DE102022101913A1 - Circuit arrangement of a DC converter for supplying a low-voltage DC network from a high-voltage DC voltage, the relevant supply method and an electric vehicle - Google Patents

Abstract

The invention relates to a circuit arrangement (1, 15) of a DC voltage converter for the electrical supply of a low-voltage DC voltage network (22) with a low-voltage DC voltage (LV) from a high-voltage DC voltage (HV, HV*) provided by a high-voltage battery (21), having a transformer (T). a variably definable winding ratio, a high-voltage converter unit (2) for converting the high-voltage direct current (HV, HV*) into a high-voltage alternating voltage supplied to the transformer (T), and a low-voltage converter unit (3) for converting a low-voltage alternating current output by the transformer (T) into the low-voltage direct current (LV ), wherein the high-voltage converter unit (2) is connected to the transformer (T) with the interposition of a plurality of controllable switching elements (S1, S2, S3) in such a way that, depending on the controlled switching states of the respective switching elements (S1, S2, S3), the effective one for the DC voltage conversion winding ratio of the transformer (T) can be changed. The invention also relates to a relevant supply method and an electric vehicle (20) with such a circuit arrangement (1, 15).

Description

The invention relates to a circuit arrangement of a DC voltage converter for the electrical supply of a low-voltage DC voltage network with a low-voltage DC voltage from a high-voltage DC voltage provided by a high-voltage battery. The invention also relates to a method for the electrical supply of a low-voltage DC voltage network with a low-voltage DC voltage from a high-voltage DC voltage provided by a high-voltage battery by means of a circuit arrangement of a DC-DC converter. Furthermore, the invention relates to an electric vehicle with such a circuit arrangement.

Electric vehicles (EV) such as hybrid electric vehicles (HEV) or battery electric vehicles (BEV) usually have a high-voltage battery (e.g. traction battery) as an energy store with a nominal voltage of 400 V or 800 V, for example. In the present context, high-voltage or HV voltage or high-voltage or HV potential is understood to mean an electrical DC voltage of greater than 60 V, in particular greater than 200 V, e.g. B. 400 V or 800 V to about 1500 V. Low-voltage or LV voltage or low-voltage or LV potential is understood to mean an electrical voltage of less than or equal to 60 V, namely z. B. 6 V, 12 V, 24 V, 48 V or 60 V. In connection with the invention disclosed herein, the terms high-voltage and low-voltage are used synonymously with the terms high-voltage and low-voltage potential with the voltage levels and voltage ranges specified above.

When charging a high-voltage battery with a high-voltage DC voltage of 800 V, in particular a traction battery of an electric vehicle, it can make sense to convert the high-voltage battery into a parallel connection of two battery sub-stacks, each with 400 V stacks.

To a low-voltage DC network, z. B. a 12 V or 24 V electrical system of an electric vehicle, from a high-voltage DC voltage of a high-voltage battery, z. B. 400 V or 800 V battery, it is known to use a DC voltage converter (also referred to herein as a DC / DC converter) for the voltage adjustment of the high-voltage DC voltage to the low-voltage DC voltage. If the low-voltage network with several different high-voltage DC voltage, the voltage range z. B. can include a few 100 V, can be supplied, results for the DC-DC converter that this is operated at least in some applications far from its optimal operating point, causing the efficiency drops sharply. The electronic components of the DC-DC converter are heavily loaded by the shift in the operating point and must be dimensioned larger because the internal currents increase extremely. Last but not least, this results in a more complex design for a cooling device for dissipating the heat loss and, overall, in a larger installation space requirement, which makes compact integration of various electronic components more difficult or even prevents it.

Against this background, the invention is based on the object of providing an improved circuit arrangement for the electrical supply of a low-voltage direct voltage network from a high-voltage direct voltage, a method for the electrical supply of a low-voltage direct voltage network from a high-voltage direct voltage and an electric vehicle, which supply the low-voltage direct voltage network from the high-voltage direct voltage with a significantly improved efficiency, the high-voltage direct voltage on the input side covering a wide voltage range. Electronic components used for voltage transformation should be less heavily loaded and more compact so that, for example, their cooling can be ensured with significantly less effort. In addition, a compact integration of several electronic components should be possible.

This object is achieved by a circuit arrangement having the features of claim 1, by an electric vehicle having the features of claim 11 and by a method having the features of claim 12. Further, particularly advantageous configurations of the invention are disclosed in the respective dependent claims.

It should be pointed out that the features listed individually in the claims can be combined with one another in any technically sensible way (even across category boundaries, for example between method and device) and show further refinements of the invention. The description additionally characterizes and specifies the invention, in particular in connection with the figures.

It should also be noted that a conjunction "and/or" used herein, standing between two features and linking them to one another, is always to be interpreted in such a way that in a first embodiment of the subject matter according to the invention only the first feature can be present, in a second embodiment only the second feature can be present and in a third embodiment both the first and the second feature can be present.

