EP2998971B1

EP2998971B1 - Power converter comprising and inductance device with shielding

Info

Publication number: EP2998971B1
Application number: EP14185731.8A
Authority: EP
Inventors: Marek Rylko; Milosz HANDZEL; Marcin Kacki; Mariusz Walczak; Jerzy Maslon
Original assignee: SMA Solar Technology AG
Current assignee: SMA Solar Technology AG
Priority date: 2014-09-22
Filing date: 2014-09-22
Publication date: 2019-07-24
Anticipated expiration: 2034-09-22
Also published as: PL2998971T3; EP2998971A1

Description

FIELD OF THE INVENTION

The present invention relates to an inductance device comprising at least two windings wound on a common core and means for shielding a magnetic stray field. The invention further relates to a filter device and a power converter comprising an inductance device, in particular a coupled differential mode choke, with at least two windings wound on a common core and means for shielding a magnetic stray field.

BACKGROUND OF THE INVENTION

In a power converter, for example an inverter for photovoltaic applications, an output filter is used to reduce unwanted ripples in the output current to be fed into an electrical supply grid. Such output filter usually comprises an inductance device that may be configured as a coupled choke for differential currents. A coupled choke comprises at least two windings wound on a common core and may be arranged at the input and/or the output of the power converter such that a first winding of the coupled choke is connected to a forward current path and a second winding is connected to a return current path, wherein the forward and the return current path are configured to transfer electric power input from a generator into the power converter or output by the power converter into an electrical supply grid.
A magnetic flux is induced into the common core by a current input to or output by the converter and running through the windings. Depending on the winding directions of the windings and the current flow directions within the windings, the magnetic flux induced by one winding may add either positively or destructively to the magnetic flux induced by another winding. In particular, the coupled choke acts as a differential mode choke having a significant inductance value for differential mode currents if said magnetic fluxes add constructively for a differential current, i.e. for normal currents running in anti-parallel direction through the input or output lines of the converter and transferring the electrical power input to or output by the converter. On the other hand, the coupled choke acts as a common mode choke having a significant inductance value for common mode currents, if said magnetic fluxes add constructively for common mode currents, i.e. for currents running in parallel through the input or output lines of the converter.
In a known configuration of a coupled differential mode choke comprising a core of rectangular cross section, two windings with identical number of turns and identical winding directions relative to the perimeter of the core are placed on opposite legs of the core. If the windings in such configuration carry differential mode currents of the same magnitude, e.g. sinusoidal currents with π phase shift, the induced magnetic flux produced by the first winding adds to the magnetic flux produced by the second winding constructively. However, if the windings in such configuration carry common mode currents, the induced magnetic flux produced by the first winding is compensated by the opposite magnetic flux produced by the second winding. The latter situation, in principle, is the same effect facilitated in a transformer wherein a current running through a primary winding induces a current running through a secondary winding such that the magnetic flux induced within the core by the current running through the primary winding is compensated by the magnetic flux induced within the core by the current running through the secondary winding
An inductance device such as a coupled differential mode choke may generate unwanted magnetic stray fields in its periphery, in particular when being subjected to common mode currents, and vice versa. Such stray fields may jeopardize the correct operation of electronic components located close to the inductance device and have to be limited according to electromagnetic interference (EMI) standards. Hence it is long known that electromagnetic components in general may be shielded in order to minimize electromagnetic interference with other components. A large variety of shielding setups to be applied to chokes or transformers are described in the prior art, some of which are mentioned in the following documents.
A very basic shielding setup was disclosed as early as 1944 in CH230974 , where an inductance device is enclosed by a shielding cage, said shielding cage comprising electrically connected closed-loop windings which are oriented in parallel to the magnetic stray field lines of the inductance coil. This setup may be considered as a Faraday cage in a very basic version.
US3290634 discloses a transformer comprising a single band made of conductive material surrounding a main core, yokes of the main core and a primary and a secondary coil, for reducing the magnitude of magnetic stray fields generated by the transformer. Such magnetic stray fields around the transformer are fields with a high energy density that mainly arise from the power transfer mode during transformer operation. Hence the single band experiences high amplitude currents and has to be dimensioned accordingly in terms of material thickness and insulation means. Furthermore, in order to close an electric path around the transformer, the end lines of the band have to be connected to each other appropriately.
GB2501104 discloses a power supply system comprising an AC to DC power converter comprising a common mode inductor with two windings wound around a core having a round or rectangular shape. WO2008097758A1 discloses an audio amplifier comprising an output filter with a magnetic core comprising a central leg having a gap and two coils wound around the outer legs of the core.
In view of the state of the art, there is still a need for a power converter comprising an inductance device that comprises a sufficient shielding of magnetic fields generated by currents flowing through coupled windings of the inductance device such that electromagnetic compatibility of the inductance device is ensured, whereby the inductance device needs to be easily manufacturable, reliably insulated and cost effective.

