SHOCK PROTECTION FOR RADIO-INTERFERENCE-SUPPRESSED VOLTAGE TRANSFORMERS IN A POTENTIAL-FREE DC VOLTAGE NETWORK

Abstract

The invention relates to a voltage transformer (1) for transformation between a direct voltage at a direct voltage gate (2) and a single-phase or multi-phase alternating voltage at an alternating voltage gate (3) by temporal clocking of an electronic switching unit (4), via which each phase (3a-3c) of the alternating voltage gate (3) can be connected either to the positive pole or to the negative pole of the direct voltage gate (2), wherein the positive pole and/or the negative pole of the direct voltage gate (2) is connected via at least one capacitor (5, 5a, 5b) to a ground connection (7), wherein the ground connection (7) can be connected to an external ground (7a), and wherein the connection between the capacitor (5, 5a, 5b) and the ground connection (7) is guided via at least one switch element (6, 6a, 6b). The invention also relates to an electric powertrain (10) for a motor vehicle (100). The invention further relates to a motor vehicle (100) having the electric powertrain (10).

Claims

1. A voltage converter (1) for converting between a DC voltage at a DC voltage gate (2) and a single-phase or multiphase AC voltage at an AC voltage gate (3) as a result of temporal clocking of an electronic switching mechanism (4) via which each phase (3a-3c) of the AC voltage gate (3) can be selectively connected to a positive pole or to a negative pole of the DC voltage gate (2), wherein the positive pole and/or the negative pole of the DC voltage gate (2) are/is connected to a ground terminal (7) via at least one capacitor (5, 5a, 5b), wherein the ground terminal (7) is configured to be connected to an external ground (7a), and wherein the connection between the capacitor (5, 5a, 5b) and the ground terminal (7) is routed via at least one switching element (6, 6a, 6b).

2. The voltage converter (1) as claimed in claim 1, wherein the voltage converter (1) is configured to interrupt the connection between the capacitor (5, 5a, 5b) and the ground terminal (7) using the switching element (6, 6a, 6b) when an acceleration force or deceleration force that exceeds a predefined threshold value acts on the voltage converter (1).

3. The voltage converter (1) as claimed in claim 1, wherein the voltage converter (1) is configured to establish the connection between the capacitor (5, 5a, 5b) and the ground terminal (7) using the switching element (6, 6a, 6b) when a consumer connected to the AC voltage gate (3) of the voltage converter (1) is activated, and to disconnect the connection again when the consumer is deactivated.

4. The voltage converter (1) as claimed in claim 1, wherein the switching element (6, 6a, 6b) comprises an arrangement composed of at least two transistors, wherein the transistors comprise bipolar transistors and/or field-effect transistors and wherein the forward directions, defined by the respective collector-emitter path or by the respective source-drain path, of the transistors are connected in antiseries to one another.

5. The voltage converter (1) as claimed in claim 1, wherein the connection between the capacitor (5, 5a, 5b) and the ground terminal (7) is routed via a series circuit composed of multiple switching elements (6a, 6b).

6. The voltage converter (1) as claimed in claim 1, wherein diagnosis means (8) that are configured to detect the correct function and/or the actual switching state of at least one switching element (6, 6a, 6b) are provided.

7. The voltage converter (1) as claimed in claim 6, wherein at least one switching element (6, 6a, 6b) is configured as a changeover switch between a first switching position and a second switching position, wherein the switching element (6, 6a, 6b) connects the ground terminal (7), or a further switching element (6, 6a, 6b) connected between this switching element (6, 6a, 6b) and the ground terminal (7), to a voltage source (81a, 81b) for a test potential in the first switching position and to the capacitor (5, 5a, 5b) in the second switching position, and wherein the diagnosis means (8) comprise means (82a, 82b) for monitoring the test potential.

8. The voltage converter (1) as claimed in claim 6, wherein the diagnosis means (8) comprise a voltage source (83a, 83b) that is connected to that side of at least one switching element (6, 6a, 6b) that is facing away from the ground terminal (7) and means (84a, 84b) for monitoring the potential on this side of the switching element (6, 6a, 6b).