Also, as used herein, a term "about" is intended to indicate a range of tolerance considered normal by those skilled in the art. In particular, the term “approximately” means a tolerance range of the related size of up to a maximum of +/-20%, preferably up to a maximum of +/-10%.

Relative terms relating to a feature, such as "larger", "smaller", "higher", "lower" and the like, are to be interpreted within the scope of the invention in such a way that manufacturing and / or implementation-related size deviations of the relevant feature, which are within the manufacturing / implementation tolerances defined for the respective production or implementation of the relevant feature, are not covered by the respective relative term. In other words, a size of a feature is only then as z. B. "larger", "smaller", "higher", "lower" and the like to be regarded as a size of a comparative feature if the two compared sizes differ so significantly in their value that this difference in size certainly does not fall within the production/performance-related tolerance range of the relevant feature, but is the result of targeted action.

According to the invention, a circuit arrangement of a DC-DC converter for the electrical supply of a low-voltage DC network (without limitation, e.g. a low-voltage vehicle electrical system of an electric vehicle) with a low-voltage DC voltage from a high-voltage DC voltage provided by a high-voltage battery (without limitation, e.g. a traction battery of an electric vehicle) has a transformer with a variably definable winding ratio, a high-voltage converter unit for converting the high-voltage DC voltage into a high-voltage AC voltage supplied to the transformer, and a low-voltage converter unit Transforming a low-voltage AC voltage emitted by the transformer into the low-voltage DC voltage. The high-voltage converter unit is connected to the transformer with the interposition of a plurality of controllable switching elements in such a way that the turns ratio of the transformer that is effective for the DC voltage conversion can be changed depending on the controlled switching states of the respective switching elements.

In this way, the turns ratio of the transformer can always be set such that, depending on the high-voltage DC voltage available on the input side, a high or optimal degree of efficiency can always be achieved when supplying the low-voltage DC voltage network from the actual high-voltage DC voltage. In particular, the circuit arrangement of the DC voltage converter can always be operated at an optimum operating point, as a result of which the electrical load on the electronic components involved in the electrical supply of the low-voltage network is significantly reduced. These components, e.g. B. power semiconductors such as semiconductor switches, etc., the transformer, capacitors, etc., can now be dimensioned smaller. They also generate less heat loss. A compact integration of the circuitry z. B. in other units can be implemented without much effort. Overall, with the circuit arrangement according to the invention, costs, weight, cooling requirements and construction volume can be reduced.

The switching elements can be actuated, for example, by an electronic control device (e.g. microcontroller, microprocessor, etc.), which is designed to determine the switching states of the switching elements in terms of a turns ratio that offers a high or optimum efficiency for the supply of the low-voltage DC network from the high-voltage DC voltage that is actually fed in, even if the level of the high-voltage DC voltage covers a wide voltage range, which otherwise means a significant shift in the operating point of the circuit arrangement from a favorable, energy-efficient operating point.

In an advantageous development of the subject matter of the invention, the circuit arrangement can have two operating modes, with the high-voltage battery providing a nominal high-voltage DC voltage in the first operating mode and providing a high-voltage DC voltage that is reduced compared to the nominal high-voltage DC voltage in the second operating mode, the switching states of the switching elements being controlled in the second operating mode in such a way that the effective turns ratio in the second operating mode is reduced compared to the effective turns ratio in the first operating mode.

The voltage range between the nominal high-voltage direct voltage and the reduced high-voltage direct voltage can be between 200 V and 900 V, for example. In particular, the input voltage range can be between about 240V and 830V. In any case, the voltage range of the high-voltage direct current can include a few (few) 100 V, as above, for example, about 590 V to 700 V.

For example, the high-voltage battery can have a nominal high-voltage direct current of z. B. provide 800 V, while in certain applications a reduced high-voltage DC voltage of only about half, namely 400 V, provides. In this case, the one includes gang voltage range a range of about 400 V. The battery can provide the nominal high-voltage DC voltage in the first operating mode described above and the reduced high-voltage DC voltage in the second operating mode.

According to a further advantageous embodiment, the first operating mode is a discharging mode of the high-voltage battery, i.e. energy is taken from the high-voltage battery, for example in order to supply electricity to a high-voltage network (e.g. an electric drive of an electric vehicle), and the second operating mode is a charging mode of the high-voltage battery, i.e. the high-voltage battery is charged, in particular when charging at a corresponding charging device. For example, in certain applications it can be beneficial to split the high-voltage battery into two battery sub-stacks connected in parallel when charging on a charging device that provides a lower charging voltage than the nominal high-voltage DC voltage of the high-voltage battery, which then each provide only half of the nominal high-voltage DC voltage.

The low-voltage DC network supplied from the high-voltage DC voltage of the high-voltage battery can have a low-voltage DC voltage in a range from approximately 6 V to 50 V, particularly preferably approximately 8 V to 14 V.

