DE102014013039A1 - Device for a motor vehicle for the galvanically decoupled transmission of an electrical voltage - Google Patents

Abstract

The invention relates to a device (10) for a motor vehicle for galvanically decoupled transmission of an electrical voltage between a high-voltage circuit (12) and a low-voltage circuit (14) with a galvanically isolated DC-DC converter (16) having a primary side (24) and a secondary side (26). and a galvanically coupled DC-DC converter (32) having an input and an output, the secondary side (26) of the galvanically isolated DC-DC converter (16) being electrically connected to the input of the galvanically coupled DC-DC converter (32) and the primary side (24) of the galvanically isolated DC converter DC voltage converter (16) to the high-voltage circuit (12) is electrically connectable and the output of the DC-coupled DC-DC converter (32) to the low-voltage circuit (14) is connectable, and wherein the galvanically isolated DC-DC converter (16) provided by the high-voltage circuit (12) high-voltage DC voltage (UH) in a ers te DC voltage (U1) converts and the DC-DC converter (32) converts the first DC voltage (U1) into a second DC voltage (U2), wherein the DC-DC converter (32) comprises an energy storage device (34), which comprises a smoothing device for smoothing second DC voltage (U2) forms.

Description

The invention relates to a device for a motor vehicle for galvanically decoupled transmission of an electrical voltage between a high-voltage circuit and a low-voltage circuit with a galvanically isolated DC-DC converter having a primary side and a secondary side and a DC-coupled DC-DC converter having an input and an output, wherein the secondary side of the galvanically isolated DC converter is electrically connected to the input of the galvanically coupled DC-DC converter and the primary side of the galvanically isolated DC-DC converter is electrically connected to the high-voltage circuit and the output of the DC-coupled DC-DC converter is connected to the low-voltage circuit, and wherein the galvanically isolated DC-DC converter provided by the high-voltage circuit high-voltage DC in a first DC voltage is converted and the DC coupled DC converter converts the first G Light voltage converts to a second DC voltage. The invention also relates to a motor vehicle and a method for galvanically decoupled transmission of an electrical voltage.

Low-voltage circuits in motor vehicles usually have a low-voltage battery which provides a low-voltage voltage for supplying low-voltage components of the low-voltage circuit. Under low voltage is here to understand an electrical voltage less than 60 volts. For charging the low-voltage battery, provision may be made for electrical energy to be transmitted to the low-voltage circuit, for example, by a high-voltage circuit likewise arranged in the motor vehicle. High-voltage circuits usually have a high-voltage battery, which provides a high-voltage. Under high voltage is here to understand an electrical voltage greater than 60 volts. In order to avoid a risk, for example, of persons, or damage to the low-voltage components, the high-voltage is usually galvanically decoupled transmitted to the low-voltage circuit and converted into a suitable voltage for charging the low-voltage battery. This transfer and adaptation usually requires a high component requirements and thus has a high cost.

It is an object of the present invention to realize a less expensive and more space-saving device with a reduced component requirement.

This object is achieved by a device, a motor vehicle and a method having the features according to the respective independent claims. Advantageous embodiments of the invention are the subject of the dependent claims, the description and the figures.

An inventive device for a motor vehicle is used for galvanically decoupled transmission of an electrical voltage between a high-voltage circuit and a low-voltage circuit. The device comprises a galvanically isolated DC-DC converter having a primary side and a secondary side and a galvanically coupled DC-DC converter having an input and an output wherein the secondary side of the galvanically isolated DC-DC converter is electrically connected to the input of the DC-coupled DC-DC converter and the primary side of the galvanically isolated DC-DC converter with the High-voltage circuit is electrically connected and the output of the galvanically coupled DC-DC converter is connectable to the low-voltage circuit, and wherein the galvanically isolated DC converter converts a provided by the high-voltage DC high-voltage direct voltage into a first DC voltage and the DC-DC converter converts the first DC voltage into a second DC voltage. According to the invention, the galvanically coupled DC-DC converter has an energy storage device, which forms a smoothing device for smoothing the second DC voltage.

