WINDING CONFIGURATION AS PART OF AN INTEGRATED STRUCTURE FOR A MEDIUM FREQUENCY TRANSFORMER

Abstract

A method for producing a coil for a transformer, in particular for a medium frequency transformer for a resonant DC/DC converter or a dual active bridge DC/DC converter, is disclosed which: providing a plurality of M>1 conductive foil strips, each having a first ending and a second ending; stacking the plurality of conductive foil strips to obtain a foil strip stack having a first ending and a second ending, wherein an electrically insulating layer is provided between any two adjacent foil strips; electrically interconnecting the first endings of all conductive foil strips to a first terminal; for each of the conductive foil strips providing a connector at the second ending of the foil strip; and coiling up the foil strip stack from the first end.

Claims

1. A method for producing a coil for a transformer, in particular for a medium frequency transformer for a resonant DC/DC converter or a dual active bridge DC/DC converter, comprising, in the following order, the steps of: a) providing a plurality M>1 of conductive foil strips each having a first ending and a second ending; b) stacking the plurality of conductive foil strips to obtain a foil strip stack having a first ending and a second ending, wherein an electrically insulating layer is provided between any two adjacent conductive foil strips; c) electrically interconnecting the first endings of all conductive foil strips to a first terminal; d) for each of the conductive foil strips providing a connector at the second ending of the foil strip; and e) coiling up the foil strip stack from the first ending.

2. The method of claim 1, wherein the foil stack is coiled up to form a coil having a central opening.

3. The method of claim 1, further comprising the step of f) providing a second terminal; g) providing a plurality of M impedance elements, h) for each connector, connecting a different one of said impedance elements between the connector and the second terminal.

4. The method of claim 1, further comprising the step of casting an insulating material around the coil, and around the impedance elements, wherein a passageway extending through the central opening is provided in the insulating material.

5. The method of claim 3, wherein the impedance elements are capacitors, all having an at least same capacitance within a range of 20%.

6. The method of claim 3, wherein the impedance elements are inductors, all having an at least same inductance within a range of 20%.

7. A coil, in particular produced according to claim 1, for a transformer, in particular a medium frequency transformer for a resonant DC/DC converter or a dual active bridge DC/DC converter, said coil comprising i) a pair of windings, said pair of windings comprising: i) a first winding made of a first conductive foil strip and comprising a first plurality of turns surrounding one another; ii) a second winding made of a second conductive foil strip and comprising a second plurality of turns surrounding one another, with each turn of the first plurality of turns adjacently surrounded by a turn of the second plurality of turns; wherein iii) innermost endings of the first and second windings are electrically interconnected and connected to and/or with a first terminal; and the first and second windings are electrically isolated from one another except for a connection wherein j) a first connector and a second connector are provided at an outermost ending of and in electrical contact with the first and second winding, respectively; k) a second terminal with a first impedance element connected between the second terminal and the first connector; and a second impedance element connected between the second terminal and the second connector.

8. The coil according to claim 7, wherein the impedance elements are capacitors, all having an at least same capacitance within a range of 20%.

9. The coil according to claim 7, wherein the impedance elements are inductors, all having an at least same inductance within a range of 20%.

10. The coil according to claim 7, wherein the first and second windings are electrically isolated from one another except for a connection via the first terminal, at the innermost ending of the windings.

11. The coil according to claim 7, wherein the pair of windings is formed from coiled up stack of conductive foil strips, each having a first end and a second end; and with an insulating layer provided between any two adjacent conductive foil strips.

12. A transformer, in particular a medium frequency transformer for a resonant DC/DC converter or a resonant solid-state-transformer cell, said transformer comprising l) a core, having an air gap; and m) at least a first coil according to claim 7.

13. A transformer, in particular a medium frequency transformer for a resonant DC/DC converter or a resonant solid-state-transformer cell, said transformer comprising a core, having an air gap; and at least a first coil according to claim 7 with the pair of windings surrounding at least a section of the core, with said section extending through the central opening of the first coil, comprising a plurality of coils according to claim 7, with the first terminals of all coils connected together.

14. A transformer according to claim 13, wherein n) the first coil has a height h.sub.1, wherein the impedance elements are all capacitors, having an at least same capacitance C.sub.1 within a range of 20%; o) a second coil has a height h.sub.2, wherein the impedance elements are all capacitors, having an at least same capacitance C.sub.2 within a range of 20%; wherein at least approximately C.sub.1/h.sub.1=C.sub.2/h.sub.2.

15. A transformer, in particular a medium frequency transformer for a resonant DC/DC converter or a resonant solid-state-transformer cell, said transformer comprising p) a core, having an air gap; q) at least a first coil produced according to claim 1, with the pair of windings surrounding at least a section of the core, with said section extending through the central opening of the first coil.

