DC voltage converter and method for operating a DC voltage converter

Abstract

1. The invention relates to a DC voltage converter (10) for energy transmission between a high-voltage network (12) and a low-voltage network (14), wherein the DC voltage converter (10) is bidirectional, having an input terminal (11), an output terminal (15), a transformer (20), having a first converter (30) between the input terminal (11) and the primary side (22) of the transformer (20) and a second converter (40) between the output terminal (15) and the secondary side (24) of the transformer (20), wherein a second capacitor (42) is connected in parallel to the second converter between the second converter (40) and the output terminal (15). A switching element (50) is connected between a connection pole of the output terminal (15) and the corresponding terminal of the second capacitor, wherein a diode (52) is connected in parallel to the switching element (50), wherein the diode (52) is aligned in such a way that when the switching element (50) is open, energy transmission from the output terminal (15) towards the input terminal (11) is prevented.

Description

[0001] Description

[0002] title and methods for operating a converter

[0003] The present invention relates to a DC-DC converter, in particular a DC-DC converter for energy transmission between a high-voltage network and a low-voltage network. Furthermore, the invention relates to a method for operating the DC-DC converter. Furthermore, the invention relates to a drive train comprising the DC-DC converter, a vehicle comprising a drive train, a computer program, and a computer-readable storage medium.

[0004] State of the art

[0005] Vehicles with an electrified powertrain include a high-voltage network or traction network. The electrical energy from a high-voltage battery or a fuel cell is transferred via this high-voltage network via an inverter to a prime mover that powers the vehicle. These vehicles also include a low-voltage network to supply the vehicle's control units. In addition to control units or other consumers, a low-voltage battery is connected to the low-voltage network. To buffer the low-voltage network and recharge the low-voltage battery, a DC-DC converter is connected between the high-voltage network and the low-voltage network. This converter transfers electrical energy from the high-voltage network to the low-voltage network. Bidirectional DC-DC converters are increasingly being used, which also enable energy transfer in the opposite direction, from the low-voltage network to the high-voltage network.This functionality is used in particular to charge the capacitances or capacitors located in a discharged high-voltage network to the voltage range of the high-voltage battery before the high-voltage battery is connected to a discharged high-voltage network. This effectively minimizes the transient currents that would otherwise result when the high-voltage battery is connected. However, this functionality requires increased safety precautions, particularly in operating situations or operating points where charging of the high-voltage network is not permitted, for example, for repair work on the high-voltage network or components connected to it, or after an accident where continuous shielding of the high-voltage network cannot be ensured.There is therefore a need to provide a DC-DC converter and a method for operating a bidirectional DC-DC converter in which, on the one hand, charging of the high-voltage network from the low-voltage network can be prevented, but, on the other hand, energy transfer from the high-voltage network to the low-voltage network is still possible.

[0006] Disclosure of the invention

[0007] A DC-DC converter for transmitting energy between a high-voltage network and a low-voltage network is provided, wherein the DC-DC converter is bidirectional. This means that the DC-DC converter is configured, depending on the control, to both transfer electrical energy from the high-voltage network to the low-voltage network in buck mode and to transfer electrical energy from the low-voltage network to the high-voltage network in boost mode. The DC-DC converter comprises an input terminal designed to be coupled to the high-voltage network and an output terminal designed to be coupled to the low-voltage network. Preferably, the input terminal is two-pole and has a positive and a negative connection pole. Preferably, the output terminal is two-pole and has a positive and a negative connection pole.In this context, coupled is used synonymously with connected, electrically connected, or switched. The DC-DC converter further comprises a transformer with a primary side and a secondary side. The transformer preferably serves to provide galvanic isolation between the input terminal and the output terminal. The DC-DC converter comprises a first converter between the input terminal and the primary side of the transformer. The first converter preferably converts a DC voltage applied to the input terminal into an AC voltage applied to the primary side of the transformer (buck operation), or vice versa (boost operation). The DC-DC converter further comprises a second converter between the output terminal and the secondary side of the transformer.The second converter preferably converts an alternating voltage applied to the secondary side of the transformer into a direct voltage applied to the output terminal (buck operation), or vice versa (boost operation). The topologies of the first and second converters preferably correspond to those of the primary and secondary sides of known bidirectional, galvanically isolated DC-DC converters, for example a flyback or active bridge topology, preferably a semiconductor switch, an active half-bridge, or a full bridge. A first capacitor is preferably connected in parallel between the first converter and the input terminal. A second capacitor is connected in parallel between the second converter and the output terminal. The capacitors preferably serve to smooth the voltage at the output and / or input terminal and / or the currents at the output and / or input terminal.

