Controllable inductor coil and method for restricting electric current

Abstract

The invention relates to a controllable inductor coil (100), comprising at least one inductor winding (2) and a magnetic coil core (3), which coil core has a direction of longitudinal extent (Z) matching the main magnetic flux direction, a first direction of transverse extent (X) and a second direction of transverse extent (Y), wherein the three directions of extent (X, Y, Z) are oriented with respect to one another at right angles in pairs, wherein the coil core (3) has at least three holes (4), - wherein the holes (4) run substantially along the second direction of transverse extent (Y), - wherein no more than one hole (4) runs in each plane of transverse extent of the coil core (3), which plane of transverse extent is defined by the first direction of transverse extent (X) and the second direction of transverse extent (Y), and - wherein a distance (x1) of at least one hole (4) from an outer edge of the coil core (3) in the first direction of transverse extent (X) is greater than - a distance (x2, z1) of the hole (4) from another periphery of the coil core (3), and / or - half a distance (d4) from another hole (4), wherein a control winding (5) runs through the holes (4) such that pre-magnetisation of the coil core (3) can be generated by energising the control winding (5).

Description

[0001] The present invention relates to a controllable choke coil and a method based thereon for limiting an electric current. STATE OF THE ART

[0002] Chokes are used as current limiters in the power supply of electrical or electronic devices, in power electronics, and in low- and high-frequency technology. For example, they function as actuators in the power grid, for filtering, as surge protection, in reactive power compensation devices, as energy storage devices, or for load flow control.

[0003] Choke coils comprise at least one choke winding and a coil core, usually made of a magnetic material, in particular a soft magnetic material, which is available in solid or laminated form, for example in the form of sintered ferrites or electrical steel. The inductance of choke coils is largely determined by the design of the magnetic circuit, and it is known in the prior art to vary the inductance of a choke coil by deliberately changing the length of an air gap in the coil core. Figure 1a shows a schematic cross-sectional view of such a choke coil 1a with a choke winding 2 and a magnetic coil core 3 with an air gap 30, the gap width δ of which can be varied by means of displacement of a movable coil core segment.

[0004] Figure 1bshows the corresponding characteristic curves of the choke coil as a function of the gap width δ, namely the flux linkage ψ, i.e. the total magnetic flux through the choke coil, and the inductance L as a function of the current I through the choke winding (each in arbitrary units). The ψ-I characteristic curves have a linear course up to saturation of the magnetization of the coil core, whereby the variation of the gap width δ leads to a symmetrical tilting of the characteristic curves. This corresponds to an inductance L that is constant over the entire operating range of the choke coil, which can be monotonically reduced by increasing the gap width δ. From a control engineering point of view, such controllability of the inductance of a choke coil is extremely desirable. A disadvantage of the concept presented, however, is the slow switching times of the choke coil caused by the mechanical displacement of the coil core segment, which are typically in the range of seconds.The slidably mounted coil core segment is also a wear part, particularly due to the vibrations caused by electromechanical forces that occur in typical application environments. This susceptibility to wear limits the service life of the choke coil and also creates a risk of failure.

[0005] An alternative is the so-called virtual air gap concept, which is disclosed, for example, in document EP 2 686 931 B1. Figure 2a shows a schematic cross-sectional view of a corresponding choke coil 1b and Figure 2bthe corresponding ψ-I or LI characteristics. The virtual air gap concept is based on an adjustable premagnetization of the coil core 3 by means of an energizable control winding, which extends through the two holes 4 in the coil core 3. The holes 4 run perpendicular to the main magnetic flux direction of the respective segment of the coil core 3. When the control winding is energized by a control current Is, a magnetic flux is introduced around the holes 4 in the coil core 3, which is schematically represented by the dashed or dash-dotted flux lines. The control current Is can thus be used to influence the flux linkage characteristic ψ(I, Is) and the inductance L(I, Is) of the choke coil. In contrast to the aforementioned choke coil with a mechanically variable air gap length, the variation in the inductance is also strongly dependent on the respective operating point of the choke coil, i.e., it is not possible to set a constant inductance over the entire operating range of the choke coil, which is unsatisfactory from a control engineering point of view.

