WO2016000786A1

WO2016000786A1 - Capacitor assembly with cooling arrangement

Info

Publication number: WO2016000786A1
Application number: PCT/EP2014/064242
Authority: WO
Inventors: Timothy PATHEY; Didier Cottet; Francesco Agostini
Original assignee: Abb Technology Ltd
Priority date: 2014-07-03
Filing date: 2014-07-03
Publication date: 2016-01-07
Also published as: CN106663537B; CN106663537A; EP3164876A1

Abstract

A capacitor assembly (200) comprising a group of wound film capacitor elements (210) and a cooling arrangement (350, 651, 652) is disclosed. Each capacitor element extends in an axial direction (A) between two axial end faces (211) and in a radial direction (R) crossing the axial direction. Each capacitor element extends more in the radial direction than in the axial direction. The cooling arrangement is adapted to provide a transfer of heat (230) through spaces (240) defined between adjacent axial end faces of neighboring capacitor elements. The transfer of heat through a space defined by the axial end faces of two neighboring capacitor elements is directed across the axial directions of the two neighboring capacitor elements. The capacitor assembly is applicable in for instance high voltage direct current, HVDC, power converters, but also in other electronic devices.

Description

CAPACITOR ASSEMBLY WITH COOLING ARRANGEMENT

TECHNICAL FIELD

The present invention generally relates to the field of capacitor assemblies comprising wound film capacitor elements. In particular, the present invention relates to such capacitor assemblies having cooling arrangements for cooling the capacitor elements. The invention is applicable in for instance high voltage direct current (HVDC) power converters.

BACKGROUND

An HVDC converter station is a type of station adapted to convert high voltage direct current (DC) to alternating current (AC) or the reverse. An HVDC converter station may comprise a plurality of elements such as the converter itself (or a plurality of converters connected in series or in parallel), an alternating current switch gear, transformers, capacitors, filters, a direct current switch gear and other auxiliary elements.

An example of a capacitor is a wound film capacitor element which comprises a stack of layers including at least two electrode layers and a dielectric layer arranged between the two electrode layers, wherein the stack of layers is wound like a roll. Wound film capacitor elements may have a round cylindrical shape, but may also have a flattened shape, e.g. oval or rectangular. Cooling of capacitor elements is typically provided in order to enhance the operation of the capacitor elements and to extend their lifetime. New alternative capacitor assemblies with improved cooling capabilities are desired, in particular for use in compact HVDC converter stations.

SUMMARY

An object of at least some embodiments of the present disclosure is to provide a capacitor assembly with improved cooling of its capacitor elements.

This and other objects are achieved by means of a capacitor assembly as defined in the appended independent claim. Other embodiments are defined by the dependent claims.

According to an embodiment, there is provided a capacitor assembly comprising a group of wound film capacitor elements. Each of the capacitor elements extends in an axial direction between two axial end faces and in a radial direction crossing the axial direction. Each of the capacitor elements extends more in the radial direction than in the axial direction. The capacitor assembly further comprises a cooling arrangement adapted to provide a transfer of heat through spaces defined between adjacent axial end faces of neighboring capacitor elements. The transfer of heat through a space defined by the axial end faces of two neighboring capacitor elements is directed across the axial directions of the two neighboring capacitor elements.

Thermal conductivity for wound film capacitor elements is higher in the axial direction than in the radial direction. Cooling of the capacitor elements may therefore be improved by providing cooling at the axial end faces of the capacitor elements rather than at other outer surfaces of the capacitor elements. Heat generated within the capacitor elements is more easily transmitted to the axial end faces of the capacitor elements for capacitor elements extending more in the radial direction than in the axial direction, than for capacitor elements having the same volume and capacitance but extending more in the axial direction than in the radial direction. Moreover, a larger area is available at the end faces for heat dissipation for capacitor elements extending more in the radial direction than in the axial direction, than for capacitor elements having the same volume and capacitance but extending more in the axial direction than in the radial direction.

Further, providing a transfer of heat through spaces between adjacent end faces of

neighboring capacitor elements allows heat to be transferred away from the capacitor elements and improves cooling of the capacitor elements. Directing the transfer of heat across the axial direction of two neighboring capacitor elements allows for a more efficient transfer of heat away from the end faces of the two neighboring capacitor elements, and further improves cooling of these capacitor elements.

