metal, superalloy, having a large surface area.

12. The generator of clause 1, wherein the ends of the electromagnet poles are very close to the return path and have a highly permeable material comprising mu metal.

Claims

1. An electrical generator, comprising:

wherein the generator further comprises:

2. The generator of claim 1 wherein the secondary winding is configured to increase or augment current induced in the armature coils from around or outside the stator, which operatively results in higher current induction and therefore generation of electrical power without increasing rotor complexity.

3. The generator of claim 1, configured to supply current to the secondary winding, and wherein the current is provided or controlled by the switching device.