[0008] According to the invention, a switching element is connected between a connection pole of the output connection and the corresponding connection of the capacitor, with a diode connected in parallel to the switching element. The diode is aligned such that, when the switching element is open, energy can be transferred from the input connection, i.e. from the high-voltage network, towards the output connection, i.e. to the low-voltage network, and energy can be transferred from the output connection, i.e. from the low-voltage network, towards the input connection, i.e. to the high-voltage network, is prevented. The connection pole of the output connection is preferably the negative or the positive connection pole of the output connection. The corresponding connection pole of the capacitor is preferably the negative or the positive connection pole of the capacitor, depending on the choice of connection pole of the output connection.The switching element is preferably a semiconductor switch, for example a MOSFET or an IGBT, which preferably already includes the parallel-connected diode as a body diode. Discrete individual switching elements and parallel-connected diodes are also possible. The anode of the diode is preferably connected to the negative terminal of the output terminal when the switching element is connected between the negative terminal of the output terminal and the negative terminal of the capacitor.The cathode of the diode is preferably connected to the positive terminal of the output terminal when the switching element is connected between the positive terminal of the output terminal and the positive terminal of the capacitor. When the switching element is open, and thus preferably also when the DC-DC converter is de-energized, the diode prevents energy transfer from the output terminal to the input terminal of the DC-DC converter and prevents a corresponding load current through the DC-DC converter. When the switching element is closed, and thus preferably also when a semiconductor switching element is activated, the diode is bridged by means of the switch and energy transfer is possible both from the output terminal to the input terminal of the DC-DC converter and vice versa. Likewise, a load current through the DC-DC converter is possible in both directions when the switching element is closed.

[0009] Advantageously, a bidirectional DC-DC converter is provided for energy transmission between a high-voltage network and a low-voltage network, in which energy transmission from the low-voltage network to the high-voltage network can be reliably prevented by means of a switch, while energy transmission from the high-voltage network to the low-voltage network is still possible.

[0010] In one embodiment, the switching element is controlled or opened depending on a load current of the DC-DC converter. Preferably, the switching element is opened when the load current is less than a predeterminable amount.

[0011] Preferably, a load current through the DC-DC converter is determined using a suitable measuring device. This can be done outside or inside the DC-DC converter. For example, a load current through the DC-DC converter can be determined using a shunt between a terminal and a connected first or second converter. Preferably, when the switching element is open, the load current flows through the diode. To prevent overloading of the diode, the switching element is opened depending on the load current. Preferably, the switching element is closed as long as the load current is greater than a predefined value.

[0012] Advantageously, a bidirectional DC-DC converter is provided in which overloading of a diode is prevented.

[0013] In one embodiment, the switching element is controlled or opened depending on the voltage of the DC-DC converter. Preferably, the switching element is opened when the voltage is less than a predeterminable value.

[0014] Preferably, a voltage at the input terminal or output terminal of the DC-DC converter is determined using a suitable measuring device. This can be done outside or inside the DC-DC converter. For example, a voltage at the DC-DC converter can be determined by measuring the voltage between the connection poles of the input or output terminal. Preferably, when the switching element is open, a load current that is dependent on the voltage flows through the diode. To prevent overloading of the diode, the switching element is opened depending on the voltage, preferably the output voltage. Preferably, the switching element is closed as long as the voltage is greater than a predeterminable amount. Preferably, the diode operation resulting when the switching element is open is used as rarely as possible in order not to shorten the service life of the diodes as much as possible.

[0015] Advantageously, a bidirectional DC-DC converter is provided in which overloading of a diode is prevented.

[0016] In one embodiment, the switching element is controlled or opened depending on a preferably currently existing operating point of the DC-DC converter. The switching element is preferably opened if, at the currently existing operating point, energy transfer from the output connection to the input connection is to be prevented. An operating point is preferably determined using a suitable control device. This can take place outside or inside the DC-DC converter. Corresponding operating points can be the parking of a vehicle, a repair mode of the vehicle, an accident, or a signal or trigger that is set at a corresponding operating point. At these operating points, a discharge of the high-voltage network must be ensured, which is why energy transfer from the output connection to the input connection is prevented.For this purpose, the switching element is opened depending on a corresponding currently existing operating point at which energy transfer from the output connection to the input connection is prevented.