SUMMARY OF THE INVENTION

The invention provides a power converter comprising the features of independent claim 1. Preferred embodiments of the invention are defined in the dependent claims.
A power converter comprising input connections, output connections and an inductance device is configured to convert a direct current supplied at the input connections into an alternating current to be output via the output connections or vice versa. The inductance device of the power converter comprises a core with a first leg, a second leg oriented parallel to the first leg, a third leg and a fourth leg, wherein the legs are in a rectangular arrangement. The inductance device further comprises a first winding wound around the first leg and a second winding wound around the second leg. The first winding and the second winding each comprise a first end and a second end, wherein the respective first ends are connected electrically in series to the respective input connections or to the respective output connections of the power converter such that magnetic fluxes generated inside the core by a differential mode current flowing through the first winding and the second winding add constructively and a coupled differential mode choke is obtained. An inductance device of a power converter according to the present invention further comprises a third winding comprising a short-circuited wire and being wound around an outer perimeter of the inductance device as defined by the outer surfaces of the first winding and the second winding, wherein a winding axis of the third winding is oriented parallel to the first leg and the second leg of the core.
The third winding does not have any significant effect on the electrical or magnetical properties of the inductance device if the first winding and the second winding are subjected to a current that generates magnetic fields that sum up constructively within the core. On the other hand, if the first winding and the second winding are subjected to a current that generates magnetic fields that compensate each other within the core, magnetic stray fields are generated outside the core which induce a current in the third winding. Since the third winding is short-circuited, the current flowing through the third winding generates a magnetic field outside the core that is oriented in an opposite direction with regard to the magnetic stray field generated by the current in the first winding and the second winding and thus compensates the magnetic stray field. Hence, the resulting emission of magnetic stray fields by the inductance device is significantly reduced by the third winding which may be implemented easily at a very low design effort and low costs.
In other words, the third winding comprises a short-circuited wire and is wound around the first leg and the second leg of the core onto the first winding and the second winding, such that the third winding is oriented perpendicular to the first leg and the second leg of the core. In such configuration, the inductance device comprises a symmetry axis such that the first leg and the second leg are arranged axially symmetrical with respect to the symmetry axis and the winding axis of the third winding coincides or overlaps with the symmetry axis. The third winding does virtually not increase the size of the inductance device and thus allows for compact design and cost reduction of the inductance device as compared to conventional shielding methods.
The first winding and the second winding of the inductance device each comprise a first end and a second end, wherein the respective first ends are connected electrically in series to respective input connections or to respective output connections of the power converter such that magnetic fluxes generated inside the core by a differential mode current flowing through the first winding and the second winding add constructively. For example, the ends of the windings may be marked by appropriate markings, geometrically encoded by comprising standardized connection plugs, or geometrically arranged unambiguously, such that each end of the windings may only be connected to a respective connection of a device the inductance device is used in, e.g. a filter device or a power converter. Thereby a power converter comprising a coupled differential mode choke is obtained, wherein the third winding of the coupled differential mode choke provides an effect in terms of a magnetic shielding for common currents only and does not have any substantial effect on the electrical or magnetical properties relevant to the regular operation of the coupled differential mode choke for differential current.
In an embodiment of the power converter, individual turns of the third winding of the inductance device are located directly adjacent to each other such that the third winding covers the outer surfaces of the first winding and the second winding. By fully covering the outer surfaces with respect to the symmetry axis of the inductance device, a third winding with a maximum number of turns of the third winding is provided and an optimum shielding effect is obtained.
