Dc-DC converter device, power supply system and method for discharging a DC link capacitor

Abstract

The invention relates to the discharging of energy stores such as, for example, DC link capacitors in a high-voltage system, in particular a high-voltage system of an electric vehicle. To this end, a DC-DC converter device having at least two DC-DC converters is provided, wherein at least one DC-DC converter transmits power from the high-voltage system to a low-voltage system and, in parallel therewith, at least one further DC-DC converter transmits power from the low-voltage system to the high-voltage system.

Description

[0001] Description

[0002] title

[0003] DC-DC converter device, power supply system and method for discharging an intermediate circuit capacitor

[0004] Technical area

[0005] The present invention relates to a DC-DC converter device, in particular a DC-DC converter device for discharging an intermediate circuit capacitor, and a method for discharging an intermediate circuit capacitor. The present invention further relates to a power supply system for an electric vehicle having such a DC-DC converter device.

[0006] State of the art

[0007] Fully or at least partially electrically powered vehicles typically have at least two voltage levels. On the one hand, a low-voltage network in the range of approximately 12 V, for example, is provided, which supplies lower-power consumers. Furthermore, a high-voltage network in the range of several hundred volts is provided, which supplies an electric drive system and usually also includes a so-called traction battery.

[0008] In the event of a fault, it is necessary to discharge energy storage elements in the high-voltage network, such as capacitors, as quickly as possible. Additional, separate discharge circuits can be provided for this purpose.

[0009] The document DE 10 2009 055 053 A1 describes, for example, a method and a device for discharging an energy storage device, in particular an intermediate circuit capacitor, in a high-voltage network of a motor vehicle.

[0010] Disclosure of the Invention The present invention discloses a DC-DC converter device, a power supply system, and a method for discharging an intermediate circuit capacitor having the features of the independent claims. Further advantageous embodiments are the subject of the dependent claims.

[0011] Accordingly, it is provided:

[0012] A DC-DC converter device comprising a first DC-DC converter and at least one second DC-DC converter. The first DC-DC converter is configured to be coupled to a first DC voltage network at a first terminal. Furthermore, the first DC-DC converter is configured to be coupled to a second DC voltage network at a second terminal. The second DC-DC converter is configured to be coupled to the first DC voltage network at a first terminal.

[0013] Furthermore, the second DC-DC converter is designed to be coupled to the second DC voltage network at a second terminal. In a first operating mode, the first DC-DC converter is designed to transmit electrical energy from the first terminal to the second terminal of the first DC-DC converter. Furthermore, in this first operating mode, the second DC-DC converter is designed to simultaneously transmit electrical energy from the second terminal to the first terminal of the second DC-DC converter.

[0014] Furthermore, it is planned:

[0015] A power supply system for an electric vehicle with a high-voltage network and a low-voltage network and a DC-DC converter device according to the invention. A DC link capacitor is provided in the high-voltage network. The first terminals of the first DC-DC converter and the second DC-DC converter are electrically coupled to the high-voltage network. The second terminals of the first DC-DC converter and the second DC-DC converter are electrically coupled to the low-voltage vehicle electrical system.

[0016] Finally, it is planned:

[0017] A method for discharging an intermediate circuit capacitor provided in a first DC voltage network. The first DC voltage network is coupled to a second DC voltage network by means of a DC voltage converter device, in particular the aforementioned DC voltage converter device according to the invention. The DC voltage converter device comprises at least two DC voltage converters. A first DC voltage converter is coupled to the first DC voltage network at a first terminal and to a second DC voltage network at a second terminal. A second DC voltage converter is coupled to the first DC voltage network at a first terminal and to the second DC voltage network at a second terminal. In the method, the following two steps are carried out simultaneously.On the one hand, the first DC-DC converter transmits electrical energy from the first terminal to the second terminal of the first DC-DC converter. On the other hand, the second DC-DC converter transmits electrical energy from the second terminal to the first terminal of the second DC-DC converter.

