Capacitor and inverter unit for powering an electric machine in a motor vehicle

Abstract

The present invention relates to a capacitor, in particular an intermediate circuit capacitor, comprising a first capacitive unit and a second capacitive unit, a first electrode with a first electrical conductor and a second electrical conductor, a second electrode with a third electrical conductor, wherein the first capacitive unit and the second capacitive unit are arranged side by side and separated from each other by a gap, wherein the first electrical conductor is configured to electrically contact the first capacitive unit at a first top surface, wherein the second electrical conductor is configured to electrically contact the second capacitive unit at a second top surface, and wherein the third electrical conductor is configured to electrically contact the first capacitive unit at a first bottom surface and the second capacitive unit at a second bottom surface.wherein the second electrical conductor is arranged in the gap between the first capacitive unit and the second capacitive unit in order to prevent the propagation of electromagnetic waves between the first capacitive unit and the second capacitive unit.

Description

State of the art

[0001] The present invention relates to a capacitor and an inverter unit, which are particularly designed to supply power to an electric machine in a motor vehicle.

[0002] In switching inverters and converters, DC link capacitors are used to buffer parasitic inductances. Different capacitor technologies are employed depending on temperature conditions, required lifespan, and power rating. The temperature occurring within a capacitor must not exceed a certain limit in the application, as this can lead to irreversible damage. Even below this absolute limit, the lowest possible maximum temperature should be aimed for to meet lifespan requirements. Furthermore, the capacitor design can have a significant impact on the overall system design and cost. It would be desirable to use a capacitor with increased power density, allowing for improved performance or, with the same performance, a reduction in capacitor volume. Disclosure of the invention

[0003] The capacitor according to the invention, with the features of claim 1, and the inverter unit according to the invention, with the features of claim 12, have the advantage that the electromagnetic behavior of the capacitor is improved, and thus the electrical losses of the capacitor can be reduced across the entire frequency range. This is achieved according to the invention by the capacitor having a first capacitive unit and a second capacitive unit. Furthermore, the capacitor has a first electrode with a first electrical conductor and a second electrical conductor, as well as a second electrode with a third electrical conductor. The electrical conductors are preferably power conductors, which can, for example, be made from sheet metal components to form busbars. The first capacitive unit and the second capacitive unit are arranged side by side and separated from each other by a gap.The first electrical conductor is configured to electrically contact the first capacitive unit at a first top surface. The second electrical conductor is configured to electrically contact the second capacitive unit at a second top surface, and the third electrical conductor is configured to electrically contact the first capacitive unit at a first bottom surface and the second capacitive unit at a second bottom surface. The second electrical conductor is positioned in the gap between the first and second capacitive units to prevent the propagation of electromagnetic waves between them. Particularly when used as an intermediate circuit capacitor, capacitors are subjected to high-frequency currents during operation.These high-frequency currents can cause electromagnetic oscillations within the capacitor, leading to increased power dissipation and heating. By dividing the capacitor into two capacitive units separated by a gap and a second electrical conductor running through it, the propagation of electromagnetic waves within the capacitor between the first and second capacitive units can be prevented. This reduces electrical losses within the capacitor, even at higher frequencies, allowing the capacitor to handle higher electrical currents with the same design. The first and second capacitive units can each contain one or more capacitive elements. A capacitive element could be, for example, a capacitive ceramic or a foil winding.Preferably, the capacitor comprises further capacitive units arranged side by side, separated from each other by gaps and electrically contacted by means of the first and second electrodes. The gaps are preferably arranged parallel to each other.

[0004] The dependent claims describe preferred embodiments of the invention.

[0005] The first electrode preferably has a first contact area for electrically contacting a first pole of a power switching module. Furthermore, the second electrode preferably has a second contact area for electrically contacting a second pole of the power switching module. Through the first and second contact areas, transient voltages from the power switching module can thus be introduced into the capacitor for filtering.

[0006] Preferably, the first and second contact areas run parallel to the gap. The high-frequency currents and electromagnetic waves propagate from the first and second contact areas along the capacitor. By arranging the gap parallel to the first and second contact areas, the propagation of electromagnetic waves throughout the entire capacitor can be reliably prevented. In particular, this reduces the propagation length within the capacitor, thereby preventing the formation of standing waves across the entire capacitor. Standing waves can propagate within the capacitor, especially when the length along which the electromagnetic waves propagate is equal to half their wavelength or a multiple thereof.