In an alternative embodiment of the power converter, the third winding of the inductance device comprises at least three turns equally spaced to each other, wherein the spacing between the turns of the third winding is greater or equal to a wire diameter of the third winding. While a third winding comprising a single turn only already provides a shielding effect to a certain degree, a third winding with at least three turns provides a symmetrical coverage of the perimeter of the inductance device and a significantly enhanced shielding of the magnetic stray field.
The inductance device in the power converter may comprises a casting compound covering the core, the first winding, the second winding, and the third winding, wherein the third winding comprises an insulation. The quality of the casting compound, especially the avoidance of any voids within the casting compound, is ensured by tightly wrapping the turns of the third winding such that spaces between the individual turn are provided where the casting compound may freely flow into during the casting process.
In a further embodiment of the power converter, the inductance device comprises a fifth leg oriented parallel to the first leg and the second leg such that the core is arranged in an El-type configuration, wherein a fourth winding is wound around the fifth leg such that magnetic fluxes generated by a three-phase differential mode current flowing through the first winding, the second winding and the fourth winding add constructively. The first winding, the second winding, and the fourth winding may be connected to a three-phase network, e.g. to the three phase lines of a three phase power supply grid.
The inductance device may be part of a filter device which is configured as a differential mode filter that comprises an inductance value effective to smooth a differential mode current. If the filter device according to the invention is subjected to a common mode current, it generates a significantly reduced magnetic stray field as compared to a conventional differential mode filter without shielding being subjected to a common mode current. At the same time, the filter device according to the invention is much smaller and easier to manufacture, i.e. cheaper, than a differential mode choke comprising a shielding means as known from the prior art.
Besides the inductance device as outlined above, the power converter comprises a variety of electronic components such as drivers, controllers, or communication means. In a conventional power converter, these electronic components would either have to be arranged at a distance to an inductance device generating magnetic stray fields, such as a differential mode choke in an input or output filter, such that the magnetic stray field does not harm the performance of the electronic devices, or the inductance device would have to be shielded in order to prevent the magnetic stray field to extent to the electronic devices in its vicinity. Using the inductance device according to the invention within the power converter, the spatial separation of electronic devices from the inductance device may be reduced, which enables a compact design of the power converter. At the same time, the power converter may be build much easier and cheaper due to the more compact design and due to the inductance device itself being shielded appropriately such that the power converter does without bulky shielding means around the inductance devices comprised in it.
In an embodiment of the invention, the power converter comprises a three-phase inductance device comprising a fifth leg and a fourth winding as described above and a three-phase inverter configured to output a three-phase current. The first winding, the second winding, and the fourth winding of the inductance device are connected to respective output connections of the power converter such that magnetic fluxes generated by a differential mode current flowing through the first winding, the second winding and the fourth winding add constructively. Using an inductance device according to the invention in such three-phase power converter enables an even further reduction of the size of the power converter as compared to a power converter comprising a conventional three-phase inductance device such as an output filter.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. In the drawings, like reference numerals designate corresponding parts throughout the several views.

Fig. 1: illustrates an power converter according to the prior art,
Figs. 2a and 2b: show an inductance device as known from the prior art being subjected to differential mode currents and common mode currents, respectively,
Fig. 3a: shows an inductance device of a power converter according to the present invention being subjected to differential mode currents,
Fig.3b: shows an inductance device being subjected to common mode currents,
Fig. 4: shows an embodiment of an inductance device of a power converter according to the present invention in an isometric view, and
Fig. 5: shows a further embodiment of an inductance device of a power converter according to the present invention in a top view.

