Bus bar for a capacitor and capacitor

Abstract

Describes a bus bar (3) for a capacitor (1), wherein the bus bar (3) is laminated and wherein the bus bar (3) has a circular shape. Further, a capacitor (1) comprising the bus bar (3) is described.

Description

Technical Field

[0001] The present invention relates to a bus bar for a capacitor. Furthermore, the present invention relates to a capacitor including the bus bar. Background Art

[0002] In high-frequency applications, capacitors must meet the requirements defined in Table 1 within the operating bandwidth.

[0003] Requirements A Low equivalent series resistance (ESR) B Frequency-stable ESR C Low equivalent series inductance (ESL) D Uniform internal current distribution E Internal resonance avoidance

[0004] Table 1: Requirements for capacitors in high-frequency applications.

[0005] Overlapping bus bars are used in high-frequency applications where low equivalent series inductance (ESL), low and frequency-stable equivalent series resistance (ESR), and uniform internal current distribution are required. Overlapping bus bars also help to avoid internal resonances between components.

[0006] Capacitors with a circular configuration are typically divided internally by axially placed windings connected in parallel. The internal construction (circular windings and connecting elements) is encapsulated in a circular housing. From a mechanical perspective, the circular shape of the capacitor makes the use of internal overlapping bus bars particularly complex.

[0007] Conventionally, capacitor windings are connected without any overlap by means of a flat band or wire. When good performance at high frequencies is requested, this construction has the following disadvantages:

[0008] - The operating bandwidth is limited to low frequencies (f sw < 10 kHz);

[0009] - DC link capacitors are divided into a number of independent capacitors that are connected in parallel by external bus bars, but if space is limited and the only dimension of the capacitor that can be increased is the height, this problem cannot be solved with an efficient mechanical solution. Summary of the Invention

[0010] The object of the present disclosure is to solve the above problems. This object is solved by the bus bar and capacitor according to the independent claims.

[0011] According to a first aspect of the present disclosure, a bus bar is provided. The bus bar is configured to be used in a capacitor. The bus bar is adapted to be integrated in a capacitor, in particular a circular capacitor. The bus bar is adapted and arranged for high-frequency applications. The bus bar is laminated. In other words, the bus bar at least partially overlaps. The bus bar is designed such that it includes a greater width / a greater extension perpendicular to the longitudinal axis of the capacitor / a greater azimuthal extension than a conventional bus bar.

[0012] The bus bar includes a circular shape. For example, the bus bar includes the shape of a part of a cylindrical housing. The bus bar is adapted to the external shape of the capacitor into which the bus bar is to be integrated. In particular, the bus bar is adapted to the winding shape of the capacitor.

[0013] By means of the laminated bus bar, the parasitic inductances and resistances (ESRi, Rp, Rp2, ESLi, Lp, Lp2) can be greatly reduced. This makes the bus bar particularly suitable for high-frequency applications.

[0014] According to one embodiment, the bus bar includes a first layer or pole. The bus bar further includes a second layer or pole. For example, the layer may include copper. The layers of the bus bar are adapted and arranged to be connected to the poles of the capacitor, in particular to the poles of the winding elements of the capacitor. The bus bar and in particular the layers include an overlapping region. In the overlapping region, the layers of the bus bar overlap each other. In this way, short and very balanced electrical connections are facilitated.

[0015] According to one embodiment, an insulating layer is arranged between the first and second layers. For example, the insulating layer may include a polymer. The insulating layer is provided at least in the overlapping region. In this way, a short circuit between the two layers of the bus bar can be efficiently avoided.

[0016] According to one embodiment, the first layer includes a plurality of first connection regions. The second layer includes a plurality of second connection regions. The overlapping region of the first layer and the corresponding first connection regions merge into each other. In other words, the first layer and the first connection regions are integrally formed. The overlapping region of the second layer and the corresponding second connection regions merge into each other, that is, the second layer and the second connection regions are integrally formed. Thus, the error-prone connection between the overlapping region and the connection regions is eliminated.

[0017] According to a further aspect, a capacitor is provided. The capacitor is adapted for high-frequency applications. The capacitor includes a plurality of winding elements, for example two, three, four or more winding elements. The winding elements are arranged axially, that is, they are arranged along the main longitudinal axis of the capacitor.