Another advantage of employing capacitor elements which extend more in the radial direction than in the axial direction is that the impedance of the capacitor elements is reduced compared to capacitor elements having the same volume and capacitance but which extend more in the axial direction than in the radial direction.

The axial directions of the respective wound film capacitor elements may be directions along, or e.g. substantially parallel to, the layers, e.g. electrode layers and/or dielectric layers, from which the capacitor elements are made. In each of the wound film capacitor elements, a plurality of layers may for example be wound around an axis extending along the axial direction of the wound film capacitor element.

The axial directions of the respective capacitor elements may coincide (or be parallel), or may be different for at least some of the respective capacitor elements. Similarly, the radial directions of the respective capacitor elements may coincide (or be parallel), or may be different for at least some of the respective capacitor elements. The radial direction of each capacitor element may be transverse to, or even perpendicular to, the axial direction of that capacitor element.

By the transfer of heat through the space defined by the axial end faces of two neighboring capacitor elements being directed across the axial directions of the two neighboring capacitor elements is meant that the transfer of heat is directed in a direction transverse to, or crossing, each of the axial directions of the two neighboring capacitor elements. In some embodiments, the transfer of heat may for example be directed along, e.g. parallel to, the axial end faces of the capacitor elements.

By each capacitor element extending more in the radial direction than in the axial direction is meant that each capacitor element is longer in the axial direction than in the radial direction.

The capacitor elements may for example be disc-shaped. The capacitor elements may for example have a round, e.g. circular or oval, cross section. The embodiments of the present disclosure are however not limited to such geometries.

According to an embodiment, a height to diameter aspect ratio of each capacitor element may be between 1 : 1 and 1 :40, i.e. each capacitor element may extend more in the radial direction than in the axial direction, but each capacitor element may extend less than forty times in the radial direction as compared to its extension in the axial direction. In other words, the diameter of each given capacitor element, e.g. measured along a radial direction of the capacitor element, may be larger than the height of that capacitor element, e.g. measured along the axial direction of that capacitor element, but smaller than forty times the height of that capacitor element. Increasing the diameter relative to the height facilitates cooling of the capacitor elements. However, if the diameter of the wound film capacitor elements is too large, e.g. at least twenty or at least forty times the height of each capacitor element, the space needed for an overlap between an electrode layer and a dielectric layer of the capacitor elements may cause a substantial loss of volume in the capacitor assembly.

According to an embodiment, the group of capacitor elements may comprise at least three capacitor elements arranged so as to define at least two spaces between adjacent axial end faces of neighboring capacitor elements. Increasing the number of capacitor elements and the number of spaces between adjacent axial end faces of neighboring capacitor elements may, in a capacitor assembly of a given volume, improve cooling of the capacitor assembly via the transfer of heat provided through these spaces.

According to an embodiment, the cooling arrangement may comprise an active element arranged to provide a forced flow of a cooling medium through the spaces between adjacent axial end faces of neighboring capacitor elements for providing the transfer of heat. The use of an active element for providing the transfer of heat may improve the cooling of the capacitor elements. The active element may comprise e.g. an impeller or a reciprocating machine (e.g. including a piston).

Alternatively, or in combination with the active element, the cooling arrangement may comprise passive elements arranged to provide a flow of a cooling medium through the spaces between adjacent axial end faces of neighboring elements, for providing the transfer of heat. For example, the passive elements may include geometries of a container in which the cooling medium is contained, wherein these geometries are adapted to cause self-circulation of the cooling medium, e.g. due to different temperatures of the cooling medium at different locations in the container.

