Adaptive filter with y capacitors for a 3-phase DC on-board electrical system

Abstract

The invention relates to a current converter (1, 1a, 1b) for an on-board electrical system (101) of an electrically driveable vehicle (100), comprising a first line (2) for a first potential (3), a second line (4) for a second potential (5), a third line (6) for a reference potential (7) and a filter unit (8) which has has first connector (10) connected to the first line (2), second connector (11) connected to the second line (4), a third connector (12) connected to the third line (6), a first capacitor (13) via which a first current path (14) is directed from the first connector (10) to the third connector (12), a second capacitor (15) via which a second current path (16) is directed from the second connector (11) to the third connector (12), a third capacitor (17) forming an electrically conductive connection between a central node (18), lying between the first capacitor (13) and the second capacitor (15), a the third connector (12), and a switch device (19) designed such that, according to control information (20), it switches between a first filter mode in which the first current path (14) and the second current path (16) are guided past the third capacitor (17) to the third connector (12) in the first filter mode, and a second filter mode in which the first current path (14) and the second current path (16) are guided via the third capacitor (17) to the third connector (12).

Description

[0001] ADAPTIVE FILTER WITH Y-CAPACITERS FOR 3-WIRE DC ON-BOARD NETWORK

[0002] The present invention relates to a power converter for an on-board power system of an electrically driven vehicle, comprising a first line for a first potential, a second line for a second potential, a third line for a reference potential and a filter device which has a first terminal connected to the first line, a second terminal connected to the second line, a third terminal connected to the third line, a first capacitor via which a first current path is led from the first terminal to the third terminal, a second capacitor via which a second current path is led from the second terminal to the third terminal, and a switching device which is designed to switch between a first filter mode and a second filter mode as a function of control information.

[0003] The invention also relates to an on-board network for an electrically powered vehicle.

[0004] DE 10 2017 220 982 A1 discloses a traction network in an electric or hybrid vehicle. The traction network comprises a high-voltage battery connected to a pulse-controlled inverter via a positive high-voltage line and a negative high-voltage line. A Y capacitor is connected to each of the positive and negative high-voltage lines. A switching element is assigned to the Y capacitors, which can be controlled by a control unit depending on at least one operating state.

[0005] DE 10 2021 003 180 A1 discloses an electrical system for an electrically operated vehicle, comprising a first electrical potential line and a second electrical potential line, between which the electrical system is supplied with a direct current. The electrical system has two first interference suppression capacitors, which are electrically connected in series and are each electrically coupled to the potential lines via a terminal. The electrical system further comprises a further interference suppression capacitor and a switch.

[0006] In electrically powered vehicles, on-board electrical systems, particularly high-voltage on-board electrical systems, are typically designed as IT systems in which a first and second potential of a traction battery are isolated from a reference potential, particularly a vehicle chassis potential. Power converters used in such on-board electrical systems and whose first and second lines can be connected to the first and second potential of the traction battery can generate high-frequency interference signals during operation, which must be filtered by means of a filter device for reasons of electromagnetic compatibility. Such a filter device typically has two capacitors, which serve in particular to divert a common-mode current on the first and second lines to a third line at the reference potential.

[0007] As the vehicle electrical system voltage increases, which corresponds to the difference between the first and second potentials, the amount of energy stored in the first and second capacitors of the filter device also increases with the square of the vehicle electrical system voltage. Relevant standards, such as ISO 6469-3, limit this amount of energy to a specified value. This allows the electrical charges stored in the capacitors and dissipating via the third line to be kept below a limit that is dangerous to the human body in the event of an insulation fault, particularly during charging of the traction battery. Therefore, when designing power converters, an energy budget specified by the design of the vehicle electrical system must be adhered to.

[0008] It has already been proposed to provide a switch in a current path between the capacitors and the third terminal in order to connect the capacitors to the third terminal of the filter device or the reference potential in a first filter mode and to separate them from it in a second filter mode. However, such switches have parasitic capacitances whose magnitude is difficult to control due to manufacturing limitations. In the second filter mode, this leads to a voltage distribution across the capacitors and the switch that is difficult to predict. This significantly complicates the precise determination of the energy budget to ensure electrical safety and, in conjunction with additional filter inductances, may lead to a very imprecisely predictable position of the filter frequencies.