[0017] Advantageously, a bidirectional DC-DC converter with increased operational reliability is provided.

[0018] Furthermore, the invention relates to a drive train of a vehicle with a high-voltage network and a low-voltage network, wherein the drive train comprises at least one described DC-DC converter.

[0019] A vehicle's drivetrain converts electrical energy from an energy source into mechanical energy, which is used to propel the vehicle. In an electric drivetrain, for example, the electrical energy from an energy source in the high-voltage network is converted by an inverter into an alternating voltage, which is used to operate an electrical machine. These vehicles also include a low-voltage network to supply the control units in the vehicle. In addition to control units or other consumers, a low-voltage battery is connected to the low-voltage network. To buffer the low-voltage network and to recharge the low-voltage battery, a DC-DC converter is connected between the high-voltage network and the low-voltage network. A drivetrain with a modified bidirectional DC-DC converter with increased operational reliability is advantageously provided.

[0020] The invention further relates to a vehicle with a drive train as previously described. Advantageously, a vehicle is provided whose operational reliability is increased. Furthermore, the invention relates to a method for operating a DC-DC converter with a control unit. The method comprises the steps of determining a load current of the DC-DC converter, a voltage of the DC-DC converter, or an operating point of the DC-DC converter, and controlling or opening the switching element depending on the determined load current, the determined voltage, or the determined operating point.

[0021] A method for operating a bidirectional DC-DC converter is provided. Depending on a load current, a voltage, and / or an operating point, a switching element is opened by the control unit. This prevents energy transfer from the output terminal to the input terminal. Advantageously, a method for operating a DC-DC converter is provided whose operational reliability is increased.

[0022] Furthermore, the invention relates to a computer program comprising instructions which, when the program is executed by the control unit, cause the control unit to carry out the steps of the method.

[0023] Furthermore, the invention relates to a computer-readable storage medium comprising instructions which, when executed by the control unit, cause it to carry out the steps of the method.

[0024] It is understood that the features, properties and advantages of the DC-DC converter apply accordingly to the process or the powertrain and the vehicle and vice versa.

[0025] Further features and advantages of embodiments of the invention will become apparent from the following description with reference to the accompanying drawings.

[0026] Brief description of the drawing In the following, the invention will be explained in more detail with the aid of some figures, which show:

[0027] Figure 1 is a schematic diagram of a DC-DC converter,

[0028] Figure 2 is a schematic representation of a vehicle with a drive train with a DC-DC converter,

[0029] Figure 3 shows a schematically illustrated method for operating a DC-DC converter.

[0030] Embodiments of the invention

[0031] Figure 1 shows a DC-DC converter 10 for transmitting energy between a high-voltage network 12 and a low-voltage network 14. The DC-DC converter 10 comprises an input terminal 11 designed to be coupled to the high-voltage network 12. Furthermore, the DC-DC converter 10 comprises an output terminal 15 designed to be coupled to the low-voltage network 14. The DC-DC converter 10 comprises a transformer 20 with a primary side 22 and a secondary side 24. The DC-DC converter 10 further comprises a first converter 30 between the input terminal 11 and the primary side 22 of the transformer 20 and a second converter 40 between the output terminal 15 and the secondary side 24 of the transformer 20. Preferably, a first capacitor 32 is connected in parallel with the first converter 30 between the first converter 30 and the input terminal 10.A second capacitor 42 is connected in parallel between the second converter 40 and the output terminal 15. The DC-DC converter 10 is bidirectional. This means that the DC-DC converter 10, and preferably the first and second converters 30, 40, are configured, depending on the control, to transmit electrical energy from the input terminal 11, i.e., from the high-voltage network 12, to the output terminal 15, i.e., into the low-voltage network 14, as well as to transmit electrical energy from the output terminal 15, i.e., from the low-voltage network 14, toward the input terminal 11, i.e., into the high-voltage network 12. A switching element 50 is connected between a terminal pole of the output terminal 15 and the corresponding terminal of the second capacitor, with a diode 52 connected in parallel with the switching element 50.The diode 52 is oriented such that, when the switching element 50 is open, energy transfer from the input terminal 11, i.e., from the high-voltage network 12, toward the output terminal 15, i.e., to the low-voltage network 14, is enabled, and energy transfer from the output terminal 15, i.e., from the low-voltage network 14, toward the input terminal 11, i.e., to the high-voltage network 12, is prevented. Preferably, a control unit 60 is provided inside or outside the DC-DC converter 10 and configured to determine a load current, a voltage, or an operating point of the DC-DC converter 10 and to control the switching element 50 depending on at least one of the determined values.