[0006] It is known in the art that the ψ-I or LI characteristics of the Figure 2b by a controlled control current Is into the characteristics of the Figure 1bcan be converted, as the final project report NR 2< -RPC (funding code BMWi 0324106A, network number 01171672) reveals. For this purpose, the control current Is contains, in addition to the direct current, an alternating current component, which consists of a spectrum of harmonics related to the inductor current I. The spectrum of the alternating current component must be determined by the control in terms of amplitude and phase shift to the inductor current I and provided by the current source of the control current Is. The determination of the harmonic spectrum by the control is not trivial, and the associated current source of the control current Is has a complex structure. The method is therefore disadvantageously complex and prone to errors. DISCLOSURE OF THE INVENTION

[0007] It is the object of the present invention to propose a controllable choke coil and an associated method for limiting an electric current, which are based on a fast, fail-safe and expedient controllability of the inductance of the choke coil.

[0008] This object is achieved on the basis of a choke coil according to claim 1 and a method according to claim 14. Advantageous developments of the invention are specified in the dependent claims.

[0009] The technical teaching of the invention discloses a controllable choke coil comprising at least one choke winding and a magnetic coil core, which has a longitudinal direction corresponding to the main magnetic flux direction, a first transverse direction and a second transverse direction, wherein the three directions of extension are oriented perpendicular to each other in pairs, wherein the coil core has at least three bores, wherein the bores extend substantially along the second transverse direction of extent, wherein in each transverse plane of extent of the coil core, which is spanned by the first transverse direction of extent and the second transverse direction of extent, at most one bore extends, and wherein a distance of at least one bore to an outer edge of the coil core in the first transverse direction of extent is greater than a distance of the bore to a further edge of the coil core, wherein a control winding runs through the bores in such a way that a premagnetization of the coil core can be generated by means of a control current through the control winding.

[0010] The invention is based on the idea of ​​making a practical modification of the virtual air gap concept, which affects the number of holes for accommodating the control winding and their arrangement relative to one another or relative to the coil core. This enables the setting of more complex premagnetization patterns in the coil core, the usefulness of which for the controllability of the choke coil will be demonstrated in detail later. In particular, the inventive concept makes it possible to vary the inductance of the choke coil across its entire operating range essentially monotonically and approximately linearly using the control current, in particular using a direct current.

[0011] To illustrate the arrangement of the holes according to the invention, the Figures 3a to 3c . These show schematic views of a section of a coil core 3, through which one or two bores 4 extend. The coil core 3 has a longitudinal direction of extent Z, which corresponds to the local main magnetic flux direction, and a transverse plane of extent orthogonal to the longitudinal direction of extent Z, which is spanned by the first transverse direction of extent X and the second transverse direction of extent Y. The bores 4 extend essentially along the second transverse direction of extent Y, with at most one bore 4 extending in each transverse plane of extent. According to the invention, the distance x1 of a bore 4 to an outer edge of the coil core 3 in the first transverse direction of extent X is greater than a distance x2 or a distance z1 of the bore 4 to another edge of the coil core 3 ( Figures 3a and 3b), the following criterion is not part of the invention: the distance x1 is greater than half the distance d4 to another bore 4 ( Figure 3c ).

[0012] Of course, not any arbitrary outer edge of the coil core constitutes the reference distance (x1) for assessing the relative arrangement of the bore in question; rather, according to the invention, only the distance to one of the two nearest outer edges of the coil core in the first transverse direction is relevant. In other words, only the dimensions of that segment of the coil core in which the bore in question is located are relevant. As will be explained in more detail below, the arrangement of the bores according to the invention always aims to create a geometric constriction for the magnetic flux introduced by the control winding, and in this context, only the distances of the bore to the nearest outer edges of the coil core are relevant.The distances to the nearest outer edges determine the resulting magnetization distribution around the energized control winding bore, and the influence of the other dimensional and geometrical design of the coil core is negligible in comparison.

[0013] In the context of the present application, the magnetic main flux direction is to be understood as the local main flux direction in a respective coil core segment, such as Figure 4illustrated. This shows, by way of example, a U-shaped coil core 3, which comprises one horizontal and two vertical coil core segments, the transitions between which are represented by the dashed boundary lines. Along with the different main flow directions of the magnetic flux Φ', Φ", Φ‴ in the three coil core segments, the longitudinal extension direction Z', Z", Z‴ and the transverse extension directions X', X", X‴ and Y', Y", Y‴ are also oriented differently locally within the meaning of the present application, wherein the inventive regulations regarding the arrangement of the bores relate to the respectively locally valid coordinate system X, Y, Z of the respective coil core segment.