[0018] Advantages of the invention

[0019] Electric drive systems, such as those used in electric vehicles, are generally supplied by a direct current in the range of several hundred volts. Capacitors, in particular so-called intermediate circuit capacitors, are typically provided to stabilize this direct current. These capacitors must, among other things, be capable of being controlled and quickly discharged in the event of a fault. If this is implemented using a separate, additional circuit, this requires additional effort in terms of costs and installation space. The present invention is based on the finding that, in electric vehicles, in addition to a high-voltage network with the electric drive system, an additional low-voltage network is generally provided. The high-voltage network and the low-voltage network can be coupled to one another via a DC-DC converter device.In this way, electrical energy can be exchanged between the high-voltage and low-voltage networks. Since losses also occur during this energy transfer between the high-voltage and low-voltage networks, one idea of ​​the present invention is to implement or at least support the discharge of the capacitances in the high-voltage network by means of the lossy DC-DC converter between the high-voltage and low-voltage networks.

[0020] Here, a device is used which comprises at least two separate DC-DC converter units. A first DC-DC converter unit converts electrical energy from the high-voltage network to the low-voltage network, while in parallel a second DC-DC converter unit converts electrical energy in the opposite direction from the low-voltage network to the high-voltage network. In this way, the electrical energy is transmitted simultaneously in both directions, whereby losses in the form of thermal energy also occur in each DC-DC converter unit. Thus, the electrical energy initially stored in the capacitors of the high-voltage network can be converted into thermal energy (e.g.current heat losses) and thus the electrical energy stored in the capacitors is reduced without the need for additional separate circuit units.

[0021] DC-DC converter arrangements, such as those used to couple the high-voltage and low-voltage networks in an electric vehicle, are in many cases designed for bidirectional operation anyway, i.e. for a DC-DC converter from the high-voltage network to the low-voltage network or vice versa, from the low-voltage network to the high-voltage network. In addition, in many applications for coupling the high-voltage and low-voltage networks, DC-DC converter arrangements with several parallel DC-DC converter units are also provided. The latter enables, for example, very good scaling. For example, depending on the power to be transferred between the high-voltage and low-voltage networks, one or more DC-DC converter units can be activated. In this way, the respectively active DC-DC converter units can be operated very close to their optimal operating point, whereby a high level of efficiency can be achieved.

[0022] According to the invention, a further operating mode is provided in which some of these DC-DC converter units (at least one) are operated such that electrical energy is transferred from the high-voltage network to the low-voltage network. At the same time, another part of the DC-DC converter units (also at least one) is operated such that electrical energy is transferred from the low-voltage network to the high-voltage network. In this way, electrical energy is transferred in a circle, so to speak. However, since all of the DC-DC converter units involved are lossy during operation, some of the energy is converted into thermal energy. In this way, the electrical energy previously stored in capacitive elements, such as the intermediate circuit capacitor, can be dissipated and converted into thermal energy. This thermal energy can be dissipated, for example, via a suitable cooling system.Since the process typically only takes a few seconds, the cooling system of the DC-DC converter device requires little or no expansion. Consequently, the electrical energy stored in capacitors on the high-voltage grid side can be dissipated very quickly when needed, without the need for complex additional components and measures.

[0023] According to one embodiment, the first terminals of the first DC-DC converter and the first terminals of the second DC-DC converter are each designed to be connected to an intermediate circuit capacitor. Furthermore, the DC-DC converter device can comprise a control device. This control device can be designed to control the first DC-DC converter and the second DC-DC converter in the first operating mode to discharge the intermediate circuit capacitor.

[0024] Thus, the control device can specifically control and carry out the discharging of the intermediate circuit capacitor.

[0025] According to one embodiment, the control device is designed to set the first operating mode to discharge the intermediate circuit capacitor until an electrical voltage across the intermediate circuit capacitor falls below a predetermined threshold. In this way, the electrical voltage across the intermediate circuit capacitor and thus in the (deactivated) high-voltage network can be reduced to a safe voltage level.

[0026] According to one embodiment, in the first operating mode, an electrical power transmitted from the first terminal to the second terminal of the first DC-DC converter is greater than an electrical power transmitted from the second terminal to the first terminal of the second DC-DC converter. In this way, it can be ensured that electrical energy is taken from the high-voltage network and the electrical energy storage devices present in the high-voltage network, such as the intermediate circuit capacitor. In addition to converting the electrical energy into thermal energy due to the electrical losses in the DC-DC converters, it is also possible to feed electrical energy from the high-voltage network into the low-voltage network and, for example, to charge a battery present in the low-voltage network or to supply consumers in the low-voltage network with energy.

