WO2005119711A1

WO2005119711A1 - Variable inductive device

Info

Publication number: WO2005119711A1
Application number: PCT/NO2005/000188
Authority: WO
Inventors: Frank Strand
Original assignee: Magtech As
Priority date: 2004-06-04
Filing date: 2005-06-03
Publication date: 2005-12-15
Also published as: NO20042291D0; NO20042291L; NO322234B1

Abstract

The invention comprises a controllable inductive device, with a first core (2), a main winding (3) and a control winding (4), where the main winding (3) and the control winding (4) are adapted to provide non-parallel magnetic fields. Said device is characterised in that the first core (2) comprises: a) two inner plate elements (5, 6) and two outer plate elements (7, 8), where the plate elements (5, 6, 7, 8) are arranged substantially parallel to one another, b) inner and outer yoke elements (9, 10 respectively) for magnetic connection of the ends of inner plate elements (14, 15) to one another and of the ends of the outer plate elements (16, 17) to one another, c) magnetic connection elements (11) for magnetic connection of the sides of one inner plate element and an adjacent outer plate element (12, 13 and 18, 19 respectively), and that the main winding (3) is adapted for placement about a first pair of plate elements formed by a first inner element (5 or 6) and a first adjacent outer element (7 or 8 respectively). The invention is also related to transformer and other devices comprising such an inductive device.

Description

Variable inductive device

Introduction/technical field

The present invention relates to the field of inductive devices and describes more specifically a variable inductive device, comprising a first core, a main winding and a control winding where the main winding and the control winding are adapted to provide non-parallel magnetic fields.

Variable inductive devices, where impedance is varied by means of a control current are described e.g. in WO 01/90835.

However, the known solutions are not meant to provide a device which can easily be adapted to different power requirements. Different power applications require variations in the inductive devices' size, since there is a direct relation between the power that can be handled by an inductive device and the amount of magnetic material in the device.

Production of inductive devices is a time demanding process, and there is a need for a solution which permits rationalisation of the production process.

With this in mind, the object of the invention is to provide an inductive device which comprises parts easily manufactured and assembled, and which can easily be adapted to different power applications.

These and other objects are achieved by means of an inductive device according to the invention, which is characterised in that the first core comprises: a) two inner plate elements and two outer plate elements, where the plate elements are arranged substantially parallel to one another, b) inner and outer yoke elements for magnetic connection of the ends of inner plate elements to one another and of the ends of the outer plate elements to one another, c) magnetic connection elements for magnetic connection of the sides of one inner plate element and an adjacent outer plate element to one another, and where the main winding is adapted for placement about a first pair of plate elements formed by one inner element and an adjacent outer element.

In one embodiment of the invention, the inductive device comprises two magnetic connection elements for magnetic connection of the sides on one inner plate element to the sides of one adjacent plate element. This embodiment of the invention can be used with a control winding situated around one or both magnetic connection elements, as will be explained later. In another embodiment of the invention, a closed magnetic path is provided for the control flux by means of four magnetic connection elements for magnetic connection of the sides of the inner plate elements to the sides of the correspondingly adjacent outer plate elements. This embodiment of the invention can be used with a control winding situated between the plate elements, as will be explained later.

In one embodiment of the invention the magnetic connection elements comprises connection elements sandwiched between foils of insulation material. In a preferred embodiment of the invention the cross section of magnetic connection elements are generally U-shaped.

The control winding can be mounted on different parts of the inductive device, and in one embodiment it extends between each inner and adjacent outer plate element and between inner and outer yoke elements. In another embodiment the control winding is wound around the magnetic connection element. The latter has the advantage that it is easy to add turns to the control winding since it is externally located.

The inductive device according to the invention can be the basis for a transformer with controllable transformation ratio. Transformation ratio control is performed by means of the current in the control winding, which changes the first core's magnetic characteristics.