According to an embodiment, the cooling arrangement may comprise conduits extending through the spaces between adjacent axial end faces of neighboring capacitor elements in the direction of the transfer of heat for conducting a cooling medium. The use of conduits for conducting the cooling medium may improve control of the cooling of the capacitor assembly. In at least some embodiments, the conduits may for example be employed to provide cooling of selected portions of the capacitor elements. According to an embodiment, the spaces between the axial end faces of neighboring capacitor elements may form channels adapted for receiving a cooling medium. In this embodiment, the capacitor elements are immersed in the cooling medium, thereby providing a direct thermal contact between the cooling medium and the (axial end faces of the) capacitor elements, which improves the heat exchange. Such a cooling arrangement does not require conduits or other additional elements for providing guiding the cooling medium. In the present embodiment, the cooling arrangement is provided by the arrangement of the capacitor elements themselves and an actuator, or other means of injecting a cooling medium within the channels, may be sufficient to provide cooling of the capacitor elements. The cooling medium may e.g. include liquid and/or gas. It will be appreciated that the cooling medium may also be a mixture of gas and liquid, in particular if phase change occurs because of e.g. temperature and/or pressure variation of the cooling medium. The cooling medium may e.g. have dielectric properties, which may be advantageous for electrical insulation purposes. The cooling medium may for example be a gas such as sulfur hexafluoride (SF₆) or a liquid such as an oil or de-ionized water. The cooling medium may for example be a refrigerant fluid such as e.g. R134a, R1234ze, R1234yf, R245fa or NH3. The cooling medium may advantageously be chemically inert with respect to the capacitor elements and any devices (or semiconductor components) connected to the capacitor elements.

According to an embodiment, the cooling arrangement may comprise a thermo-electric cooling device arranged in the spaces between adjacent axial end faces of neighboring capacitor elements. The thermo-electric cooling device provides the transfer of heat and reduces the need for moving parts and/or a circulating cooling medium for cooling of the capacitor assembly. The thermo-electric cooling device may increase durability of the capacitor assembly and/or may eliminate or reduce the risk of leakage of the cooling medium from the capacitor assembly.

According to an embodiment, the capacitor assembly may further comprise a first electrical conductor arranged to electrically connect positive electrodes of the capacitor elements to a device, and a second electrical conductor arranged to electrically connect negative electrodes of the capacitor elements to the device. Each one of the first and second electrical conductors may comprise a main portion and branches branching from the main portion and being coupled to the electrodes of the capacitor elements, i.e. the branches may be coupled to the electrodes of the capacitor elements and may electrically connect these electrodes to the main portion of the respective electrical conductor.

According to an embodiment, the main portions of the first and second electrical conductors may be arranged on opposite sides of the capacitor elements along a radial direction, i.e. for each of the capacitor elements, the main portions of the first and second electrical conductors may be arranged on opposite sides the capacitor element along a radial direction of the capacitor element.

Alternatively, the main portions of the first and second electrical conductors may be arranged in proximity to each other on the same side of the capacitor elements, i.e. for each of the capacitor elements, the main portions of the first and second electrical conductors may be arranged in proximity of each other on the same side of the capacitor element, e.g. with respect to the radial direction of the capacitor element.

According to an embodiment, the capacitor elements may be axially aligned with each other. For example, the axial directions of the respective capacitor elements may be at least approximately parallel. The capacitor elements may for example be arranged beside each other in a row. Axial alignment of the capacitor elements may facilitate cooling of the capacitor elements since it may facilitate provision of the transfer of heat (or e.g. a flow of a cooling medium) directed across the axial directions of the respective capacitor elements. In a specific embodiment, the centers of the capacitor elements may be axially aligned, i.e. the centers of the capacitor elements may be arranged along the same axis.

According to an embodiment, the capacitor elements may be arranged beside each other in a circle-like arrangement. The circle-like arrangement of the capacitor elements may provide a more homogeneous inductive field, which in its turn reduces the need for electric insulation of neighboring electronic components from the capacitor assembly. The circle-like arrangement of the capacitor elements may also serve to protect a device arranged within the circle. The circle-like arrangement of the capacitor elements may for example form an object shaped like a torus. The circle-like arrangement may for example be oval. The capacitor assembly may for example include multiple circle-like arrangements of capacitor elements, e.g. arranged on top of each other in a stack, and/or arranged concentrically. According to an embodiment, the capacitor elements may be arranged beside each other in an undulated arrangement. The undulated arrangement may for example be shaped to fit requirements or geometric constrains of neighboring devices and/or of an enclosure. The undulated arrangement of the capacitor elements may undulate in two dimensions, or may undulate in three dimensions, e.g. to form an object shaped like a helix.

