EP1431986A1 - Coil assembly with variable inductance - Google Patents

Abstract

The coil arrangement has two separate round ring cores (40,42) with operation windings (46,48) and a control winding (50). The control winding is wrapped around both ring cores for pre-magnetizing the ring cores.

Description

The invention relates to a coil arrangement, the inductance of which can be changed by a control current is.

From the U.S. Patent 2,274,059 a coil arrangement with variable inductance is known, which has two rectangular toroidal cores, the working windings and two each Apply interconnected control windings on separate legs of the cores.

EP-A-0 737 989 discloses a coil assembly with variable inductance, the two has rectangular toroidal cores which have working windings on one leg and control windings wear on an opposite leg of the rectangular toroid.

DE-C-36 21 573 discloses a current-compensated radio interference suppressor with two or more toroidal cores and with windings evenly distributed over the circumference of the toroidal cores.

Coil arrangements with variable inductance are used in energy technology and communications technology Applications. Such an application of coils with variable Inductance is in the range of switching power supplies, in the high frequency range adapting energy transfer to the fluctuating load requirements.

The earliest way to vary the inductance of a coil was to position one To change the iron core, or ferrite core, mechanically in the coil. Such a change the inductance of the coil was e.g. with a single adjustment of a resonant circuit performed. As soon as the variable inductance of the coil, however, as an element of a control loop is used, it must be possible to use the inductance of the coil as quickly as possible to change an electrical signal. For the realization of such an electrically controllable Inductance can take advantage of the effect of relative magnetic permeability of ferro- and ferrimagnetic materials with the magnetic flux density in Material drops. Building on this principle of action, there have been numerous in the past Coil arrangements proposed that a by means of a current in a control coil Premagnetize a magnetically highly permeable coil core and thus the inductance the work winding, which is also applied to the coil core, control.

One of the first publications on this is the U.S. Whiteley and U.S. Patent 2,229,952 Ludbrook with the title "Magnetic Amplifier" from 1941. The one described there Coil has an EE core, which has a control winding on its middle leg the outer legs carry the work windings. The tax winding is done by one Direct current flows through and thereby creates a magnetic flux in the EE core spread over all three legs. The core material is through the control winding flowing current premagnetized. The effective Permeability of the core material changes and thus also the inductance of the working windings.

As the control current increases and permeability decreases, it deteriorates the magnetic flux guiding properties for that generated by the outer windings high-frequency flow in the outer legs, so that especially in areas of low inductance strong electromagnetic interference emissions occur.

A disadvantage of these and similar arrangements known from the prior art lies in that the AC voltage applied to the working windings in the control coil is transformed, whereby the electrical properties of the arrangement deteriorate. In addition, the control coil has a significantly larger number of turns in many applications has than the work coils, which exacerbates this problem.

This disadvantage has been recognized in the prior art and attempts have been made to fix it. British patent application GB 2 195 850 A1 proposes to connect a capacitor in parallel to the control winding. In the U.S. patent 6,317,021 is proposed to avoid this problem, a parallel connection of the To provide work windings. The first method has the disadvantage of additional losses due to a short circuit current in the control winding. In solving the U.S. patent 6,317,021, the working windings are interconnected so that they pass through these windings cancel the generated magnetic fluxes for the control winding. The abolition of the rivers (Flux anihilation) in the control winding only occurs when the magnetic Conductivity in the outer legs and the middle leg for both sides of the EE core is equal to. The manufacturing-related inevitable parasitic air gaps on the abutting surfaces However, the two EE core halves are often causes for asymmetries in the magnetic Conductance. According to the U.S. Patent 6,317,021 is based on suitable cross-sectional ratios the leg of the core for work coils and control coils set whether the Middle leg goes into saturation and thus a change in inductance also of the control coil is effected. In order to avoid that the middle Thigh, which carries the control coil, saturates faster than the outer Thigh beats the U.S. Patent that the middle leg has a cross-sectional area, which is at least twice the cross-sectional area of the outer one Leg.

A major disadvantage of all arrangements based on EE cores is that high levels of the magnetic field of the work coils to a large extent then low permeable core leaves and EMC-relevant interference fields arise. This is particularly so for applications with high-frequency and very strong currents in the working windings the case, for example, when the controllable inductance is used as a reactive pre-resistance Regulation of the power in switching power supplies is used.