Galvanically isolated DC-DC converters, which are also referred to as galvanically decoupled DC-DC converter or galvanically decoupled DC / DC converter, can transmit an electrical voltage between two voltage circuits floating. The galvanically isolated DC-DC converter can galvanically separate the high-voltage voltage provided by the high-voltage circuit, in particular from a high-voltage battery of the high-voltage circuit, and convert it into a first DC voltage. This first DC voltage is supplied to a galvanically coupled DC-DC converter, which is connected in series with the galvanically decoupled DC-DC converter. This galvanically coupled DC-DC converter is designed to convert the first DC voltage into a second DC voltage suitable for the low-voltage circuit. By means of this galvanically coupled, in particular controllable, DC-DC converter can be prevented that the low-voltage components are damaged by an increased high-voltage DC voltage, which may occur, for example, temporarily in the high-voltage circuit. A known from the prior art galvanically isolated DC-DC converter has at the output of the secondary side usually a filter, which for example, an inductance and a capacitance, on. This filter is used to smooth the transmitted voltage, so here the first DC voltage. The galvanically coupled DC-DC converter has for converting between two DC voltages, that is, here between the first DC voltage in the second DC voltage, for example, a controllable switching device and the energy storage device. The energy storage device may also comprise an inductor and a capacitor and thus be designed identical to the filter of the DC decoupled DC-DC converter. The energy storage device thus also represents a smoothing device for smoothing the second DC voltage.

According to the invention, it is now provided to remove the filter of the galvanically isolated DC-DC converter and supply the first DC voltage unsmoothed to the DC-coupled DC-DC converter. The first DC voltage is thus first converted into the second DC voltage and smoothed by the energy storage device of the galvanically coupled. The DC voltage transmitted from the high-voltage circuit to the low-voltage circuit is thus smoothed only once, by means of the energy storage device of the galvanically coupled DC-DC converter. By removing the filter thus only a single inductance, namely that of the galvanically coupled DC-DC converter, required instead of two inductors so far. Thus, the component requirement in the series connection of the galvanically isolated or galvanically isolated and the DC-coupled DC-DC converters are advantageously minimized and costs are saved. As a result, the construction volume and thus the weight of the device are additionally reduced.

Particularly preferably, the galvanically isolated DC-DC converter for galvanically decoupled transmitting an AC voltage between the primary side and the secondary side of a transformer having a first winding which is electrically connected to the primary side, and a second winding which is electrically connected to the secondary side, wherein the primary side has an inverter for converting the high-voltage direct voltage into the alternating voltage, and the secondary side has a rectifier for converting the alternating voltage into the first direct voltage. According to the prior art, single-ended flux transducers or push-pull type flux transducers are known as examples of galvanically isolated DC-DC converters. Such Eintaktflusswandler or Gegentaktflusswandler according to the prior art generally have on the secondary side at the output of the rectifier, an LC filter, consisting of an inductor and a capacitor, for smoothing the DC voltage. As a rule, such an LC filter serves to prevent a so-called ripple current or a so-called ripple voltage at the output of the DC-DC converter. According to the invention, this LC element can now be dispensed with, since the smoothing is taken over by the energy storage device of the series-connected, galvanically coupled DC-DC converter.

It can be provided that the galvanically coupled DC-DC converter is designed as a step-up converter and / or as a step-down converter. A buck converter, also referred to as a buck converter, converts an input voltage to an output voltage whose magnitude is less than the magnitude of the input voltage. A boost converter, also referred to as a boost converter, converts an input voltage to an output voltage whose magnitude is greater than the magnitude of the input voltage. DC-DC converters, which can be used both as a step-up converter and as a step-down converter, are referred to as synchronous converters. The conversion of the input voltage into the output voltage is generally carried out with the aid of a periodically operating electronic switching device and an energy storage device. This energy storage device may comprise, for example, an inductor and a capacitor. The energy storage device consisting of an inductance and a compensator can equally function as a smoothing device and provide a smoothed output voltage at the output of the DC-DC converter.

In a preferred embodiment, the transformer has a third winding, which is electrically connectable to a charging device for providing a charging voltage, wherein the charging voltage is transmitted via the transformer to the high-voltage circuit and / or the low-voltage circuit. The charging voltage serves, for example, to charge the high-voltage battery of the high-voltage circuit. In this embodiment, therefore, the transformer of the galvanically isolated DC-DC converter is used repeatedly, namely on the one hand for transmitting the high-voltage of the high-voltage circuit to the low-voltage circuit and on the other hand for transmitting the charging voltage to the high-voltage circuit and / or to the low-voltage circuit. Above all, this multiple use of the transformer makes a combination of a galvanically insulating DC-DC converter and a DC-DC converter required to allow a variable voltage adjustment at low-voltage circuit input, if during the charging of the high-voltage battery due to the increase in state of charge in the high-voltage battery, the high-voltage DC voltage in the high-voltage circuit increases. Due to the controllability of the galvanically coupled DC-DC converter, which converts the DC voltage provided by the galvanically decoupled DC-DC converter into an output voltage suitable for the low-voltage circuit, the transformer of the galvanically isolated DC-DC converter can be used multiple times, without any increased high-voltage DC voltage in the high-voltage circuit causing damage in the low-voltage circuit.