According to an embodiment, the group of capacitor elements may be a first group, and the capacitor assembly may further comprise a second group of wound film capacitor elements. Each capacitor element of the second group may extend in an axial direction between two axial end faces and in a radial direction crossing the axial direction. Each capacitor element of the second group may extend more in the radial direction than in the axial direction. The capacitor elements of the second group may be arranged so as to define spaces between adjacent axial end faces of neighboring capacitor elements. The cooling arrangement may be further adapted to provide a transfer of heat through the spaces defined between adjacent axial end faces of neighboring capacitor elements of the second group. The transfer of heat through a space defined by the axial end faces of two neighboring capacitor elements of the second group may be directed across the axial directions of the two neighboring capacitor elements.

According to an embodiment, there is provided a circuit comprising a capacitor assembly as defined in any one of the preceding embodiments, and a device electrically connected to the capacitor assembly.

It will be appreciated that other embodiments using all possible combinations of features recited in the above described embodiments may be envisaged.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplifying embodiments will now be described in more detail, with reference to the following appended drawings:

Figure 1 shows a schematic perspective view of a prior art capacitor assembly;

Figure 2 shows a schematic perspective view of a capacitor assembly in accordance with an embodiment;

Figure 3 shows a schematic side view of a capacitor assembly in accordance with an embodiment; Figures 4 and 5 show schematic top views of capacitor assemblies arranged around a device, in accordance with embodiments; and

Figure 6 shows a schematic front view of respective axial end faces of two capacitor elements electrically connected to a device, and parts of a cooling arrangement for cooling the capacitor elements, in accordance with an embodiment.

All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the embodiments, wherein other parts may be omitted or merely suggested. Like reference numerals refer to like elements throughout the description.

DETAILED DESCRIPTION

Exemplifying embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments are shown. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person.

Figure 1 shows a schematic perspective view of a prior art capacitor assembly 100 for use in a high voltage direct current (HVDC) power converter. The capacitor assembly 100 comprises a group of wound film capacitor elements 110 in the form of bi-axially wound polypropylene (BOPP) film capacitors. The capacitor elements 110 are cylindrical and extend more in an axial direction A than in a radial direction R. The capacitor elements 110 are connected to electrical conductors 120a and 120b at axial end faces 111 on opposite sides of the capacitor elements 110.

Figure 2 shows a schematic perspective view of a capacitor assembly 200 in accordance with some embodiments. The capacitor assembly 200 comprises a group of wound film capacitor elements 210. Each of the capacitor elements 210 extends in an axial direction A between two axial end faces 211 and in a radial direction R crossing the axial direction A. Each capacitor element 210 extends more in the radial direction R than in the axial direction A.

The capacitor assembly 200 may further comprise a cooling arrangement (not shown in Figure 2 but in e.g. Figures 3 and 6) adapted to provide a transfer of heat 230 through spaces 240 defined between adjacent axial end faces 211 of neighboring capacitor elements 210. The transfer of heat 230 through a space 240 defined by the axial end faces 211 of two neighboring capacitor elements 210 is directed across the axial directions A of the two neighboring capacitor elements 210. It is to be noted that in Figure 2 (as well as in the other figures), the dimensions of the capacitor elements 210 and the distances between the capacitor elements 210 may not be to scale.

In an embodiment, the spaces 240 between the axial end faces 211 of neighboring capacitor elements 210 may form channels adapted for receiving a cooling medium. In such an embodiment, the capacitor elements 210 may be immersed in the cooling medium, thereby providing a direct thermal contact between the cooling medium and the axial end faces 211 of the capacitor elements 210, which improves the heat exchange. An actuator (not shown in Figure 2), or other means of injecting a cooling medium within the channels, may provide a flow of the cooling medium through the spaces 240 in order to provide the transfer of heat 230. The cooling medium may e.g. include liquid and/or gas. The cooling medium may e.g. have dielectric properties, which may be advantageous for electrical insulation purposes. The cooling medium may for example be a gas such as sulfur hexafluoride (SF₆) or a liquid such as an oil or de-ionized water. The cooling medium may for example be a refrigerant fluid such as e.g. R134a, R1234ze, R1234yf, R245fa or NH3. The cooling medium may advantageously be chemically inert with respect to the capacitor elements 210 and any devices (or

semiconductor components) connected to the capacitor elements 210. In the present embodiment, the cooling medium may e.g. be considered as a part of the cooling arrangement of the capacitor assembly 200.