[0027] According to one embodiment, in the first operating mode, the electrical power supplied by the first DC-DC converter to the second terminal of the first DC-DC converter corresponds to the electrical power supplied to the second terminal of the second DC-DC converter. In other words, the second DC-DC converter completely absorbs the electrical energy supplied by the first DC-DC converter. Thus, no electrical energy is fed into the second DC voltage network. Optionally, a switching element, such as a circuit breaker or the like, can be provided between the second terminals of the first and second DC-DC converters and the second DC voltage network.Thus, for example, in a hazardous situation, the second DC voltage network can be electrically disconnected from the DC-DC converter, and the electrical energy stored in the first DC voltage network can be dissipated through the electrical losses in the DC-DC converters. However, it is important to ensure that the electrical voltage at the second terminals of the DC-DC converters remains within specified voltage ranges and, in particular, does not exceed a maximum limit.

[0028] According to one embodiment, the second DC voltage network comprises a first DC voltage sub-network and a second DC voltage sub-network. The first DC voltage converter can be configured to be coupled to the first DC voltage sub-network of the second DC voltage network at the second terminal of the first DC voltage converter. Furthermore, the second DC voltage converter can be configured to be coupled to the second DC voltage sub-network of the second DC voltage network at the second terminal of the second DC voltage converter. In other words, the first DC voltage converter and the second DC voltage converter are each connected to separate DC voltage sub-networks. Thus, the individual DC voltage sub-networks can be supplied with electrical energy independently of one another via separate DC voltage converters. Furthermore, the DC voltage converter device can comprise a coupling element.This coupling element is designed to electrically couple the first DC voltage sub-grid and the second DC voltage sub-grid to one another in the first operating mode. Thus, in this first operating mode, electrical energy can be exchanged at the second terminals of the DC-DC converters. This makes it possible to feed the energy delivered by the first DC-DC converter to the second DC-DC converter into the second terminal of the second voltage converter, thus dissipating the electrical energy stored in the first DC voltage network through the electrical losses in the two DC-DC converters. According to one embodiment, the first DC voltage network comprises a first sub-grid and a second sub-grid.Here, the first DC-DC converter can be designed to be coupled to the first sub-network of the first DC voltage network at the first terminal of the first DC-DC converter, and the second DC-DC converter can be designed to be coupled to the second sub-network of the first DC voltage network at the first terminal of the second DC-DC converter. In other words, the two DC-DC converters can each be connected to separate sub-networks of the first DC voltage network at the first terminals. Furthermore, the DC-DC converter device can comprise a coupling element. This coupling element can be designed to electrically couple the first sub-network and the second sub-network of the first DC voltage network to one another in the first operating mode. Thus, on the one hand, the two DC-DC converters can be supplied with electrical energy from separate sub-networks during normal operation.Furthermore, for the discharge of electrical energy according to the invention in the first operating mode, the two sub-networks can be electrically coupled to one another.

[0029] According to one embodiment, the first DC-DC converter and / or the second DC-DC converter is designed to alternately transmit electrical energy from the first DC-DC network to the second DC-DC network and from the second DC-DC network to the first DC-DC network. In particular, the periods for changing the transmission direction of the electrical energy can be selected to be relatively short. For example, the change can occur regularly with a period duration of a few milliseconds, 10 or 100 ms. In particular, the maximum amount of energy that can be transmitted in each case is equal to the amount that can be absorbed by the respective DC-DC network, in particular the second DC-DC network. In this way, the electrical energy in the first DC-DC network can also be dissipated by means of a single DC-DC converter, for example in the event of a failure of one of the two DC-DC converters.According to one embodiment, a second operating mode is provided in the DC-DC converter device. In this second operating mode, the first DC-DC converter and / or the second DC-DC converter is designed to transmit electrical energy from the first terminal to the second terminal of the first DC-DC converter. Furthermore, in a third operating mode, the first DC-DC converter and / or the second DC-DC converter can be designed to transmit electrical energy from the second terminal to the first terminal of the first DC-DC converter. These can be operating modes, for example, that are used to transmit electrical energy in a conventional manner, either from the high-voltage network to the low-voltage network or vice versa, from the low-voltage network to the high-voltage network.

