Switching device for a high-voltage system having two precharging circuits

Abstract

The invention relates to a switching device (8) for a high-voltage system (1) of a motor vehicle for electrically interconnecting a first IT subsystem (2) of the high-voltage system (1) and a second IT subsystem (3) of the high-voltage system (1), comprising: - a main switching device (10) having two main switching units (10a, 10b), which are to be closed in succession, for interconnecting the two IT subsystems (2, 3) by successively connecting first poles (6a, 7a) of the IT subsystems (2, 3) and second poles (6b, 7b) of the IT subsystems (2, 3); - a first precharging circuit (11) for precharging Y capacitors (Cy) of the high-voltage system (1) when the two IT subsystems (2, 3) are interconnected; and - a second precharging circuit (13) for precharging an X capacitor (Cx) of the high-voltage system (1) when the two IT subsystems (2, 3) are interconnected, wherein the first precharging circuit (11) is connected in parallel with the main switching unit (10a) to be closed first, and the second precharging circuit (13) is connected in parallel with the main switching unit (10b) to be closed last.

Description

[0001] Switching device for a high-voltage system with two pre-charging circuits

[0002] The invention relates to a switching device for a high-voltage system of a motor vehicle for electrically connecting a first IT subsystem of the high-voltage system and a second IT subsystem of the high-voltage system. The invention also relates to a high-voltage system and a motor vehicle.

[0003] In the present case, interest is focused on high-voltage systems for electrified motor vehicles, such as electric vehicles, hybrid vehicles, and fuel cell vehicles. Such high-voltage systems typically have at least two IT (Isole Terre) subsystems. A first IT subsystem can, for example, comprise a high-voltage energy storage device, and a second IT subsystem can, for example, comprise a high-voltage electrical system with high-voltage components. The high-voltage energy storage device can, for example, be a traction battery that supplies energy to a high-voltage component in the form of an electric drive motor. The IT subsystems are typically electrically connectable via a switching device. This switching device can, for example, be used to switch off the high-voltage electrical system by isolating the high-voltage energy storage device, in particular galvanically, from the high-voltage electrical system.

[0004] The high-voltage electrical system also contains capacitances that are either deliberately introduced, for example in the form of interference suppression capacitors, or parasitically, for example due to the design. When the switching device is closed, an X-capacitance is connected to high-voltage terminals of the high-voltage energy storage system. When the switching device is closed, Y-capacitances are each connected to one of the HV terminals and a ground potential, the so-called vehicle ground. Apart from strictly monitored parasitic insulation resistances, the two IT subsystems have no electrical connection to the ground potential. When the high-voltage system is started up, i.e., when the IT subsystems are connected together, the charge of these IT subsystems is equalized by charging or recharging the parasitic Y-capacitances.These compensating currents can be critical for the high-voltage system both in terms of their magnitude and their edge steepness, as they can, for example, disrupt sensitive measurement and communication technology in the high-voltage energy storage system, for example by falsifying measured values.

[0005] It is an object of the present invention to provide a reliable solution for minimizing disturbances in a high-voltage system of a motor vehicle when electrically connecting two IT subsystems of the high-voltage system.

[0006] This object is achieved according to the invention by a switching device, a high-voltage system, and a motor vehicle having the features according to the respective independent patent claims. Advantageous embodiments of the invention are the subject of the dependent patent claims, the description, and the figures.

[0007] A switching device according to the invention for a high-voltage system of a motor vehicle serves for electrically connecting a first IT subsystem of the high-voltage system and a second IT subsystem of the high-voltage system. The switching device comprises a main switching device with two main switching units that are to be closed one after the other for connecting the two IT subsystems by successively connecting first poles of the IT subsystems and second poles of the IT subsystems. The switching device also comprises a first precharging circuit for precharging Y-capacitances of the high-voltage system when connecting the two IT subsystems and a second precharging circuit for precharging an X-capacitance of the high-voltage system when connecting the two IT subsystems. The first precharging circuit is connected in parallel to the main switching unit that is to be closed first, and the second precharging circuit is connected in parallel to the main switching unit that is to be closed last.