[0032] Figure 2 shows a schematic representation of a vehicle 200 with an electric drive train 100. The vehicle 200 is shown here only as an example with four wheels, although the invention can equally be used in any vehicle with any number of wheels on land, on water and in the air. The drive train 100 comprises a high-voltage network 12 and a low-voltage network 14 and at least one DC-DC converter 10. The high-voltage network 12 preferably comprises a plurality of high-voltage components, preferably a high-voltage battery 120, an inverter 130 or power inverter and / or an electric machine 140 as the drive machine for the vehicle 200. The high-voltage components are electrically connected to one another via a high-voltage power network, i.e. via the electrical lines of the high-voltage network. The low-voltage network 14 preferably comprises a plurality of low-voltage components, preferably at least a first photovoltaic module 210 or a driving dynamics module, possibly.an energy storage device 220, for example a capacitor or an on-board network battery, and / or further low-voltage consumers 230, for example further control units for the vehicle 200. The low-voltage components are electrically connected to one another via a low-voltage power network, i.e. via the electrical lines of the low-voltage network. Figure 3 shows a schematically illustrated method 300 for operating a DC-DC converter 10. The method begins with step 305. In step 320, a load current of the DC-DC converter 10, a voltage of the DC-DC converter 10 and / or an operating point of the DC-DC converter 10 are determined. In step 330, the switching element 50 is controlled or opened depending on the determined load current, the determined voltage and / or the determined operating point. The method ends with step 335.

Claims

Claims 1 . A DC-DC converter (10) for transmitting energy between a high-voltage network (12) and a low-voltage network (14), the DC-DC converter (10) being bidirectional, comprising: an input terminal (11) configured to be coupled to the high-voltage network (12); an output terminal (15) configured to be coupled to the low-voltage network (14);a transformer (20) with a primary side (22) and a secondary side (24), with a first converter (30) between the input connection (11) and the primary side (22) of the transformer (20) and a second converter (40) between the output connection (15) and the secondary side (24) of the transformer (20), wherein a second capacitor (42) is connected in parallel with the second converter between the second converter (40) and the output connection (15), characterized in that a switching element (50) is connected between a connection pole of the output connection (15) and the corresponding connection of the second capacitor, wherein a diode (52) is connected in parallel with the switching element (50), wherein the diode (52) is aligned such that when the switching element (50) is open, energy is transferred from the input connection (11) in the direction of the output connection (15) and an energy; Transmission from the output terminal (15) towards the input terminal (11) is prevented.

2. DC voltage converter according to claim 1, wherein opening of the switching element takes place as a function of a load current of the DC voltage converter (10), in particular when the amount of the load current is less than a predeterminable amount.

3. DC voltage converter according to claim 1, wherein opening of the switching element takes place as a function of a voltage of the DC voltage converter (10), in particular when the amount of the voltage is less than a predeterminable amount.

4. DC voltage converter according to claim 1, wherein opening of the switching element takes place as a function of an operating point of the DC voltage converter (10), in particular when energy transfer from the output terminal (15) to the input terminal (11) is to be prevented at the operating point.

5. Drive train (100) of a vehicle (200) with a high-voltage network (12) and a low-voltage network (14), wherein the drive train comprises at least one DC-DC converter (10) according to one of claims 1 to 4.

6. Vehicle (200) having a drive train (100) according to claim 5.

7. Method (300) for operating a DC-DC converter (10) according to one of claims 1 to 4 with a control unit (60), comprising the steps: Determining (320) a load current of the DC-DC converter (10), a voltage of the DC-DC converter (10) or an operating point of the DC-DC converter (10) and Controlling or opening (330) the switching element (50) depending on the determined load current, the determined voltage and / or the determined operating point.

8. A computer program comprising instructions which, when executed by the control unit, cause the control unit to perform the steps of the method (300) according to claim 7.

9. A computer-readable storage medium comprising instructions which, when executed by the control unit, cause the control unit to perform the steps of the method (300) according to claim 7.

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