16. A transformer according to claim 12, comprising: a core, having an air gap; and at least a first coil according to claim 8 with the pair of windings surrounding at least a section of the core, with said section extending through the central opening of the first coil, comprising a plurality of coils, with the first terminals of all coils connected together.

17. A transformer according to claim 12, in particular a medium frequency transformer for a resonant DC/DC converter or a resonant solid-state-transformer cell, said transformer comprising: a core having an air gap; and at least a first coil with the pair of windings surrounding at least a section of the core, with said section extending through the central opening of the first coil, comprising a plurality of coils with the first terminals of all coils connected together.

18. The coil according to claim 9, wherein the first and second windings are electrically isolated from one another except for a connection via the first terminal, at the innermost ending of the windings.

19. The transformer according to claim 16, wherein the first and second windings are electrically isolated from one another except for a connection via the first terminal at the innermost ending of the windings.

20. The transformer according to claim 14, wherein the impedance elements are inductors, all having an at least same inductance within a range of 20%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The subject matter of the invention will be explained in more detail in the following text with reference to exemplary embodiments which are illustrated in the attached drawings.

[0043] FIG. 1 illustrates a basic, generic, prior art DC/DC converter.

[0044] FIG. 2a) illustrates a basic, prior art DC/DC dual active bridge (DAB) converter.

[0045] FIG. 2b) illustrates a basic, prior art resonant DC/DC converter.

[0046] FIG. 3 shows a more detailed schematic of one possible embodiment of the DC/DC converter from FIG. 1.

[0047] FIG. 4 schematically illustrates a coil in accordance with the present invention.

[0048] FIG. 5 shows illustrates a stack of three coils in accordance with the present invention.

[0049] FIG. 6 shows a schematic of an exemplary resonant DC/DC converter.

[0050] FIG. 7 shows a schematic of another exemplary resonant DC/DC converter.

[0051] In principle, identical reference symbols in the figures denote identical features or elements.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0052] For background information, FIG. 1a) illustrates a basic, generic, prior art DC/DC converter 1 as part of which the present invention may be used. A DC/AC converter 11 is configured to convert a DC voltage and/or current from a DC source, preferably comprising a DC link capacitor, connected to its input into an AC voltage and/or current of medium frequency, i.e. preferably in a frequency range between 500 Hz and 500 kHz. Said AC voltage and/or current is fed into an AC intermediate circuit 12 comprising a transformer 141, in particular a medium frequency transformer (MFT), said transformer comprising a primary and a secondary side, and providing galvanic insulation between said sides. The transformer may, inter alia, be characterized by coupled inductances L.sub.m and L.sub.m′ and a stray inductance L.sub.s, with its primary side winding or windings connected to the DC/AC converter via an inductance element having an impedance Z.sub.1, which may also be a parasitic inductance, in particular of a wire or other connection. The transformer transforms voltage and/or current at its primary side in a known manner to a secondary side voltage and/or current. Said secondary side voltage and/or current is subsequently converted by AC/DC converter 16, in particular a rectifier, into a DC voltage and/or current at the output of said AC/DC converter 16. DC/AC converter 12 may, in particular, comprise a plurality of semiconductor switches arranged in a half-bridge configuration as shown in FIG. 1a, or arranged in a full-bridge configuration as shown in FIG. 1b). Likewise, AC/DC converter 16 may, in particular, comprise a plurality of semiconductor switches arranged in a half-bridge configuration corresponding to the one shown in FIG. 1a, or arranged in a full-bridge configuration corresponding to the one shown in FIG. 1c).