[0014] Furthermore, the Figures 5a to 5c schematic views of a coil core 3 with alternative bores 4, which are not arranged according to the invention, through which the control winding 5 runs, which in the case of the Figure 5aeach hole 4 passes through only once and in the case of Figures 5b and 5c runs multiple times through each bore 4. In the latter case, a higher control current is generated by the control current, or a lower control current is required to generate an identical control current. In this alternative or within the scope of the present invention, different winding concepts of the control winding can be used to expediently influence the premagnetization of the coil core.

[0015] To illustrate the basic idea of ​​the present invention, the Figures 6, 7 , 8 and 9aSimulated distributions of the magnetic flux density in soft magnetic coil cores 3 are shown as field line images, which result when the control winding is energized under different arrangements of the holes 4. The left-hand sub-image shows a schematic representation of the underlying model, i.e. the position of the holes 4 in the coil core 3, whereby the position is varied systematically in each case, on which the distributions of the magnetic flux density shown in the other sub-images are based. The simulation is based on a fixed control magnetic flux through the holes 4, whereby the choke winding of the associated choke coil is de-energized in each case. The sign of the control magnetic flux of each hole 4 is represented by a dot or cross symbol.

[0016] In Figure 6a systematic variation of the distance between the holes 4 and the outer edges of the coil core 3 in the first transverse direction of extension X, i.e., a variation of the ratio x2 / x1 is carried out. With a central arrangement of the holes 4, i.e., with x2 / x1 = 1, a symmetrical flux density distribution results, which corresponds to a corresponding distribution of the premagnetization of the coil core 3. With a sufficiently high control current, the premagnetization in the extension planes of the two holes 4 is completely driven to saturation, so that the coil core 3 is unable to absorb any further magnetic flux from energizing the choke winding and thus the inductance of the choke coil is greatly reduced. This exclusively central arrangement of the holes 4 corresponds to the virtual air gap concept according to the state of the art and results in characteristic curves which correspond to the representations of the Figure 2bcorrespond. If the bores 4 are shifted in the first transverse direction X, i.e., if the ratio x2 / x1 is reduced, an asymmetrical distribution of magnetic flux density and pre-magnetization of the coil core 3 is formed in the transverse planes XY. With these off-center arrangements of the bores 4, it is practically impossible to generate complete saturation of the pre-magnetization in the entire transverse plane of the respective bore 4 using the control current, since due to the source-free nature of the magnetic flux density, the bottleneck defined by the distance x2 limits the magnetic flux. Thus, at x2 / x1 = 0.33, the flux density introduced into the coil core is already significantly lower than, for example, at x2 / x1 = 1, and in the extreme case x2=0 (of little relevance in practice), (almost) no magnetic flux is introduced into the coil core 3 given the underlying control magnetic flux through the bores 4.

[0017] In Figure 7 The flux distributions are shown with a variation in the ratio of length Lz to width Bx of the coil core 3, i.e., with a variation in the ratio z1 / x1. In arrangements with z1 / x2 < 1, the distance z1 between the bore 4 and the outer edge of the coil core 3 represents a bottleneck that limits the magnetic flux, so that in these arrangements, practically no complete saturation of the premagnetization of the coil core 3 in the transverse plane XY of the bore 4 can be generated by means of the control current.

[0018] Figure 8 shows the distribution of the magnetic flux density in the coil core 3 when varying the distance ratio x2 / x1 of the holes 4 to the outer edges of the coil core 3 in the first transverse direction X, wherein the holes 4 are offset in opposite directions and have a control flux in the same direction. In comparison to the example of Figure 6Similar flux distributions result in the transverse planes of the bores 4, whereas the area between the bores 4 is differently premagnetized due to the differences in the orientation of the control magnetic flux.

[0019] Figure 9a shows the distributions of the magnetic flux density in the coil core 3 while varying the distance d4 in the longitudinal direction Z between the two oppositely flowing bores 4. In the area between the bores 4, there is a constructive superposition of the partial magnetic fluxes, so that the coil core 3 is first converted into a state of completely saturated premagnetization there, which again results in a limitation of the magnetic flux in the respective transverse planes XY of the bores 4, so that essentially no complete saturation of the premagnetization can be generated there by means of the control current.