[0009] The invention is based on the object of providing an improved possibility for operating a power converter in an on-board network of an electrically driven vehicle.

[0010] This object is achieved according to the invention in a power converter of the type mentioned at the outset in that the filter device further comprises a third capacitor which forms an electrically conductive connection between a center node which lies between the first capacitor and the second capacitor and the third terminal, wherein the first current path and the second current path are guided past the third capacitor to the third terminal in the first filter mode and via the third capacitor to the third terminal in the second filter mode.

[0011] The power converter according to the invention has a first line for a first potential, a second line for a second potential and a third line for a reference potential. The power converter further has a filter device. The filter device has a first terminal, a second terminal and a third terminal. The first terminal is connected to the first line. The second terminal is connected to the second line. The third terminal is connected to the third line. The filter device further has a first capacitor, a second capacitor and a third capacitor. A first current path is led from the first terminal to the third terminal via the first capacitor. A second current path is led from the second terminal to the third terminal via the second capacitor. The third capacitor forms an electrically conductive connection between a center node and the third terminal.The center node lies between the first capacitor and the second capacitor. The filter device further comprises a switching device. The switching device is configured to switch between a first filter mode and a second filter mode depending on control information. In the first filter mode, the first current path and the second current path are routed past the third capacitor to the third terminal. In the second filter mode, the first current path and the second current path are routed via the third capacitor to the third terminal.

[0012] In the power converter according to the invention, the first and second current paths are routed past the third capacitor in the first filter mode, so that the capacitances of the first capacitor and the second capacitor can act essentially as Y capacitances. This enables particularly efficient suppression of common-mode interference on the first line and the second line. In the second filter mode, the first current path and the second current path are routed via the third capacitor. The third capacitor can thus advantageously provide a well-defined capacitance between the center node and the third terminal, which allows precise determination of an energy budget when designing the power converter. At the same time, the effective Y capacitances of the filter device can be reduced in the second filter mode compared to the first filter mode.

[0013] With regard to electrical safety, the temporal progression of a body current in the event of an insulation fault can also be more precisely limited, with additional advantage, since by specifying the capacitance of the third capacitor, the equivalent capacitance in the second filter mode and thus the discharge time constant resulting from the equivalent capacitance and the body resistance can be placed in a range with no or low risk of fibrillation. A further advantage of the converter according to the invention is that, due to the presence of the third capacitor in the second filter mode, the capacitances of the first capacitor and the second capacitor also partially act as X-capacitances, thus enabling greater suppression of differential mode interference.

[0014] The power converter according to the invention can be designed as an inverter, a DC-DC converter, or an active rectifier. The power converter according to the invention can further comprise a housing in which at least the first line, the second line, the third line, and the filter device are accommodated. The third line can be electrically conductively connected to the housing. The reference potential can therefore also be considered the housing potential.

[0015] Typically, the first potential differs from the second potential. Preferably, the first potential is greater than the second potential. The reference potential is preferably between the first potential and the second potential. The reference potential can also be understood as ground potential. In a preferred embodiment, the first line and the second line are each designed entirely or at least in sections as solid busbars. The first and the second line can be connected to a DC voltage terminal of the power converter, on which, in particular, a connection device for electrically contacting the power converter with a DC voltage source is formed. The filter device is preferably arranged on the DC voltage terminal side.

[0016] The third line is not necessarily designed as a busbar. The third line can be formed by a cable, a ground plane, or by a fastening means by which the filter device is fastened in the power converter, in particular to the housing. The first capacitor, the second capacitor, and the third capacitor can each have a first terminal and a second terminal, between which the capacitance of the capacitor is provided. The first terminal of the first capacitor can be connected to the first terminal of the filter device. The second terminal of the second capacitor can be connected to the second terminal of the filter device.

[0017] The first capacitor, the second capacitor, and the third capacitor can each be formed by a capacitor component or a plurality of interconnected capacitor components. The switching device is preferably a semiconductor switching device, which in particular has one or more transistor structures. Alternatively, it is also possible for the switching device to be an electromechanical switching device, which, for example, has one or more relays.

[0018] Preferably, in the first filter mode, an electrically conductive connection from the center node to the third terminal completely bypasses the third capacitor. However, it is also possible for an additional current path to be routed along the third capacitor in the first filter mode. This additional current path preferably has a higher impedance than the sections of the first and second current paths that bypass the third capacitor.