According to a preferred refinement, the transformer has a first primary-side winding with a first winding connection and a second winding connection, and a second primary-side winding which is magnetically coupled to the first winding and has a first winding connection and a second winding connection, with the second winding connection of the first winding being designed as a common winding connection with the first winding connection of the second winding, which connects the first winding and the second winding in series. The first winding connection of the first winding is connected to a first output pole of the high-voltage converter unit, and the common winding connection and the second winding connection of the second winding are each connected to a second output pole of the high-voltage converter unit, which is different from the first output pole, with the interposition of one of the switching elements.

The two output poles of the high-voltage converter device are to be understood as two starting points between which an electrical voltage is generally present during operation of the circuit arrangement, which means that they have different electrical potentials.

The circuit arrangement with two switching elements described above makes it possible to reduce the series connection of the two primary-side windings to only one active, ie. H. to switch over the winding that is effectively involved in the voltage conversion, namely to selectively switch the common winding connection and/or the second winding connection of the second winding to the second output pole of the high-voltage converter unit. Depending on the number of turns of the respective windings, the operating point of the circuit arrangement can be adapted to the actually fed high-voltage direct current in the sense of a favorable efficiency. For example, the number of turns of the first winding can correspond to the number of turns of the second winding, whereby the turns ratio of the transformer is optimally matched to a nominal high-voltage DC voltage, e.g. B. 800 V, and reduced by about half, reduced high-voltage DC, z. B. 400 V, can be adjusted.

According to a further advantageous embodiment, the transformer has a first primary-side winding with a first winding terminal and a second winding terminal and a second primary-side winding magnetically coupled to the first winding with a first winding terminal and a second winding terminal, the first winding terminal of the first winding being connected to a first output pole of the high-voltage converter unit and the second winding terminal of the second winding being connected to a second output pole of the high-voltage converter unit that is different from the first output pole. The first winding connection of the first winding and the first winding connection of the second winding are connected to one another with the interposition of a first of the switching elements. The second winding short circuit of the first winding is connected to the first winding connection of the second winding with the interposition of a second of the switching elements. The second winding connection of the first winding is connected to the second output pole with the interposition of a third of the switching elements.

The above-described circuit arrangement with three switching elements makes it possible to switch the two primary-side windings of the transformer either in a series connection according to a first turns ratio or to switch the two primary-side windings individually in parallel with one another according to a second turns ratio. In other words, both primary-side windings are actively involved in the voltage conversion in all operating states, so that the circuit arrangement is essentially always operated at its optimal operating point and the efficiency is only compared to use one of the two primary-side windings for voltage conversion can be increased again. Depending on the number of turns of the respective windings, the operating point of the circuit arrangement can be adapted to the actually fed high-voltage direct current in the sense of a favorable efficiency. For example, the number of turns of the first winding can correspond to the number of turns of the second winding, whereby the turns ratio of the transformer is optimally matched to a nominal high-voltage DC voltage, e.g. B. 800 V, and reduced by about half, reduced high-voltage DC, z. B. 400 V, can be adjusted.

In a particularly preferred embodiment, the switching elements are in the form of bidirectional isolating switches in the form of N-FETs connected back-to-back in series, photoMOS relays, triacs, electromechanical relays or a combination thereof. The switching elements can be switched via a correspondingly supplied switching signal (e.g. output by a control device) into an open switching state, in which a current flow in both current directions is prevented, and into a closed switching state, in which a current flow in both current directions is permitted.

To further ensure high efficiency of the circuit arrangement with high-voltage direct voltages of different magnitudes on the input side, another embodiment of the subject invention provides that the frequency of the high-voltage alternating voltage is at least 50 kHz, preferably at least 100 kHz. In other words, the high-voltage converter unit uses the fed-in high-voltage direct voltage to generate the high-voltage alternating voltage fed to the transformer on the primary side at the frequency described above.

The high-voltage converter unit can preferably be designed as a full bridge with four electronically controllable semiconductor switches.

Furthermore, the low-voltage converter device can have a rectifier, which converts the low-voltage AC voltage output by the transformer into the low-voltage DC voltage for supplying the low-voltage DC voltage network. In addition, further electronic components can be provided, for example a safety switching unit, which interrupts the feeding of the low-voltage DC voltage into the low-voltage network in the event of a fault/fault (e.g. short circuit) in the circuit arrangement and/or ensures current limitation to protect the electrical consumers supplied in the low-voltage network.

According to a further aspect of the invention, an electric vehicle has a high-voltage battery, e.g. B. 800 V traction battery, a low-voltage vehicle electrical system (e.g. 12 V network) for the low-voltage supply of electrical consumers in the vehicle and a circuit arrangement of a DC voltage converter for the electrical supply of the low-voltage vehicle electrical system with a low-voltage DC voltage from a high-voltage DC voltage provided by the high-voltage battery. In particular, the circuit arrangement can be designed according to one of the configurations disclosed herein, that is to say the low-voltage DC voltage network mentioned in this context corresponds to the low-voltage on-board network of the vehicle.