[0018] The capacitor further includes at least one bus bar. Preferably, the capacitor includes exactly one bus bar. The bus bar may be the bus bar described previously. Thus, all the features described in connection with the bus bar also apply to the capacitor.

[0019] The capacitor includes a circular shape. The capacitor may include the shape of a cylinder. Thus, the corresponding winding elements also include the shape of a cylinder. The laminated / overlapping bus bar is adapted and arranged to connect the winding elements in parallel.

[0020] Compared with conventional capacitors, laminated busbars provide shorter and more balanced electrical connections for capacitors, and thus improve the electrical performance of capacitors. Parasitic inductance and resistance can be greatly reduced independently of the width of the capacitor metallization film. In addition, considering that C is uniform, the impedance (Z) from the terminals of the capacitor to each independent winding element is uniform across all bandwidths.

[0021] According to one embodiment, the busbar is arranged within the housing of the capacitor. Thus, the busbar is an internal busbar. Preferably, the busbar is arranged on the outer side of the winding element. Preferably, the busbar covers 20% to 50% of the outer side of the winding element. The laminated busbar is very space-saving. In particular, a capacitor having the laminated busbar described above can maintain a size similar to that of a capacitor with a standard connection (copper strip). Due to the fact that the standard size of the capacitor diameter is maintained, good integration in a power converter can be achieved.

[0022] According to one embodiment, the busbar includes a first layer or pole. The busbar further includes a second layer or pole. The first and second layers are electrically insulated from each other. In particular, the layers are electrically insulated by means of the insulation layer described above.

[0023] The layers of the busbar extend at least partially along the outer side of the corresponding winding element. In other words, the busbar extends along the longitudinal axis on the outer side of the winding element.

[0024] The busbar includes an overlapping region. In the overlapping region, the layers / poles of the busbar overlap each other. Since the busbar extends along the longitudinal axis of the capacitor, the busbar is a transversely overlapping busbar.

[0025] Preferably, the overlapping region of the busbar covers 5% to 40% of the outer side of the winding element. In other words, the extension of the busbar in the longitudinal and azimuthal directions is such that the region where the two layers overlap occupies up to 40% of the outer surface of the winding element. Thus, the greater the overlap, the better the compensation of parasitic inductance and resistance. The size of the overlapping region depends on the size of the capacitor and the number of windings.

[0026] According to one embodiment, the busbar has a shape adapted to the diameter of the corresponding winding element. In particular, the busbar includes a circular shape, such as the shape of a part of a cylindrical shell. The busbar can be used with any number of windings. In other words, the length and / or azimuthal extension of the busbar can be adapted to the size and number of winding elements. Thus, a very flexible supply of busbars is provided.

[0027] According to one embodiment, the busbar includes a plurality of connection regions. In particular, the first layer includes a plurality of first connection regions. The second layer includes a plurality of second connection regions.

[0028] The number of first connection regions corresponds to the number of winding elements. Additionally, the number of second connection regions corresponds to the number of winding elements.

[0029] The connection regions are adapted and arranged to be electrically and mechanically connected to the poles of the winding elements. The connection regions can be welded to the poles of the winding elements. Thus, the first layer can be connected to the first pole of the corresponding winding element. The second layer can be connected to the second pole of the corresponding winding element. Thereby, a short and very balanced electrical connection between the bus bar and the electrodes can be achieved. In this way, the electrical performance of the capacitor is increased. Description of the Drawings

[0030] Further features, refinements, and advantages become apparent from the following description of exemplary embodiments in conjunction with the accompanying drawings.

[0031] FIG. 1 schematically shows a simplified electrical model of a capacitor unit according to the prior art,

[0032] FIG. 2 schematically shows a simplified electrical model of a DC link capacitor according to the prior art,

[0033] FIGS. 3a and 3b schematically show perspective views of a capacitor according to the prior art,

[0034] Figure 4a and 4b schematically shows a perspective view of a part of the capacitor,

[0035] Figure 5a and 5b schematically shows a cross-sectional view of a part of the capacitor,

[0036] Figure 6 schematically shows a cross-sectional view of a part of the capacitor,

[0037] Figure 7 schematically shows a perspective view of a part of the capacitor,