In transformers according to the prior art the rated transformer ratio is fixed. It is dependent on the ratio between the number of turns in the primary and the secondary winding. To permit some adjustment of the voltage, tappings on the windings are brought out to terminals so that the number of turns on one winding can be changed. The voltage induced in each turn is a certain fraction of the winding's voltage. The voltage change is performed in steps and the step voltage is dependent on the number of turns between each tapping. For a fine voltage regulation there are only a few turns between each tap, and for a coarse regulation there are more turns between the taps. The taps are connected to a tap changer, which is a special type of power switch. The tap-changer arrangements are mechanically complicated and expensive to maintain. Voltage change adjustment takes place very slowly since mechanical devices have to change their state. The mechanical tap-changer is exposed to mechanical wear and its construction complicates the winding of the transformer.

Some attempts are made to address this problem by providing transformers where the core's permeability is controlled in order to control power transference between the primary and the secondary winding. In some examples (see WO 01/90835) a "barrel/tube based" structure has been used. This means that a magnetically influenced voltage converter typically consists of an external tube and an internal tube to form a permeability controlled core. A primary and a secondary winding are wound round the tubes. A control winding is wound round the internal tube, an external secondary core with windings is located concentric around the controlled core and a primary winding encloses all cores. The construction of the flux controlled part of the core and the toroidal shape itself are not as flexible as needed for construction of High Voltage- applications and other special applications. The design also has some limitations regarding the thermal performance, and hence it is limited to a certain level of power control. Another example is US patent 3,403,323 which describes an electrical energy transforming device and regulator. In this patent the core topology is a cubic form with four legs and openings for the windings in the side areas of the cube. A controlled transformer is provided based on a winding parallel to the DC control winding and the transfer of power is based on transformer action in this cube by partly orthogonal fields and partly fields that are in the same direction for primary and secondary. This transformer is not efficient enough for power applications, and is best suited for signal applications. For larger transfer of electrical energy more efficient solutions regarding topology are necessary.

A transformer device with controllable transformation ratio according to the invention comprises, apart from the basic elements mentioned before which constitute a variable inductive device (a first core, a main winding and a control winding), a secondary winding adapted for placement about a second pair of plate elements formed by one inner plate element and an adjacent outer plate element. In this embodiment of the invention the main winding constitutes the primary winding.

In an alternative embodiment, the transformer device with controllable transformation ratio according to the invention comprises, apart from the basic elements that have been mentioned before which constitute a variable inductive device (a first core, a main winding and a control winding), a second core comprising: two inner plate elements and two outer plate elements, where the plate elements are arranged substantially parallel to one another and parallel to the plate elements in the inductive device, inner and outer yoke elements for magnetic connection of the ends of the inner plate elements to one another and of the ends of the outer plate elements to one another, and a primary winding adapted for placement around a second pair of plate elements formed by one inner plate element and an adjacent outer plate element in the first inductive device and a pair of plate elements formed by one inner plate element and one outer plate element in the second core. In this embodiment of the invention, the main winding constitutes the secondary winding. In a preferred embodiment, the transformer device is given further flexibility by the second core comprising a magnetic connection element for magnetic connection of the sides of one inner plate element and an adjacent outer plate element, and a control winding adapted to provide a magnetic field which is non-parallel to the magnetic field of the main winding. The second core in these embodiments of the invention can be dimensioned taking into consideration not only the dimensions of the first core, but also the percentage of voltage regulation needed.

In another embodiment, the invention comprises a controllable inductive device for use together with transformers, comprising a variable inductive device wherein the main winding is adapted for receiving part of the transformer's core. This embodiment of the invention is particularly useful in three phase applications, where a bypass path can easily be added to a traditional transformer construction. By using such a core topology as an add-on flux path for the main core flux linking, with the primary and or secondary winding dependent on the winding layout, it is easy to implement continuous voltage regulation control. In this kind of voltage control the divided flux introduces a controlled inductance that is in series with the load winding, also the magnetizing inductance can be made controllable. The ratio of voltage regulation depends on the ratio of the series inductance to the magnetising inductance. There is also an inductive voltage drop proportional to the load current. The first core in the inductive devices according to the invention and the second core in the transformer device according to the invention permit easy and flexible production of the core parts. The core parts can be produced by wound sheet material, by lamination or other corresponding processes, and due to the core part's simple geometry these processes can be performed with low costs. The invention comprises a module which can be used as an inductive or transformer device, and which can also be expanded by means of similar modules to provide further flexibility or to permit higher power applications.