It should be pointed out that with regard to vehicle-related definitions of terms and the effects and advantages of vehicle-specific features, reference can be made in full to the disclosure of analogous definitions, effects and advantages of the circuit arrangement according to the invention and vice versa. In this respect, explanations of the same features, their effects and advantages are largely dispensed with in favor of a more compact description, without such omissions having to be interpreted as a restriction for the respective subject matter of the invention.

The high-voltage battery can, for example, be provided, without any mandatory restriction, to supply a high-voltage electrical system of the vehicle, for example an electric drive of the electric vehicle, such as a hybrid electric vehicle (HEV) or battery electric vehicle (BEV).

With the advantages already known from the explanation of the circuit arrangement according to the invention, the circuit arrangement in the electric vehicle can be operated with high efficiency at different high-voltage DC voltages by the operating point of the circuit arrangement being adapted depending on the actually feeding high-voltage DC voltage by appropriate switching of the switching elements to determine a suitable winding ratio of the transformer.

The electric vehicle having the circuit arrangement according to the invention proves to be particularly advantageous during charging processes of the high-voltage battery (e.g. on vehicle-external charging devices) if the high-voltage battery (e.g. 800 V battery) is divided into two battery sub-stacks connected in parallel, each of which only provides half (ie 400 V) of a nominal high-voltage DC voltage of the high-voltage battery. In these applications (ie during charging), the working point of the circuit arrangement can despite a wide input voltage range of several 100 V depending on the actual level of the input voltage in an optimal range and the low-voltage vehicle electrical system can continue to be supplied with high efficiency from the high-voltage DC voltage.

Furthermore, the compact design of the circuit arrangement makes it possible to integrate the circuit arrangement in a so-called "power module" of the electric vehicle, i.e. to combine the DC-DC converter including the high-voltage converter unit, which is preferably designed as a full bridge, the low-voltage converter unit with a rectifier, the switching unit and the transformer in one compact component.

According to yet another aspect of the invention, in a method for electrically supplying a low-voltage DC network (e.g. low-voltage vehicle electrical system of an electric vehicle) with a low-voltage DC voltage from a high-voltage DC voltage provided by a high-voltage battery (e.g. traction battery of an electric vehicle) by means of a circuit arrangement of a DC-DC converter, which has a transformer with a variably definable winding ratio, a high-voltage converter unit for converting the high-voltage DC voltage into a high-voltage AC voltage supplied to the transformer and a low voltage converter unit for converting a low-voltage AC voltage output by the transformer into low-voltage DC voltage, the high-voltage converter unit is connected to the transformer with the interposition of a plurality of controllable switching elements and the turns ratio of the transformer that is effective for the DC voltage conversion is controlled by controlling the switching states of the respective switching elements.

With regard to process-related definitions of terms and the effects and advantages of process-related features, reference can also be made in full to the disclosure of analogous definitions, effects and advantages of the circuit arrangement according to the invention, and vice versa. Once again, explanations of the same features, their effects and advantages are largely omitted in favor of a more compact description, without such omissions having to be interpreted as a restriction for the respective subject matter of the invention.

According to a preferred development of the subject matter of the invention, a nominal high-voltage DC voltage is provided by the high-voltage battery in a first operating mode (e.g. driving an electric vehicle) and a high-voltage DC voltage which is reduced compared to the nominal high-voltage DC voltage is provided by the high-voltage battery in a second operating mode (e.g. a state of charge of an electric vehicle). The switching states of the switching elements are controlled in such a way that the effective turns ratio in the second operating mode is reduced compared to the effective turns ratio in the first operating mode. As a result, the working point of the circuit arrangement can be adapted to the high-voltage direct current fed in at the moment in terms of optimum efficiency of the voltage transformation from the high-voltage level to the low-voltage level by changing the transformer winding ratio.

In a particularly preferred development of the subject matter of the invention, the reduced high-voltage direct current is reduced to half the nominal high-voltage direct current, as this—as explained herein—can be advantageous, for example, when charging an 800 V high-voltage battery on a 400 V charging device.

The high-voltage battery can be discharged during the first operating mode by supplying electrical consumers such as an electric drive of an electric vehicle with energy, and charged during the second operating mode, in particular at a charging device such. B. a charging station for an electric vehicle.

• 1 ein Schaltungsdiagramm eines ersten Ausführungsbeispiefs einer Schaltungsanordnung gemäß der Erfindung,
• 2 ein Schaltungsdiagramm eines zweiten Ausführungsbeispiels einer Schaltungsanordnung gemäß der Erfindung,
• 3 Schaltungsdiagramme mehrerer bevorzugter Schaltelemente zur Verwendung in Ausführungsformen einer Schaltungsanordnung gemäß der Erfindung und
• 4 ein Blockdiagramm eines Ausführungsbeispiel eines Elektrofahrzeugs gemäß der Erfindung.