[0007] Preferably, the first contact area and the second contact area extend along the front side of the first capacitive unit, with the gap extending along the back side of the first capacitive unit. This allows the capacitor's loss resistance to be further reduced while ensuring easy contactability.

[0008] The first top surface is preferably arranged coplanarly with the second top surface. Furthermore, the first bottom surface is preferably arranged coplanarly with the second bottom surface. This enables efficient current flow and a compact design of the capacitor.

[0009] The gap preferably runs along a dividing plane that is perpendicular to the first top and the first bottom surfaces. This allows the volume of the gap to be reduced, thereby increasing the ratio of the first capacitive unit and the second capacitive unit to the total volume of the capacitor.

[0010] The second electrical conductor preferably runs between the third electrical conductor and the first capacitive unit, the second electrical conductor having at least one through-opening. Through this first through-opening, the third electrical conductor can be electrically connected to the first underside of the first capacitive unit. The overlapping routing of the second and third electrical conductors reduces the inductance of the capacitor. The second electrical conductor is preferably electrically insulated from the third electrical conductor and the first capacitive unit by means of an insulator. By routing the second electrical conductor between the third electrical conductor and the first capacitive unit, the second electrical conductor can be guided directly from the first underside through the gap to the second top side without crossing the third electrical conductor.

[0011] The through-holes are preferably circular. This ensures that the through-holes have little influence on the electrical conductivity of the second electrical conductor, allowing it to efficiently conduct high electrical currents.

[0012] Alternatively, the second electrical conductor preferably runs outside the third electrical conductor, the third electrical conductor having at least one second through-opening. The second electrical conductor extends through this second through-opening into the gap. Thus, the second and third electrical conductors can be arranged overlapping, enabling low-inductance contact between the first and second capacitive elements. The second through-opening is preferably located between the first and second capacitive elements.

[0013] The first electrode preferably completely overlaps the first top surface and the second top surface. Furthermore, the second electrode preferably completely overlaps the first bottom surface and the second bottom surface. This allows the first and second capacitive units to be contacted with low electrical losses. Additionally, the overlapping arrangement can shield the first and second capacitive units from electromagnetic interference.

[0014] Furthermore, the invention relates to an inverter unit, which is particularly suitable for supplying power to an electric motor in a motor vehicle. The inverter unit comprises at least one power switching module configured to convert direct current into alternating current. In generator mode of the electric motor, the inverter unit can also be configured to convert alternating current into direct current. The inverter unit further comprises a previously described capacitor for filtering parasitic inductances at the power switching module. Brief description of the drawings

[0015] Exemplary embodiments of the invention are described in detail below with reference to the accompanying drawings. The drawing shows: Fig. 1 a schematic perspective view of a capacitor according to a first embodiment of the invention, Fig. 2 a schematic side view of the capacitor according to the first embodiment of the invention, Fig. 3 a schematic perspective view of individual components of the capacitor according to the first embodiment of the invention, Fig. 4 a side view of a capacitor according to a second embodiment of the invention and Fig. 5 a line diagram of the power loss compared to the frequency of the current load of the capacitor according to the first embodiment of the invention compared to a capacitor according to the prior art. Embodiments of the invention

[0016] Preferably, all identical components, elements and / or units in all figures are provided with the same reference numerals.

[0017] The Fig. 1, Fig. 2, Fig. 3, Fig. 4 to Fig. Section 5 describes a capacitor 1 for an inverter unit in detail.

[0018] Fig. Figure 1 shows the capacitor 1 according to a first embodiment of the invention. The capacitor 1 has a first capacitive element 2 and a second capacitive element 3, which are arranged side by side and separated from each other by a gap 8. Furthermore, the capacitor 1 has a first electrode 10 and a second electrode 20.