DETAILED DESCRIPTION OF THE DRAWINGS

The power converter 10 depicted in Fig. 1 comprises input connections 11 and output connections 12 and is configured to convert a direct current supplied at the input connections 11 into an alternating current to be output via the output connections 12 or vice versa. The direct current may be supplied by a direct current source being connected to the input connections 11. The alternating current may be fed into a power supply grid being connected to the output connections 12. For that exemplary purpose, the power converter 10 further comprises a DC-DC converter 13 and an inverter 14. Furthermore, the power converter 10 comprises buffer capacitors 15 for stabilizing an input voltage and an intermediate voltage, respectively, a common mode choke 16 arranged at the input side of the power converter 10, an output filter 17 comprising a filter capacitor 18 and a coupled differential mode choke 19, and another common mode choke 16 arranged at an output side of the power converter 10. If the power converter 10 is connected to a power supply grid, the output filter 17 is configured to filter the output current of the power converter 10 such that harmonics and common mode currents contained in the alternating current generated by the inverter 14 are reduced to meet predefined grid requirements.
Each of the common mode chokes 16 and the differential mode choke 19 may comprise two windings placed on the same magnetic path, i.e. sharing the same core. For example, the differential mode choke 19 may comprise one winding that may be connected to a forward output current path of the power converter 10 and the other winding may be electrically in series with a return current path. Such configuration provides current path symmetry with regard to magnetic coupling of the windings of the coupled differential mode choke 19.
In a configuration known from the prior art, the common mode chokes 16 as well as the coupled differential mode choke 19 may comprise an inductance device 20 according to the Figs. 2a and 2b . The inductance device 20 comprises a core 21 comprising a magnetic material. The core 21 comprises four legs 21a, 21b, 21c, 21d in a rectangular arrangement. A first winding 22a comprising a first end 23a and a second end 24a is wound around the first leg 21a. A second winding 22b comprising a first end 23b and a second end 24b is wound around and the second leg 21b.
The first end 23a of the first winding 22a and the first end 23b of the second winding 22b are configured to be connected to the input connections 11 or to an output of the inverter 14 of the power converter 10. The second end 24a of the first winding 22a and the second end 24b of the second winding 22b are configured to be connected to the output connections 12, to an input of the DC-DC converter 13, or to an input of the inverter 14 of the power converter 10. Since the inductance device 20 is setup symmetrically with respect to the electrical properties of the first winding 22a and the second winding 22b, it is apparent that the assignment of the first ends and the second ends to the input side and the output side of the power converter 10 may be exchanged as long as such exchange is done pairwise.
The inductance device 20 may be subjected to a differential mode current I_DM according to Fig. 2a, e.g. a current I_DM flowing through the first winding 22a from its first end 23a to its second end 24a and, at the same time and with substantially the same amplitude, flowing through the second winding 22b from its second end 23b to its first end 23a. The winding directions of the windings 22a and 22b are configured such that said differential mode current I_DM flowing through the windings 22a and 22b generates magnetic fields in the core 21 that are oriented in the same direction as seen along the perimeter of the core 21 and said magnetic fields add to each other constructively. This constructive addition is depicted in Fig. 2a by arrows 25 representing a magnetic flux being substantially confined within the legs 21a-d of the core 21. In other words, the differential mode current I_DM produces cumulative magnetic flux that is closed in the magnetic core 21 while negligible stray fields are produced outside the inductance device 20.
The inductance device 20 may alternatively or additionally be subjected to a common mode current according to Fig. 2b, e.g. a current I_CM flowing through the first winding 22a from its first end 23a to its second end 24a and, at the same time and with substantially the same amplitude, flowing through the second winding 22b from its first end 23a to its second end 23b. If the inductance device is connected at the output of the inverter 14 according to Fig. 1, such common mode current may be generated in operation of the power converter 10 as a side effect of periodic switching of power switches of the inverter 14. The common mode current I_CM flowing through the windings 22a and 22b generates magnetic fields in the first leg 21a and in the second leg 21b of the core 21, respectively, that are oriented in the opposite direction as seen along the perimeter of the core 21 such that said magnetic fields add to each other destructively. These magnetic fields are depicted in Fig. 2b by arrows 26a representing the magnetic flux within the legs 21a and 21b, respectively, of the core 21. Note that there is substantially no magnetic flux within the legs 21c and 21d of the core 21. Furthermore, since the magnetic flux lines 26a have to be closed due to fundamental laws of electromagnetism, a substantial magnetic stray field represented by the magnetic flux lines 26b is generated outside the core 21. For the sake of comparison, the magnetical behaviour of the inductance device 20 when being subjected to common mode currents is an equivalent to a rod inductor as the surface integral of the current density within the winding cross section is 0. By default, a rod inductor produces substantial stray field in its vicinity.