[0053] FIG. 2a) illustrates a basic, prior art DC/DC dual active bridge (DAB) converter 1′ which may be considered as an embodiment of the DC/DC converter 1 shown in FIG. 1a), and as another potential starting point for the present invention. DC/AC converter 11 is configured to convert a DC voltage and/or current from a DC source, preferably comprising a DC link capacitor, connected to its input into an AC voltage and/or current of medium frequency, i.e. preferably in a frequency range between 500 Hz and 500 kHz. Said AC voltage and/or current is fed into an AC intermediate circuit 14′ comprising a transformer 141′, in particular a medium frequency transformer (MFT), said transformer comprising a primary and a secondary side, and providing galvanic insulation between said sides. The transformer may, inter alia, be characterized by coupled inductances L.sub.m and L.sub.m′ and a stray inductance L.sub.s, with its primary side winding or windings connected to the DC/AC converter via an inductor as impedance element, with said inductor, sometimes referred to as an energy transfer inductor, having an inductance L.sub.DAB 1. The transformer transforms voltage and/or current at its primary side in a known manner to a secondary side voltage and/or current. Said secondary side voltage and/or current is subsequently converted by AC/DC converter 16′, in particular a rectifier, into a DC voltage and/or current at the output of said AC/DC converter 16. An optional inductor connected between the secondary side of the transformer and the AD/DC converter preferably has an inductance L.sub.DAB 2 which preferably is at least essentially identical to L.sub.DAB 1. DC/AC converter 12 may, in particular, comprise a plurality of semiconductor switches arranged in a half-bridge configuration corresponding to the one shown in FIG. 1b), or arranged in a full-bridge configuration corresponding to the one shown in FIG. 1c). Likewise, AC/DC converter 16 may, in particular, comprise a plurality of semiconductor switches arranged in a half-bridge configuration corresponding to the one shown in FIG. 1b), or arranged in a full-bridge configuration corresponding to the one shown in FIG. 1c). Dual active bridge converters are also exemplary described in Swiss patent application publication CH 707 533 A2 or US patent application publication US 2018/0159435 A1.

[0054] FIG. 2b) illustrates a basic, prior art resonant DC/DC converter 1″ which may be considered as another embodiment of the DC/DC converter 1 shown in FIG. 1a), and as yet another potential starting point for the present invention. DC/AC converter 11 is configured to convert a DC voltage and/or current from a DC source, preferably comprising a DC link capacitor, connected to its input into an AC voltage and/or current of medium frequency, i.e. preferably in a frequency range between 500 Hz and 500 kHz. Said AC voltage and/or current is fed into an AC intermediate circuit 14″ comprising a transformer 141″, in particular a medium frequency transformer (MFT), said transformer comprising a primary and a secondary side, and providing galvanic insulation between said sides. The transformer may, inter alia, be characterized by coupled inductances L.sub.m and L.sub.m′ and a stray inductance L.sub.s, with its primary side winding or windings connected to the DC/AC converter via capacitor as impedance element, with said capacitor having a capacitance C.sub.res1. The capacitor together with the stray inductance is part of a resonant tank comprised by the AC intermediate circuit, which may store electric energy, and which is characterized by a resonance frequency, which in turn depends on the values of L.sub.s and C.sub.res1. The capacitor is therefore commonly referred to as a resonant capacitor. The transformer transforms voltage and/or current at its primary side in a known manner to a secondary side voltage and/or current. Said secondary side voltage and/or current is subsequently converted by AC/DC converter 16, in particular a rectifier, into a DC voltage and/or current at the output of said AC/DC converter 16. DC/AC converter 12 may, in particular, comprise a plurality of semiconductor switches arranged in a half-bridge configuration corresponding to the one shown in FIG. 1b), or arranged in a full-bridge configuration corresponding to the one shown in FIG. 1c). Likewise, AC/DC converter 16 may, in particular, comprise a plurality of semiconductor switches arranged in a half-bridge configuration corresponding to the one shown in FIG. 1b), or arranged in a full-bridge configuration corresponding to the one shown in FIG. 1c). As an alternative to the variant comprising active bridges as described above and allowing for bi-directional electric power flow, AC/DC converter 16 may, in particular, be embodied without semiconductor switches and comprise diodes only arranged in a half-bridge or full-bridge configuration if only unidirectional electric power flow is required. Resonant DC/DC converters are exemplary described in PCT patent application publication WO 2018/141092 A1.

[0055] FIG. 3 shows a more detailed schematic of one possible embodiment of the DC/DC converter from FIG. 1a), where two parallel windings are provided on both the primary side 1001 and the secondary side 1002 of the transformer, and impedance elements Z1 and Z2 have been split and distributed between the parallel windings. Also shown, merely for background information, is a voltage source connected to the first DC link 10, a resistive load connected to the second DC link 18 and characterized by a resistance Road, and (in gray) a reluctance network 19 of a core and a stray flux of the transformer.

[0056] FIG. 4 schematically illustrates a coil 100 in accordance with the present invention. Coil 100 comprises a first winding 101 made of a first conductive foil strip 111 and a second winding 102 made of a second conductive foil strip 112 which have been layered and coiled up to form a plurality of N.sub.1=3 turns around a central opening 109, which may receive a transformer core not shown in FIG. 3. Innermost endings of the first and second windings are electrically connected to one another at T.sub.10, and to/with a first terminal T.sub.1. A first connector T.sub.21 and a second connector T.sub.22 are provided at an outermost ending of and in contact with the first and second winding, respectively. An electrically insulating layer 113 is provided between the first conductive foil strip 111 and the second conductive foil strip 112. Further insulating layers 114 are provided on both sides of the first conductive foil strip 111 and the second conductive foil strip 112. The first and second windings are directly electrically connected only at the innermost ending of the windings at T.sub.10. The coil further comprises a second terminal T.sub.2, a capacitor 121 connected between the second terminal and the first connector T.sub.21; and a second capacitor 122 connected between the second terminal and the second connector T.sub.22. A height h of coil 100 corresponds to a width w of the first and second conductive foil strip.