Further features and advantages of the invention result from the following description of exemplary embodiments of the invention, which are not to be understood as limiting, which are explained in more detail below with reference to the drawing. In this drawing show schematically:

• 1 a circuit diagram of a first exemplary embodiment of a circuit arrangement according to the invention,
• 2 a circuit diagram of a second embodiment of a circuit arrangement according to the invention,
• 3 Circuit diagrams of several preferred switching elements for use in embodiments of a circuit arrangement according to the invention and
• 4 12 is a block diagram of an embodiment of an electric vehicle according to the invention.

In the different figures, parts that are equivalent in terms of their function are always provided with the same reference symbols, so that they are usually only described once.

1 shows a circuit diagram of a first exemplary embodiment of a circuit arrangement 1 according to the invention. The circuit arrangement 1 shown essentially implements a DC-DC converter for the electrical supply of a low-voltage DC voltage network (not shown) with a low-voltage DC voltage LV from a high-voltage battery (in 1 not shown) provided high-voltage DC voltage HV, HV *. The circuit arrangement 1 has a transformer T with a variably definable winding ratio, a high-voltage converter unit 2 for converting the high-voltage direct voltage HV into a high-voltage alternating voltage supplied to the transformer T, and a low-voltage converter unit 3 for converting a low-voltage alternating voltage output by the transformer T into the low-voltage direct current LV. How 1 can be seen, the high-voltage converter unit 2 is connected to the transformer T with the interposition of a plurality of controllable switching elements, in this case two switching elements S1 and S2, in such a way that the effective winding ratio of the transformer T for the DC voltage conversion can be changed depending on the controlled switching states of the respective switching elements S1 and S2.

In the present case, the high-voltage converter unit 2 is in the form of a full bridge, which is known per se, with four bridge switches Q1, Q2, Q3 and Q4. The low-voltage conversion unit has a rectifier REC and an optional safety switching unit SX. The rectifier REC converts the low-voltage AC voltage output by the transformer into the low-voltage DC voltage LV. In the present case, the safety switching unit SX is used for current limitation and current interruption in an error state of the circuit arrangement 1. It is to be understood that both the high-voltage converter unit 2 and the low-voltage converter unit 3 can have additional or alternative components and the invention does not necessarily refer to the 1 specifically illustrated embodiments of the high-voltage and low-voltage conversion unit 2 and 3 is limited.

The preferred voltage range between a nominal high-voltage direct voltage HV and a reduced high-voltage direct voltage HV* is in 1 shown embodiment of the circuit arrangement 1 between about 200 V and 900 V, in particular between about 240 V and 830 V, without being necessarily limited to these voltage ranges.

For example, the reduced high-voltage DC voltage HV* can be approximately half the nominal high-voltage DC voltage HV, without being necessarily limited to this ratio, even if this ratio represents a particularly preferred embodiment, since, for example, a high-voltage battery with a nominal high-voltage DC voltage HV of 800 V, e.g. B. a traction battery of an electric vehicle, in a parallel circuit of two partial battery stacks with a half (z. B. 400 V) reduced high-voltage DC voltage HV * can be connected, for example during a charging process of the high-voltage battery.

Accordingly, it is preferred that the circuit arrangement 1 has two operating modes, with the high-voltage battery providing the nominal high-voltage DC voltage HV in the first operating mode and providing a high-voltage DC voltage HV* that is reduced compared to the nominal high-voltage DC voltage HV in the second operating mode, the switching states of the switching elements S1 and S2 being controlled in such a way that the effective turns ratio in the second operating mode is reduced compared to the effective turns ratio in the first operating mode.

For example, the first operating mode can be a discharging mode (e.g. driving an electric vehicle or generally supplying power to high-voltage consumers) while the high-voltage battery is being discharged, and the second operating mode can be a charging mode while the high-voltage battery is being charged (e.g. charging at a charging device).

The low-voltage direct voltage LV is at the in 1 shown embodiment in a range of about 8 V to 14 V. It is to be understood that the low-voltage DC voltage in other embodiments of the circuit arrangement according to the invention can deviate from this and can be selected from a range of about 6 V to about 50 V, for example.

In the exemplary embodiment shown, the switching elements S1, S2 are in the form of bidirectional isolating switches. Possible preferred designs of such bidirectional isolating switches are shown by way of example 3 in the form of back-to-back N-FETs 4, PhotoMOS relays 5, triacs 6 and electromechanical relays 7.

The frequency of the high-voltage alternating voltage output by the high-voltage converter unit 2 is at least 50 kHz, preferably at least 100 kHz.