The invention also relates to a motor vehicle having a device according to the invention, a high-voltage circuit, a low-voltage circuit and a charging device. The charging device can be designed as a so-called on-board loader of the motor vehicle. The motor vehicle is configured in particular as an electric vehicle or as a hybrid vehicle.

The invention also includes a method for transmitting an electrical voltage between a high-voltage circuit and a low-voltage circuit. The method comprises providing a high voltage voltage, converting the high voltage voltage into an alternating voltage by means of an inverter, galvanically decoupling the AC voltage by means of a transformer, converting the galvanically decoupled transmitted AC voltage into a first DC voltage by means of a rectifier and converting the first DC voltage into a second DC voltage by means of a galvanically coupled DC-DC converter. According to the invention, the method comprises smoothing the second DC voltage by means of an energy storage device of the galvanically coupled DC-DC converter.

The preferred embodiments presented with reference to the device according to the invention and their advantages apply correspondingly to the motor vehicle according to the invention and to the method according to the invention. In the following the invention will now be explained in more detail with reference to a preferred embodiment and with reference to the accompanying drawings.

Showing:

1 a schematic representation of a circuit topology with a device according to the prior art;

2 a schematic representation of a circuit topology with an embodiment of a device according to the invention; and

3 Examples of galvanically isolated DC-DC converter and galvanically coupled DC-DC converter according to the prior art.

The exemplary embodiment explained below is a preferred embodiment of the invention. In the exemplary embodiment, however, the described components of the embodiment each represent individual features of the invention that are to be considered independently of each other, which also develop the invention independently of each other and thus also individually or in a combination that is to be regarded as part of the invention. Furthermore, the described embodiment can also be supplemented by further features of the invention already described.

1 shows a circuit topology 1 with a device 10 for the galvanically decoupled transmission of an electrical voltage between a high-voltage circuit 12 and a low-voltage circuit 14 according to the prior art. The circuit topology 1 can be arranged for example in a motor vehicle (not shown here). The high-voltage circuit 12 may for example comprise a high-voltage battery (not shown here), which provides a high-voltage DC voltage U _H. The low-voltage circuit 14 can be a low voltage battery 15 exhibit.

The device 10 is designed to galvanically decouple the high-voltage DC voltage U _H to the low-voltage circuit 14 to transfer and thereby convert them into a DC voltage U ₂ , which is in particular smaller than the high-voltage U _H. The second DC voltage U ₂ can, for example, for charging the low-voltage battery 15 serve.

The device 10 has a series circuit of a galvanically decoupled DC-DC converter 16 and a DC coupled DC-DC converter 32 on. The galvanically decoupled DC-DC converter 16 serves for the potential-free transmission of the high-voltage direct voltage U _H. The galvanically decoupled DC-DC converter 16 is here embodied as a push-pull type flux converter according to the prior art. The galvanically decoupled DC-DC converter 16 can be a transformer 18 with a first winding 20 and a second winding 22 include. The first winding 20 is with a primary page 24 the galvanically decoupled DC-DC converter 16 electrically connected. The primary side 24 is here designed as an inverter and with the high-voltage circuit 12 electrically connected. The inverter has four controllable switching elements T, by means of which the high-voltage DC voltage U _H can be converted into an AC voltage. The AC voltage is through the transformer 18 to the second winding 22 transferred, which with a secondary side 26 the galvanically isolated DC-DC converter 16 connected is. Of the galvanically isolated DC-DC converter 16 is here with the low-voltage circuit 14 electrically connected.

The secondary side 26 here includes a rectifier 28 and an LC filter 30 , The rectifier 28 serves to rectify the AC voltage. The rectified voltage becomes the LC filter 30 supplied, which comprises an inductance L and a capacitor C. The LC filter 30 smoothes the rectified voltage and provides a smoothed first DC voltage U ₁ 'at the output. The smoothed first DC voltage U ₁ 'is the galvanically coupled DC-DC converter 32 fed, which in series with the galvanically decoupled DC-DC converter 16 is switched. The galvanically coupled DC-DC converter 32 has a controllable switch device S and an energy storage device 34 , which comprises an inductance L and a capacitor C, on. The galvanically coupled DC-DC converter 32 is executed here as a buck converter. The buck converter uses a PWM (Pulse Width Modulation) clocking the output voltage of the galvanically isolated DC-DC converter 16 down and thus provides at the output a second DC voltage U ₂ , the amount of which is smaller than the amount of the smoothed first DC voltage U ₁ '. The galvanically coupled DC-DC converter 32 is designed to control the output voltage U ₂ with a changing input voltage U ₁ '.