[0057] Merely for illustration, FIG. 4 also shows a DC link 10 and a DC/AC converter 12′ comprising an active half bridge comprising a plurality of two semiconductor switches S.sub.1, S.sub.2 for applying an AC voltage to the coil 100.

[0058] FIG. 5 illustrates a stack of three coils, two first coils 100′ and a second coil 100″, each of which three coils essentially corresponds to coil 100 from FIG. 3 albeit for a height, which is h′ for the first two coils 100′, and h″ for the second coil 100″. By choosing different values for the capacitances 121′, 122′ and 121″, 122″, a current in the coils 100′ will be different from a current in the coil 100″. This may be used to advantage to make a current density at least approximately identical in the three coils by selecting appropriate capacitances, including compensation of any possibly increased current in outermost foils 100′ due to distortions in a transformer stray field, in particular a winding window stray field.

[0059] As illustrated in FIG. 5 some embodiments include a DC link 10 and DC/AC converter 12′ comprising an active half bridge comprising a plurality of two semiconductor switches S.sub.1, S.sub.2 for applying an AC voltage to coils 100′, 100″.

[0060] FIG. 6 shows a schematic of an example resonant DC/DC converter as an embodiment of the DC/DC converter from FIG. 3. Coil 100 comprising a pair of M=2 windings, and a pair of capacitors 121, 122 is connected between an output of the DC link 10 and a neutral terminal of the DC link 10.

[0061] FIG. 7 shows a schematic of another example resonant DC/DC converter as part of which various embodiments of a coil in accordance with the invention or produced in accordance with the invention may be used. The converter comprises a first DC link 10, a DC/AC converter 212 comprising a plurality of semiconductor switches S.sub.1, S.sub.2, S.sub.3, . . . , S.sub.6, an AC intermediate circuit 214, an AC/DC converter 216, and a second DC link 18. The converter comprises a plurality of active half bridges which are connected to a single, first DC link 10, while each of their outputs is connected via an individual one of a first plurality (N=3) of capacitors C.sub.resA and a common node C to a primary coil of a medium frequency transformer 2141, said transformer providing, inter alia, for galvanic insulation between a primary and a secondary side of said transformer. Coil 100 comprising a pair of M=2 windings, and a pair of capacitors 121, 122 is connected between common node C and a neutral terminal of the DC link 10. Also shown, merely for background information, is a voltage source connected to the first DC link 10, a resistive load connected to the second DC link 18 and characterized by a resistance R.sub.load, and (in gray) a reluctance network 19 of a core and a stray flux of the transformer 2141.

