|Title of Invention||
A TOROIDAL CORE
|Abstract||The present invention relates to a toroidal core comprising materials which are wound on with at least two layers, wherein the first material layer comprises a magnetically and electrically conducting material and the second material layer comprises a non-magnetic and an non-electrically conducting material, characterized in that the second material layer comprises paper or a foil of a thickness of between about 0,1 mm and the I layer thickness of the first material layer is about 0,23mm.|
Toroidal cores are used in many situations in electrical engineering, in particular in coils for increasing inductance. By way of example mention may be made here of a choke or inductor coil whose ohmic resistance is low in comparison with the inductive reactance. Fitting a toroidal core, for example a laminated iron core, substantially increases the inductance of such a choke coil (iron-cored inductors). If the iron path is closed, it frequently involves air gaps in order to reduce the influence of iron saturation (air-gap chokes).
The magnetisation characteristics of coils or inductors can be set to a desired value by means of the toroidal core. Such inductors are increasingly used in modern power electronics in the higher power range. Just by way of example, mention may be made of an area of use such as for example smoothing pulsating direct current, filtering direct current, decoupling systems or for voltage regulators (reducing units, booster units). Further areas of use for inductors with a toroidal core are short-circuit limiting chokes in an inverter branch or filter chokes. Depending on the respective magnitude of the toroidal core air gap, it is then possible to set various magnetisation characteristics, as are shown by way of example in Figure 1. Those magnetisation characteristics are then also referred to as hysteresis loops or curves.
In the hysteresis curve in Figure 1 of type a the toroidal core does not have an air gap. In the case of the hysteresis magnetisation characteristic of type b the toroidal core has a relatively small air gap while in the case of the hysteresis magnetisation characteristic of type c the toroidal core has a very large air gap.
The air gap of a toroidal core can be concentrated at one location so that it is possible to see and also measure off the gap (macroscopic air gap). It is however also possible for a plurality of small air gaps to be distributed over the magnetic circuit or the toroidal core. In that case reference is made to what is known as a 'microscopic air gap'. In that respect, in the case of iron powder cores, the effective air gap is distributed over the entire periphery by admixing non-magnetic substances. Figure 2 shows embodiments of macroscopic and microscopic air gaps.
EP 0 401 805 discloses a toroidal core in which very thin-layer materials in the range of a few ^m are processed to constitute a •toroidal core. It will be noted however that the manufacture of those toroidal cores is highly complicated and expensive and the toroidal cores are not very suitable for use in power electronics.
The manufacture of a toroidal strip core with a macroscopic air gap is generally implemented as follows. Firstly, a dynamo sheet is wound on to a core which is removed again after the winding operation. Then an air gap is cut into the ring by means of a saw, a laser or a similar tool. It will be appreciated that very small gaps can be produced with that method only with difficulty and in a complicated procedure as the air gap width is always directedly dependent on the width of the tool.
Difficulties are also incurred in the manufacture of toroidal cores with a microscopic air gap, in regard to accurately defining the air gap value, as the distribution of the magnetic and non-magnetic materials over the periphery is generally not 100% homogeneous.
The object of the invention is to provide a toroidal core which does not suffer from the above-described disadvantages and which can be produced in an easier and less expensive manner. The aim is also to enjoy further advantages such as an accurate definition for the configuration of the magnetisation characteristic and very low levels of leakage fields.
According to the invention that object is attained by a toroidal core having the features of claim 1. Advantageous developments are set forth in the appendant claims.
The invention is based on the approach of producing the toroidal core from at least two material plies/layers which are wound one on to the other, wherein the first layer is of a magnetically and electrically conducting material and the second layer comprises a non-magnetic and non-electrically conducting material. It is possible for example to use a dynamo sheet as the first laminated layer while paper or foil or film can be used for the second layer. It is possible to set the desired magnetisation characteristics by virtue of the choice of the thickness of the nonconducting material, that is to say the second layer. For example, when using very thin layer material such as very thin paper, that gives a
characteristic which is only very shgntiy snearea, wnicn corresponas to a very, very small air gap. If the shearing effect of the characteristic-is to be greater, it is possible to use correspondingly thicker, non-conducting layer material.
The advantages of the toroidal core according to the invention are apparent. As only one winding operation is necessary and as there is also no need to' use special materials as in the case of previous toroidal cores with a microscopic air gap, it is possible, with conventional materials which are available on the market, to produce toroidal cores which, depending on the respective choice of the materials involved and in particular the material thicknesses, have a desired magnetisation characteristic. In particular the production of toroidal cores with a very slightly sheared characteristic is easy to implement insofar as only very thin, nonconducting material is used. The consequence of this is that an inductor with such a toroidal core with a very slightly sheared characteristic also has only very low levels of leakage fields so that no leakage fields occur in very high-power uses in power electronics. Such a toroidal core does not experience any deformation even when high currents/magnetic fields are involved and it is therefore also preferentially suitable for power electronics.
The invention is described in greater detail hereinafter with reference to a part of the illustrated embodiment. In the drawings:
Figure 1 shows magnetisation characteristics for various types of toroidal cores,
Figure 2 shows embodiments of toroidal cores with macroscopic and microscopic air gaps,
Figure 3 shows a view of a toroidal core according to the invention, and
Figure 4 shows a view of a toroidal core according to the invention.