Another fundamental problem with the use of EE cores arises from the inevitable parasitic air gaps at the contact surfaces of the two core halves. These cause different magnetic conductivities for the field line paths through the two work coils and therefore different biases. The result on the one hand considerable tolerances for the adjustable inductance range of the coil configuration, on the other hand, there are inductance differences between the windings of the work coils on. The latter means that the coil configuration has positive and negative half-waves of the signal on the work coils conducts differently.

It is therefore the object of the invention to provide a coil arrangement with a variable inductance to be specified, which has a large modulation range and low electromagnetic interference fields generated, the heat loss of the coil assembly should be kept low. These properties are particularly relevant in switching power supplies with high power density.

This object is achieved by a coil arrangement with the features of claim 1.

The invention provides a coil arrangement with variable inductance, the two separate Has toroidal coils, which carry working windings, as well as a control winding, which wound the two to pre-magnetize the core material of the toroid coils Encompasses toroidal coils. According to the invention, the cylindrical symmetry of the ring cores and a preferably even distribution of the work windings over the circumference the ring cores significantly reduce the magnetic field strength outside the windings, and independent of the permeability of the core.

In the prior art, namely, the electromagnetic interference fields of controllable inductances occur especially when due to the magnetic permeability of the core material the premagnetization has become small, because then the magnetic field of the coil is increasing runs outside the core. In addition, the coil impedance is at low permeability low and the coil current particularly large. By providing evenly wound Toroidal coils can largely avoid the interference fields outside the core become.

Since the arrangement according to the invention has no parasitic air gaps in the field line path, the associated tolerance and asymmetry problems do not occur. Also enables the increased magnetic conductance due to the absence of air gaps better control of the core or a larger achievable inductance range. Furthermore, the manufacturing effort for two toroids is less than for two E-core halves. There the working windings according to the invention the entire core and not only the outer part surrounded the leg, there is an enlarged compared to the prior art Winding width. This allows more copper to be stored per layer, which is less Energy losses in the working windings causes.

In particular, the present invention can use ring cores whose Symmetry and constant cross-sectional area enable optimal magnetic properties. The unwanted stray fields are reduced to a minimum, and by the rotational symmetry it is ensured that every area of the core is premagnetized to the same extent is. The cores can be stacked along their axis of rotation without their electrical properties lose, and allow a compact design with good cooling properties.

According to the invention, the coil arrangement is made up of at least two closed ring core coils built up. The toroidal shape is chosen because the magnetic saturation of the Core material can be achieved particularly advantageously here. Rotationally symmetrical ring cores are the EE kemen usual in the state of the art with regard to the EMC relevant Interference fields and the utilization of the winding space. It can all commercially available round ring cores are used, the ring cores preferably a rectangular one Have a basic cross-section.

According to the invention, the coil arrangement preferably comprises two toroidal coils, which either are arranged so that their axes of symmetry coincide or that in one common plane are arranged side by side.

In the case of a coaxial arrangement of the toroidal core coils, with axes of symmetry aligned, it is also possible to use integer multiples of two toroidal coils each to arrange the common axis of symmetry. Even if the toroidal cores are in one plane are arranged, the coil arrangement is not limited to two toroidal cores. It is possible, a third toroid coil in the same plane, adjacent to the first two toroid coils to be arranged, the three coils then being coupled via three control windings, which each encompass two of the toroidal coils. Because this changes the electrical properties in terms of power density and efficiency, it is however, cheaper to couple an even number of toroidal coils together.

In the embodiment with toroidal coils arranged coaxially one above the other Windings of the control winding preferably evenly over the circumference of both ring core coils distributed. This results in a particularly good, uniform premagnetization of the core material.

Each of the toroidal coils is preferably wound in one layer with its working winding. Thereby the copper losses due to the high-frequency current can be kept low.

Each working winding can consist of a single insulated wire, a group of parallel ones untwisted insulated single wires or from a strand of twisted insulated Individual wires are formed. When using single wires, the wire diameter preferably limited to a maximum of three times the skin effect penetration depth. For minimal Energy losses, i.e. Copper losses should be the effective copper cross section of the windings be as large as possible. With regard to the energy losses, one should therefore, if possible thick wire can be selected. When using AC, however, due to the Skin effect is the area of the winding wire that is significantly wider than a skin effect penetration depth removed from the edge of the wire, largely ineffective. A winding wire that thicker than three times the skin effect penetration depth would therefore be for reasons of energy efficiency and material utilization unfavorable.