[0062] Preferred embodiments of the present invention, in particular as described above, may be realized as detailed in the numbered variants and/or embodiments in accordance with the items listed below, advantageously in combination with one or more of the features as detailed above, or in accordance with the claims as presented further below. [0063] 1) A method for producing a coil (100, 100′) for a transformer, in particular for a medium frequency transformer for a resonant DC/DC converter 1″ or a dual active bridge DC/DC converter 1′, comprising the steps of: [0064] a) providing a plurality M>1 of, conductive foil strips (111, 112, 111′, 112′, 111″, 112″), in particular elongate conductive foil strips, each having a first ending and a second ending; [0065] b) stacking the plurality of conductive foil strips to obtain a foil strip stack having a first ending and a second ending, wherein an electrically insulating layer 113 is provided between any two adjacent conductive foil strips; [0066] c) electrically connecting the first endings of all conductive foil strips to a first terminal (T1, T1′); [0067] d) for each of the conductive foil strips providing a connector (T.sub.21, T.sub.22, T.sub.21′, T.sub.22′, T.sub.21′, T.sub.22′) at the second ending of the foil strip; and [0068] e) coiling up the foil strip stack from the first end. [0069] 2) The method of variant 1, wherein the foil stack is coiled up to form a coil (100, 100′) having a central opening 109, in particular extending in a lateral direction. [0070] 3) The method of any preceding variant, further comprising the step of [0071] a) providing a second terminal (T.sub.2, T.sub.2); [0072] b) providing a plurality of M impedance elements, [0073] c) for each connector (T.sub.21, T.sub.22, T.sub.21′, T.sub.22′, T.sub.21′, T.sub.22′), connecting a different one of said impedance elements between the connector and the second terminal. [0074] 4) The method of any preceding variant, further comprising the step of casting an insulating material around the coil (100, 100′), and preferably around the impedance elements, wherein a passageway extending through the central opening 109 is provided in the insulating material. [0075] 5) The method of any preceding variant, wherein the impedance elements are capacitors (121, 122, 121′, 122′, 121″, 122″), preferably all having an at least approximately identical capacitance. [0076] 6) The method of any of method variants 1 to 4, wherein the impedance elements are inductors, preferably all having an at least approximately identical inductance. [0077] 7) A coil (100, 100′) or winding configuration, in particular produced according to one of method variants 1 to 6, for a transformer, in particular a medium frequency transformer for a resonant DC/DC converter 1″ or a dual active bridge DC/DC converter 1′, said coil comprising [0078] a) a pair of windings 101, 102 wound around a central opening 109, said pair of windings comprising: [0079] i) a first winding 101 made of a first conductive foil strip (111, 111′, 111″) and comprising a first plurality of turns surrounding one another; [0080] ii) a second winding 102 made of a second conductive foil strip (112, 112′, 112″) and comprising a second plurality of turns surrounding one another, with each turn of the first plurality of turns adjacently surrounded by a turn of the second plurality of turns; wherein [0081] iii) innermost endings of the first and second windings are electrically connected to and/or with a first terminal T.sub.1, in particular to provide an output terminal; [0082] wherein [0083] b) a first connector T.sub.21 and a second connector T.sub.21 are provided, in particular as input terminal, at an outermost ending of and in contact with the first and second winding, respectively. [0084] 8) The coil according to embodiment 7, wherein the first connector T.sub.21 is not in contact with the second winding, and the second connector T.sub.21 is not in contact with the first winding. [0085] 9) The coil according to one of embodiments 7 or 8, wherein the pair of windings 101, 102 is intertwined. [0086] 10) The coil according to one of embodiments 7 to 9, wherein the pair of windings 101, 102 is not twisted. [0087] 11) The coil according to one of embodiments 7 to 10, wherein the pair of windings 101, 102 is free of transpositions. [0088] 12) The coil according to one of embodiments 7 to 11, further characterized in that the coil further comprises [0089] a) a second terminal T.sub.2; [0090] b) a first impedance element connected between the second terminal and the first connector T.sub.21; and [0091] c) a second impedance element connected between the second terminal and the second connector T.sub.22. [0092] 13) The coil according to the preceding embodiment, wherein the impedance elements are capacitors (121, 122, 121′, 122′, 121″, 122″), preferably all having an at least approximately identical capacitance. [0093] 14) The coil according to embodiment 12, wherein the impedance elements are inductors, preferably all having an at least approximately identical inductance. [0094] 15) The coil according to one of embodiments 7 to 14, wherein the first and second windings are electrically isolated from one another except for a connection, in particular via the first terminal T.sub.1, at the innermost ending of the windings. [0095] 16) The coil according to one of embodiments 7 to 15, further characterized in that the first and second windings are electrically exclusively connected via the first terminal, and are otherwise electrically isolated from one another. [0096] 17) The coil according to one of embodiments 7 to 16, comprising at least one further winding intertwined with the first and second winding and comprising a further plurality of turns surrounding one another, with [0097] a) an innermost ending of the at least one further winding electrically connected to the first terminal T.sub.1; [0098] b) a further connector is provided, in particular as input terminal, for each of the at least one further winding at the outermost