In Figure 2, the capacitor elements 210 are exemplified by disc-shaped capacitor elements 210, but the capacitor elements 210 may have other shapes, such as e.g. oval or elliptic. The capacitor elements 210 are wound film capacitor elements which may comprise e.g. a single stack of layers including at least two electrode layers and a dielectric layer arranged between the two electrode layers, wherein the stack of layers is wound like a roll. Alternatively, the capacitor elements 210 may comprise multiple stacks of layers, e.g. arranged as sub-elements in the capacitor elements 210, each comprising an individually wound stack of layers. The sub-elements may for example be rectangular or square-shaped, i.e. the sub-elements may have a rectangular or square-shaped cross-section, and may be arranged together so as to form the capacitor elements 210. The dielectric layer may be e.g. a plastic film. The electrode layers may be metal films or foils of e.g. aluminum. Alternatively, the electrode layers may be provided via metallization (deposition) of e.g. aluminum on the dielectric layer. Thermal conductivity in the capacitor elements 210 is directionally dependent due to the orientation of the electrode layers and the dielectric layer(s). The electrode layers are oriented along the axial direction A of the capacitor elements 210, and the heat transfer is therefore more efficient in the axial direction A than heat transfer in the radial direction R in which the heat has to pass though the dielectric layer(s) which typically has lower thermal conductivity than the electrode layers. Cooling of the disc-shaped capacitor elements 210 in the capacitor assembly 200 described with reference to Figure 2 is therefore more efficient than cooling of the longer capacitor elements 110 in the capacitor assembly 100 described with reference to Figure 1. With such disc-shaped capacitor elements, cooling of a capacitor assembly may in at least some embodiments be improved while the shape and/or size of the capacitor assembly is kept within geometric constraints caused by neighboring devices and/or by an enclosure in which the capacitor assembly is to be arranged.

In Figure 2, the group of capacitor elements 210 is exemplified by three capacitor elements

210 arranged so as to define two spaces 240 between adjacent axial end faces 211 of neighboring capacitor elements 210, but the number of capacitor elements 210 may be any number larger than two, and the number of spaces 240 defined between adjacent end faces

211 may be any number larger than one.

The height to diameter aspect ratio of the capacitor elements 210 may be between 1 : 1 and 1 :40, i.e. the diameter of the capacitor elements 210 in the radial direction R may be larger than the height of the capacitor elements 210 in the axial direction A, but smaller than forty times the height of the capacitor elements 210 in the axial direction A. Cooling of a capacitor element 210 may be improved by reducing the height of the capacitor element 210 in the axial direction A. However, when the height becomes too low relative to the diameter of the capacitor elements 210 in the radial direction R, a substantial portion of the volume of the capacitor elements 210 may be needed for providing overlaps between the electrode layers and dielectric layers, which may cause a substantial loss of volume.

The capacitor assembly 200 may further comprise a first electrical conductor 220a arranged to electrically connect positive electrodes of the capacitor elements 210 to a device (not shown in Figure 2, but see Figures 4-6 for examples) with which the capacitor elements 210 interact, and a second electrical conductor arranged 220b to electrically connect negative electrodes of the capacitor elements 210 to the device. The first electrical conductor 220a and the second electrical conductor 220b may comprise respective main portions 221a and 221b, and respective branches 222a and 222b, which branch from the respective main portions 221a and 221b, and which are coupled to the electrodes of the capacitor elements 210. In the embodiment described with reference to Figure 2, the main portions 221a and 221b of the first and second electrical conductors 220a and 220b are arranged on opposite sides of the capacitor elements 210 along the radial direction R. The electrical conductors 220a and 220b may e.g. be provided in the form of a bus bar system, e.g. made of copper.

In the embodiments described with reference to Figure 2, the capacitor elements 210 are axially aligned with each other. In the particular example shown in Figure 2, the capacitor elements 210 are arranged beside each other in a row such that the axial directions A of the respective capacitor elements 210 coincide. Alternative arrangements are also envisaged in which the capacitor elements 210 are arranged beside each other in an undulated arrangement, e.g. so as to fit requirements of adjacent devices and/or an enclosure in which the capacitor assembly is to be arranged.