The invention also comprises transformer structures with one or several assembled cores with equal or different size and one or several windings enclosing one or more cores partly or completely.

Detailed description

The invention will now be described in more detail and with reference to the figures where:

Figure 1 shows the principle of a variable inductive device,

Figure 2 shows the components in an inductive device according to the invention in an exploded view. Figure 3 shows a device according to the invention with the main and control flux directions shown.

Figure 4 shows the plate elements in greater detail.

Figure 5 shows how the yoke elements can be produced.

Figure 6 shows how elements in the magnetic connection elements can be produced.

Figure 7 shows placement of the control winding in one embodiment of the invention.

Figure 8 shows the control winding in another embodiment of the invention.

Figures 9-1 1 illustrate the assembling of a transformer according to the invention.

Figures 12 and 13 illustrate the principle behind a second embodiment of a transformer according to the invention.

Figures 14 and 15 show some steps in the production of a transformer 61 according to an embodiment of the invention.

Figure 15 shows a transformer according to one embodiment of the invention.

Figure 16 shows a controllable inductive device according to the invention for use together with transformers.

Figure 1 shows the principle behind a device according to the invention. Such a device 1 comprises a first core 2, a main winding 3 and a control winding 4, where the main winding 3 and the control winding 4 are adapted to provide non-parallel magnetic fields. As mentioned before, variable inductive devices of this type are mentioned e.g. in WO 01/90835, the contents of which are incorporated by reference.

Figure 2 shows the components in an inductive device according to the invention in an exploded view. These are: a) two inner plate elements (5, 6) and two outer plate elements (7, 8), where the plate elements (5, 6, 7, 8) are arranged substantially parallel to one another, b) inner (9) and outer (10) yoke elements for magnetic connection of the ends of inner plate elements (14, 15) to one another and of the ends of the outer plate elements (16, 17) to one another, c) magnetic connection elements (1 1) for magnetic connection of the sides of one inner plate element and an adjacent outer plate element (12 and 13, or 18 and 19). For clarity, only one magnetic connection element is shown in the figure for connection of the front sides of plate elements 12 and 13, but a second magnetic connection element is provided for connection of the rear sides of plate elements 12 and 13, as will be shown later. According to the invention the main winding 3 is adapted for placement about a first pair of plate elements formed by one inner element and an adjacent outer element (5, 7 or 6, 8).

As one can see, the inductive device 1 according to the invention comprises parts with a simple geometry, which are specially designed for easy production and assembly.

Figure 3 shows a device 1 according to the invention. In the figure the working and control flux directions are shown. The working flux or main flux links the turns in the winding(s) and then contributes to inductance and power transference between a primary and a secondary winding. This flux will have a direction 21 defined by the winding axis of the main winding 3 (not shown). As mentioned before, the device 1 according to the invention comprises means for controlling core permeability, that is, it comprises a control winding 4 which is adapted to create a flux mainly perpendicular to the main flux. In the device according to the invention, plate elements 5, 6, 7, 8 provide a path for the main flux in their longitudinal direction 21. Yoke elements 9, 10 provide, together with plate elements 5, 6, 7, 8 a closed path for the main flux. Moreover, the device comprises generally U-shaped magnetic connection elements 1 1 , which provide a closed, low reluctance path for control flux (direction 22). To have a high reluctance path for the main/working flux that can flow in the transversal direction in the control magnetic connection element 1 1 (23, same as the longitudinal direction of the total structure), magnetic connection elements 1 1 can comprise elements 24 by a small spacer of non- magnetizable material.