ending of and in contact with said further winding. [0099] 18) The coil according to the previous embodiment, wherein all the windings are electrically exclusively connected via the first terminal, and are otherwise electrically isolated from one another. [0100] 19) The coil according to one of embodiments 7 to 18, wherein the pair or plurality of windings is formed from a coiled up stack of conductive foil strips, each having a first end and a second end; and with an insulating layer provided between any two adjacent conductive foil strips. [0101] 20) A transformer, in particular a medium frequency transformer for a resonant DC/DC converter or a resonant solid-state-transformer cell, said transformer comprising [0102] a) a core, preferably having a core gap; [0103] b) at least a first coil (100, 100′, 100″) according to one of embodiments 7 to 19 or produced according to one of method variants 1 to 6, with the pair of windings surrounding at least a section of the core, with said section extending through the central opening 109 of the windings. [0104] 21) A transformer, according to the previous embodiment, wherein the first winding 101 and the second winding are primary windings of the transformer. [0105] 22) A transformer according to the previous embodiment, further comprising at least a second coil (100, 100′, 100″) according to one of embodiments 7 to 19 or produced according to one of method variants 1 to 6, with the pair of windings of the second coil surrounding at least another section of the core, with said another section extending through the central opening of the windings, and wherein the pair of windings of the second coil are secondary windings of the transformer. [0106] 23) A transformer, according to the previous embodiment, wherein the first winding 101 and the second winding 102 of the second coil are secondary windings of the transformer. [0107] 24) A transformer according to one of embodiments 20 to 21, comprising a plurality of coils (100, 100′, 100″) according to one of embodiments 7 to 19 or produced according to one of method variants 1 to 6, with the first terminals of all coils connected together. [0108] 25) A transformer according to the previous embodiment, wherein [0109] a) a first coil has a height h.sub.1, wherein the impedance elements are all capacitors, having an at least approximately identical capacitance C.sub.1; [0110] b) a second coil has a height h.sub.2, wherein the impedance elements are all capacitors, having an at least approximately identical capacitance C.sub.2; [0111] c) wherein at least approximately C.sub.1/h.sub.1=C.sub.2/h.sub.2. [0112] 26) A transformer according to embodiment 24, wherein [0113] a) a first coil has a height h.sub.1, wherein the impedance elements are all inductances, having an at least approximately identical inductance L.sub.1; [0114] b) a second coil has a height h.sub.2, wherein the impedance elements are all capacitors, having an at least approximately identical inductance L2; [0115] c) wherein at least approximately L.sub.1.Math.h.sub.1=L.sub.2.Math.h.sub.2. [0116] 27) A transformer according to one of embodiment 24 to 26, wherein [0117] a) two neighboring coils are spaced apart by a coil gap between said neighboring coils; [0118] b) the core has a core gap, in particular an air gap; [0119] c) the coil gap is aligned with, overlaps and/or or coincides with the core gap, in particular with respect to a lateral direction. [0120] 28) A transformer according to one of embodiment 20 to 27, wherein the or a second coil surrounds the first coil, preferably with the first coil extending within and/or through the central opening 109 of the windings of the first coil. [0121] 29) A transformer according to one of embodiment, wherein the windings of the first coil are primary windings of the transformer, and the windings of second first coil are secondary winding; or vice versa. [0122] 30) A resonant DC/DC converter or a resonant solid-state-transformer cell comprising a transformer according to one of the above embodiments. [0123] 31) A DC/DC converter, comprising [0124] a) a first DC link, preferably comprising a first DC link capacitor; [0125] b) an inverter bridge connected to the first DC link; [0126] c) a transformer, preferably a medium frequency transformer, in particular according to one of embodiments 20 to 29, preferably having a primary side and a secondary side; [0127] d) the primary side of the transformer comprising at least one coil according to one of embodiments 7 to 19 or produced according to one of method variants 1 to 6. [0128] 32) A DC/DC converter, comprising [0129] a) a first DC link, preferably comprising a first DC link capacitor; [0130] b) a plurality of N>1 inverter bridges connected in parallel to the first DC link; [0131] c) a transformer, in particular according to one of embodiments 20 to 29, preferably a medium frequency transformer, preferably having a primary side and a secondary side; [0132] d) the primary side of the transformer comprising at least one coil according to one of embodiments 7 to 19 or produced according to one of method variants 1 to 6; wherein [0133] e) the converter further comprises a first plurality of N further impedance elements, wherein [0134] f) for each converter bridge, a different one from the first plurality of impedance elements is connected between said converter bridge and the coil, in particular between said converter bridge and the second terminal of the coil. [0135] 33) A DC/DC converter, comprising [0136] a) a first DC link, preferably comprising a first DC link capacitor; [0137] b) a DC/AC converter having an input connected to the first DC link and comprising: [0138] i) a converter bridge connected to the first DC link; [0139] c) an AC intermediate circuit having an input connected to an output of the DC/AC converter and comprising [0140] i) a transformer, preferably a medium frequency transformer, having a primary side and a secondary side; [0141] ii) the primary side comprising at least one coil according to one of embodiments 7 to 