[0019] Preferably, the filter device of the power converter according to the invention is configured to set a higher pole frequency for filtering a common-mode current on the first line and the second line in the second filter mode along the first current path and the second current path than in the first filter mode. In the event of a first insulation fault, the discharge time constant, which results from the effective Y-capacitance and a body resistance, can thereby be advantageously modified. In a preferred embodiment of the power converter according to the invention, the center node is a common node of a terminal of the third capacitor facing away from the third terminal, a terminal of the first capacitor facing away from the first terminal and / or facing the second capacitor, and a terminal of the second capacitor facing away from the second terminal and / or facing the first capacitor.The terminal of the third capacitor facing away from the third terminal can correspond to the second terminal of the third capacitor. The terminal of the first capacitor facing away from the first terminal of the filter device or facing the second capacitor can correspond to the second terminal of the first capacitor. The terminal of the second capacitor facing away from the second terminal of the filter device or facing the first capacitor can correspond to the first terminal of the second capacitor.

[0020] Preferably, a terminal of the third capacitor facing away from the center node is connected to the third terminal. The terminal of the third capacitor facing away from the center node can correspond to the first terminal of the third capacitor.

[0021] With regard to the switching device of the power converter according to the invention, it is preferred if the switching device has a first terminal and a second terminal and a switching path that can be controlled as a function of the control information.

[0022] The first terminal of the switching device can be connected to the center node and / or to the third capacitor, in particular to its second terminal. Preferably, the first terminal of the switching device, the center node, and the second terminal of the third capacitor form a common circuit node. The second terminal of the switching device can be connected to the third terminal of the filter device and / or to the third capacitor, in particular to its first terminal. Preferably, the second terminal of the switching device, the third terminal of the filter device, and the first terminal of the third capacitor form a common circuit node.

[0023] In a preferred development, it is further provided that the switching device is designed to switch the switching path conductive for adopting the first filter mode and / or to switch it blocking for adopting the second filter mode.

[0024] In general, it is advantageous in the power converter according to the invention if the switching device is connected in parallel with the third capacitor. Then, in the first filter mode, the first current path and the second current path can be routed past the third capacitor via the switching device.

[0025] In order to filter common-mode currents particularly efficiently in the first filter mode, the switching device can be designed as a bidirectionally conducting and / or blocking switch.

[0026] Regarding the dimensioning of the capacitors, the following can be provided: The capacitance of the third capacitor can be smaller than the capacitance of the first capacitor. The capacitance of the third capacitor can be smaller than the capacitance of the second capacitor.

[0027] The capacitances of the first and second capacitors can be equal. This allows for a particularly symmetrical voltage distribution across the first and second capacitors.

[0028] In order to enable efficient suppression of differential mode interference in the first filter mode as well, the filter device can further comprise a fourth capacitor which is connected in parallel to the first capacitor and the second capacitor to the first terminal of the filter device and to the second terminal of the filter device. In other words, the fourth capacitor can provide a fixed X-capacitance. In a preferred embodiment of the power converter according to the invention, the filter device has a printed circuit board. The first to third capacitors can be arranged on the printed circuit board. The fourth capacitor can also be arranged on the printed circuit board. The first to third terminals of the filter device can be arranged on the printed circuit board. The switching device can be arranged on the printed circuit board.

[0029] The power converter according to the invention may further comprise an intermediate circuit capacitor connected between the first line and the second line.

[0030] The power converter according to the invention can further comprise a converter circuit connected between the first line and the second line. The converter circuit can comprise power semiconductor switches, which are connected in particular as a switching cell, power bridge, or B6 bridge circuit, in order to convert the voltage present between the first line and the second line in a switching mode. The filter device is preferably arranged on the side of the intermediate circuit capacitor facing away from the converter circuit.

[0031] The power converter according to the invention can further comprise inductive filter elements that act as series inductors in the first line and the second line and are arranged on the intermediate circuit capacitor side and / or the DC voltage input side, in particular spatially close to the filter device. The filter elements can be formed by ferrite cores, for example nanocrystalline cores, iron powder cores, or other cores made of magnetic material, around the lines.