[0030] According to one embodiment, a further operating mode is provided in the DC-DC converter device, in which the first DC-DC converter is configured to alternately transmit electrical energy from the first terminal to the second terminal of the first DC-DC converter and electrical energy from the second terminal to the first terminal of the second DC-DC converter. Thus, discharging the electrical energy stored on the high-voltage network side is also possible using only one DC-DC converter, for example, if the second DC-DC converter cannot be used due to a malfunction or the like.

[0031] The above embodiments and further developments can be combined with one another as desired, where appropriate. Further embodiments, further developments, and implementations of the invention also include combinations of features of the invention not explicitly mentioned above or described below with respect to the exemplary embodiments. In particular, those skilled in the art will also add individual aspects as improvements or additions to the respective basic forms of the invention.

[0032] Brief description of the drawings Further features and advantages of the invention are explained below with reference to the figures. They show:

[0033] Fig. 1: a schematic representation of a block diagram of an arrangement of a power supply network with a DC-DC converter device according to an embodiment;

[0034] Fig. 2: a schematic diagram illustrating the energy flow through a DC-DC converter device in an operating mode;

[0035] Fig. 3: a schematic diagram illustrating the energy flow through a DC-DC converter device in a further operating mode;

[0036] Fig. 4: a schematic diagram illustrating the energy flow through a DC-DC converter device in an operating mode for discharging the intermediate circuit capacitor;

[0037] Fig. 5: a schematic representation of a block diagram of an arrangement of a power supply network with a DC-DC converter device according to another embodiment;

[0038] Fig. 6: a schematic representation of a block diagram of an arrangement of a power supply network with a DC-DC converter device according to yet another embodiment; and

[0039] Fig. 7: a flowchart underlying a method according to an embodiment.

[0040] Description of the embodiments

[0041] Figure 1 shows a schematic representation of a block diagram of a DC-DC converter device 10 for coupling a high-voltage network 2 with a low-voltage network 1. The high-voltage network 2 and the low-voltage network 1 can, for example, be the corresponding on-board electrical systems of an electric vehicle. For example, the low-voltage network 1 can supply electrical energy to electrical consumers such as control units, ventilation, comfort functions, multimedia components, or the like. The electrical voltage of the low-voltage network 1 is typically a maximum of 48 V, typically approximately 12 or 24 V.

[0042] The high-voltage network 2 can, for example, comprise an electric drive system with an electric machine 23. For example, a direct voltage of the high-voltage network 2 can be converted by means of an electric power converter 22 into a single- or multi-phase alternating voltage, which is suitable for controlling the electric machine 23 according to setpoint specifications. To stabilize the direct voltage at the input of the power converter 22, an intermediate circuit capacitor 21 can be provided, for example. The electrical voltage in the high-voltage network 2 can be several hundred volts. For example, the electrical voltage in the high-voltage network 2 can be in the range between 350 and 400 V or 800 V.

[0043] Furthermore, an electrical energy storage device, for example a traction battery 30, can be provided in the high-voltage network 2, which is coupled to the high-voltage network 2 via a disconnector 31.

[0044] The low-voltage network 1 and the high-voltage network 2 can be electrically coupled to one another by means of a DC-DC converter device 10. In particular, the DC-DC converter device 10 can be a device that enables bidirectional DC-DC conversion between the low-voltage network 1 and the high-voltage network 2. In other words, the DC-DC converter device 10 can transfer electrical energy from the high-voltage network 2 to the low-voltage network 1, as well as electrical energy from the low-voltage network 1 to the high-voltage network 2.

[0045] As further illustrated in Figure 1, the DC-DC converter device 10 can comprise multiple units with DC-DC converters 11, 12. The number of two DC-DC converters 11, 12 shown here is merely an example to explain the basic principle of the invention and is not intended to represent a limitation of the present invention. Furthermore, three or more DC-DC converter units are also possible.