[0038] Figure 8 schematically shows according to Figure 7 a perspective view of the capacitor,

[0039] Figures 9a to 9c schematically shows according to Figure 7 and 8 a perspective view of a part of the capacitor,

[0040] Figure 10 schematically shows a comparison ESR measurement between a capacitor according to the prior art and a capacitor according to the present disclosure. Detailed Description

[0041] Figures 1, 2, 3a and 3b relate to capacitors according to the prior art. In particular, FIGS. 3a and 3b show a conventional capacitor 100 from a first side (FIG. 3a) and from the opposite side (FIG. 3b). The capacitor 100 is divided into cells Ci (see FIGS. 1 and 2) connected in parallel by flat copper strips 102. Each capacitive cell Ci contains a capacitive element (winding element 101) and its connection to the copper strip 102.

[0042] The winding elements 101 are connected in parallel by the copper strips 102 without any overlap of the copper strips 102. The copper strips 102 electrically connect the terminals / poles 103 of the winding elements 101. The respective copper strips 102 are fixed to the respective terminals 103 by means of screws 104. The respective copper strips 102 extend along the outer side of the capacitor 100 and, in particular, extend outside the housing of the capacitor 100 (external busbars). In other words, one copper strip 102 extends on the first outer side of the capacitor 100 and the other copper strip 102 extends on the second (opposite) outer side of the capacitor 100.

[0043] In this context, FIG. 1 shows a simplified electrical model of the capacitive cell Ci (winding element 101 and its connection to the copper strip 102). Thereby, ESRi denotes the parasitic ESR of the capacitive cell Ci and ESLi denotes the parasitic ESL of the capacitive cell Ci.

[0044] A simplified electrical model of the complete DC link capacitor (with a plurality of capacitive cells Ci) is shown in FIG. 2, where

[0045] - Ci: Capacitive cell - capacitance value,

[0046] - ESRi: Capacitive cell - parasitic ESR,

[0047] - ESLi: Capacitive cell - parasitic ESL,

[0048] - Cp: Connector between capacitive cells - parasitic capacitance,

[0049] - Rp, Rp2: Connector between capacitive cells - parasitic resistance,

[0050] - Lp, Lp2: Connector between capacitive cells - parasitic inductance,

[0051] - Rt: Terminal - parasitic resistance,

[0052] - Lt: Terminal - parasitic inductance.

[0053] The electrical requirements achieved with this solution are summarized in Table 2.

[0054] Requirements Achieved by the prior art A Low equivalent series resistance (ESR) No B Frequency-stable ESR No C Low equivalent series inductance (ESL) No D Uniform internal current distribution No E Internal resonance avoidance No

[0055] Table 2: Requirements for capacitors in high - frequency applications as implemented by capacitors according to the prior art.

[0056] Figures 4 to 9 schematically show a capacitor 1 according to the invention. The capacitor 1 has a circular configuration. In other words, the capacitor 1 has a circular outer shape. In particular, the capacitor 1 includes the outer shape of a cylinder (see in particular Figure 4a , 4b , 8 and 9a to 9c). The capacitor 1 is particularly adapted for use in high - frequency applications.

[0057] The capacitor 1 includes a plurality of winding elements 2. In this embodiment, the capacitor 1 includes three winding elements 2 ( Figure 4a ). Of course, the capacitor 1 may include more than three winding elements 2, such as four, five or six winding elements 2. The capacitor 1 may also include less than three winding elements 2, such as two winding elements 2. In particular, the number of winding elements 2 is freely selectable. In other words, the construction described below can be implemented with any number of winding elements 2. As can be seen from Figure 8 , an insulator 9 is arranged between subsequent winding elements 2. For example, the insulator 9 may include a polymer.

[0058] The winding elements 2 are arranged axially, i.e., they are arranged along the main longitudinal axis 18 of the capacitor 1. The winding elements 2 are electrically connected in parallel. For this purpose, laminated busbars 3 are provided ( Figure 4b ). In this context, the term "laminated" means that the busbar 3 includes several layers (4a, 4b, 5; see for example Figure 6 ). The said layers, which will be explained in more detail later, overlap each other at least partially along the outer side of the winding element 2. In other words, the busbar 3 is a (laterally) overlapping busbar.