Figure 4 shows plate elements 5, 6, 7, 8 with plate elements ends 14, 15, 16, 17 and sides 12, 13, 18, 19. These core elements are, in a preferred embodiment of the invention made of high quality grain oriented silicon steel. The main flux path is in the grain oriented or longitudinal direction 21, and each plate element comprises laminated sheet strips of a rectangular shape. In a preferred embodiment of the invention, the plate elements 5, 6, 7, 8 comprise slots 31 at the end faces. The object of slots 31 is to concentrate the control flux, transmitted in the transversal direction 22 in the plate elements. One or more of these slots 31, with a small width makes the reluctance for the transversal flux path through the slot area much higher than the reluctance in the other parts of the core. It is possible to equip all plate elements with slots 31 but it will also be possible to limit the number of "slotted" elements to 3, 2 or 1 . In the elements the grain oriented direction is parallel to direction 21.

Figure 5 shows how yoke elements 9 and 10 can be produced by using wound sheet material, e.g. steel. The sheet material is rolled to an outer pipe 41 and an inner pipe 42 and thereafter pipes 41 and 42 are cut into two halves (10, 9 respectively). Each half will form a yoke (9, 10). Figure 6 shows how elements 24 in magnetic connection element 1 1 can be produced. Again sheet material (e.g. steel) is rolled to a pipe configuration, and the pipe is cut into slices 43 and these into two halves 24. Each half slice will constitute an element 24.

As an alternative, the yokes and the magnetic connection element can be made of magnetic composites [Somaloy™] or sintered materials (e.g. as produced by Høganes in Sweden).

Figure 7 shows placement of the control winding 4 in one embodiment of the invention. In this embodiment, control winding 4 (broken line) extends between each inner and the adjacent outer plate element (7, 5 and 6, 8 respectively) and between inner and outer yoke elements (9, 10). The advantage of this embodiment of the invention is that control winding 4 is protected from external stresses. The main disadvantage is that this embodiment of the invention requires winding control winding 4 on a partly assembled core. Some problems related to winding cooling can also be present.

In another embodiment of the invention (figure 8), especially advantageous regarding this aspect, the control winding 4 is adapted for being situated around the magnetic connection elements 1 1. In this way, control winding 4 can be assembled by inserting part 1 1 in the space surrounded by the turns in control winding 4. Control winding 4 can be produced as a single piece at one location, and thereafter be transported to the assembly plant for assembly of the inductive device 1. The illustration of the assembly shows that there is a lot of free space for more turns if wanted, as most of the space in between plate elements is vacant. This gives the device according to the invention flexibility regarding voltage and power transfer regulation, since these properties will depend among other things on the amount of turns in control winding 4.

Figures 9-11 show some of the assembly steps for a transformer 51 according to the invention. A transformer according to the invention will comprise a primary winding 52, a secondary winding 53 and a control winding 4 (figure 9). Figure 10 shows one step in the process of implementing a transformer 51. In a first step four plate elements 5, 6, 7, 8, and magnetic connection elements (not shown) are provided, and a control winding 4 is arranged around the magnetic connection elements.

Next, a primary winding 52 and a secondary winding 53 are placed around a first and a second pair of plate elements. This is shown in figure 11, which represents an embodiment of the invention, where the inductive device's main winding provides the transformer's primary winding 52, and which comprises a secondary winding 53 adapted for placement about a second pair of plate elements formed by one inner element and an adjacent outer element (6, 8). In the same manner as explained earlier in relation to control winding 4, this embodiment of the invention permits use of a preproduced winding, that is, it does not require expensive and time consuming winding equipment at the assembly site. Preproduced windings in most power ranges can be made available. In this embodiment of the invention, a variable inductance (not shown) must be connected in series with the primary winding to avoid that an increase in magnetising current leads to a shortcircuit of the voltage source for the primary winding.

Figures 12 and 13 illustrate the principle behind a second embodiment of a transformer according to the invention. Said transformer 61 comprises (see figure 12) a primary winding 52, a secondary winding 53, one or two control windings (not shown) and two cores: a main core 2 for flux that is common to the primary and secondary winding (52, 53 respectively) and a by-pass core 62 for flux that is not common to both windings (hereafter called leakage flux). The following nom en cl atur e i s us ed :

Icl control current for main core 2 Ic2 control current for by-pass core 62 Vp Primary voltage Vs Secondary voltage

Transformer 61 is supplied with a primary voltage on terminal Vp which generates a flux. In this example, transformer 61 is connected to a variable load impedance 63 on terminal Vs, and a magnetic flux path is also shown. In transformer 61, main core 2 and bypass core 62 provide first and second flux paths. Core 2 provides a common flux path for the primary winding 52 and the secondary winding 53, and core 62 provides a bypass flux path for leakage flux. Leakage flux in this context is flux which is not linked by both windings but which is comprised in the magnetic path.