[0020] Figure 9bshows the simulations of the Figure 9a corresponding characteristics of the magnetic flux Φ (in units of the saturation flux Φsat) in the coil core as a function of a magnetic voltage V generated by energizing the choke winding at a constant control magnetic flux Ξs of the control winding while varying the d4 / x1 ratio according to the representation of the Figure 9a. At d4 / x1=0, i.e., with an arrangement of the holes by means of which practically no magnetic flux can be introduced into the coil core via a control current, the characteristic curve Φ(V) corresponds to a conventional coil with a soft magnetic core. When the d4 / x1 ratio is increased, i.e., when there is a premagnetization of the coil core caused by the control magnetic flux Ξs, the characteristic curves Φ(V) exhibit characteristic plateaus, which reflect remagnetization processes of the premagnetization due to the applied magnetic voltage V. Depending on the specific arrangement of the holes, the premagnetization is of varying intensity, so that the position of the plateaus in the Φ(V) characteristic curves varies. An essential aspect of the present invention is based on this finding, namely a practical embodiment, i.e., in particular a linearization of the Φ(V) characteristics by means of a combination of holes in different arrangements for sectionally differently pronounced premagnetization of the coil core.

[0021] This is shown by Figure 10a , in which the results of a simulation of the distribution of the magnetic flux density and the resulting Φ(V) characteristic curve are shown based on a coil core 3 with three pairs of bores 4, wherein the pairs have different distances d4 in the longitudinal direction Z between the associated bores 4. In the Φ(V) characteristic curves when a control current Is is applied as a direct current, a plurality of steps corresponding to the magnetization reversal processes around the individual bores 4 are shown, and increasing the control current Is results in a tilting of the characteristic curves.

[0022] In Figure 10bThe corresponding characteristic curves of the flux linkage Ψ in the coil core and the inductance L of the choke coil are plotted against the current I through the choke winding. This shows the desired characteristic, which approximates the ideal behavior of a choke coil with a mechanically variable air gap width according to the Figures 1a and 1b corresponds, i.e., an inductance which is approximately constant over the entire operating range of the choke coil and which can be varied monotonically and approximately linearly (power function with an exponent between 1 and 2) over a wide range of values ​​by means of the control current Is. A particular advantage of the invention is that only a direct current is required as the control current Is for the aforementioned control of the inductance of the choke coil, i.e., the complex structure according to the prior art for generating an adapted alternating current as the control current can be dispensed with.

[0023] For example, the coil core of the choke coil according to the invention has at least one air gap extending in a transverse plane of the coil core, with the air gap forming a boundary of the coil core. The provision of air gaps serves to "statically" influence the inductance of the choke coil.

[0024] As already exemplified by the Figure 10aAs shown, the coil core has, for example, a plurality of pairs of bores, wherein the pairs have different distances between the associated bores. Furthermore, the bores can, for example, have different distances from an outer edge of the coil core in the first transverse direction. This creates differently dimensioned constrictions for the magnetic flux in the transverse planes of the bores, resulting in the desired quasi-linearization of the characteristics of the magnetic flux as a function of the magnetic voltage.

[0025] For example, at least one of the holes can be designed as an elongated hole. An elongated hole can accommodate a larger number of turns of the control winding, allowing for a higher control current flow.

[0026] In a specific embodiment, the coil core has a plurality of cuboid-shaped coil core segments which are separated from one another by air gaps, wherein each coil core segment has a bore and wherein the coil core segments have different dimensions in the longitudinal direction relative to the dimension in the first transverse direction.

[0027] In a further embodiment, the choke coil according to the invention is designed to be multi-phase, wherein the choke coil comprises a plurality of choke windings and a plurality of associated coil core legs, wherein the choke windings are each provided for one phase of a multi-phase alternating current.

[0028] For example, the choke coil according to the invention comprises a direct current source and an associated control, by means of which the control current can be introduced into the control winding to generate a desired premagnetization in the coil core.

[0029] The invention further relates to a method for limiting an electric current by means of a controllable choke coil according to the invention, wherein the current to be limited is introduced into the choke winding and wherein a control current is introduced into the control winding, which generates a bias in the coil core of the choke coil that is suitable for the desired current limitation.

[0030] The control current is generated, for example, by a direct current source.