[0059] As can be seen from Figure 4b , the busbar 3 extends along the outer side of the winding element 2 (lateral busbar). The busbar 3 extends along the outer side of the winding element 2 from the first end side 10 of the capacitor 1 towards the second end side 11 of the capacitor 1 (see Figure 8 ). The busbar 3 at least partially covers the outer side of the corresponding winding element 2. Overall, the entire busbar 3 covers 20% to 50% of the outer side of the winding element 2. The busbar 3 is an internal busbar. In other words, the busbar 3 is arranged within the housing 16 of the capacitor 1 (see Figure 9c ).

[0060] The busbar 3 has a circular shape, which can be seen from Figure 5aObtained particularly well. The bus bar 3 has the shape of an (incomplete) cylindrical housing. The bus bar 3 has a shape adapted to the external shape and / or diameter of the corresponding winding element 2 of the capacitor 1 and the housing 16. The bus bar 3 can be used with any number of windings. The length of the bus bar 3 (axial extension, i.e., the extension along the main longitudinal axis 18 of the capacitor 1) is adapted to the number of winding elements 2.

[0061] The bus bar 3 includes the previously mentioned layers. In particular, the bus bar 3 includes, for example, a first layer (first pole) 4a and a second layer (second pole) 4b, which can be obtained from Figure 5b and 6 obtained. The layers 4a, 4b include copper. The layers 4a, 4b have a thickness between 0.3 mm and 1.5 mm, preferably 0.5 mm.

[0062] The layers 4a, 4b at least partially overlap. In particular, in a sub-region (overlap region 6) of the bus bar 3, the first layer 4a and the second layer 4b are stacked in the radial direction of the capacitor 1. The size of the overlap region 6 (axial and azimuthal extension) is such that the overlap region 6 covers 5% to 40% of the outside of the winding element 2. Preferably, the overlap region 6 covers 30% of the outside of the winding element 2.

[0063] The layers 4a, 4b are electrically insulated from each other by an insulating layer 5. The insulating layer 5 includes a polymer. The thickness of the insulating layer 5 is between 0.2 mm and 2.5 mm. Preferably, the total thickness of the insulating layer 5 is 0.5 mm.

[0064] The insulating layer 5 is arranged at least in the overlap region 6 between the first layer 4a and the second layer 4a. In fact, the insulating layer 5 extends in the azimuthal and / or axial direction beyond the overlap region 6, for example as can be seen from Figure 5b In other words, the azimuthal and / or longitudinal extension of the entire bus bar 3 including the layers 4a, 4b and the insulating layer 5 is greater than the azimuthal extension of the overlap region 6 (see, for example, Figure 7 and 8 ).

[0065] The first layer 4a is connected to the first pole 17a (e.g., negative pole) of the corresponding winding element 2 ( Figure 7 ). The second layer 4b is connected to the second pole 17b (e.g., positive pole) of the corresponding winding element 2.

[0066] For this purpose, the first layer 4a includes a plurality of first connection regions 7a. The second layer 4b includes a plurality of second connection regions 7b. In this embodiment, the corresponding layers 4a, 4b include three corresponding connection regions 7a, 7b. The number of corresponding connection regions 7a, 7b corresponds to the number of winding elements 2.

[0067] The first connection region 7a and the first layer 4a are integrally formed. The second connection region 7b and the second layer 4b are integrally formed. The corresponding connection regions 7a, 7b are in the shape of a strip. The corresponding connection regions 7a, 7b extend along the outer surface of the corresponding winding element 2 parallel to the layers 4a, 4b. In the intermediate sections 19a, 19b (see Figure 7 and 8 ), the corresponding layers 4a, 4b pass over into the corresponding connection regions 7a, 7b. The intermediate sections 19a, 19b extend perpendicular to the connection regions 7a, 7b.

[0068] The corresponding connection regions 7a, 7b are electrically and mechanically connected to the corresponding poles 17a, 17b of the winding element 2 for connecting the winding elements 2 in parallel. The connection regions 7a, 7b are connected to the poles 17a, 17b by means of connection elements 8 (such as metal strips) ( Figure 7 and 8 ). The connection regions 7a, 7b can be welded to the poles 17a, 17b.