[0008] The invention also relates to a high-voltage system for a motor vehicle. The high-voltage system comprises a first IT subsystem, a second IT subsystem, and a switching device according to the invention, wherein a first main switching unit of the main switching device is electrically connected to first poles of the IT subsystems, and a second main switching unit of the main switching device is electrically connected to second poles of the IT subsystems. In particular, the first IT subsystem comprises a high-voltage energy storage device, and the second IT subsystem comprises a high-voltage on-board electrical system with at least one high-voltage consumer. A motor vehicle according to the invention comprises a high-voltage system according to the invention. The motor vehicle is, in particular, an electrified motor vehicle and has a high-voltage energy storage device in the form of a traction battery, which supplies energy to at least one high-voltage consumer in the form of an electric drive motor.

[0009] Each IT subsystem has high-voltage connections or HV connections in the form of a first pole, for example, a positive pole, and a second pole, for example, a negative pole. The IT subsystems are electrically connected to the switching device, via which an electrical connection between the IT subsystems can be established and broken. The switching device can be arranged, for example, internal to the high-voltage storage unit or external to the high-voltage storage unit, for example, in a relay box. The switching device has the main switching device with the main switching units. The main switching units can, for example, each have at least one HV relay or one contactor.

[0010] In addition, the high-voltage system has a capacitance arrangement with one X-capacitance and two Y-capacitances. The capacitances can at least partially be interference suppression capacitors of a filter device of the high-voltage system. The capacitances can also at least partially be parasitic, design-related capacitances of the high-voltage system. The X-capacitance can include all parasitic and non-parasitic capacitances connected between the poles of the high-voltage electrical system and thus have no connection to a ground potential of the motor vehicle. In particular, the X-capacitance includes an intermediate circuit capacitor of the high-voltage electrical system. A first Y-capacitance can include all parasitic and non-parasitic capacitances connected to the first, for example, positive-side, pole and the ground potential.A second Y-capacitance can include all parasitic and non-parasitic capacitances that are connected to the second, for example negative, pole and the ground potential.

[0011] To start up the high-voltage system, i.e. to interconnect the two IT subsystems, the switching device is closed. For this purpose, the two main switching devices are closed one after the other, for example by a control device of the high-voltage system, so that in particular the positive poles and then the negative poles of the IT systems are connected first. In order to reduce a compensating current flowing between the Y-capacitors when the first main switching unit is closed, for example with regard to its magnitude and / or edge steepness, the first pre-charging circuit connected in parallel to the first main switching unit is activated before the first main switching unit is closed. The first pre-charging circuit is designed as a Y-capacitor pre-charging circuit. The first pre-charging circuit has in particular a series circuit comprising a first pre-charging resistor and a first pre-charging switching unit.To activate the first precharge circuit, the control device closes the first precharge switching unit, so that the compensating current flows through the first precharge resistor. After a predetermined period of time, after which the first precharge is completed and which is in particular in the millisecond range, the control device closes the first main switching unit. Immediately or with a time delay after the closing of the first main switching unit, the control device can reopen the first precharge switching unit.

[0012] In order to limit the current flowing through the X-capacitance when the second main switching unit is closed, the second pre-charging circuit connected in parallel to the second main switching unit is activated before the second main switching unit is closed. The second pre-charging circuit is designed as an X-capacitance pre-charging circuit. The second pre-charging circuit has, for example, a series circuit comprising a second pre-charging resistor and a second pre-charging switching unit. To activate the second pre-charging circuit, the control device closes the second pre-charging switching unit so that the compensating current flows through the second pre-charging resistor. After the second pre-charging is complete, the control device closes the second main switching unit. Immediately or after a time delay after the second main switching unit has closed, the control device can also reopen the second pre-charging switching unit.

[0013] The pre-charging switching units can be designed as mechanical switching units, for example, with contactors or relays. It can also be provided that one of the two pre-charging switching units is designed as a mechanical switching unit and the other pre-charging switching unit is designed as an electronic switching unit, for example, with at least one semiconductor switch. The second pre-charging resistor is in particular smaller than the first pre-charging resistor.