[0032] Preferably, parasitic inductances along the first line and the second lines between the DC voltage connection on the one hand and the first connection and the second connection of the filter device or the DC voltage connection-side filter elements on the other hand are lower than parasitic inductances between the first connection and the second connection of the filter device or the intermediate circuit capacitor-side filter elements on the one hand and the intermediate circuit capacitor on the other hand.

[0033] The object underlying the invention is further achieved by an on-board electrical system for an electrically driven vehicle, comprising at least one previously described power converter, a traction battery, a charging device which can be connected to an electrical network external to the vehicle for charging or discharging the traction battery, and a control device which is configured to provide the control information for adopting the second filter mode if and / or as long as the charging device is connected to the electrical network external to the vehicle.

[0034] Thus, the first filter mode can advantageously be specified in a ferry operation of the vehicle or the on-board network and the second filter mode can be specified in a charging operation.

[0035] The traction battery preferably has a nominal voltage of at least 400 volts, preferably at least 600 volts, particularly preferably at least 800 volts.

[0036] A power converter of the vehicle electrical system can be designed as an inverter which is designed to electrically supply an electrical machine, in particular a permanent or electrically excited synchronous machine, an axial flux motor or an asynchronous machine, with a multi-phase alternating voltage for driving the vehicle.

[0037] A power converter of the vehicle electrical system can form part of the charging device and be configured to convert a direct or alternating voltage provided by the vehicle's external electrical network into a direct voltage for charging the traction battery. A power converter of the vehicle electrical system can be configured as a DC-DC converter configured to couple the vehicle electrical system to another vehicle electrical system, in particular a low-voltage vehicle electrical system. A potential of the low-voltage vehicle electrical system can correspond to the reference potential.

[0038] The vehicle electrical system may further comprise an electrical line, for example an electrically conductive fastening or a ground strap, by means of which the third line of the at least one power converter is electrically conductively connected to a body of the vehicle.

[0039] Further advantages and details of the present invention will become apparent from the exemplary embodiments described below and from the drawings. These are schematic representations and show:

[0040] Fig. 1 is a circuit diagram of an embodiment of the power converter according to the invention;

[0041] Fig. 2 is a schematic diagram of the power converter according to the embodiment; and

[0042] Fig. 3 is a block diagram of an embodiment of the on-board network according to the invention in a vehicle.

[0043] Fig. 1 is a circuit diagram of an embodiment of a power converter 1 .

[0044] The power converter 1 has a first line 2 for a first potential 3, a second line 4 for a second potential 5, and a third line 6 for a reference potential 7, which can also be regarded as ground potential. For example, the first potential 3 is higher than the second potential 5 and the power converter 1 is designed to be operated with a potential difference between the first potential 3 and the second potential 5 of 800 volts. The reference potential 7 is located, for example, between the first potential 3 and the second potential 5. The power converter 1 further has a filter device 8. Specifically, the filter device 8 serves as an interference filter, i.e. to improve the electromagnetic compatibility of the power converter 1, and is preferably arranged close to a DC voltage connection 9.

[0045] The filter device 8 has a first terminal 10 connected to the first line 2, a second terminal 11 connected to the second line 4, and a third terminal 12 connected to the third line 6. The filter device also has a first capacitor 13, via which a first current path 14 is led from the first terminal 10 to the third terminal 12, and a second capacitor 15, via which a second current path 16 is led from the second terminal 11 to the third terminal 12. The current paths 14, 16 are illustrated purely schematically in Fig. 1 by dashed lines. In addition, the filter device has a third capacitor 17, which forms an electrically conductive connection between a center node 18, which lies between the first capacitor 13 and the second capacitor 15, and the third terminal 12.

[0046] Furthermore, the filter device 8 has a switching device 19. The switching device 19 is configured to switch between a first filter mode and a second filter mode depending on control information 20. In the first filter mode, the first current path 14 and the second current path 16 are routed past the third capacitor 17 to the third terminal 12. In the second filter mode, the first current path 14 and the second current path 16 are routed via the third capacitor 17 to the third terminal 12.

[0047] The capacitances Ci, C2 of the first capacitor 13 and the second capacitor 15 can act as Y-capacitances for filtering common-mode interference on the first and second lines 2, 4 in the first filter mode. In the second filter mode, the capacitances Ci, C2 together with the capacitance C3 of the third capacitor 17 form a capacitor network which, in particular, provides a well-defined capacitance between the center node 18 and the third terminal 12 and additionally provides an X-capacitance for filtering differential-mode interference on the first line 2 and the second line 4. The filter device 8 is designed to set a higher pole frequency for filtering a common-mode current on the first line 2 and the second line 4 in the second filter mode along the first current path 14 and the second current path 16 than in the first filter mode.