[0046] The individual DC-DC converters 11, 12 can be identical or at least similar in design. Alternatively, it is also possible for the individual DC-DC converters 11, 12 to be designed differently, and in particular, for different maximum power transmissions. By using multiple DC-DC converters 11, 12 in parallel, for example, the number of active DC-DC converters can be adjusted depending on the electrical power to be transmitted. In this way, the DC-DC converters can be operated as close as possible to their optimal operating point. This increases the efficiency of the DC-DC converters.

[0047] Figure 2 shows a schematic representation of the energy flow in an operating mode in which, for example, electrical energy is provided by the traction battery 30. In this case, the isolating switch 31 between the traction battery 30 and the high-voltage network 2 is closed. The electrical energy can be used, on the one hand, to control the electric machine 23 via the power converter 22. Furthermore, electrical energy provided by the traction battery 30 can also be transferred to the low-voltage network 1 by means of the DC-DC converter device 10 in order to supply electrical consumers in the low-voltage network 1 with energy and / or to charge a battery in the low-voltage network 1. In this case, as already indicated above, one or more DC-DC converters 11, 12 can actively carry out a DC voltage conversion from the high-voltage network 2 to the low-voltage network 1.

[0048] Figure 3 shows a schematic representation of the energy flow in a further operating mode, in which, for example, electrical energy is transferred from an energy storage device in the low-voltage network 1 to the high-voltage network 2. In this case, the isolating switch 31 between the traction battery 30 and the high-voltage network 2 is open. For example, such an energy flow can charge the intermediate circuit capacitor 21 in the high-voltage network 2. Thus, the electrical voltage in the high-voltage network 2 can be adjusted to match the electrical voltage at the traction battery 30. The isolating switch 31 can then be closed without a significant current flowing at the time of closing. In this way, sparking or similar incidents when the isolating switch 31 is closed can be avoided.

[0049] Finally, Figure 4 shows a schematic representation of the energy flow in a further operating mode according to the invention. Here, the isolating switch 31 between the traction battery 30 and the high-voltage network 2 is open. Immediately after opening this isolating switch 31, the intermediate circuit capacitor 21 is still charged. For an active discharge of the intermediate circuit capacitor 21, at least one DC-DC converter 11, 12 of the DC-DC converter device 10 can transfer electrical energy from the high-voltage network and thus from the intermediate circuit capacitor 21 into the low-voltage network 1. If the electrical energy transferred in this way cannot be completely absorbed or consumed in the low-voltage network 1, at least one further DC-DC converter 11, 12 can convert electrical energy from the low-voltage network 1 toward the high-voltage network 2.In this case, electrical energy is transferred from the high-voltage network 2 to the low-voltage network 1 simultaneously with a first part of the DC-DC converters 11, 12 and electrical energy is transferred from the low-voltage network 1 to the high-voltage network 2 with a further part of the DC-DC converters 11, 12.

[0050] Since the DC-DC converters 11, 12 are lossy assemblies, losses occur during DC-DC conversion. This involves converting electrical energy into thermal energy. Consequently, during the simultaneous voltage conversion from the high-voltage network 2 to the low-voltage network 1 and back to the high-voltage network 2, electrical energy is continuously converted into thermal energy. Thus, the electrical energy stored in the high-voltage network 2, for example the electrical energy in the intermediate circuit capacitor 21, is gradually dissipated and converted into thermal energy. This thermal energy can be dissipated to the DC-DC converters 11, 12 by means of appropriate cooling devices. Thus, the electrical energy in the high-voltage network 2 can be dissipated even when no or only a small amount of electrical energy can be absorbed by the low-voltage network 1.

[0051] Even if the low-voltage network 1 can absorb some of the electrical energy from the high-voltage network 2, additional electrical energy can be dissipated from the high-voltage network 2 through the simultaneous voltage conversion from the high-voltage network 2 to the low-voltage network 1 and vice versa from the low-voltage network 1 to the high-voltage network 2. This allows for rapid discharge of the electrical energy stored in the high-voltage network 2. This process for actively discharging the high-voltage network 2 or the capacitances in the high-voltage network 2 will generally take place within a few seconds. In particular, the process for dissipating the electrical energy from the high-voltage network 2 can be carried out until the electrical voltage in the high-voltage network 2 falls below a predetermined threshold.