[0031] In one embodiment of the method, the current to be limited is embodied as a pulsed direct current, which, after passing through the choke winding, passes through the control winding, thereby forming the control current. The pulsed direct current has a direct current and an alternating current component, with the alternating current component preferably being significantly smaller than the direct current component, for example, being one-third of the direct current component. In this embodiment, the inductance of the choke coil is therefore determined by the current to be limited.

[0032] If the current to be limited is a mixed current, the direct current component and the alternating current component of the mixed current can be separated from one another within the scope of the method according to the invention, with the control current being formed by the direct current component. The separation into direct current and alternating current components can be carried out, for example, by means of a choke winding which comprises two parallel windings, one of which is formed from a stranded wire bundle and the other from a low-resistance solid wire or another solid conductor, e.g. with a rectangular profile, so that the alternating current component runs through the stranded wire bundle and the direct current component through the solid conductor, with the direct current component then passing through the control winding as the control current.

[0033] Within the scope of the method according to the invention, the control current can also be formed from a combination of a component supplied by a direct current source and a component from the current to be limited. For this purpose, two separate control windings can be provided, for example. PREFERRED EMBODIMENTS OF THE INVENTION

[0034] Further measures improving the invention are presented in more detail below with the description of preferred embodiments of the invention with reference to figures.

[0035] Figure 11 to Figure 20 show inventive choke coils 100 in a schematic cross-sectional view. For the sake of clarity, the control windings are not shown in most figures. According to the previous description, the control windings each run through the holes in the coil core. The arrangement of the holes corresponds to the technical teaching of claim 1.

[0036] Figure 11 shows a choke coil 100 with a coil core 3, which comprises two U-shaped coil core segments 3U, which are separated from one another by an air gap 30, wherein the bores 4 are introduced into both coil core segments 3U. Alternatively, bores could be introduced into only one of the coil core segments 3U. The bores 4 form pairs, wherein the pairs have different distances between the associated bores 4. The choke winding 2 rotates around the coil core 3 in sections, wherein the choke winding 2 comprises, for example, two winding sections, which can be connected either in parallel or in series.

[0037] Figure 12shows a choke coil 100 whose coil core 3 comprises two E-shaped coil core segments 3E, which are separated from each other by an air gap 30, with the bores 4 being introduced into both coil core segments 3E. Alternatively, bores could be introduced into only one of the coil core segments 3E. One of the bores 4 is designed as an elongated hole, which allows for a higher control current flow. Alternatively, the coil core can also be designed as a shell core with only one air gap in the middle or air gaps only in the outer legs.

[0038] Figure 13shows a choke coil 100, the coil core 3 of which comprises four I-shaped coil core segments 3I, which are separated from one another in a rectangular arrangement by air gaps 30, wherein the bores 4 are introduced here, for example, into two of the coil core segments 3I. The bores 4 are grouped in pairs, wherein the pairs have different distances between the bores 4 and wherein the bores 4 have different distances from an outer edge of the coil core 3 in the first transverse direction of extent.

[0039] Figure 14 and Figure 15 show choke coils 1, whose coil cores 3 each comprise an I-shaped coil core segment 3I and two U-shaped coil core segments 3U, which are separated from one another by air gaps 30, wherein the bores 4 are introduced, for example, into the I-shaped coil core segment 3I. Alternatively, the outer coil core segments can also be designed as half toroidal cores.

[0040] Figure 16 and Figure 17 show choke coils 1, whose coil cores 3 are ring-shaped, with the bores 4 in the axial direction ( Figure 16 ) or in the radial direction ( Figure 17 ) through the coil core 3. The main flow direction of the magnetic flux Φ corresponding to the longitudinal direction Z of the coil core 3 is circular here and the first transverse direction X', X" ( Figure 16 ) or the second transverse extension direction Y', Y" ( Figure 17 ) are radially oriented, i.e. different for each hole 4.

[0041] Figure 18shows a current limiter 100 according to the invention for a two-phase current with a choke coil 100, which comprises two choke windings 2.1, 2.2 and two associated coil core legs 3.1, 3.2, wherein the choke windings 2.1, 2.2 are each provided for one phase of the two-phase current. The coil core legs 3.1, 3.2 each have three cuboid coil core segments 3a, 3b, 3c, which are separated from one another by air gaps 30, wherein each of the coil core segments 3a, 3b, 3c has a bore 4, and wherein the coil core segments 3a, 3b, 3c have different dimensions in the longitudinal direction relative to the dimension in the first transverse direction. Alternatively, the choke coil 100 can also be operated in single-phase mode, for which purpose the two choke windings 2.1, 2.2 must be connected in series or parallel.