[0014] By pre-charging the high-voltage system for the Y-capacitances during start-up, compensating currents, which generate interference signals for the measurement and communication technology of the high-voltage energy storage system, can be reduced in a simple and reliable manner.

[0015] The embodiments presented with reference to the switching device according to the invention and their advantages apply accordingly to the high-voltage system according to the invention and to the motor vehicle according to the invention.

[0016] Further features of the invention emerge from the claims, the figures, and the description of the figures. The features and combinations of features mentioned above in the description, as well as the features and combinations of features mentioned below in the description of the figures and / or shown alone in the figures, can be used not only in the respective specified combination, but also in other combinations or on their own.

[0017] The invention will now be explained in more detail using a preferred embodiment and with reference to the drawings. They show:

[0018] Fig. 1 is an exemplary representation of a circuit diagram of a high-voltage system of a motor vehicle;

[0019] Fig. 2 Current curves when starting up the high-voltage system.

[0020] In the figures, identical and functionally identical elements are provided with the same reference numerals.

[0021] Fig. 1 shows a high-voltage system 1 for a motor vehicle with a first IT subsystem 2 and a second IT subsystem 3. The first IT subsystem 2 comprises a high-voltage energy storage device 4, and the second IT subsystem 3 comprises a high-voltage electrical system 5 of the motor vehicle. The first IT subsystem 2 has first HV connections 6a, 6b, and the second IT subsystem 3 has second HV connections 7a, 7b. The HV connections 6a, 6b and 7a, 7b are connected to one another via a switching device 8. The switching device 8 is arranged here in a battery control unit 9 of the high-voltage system 1. The switching device 8 comprises a main switching device 10 with a first main switching unit 10a, which electrically connects first poles 6a, 7a of the HV terminals 6a, 6b, 7a, 7b, and with a second main switching unit 10b, which electrically connects second poles 6b, 7b of the HV terminals 6a, 6b, 7a, 7b. The main switching units 10a, 10b are designed, for example, as contactors.A fuse F1, for example a fuse, is also connected between the first pole 6a of the high-voltage energy storage device 4 and the first main switching unit 10a.

[0022] The high-voltage system 1 has an X-capacitance Cx, which can, for example, comprise an intermediate circuit capacitor of the high-voltage on-board network 5 and is located between the HV connections 7a, 7b of the high-voltage on-board network 5. In addition, the high-voltage system 1 has a plurality of, in particular parasitic, Y-capacitances Cy, which are located between one of the HV connections 6a, 6b and a vehicle ground M. The Y-capacitances are very small compared to the X-capacitance. For example, the Y-capacitances are a few hundred nF, while the X-capacitance is in the range between 0.5 mF and 1.5 mF. These capacitances Cx, Cy are recharged or charged when the switching device 8 is closed and can damage the main switching units 10a, 10 and the intermediate circuit capacitor or impair the electronics of the high-voltage energy storage device 4.

[0023] Fig. 2 shows a first curve V1 of a compensating current I over time t, which would flow without current limitation when the first main switching unit 10a is closed during the charging and recharging of the Y-capacitors Cy. The compensating current I of curve 1 is limited only by a contact resistance of the first main switching unit 10a. However, since the main switching units 10a, 10b have a very low contact resistance, for example in the range of a few 10 pOhm to a few 100 pOhm, to minimize losses when the motor vehicle is in operation or when the high-voltage energy storage device 4 is being charged, considerable currents arise when the first main switching unit 10a is closed due to the charge exchange or the charging and recharging of the Y-capacitors Cy, even though the main circuit is not yet closed due to the open second main switching unit 10b.