[0019] The first electrode 10 comprises a first electrical conductor 11, which electrically contacts the first capacitive unit 2 at a first top surface 4a. Furthermore, the first electrode 10 has a second electrical conductor 12, which contacts the second capacitive unit 3 at a second top surface 4b. The second electrode 20 has a third electrical conductor 21, which electrically contacts the first capacitive unit 2 at a first bottom surface 5a and the second capacitive unit 3 at a second bottom surface 5b. The second electrical conductor 12 extends through the gap 8 between the first capacitive unit 2 and the second capacitive unit 3 to prevent the propagation of electromagnetic waves between the first capacitive unit 2 and the second capacitive unit 3.

[0020] Capacitor 1 has a first contact area 13 and a second contact area 23, which extend along a front face 6 of the first capacitive unit 2 and are arranged parallel to the gap 8. The first contact area 13 is configured to electrically contact a first pole of a power switching module. The second contact area 23 is configured to electrically contact a second pole of the power switching module. The first contact area 13 is part of the first electrode 10, and the second contact area 23 is part of the second electrode 20. The first contact area 13 and the second contact area 23 are located at an edge between the front face 6 and the first bottom face 5a of the first capacitive unit 2.

[0021] The first capacitive unit 2 and the second capacitive unit 3 are represented as cuboids of equal size. The first capacitive unit 2 and the second capacitive unit 3 can each have one or more capacitive elements, which can be implemented, for example, using electrolyte, film, ceramic, or multilayer technology.

[0022] The first top surface 4a and the first bottom surface 5a of the first capacitive unit 2 are aligned parallel to each other. Furthermore, the second top surface 4b and the second bottom surface 5b are aligned parallel to each other. The first top surface 4a and the second top surface 4b are aligned coplanarly to each other. Thus, the first bottom surface 5a and the second bottom surface 5b are also aligned coplanarly to each other. The front surface 6 and the back surface 7 of the first capacitive unit 2 are also aligned parallel to each other. The gap 8 between the first capacitive unit 2 and the second capacitive unit extends along a parting plane T (in Fig. 2 shown), which is arranged perpendicular to the first top surface 4a and the first bottom surface 5a.

[0023] The first electrical conductor 11 of the first electrode 10 runs from the first contact area 13 parallel to the front surface 6a of the first capacitive unit 2 to the first top surface 4a, where the first electrical conductor 11 has a 90° bend and now overlaps the first top surface 4b. The first electrical conductor 11 completely overlaps the first top surface 4a and makes electrical contact with it. The front surface 6 of the first capacitive unit 2 is separated from the first electrical conductor 11 by an air gap.

[0024] The second electrical conductor 12 of the first electrode 10 extends from the first contact area 13 along the first underside 5a of the first capacitive unit 2 to the gap 8. There, the second electrical conductor 12 changes its direction and then runs parallel to the gap 8. The second electrical conductor 12 is insulated from the rear side 7 of the first capacitive unit 2 and the second capacitive unit 3 by an air gap. In the area of ​​the second top side 4b, the second electrical conductor 12 again changes its direction and now overlaps the second top side 4b. The second electrical conductor 12 extends along the entire second surface 4b and electrically contacts the second capacitive unit 3 via the second surface 4b.

[0025] The third electrical conductor 21 of the second electrode 20 extends from the second contact area 23 in a plane along the first underside 5a and the second underside 5b. The third electrical conductor 21 is electrically insulated from the second electrical conductor 12 by means of an insulator 9. The separation of the first capacitive unit 2 and the second capacitive unit 3 by the gap 8, in which the second electrical conductor 12 is located, prevents or reduces the propagation of electromagnetic waves between the first capacitive unit 2 and the second capacitive unit 3. In particular, the resonant frequencies of the capacitor 1 can be shifted to higher frequencies, thus significantly reducing the power dissipation of the capacitor 1 and allowing it to be subjected to higher electrical currents without overheating.

[0026] Fig. Figure 2 shows a side view of capacitor 1 according to the first embodiment of the invention. Fig. Figure 2 clearly shows that the insulator 9 is positioned between the first capacitive unit 2 and the second electrical conductor 12, the second capacitive unit 3 and the second electrical conductor 12, and the second electrode 20 and the second electrical conductor 12 to electrically isolate these components from each other. The overlapping, closely spaced routing of the second electrical conductor 12 and the third electrical conductor 21 along the first underside 5a can reduce the inductance of the capacitor 1.