An advantage of the disc-shaped capacitor elements 210 described with reference to Figure 2, as compared to the longer capacitor elements 110 described with reference to Figure 1, is that the disc-shaped capacitor elements 210 allow for a modular assembly of the capacitor elements of a capacitor assembly, such that the capacitor assembly may more easily be adapted to the shape of a device which the capacitor elements are adapted to power, and or to the restrictions of the available space around the device, e.g., due to neighboring devices.

Figure 3 shows a schematic side view of a capacitor assembly 300 in accordance with other embodiments. Similarly to the capacitor assembly 200 described with reference to Figure 2, the capacitor assembly 300 comprises a group of disc-shaped wound film capacitor elements 310. The capacitor assembly 300 further comprises a cooling arrangement 350, exemplified herein by thermo-electric cooling devices 350 arranged in the spaces between adjacent axial end faces of neighboring capacitor elements 310. The thermo-electric cooling devices 350 are adapted to provide a transfer of heat 330 through the spaces defined between adjacent axial end faces of neighboring capacitor elements 310, in a direction across the axial directions A of the neighboring capacitor elements 310. Other cooling arrangements 350 are also envisaged for providing the flow of heat 330 (see e.g. Figure 6). For example, a forced flow of air or of liquid cooling medium may be employed to provide the follow of heat 330.

Similarly to the capacitor assembly 200 described with reference to Figure 2, the capacitor assembly 300 may comprise first and second electrical conductors 320a and 320b, e.g. bus bars, for connecting the positive and negative electrodes of the capacitor elements 310 to a device (not shown in Figure 3, but see Figures 4-6 for examples). In the embodiment described with reference to Figure 3, the main portions 321a and 321b of the first and second electrical conductors 320a and 320b are arranged in proximity to each other on the same side of the capacitor elements 320, and branches 322a and 322b of the respective electrical conductors 320a and 320b branch from the respective main portions 321a and 321b and are coupled to the electrodes of the capacitor elements 310.

Figure 4 shows a schematic top view of a capacitor assembly 400 arranged around a device 490, in accordance with some embodiments. The capacitor assembly 400 and the device 490 may for example form part of a power electronic building block (PEBB), e.g. in a high voltage direct current (HVDC) power converter. The capacitor assembly 400 comprises a first group 460 of capacitor elements 410, e.g. according to any of the embodiments described with reference to Figures 2 and 3. The capacitor elements 410 in the first group 460 are all associated with a first axial direction Al and a first radial direction Rl . The capacitor assembly comprises additional groups of wound film capacitor elements 410, similar to the first group 460 of capacitor elements 410, wherein the groups of capacitor elements 410 are arranged to form a square-shaped arrangement around the device 490. The additional groups of capacitor elements 410 include a second group 470 of capacitor elements 410 which are arranged perpendicularly relative to the capacitor elements 410 in the first group 460. Each capacitor element 410 of the second group 470 extends in a second axial direction A2 between two axial end faces and in a second radial direction R2 crossing the second axial direction A2. In the present example, the relative orientations of the capacitor elements of the first and second groups 460 and 470 cause the first axial direction Al to coincide with the second radial direction R2, and the first radial direction Rl to coincide with the second axial direction A2. Analogously to the capacitor elements in the first group 460, each capacitor element 410 of the second group 470 extends more in the second radial direction R2 than in the second axial direction A2, and the capacitor elements 410 of the second group 470 are arranged so as to define spaces between adjacent axial end faces of neighboring capacitor elements 410. A cooling arrangement, for instance in the form of total immersion of the capacitor elements 410 in a cooling medium provided from an inlet of an enclosure in which the capacitor assembly 400 is located, may be adapted to provide a transfer of heat through the spaces of one or more, e.g. all, of the groups of capacitor elements 410, wherein the transfer of heat through a space defined by the axial end faces of two neighboring capacitor elements 410 is directed across the axial directions of the two neighboring capacitor elements 410. In some embodiments, the capacitor assembly may comprise multiple square-shaped arrangements of capacitor elements be stacked on top of each other, or as multiple layers around the device. In some embodiments, the arrangement described with reference to Figure 4 may be extended into a three-dimensional arrangement around the device 490, i.e. a box- shaped arrangement of capacitor elements around the device 490.