The skin effect penetration depth δ is calculated approximately as follows for copper wire at realistic working temperatures: δ [ mm ] ≈ ƒ [ kHz ] 2.2

According to the invention, each work winding is as uniform as possible over the scope of the corresponding one Toroidal core coil distributed. As mentioned, the winding is preferably single-ply. In order to minimize the heat loss, the winding width of the toroid should be that of the inner one Corresponds to the ring core circumference, be used as completely as possible. Provided the work winding has a number of turns which does not cover the entire winding width of the ring core would cover, it is appropriate to divide the work winding into partial windings and connect them in parallel. This can also ensure that the current flow is evenly distributed over the core so as to suppress external magnetic interference fields.

Instead of a single wire or parallel single wires, the work winding can also can be realized by a twisted high frequency stranded wire. With high frequency strands, the The diameter of the individual wires of the strand may be smaller than the simple skin effect penetration depth.

The working windings of the two toroid coils can be connected in parallel or in series become. In any case, the connection of the work winding should be chosen so that when the working windings have current flowing through them, the magnetic field directions generated by them are opposed to each other in the control coil, so that through the work windings no currents are induced in the control winding. An interaction between Working windings and control windings are excluded.

Any currents induced in the control winding from the working windings can cause faults in the control winding and in energy technology applications also cause undesirably high additional heating in the control winding. At the same time, such an interaction causes energy from the work windings transmit the control winding, thereby reducing the quality of the coil assembly. Consist no interaction between tax winding and work winding, so join Flow changes through the control winding no disturbances in the working windings.

Combinations of series and parallel connections can also be provided.

The cores are advantageously made of the same material, so that all cores are on a corresponding degree of bias react with the same effective permeability.

Fig. 1

eine schematischen Darstellung des Aufbaus einer Spulenanordnung mit veränderbarer Induktivität gemäß dem Stand der Technik;

Fig. 2A, 2B, 2C

eine Draufsicht, eine Seitenansicht und eine schematische perspektivische Darstellung einer Spulenanordnung mit veränderbarer Induktivität gemäß einer ersten Ausführungsform der Erfindung;

Fig. 3

eine Draufsicht auf eine Spulenanordnung mit veränderbarer Induktivität gemäß einer zweiten Ausführungsform der Erfindung;

Figur 4 und 5

eine schematische Darstellung der Verschaltung der Wicklungen der erfindungsgemäßen Spulenanordnung in Parallelschaltung bzw. in Reihenschaltung; und

Fig. 6

eine schematische Darstellung der Verschaltung einer Arbeitswicklung einer Ringkernspule, die in mehrere Teilwicklungen aufgeteilt ist.

The invention is explained below with reference to preferred embodiments with reference to the drawings. The figures show:

Fig. 1

a schematic representation of the structure of a coil arrangement with variable inductance according to the prior art;

2A, 2B, 2C

a plan view, a side view and a schematic perspective view of a coil arrangement with variable inductance according to a first embodiment of the invention;

Fig. 3

a plan view of a coil arrangement with variable inductance according to a second embodiment of the invention;

Figures 4 and 5

a schematic representation of the connection of the windings of the coil arrangement according to the invention in parallel connection or in series connection; and

Fig. 6

is a schematic representation of the connection of a working winding of a toroidal core coil, which is divided into several partial windings.

Figure 1 shows a coil arrangement with variable inductance according to the prior art consisting of an EE core 10 with a central 12 and two outer legs 14, 16. The two outer legs each carry a working winding 20, 22, which are connected in parallel to each other. The middle leg 12 has a larger cross section than the outer legs 14, 16 and carries a control winding 24. A control current 30 flows through the control winding 24 and has essentially no AC component. This generates a control flux 32, which, according to the magnetic coupling, is distributed evenly over the two outer legs 14, 16 32a, b and there generates the premagnetization dependent on the control current 30. The two rivers 34a, b generated in the outer leg result in opposite rivers 34a, b in the middle leg 12 due to the antisymmetric winding direction of the outer working windings 20, 22, the amounts of which are equal, so that they cancel each other out. As a result, there is no interaction between the outer working windings 20, 22 and the control winding 24. Due to the premagnetization generated by the control winding 24 in the outer working windings 20, 22, these have a variable inductance I _var which is dependent on the control current 30.