At the in 1 The exemplary circuit arrangement 1 shown has the transformer T a first primary-side winding L1 with a first winding terminal 8 and a second winding terminal 9 and a second primary-side magnetically coupled to the first winding L1 Winding L2 with a first winding connection 10 and a second winding connection 11 . The second winding connection 9 of the first winding L1 is presently designed with the first winding connection 10 of the second winding L2 as a common winding connection 9, 10, which connects the first winding L1 and the second winding L2 in series. As in 1 is shown, the first winding connection 8 of the first winding L1 is connected to a first output pole 12 of the high-voltage converter unit 2 . The common winding connection 9, 10 and the second winding connection 11 of the second winding L2 are each connected to a second output pole 13 of the high-voltage converter unit 2, which is different from the first output pole 12, with one of the switching elements S1 or S2 being interposed.

Furthermore 1 it can be seen that the transformer T has further windings L3 and L4 on the secondary side, which are magnetically coupled to one another and to which the rectifier REC is connected.

The windings L1, L2, L3 and L4 of the transformer T of the in 1 The circuit arrangement 1 shown has, for example, a ratio of 11:11:1:1, but without being necessarily limited to these specific values.

In the 1 The circuit arrangement 1 shown with the two switching elements S1 and S2 makes it possible to switch the series connection of the two primary-side windings L1 and L2 to an active winding L1, i.e. one that is actively involved in the voltage conversion, namely to selectively switch the common winding connection 9, 10 and/or the second winding connection 11 of the second winding L2 to the second output pole 13 of the high-voltage converter unit 2.

In the first operating mode of the circuit arrangement 1, the nominal high-voltage direct voltage HV is approximately 800 V in the present case and is preferably in a range between approximately 600 V and 830 V. In this operating mode, the circuit arrangement 1 provides a low-voltage direct voltage LV of approximately 8 V to 14 V on the low-voltage side and is able to supply a current of approximately 265 A.

In the second operating mode of the circuit arrangement 1, the reduced high-voltage direct voltage HV* is approximately 400 V in the present case and is preferably in a range between approximately 240 V and 430 V. In this operating mode, the circuit arrangement 1 provides a low-voltage direct voltage LV of also approximately 8 V to 14 V on the low-voltage side and is able to supply a current of approximately 133 A.

By specifically setting the switching states of the switches S1 and S2 as a function of the fed-in high-voltage direct current HV, HV*, i. H. for example 800 V or 400 V, the turns ratio of the transformer T effective for the DC voltage conversion is changed in the sense of a high degree of efficiency. In this way, the low-voltage direct voltage network can always be supplied with high efficiency from the high-voltage direct voltage HV, HV* despite the large input voltage range between, for example, 240 V and 830 V.

In this case, the windings L1 and L2 of the transformer T are switched on the primary side by means of the switching elements S1, S2, which are active bidirectional isolating switches—preferably designed as anti-serial N-FETs, PhotoMOS relays, triacs, relays, etc. The primary-side magnetically coupled windings L1 and L2 are switched from a series connection of two windings (present in the first operating mode with 800 V nominal high-voltage direct current HV) to one winding (present in the second operating mode with high-voltage direct current HV* reduced to 400 V). This reduces i.a. the secondary voltage occurring at the transformer T in 800 V mode, which allows the use of low-loss rectifier components in the rectifier REC. Furthermore, high peak currents are reduced due to a lower bandwidth of the pulse width for driving the semiconductor elements in the border area, which increases the efficiency in these areas.

2 shows a circuit diagram of a second embodiment of a circuit arrangement 15 according to the invention 1 can be seen in the type of connection of the primary-side windings L1 and L2 and the connection of these to the high-voltage converter unit 2 .

In particular, the transformer T of the circuit arrangement 2 also has a first primary-side winding L1 with a first winding connection 8 and a second winding connection 9 and a second primary-side winding L2 magnetically coupled to the first winding L1 with a first winding connection 10 and a second winding connection 11. The first winding connection 8 of the first winding L1 is connected to the first output pole 12 of the high-voltage converter unit 2 . The second winding connection 11 of the second winding L2 is connected to the second output pole 13 of the high-voltage converter unit 2, which is different from the first output pole 12. The first winding terminal 8 of the first winding L1 and the first winding terminal 10 of the second winding L2 are one with the interposition first switching element S1 of three switching elements S1, S2 and S3 connected to one another. The second winding connection 9 of the first winding L1 is connected to the first winding connection 10 of the second winding L2 with the interposition of the second switching element S2 of the switching elements S1, S2, S3. The second winding connection 9 of the first winding L1 is connected to the second output pole 13 with the interposition of the third switching element S3 of the switching elements S1, S2, S3.