At least one of the flux paths has controllable relative permeability, that is, a control winding (not shown) is arranged to provide permeability control in one of the cores or in both cores. Desired characteristics of transformer 61 can, according to the present invention, be achieved by using different building blocks put together by preproduced parts.

The induced voltage in the secondary winding 53 is dependent on the flux linking that winding. When a primary winding 52 shares the same core 2 as a secondary winding 53 almost all the flux links both windings. In order to control the efficient transformer ratio, one needs to control the flux linking between the primary and the secondary winding of the transformer. To control the flux linking or mutual inductance between the two windings, a new by-pass flux path provided by core 62 and linking only one of the windings is made. By controlling the reluctance of the by-pass flux path (control winding 4) the flux linking is controlled.

Figure 13 shows an equivalent circuit for a controllable, single phase transformer according to the invention. Leakage flux as mentioned above is represented in the transformer equivalent diagram as a series inductance LI, this inductance corresponds to the leakage inductance in ordinary transformers. If both the main core 2 and the bypass core 62 are reluctance controlled, (e.g. by means of a control field which is mainly perpendicular to the main core field direction) the flexibility of control is increased. This is due to the fact that when there are two independent flux paths the inductances involved are also independent on each other. By also controlling the main core 2, the magnetizing current is controlled. This is represented in the equivalent circuit by a variable magnetizing impedance Lm. By having both the common core 2 and the by-pass core 62 controllable, one can adjust the output Vs by changing the inductances LI and Lm.

The transformer's 61 transformation ratio can thus be controlled by means of control currents which cause changes in the cores' permeability. Besides, the variation range of the transformation ratio depends on the relative size of the bypass core 62 and the main core 2. By means of the present invention the by-pass core can be dimensioned taking into account the amount of voltage regulation, because the size of the cores in a transformer according to the invention can be changed easily by adding plate elements or by replacing existing plate elements by new elements of a different size, as long as flux density (and flux leakage) limits are respected. Flux density in the cores must not for any combination of control current and load, exceed certain limits (e.g. 1,5T). The limits are set to avoid saturation. At the same time, flux leakage in the air at full load must be kept to a minimum. The size of the bypass flux path is dependent on how much flux one needs to divide. If the voltage is to be controlled 0-100% one needs an additional core of the same size as the original transformer core. If only a fraction of the voltage is to be controlled one need an additional core of only a fraction of the original transformer.

Figures 14 and 15 show some steps in the production of a transformer 61 according to the embodiment of the invention newly discussed. This device comprises an inductive device according to the invention with a first core 2, where only plate elements 5, 6, 7, 8 are shown in figure 14 and a second core 62 comprising two inner plate elements (71, 72) and two outer plate elements (73, 74), where plate elements 71 , 72, 73, 74 are arranged substantially parallel to one another and parallel to plate elements 5, 6, 7, 8 and magnetic connection elements (not shown) for magnetic connection of the sides of one inner plate element and an adjacent outer plate element. As mentioned before, preproduced primary, secondary and control windings can easily be arranged on this core.

Figure 15 shows transformer 61 with primary, secondary and control winding in place. As one can see, a primary winding 52 is placed around a second pair of plate elements (6, 8) formed by one inner plate element and an adjacent outer plate element in the first core 2 a pair of plate elements (71 , 73) formed by one inner plate element and one outer plate element in the second core 62, and inner and outer yoke elements (81, 82) for magnetic connection of the ends of the inner plate elements to one another and of the ends of the outer plate elements to one another. Main core 62 and bypass core 2 in transformer 61 are of the same size. In another application the cores might be of different sizes as mentioned above, dependent on the amount of voltage control needed.

The mechanical solution or core topology will lead to material savings without compromising the transformer's efficiency.