This magnetic stray field is relevant for EMI considerations and potentially hazardous to the correct operation of electronic devices located in the periphery of the inductance device. Hence there is a need to reduce the magnetic stray field outside the inductance device as far as possible.
Fig. 3a shows an inductance device 30 according to an embodiment of the present invention. Fig.3b shows another inductance device 30. The inductance device 30 comprises a core 21 comprising four legs 21a, 21b, 21c, 21d in a rectangular arrangement. A first winding 22a comprising a first end 23a and a second end 24a is wound around the first leg 21a, and a second winding 22b comprising a first end 23b and a second end 24b is wound around and the second leg 21b. A third winding 31 is wound around an outer perimeter of the inductance device 30 such that the third winding 31 is wound around respective outer surfaces of the first winding 22a and the second winding 22b. The winding axis of the third winding 31 is oriented parallel to the first leg 21a and the second leg 21b. Hence, the winding axis of the third winding 31 is oriented parallel to the winding axes of the first winding 22a and the second winding 22b, too.
The third winding is short-circuited by connecting the short-circuiting connection points SC to each other; this connection is omitted in Figs. 3a and 3b for the sake of clarity but rather implied by denoting the short-circuiting connection points SC with the same reference sign SC.
Fig. 3a shows the inductance device 30 being subjected to a differential mode current I_DM flowing through the first winding 22a and the second winding 22b. In comparison to the inductance device 20 according to Fig. 2a, magnetic fields of similar strength and orientation are generated in the core 21 by both windings. Hence, the third winding 31 has substantially no effect on the operation of the inductance device 30. In particular, the inductivity of the inductance device 30 for differential mode currents is the same as the inductivity of the inductance device 20 without the third winding 31.
In contrast, Fig. 3b illustrates the effect of the third winding 31 on the magnetic fields generated in the periphery of inductance device 30 being subjected to a common mode current I_CM flowing through the first winding 22a and the second winding 22b. The magnetic field generated by the common mode current I_CM, in particular the magnetic field inside the legs 21a and 21b of the core 21 represented by the magnetic flux lines 32a, induces a current I_S in the short-circuited third winding 31. This current I_S in turn generates a magnetic field represented by the magnetic flux lines 33 substantially extending outside the inductance device 30. Such interaction of the common mode currents I_CM in the first winding 22a and in the second winding 22b with induced currents I_S in the third winding 31 is similar to transformer operation.
A major part of the magnetic field 33 generated by the current I_S is located outside the inductance device 30. This part of the magnetic field 33 is oriented in an opposite direction as compared to the magnetic stray field represented by the magnetic flux lines 32a and 32b. The resulting total magnetic field strength of the magnetic field located outside the inductance device 30 is the sum of the magnetic stray field generated by the common mode current I_CM and the magnetic field generated by the current I_S within the short-circuited third winding 31. As a result of this summation, the total magnetic field strength in the periphery of the inductance device 30 is significantly reduced as compared to the magnetic field strength of the magnetic stray field as represented by magnetic flux lines 26b generated by the common mode current I_CM outside the inductance device 20 according to Fig. 2b.
For an ideal implementation of the inductance device 30, the current density induced in the third winding 31 should be equal to the current density of the common mode current I_CM in the first winding 22a and in the second winding 22b, but in opposite direction, such that the stray field of the inductance device 20 according to Fig. 2b and the counteracting magnetic field generated by the current I_S induced in the third winding 31 completely eliminate each other. In a practical setup an identity of the magnetic stray field and the magnetic field generated by the third winding 31 is hardly achievable and the inductance device 30 will still generate a residual stray field, but the strength of the residual stray field is significantly reduced to a value that will not impede operation of other components in the vicinity of the inductance device 30.