[0027] The second electrical conductor 12 also runs electrically insulated between the third electrical conductor 21 and the second capacitive unit 3, so that theoretically further capacitive units can be connected at its end separated by a gap.

[0028] Fig. Figure 3 shows a perspective view of the capacitor 1 according to the first embodiment, with the first capacitive unit 2 and the second capacitive unit 3 hidden. Furthermore, the insulator 9 between the first capacitive unit 2 and the second electrical conductor 12 is hidden. Thus, the first through-holes 14 in the second electrical conductor 12 are visible. The first through-holes 14 are circular and allow the passage of the third electrical conductor 21 to electrically contact the first bottom surface 5a and the second bottom surface 5b. Six first through-holes 14 are arranged on both the first bottom surface 5a and the second bottom surface 5b in a 2x3 pattern.

[0029] The insulator 9 between the second capacitive unit 3 and the second electrical conductor 12 has circular recesses for the third electrical conductor 21, allowing it to electrically contact the second capacitive unit 3 on the second underside 5b. The insulator 9 between the second electrical conductor 12 and the first capacitive unit 2 is preferably identical to the insulator 9 (not shown) between the second capacitive unit 3 and the second electrical conductor 12.

[0030] Fig. Figure 4 shows a second embodiment of the invention. The second embodiment is similar to the first embodiment and differs essentially in the routing of the second electrical conductor 12 and the third electrical conductor 21.

[0031] In the second embodiment, the third electrical conductor 21 extends from the second contact area 23 in a plane along the first underside 5a and the second underside 5b. No second electrical conductor 12 is arranged between the third electrical conductor 21 and the first underside 5a or the second underside 5b.

[0032] The second electrical conductor 12 extends from the first contact area 13, which is located below the second contact area 23, outside the third electrical conductor 21 parallel to the first underside 5a. Thus, the third electrical conductor 21 runs between the second electrical conductor 12 and the first capacitive unit 2.

[0033] In the area of ​​the gap 8, the third electrical conductor 21 has a second through-opening 24. The second electrical conductor 12 extends through the second through-opening 24 to cross the third electrical conductor 21 and through the gap 8 to the second top surface 4b, making electrical contact with it.

[0034] The third electrical conductor 21 can also have a second through-opening 24 in the area of ​​the second contacting area 23, so that the first electrical conductor 11 can extend from the first contacting area 13 through the third electrical conductor 21 parallel to the front side in order to subsequently electrically contact the first top surface 5a of the first capacitive unit 2.

[0035] Fig.Figure 5 shows a loss resistance R as a function of a frequency f of the capacitor 1 according to the invention compared to a reference capacitor 100 according to the prior art. The loss resistance R describes the equivalent series resistance (ESR) of the capacitor 1 and the reference capacitor 100. The frequency f refers to the stimulus of the impedance analysis.

[0036] The comparison capacitor 100 is similar to the capacitor 1 according to the invention in terms of contact and geometric dimensions, but has no gap 8 and no second electrical conductor 12.

[0037] The loss resistance R of capacitor 1 and the comparator capacitor 100 are negligibly small up to a frequency of about 10 kHz.

[0038] For the comparator capacitor 10, the loss resistance R increases constantly between 10 kHz and 150 kHz, with the comparator capacitor 10 exhibiting a maximum loss resistance R at a frequency f of approximately 150 kHz. This frequency f of the comparator capacitor 100 corresponds to its resonant frequency, so that the comparator capacitor 100 forms a standing electromagnetic wave at a frequency of approximately 150 kHz.

[0039] The loss resistance R of the capacitor 1 according to the invention increases slowly from 20 kHz up to a frequency f of approximately 300 kHz, with the capacitor 1 exhibiting a maximum loss resistance R at the frequency f of 300 kHz. For frequencies f > 300 kHz, the loss resistance R of the capacitor 1 decreases slightly but remains at an elevated level. The loss resistance R of the capacitor 1 remains permanently lower than the loss resistance R of the reference capacitor 100 for frequencies above 5 kHz.