Figure 16 shows a controllable inductive device 91 according to the invention for use together with transformers. This device 91 comprises an inductive element according to the invention, and is characterised by the main winding 3 being adapted for receiving a part of the transformer's core. The figure shows one of three identical legs 92 of a three phase transformer, where an inductive device according to the invention (with plate elements, yoke elements, magnetic connection elements, main winding 3 and control winding 4) is added to achieve voltage control (step down function) of the output of the transformer. The main winding 3 shown is either one of three primary- or one of three secondary windings.

It should be clear that a skilled person is able to derive other effective constructions from preproduced parts depending on desired relevant transformer characteristics.

Claims

CLAIMS 1. Controllable inductive device, comprising a first core (2), a main winding (3) and a control winding (4), where the main winding (3) and the control winding (4) are adapted to provide non-parallel magnetic fields, characterised in that the first core (2) comprises: a) two inner plate elements (5, 6) and two outer plate elements (7, 8), where the plate elements (5, 6, 7, 8) are arranged substantially parallel to one another, b) inner and outer yoke elements (9, 10 respectively) for magnetic connection of the ends of inner plate elements (14, 15) to one another and of the ends of the outer plate elements (16, 17) to one another, c) magnetic connection elements (1 1) for magnetic connection of the sides of one inner plate element and an adjacent outer plate element to one another (12, 13 and 18, 19 respectively), and that the main winding (3) is adapted for placement about a first pair of plate elements formed by a first inner element (5 or 6) and a first adjacent outer element (7 or 8 respectively).

2. Inductive device according to claim 1, characterised in that it comprises two magnetic connection elements for magnetic connection of the sides of one inner plate element to the sides of an adjacent outer plate element.

3. Inductive device according to claim 1 , characterised in that it comprises four magnetic connection elements (1 1) for magnetic connection of the sides of the inner plate elements to the sides of the correspondingly adjacent outer plate elements.

4. Inductive device according to any of the preceding claims, characterised in that the magnetic connection elements (1 1) comprise connection elements (24) sandwiched between foils of insulation material.

5. Inductive device according to any of the preceding claims, characterised in that the control winding (4) extends between each inner and adjacent outer plate element (5, 7 and 6, 8 respectively) and between inner and outer yoke elements (9, 10).

6. Inductive device according to any of the preceding claims 1 -5, characterised in that the control winding (4) is wound around the magnetic connection elements (1 1).

7. Inductive device according to any of the preceding claims, characterised in that the cross section of the magnetic connection elements (1 1) is generally U-shaped.

8. Transformer device (51), characterised in that it comprises an inductive element according to any of the preceding claims, where the main winding provides the transformer's primary winding (52), and a secondary winding (53) adapted for placement about a second pair of plate elements formed by a second inner element (6 or 5) and a second adjacent outer element (8 or 7 respectively).

9. Transformer device (61), characterised in that it comprises: - an inductive device according to any of the preceding claims 1-7 with a first core (2) and where the main winding provides the transformer's secondary winding (53), -a second core (62) comprising: two inner plate elements (71 , 72) and two outer plate elements (73, 74) where the plate elements (71, 72, 73, 74) are arranged substantially parallel to one another and parallel to the plate elements in the inductive device (5, 6, 7, 8), inner and outer yoke elements (81, 82) for magnetic connection of the ends of the inner plate elements to one another and of the ends of the outer plate elements to one another, and a primary winding (52) adapted for placement around a second pair of plate elements formed by one inner plate element and an adjacent outer plate element in the first inductive device (6, 8) and a pair of plate elements formed by one inner plate element and one outer plate element in the second core (71 , 73).

10. Transformer device according to claim 8, characterised in that the second core (62) comprises a magnetic connection device for magnetic connection of the sides of one inner plate element and an adjacent outer plate element, and a control winding adapted to provide a magnetic field which is non- parallel to the magnetic field of the main winding.

1 1. Controllable inductive device (81) for use together with transformers, characterised in that it comprises an inductive element according to any of claims 1-6, wherein the main winding (3) is adapting for receiving a part of the transformer's core (82).