In order to further decrease high frequency radiated field emission, the short-circuiting connection point SC may additionally be connected to one of the ends 23a, 23b, 24a, 24b of the first winding 22a or the second winding 22b. Additionally, a magnetic material, e.g. a sheet or foil, may be arranged between the perimeter of the inductance device 30 and the third winding 31, i.e. between the outer surfaces of the first winding 22a and the second winding 22b and the inner surface of the third winding 31. Such additional material may increase the common mode inductance value of the inductance device 30 while the differential mode inductance value of the inductance device 30 is unaffected.
Figs. 4 and 5 show another embodiment of an inductance device according to the present invention. In addition to the illustrative examples shown in Figs. 3a and 3b, it can be seen from Figs. 4 and 5 that the third winding 31 comprises a wire being wrapped around the first winding 22a and the second wining 22b. The third winding 31 is short-circuited by connecting the ends of the wire at the short-circuiting connection point SC. An electrically conductive joining of the two ends of the wire of the third winding 31 is much easier than, e.g. for a copper foil as known from the prior art.
While for an optimum shielding effect it is preferred to select the diameter of the wire and the number of turns of the third winding 31 such that the third winding 31 completely covers the outer surfaces of the first winding 22a and the second winding 22b, such optimum shielding and hence such complete coverage may not be necessary in each case. In contrast, the advantage of reduced effort, material and costs achievable by wrapping the third winding 31 such that the individual turns are separated by a significant distance may outweigh the disadvantage of a reduced shielding effect.
Moreover, the inductance device 30 may be completely encapsulated in a casting compound, e.g. an electrically insulating material. While the first winding 22a and the second winding 22b may be already enclosed in a proper casting, it may be beneficial to leave a significant space between the individual turns of the third winding 31 in order to enable the potting material to flow freely and cover the inductance device 30 completely, i.e. without leaving voids which may occur between the third winding 31 and the first winding 22a and/or the second winding 22b, respectively, if the third winding 31 completely covers outer surfaces of the first winding 22a and the second winding 22b. The problem of voids within the casting is especially eminent when using a third winding 31 made of a single foil since a foil reduces the free flow of the potting material significantly and may cause a problem with the potting adhesion while a third winding 31 made of a wire does not constitute a significant barrier for the potting material.
The wire constituting the third winding 31 may be insulated by a non-conductive coating. The diameter of the wire and the number of turns of the third winding 31 may be selected, as a rule of thumb, such that the distance between adjacent turns of the third winding 31 at least equals the diameter of the wire such that the relevant perimeter of the inductance device 30 is covered by the third winding 31 by 50 percent at most.
Simulations and laboratory tests were conducted with an inductance device 30 according to the model depicted in Figs. 4 and 5 being subjected to common mode currents I_CM of 100 mA and frequency 100 kHz. The results showed that the magnetic field strength in the vicinity the inductance device 30, i.e. at a distance where other electronic components may be located, is reduced by 90 % as compared to the magnetic field strength generated by a conventional inductance device 20 without a third winding 31. The magnetic field strength may be further reduced by 99,5 % as compared to the conventional setup when using a short-circuited copper foil wrapped around the inductance device 20; however, the drawbacks of using a copper foil in terms of manufacturability and costs by far outweigh the advantages achievable in terms of better shielding. In other words, using a third winding 31 made of a short-circuited wire already provides a sufficient shielding of the magnetic stray field of the inductance device 30 and additionally provides a robust solution that is much easier to manufacture and thus significantly cheaper.
Many variations and modifications may be made to the preferred embodiments of the invention within the scope of the present invention, as defined by the following claims.
Advantages of features and of combinations of several features mentioned in the introduction of the description are only exemplary and may come into effect alternatively or cumulatively, without the necessity that the advantages have to be achieved by embodiments of the invention. Further preferred features may be taken from the drawings - particularly from the depicted relative arrangement and operational connections of several parts. The combination of preferred features of different embodiments of the invention and of preferred features of different claims is also possible and is encouraged herewith. This also applies to such preferred features which are depicted in separate drawings or mentioned in their description. These preferred features may also be combined with preferred features of different claims.