[0048] The first capacitor 13 has a first terminal 13a and a second terminal 13b. The second capacitor 15 has a first terminal 15a and a second terminal 15b. The third capacitor has a first terminal 17a and a second terminal 17b. The switching device has a first terminal 19a and a second terminal 19b, between which a switching path is formed that can be controlled depending on the control information 20.

[0049] In terms of circuitry, the filter device 8 in the present exemplary embodiment is implemented in particular by the switching device 19 being connected in parallel with the third capacitor 17 and being configured to switch the switching path to conduct to enter the first filter mode and to block to enter the second filter mode. In detail, the first terminal 19a of the switching device 19 is connected to the second terminal 17b of the third capacitor 17, and the second terminal 19b of the switching device 19 is connected to the first terminal 17a of the third capacitor 17.

[0050] In addition, the first terminal 17a of the third capacitor 17, facing away from the center node 18, is connected to the third terminal 12 of the filter device 8. The second terminal 17b of the third capacitor 17 is connected to the center node 18. In particular, the third terminal 12 of the filter device 8, the first terminal 17a of the third capacitor 17, and the second terminal 19b of the switching device 19 form a common circuit node of the filter device 8. Accordingly, the center node 18, the second terminal 17b of the third capacitor 17, and the first terminal 19a of the switching device 19 form a common circuit node of the filter device 8.

[0051] In the present embodiment, the first terminal 13a of the first capacitor 13 is connected to the first terminal 10 of the filter device 8. The second terminal 15b of the second capacitor 15 is connected to the second terminal 11 of the filter device 8. The center node 18 further forms a common node of the second terminal 13b of the first capacitor 13, the first terminal 15a of the second capacitor 15, and the second terminal 17b of the third capacitor 17.

[0052] If in the present embodiment the switching device 19 assumes the second filter mode by opening the switching path, the following equivalent capacitance Ceq results for the filtering of common-mode interference:

[0053] Assuming that Ci = C2 = Co are equal, it follows that:

[0054] If C3 is now expressed as a ratio to Co by C3 = k Co, it follows that: By choosing k < 1, the equivalent capacitance for filtering common-mode noise in the second filter mode can be significantly reduced, which correspondingly reduces the amount of energy to be considered for determining an energy budget.

[0055] Optionally, according to the present exemplary embodiment, a fourth capacitor 21 with a first terminal 21a and a second terminal 21b of the filter device 8 is provided. The fourth capacitor 21 is connected in parallel to the first capacitor 13 and the second capacitor 15 to the first terminal 10 of the filter device 8 and to the second terminal 11 of the filter device 8. The first terminal 10 of the filter device 8, the first terminal 13a of the first capacitor 13, and the first terminal 21a of the fourth capacitor 21 form a common circuit node. Furthermore, the second terminal 11 of the filter device 8, the second terminal 15b of the second capacitor 15, and the second terminal 21b of the fourth capacitor 21 form a common circuit node. The fourth capacitor 21 provides a fixed X-capacitance.

[0056] Fig. 1 further shows an intermediate circuit capacitor 40 connected between the first line 2 and the second line 4, and a converter circuit 41 connected between the first line 2 and the second line 4. As can be seen, the filter device 8 is arranged on the side of the intermediate circuit capacitor 40 facing away from the converter circuit 41.

[0057] The power converter 1 further comprises four inductive filter elements 42, 43, 44, 45, which act as series inductances in the lines 2, 4 and are formed, for example, by ferrite cores around the lines 2, 4. The filter elements 42 to 45 are arranged close to the filter device 8. The filter elements 42, 44 are arranged on the DC voltage input side with respect to the filter device 8. The filter elements 43, 45 are arranged on the intermediate circuit capacitor side with respect to the filter device 8. Furthermore, parasitic inductances Li are shown schematically in Fig. 1. P, Lin along the first line 2 or the second line 4 between the DC voltage connection 9 and the filter device 8 or the filter elements 42, 44 as well as parasitic inductances L2 P , L2n along the first line 2 or the second line 4 between the filter device 8 or the filter elements 43, 45 and the intermediate circuit capacitor 40. The arrangement of the filter device 8 can be selected such that Li P and Lin less than L2 P and L2n to enable the most efficient filtering possible.