Figure 5 shows a schematic top view of a capacitor assembly 500 arranged around a device 590, in accordance with some embodiments. In contrast to the capacitor assembly 400 described with reference to Figure 4, the capacitor elements 510 of the capacitor assembly 500 are arranged beside each other in a circle-like arrangement around the device 590, so as to form a torus-like shape around the device 590. The capacitor elements 510 in the present embodiment are distributed around the device 590 and are oriented such that their respective axial directions are directed along a circle around the device 590. In other words, the respective axial directions A3 and A4 of two neighboring capacitor element 510a and 510b are not parallel but form a non-zero angle a relative to each other. Similarly, respective radial directions R3 and R4 of neighboring capacitor elements 510a and 510b also form a non-zero angle a. The angle a may depend on the number of capacitor elements 510 employed to form the circle-like arrangement. The angle a may for example be between 0 and 45 degrees.

Employing a circular-like arrangement provides a more homogenous inductive field than e.g. employing the square-shaped arrangement described with reference to Figure 4. The capacitor elements 510 are exemplified in Figure 5 by twelve capacitor elements 510 uniformly distributed around the device 590, which may provide an even more homogenous inductive field.

The choice of shape for the arrangement of capacitor elements may be based on other factors, such as the geometry of adjacent devices and/or an enclosure in which the capacitor assembly is to be arranged, and it may therefore be necessary to deviate from an e.g. perfectly circular arrangement. According to some embodiments, a capacitor assembly may comprise two or more circle-like arrangements of capacitor elements 510, e.g. arranged concentrically around the device 590 and/or in a stack of circle-like arrangements.

Other arrangements of the capacitor elements are also envisaged. For example, the capacitor elements may be arranged along any two- or three-dimensional spline, e.g. in the form of a single, double or triple helix around an elongate device. The angle a between axial directions of consecutive capacitor elements (illustrated in Figure 5) may e.g. be at most e.g. 45 or 30 degrees.

Figure 6 shows a schematic front view of respective axial end faces of two capacitor elements 610 electrically connected to a device 690. The capacitor elements 610 may for example be of the same type as the capacitor elements 210 described with reference to Figure 2, and may be part of a capacitor assembly with a circular-like arrangement, as described with reference to Figure 5. The front view shown in Figure 6 is provided in an axial direction of the capacitor elements 610. A cooling arrangement 651 and 652 is adapted to provide a transfer of heat 630 through spaces at end faces of the capacitor elements 610. The cooling arrangement comprises conduits 651 extending through the spaces at the end faces of the capacitor elements 610 for conducting a cooling medium. The conduits 651 are exemplified herein by six pipes arranged along each of the two end faces of the capacitor elements 610 shown in Figure 6. The cooling arrangement further comprises an active element 652 arranged to provide a forced flow of cooling medium through the conduits 651 , and thereby through the spaces at the axial end faces of the capacitor elements 610. The active element 652 may for example be a pump. The active element 652 may include e.g. a piston and/or an impeller for providing the forced flow of cooling medium. It is to be noted that a cooling arrangement for cooling a capacitor assembly may include additional parts, such as additional conduits or pipes, not shown in Figure 6.

Other embodiments are also envisaged in which a cooling medium is provided between the axial end faces of neighboring capacitor elements with or without the use of conduits at the end faces. For example, a cooling arrangement may be adapted to surround the capacitor elements 610 by a cooling medium and to provide a flow of cooling medium through the spaces at the end faces of the capacitor elements 610. The flow may be provided via active elements such as a pump. Alternatively, or in combination with the use of an active element, the cooling arrangement may include geometries of a container in which the cooling medium is contained (e.g. including the conduits 651 described with reference to Figure 6), wherein these geometries are adapted to cause self-circulation of the cooling medium, e.g. due to different temperatures of the cooling medium at different locations in the container.

In the embodiment described with reference to Figure 6, the capacitor elements 610 are electrically connected to a device 690 via electrical conductors 620a and 620b, e.g. in the form of bus bars. The electrical conductors 620a and 620b are electrically connected to the capacitor elements via end caps at axial end faces of the capacitor elements 610.