The circuit arrangement 15 described above with the three switching elements S1, S2, S3 makes it possible to switch the two primary-side windings L1 and L2 of the transformer T either in a series connection according to a first winding ratio (ie S1 and S3 open, S2 closed) or to switch the two primary-side windings L1, L2 individually in parallel with one another according to a second winding ratio (ie S1 and S3 closed, S2 open). In all operating states, both primary-side windings L1, L2 are thus actively involved in the voltage conversion, so that the efficiency of the circuit arrangement 15 compared to the circuit arrangement 1 is reduced 1 is increased again. The series connection of the windings L1 and L2 is preferably carried out in the first operating mode of the circuit arrangement 15, z. B. when feeding a nominal high-voltage DC voltage HV of 800 V. The parallel connection of the windings L1 and L2 is preferably in the second operating mode of the circuit arrangement 15, z. B. when feeding in a reduced high-voltage DC voltage HV* of 400 V.

4 schematically illustrates an embodiment of an electric vehicle 20 according to the invention. The electric vehicle 20 has a high-voltage battery 21, for example a traction battery with a nominal high-voltage DC voltage HV of 800 V, and a low-voltage vehicle electrical system 22, in which low-voltage consumers of the electric vehicle 20 are supplied. Furthermore, the electric vehicle 20 has a circuit arrangement, for example the circuit arrangement 1 1 or the circuit arrangement 2 from 2 or yet another embodiment of a circuit arrangement according to the invention. In 4 For example, the electric vehicle 20 is made with the circuit arrangement 15 2 fitted. The circuit arrangement 15 converts the high-voltage DC voltage HV provided by the high-voltage battery 21 into a low-voltage DC voltage LV provided for the low-voltage vehicle electrical system. Other electrical components of the vehicle 20, in particular, for example, an electric drive, which is also powered by the high-voltage battery 21, are in 4 not shown as they are not essential to the practice of the invention disclosed herein.

The circuit arrangement according to the invention disclosed herein, the electric vehicle and the method according to the invention are not limited to the concrete embodiments described in each case, but also include other embodiments which have the same effect and which result from technically meaningful further combinations of the features of all the subjects of the invention described herein. In particular, the features and feature combinations mentioned above in the general description and the description of the figures and/or shown alone in the figures can be used not only in the combinations explicitly stated herein, but also in other combinations or on their own, without departing from the scope of the present invention.

In a particularly preferred embodiment, the circuit arrangement according to the invention is used for the electrical supply of a low-voltage vehicle electrical system (e.g. 12 V, 24 V or 48 V vehicle electrical system, of an electric vehicle from a high-voltage DC voltage (e.g. 800 V) of a high-voltage battery, in particular a traction battery, of the electric vehicle.

Reference List

1

circuit arrangement

2

high-voltage conversion unit

3

low voltage conversion unit

4

Back-to-back N-FETs

5

PhotoMOS relay

6

triac

7

Electromechanical relay

8th

First winding connection

9

Second winding connection

10

First winding connection

11

Second winding connection

12

First output pole

13

Second output pole

15

circuit arrangement

20

electric vehicle

21

high-voltage battery

22

low-voltage network

HV

Nominal high-voltage direct current

HV*

Reduced high-voltage direct current

HV+

Positive high-voltage potential

HV

Negative high-voltage potential

LV

low-voltage direct current

LV+

Positive low-voltage potential

LV

Negative low-voltage potential

L1, L2

Primary-side transformer winding

L3, L4

Secondary side transformer winding

Q1-Q4

bridge switch

REC

rectifier

S1-S3

Controllable switching element

SX

safety switching unit

T

transformer

Claims (15)