[0052] To control the DC-DC converters 11, 12 in the previously described operating model, a control device 13 can be provided, for example. This control device 13 can, for example, specify setpoints for the direction of the voltage converters as well as the level of the output voltage at the individual DC-DC converters 11, 12, depending on the operating mode.

[0053] Figure 5 shows a schematic representation of a block diagram of a DC-DC converter device 10 according to a further embodiment. The DC-DC converter device 10 of this embodiment differs from the previously described embodiments in particular in that an additional isolating element 16, for example a circuit breaker or the like, can be provided between the DC-DC converter device 10 and the low-voltage network 1. This isolating element 16 can be used to electrically connect or disconnect the low-voltage network 1 from the DC-DC converter device 10. In particular, in a dangerous situation, for example, it is possible to open the isolating element 16 to prevent further energy flow into the low-voltage network 1. In addition, all statements already made previously in connection with the DC-DC converter device 10 apply.

[0054] Instead of the above-described isolating element 16 between the DC-DC converter device 10 and the low-voltage network 1, it is also possible for the electrical connection between the DC-DC converter device 10 and the low-voltage network 1 to be interrupted in the event of a fault, for example, as a result of an accident or similar event. This can occur, for example, due to a broken cable, a torn-off plug, or the like. In this case, the high-voltage network 2 can be discharged analogously to the procedure with the trend device 16 open.

[0055] If electrical energy is to be removed from the high-voltage network 2 when the separating element 16 is open, as previously described, the electrical energy output by one DC-DC converter 11 on the low-voltage side must be completely absorbed by the other DC-DC converter 12. When controlling the DC-DC converters 11, 12, care must be taken to ensure that the electrical voltage on the low-voltage network 1 side remains within a permissible range. In particular, the DC-DC converters 11, 12 must be controlled such that the output electrical voltage does not exceed a maximum permissible value.

[0056] Figure 6 shows a schematic representation of a block diagram of a DC-DC converter device 10 according to yet another embodiment. The DC-DC converter device 10 of this embodiment differs from the previously described embodiments in particular in that the DC-DC converters 11, 12 on the high-voltage network side and / or the low-voltage side can each be connected to separate high-voltage network sub-networks 2a, 2b or low-voltage network sub-networks 1a, 1b. Preferably, the respective high-voltage network sub-networks 2a, 2b have at least approximately the same electrical voltage level, and the respective low-voltage network sub-networks 1a, 1b also preferably have at least approximately the same electrical voltage level. Furthermore, this embodiment provides coupling elements 14, 15 which can electrically connect the sub-networks 2a, 2b or 1a, 1b on the low-voltage side or the high-voltage side.If, for example, several sub-networks 1a, 1b are provided on the low-voltage side, these sub-networks 1a, 1b can be electrically connected to one another by means of the coupling element 14. Similarly, several sub-networks 2a, 2b on the high-voltage side can be electrically connected to one another by means of a coupling element 15. In particular, the respective sub-networks 1a, 1b or 2a, 2b can be electrically connected to one another when electrical energy is to be dissipated in the high-voltage network 2 or one of the sub-networks 2a, 2b on the high-voltage side, as already explained in connection with the previous exemplary embodiments.

[0057] The coupling element 15 between the sub-networks 2a, 2b on the high-voltage side can, for example, comprise a 400 / 800V battery switch, such as that used in 800V high-voltage on-board electrical systems for charging at 400V DC charging stations. In this case, modules of the traction battery 30 are changed from serial to parallel connection. This corresponds to a connection of the high-voltage sub-networks 2a, 2b analogous to a closed coupling element 15.

[0058] Furthermore, it is also possible to arrange two or more DC-DC converter devices 10 in parallel. In this way, multiple forward and reverse feed paths, as well as isolation and coupling paths, can be created between the sub-networks 2a, 2b or 1a, 1b on the low-voltage side and the high-voltage side, respectively. Thus, a total of multiple DC-DC converters 11, 12 can be present.