19 or produced according to one of method variants 1 to 6; [0142] d) an AC/DC converter having an input connected to the secondary side of the AC intermediate circuit, [0143] e) a second DC link, preferably a second DC link capacitor, connected to an output of the AC/DC converter. [0144] 34) A DC/DC converter, comprising [0145] a) a first DC link, preferably comprising a first DC link capacitor; [0146] b) a DC/AC converter having an input connected to the first DC link and comprising: [0147] i) a first plurality of N>1 converter bridges connected in parallel to the first DC link; [0148] c) an AC intermediate circuit having an input connected to an output of the DC/AC converter and comprising [0149] i) a transformer, preferably a medium frequency transformer, having a primary side and a secondary side; [0150] ii) the primary side comprising at least one coil according to one of embodiments 7 to 19 or produced according to one of method variants 1 to 6; [0151] d) an AC/DC converter having an input connected to the secondary side of the AC intermediate circuit, [0152] e) a second DC link, preferably a second DC link capacitor, connected to an output of the AC/DC converter; wherein [0153] f) the AC intermediate circuit further comprises a first plurality of N impedance elements, wherein [0154] g) for each converter bridge, a different one from the first plurality of impedance elements is connected between said converter bridge and the at least one coil, in particular between said converter bridge and the second terminal of the at least one coil. [0155] 35) The DC/DC converter in accordance with any of embodiments 28 to 31, wherein each of the converter bridges is an inverter half-bridge comprising a first input terminal and a second input terminal, an inverter bridge output (alternatively conductively connectable to the first or second input terminal by means of a plurality of semiconductor switches), wherein for each inverter half-bridge, a different one of the first plurality of impedance elements is connected in series with the inverter bridge output. [0156] 36) The DC/DC converter in accordance with any of the preceding embodiments, wherein [0157] a) the first DC link has a positive terminal and negative terminal, [0158] b) the first input terminals of all inverter half-bridges are connected to the positive terminal, and [0159] c) the second input terminals of all inverter half-bridges are connected to the negative terminal. [0160] 37) The DC/DC converter in accordance with any of the embodiments 31 to 36, wherein the first DC link further has a neutral terminal and the second terminals of all of the plurality of primary windings are connected to the neutral terminal. [0161] 38) The DC/DC converter in accordance with any of the embodiments 31 to 37, wherein the converter is a resonant converter, and each of the plurality of impedance elements is a capacitor. [0162] 39) The DC/DC converter in accordance with any of the embodiments 31 to 38, wherein the converter is a dual active bridge converter, and each of the plurality of impedance elements is an inductor. [0163] 40) The DC/DC converter in accordance with any of the embodiments 31 to 3639 further comprising [0164] a) a second DC link, preferably comprising a second DC link capacitor [0165] b) a rectifier bridge connected to the second DC link; [0166] c) the secondary side of the transformer comprising at least one coil according to one of embodiments 7 to 19 or produced according to one of method variants 1 to 6. [0167] 41) The DC/DC converter in accordance with any of the embodiments 31 to 40, further comprising [0168] a) a second DC link, preferably comprising a second DC link capacitor; [0169] b) a plurality of N′>1 rectifier bridges connected in parallel to the second DC link; [0170] c) the secondary side of the transformer comprising at least one further coil according to one of embodiments 7 to 19 or produced according to one of method variants 1 to 6; wherein [0171] d) the converter further comprises a third plurality of N′ further impedance elements, wherein [0172] e) for each converter bridge, a different one from the third plurality of impedance elements is connected between said converter bridge and the coil, in particular between said converter bridge and the second terminal of the coil. [0173] 42) A stack of coils comprising a plurality of coils according to one of embodiments 7 to 19 or produced according to one of method variants 1 to 6. [0174] 43) A stack of coils according to embodiment 42, wherein the central openings of all coils are aligned with respect to one another, and/or with respect to a lateral direction. [0175] 44) A stack of coils according to embodiment 42 or 43, wherein the first terminals of all coils are connected. [0176] 45) A stack of coils according to one of embodiments 42 to 45, said stack cast or molded into an insulating material surrounding, in particular integrally surrounding, all the coils, in particular with the central openings of all the coils be at least essentially aligned, and in particular configured to receive a section or portion of a transformer core, which may be essentially straight and/or elongated, so that said section extends or portion through the central openings of all the coils. [0177] 46) A transformer, in particular a medium frequency transformer for a resonant DC/DC converter or a resonant solid-state-transformer cell, said transformer comprising [0178] a) a core, preferably having an air gap; [0179] b) at stack of coils according to one of embodiments 42 to 45, wherein [0180] c) a section of the core extends through the central opening 109 of all the coils of the stack. [0181] 47) A transformer according to the previous embodiment wherein [0182] a) two neighboring coils in the stack of coils are spaced apart by a coil gap between said neighboring coils; [0183] b) the core has a core gap, in particular an air gap; [0184] c) the coil gap is aligned with, overlaps and/or or coincides with the core gap, in particular with respect to a lateral direction.