[0042] Figure 19shows a further two-phase choke coil 100 with a coil core 3, which comprises an annular coil core segment 3R and an I-shaped coil core segment 3I arranged therein, wherein the bores 4 are, for example, only introduced into the I-shaped coil core segment 3I. The choke windings 2.1, 2.2 for the two current phases are arranged in sections around the annular coil core segment 3R.

[0043] Figure 20shows a choke coil 100 for a three-phase alternating current. The three choke windings 2.1, 2.2, 2.3 are each provided for one phase IL1, IL2, IL3 of the three-phase alternating current, and the associated coil core legs 3.1, 3.2, 3.3 each comprise four cuboid coil core segments 3a, 3b, 3c, 3d, through each of which a bore 4 extends. The control current Is is conducted through all bores 4 by means of the control winding 5, with successive bores 4 being flowed through in opposite directions, and the coil core segments 3I, which function as a yoke, guide the control winding 5 between the coil core legs 3.1, 3.2, 3.3. List of characters:

[0044] Fig. 1a: schematic cross-sectional view of a first choke coil according to the prior art, Fig. 1b: simulated characteristics of Fig. 1a , Fig. 2a: schematic cross-sectional view of a second choke coil according to the prior art, Fig. 2b: simulated characteristics of Fig. 2a, Fig. 3a - 3c: schematic representations of the inventive arrangement of the bores, Fig. 4: schematic representation of the inventive directional designation, Fig. 5a - 5c: schematic representations of the inventive control windings, Fig. 6: simulated flux density distributions in a coil core with variation of the bore arrangement, Fig. 7: simulated flux density distributions in a coil core with variation of the coil core geometry, Fig. 8: simulated flux density distributions in a coil core with variation of the bore arrangement, Fig. 9a: simulated flux density distributions in a coil core with variation of the bore arrangement, Fig. 9b: characteristic curves for Fig. 9a , Fig. 10a: simulated flux density distributions in a coil core with variation of the bore arrangement and associated characteristic curves, Fig. 10b: characteristic curves for Fig. 10a, Fig. 11: first embodiment of a choke coil according to the invention, Fig. 12: second embodiment of a choke coil according to the invention, Fig. 13: third embodiment of a choke coil according to the invention, Fig. 14: fourth embodiment of a choke coil according to the invention, Fig. 15: fifth embodiment of a choke coil according to the invention, Fig. 16: sixth embodiment of a choke coil according to the invention, Fig. 17: seventh embodiment of a choke coil according to the invention, Fig. 18: eighth embodiment of a choke coil according to the invention, Fig. 19: ninth embodiment of a choke coil according to the invention, and Fig. 20: tenth embodiment of a choke coil according to the invention. List of reference symbols:

[0045] 100 Choke coil 1a, 1b Choke coil according to the state of the art 2 Choke winding 2.1, 2.2, 2.3 Choke winding for three-phase current 3 Coil core 3a, 3b, 3c Coil core segment 3 UU-shaped coil core segment 3 EE-shaped coil core segment 3 II-shaped coil core segment 3 R Ring-shaped coil core segment 3.1, 3.2, 3.3 Coil core leg 30 Air gap 4 Bore 5 Control winding XFirst transverse direction YSecond transverse direction ZLongitudinal direction x1, x2, z1Distance to edge d4Distance between holes BxDimension of first transverse direction LzDimension of longitudinal direction δGap width ICurrent to be limited IsControl current ΞsControl magnetic flux ΦMagnetic flux ΨFlux linkage VMagnetic voltage LInductance

Claims

1. Controllable choke coil (100), comprising at least one choke winding (2) and a magnetic coil core (3) which has a longitudinal extension direction (Z) corresponding to the main magnetic flux direction, a first transverse extension direction (X) and a second transverse extension direction (Y), the three extension directions (X, Y, Z) being orientated in pairs perpendicular to one another, the coil core (3) having at least three boreholes (4), - wherein the boreholes (4) extend substantially along the second transverse direction of extension (Y), - wherein at most one borehole (4) extends in each transverse extension plane of the coil core (3), which is spanned by the first transverse extension direction (X) and the second transverse extension direction (Y), and - wherein a distance (x1) of at least one borehole (4) from an outer edge of the coil core (3) in the first transverse extension direction (X) is greater than a distance (x2, z1) of the borehole (4) from a further outer edge of the coil core (3), wherein a control winding (5) passes through the boreholes (4) in such a way that a pre-magnetisation of the coil core (3) can be generated by a control current (Is) through the control winding (5).