Circuit arrangement (1, 15) of a DC-DC converter for the electrical supply of a low-voltage DC network (22) with a low-voltage DC voltage (LV) from a high-voltage DC voltage (HV, HV*) provided by a high-voltage battery (21), having a transformer (T) with a variably definable winding ratio, a high-voltage converter unit (2) for converting the high-voltage DC voltage (HV, HV*) into a high-voltage AC voltage fed to the transformer (T) and a low voltage converter unit (3) for converting a low-voltage AC voltage output by the transformer (T) into low-voltage DC voltage (LV), the high-voltage converter unit (2) being connected to the transformer (T) with the interposition of a plurality of controllable switching elements (S1, S2, S3) in such a way that the effective winding ratio of the transformer (T) for the DC voltage conversion can be changed depending on the controlled switching states of the respective switching elements (S1, S2, S3). Circuit arrangement according to claim 1 , characterized by two operating modes, wherein the high-voltage battery (21) provides a nominal high-voltage direct current (HV) in the first operating mode and in the second operating mode provides a high-voltage direct current (HV*) that is reduced compared to the nominal high-voltage direct current (HV), in which the switching states of the switching elements (S1, S2, S3) are controlled in such a way that the effective turns ratio in the second operating mode is reduced compared to the effective turns ratio in the first operating mode. Circuit arrangement according to the preceding claim, characterized in that the voltage range between the nominal high-voltage direct voltage (HV) and the reduced high-voltage direct voltage (HV*) is between 200 V and 900 V. Circuit arrangement according to one of the two preceding claims, characterized in that the reduced high-voltage direct voltage (HV*) is half the nominal high-voltage direct voltage (HV). Circuit arrangement according to one of the three preceding claims, characterized in that the first operating mode is a discharging mode during discharging of the high-voltage battery (21) and the second operating mode is a charging mode during charging of the high-voltage battery (21). Circuit arrangement according to one of the preceding claims, characterized in that the low-voltage direct voltage (LV) is in a range from 6 V to 50 V, particularly preferably from 8 V to 14 V. Circuit arrangement according to one of the preceding claims,characterizedthat the transformer (T) has a first primary-side winding (L1) with a first winding terminal (8) and a second winding terminal (9) and a second primary-side winding (L2) magnetically coupled to the first winding (L1) and having a first winding terminal (10) and a second winding terminal (11), the second winding terminal (9) of the first winding (L1) having the first winding terminal (10) of the second winding (L2) as a common winding terminal (9 , 10) which connects the first winding (L1) and the second winding (L2) in series, with the first winding connection (8) of the first winding (L1) being connected to a first output pole (12) of the high-voltage converter unit (2) and the common winding connection (9, 10) and the second winding connection (12) of the second winding (L2) being connected to a second output pole which is different from the first output pole (12), each with the interposition of one of the switching elements (S1, S2). (13) of the high-voltage converter unit (2) are connected. Circuit arrangement according to one of Claims 1 until 6 , characterized in that the transformer (T) has a first primary-side winding (L1) with a first winding connection (8) and a second winding connection (9) and a second primary-side winding (L2) magnetically coupled to the first winding (L1) with a first winding connection (10) and a second winding connection (11), the first winding connection (8) of the first winding (L1) being connected to a first output pole (12) of the high-voltage converter unit (2) is connected and the second winding connection (11) of the second winding (L2) is connected to a second output pole (13) of the high-voltage converter unit (2) which is different from the first output pole (12), the first winding connection (8) of the first winding (L1) and the first winding connection (10) of the second winding (L2) being connected to one another with the interposition of a first (51) of the switching elements (S1, S2, S3), the second winding connection ( 9) the first winding (L1) is connected to the first winding connection (10) of the second winding (L2) with the interposition of a second (S2) of the switching elements (S1, S2, S3) and the second winding connection (9) of the first winding (L1) is connected to the second output pole (13) with the interposition of a third (53) of the switching elements (S1, S2, S3). Circuit arrangement according to one of the preceding claims, characterized in that the switching elements (S1, S2, S3) are designed as bidirectional isolating switches in the form of anti-serially connected N-FETs (4), PhotoMOS relays (5), triacs (6), electromechanical relays (7) or a combination thereof. Circuit arrangement according to one of the preceding claims, characterized in that the frequency of the high-voltage alternating voltage is at least 50 kHz, preferably at least 100 kHz. Electric vehicle (20) having a high-voltage battery (21), in particular a traction battery, and a low-voltage vehicle electrical system (22), characterized by a circuit arrangement (1, 15), in particular a circuit arrangement according to one of the preceding claims, a DC voltage converter for the electrical supply of the low-voltage vehicle electrical system (22) with a low-voltage direct current (LV) from a high-voltage direct current (HV, HV*) provided by the high-voltage battery (21). Method for the electrical supply of a low-voltage DC network (LV) with a low-voltage DC voltage (LV) from a high-voltage DC voltage (HV, HV*) provided by a high-voltage battery (21) by means of a circuit arrangement (1, 15) of a DC-DC converter which has a transformer (T) with a variably definable winding ratio, a high-voltage converter unit (2) for converting the high-voltage DC voltage (HV, HV*) into a high-voltage AC voltage fed to the transformer (T) and a Low-voltage converter unit (3) for converting a low-voltage AC voltage output by the transformer (T) into low-voltage DC voltage (LV), the high-voltage converter unit (2) being connected to the transformer (T) with the interposition of a plurality of controllable switching elements (S1, S2, S3) and the effective winding ratio of the transformer (T) for the DC voltage conversion being controlled by controlling the switching states of the respective switching elements (S1, S2, S3). Method according to the preceding claim, characterized in that a nominal high-voltage direct voltage (HV) is provided by the high-voltage battery (21) in a first operating mode and a high-voltage direct voltage (HV*) that is reduced compared to the nominal high-voltage direct voltage (HV) is provided by the high-voltage battery (21) in a second operating mode and the switching states of the switching elements (S1, S2, S3) are controlled in such a way that the effective winding ratio in the second operating mode is reduced compared to the effective winding ratio in the first operating mode . Method according to the preceding claim, characterized in that the reduced high-voltage direct voltage (HV*) is reduced to half the nominal high-voltage direct voltage (HV). Method according to one of the three preceding claims, characterized in that the high-voltage battery (21) is discharged during the first operating mode and is charged during the second operating mode.

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