LIST OF REFERENCE NUMERALS

10: Power converter
11: Input connections
12: Output connections
13: DC-DC converter
14: Inverter
15: Buffer capacitor
16: Common mode choke
17: Output filter
18: Filter capacitor
19: Differential mode choke

20: Inductance device
21: Core
21a, 21b: Leg
21c, 21d: Leg
22a, 22b: Winding
23a, 23b: First End
24a, 24b: Second End
25: Magnetic flux line
26a, 26b: Magnetic flux line

30: Inductance device
31: Shield Winding
32a, 32b: Magnetic flux line
33: Magnetic flux line

I_DM: Differential mode current
I_CM: Common mode current
I_S: Shielding current
SC: Short circuit connection

Claims

Power converter (10) comprising input connections (11), output connections (12) and an inductance device (30), the power converter (10) being configured to convert a direct current supplied at the input connections (11) into an alternating current to be output via the output connections (12) or vice versa, wherein the inductance device (30) comprises
- a core (21) with a first leg (21a), a second leg (21b) oriented parallel to the first leg (21a), a third leg (21c) and a fourth leg (21d), wherein the legs (21a, 21b, 21c, 21d) are in a rectangular arrangement; and

- a first winding (22a) wound around the first leg (21a) and a second winding (22b) wound around the second leg (21b), the first winding (22a) and the second winding (22b) each comprising a first end (23a, 23b) and a second end (24a, 24b), wherein the respective first ends (23a, 23b) are connected electrically in series to the respective input connections (11) or to the respective output connections (12) of the power converter such that magnetic fluxes (25) generated inside the core (21) by a differential mode current (I_DM) flowing through the first winding (22a) and the second winding (22b) add constructively and a coupled differential mode choke (19) is obtained,
characterised in that the inductance device (30) further comprises a third winding (31) comprising a short-circuited wire and being wound around an outer perimeter of the inductance device (30) as defined by the outer surfaces of the first winding (22a) and the second winding (22b), wherein a winding axis of the third winding (31) is oriented parallel to the first leg (21a) and the second leg (21b) of the core (21).
Power converter (10) according to claim 1, characterised in that individual turns of the third winding (31) of the inductance device (30) are located directly adjacent to each other such that the third winding (31) covers the outer surfaces of the first winding (22a) and the second winding (22b).
Power converter (10) according to claim 1, characterised in that the third winding (31) of the inductance device (30) comprises at least three turns equally spaced to each other, wherein the spacing between the turns of the third winding (31) is greater or equal to a wire diameter of the third winding (31).
Power converter (10) according to any of the preceding claims, characterised in that the inductance device (30) comprises a casting compound covering the core (21), the first winding (22a), the second winding (22b), and the third winding (22c), wherein the third winding comprises an insulation.
Power converter (10) according to any of the preceding claims, characterised in that the core (21) of the inductance device (30) comprises a fifth leg oriented parallel to the first leg (21a) and the second leg (21b) such that the core (21) is arranged in an EI-type configuration, wherein a fourth winding is wound around the fifth leg such that magnetic fluxes generated by a three-phase differential mode current (I_DM) flowing through the first winding (22a), the second winding (22b) and the fourth winding add constructively.
Power converter (10) according to claim 5, wherein the power converter (10) comprises a three-phase inverter (14) configured to output a three-phase current and wherein the first winding (22a), the second winding (22b), and the fourth winding of the inductance device (30) are connected to respective output connections (12) of the power converter (10) such that magnetic fluxes (25) generated by a differential mode current (I_DM) flowing through the first winding (22a), the second winding (22b) and the fourth winding add constructively.