[0058] Fig. 2 is a schematic diagram of the power converter 1 according to the embodiment.

[0059] The filter device 8 has a printed circuit board 50 on which the terminals 10, 11, 12, the capacitors 13, 15, 17, 21, and the switching device 19 are arranged. The first line 2 and the second line 4 are each formed by solid busbars 51, 52, which are contacted with the terminals 10, 11 on the printed circuit board 50. The DC voltage terminal 9, designed as a connection device 53, is connected to a first end of the busbars 51, 52. The converter circuit 41 is connected to a second end of the busbars 51, 52. The intermediate circuit capacitor 40 is also contacted with the busbars 51, 52 and, based on the length of the busbars 51, 52, can be located closer to the converter circuit 41 than to the filter device 8.

[0060] The third terminal 12 of the filter device 8 is not connected to the busbars 51, 52, but is connected to a housing 55 of the power converter 1 by means of a fastening means 54, which forms the third line 6. The reference potential 7 can therefore also be considered the housing potential. The lines 2, 4 or the busbars 51, 52, the filter device 8, the intermediate circuit capacitor 40, and the converter circuit 41 are housed in the housing 55. The power converter 1 can be designed as an inverter, a DC-DC converter, or an active rectifier. The converter circuit 41 has suitable semiconductor switching elements for this purpose.

[0061] Fig. 3 is a block diagram of an embodiment of an on-board network 101 in a vehicle 100.

[0062] The on-board electrical system 101 includes a traction battery 102 with a nominal voltage of, for example, 800 volts, a charging device 103 that can be connected to an external electrical network 104 for charging or discharging the traction battery 102, and a control device 105 configured to provide the control information 20. The on-board electrical system 101 can be considered a high-voltage electrical system because its operating voltage is regularly above 60 V.

[0063] The vehicle electrical system 101 includes a power converter 1 according to the previously described embodiment, which is designed as an inverter. The power converter 1 is configured to electrically supply an electric machine 106 of the vehicle electrical system 101 with a multiphase alternating voltage for driving the vehicle 100. The electric machine 106 is, for example, a permanently or electrically excited synchronous machine, an axial flux machine, or an asynchronous machine.

[0064] The vehicle electrical system 101 has a further power converter 1a according to the previously described embodiment, which is designed as an active rectifier or as a DC-DC converter and forms part of the charging device 103. The power converter 1a is configured to convert a DC or AC voltage provided by the vehicle-external electrical network 104 into a DC voltage for charging the traction battery 102.

[0065] The vehicle electrical system 101 has a further power converter 1b according to the previously described embodiment, which is designed as a DC-DC converter. The power converter 1b is configured to couple the vehicle electrical system 101 to a further vehicle electrical system 107 of the vehicle 100. The further vehicle electrical system 107 is, for example, a low-voltage vehicle electrical system with an operating voltage of less than 60 volts, for example, 12 volts, 24 volts, or 48 volts.

[0066] The control device 105 communicates with the charging device 103 via a signal line symbolized by a double arrow. The control device 105 is configured to provide the power converters 1, 1a, 1b with the control information 20 for entering the second filter mode if and as long as the charging device 103 is connected to the vehicle-external electrical network 104. The second filter mode can therefore be understood in particular as a charging mode.

[0067] The control information 20, however, is provided in particular for entering the first filter mode when the charging device 103 is disconnected from the vehicle-external electrical network 104 and when the vehicle 100 is moving. The first filter mode can therefore also be considered a driving mode.

[0068] The vehicle electrical system 101 can further comprise electrical conductors by means of which the third line 6 (see Fig. 1) of a respective power converter 1, 1a, 1b is electrically connected to a body 108 of the vehicle 101, so that the reference potential 7 can also be considered a body potential. This is simultaneously one of the potentials of the further vehicle electrical system 107.

[0069] The vehicle 100 can accordingly be designed as a battery electric vehicle (BEV) or as a hybrid vehicle.