[0069] In order to electrically and mechanically connect the bus bar 3 to the terminals 13a, 13b of the capacitor 1, the capacitor 1 further includes first and second connection members 12a, 12b ( Figure 8 and 9a ). The connection members 12a, 12b are arranged in the first end region 10 of the capacitor 1. The connection members 12a, 12b include, for example, metal strips. The connection members 12a, 12b are bent to connect the bus bar 3 arranged on the side surface of the winding element 2 to the terminals 13a, 13b arranged on the first end side 10 of the capacitor 1. A termination member 20 is arranged at the first end side 10 between the winding element 2 and the connection members 12a, 12b ( Figure 8 ). The termination member 20 includes an insulating material, such as a polymer.

[0070] In the first end section, the first connection member 12a is connected to the first layer 4a of the bus bar 3, for example, by welding ( Figure 8 and 9a ). Similarly, in the first end section, the second connection member 12b is connected to the second layer 4b of the bus bar 3, for example, by welding ( Figure 8 and 9a ).

[0071] In the second or opposite end section, the first connection member 12a is connected to the first terminal 13a, for example, by screws or welding ( Figure 9a ). Similarly, in the second or opposite end section, the second connection member 12b is connected to the second terminal 13b, for example, by screws or welding ( Figure 9a ).

[0072] The external insulator 14 is disposed on top of the connection members 12a, 12b on the side surface of the winding element 2 ( Figure 9b ). The external insulator 14 has a strip-like shape. The external insulator 14 has a circular shape and extends partially around the outer surface of the winding element 2 disposed near the first end side 10 of the capacitor 1. The external insulator 14 electrically insulates the connection members 12a, 12b from the housing 16 of the capacitor 1, and the housing 16 is disposed on the external insulator 14 and completely covers the winding element 2 and the bus bar 3 ( Figure 9c ).

[0073] Furthermore, on the first end side 10, the cover 15 is disposed on the connection members 12a, 12b ( Figure 9b and 9c ). The cover 15 includes two cutouts. The cutouts are adapted and arranged to receive the terminals 13a, 13b. The terminals 13a, 13b project from the cutouts in the axial direction. In this way, the electrical connection of the capacitor 1 can be achieved. The cover 15 serves as a termination element for the first end side 10 of the capacitor 1. A corresponding cover without cutouts is disposed on the second side surface 11 of the capacitor 1 (not shown explicitly).

[0074] By means of the construction described above, the parasitic inductance and resistance (ESRi, Rp, Rp2, ESLi, Lp, Lp2) can be greatly reduced independently of the width of the metallization film of the capacitor. Furthermore, considering that C is uniform, the impedance from the terminals 13a, 13b to each independent winding is uniform over all bandwidths. Therefore, the requirements summarized in Table 3 can be achieved.

[0075] Requirements Achieved by the prior art Achieved by the present invention A Low equivalent series resistance (ESR) No Yes B Frequency-stable ESR No Yes C Low equivalent series inductance (ESL) No Yes D Uniform internal current distribution No Yes E Internal resonance avoidance No Yes

[0076] Table 3: Requirements for capacitors in high-frequency applications as achieved by capacitors according to the prior art compared to capacitors according to the present invention.

[0077] Figure 10 A comparison of ESR measurements between a capacitor 100 according to the prior art (Figs. 3a, 3b) and a capacitor 1 according to the present disclosure (Figs. 4 to 9) is schematically shown. It can be observed that in the prior art, the ESR is not as frequency-stable as that of the capacitor according to the present invention. This is due to the higher skin effect, non-uniform internal current distribution, and internal resonance in the capacitor design based on the prior art.

[0078] In the drawings, elements of the same structure and / or function may be referred to by the same reference numerals. It is to be understood that the embodiments shown in the drawings are illustrative representations and are not necessarily drawn to scale.