9. The voltage converter (1) as claimed in claim 1, wherein the capacitor (5, 5a, 5b) has a capacitance of at least 500 nF, preferably of at least 1 μF and very particularly preferably of at least 10 μF.

10. An electrical drivetrain (10) for a motor vehicle (100), comprising a voltage converter (1) for converting between a DC voltage at a DC voltage gate (2) and a single-phase or multiphase AC voltage at an AC voltage gate (3) as a result of temporal clocking of an electronic switching mechanism (4) via which each phase (3a-3c) of the AC voltage gate (3) can be selectively connected to a positive pole or to a negative pole of the DC voltage gate (2), wherein the positive pole and/or the negative pole of the DC voltage gate (2) are/is connected to a ground terminal (7) via at least one capacitor (5, 5a, 5b), wherein the ground terminal (7) is configured to be connected to an external ground (7a), and wherein the connection between the capacitor (5, 5a, 5b) and the ground terminal (7) is routed via at least one switching element (6, 6a, 6b); and an electric motor (11) connected to the AC voltage gate (3) of the voltage converter (1).

11. A motor vehicle (100) having an electrical drivetrain (10) as claimed in claim 10, wherein the electric motor (11) and the ground terminal (7) of the voltage converter (1) are connected to a common ground (110) of the motor vehicle (100).

12. The motor vehicle (100) as claimed in claim 11, further comprising a rechargeable battery (120) for supplying the drivetrain (10) and a safety device (130) that is configured to prevent charging of the battery (120) from an energy source (200) external to the vehicle in response to diagnosis means (8) of the voltage converter (1) determining that the connection between the capacitor (5, 5a, 5b) and the ground terminal (7) of the voltage converter (1) cannot be interrupted due to a malfunction of one or more switching elements (6, 6a, 6b).

13. The motor vehicle (100) as claimed in claim 11, further comprising a safety device (135) that is configured to output a warning to the driver and to prevent restarting of the motor vehicle (100) after a predefined driving distance or time has elapsed and/or to restrict the rotational speed and/or the torque of the electric motor (11) in response to diagnosis means (8) of the voltage converter (1) determining that the connection between the capacitor (5, 5a, 5b) and the ground terminal (7) of the voltage converter (1) cannot be established due to a malfunction of one or more switching elements (6, 6a, 6b).

Description

[0031] According to FIG. 1, the voltage converter 1 in the drivetrain 10 of the motor vehicle 100 is used to convert a DC voltage applied to its DC voltage gate 2 into a three-phase AC voltage that is output on the three phases 3a, 3b, 3c of its AC voltage gate 3. The electric motor 11 in the drivetrain 10 is supplied with this AC voltage. The conversion takes place as a result of temporal clocking of an electronic switching mechanism 4 that is not shown in more detail.

[0032] The AC voltage is subjected to high-frequency interference as a result of the temporal clocking in the switching mechanism 4. Since the electric motor 11 is connected to the ground 110 of the motor vehicle 100 at the point 101, this interference couples into metal parts of the motor vehicle 100. These metal parts act as antennas that emit the high-frequency interference. The pole T+ of the DC voltage gate 2 is therefore connected to the ground terminal 7 of the voltage converter 1 via the capacitor 5a. The pole T− of the DC voltage gate 2 is connected to the ground terminal 7 of the voltage converter 1 via the capacitor 5b. These connections are routed via the switching element 6. The ground terminal 7 is connected to the ground 110 of the motor vehicle 100 as external ground 7a at the point 102.

[0033] Within the drivetrain 10, multiple capacitors can also be combined at a common ground potential which for its part is connected to the ground 110 of the motor vehicle 100. This can then, for example, be particularly easily incorporated into the motor vehicle 100 when the drivetrain 10 is a closed assembly that is integrated as a whole into the motor vehicle 100.