[0040] By dividing capacitor 1 into the first capacitive unit 2 and the second capacitive unit 3, which are separated from each other by the gap 8 and the second electrical conductor 12, the length of capacitor 1 along which electromagnetic waves can propagate can be halved. This essentially doubles the resonant frequency of capacitor 1 compared to reference capacitor 100. Due to the higher resonant frequency, the loss resistance R in capacitor 1 increases more slowly in the range between 10 kHz and 300 kHz compared to reference capacitor 100.Since the current spectrum of an inverter unit for powering an electric motor in a motor vehicle is typically between 20 kHz and 200 kHz during operation, the reduced loss resistance R of capacitor 1 compared to the reference capacitor 100 significantly reduces its power dissipation. This allows capacitor 1 to handle higher currents without overheating. Alternatively, with the same current load, capacitor 1 can be made smaller to reduce costs and space requirements.

Claims

[1] Capacitor, in particular intermediate circuit capacitor, comprising - a first capacitive unit (2) and a second capacitive unit (3), - a first electrode (10) with a first electrical conductor (11) and a second electrical conductor (12), - a second electrode (20) with a third electrical conductor (21), - wherein the first capacitive unit (2) and the second capacitive unit (3) are arranged next to each other and are separated from each other by a gap (8), - wherein the first electrical conductor (11) is arranged to electrically contact the first capacitive unit (2) at a first top surface (4a), - wherein the second electrical conductor (12) is arranged to electrically contact the second capacitive unit (3) on a second top surface (4b), - wherein the third electrical conductor (21) is arranged to electrically contact the first capacitive unit (2) on a first underside (5a) and the second capacitive unit (3) on a second underside (5b), - wherein the second electrical conductor (12) is arranged in the gap (8) between the first capacitive unit (2) and the second capacitive unit (3) to prevent the propagation of electromagnetic waves between the first capacitive unit (2) and the second capacitive unit (3). [2] Capacitor according to claim 1, wherein the first electrode (10) has a first contacting area (13) for electrical contacting a first pole of a power switching module and wherein the second electrode (20) has a second contacting area (23) for electrical contacting a second pole of the power switching module. [3] Capacitor according to claim 2, wherein the first contact area (13) and the second contact area (23) run parallel to the gap (8). [4] Capacitor according to one of claims 2 or 3, wherein the first contacting area (13) and the second contacting area (23) extend along a front side (6) of the first capacitive unit (2), wherein the gap (8) extends along a rear side (7) of the first capacitive unit (2). [5] Capacitor according to one of the preceding claims, wherein the first top surface (4a) is arranged coplanar to the second top surface (4b) and wherein the first bottom surface (5a) is arranged coplanar to the second bottom surface (5b). [6] Capacitor according to one of the preceding claims, wherein the gap (8) extends along a separating plane (T) which is arranged perpendicular to the first top (4a) and first bottom (5a). [7] Capacitor according to one of the preceding claims, wherein the second electrical conductor (12) runs along the first underside (5a). [8] Capacitor according to claim 7, wherein the second electrical conductor (12) runs between the third electrical conductor (21) and the first capacitive unit (2) and wherein the second electrical conductor (12) has at least one first through-hole (14), wherein the third electrical conductor (21) and the first underside (5a) of the first capacitive unit (2) can be electrically contacted through the first through-hole (14). [9] Capacitor according to claim 8, wherein the first through-opening (14) is circular. [10] Capacitor according to claim 7, wherein the second electrical conductor (12) extends outside the third electrical conductor (21) and wherein the third electrical conductor (21) has at least one second through-opening (24), wherein the second electrical conductor (12) extends through the second through-opening (24) into the gap (8). [11] Capacitor according to any of the preceding claims, wherein the first electrode (10) completely overlaps the first top surface (4a) and the second top surface (4b) and / or wherein the second electrode (20) completely overlaps the first bottom surface (5a) and the second bottom surface (5b). [12] Inverter unit, in particular for supplying power to an electric machine in a motor vehicle, comprising at least one power switching module configured to convert a direct current into an alternating current, and a capacitor (1) according to one of the preceding claims for filtering parasitic inductances at the power switching module.

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