[0024] In order to limit this compensating current I and to significantly reduce a maximum amplitude A1 of the waveform V1, a first pre-charging circuit 11 is connected in parallel to the first main switching unit 10a. This circuit has a first pre-charging resistor R1 and a first pre-charging switching unit 12, wherein the first pre-charging resistor R1 and the first pre-charging switching unit 12 are connected in series. Before the main switching device 10 is closed, the first pre-charging switching unit 12 is first closed by a control device (not shown here). By suitably selecting the pre-charging resistor R1, the pre-charging can be designed such that a virtually interference-free adjustment of the different charge states is possible. Fig. 2 shows a second waveform V2 of the compensating current I when using the first pre-charging circuit 11. A maximum amplitude A2 of the waveform V2 is significantly lower than the maximum amplitude A1 of the waveform V1.In this way, any negative influence on the storage electronics, for example on the measuring and communication devices of the high-voltage energy storage unit 4, can be excluded.

[0025] After the first main switching unit 10a is closed and before the second main switching unit 10b is closed, a second precharging circuit 13 is also activated, which is connected in parallel to the second main switching unit 10a. This circuit comprises a series circuit consisting of a second precharging resistor R2 and a second precharging switching unit 14 and limits the current flowing through the intermediate circuit capacitor. After the precharging is complete, the second main switching unit 10a is closed, electrically connecting the two IT subsystems 2, 3.

Claims

Patent claims 1. Switching device (8) for a high-voltage system (1) of a motor vehicle for electrically connecting a first IT subsystem (2) of the high-voltage system (1) and a second IT subsystem (3) of the high-voltage system (1), comprising: - a main switching device (10) with two main switching units (10a, 10b) to be closed one after the other for connecting the two IT subsystems (2, 3) by successively connecting first poles (6a, 7a) of the IT subsystems (2, 3) and second poles (6b, 7b) of the IT subsystems (2, 3), - a first pre-charging circuit (11) for pre-charging Y-capacitances (Cy) of the high-voltage system (1) when connecting the two IT subsystems (2, 3), - a second pre-charging circuit (13) for pre-charging an X-capacitance (Cx) of the high-voltage system (1) when connecting the two IT subsystems (2, 3), wherein the first pre-charging circuit (11) is connected in parallel to the main switching unit (10a) to be closed first and the second pre-charging circuit (13) is connected in parallel to the main switching unit (10b) to be closed last.

2. Switching device (8) according to claim 1, characterized in that the first pre-charging circuit (11) has a series circuit comprising a first pre-charging resistor (R1) and a first pre-charging switching unit (12) and the second pre-charging circuit (13) has a series circuit comprising a second pre-charging resistor (R2) and a second pre-charging switching unit (14).

3. Switching device (8) according to claim 2, characterized in that the switching device (8) has a control device which is designed to combine the IT subsystems (2, 3), first the first pre-charging switching unit (11), then the first main switching unit (10a) connectable to first poles (6a, 7a), in particular positive poles, of the IT subsystems (2, 3), then the second pre-charging switching unit (13) and finally the first main switching unit (10a) connectable to second poles (6b, 7b), in particular negative poles, of the IT subsystems (2, 3) to close the second main switching unit (10b).

4. Switching device (8) according to claim 3, characterized in that the control device is designed to reopen the pre-charging switching units (11, 13) after completion of the respective pre-charging.

5. Switching device (8) according to claim 2 or 3, characterized in that one of the pre-charging switching units (11, 13) is designed as an electronic switching unit and the other of the pre-charging switching units (13, 11) is designed as a galvanically isolating, mechanical switching unit.

6. Switching device (8) according to one of claims 2 to 4, characterized in that the second precharging resistor (R2) is smaller than the first precharging resistor (R1).

7. High-voltage system (1) for a motor vehicle with a first IT subsystem (2), a second IT subsystem (3) and a switching device (8) according to one of the preceding claims, wherein a first main switching unit (10a) of the main switching device (10) is electrically connected to first poles (6a, 7a) of the IT subsystems (2, 3) and a second main switching unit (10b) of the main switching device (10) is electrically connected to second poles (6b, 7b) of the IT subsystems (2, 3).

8. High-voltage system (1) according to claim 7, characterized in that the first IT subsystem (2) comprises a high-voltage energy storage device (4) and the second IT subsystem (3) comprises a high-voltage vehicle electrical system (5) with at least one high-voltage consumer.

9. Motor vehicle with a high-voltage system (1) according to claim 7 or 8.

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