Figure 1 shows three different types of characteristics. The characteristic of type a shows a hysteresis loop of an inductor with a toroidal core without an air gap. In the case of the characteristic of type b, the characteristic is slightly sheared and the toroidal core has a relatively small air gap. In the case of the characteristic of type c the characteristic is very substantially sheared and the toroidal core has a very large air gap.
Figure 2 shows the structure in principle of a toroidal core with a macroscopic air gap - type 1 - and a toroidal core with a microscopic air gap - type 2. The toroidal core of type 1 comprises for example a magnetically and electrically conducting material such as dynamo sheet. The toroidal core of type 2 also comprises a magnetically and electrically conducting material to which however non-magnetic substances are admixed. -
Figure 3 shows a wound toroidal core consisting of two layers. The first layer or ply - solid line - in this arrangement comprises a dynamo sheet and the second layer/ply - dotted line - comprises a magnetically and electrically non-conducting material, for example of paper or a film or foil. With such a wound toroidal core, the desired magnetisation characteristic can be determined by the number of windings and by the choice of material and layer thicknesses. If a relatively small thickness in comparison with the dynamo sheet is adopted for the non-conducting material, as a result that gives a slightly sheared characteristic, whereby it is possible to produce an inductance in a toroidal core with a very small air gap. If the shear of the characteristic is to be increased, instead of very thin non-conducting material correspondingly thicker non-conducting material is used. It will be appreciated that the magnetisation characteristic can also be adjusted by the appropriate choice of the thickness of the conducting material, in which respect it is always the relationship of the layer thicknesses of conducting and non-conducting material that is the important factor.
The dynamo sheet can be of a thickness of between about 0.05 and 0.6 mm for uses for low frequencies, for example 50 Hertz. For uses involving higher operating frequencies, it is possible to use sheet thicknesses of between 0.1 and 0.3 mm. In the case of a specific use of the toroidal core in a short-circuit choke or in a booster, it was possible to find that a thickness of 0.23 mm for the thickness of the layer of material forming the dynamo sheet was highly suitable. Layer thicknesses of between about 0.01 and 0.5 mm can be considered for the thickness of the magnetically non-conducting material. In use, that material thickness reproduces the level of the maximum current of the choke. A layer
thickness of 0.1 mm for the non-conducting layer of material is very highly suitable for short-circuit chokes.
As is known chokes with air gaps produce a leakage field. Figure 5 shows a known arrangement of that kind, in which the leakage flux is also shown, besides the main flux. Magnetic field lines always endeavour to follow the easiest path. In the illustrated geometry (Figure 5), they should flow through the limbs and the two yokes. In that situation the magnetic field lines however have to traverse four air gaps (magnetically nonconducting sections). With this geometry, leakage fields are easily formed as they represent an alternative to the desired path.
Figure 4 shows a toroidal core according to the invention and the associated main flux and leakage flux distribution. As the effective air gap in the toroidal core shown in Figure 4 is distributed uniformly over the entire periphery, magnetic conductivity is homogeneously the same over the entire magnetic length. There are no pronounced barriers like a concentrated air gap, in the arrangement shown in Figure 5.
Leakage fields only occur when in part the magnetic reluctance is less than the magnetic reluctance of the main path. That is the case with the normal embodiment with concentrated air gaps (Figure 5). This is less severely pronounced in the case of a toroidal core with a homogeneously distributed air gap. Therefore the leakage or scatter effect (of the leakage flux) is substantially less in the case of the toroidal core shown in Figure 4. A greater degree of leakage or scatter would mean that the effective inductance is reduced. That means that the toroidal core according to the invention requires fewer turns and less copper so that its efficiency is higher than that of toroidal cores in accordance with the state of the art.
1. A toroidal core comprising materials which are wound on with at least two layers, wherein the first material layer comprises a magnetically and electrically conducting material and a second material layer comprises a non-magnetic and non-electrically conducting material.
2. A toroidal core according to claim 1 wherein the layer thicknesses of the first and further layers are different.
3. A toroidal core according to claim 1 or claim 2 wherein the second material layer is of a very small thickness.
4. A toroidal core according to one of the preceding claims wherein paper or a foil is used for the second material layer.
5. A toroidal core according to one of the preceding claims wherein dynamo sheet is used for the first material layer.
6. A toroidal core according to one of the preceding claims wherein the thickness of the non-conducting material layer is in a range of between about 0.01 and 0.05 mm.
7. A toroidal core according to one of the preceding claims wherein the layer thickness of the first material layer is between about 0.1 and 0.7 mm.
8. A toroidal core comprising materials which are wound on with at least two layers, wherein the first material layer comprises a magnetically and electrically conducting material and the second material layer comprises a non-magnetic and non-electrically conducting material, characterised in that the second material layer comprises paper or a foil of a thickness of between about 0.01 and 0.05 mm and the layer thickness of the first material layer is between about 0.1 and 0.7 mm.
9. Use of a toroidal core according to one of the preceding daims in an inductor for power electronics.
10. A toroidal core comprising materials substantially as herein described with reference to the accompanying drawings.
|Indian Patent Application Number||35/MAS/2000|
|PG Journal Number||30/2007|
|Date of Filing||13-Jan-2000|
|Name of Patentee||SHRI. ALOYS WOBBEN|
|Applicant Address||ARGESTRASSE 19, 26607 AURICH.|
|PCT International Classification Number||H 01 F 3/04|
|PCT International Application Number||N/A|
|PCT International Filing date|