2. Choke coil (100) according to claim 1, characterised in that the coil core (3) has at least one air gap (30) which extends in a transverse extension plane of the coil core (3), wherein an outer edge of the coil core (3) is formed by the air gap (30).

3. Choke coil (100) according to claim 1 or 2, characterised in that the coil core (3) has a plurality of pairs of boreholes (4), the pairs having different distances (d4) between the associated boreholes (4).

4. Choke coil (100) according to one of the preceding claims, characterised in that the boreholes (4) have different distances (x1) from an outer edge of the coil core (3) in the first transverse extension direction (X).

5. Choke coil (100) according to one of the preceding claims, characterised in that at least one of the boreholes (4) is formed as an elongated borehole.

6. Choke coil (100) according to one of the preceding claims, characterised in that the coil core (3) has a plurality of cuboidal coil core segments (3a, 3b, 3c, 3d) which are separated from one another by air gaps (30), each coil core segment (3a, 3b, 3c, 3d) has a borehole (4), and wherein the coil core segments (3a, 3b, 3c, 3d) have different dimensions (Lz) in the longitudinal direction of extension (Z) relative to the dimension (Bx) in the first transverse direction of extension (X).

7. Choke coil (100) according to any one of claims 1 to 5, characterised in that the coil core (3) comprises two U-shaped coil core segments (3U) which are separated from one another by an air gap (30), the boreholes (4) being formed in one of the coil core segments (3U) or in both coil core segments (3U).

8. Choke coil (100) according to one of claims 1 to 5, characterised in that the coil core (3) comprises two E-shaped coil core segments (3E) which are separated from one another by an air gap (30), the boreholes (4) being formed in one of the coil core segments (3E) or in both coil core segments (3E).

9. Choke coil (100) according to one of claims 1 to 5, characterised in that the coil core (3) comprises four I-shaped coil core segments (3I) which are separated from one another in a rectangular arrangement by air gaps (30), the boreholes (4) being formed in one of the coil core segments (3I) or in a plurality of coil core segments (3I).

10. Choke coil (100) according to one of claims 1 to 5, characterised in that the coil core (3) comprises an I-shaped coil core segment (3I) and one or two U-shaped coil core segments (3U), which are separated from one another by air gaps (30), the boreholes (4) being formed in one of the coil core segments (3I, 3U) or in a plurality of coil core segments (3I, 3U).

11. Choke coil (100) according to one of claims 1 to 5, characterised in that the coil core (3) is annular in shape, the boreholes (4) extending through the coil core (3) in the radial or axial direction, or in that the coil core (3) comprises at least one annular coil core segment (3R).

12. Choke coil (100) according to one of claims 1 to 6, characterised in that the choke coil (100) is of multiphase design, wherein the choke coil (100) comprises a plurality of choke windings (2.1, 2.2, 2.3) and a plurality of corresponding coil core legs (3.1, 3.2, 3.3), wherein the choke windings (2.1, 2.2, 2.3) are each provided for one phase of a multiphase alternating current.

13. Choke coil (100) according to one of the preceding claims, characterised in that the choke coil (100) comprises a direct current source and a related controller, by means of which the control current (Is) can be introduced into the control winding (5) to generate a desired pre-magnetisation in the coil core (3).

14. Method for limiting an electric current by means of a controllable choke coil (100) according to one of the above-mentioned claims, wherein the current (I) to be limited is introduced into the choke winding (2), and wherein a control current (Is) is introduced into the control winding (5), which generates a pre-magnetisation in the coil core (3) of the choke coil (100) which is suitable for the desired current limitation.

15. Method according to claim 14, characterised in that the control current (Is) is generated by a direct current source.

16. Method according to claim 14, characterised in that the current (I) to be limited is a pulsed direct current which, after passing through the choke winding (2), passes through the control winding (5), whereby the control current (Is) is formed.

17. Method according to claim 14, characterised in that the current (I) to be limited is a mixed current, the direct current component and the alternating current component of the mixed current being separated from one another, and the control current (Is) being formed by the direct current component.

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