2A and 2B show a top view and a side view of a coil arrangement with changeable inductance according to a first embodiment of the invention. The coil arrangement comprises two toroidal cores 40, 42 with the same dimensions, which are coaxial with each other are arranged so that their axes of symmetry, which are shown schematically in Fig. 2A by a Cross 44 are indicated, come to cover. The toroidal cores 40, 42 preferably have a rectangular base cross-section, as can be seen better in FIG. 2C. The ring cores exist made of a ferro- or ferrimagnetic material. Each toroidal core 40, 42 carries one Working winding 46 or 48, of which only one, 46, is visible in FIG. 2A. A tax winding 50 is wound around the two wound toroid coils 40, 46 and 42, 48. Preferably the working windings 46, 48 are single-ply on their associated toroidal cores 40, 42 wound, whereby the winding width should be used as much as possible. The same is true Control winding 50 evenly distributed around the circumference of both toroids 40, 42 to one optimal guidance of the magnetic field and homogeneous control of the cores to reach. This results in a maximum controllable inductance range. additionally become interference fields resulting from rapid changes in the control signals of the control coil 50 can be generated, suppressed to the outside.

Depending on the application, the working windings 46, 48 can be electrically parallel or in series be switched. The winding direction of the working windings 40, 42 should, however, be chosen in this way be that for the magnetic fields Bx and By, which are affected by the current Windings 46, 48 are generated in opposite magnetic field directions for both Ring cores common control coil 50 result. The magnetic field directions are in Fig. 2B for the work winding 46 with Bx, for the work winding 48 with By and for the control winding 50 labeled Bc. Through a suitable connection of the working windings 46, 48 can thus have a reaction of the magnetic fields generated by the working windings minimized or even avoided on the control winding 50. Through the common Control winding 50 is sent a control direct current that has the magnetic permeability of the ring cores 40, 42 and thereby change the inductance of the working windings 46, 48 and in particular can reduce. The working windings 46, 48 are used in practice be operated with a high-frequency alternating current.

2B, the two toroidal coils 40, 46 and 42, 48 are common Axes of rotation, but spaced apart from each other, around the winding of the To be able to display coils better. In practice, however, the two coils can also be close be arranged next to each other. While the work windings 46, 48 if possible are to be wound in one layer, evenly and tightly on the cores 40 and 42, respectively Control coil 50 winding requirements less stringent. This should, too distributed around the circumference of both coil cores 40, 42 are wound, the distribution must however not be even. It is also not important whether the winding is on or off done in several layers.

The evenly wound coil geometry is inherently self-shielding and prevents magnetic stray fields emerge from the cores 40, 42. This makes EMC relevant Stray fields prevented. Also compared to the arrangements of the prior art achieved a more uniform magnetization.

FIG. 2C only serves to explain the embodiments of FIGS. 2A and 2B, the Working windings 46, 48 and the control winding 50 are only shown schematically in order to illustrate how the toroidal cores 40, 42 and the windings 46, 48, 50 relative to each other are arranged. In practice, the working windings 46 and 48 as well as the tax winding 50, as explained above, preferably distributed around the circumference of the ring cores 40, 42 arranged.

3 schematically shows a further embodiment of the coil arrangement according to the invention in top view. In the embodiment of FIG. 3, the coil arrangement comprises one first toroidal core 52 and a second toroidal core 54, each having a working winding 56 or wear 58. The working windings 56, 58 should extend over the circumference of the toroidal cores 52 or 54 evenly distributed. However, they are preferably single-ply, uniform wrapped around the entire circumference of the toroidal cores 52, 54 as in Figs. 2A and 2B shown for the first embodiment. The two ring coils 52, 56 and 54, 58 are in one level next to each other, with a control winding 60 only over one narrow part of the circumference of the two toroidal cores 52, 54, where they touch each other, coiled is. The advantage of the arrangement of FIG. 3 consists essentially in the particularly flat Design and the large surface area, which is advantageous for cooling the coil arrangement is.

In Figures 2B and 2C, in Figure 3 and in Figures 4 and 5, the work windings are also denoted by X and Y, and the control winding is denoted by C. The ends of the working windings X and Y can be connected in parallel, as shown in Fig. 4, or in Be connected in series, as shown in Fig. 5. 4 and 5 also show the interaction between the work coils X, Y and the control coil C. By means of suitable wiring The work coils X and Y and the choice of their winding sense ensures that the magnetic fields Bx and By generated by the work coils are directed so that they are in cancel the common control coil C so as not to have any retroactive effect due to the working windings generated magnetic field to generate the control winding.

As explained above, the work windings 46, 48; 56, 58 on the ring cores 40, 42 or 52, 54 are distributed around the circumference in a single layer to the copper losses to be kept as low as possible by the high-frequency current that passes through the working winding. The wire diameter is limited to a maximum of three times the skin effect penetration depth.