[0059] In the preceding embodiment, in order to reduce the electrical energy stored in the high-voltage network 2, at least one DC-DC converter 11, 12 converts electrical energy from the high-voltage network 2 towards the low-voltage network 1 and, at the same time, at least one further DC-DC converter 11, 12 converts electrical energy from the low-voltage network 1 towards the high-voltage network 2.

[0060] In addition, a further operating mode can optionally be provided in which at least one DC-DC converter 11, 12 periodically alternately transfers electrical energy first from the high-voltage network 2 towards the low-voltage network 1 and from the low-voltage network 1 towards the high-voltage network 2. In this way, the electrical energy in the high-voltage network 2 can be dissipated even if only one DC-DC converter 11 or 12 is available, for example because the other DC-DC converter 11 or 12 has failed. This makes a type of emergency operation possible, for example, in the event of the failure of a DC-DC converter 11 or 12. The individual periods for the alternating transfer of electrical energy between the high-voltage network 2 and the low-voltage network 1 should be as short as possible.This prevents the electrical voltage, particularly on the low-voltage side 2, from becoming too high and possibly exceeding a maximum limit. In principle, even with this mode of operation, care must be taken to ensure that electrical voltages remain within specified ranges and, in particular, do not exceed maximum limit values.

[0061] Figure 7 shows a flowchart underlying a method for discharging an intermediate circuit capacitor according to one embodiment. The method can be carried out, in particular, with a DC-DC converter device 10, as previously described in connection with Figures 1 to 6. In particular, the method can comprise any desired steps, as also previously explained in connection with Figures 1 to 6 for the operation of the DC-DC converter device 10. Analogously, the previously described DC-DC converter device 10 can also comprise any desired components that may be required to implement the method described below.

[0062] To discharge the electrical energy in the high-voltage network 2, in particular to discharge an intermediate circuit capacitor 21 in the high-voltage network 2, the following two steps are carried out simultaneously.

[0063] In a step S1, a DC voltage conversion takes place from the

[0064] High-voltage network 2 into the low-voltage network 1. At least one

[0065] DC-DC converters 11, 12 of the DC-DC converter device 10 carry out the said DC voltage conversion before the high-voltage network 2 into the low-voltage network 1.

[0066] At the same time, in a step S2, a DC voltage conversion takes place from the low-voltage network 1 to the high-voltage network 2. At least one further DC voltage converter 11, 12 of the DC voltage converter device 10 carries out the DC voltage conversion from the low-voltage network 1 to the high-voltage network 2.

[0067] The described DC voltage conversions can be carried out at least until an electrical voltage in the high-voltage network 2 and thus across the intermediate circuit capacitor 21 falls below a predetermined threshold value.

[0068] In summary, the present invention relates to discharging energy storage devices in a high-voltage network. For this purpose, a DC-DC converter device with at least two DC-DC converters is provided, wherein at least one DC-DC converter transfers energy from the high-voltage network to a low-voltage network, and in parallel, at least one further DC-DC converter transfers energy from the low-voltage network to the high-voltage network.

Claims

Claims 1. A DC-DC converter device (10), comprising: a first DC-DC converter (11) configured to be coupled to a first DC voltage network (2) at a first terminal and to a second DC voltage network (1) at a second terminal; and a second DC-DC converter (12) configured to be coupled to the first DC voltage network (2) at a first terminal and to the second DC voltage network (1) at a second terminal; wherein, in a first operating mode, the first DC-DC converter (11) is configured to transmit electrical energy from the first terminal to the second terminal of the first DC-DC converter (11), and the second DC-DC converter (12) is configured to simultaneously transmit electrical energy from the second terminal to the first terminal of the second DC-DC converter (12).

2. DC-DC converter device according to claim 1, wherein the first terminals of the first DC-DC converter (11) and the second DC-DC converter (12) are designed to be connected to an intermediate circuit capacitor (21), and wherein the DC-DC converter device (10) comprises a control device (13) which is designed to control the first DC-DC converter (11) and the second DC-DC converter (12) in the first operating mode in order to discharge the intermediate circuit capacitor (21).