The transformer 18 here has a third winding 36 on top of that with a loader 38 connected is. The loading device 28 can be designed as a so-called on-board loader and be arranged in the motor vehicle. About the charger 38 can be provided a charging voltage, which in particular the high-voltage circuit 12 can be provided for charging the high-voltage battery. The transformer 18 So is on the one hand for floating transfer of the high-voltage DC voltage U _H between the high-voltage circuit 12 and the low-voltage circuit 14 as well as for the potential-free transfer of the charging voltage between the charging device 38 and the high-voltage circuit 12 used. This multiple use of the transformer 18 makes the galvanically coupled DC-DC converter 32 necessary, because by means of the galvanically coupled DC-DC converter 32 a controllable voltage adjustment can be performed, so a defined second DC voltage U ₂ can be provided, even if the high-voltage U _H in the high-voltage circuit 12 For example, during charging by the charging device 38 , is increased.

From the circuit topology 1 According to the prior art, it can be seen that both the galvanically decoupled DC-DC converter 16 as well as the galvanically coupled DC-DC converter 32 an inductance L and a capacitor C, that is, an LC element. Especially the inductors L are expensive components. Therefore, it is desirable to have a circuit topology 1 to realize which in particular requires only one inductance L.

2 shows a circuit topology 1 with a device according to the invention 10 , Here is the secondary page 26 the galvanically decoupled DC-DC converter 16 only a rectifier 28 on, which provides an unsmoothed first DC voltage U ₁ at the output. This unsmoothed first DC voltage U ₁ is the galvanically coupled DC-DC converter 32 supplied and by means of the controllable switching device S and the energy storage device 34 converted into a smoothed second DC voltage U ₂ . This smoothed second DC voltage U ₂ is the low-voltage circuit 14 provided at the entrance and can be used to charge the low-voltage battery 15 be used. Compared to 1 is recognizable that the secondary side 26 the galvanically decoupled DC-DC converter 16 no LC filter 30 having. Nevertheless, a current ripple or a voltage ripple at the output of the device 10 or at the entrance of the low-voltage circuit 14 To avoid being smoothing properties of the energy storage device 34 of the galvanically coupled DC-DC converter 32 used. Thus, the LC filter 30 the galvanically decoupled DC-DC converter 16 omitted, wherein the control of the output voltage of the DC-coupled DC-DC converter 32 is still given at a changing input voltage.

3 shows examples of DC decoupled DC-DC converters 40 . 42 and galvanically coupled DC-DC converters 44 . 46 according to the prior art. A single-ended flux converter 40 and a push-pull flux converter 42 are examples of DC decoupled DC-DC converters 16 , In area B1, both the single-ended flux converter 40 as well as the push-pull flow converter 42 an input DC voltage U _{E converted} into an AC voltage, by means of the transformer 18 galvanically decoupled transmitted and rectified. In area B2, the single-ended flux converter 40 and the push-pull flow converter 42 one LC filter each 30 for smoothing the rectified voltage. Both the single-ended flux converter 40 as well as the push-pull flow converter 42 According to the state of the art, the output side provides a smoothed DC output voltage U _A.

A buck converter 44 as well as a synchronous converter 46 are examples of galvanically coupled DC-DC converters 32 , The Tiefsetzstellter 44 is a unidirectional device which converts the DC input voltage U _E into a smaller DC output voltage U _A. A step-up converter, not shown here, which is another example of a galvanically coupled DC-DC converter, is a unidirectional component which converts the DC input voltage U _E into a larger DC output voltage U _A. The synchronous converter 46 is a bidirectional component, which can convert the input DC voltage U _E into a smaller or larger DC output voltage U _A. The buck converter 44 and the synchronous converter 46 have a controllable switching device S and an energy storage device 34 which can also be used to smooth out the tension. Not shown here is a high-level converter, which also represents an example of a galvanically coupled DC-DC converter.