As described above, embodiments of the capacitor assemblies of the present disclosure may e.g. be employed in high voltage direct current (HVDC) power converters. However, the present disclosure is not restricted to such applications. Embodiments of capacitor assemblies for use in other electronic arrangements or devices, such as e.g. other types of power converters, may also be envisaged.

Although features and elements are described above in particular combinations, each feature or element can be used alone without the other features and elements or in various combinations with or without other features and elements.

Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be used to advantage.

Claims

1. A capacitor assembly (200) comprising:

a group of wound film capacitor elements (210), each capacitor element extending in an axial direction (A) between two axial end faces (211) and in a radial direction (R) crossing the axial direction, wherein each capacitor element extends more in the radial direction than in the axial direction, and

a cooling arrangement (350, 651, 652) adapted to provide a transfer of heat through spaces (240) defined between adjacent axial end faces of neighboring capacitor elements, wherein the transfer of heat through a space defined by the axial end faces of two neighboring capacitor elements is directed across the axial directions of the two neighboring capacitor elements.

2. The capacitor assembly as defined in claim 1, wherein a height to diameter aspect ratio of each capacitor element is between 1 : 1 and 1 :40.

3. The capacitor assembly as defined in claim 1 or 2, wherein the group of capacitor elements comprises at least three capacitor elements arranged so as to define at least two spaces between adjacent axial end faces of neighboring capacitor elements.

4. The capacitor assembly as defined in any one of the preceding claims, wherein the cooling arrangement comprises an active element (652) arranged to provide a forced flow of a cooling medium through said spaces for providing said transfer of heat.

5. The capacitor assembly as defined in any one of the preceding claims, wherein the cooling arrangement comprises conduits (651) extending through said spaces in the direction of the transfer of heat for conducting a cooling medium.

6. The capacitor assembly as defined in any one of the preceding claims, wherein said spaces form channels adapted to receive a cooling medium.

7. The capacitor assembly as defined in any one of the preceding claims, wherein the cooling arrangement comprises a thermo-electric cooling device (350) arranged in said spaces.

8. The capacitor assembly as defined in any one of the preceding claims, further

comprising a first electrical conductor (220a, 620a) arranged to electrically connect positive electrodes of the capacitor elements to a device (690), and a second electrical conductor (220b, 620b) arranged to electrically connect negative electrodes of the capacitor elements to the device,

wherein each one of the first and second electrical conductors comprises a main portion (221a, 221b) and branches (222a, 222b) branching from the main portion and being coupled to the electrodes of the capacitor elements.

9. The capacitor assembly as defined in claim 8, wherein the main portions of the first and second electrical conductors are arranged on opposite sides of the capacitor elements along a radial direction.

10. The capacitor assembly as defined in claim 8, wherein the main portions of the first and second electrical conductors are arranged in proximity to each other on the same side of the capacitor elements.

11. The capacitor assembly as defined in any one of the preceding claims, wherein the capacitor elements are axially aligned with each other.

12. The capacitor assembly as defined in any one of the preceding claims, wherein the capacitor elements are arranged beside each other in a circle-like arrangement.

13. The capacitor assembly as defined in any one of the preceding claims, wherein the capacitor elements are arranged beside each other in an undulated arrangement.

14. The capacitor assembly as defined in any one of the preceding claims, wherein said group of capacitor elements is a first group (460),

wherein the capacitor assembly further comprises a second group (470) of wound film capacitor elements, each capacitor element of the second group extending in an axial direction between two axial end faces and in a radial direction crossing the axial direction, wherein each capacitor element of the second group extends more in the radial direction than in the axial direction, wherein the capacitor elements of the second group are arranged so as to define spaces between adjacent axial end faces of neighboring capacitor elements, and

wherein the cooling arrangement is further adapted to provide a transfer of heat through the spaces of the second group, wherein the transfer of heat through a space defined by the axial end faces of two neighboring capacitor elements of the second group is directed across the axial directions of the two neighboring capacitor elements.

15. A circuit comprising a capacitor assembly as defined in any one of the preceding

claims, and a device (690) electrically connected to the capacitor assembly.