[0034] When the switching element 6 is switched on, the high-frequency interference is drawn from the vehicle ground 110 back into the voltage converter 1 and in this respect short-circuited. In this way, emission of this interference into the environment is considerably reduced. However, in this state the vehicle ground 110 is connected to a respective pole of each of the two capacitors 5a, 5b. During manipulation of the vehicle 100, touching just one of the two poles T+, T− of the DC voltage gate 2 is enough to receive an electric shock from the energy stored in one of the capacitors 5a, 5b.

[0035] When the electric motor 11 is not active and the radio interference suppression through the capacitors 5a and 5b is not needed, the switching element 6 is therefore advantageously switched off. The pole of each of the two capacitors 5a, 5b that is respectively connected to the switching element 6 is then no longer accessible for people such that the capacitances of these capacitors 5a, 5b no longer constitute a hazard potential.

[0036] This is particularly important when the traction battery 120 of the motor vehicle 120 is charged from an external charging station 200 because the charging station 200 and the cable connection to the motor vehicle 100 introduce further capacitances.

[0037] Diagnosis means 8 are provided for monitoring this safety-relevant function. There are two types of malfunction that can arise.

[0038] On the one hand, the switching element 6 can be stuck in the on switching position, which has the result that the connection between the capacitors 5a, 5b and the ground terminal 7 can no longer be interrupted. There would be a risk of electric shock in particular during charging of the traction battery 120 from the charging station 200. In this case, charging is therefore prevented by the safety device 130. The driver of the vehicle 100 has to manage with the energy supply remaining in the battery 120 and visit a garage.

[0039] On the other hand, the switching element 6 can be stuck in the off switching position. In this case, the vehicle 100 is always safe to touch but there is no radio interference suppression. In this case, therefore, a warning is output to the driver by the safety device 135. If the fault is not remedied within a predefined driving distance or time, the vehicle 100 is prevented from restarting. In the case of this fault there is also an obligation to carry out repairs. Instead of completely preventing restarting of the vehicle 100, the rotational speed and/or the torque of the electric motor 11 can also just be restricted so that the vehicle 100 can at least reach a garage under its own power (“limp home function”).

[0040] In order to reduce the likelihood of the charging having to be prevented due to a fault, two switching elements 6a and 6b are connected in series in the exemplary embodiment shown in FIG. 2. The switching elements 6a, 6b are in the form of relays in this case.

[0041] The switching element 6a connects the second switching element 6b to the voltage source 81a for a test potential in its switching position shown in FIG. 2. The switching element 6a connects the second switching element 6b to the capacitors 5a and 5b in its switching position not shown in FIG. 2.

[0042] The switching element 6b connects the ground terminal 7 to the voltage source 81b for a test potential in its switching position shown in FIG. 2. The switching element 6b connects the ground terminal 7 to the capacitors 5a and 5b in its switching position not shown in FIG. 2, wherein this connection is still provided by the switching element 6a.

[0043] In addition to the voltage sources 81a and 81b for the test potentials, the diagnosis means 8 also comprise means 82a, 82b for monitoring these test potentials, which means are realized as analog-to-digital converters with series resistors in this example. Each of the four combinations of switching states of the switching elements 6a and 6b leads nominally to a unique combination of voltage values that are registered by the analog-to-digital converters 82a, 82b. In this way, the actual switching states of the switching elements 6a and 6b can be identified.

[0044] In the exemplary embodiment shown in FIG. 3, a series circuit composed of two switching elements 6a, 6b is also provided between the capacitors 5a, 5b and the ground terminal 7. In contrast to FIG. 2, the switching elements 6a, 6b are realized in each case as an antiseries connection of two MOSFET transistors, however. Switching elements of this kind do not function, as the relays in FIG. 2 do, as changeover switches, but rather can only either be switched on or off, according to the illustration of the switching element 6 in FIG. 1. The diagnosis means 8 are therefore arranged differently in this case. On that side of each of the switching elements 6a, 6b that is facing away from the ground terminal 7, a voltage source 83a, 83b supplies a test voltage by way of a respective series resistor. In each case the potential is monitored there by means 84a, 84b. In this way, it can be determined whether there is conduction between the means 84a, 84b and the ground terminal 7.