In order to minimize heat loss, the winding width should also be used as fully as possible become. In other words, the changing room, i.e. the inner circumference of the ring core coils be filled as completely as possible with copper in order to achieve maximum efficiency receive. If the work windings 46, 48; 56, 58 not a sufficiently high number of turns have, it is useful to divide them into partial windings, which are connected in parallel become. 6 shows the division of a working winding 62 into four partial windings 63, 64, 65, 66, which are connected in parallel.

For a given number of turns N (e.g. N = 4), the number of required partial windings connected in parallel is determined by first determining a real number m from the inner toroidal circumference U _i and the skin effect penetration depth δ, m then being the next whole Number M is rounded up. Since the wire diameter should be limited to three times the skin effect depth of penetration, as discussed above, a factor of 3 is introduced to account for this three times the skin effect depth of penetration. Furthermore, a factor 0.9 is introduced, which takes into account the fact that the total winding width is not 100% available in a practical implementation of a wound toroid. This results in the following formula for the real number m: m = 0.9 · U i 3 · δ · N

Depending on the number of turns N of the respective working winding are therefore preferred M partial windings are provided on each toroid and in parallel as shown in Fig. 6 connected.

The corresponding wire diameter d, which should preferably be used, results from this as follows: d = 0.9 · U i N · M

Instead of a single wire or several parallel single wires can be used for the working windings twisted high-frequency strands are also used, the diameter then the individual wires must be adjusted accordingly and preferably smaller than that is simple skin effect penetration depth.

The features disclosed in the above description, the figures and the claims can be used individually as well as in any combination for the realization of the Invention in its various configurations may be of importance.

LIST OF REFERENCE NUMBERS

10

core

12

middle thigh

14, 16

outer thighs

20, 22

coil windings

24

control winding

30

control current

32

control flow

34a, b

rivers

40, 42, 46, 48

working windings

50

control winding

52, 54

toroidal

56, 58

working windings

60

control winding

62

working winding

63, 64, 65, 66

partial windings

Claims (12)

Coil arrangement with variable inductance, with two separate round ring cores (40, 42; 52, 54), each carrying working windings (46, 48; 56, 58), and a control winding (50) used to premagnetize the core material of the ring cores (40, 42; 52, 54) the two wrapped ring cores. Coil arrangement according to Claim 1, characterized in that the toroidal cores (40, 42) are arranged next to one another in such a way that their axes of symmetry (44) come to coincide. Coil arrangement according to claim 2, characterized in that the turns of the control winding (50) are evenly distributed over the circumference of both toroidal cores (40, 42). Coil arrangement according to claim 1, characterized in that the two toroidal cores (52, 54) are arranged side by side in a common plane. Coil arrangement according to one of the preceding claims, characterized in that each toroidal core (40, 42; 52, 54) is wound in one layer with the working winding (46, 48; 56, 58). Coil arrangement according to one of the preceding claims, characterized in that each working winding (46, 48; 56, 58; 62) is formed by a single insulated wire, a group of unwired insulated wires connected in parallel, or by a strand of twisted insulated single wires. Coil arrangement according to one of the preceding claims, characterized in that each working winding (46, 48; 56, 58; 62) is distributed uniformly over the circumference of the corresponding ring cores. Coil arrangement according to one of the preceding claims, characterized in that the two toroidal cores (40, 42; 52, 54) have identical dimensions and the two work coils (46, 48; 56, 58) have essentially identical numbers of turns and identical wire thicknesses. Coil arrangement according to one of the preceding claims, characterized in that the working windings (46, 48; 56, 58; 62) consist of a single wire or untwisted individual wires connected in parallel, the individual wire diameter not being greater than three times the skin effect penetration depth of the working frequency. Coil arrangement according to one of claims 1 to 8, characterized in that the working windings (46, 48; 56, 58; 62) consist of a twisted strand whose individual wire diameter is not greater than the simple skin effect penetration depth of the working frequency. Coil arrangement according to one of the preceding claims, characterized in that the working windings (46, 48; 56, 58) are connected in parallel and the winding sense of the working windings (46, 48; 56, 58; 62) is selected in such a way that when current flows in the working windings whose magnetic field directions in the control coil (50) are opposite to each other. Coil arrangement according to one of Claims 1 to 10, characterized in that the working windings (46, 48; 56, 58) are connected in series and the winding direction of the working windings (46, 48; 56, 58; 62) is selected in such a way that when current flows in the working windings, their magnetic field directions in the control coil (50) are opposite to each other.

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