The device according to the invention 10 can be realized by one of the galvanically decoupled DC-DC converter 40 . 42 with one of the galvanically coupled DC-DC converter 44 . 46 or the boost converter is connected in series. In this case, the LC filter according to the invention 30 each galvanically decoupled DC-DC converter 40 . 42 omitted.

LIST OF REFERENCE NUMBERS

1

circuit topology

10

contraption

12

High-voltage circuit

14

Low-voltage circuit

15

Low-voltage battery

16

Galvanically isolated DC-DC converter

18

transformer

20

first winding

22

second winding

24

primary

26

secondary side

28

rectifier

30

LC filter

32

Galvanically coupled converter

34

Energy storage device

36

third winding

38

loader

40

forward converter

42

Push-pull converter

44

Buck converter

46

synchronous converter

U _H

High-voltage direct current

U ₁

first DC voltage

U ₁ '

smoothed first DC voltage

U ₂

second DC voltage

U _E

input voltage

U _A

output voltage

I

inductance

C

capacitor

T

Controllable switching element

S

switching device

B1, B2

areas

Claims (6)

Contraption ( 10 ) for a motor vehicle for galvanically decoupled transmission of an electrical voltage between a high-voltage circuit ( 12 ) and a low-voltage circuit ( 14 ) with a galvanically isolated DC-DC converter ( 16 ) with a primary page ( 24 ) and a secondary side ( 26 ) and a galvanically coupled DC-DC converter ( 32 ) having an input and an output, the secondary side ( 26 ) of the galvanically isolated DC-DC converter ( 16 ) with the input of the galvanically coupled DC-DC converter ( 32 ) is electrically connected and the primary side ( 24 ) of the galvanically isolated DC-DC converter ( 16 ) with the high-voltage circuit ( 12 ) is electrically connectable and the output of the galvanically coupled DC-DC converter ( 32 ) with the low-voltage circuit ( 14 ) is connectable, and wherein the galvanically isolated DC-DC converter ( 16 ) one of the high-voltage circuit ( 12 ) provided high-voltage DC voltage (U _H ) in a first DC voltage (U ₁ ) converts and the DC-coupled DC-DC converter ( 32 ) converts the first DC voltage (U ₁ ) into a second DC voltage (U ₂ ), characterized in that the galvanically coupled DC-DC converter ( 32 ) an energy storage device ( 34 ), which forms a smoothing device for smoothing the second DC voltage (U ₂ ). Contraption ( 10 ) according to claim 1, characterized in that the galvanically isolated DC-DC converter ( 16 ) for the galvanically decoupled transmission of an AC voltage between the primary side ( 24 ) and the secondary side ( 26 ) a transformer ( 18 ) with a first winding ( 20 ) which is electrically connected to the primary side ( 24 ), and a second winding ( 22 ) electrically connected to the secondary side ( 26 ), wherein the primary side ( 24 ) an inverter for converting the high-voltage direct voltage (U _H ) into the AC voltage and the secondary side ( 26 ) a rectifier ( 28 ) for converting the AC voltage into the first DC voltage (U ₁ ). Contraption ( 10 ) according to one of the preceding claims, characterized in that the galvanically coupled DC-DC converter ( 32 ) as a boost converter and / or as a buck converter ( 44 ) is trained. Contraption ( 10 ) according to one of claims 2 or 3, characterized in that the Transformer ( 18 ) of the device ( 10 ) a third winding ( 36 ), which with a loading device ( 38 ) is electrically connectable for providing a charging voltage, wherein the charging voltage across the transformer ( 18 ) to the high-voltage circuit ( 12 ) and / or the low-voltage circuit ( 14 ) is transmitted. Motor vehicle with a device ( 10 ) according to one of claims 1 to 4, a high-voltage circuit ( 12 ), a low-voltage circuit ( 14 ) and a loading device ( 38 ). Method for transmitting an electrical voltage between a high-voltage circuit ( 12 ) and a low-voltage circuit ( 14 ) comprising the steps: - providing a high-voltage voltage (U _H ), - converting the high-voltage voltage (U _H ) into an AC voltage by means of an inverter, - galvanically decoupled transmission of the AC voltage by means of a transformer ( 18 ), - converting the galvanically decoupled transmitted AC voltage into a first DC voltage (U ₁ ) by means of a rectifier ( 28 ) and - converting the first DC voltage (U ₁ ) into a second DC voltage (U ₂ ) by means of a galvanically coupled DC-DC converter ( 32 ), characterized by - smoothing the second DC voltage (U ₂ ) by means of an energy storage device ( 34 ) of the galvanically coupled DC-DC converter ( 32 ).

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