3. DC-DC converter device according to claim 2, wherein the control device (13) is designed to set the first operating mode for discharging the intermediate circuit capacitor (21) until an electrical voltage across the intermediate circuit capacitor (21) falls below a predetermined threshold value.

4. DC-DC converter device (10) according to one of claims 1 to 3, wherein in the first operating mode, an electrical power transmitted from the first terminal to the second terminal of the first DC-DC converter (11) is greater than an electrical power transmitted from the second terminal to the first terminal of the second DC-DC converter (12).

5. DC-DC converter device (10) according to one of claims 1 to 3, wherein in the first operating mode, an electrical power provided by the first DC-DC converter (11) to the second terminal of the first DC-DC converter (11) corresponds to an electrical power fed to the second terminal of the second DC-DC converter (12).

6. DC-DC converter device (10) according to one of claims 1 to 5, wherein the second DC voltage network (1) comprises a first DC voltage sub-network (1a) and a second DC voltage sub-network (1b), wherein the first DC-DC converter (11) is designed to be coupled to the first DC voltage sub-network (1a) of the second DC voltage network (1) at the second terminal of the first DC-DC converter (11), and the second DC-DC converter (12) is designed to be coupled to the second DC voltage sub-network (1b) of the second DC voltage network (1) at the second terminal of the second DC-DC converter (12), and wherein the DC-DC converter device (10) comprises a coupling element (14) which is designed to couple the first DC voltage sub-network (1a) and the second DC voltage sub-network (lb) to be electrically coupled together in the first operating mode.

7. DC-DC converter device (10) according to one of claims 1 to 6, wherein the first DC-DC network (2) comprises a first sub-network (2a) and a second sub-network (2b), wherein the first DC-DC converter (11) is designed to be coupled to the first sub-network (2a) of the first DC-DC network (2) at the first terminal of the first DC-DC converter (11), and the second DC-DC converter (12) is designed to be coupled to the second sub-network (2b) of the first DC-DC network (2) at the first terminal of the second DC-DC converter (12), and wherein the DC-DC converter device (10) comprises a further coupling element (15) which is designed to electrically couple the first sub-network (2a) and the second sub-network (2b) of the first DC-DC network (2) to one another in the first operating mode.

8. DC voltage converter device (10) according to one of claims 1 to 7, wherein in a second operating mode the first DC voltage converter (11) and / or the second DC voltage converter (12) are designed to transmit electrical energy from the first DC voltage network (2) to the second DC voltage network (1), and in a third operating mode the first DC voltage converter (11) and / or the second DC voltage converter are designed to transmit electrical energy from the second DC voltage network (1) to the first DC voltage network (2).

9. DC voltage converter device (10) according to one of claims 1 to 8, wherein in a further operating mode the first DC voltage converter (11) is designed to supply electrical energy alternately from the first terminal the second terminal of the first DC-DC converter (11) and from the second terminal to the first terminal of the second DC-DC converter (11).

10. An electric vehicle, comprising: a high-voltage network (2) with an intermediate circuit capacitor (21); a low-voltage network (1); and a DC-DC converter device (10) according to one of claims 1 to 9, wherein the first terminals of the first DC-DC converter (11) and the second DC-DC converter (12) are electrically coupled to the high-voltage network (1), and wherein the second terminals of the first DC-DC converter (11) and the second DC-DC converter (12) are electrically coupled to the low-voltage network.

11. A method for discharging an intermediate circuit capacitor (21) in a first DC voltage network (2) by means of a DC voltage converter device (10) comprising at least two DC voltage converters (11, 12), wherein a first DC voltage converter (11) is coupled to the first DC voltage network (2) at a first terminal and to a second DC voltage network (1) at a second terminal, and a second DC voltage converter (12) is coupled to the first DC voltage network (2) at a first terminal and to the second DC voltage network (1) at a second terminal, and wherein the following steps are carried out simultaneously in the method: Transferring (Sl) electrical energy from the first terminal to the second terminal of the first DC-DC converter (11), and Transferring (S2) electrical energy from the second terminal to the first terminal of the second DC-DC converter (12).

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