Claims

Patent claims 1 . Power converter (1, 1 a, 1 b) for an on-board network (101) of an electrically driven vehicle (100), comprising a first line (2) for a first potential (3), a second line (4) for a second potential (5), a third line (6) for a reference potential (7) and a filter device (8), which - a first terminal (10) connected to the first line (2), - a second terminal (11) connected to the second line (4), - a third terminal (12) connected to the third line (6), - a first capacitor (13) through which a first current path (14) is led from the first terminal (10) to the third terminal (12), - a second capacitor (15), via which a second current path (16) is led from the second terminal (11) to the third terminal (12), and - a switching device (19) which is designed to switch between a first filter mode and a second filter mode as a function of control information (20), characterized in that the filter device (8) further comprises a third capacitor (17) which forms an electrically conductive connection between a central node (18) which lies between the first capacitor (13) and the second capacitor (15), and the third terminal (12), wherein the first current path (14) and the second current path (16) are guided past the third capacitor (17) to the third terminal (12) in the first filter mode and via the third capacitor (17) to the third terminal (12) in the second filter mode.

2. Power converter according to claim 1, wherein the filter device (8) is configured to set a higher pole frequency for filtering a common-mode current on the first line (2) and the second line (4) in the second filter mode along the first current path (14) and the second current path (16) than in the first filter mode.

3. Power converter according to claim 1 or 2, wherein the center node (18) is a common node - a terminal (17b) of the third capacitor (17) facing away from the third terminal (12), - a terminal (13b) of the first capacitor (13) facing away from the first terminal (10) and / or facing the second capacitor (15) and - a terminal (15a) of the second capacitor (15) facing away from the second terminal (11) and / or facing the first capacitor (13).

4. Power converter according to one of the preceding claims, wherein a terminal (17a) of the third capacitor (17) facing away from the center node (18) is connected to the third terminal (12).

5. Power converter according to one of the preceding claims, wherein the switching device (19) has a first terminal (19a) and a second terminal (19b) and a switching path which can be controlled as a function of the control information (20).

6. Power converter according to claim 5, wherein the first terminal (19a) of the switching device (19) is connected to the center node (18) and / or to the third capacitor (17).

7. Power converter according to claim 5 or 6, wherein the second terminal (19b) of the switching device (19) is connected to the third terminal (12) of the filter device (8) and / or to the third capacitor (17).

8. Power converter according to one of claims 5 to 7, wherein the switching device (19) is designed to switch the switching path conductive to assume the first filter mode and / or to switch it blocking to assume the second filter mode.

9. Power converter according to one of the preceding claims, wherein the switching device (19) is connected in parallel to the third capacitor (17).

10. Power converter according to one of the preceding claims, wherein the switching device (19) is designed as a bidirectionally conductive and / or blocking switch. 11 . Power converter according to one of the preceding claims, wherein - the capacitance (Cs) of the third capacitor (17) is smaller than the capacitance (Ci, C2) of the first capacitor (13) and / or the second capacitor (15) and / or - the capacitances (Ci, C2) of the first capacitor (13) and the second capacitor (15) are equal.

12. Power converter according to one of the preceding claims, wherein the filter device (8) further comprises a fourth capacitor (21) which is connected in parallel to the first capacitor (13) and the second capacitor (15) to the first terminal (10) of the filter device (8) and to the second terminal (11) of the filter device (8).

13. Power converter according to one of the preceding claims, wherein the filter device (8) comprises a printed circuit board (50), wherein - the first to third capacitors (13, 15, 17), in particular also the fourth capacitor (21), are arranged on the printed circuit board (50) and / or - the first to third terminals (10, 11, 12) of the filter device (8) are arranged on the printed circuit board (50) and / or - the switching device (19) is arranged on the printed circuit board (50).

14. Power converter according to one of the preceding claims, further comprising an intermediate circuit capacitor (40) which is connected between the first line (2) and the second line (4), and a converter circuit (41) which is connected between the first line (2) and the second line (4), wherein the filter device (8) is arranged on the side of the intermediate circuit capacitor (40) facing away from the converter circuit (41).

15. On-board electrical system (101) for an electrically driven vehicle (100), comprising at least one power converter (1, 1a, 1b) according to one of the preceding claims, a traction battery (102), a charging device (103) which can be connected to an electrical network (104) external to the vehicle for charging or discharging the traction battery (102), and a control device (105) which is designed to provide the control information (20) for adopting the second filter mode if and / or as long as the charging device (103) is connected to the electrical network (104) external to the vehicle.

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