[0185] Unless specified otherwise, a connection, in particular between any two entities, including in particular nodes, points, terminals, elements, devices, etc. or combinations thereof, refers to an electrically conductive connection, as in particular established by a wire, cable, busbar, a conductive track, trace or line on e.g. a (printed) circuit board, solder, etc. The electrically conductive connection is preferably at least substantially direct, in particular without any discrete elements, as, in particular, resistors, capacitors, inductors, or other passive or active elements or devices connected between the connected entities. The electrically conductive connection thus has at least essentially negligible resistance, capacitance and inductance, preferably at least essentially zero resistance, capacitance and inductance. In particular, resistance, capacitance and inductance of the electrically conductive connection are exclusively parasitic by nature. Further, resistance, capacitance and inductance of the electrically conductive connection significantly smaller (preferably by a factor of 1/100, 1/1000 or 1/10000) than resistances, capacitances and impedances of resistors, capacitors or inductors, respectively, connected by the electrical conductive connection, and/or comprised by an electric circuit or network which comprises the electrically conductive connection.

[0186] Unless specified otherwise, an electric connection or electrical connection is identical to connection as defined above.

[0187] Unless specified otherwise, if two entities, including in particular nodes, points, terminals, elements, devices, etc. or combinations thereof, are said to be connected, electrically connected or to be (electrically) connected together, a connection as defined above exists between the two entities.

[0188] Unless specified otherwise, if a first and a second entity, including in particular a first and second node, point, terminal, element, device, etc. or combinations thereof, are said to be connected via a third entity, including in particular a third node, point, terminal, element, device, or with such a third entity (in) between, a connection as described above exists between the first and third entities as well as between the third and second entities. However, no connection as described above, in particular no at least substantially direct connection exists between the first and second entities. If explicitly specified, the third element may in particular also be a connection, in particular a conductor, wire, cable, busbar etc. In such case, it may be assumed that no connection as described above other than the specified one is present.

[0189] Unless stated otherwise, it is assumed that throughout this patent application, a statement a≈b implies that |a−b|/(|a|+|b|)<10, preferably |a−b|/(|a|+|b|)<100, wherein a and b may represent arbitrary variables as described and/or defined anywhere in this patent application, or as otherwise known to a person skilled in the art. Further, a statement that a is at least approximately equal or at least approximately identical to b implies that a≈b, preferably a=b. Further, unless stated otherwise, it is assumed that throughout this patent application, a statement a>>b implies that a>10b, preferably a>100b; and statement a<<b implies that 10a<b, preferably 100a<b. Further, unless stated otherwise, it is assumed that throughout this patent application, a statement that a>>b, or that a is significantly larger or much larger than b, implies that a>10b, preferably a>100b; and statement that a<<b, or that a is significantly smaller or much smaller than b implies that 10a<b, preferably 100a<b. Further, a statement that two values a and b substantially deviate from one another, or differ significantly, implies that a≈b does not hold, in particular that a>>b or a<<b.

[0190] This description and the accompanying drawings that illustrate aspects and embodiments of the present invention should not be taken as limiting the claims defining the protected invention. In other words, while the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. Various mechanical, compositional, structural, electrical, and operational changes may be made without departing from the spirit and scope of this description and the claims. In some instances, well-known circuits, structures and techniques have not been shown in detail in order not to obscure the invention. Thus, it will be understood that changes and modifications may be made by those of ordinary skill within the scope of the following claims. In particular, the present invention covers further embodiments with any combination of features from different and/or individual embodiments as described above and below. Embodiments in accordance with the invention may, in particular, include further and/or additional features, elements, aspects, etc. not shown in the drawings or described above.

[0191] Method steps listed in the description and, in particular, in the claims, are preferably carried out in the order as listed, but may alternatively be carried out in any other order in as far as technically and practically feasible.

[0192] The disclosure also covers all further features shown in the Figures, individually, although they may not have been described in the afore or following description. Also, individual alternatives of the embodiments described in the Figure and the description and individual alternatives of features thereof can be disclaimed from the subject matter of the invention or from disclosed subject matter. The disclosure comprises subject matter consisting of the features defined in the claims or the exemplary embodiments as well as subject matter comprising said features.

[0193] Furthermore, in the claims the word “comprising” does not exclude further or additional features, elements, steps etc., and the indefinite article “a” or “an” does not exclude a plurality. A single unit or step may fulfil the functions of several features recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. The terms “essentially”, “about”, “approximately” and the like in connection with an attribute, property or a value particularly also comprise exactly the attribute, property or value, respectively, as stated. The term “approximately” or “about” in the context of a given numerate value or range refers to a value or range that is, e.g., within 20%, within 10%, within 5%, or within 2% of the given value or range, and, in particular, also comprises the exact value or range as stated. Components described as coupled or connected may be electrically or mechanically directly coupled, or they may be indirectly coupled via one or more intermediate components. Any reference signs in the claims shall not be construed as limiting the scope.