[0079] Reference Mark

[0080] 1 Capacitor

[0081] 2 Winding Element

[0082] 3 Bus Bar

[0083] 4a First Layer

[0084] 4b Second Layer

[0085] 5 Insulation Layer

[0086] 6 Overlap Region

[0087] 7a First Connection Region

[0088] 7b Second Connection Region

[0089] 8 Connection Element

[0090] 9 Insulator

[0091] 10 First End Side of Capacitor

[0092] 11 Second End Side of Capacitor

[0093] 12a First Connection Member

[0094] 12b Second Connection Member

[0095] 13a First Terminal

[0096] 13b Second Terminal

[0097] 14 Insulation Element

[0098] 15 Cover

[0099] 16 Housing

[0100] 17a First Pole

[0101] 17b Second Pole

[0102] 18 Main Longitudinal Axis

[0103] 19a First Intermediate Portion

[0104] 19b Second Intermediate Portion

[0105] 20 Termination Element

[0106] 100 Capacitor

[0107] 101 Winding Element

[0108] 102 Copper Strip

[0109] 103 Terminal

[0110] 104 Screw

[0111] Ci Capacitance Unit - Capacitance Value

[0112] ESRi Capacitance Unit - Parasitic ESR

[0113] ESLi Capacitance Unit - Parasitic ESL

[0114] Cp Connector between Capacitance Units - Parasitic Capacitance

[0115] Rp, Rp2 Connector between Capacitance Units - Parasitic Resistance

[0116] Lp, Lp2 Connector between Capacitance Units - Parasitic Inductance

[0117] Rt Terminal - Parasitic Resistance

[0118] Lt Terminal - Parasitic Inductance.

Claims

1. A capacitor (1), comprising - a circular shape, - a plurality of winding elements (2), - a bus bar (3) which is adapted and arranged to connect the winding elements (2) in parallel, wherein the bus bar (3) is laminated and has a circular shape, wherein the bus bar (3) is a single overlapping bus bar and all the winding elements (2) are connected to the single overlapping bus bar (3), wherein the bus bar (3) includes a plurality of connection regions (7a, 7b) which are adapted and arranged to electrically and mechanically connect to the poles (17a, 17b) of the winding elements (2), and wherein the connection regions (7a, 7b) are connected to the poles (17a, 17b) by means of connection elements (8).

2. The capacitor (1) according to claim 1, wherein the bus bar (3) is arranged within the housing (16) of the capacitor (1).

3. The capacitor (1) according to claim 1 or claim 2, wherein the bus bar (3) includes a first layer (4a) and a second layer (4b) which at least partially extend along the outer sides of the respective winding elements (2), and wherein the bus bar (3) includes an overlapping region (6) in which the layers (4a, 4b) overlap each other.

4. The capacitor (1) according to claim 3, wherein the first layer (4a) is connected to the first pole (17a) of the respective winding element (2), and wherein the second layer (4b) is connected to the second pole (17b) of the respective winding element (2).

5. The capacitor (1) according to claim 3 or claim 4, wherein an insulating layer (5) is arranged between the first and second layers (4a, 4b) at least in the overlapping region (6).

6. The capacitor (1) according to any one of the preceding claims, wherein the bus bar (3) has a shape adapted to the diameter of the respective winding element (2).

7. The capacitor (1) according to any one of the preceding claims, wherein the respective connection regions (7a, 7b) are welded to the respective poles (17a, 17b) of the winding elements (2).

8. The capacitor (1) according to any one of claims 3 to 7, wherein the first layer (4a) includes a plurality of first connection regions (7a), and the second layer (4b) includes a plurality of second connection regions (7b), wherein the overlapping region (6) of the first layer (4a) and the respective first connection regions (7a) merge into each other, and wherein the overlapping region (6) of the second layer (4b) and the respective second connection regions (7b) merge into each other.

9. The capacitor (1) according to claim 8, wherein the number of the first connection regions (7a) corresponds to the number of the winding elements (2), and wherein the number of the second connection regions (7b) corresponds to the number of the winding elements (2).

10. The capacitor (1) according to any one of the preceding claims, wherein the bus bar (3) is adapted and arranged for high-frequency applications.

11. The capacitor (1) according to any one of the preceding claims, The busbar (3) is adapted to the number of winding elements (2) along the extension of the main longitudinal axis (18) of the capacitor (1).

12. The capacitor (1) according to any one of the preceding claims, wherein the busbar (3) extends along the outer side of the winding element (2) from the first end side (10) to the second end side (11) of the capacitor (1).

13. The capacitor (1) according to any one of the preceding claims, wherein the connecting element (8) comprises a metal strip.

14. Use of a capacitor (1) according to any one of the preceding claims in high-frequency applications.

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