DE102021200628A1 - Galvanically coupled DC-DC converter and vehicle electrical system - Google Patents

Abstract

A galvanically coupled DC/DC converter having a first side (A1) and a second side (A2) is described. The first side (A1) and the second side (A2) each have a first potential (U+, V+) and a second potential (U-, V-). The DC-DC converter has a first and a second series connection (R1, R2) of a respective first, second and third transistor device (S1, S2, S3; S4, S5, S6) which are connected via a first and a second connection point (VP1, VP2) are serially connected. The first series circuit (R1) is provided between the potentials (U+, U-) on the first side (A1). The second series connection (R2) is provided between the potentials (V+, V-) of the second side (A2). The first connection point (VP1) of the first series circuit (R1) is connected to the first connection point (VP1') of the second series circuit (R2) via a first working inductance (L1). The second connection point (VP2) of the first series circuit is connected to the second connection point (VP2') of the second series circuit via a second working inductance (L1').

Description

Vehicles with an electric drive have an on-board electrical system that has high operating voltages to provide high power. These so-called high-voltage vehicle electrical systems with voltages well above 60 V can also be divided into vehicle electrical system branches with a nominal voltage that is suitable for some components or for charging, and with higher nominal voltages, such as vehicle electrical system branches with an accumulator, which has a higher voltage in comparison. For example, it can be made possible that a voltage of 400 V is available for driving, while higher voltages can be used for fast charging, for example 800 V a high-voltage air conditioning compressor can also be operated at 400 V without having to do without a charging process with a higher voltage.

In order to be able to transfer energy between the vehicle electrical system branches with different nominal voltages, DC voltage converters are used. These should be as inexpensive as possible and designed for high performance and should also offer the highest possible protection against dangerous contact voltages, especially with regard to contact voltages during the charging process.

It is an object of the invention to indicate a possibility with which circuits of this type can be implemented for transmitting energy with high-voltage networks with different voltages.

This task is fulfilled by the DC-DC converter and the vehicle electrical system according to the independent claims. Further properties, features, embodiments and advantages result from the dependent claims, the figures and the description.

It is proposed to provide a galvanically coupled DC/DC converter having two sides, each side having a series connection of at least three transistor devices. The transistor devices have either a single transistor element or a series connection of a plurality of transistor elements. Working inductances are provided between the resulting (at least) two connection points between the transistor devices of the series circuits. The working inductances result in a symmetrical connection between the series circuits on the different sides. The connection is symmetrical with respect to the (DC) potentials of the sides. Furthermore, the connection provides symmetry in the sense that the sides are mirrored with respect to the connection (or its center) and have three transistor devices on either side. Because the (at least) two working inductances (related to the potentials) connect the two sides symmetrically, a potential offset can be generated in a targeted manner by clocking the transistor devices of the series circuits, so that, for example, a voltage compared to a reference potential such as ground is minimized or set to zero can be. In addition, it is possible to set the transformation ratio between the two sides of the DC-DC converter by clocking. It is also possible to optimize a transformation ratio between the voltage between the working inductances on the one hand and the voltage between the potentials of the sides on the other hand, for example in order to optimize efficiency.

When using high voltages between the potentials, such as voltages of 400 V or 800 V, the series connection of the transistors allows them to be designed for only a portion of the total voltage. This applies in particular to embodiments in which a second transistor is designed as a series connection of two transistor elements. It is possible to construct the transistor elements of the transistor devices as superjunction FETs since the total voltage is divided between the transistor devices.

Symmetrical clocking is provided in each of the series circuits (in operation without insulation faults). This means that the transistor device between the connection points on the one hand and the two outer transistor devices on the other hand are connected complementarily to one another, i. H. be switched on and off alternately. The two outer transistor devices are clocked synchronously (in insulation-fault-free operation). In relation to the middle, second transistor device, the clocking of the first transistor device is therefore also symmetrical to the third transistor device. This means that, starting from the middle of the series connection, the two outer transistor devices (first and third transistor) are clocked synchronously and are clocked complementary to the middle, second transistor device. The first and third transistor devices are referred to as outer transistor devices, and in particular transistor devices that are connected to one of the potentials of the sides directly and not via a further transistor device. Depending on the use, the potentials are the input potentials or the output potentials of the converter. In particular, the converter is designed to be bidirectional.

A galvanically coupling DC-DC converter with a first side and a second side is thus proposed. The first side can have an input side and the second side can have an output side, but the DC/DC converter is preferably bidirectional and the second side can therefore also have the function of an input and the first side can have the function of an output. For this reason, a first and second side is generally spoken of below, and only one embodiment of this provides that the first side has an input function, while the second side has an output function. In other embodiments or operating variants, the assignment of functions (input/output) is reversed.

The first and second sides each have a first and a second potential. The first potential is preferably the positive potential and the second potential is the negative potential. The potentials are potentials of an input or output voltage of the converter. Furthermore, there is in particular a reference potential, in particular ground, with the first and the second potential preferably being symmetrical to the reference potential at least on one side. In operation with no insulation faults, the reference potential is electrically isolated from both potentials of the converter.

The DC-DC converter has a first and a second series connection. The series connection (the first and the second) each have a first, second and third transistor device. A single transistor element is referred to as a transistor device, although a series connection of two transistors can also be referred to as a transistor device. In particular, the second transistor device can have two series-connected transistor elements. The first and the third transistor device are formed symmetrically to the second transistor device. If the second transistor device is formed as a single transistor element, the first and third transistor devices are arranged symmetrically with respect to this transistor element (in the series connection). If the second transistor device is implemented by two serial transistor elements which are connected to one another via a connection point (designation: intermediate connection point), then the first and the third transistor device in the series connection are arranged symmetrically to the intermediate connection point.

In relation to the transistor device, there are two connection points in the series connection. The first transistor device is connected to the second transistor device via a first connection point. The second transistor device is connected to the third transistor device via a second connection point. This applies to both series connections and thus to both sides. If the second transistor device is formed with two transistor elements, then the second connection point exists as a connection point between the first transistor device and an outer end of the second transistor device, the second connection point being provided between the third transistor device and the other outer end of the second transistor device.

The first series connection is provided between the potentials of the first side. These potentials are, in particular, DC voltage potentials, for example supply potentials or input or output potentials. The second series connection is provided between the potentials of the second side. These are also direct voltage potentials, for example supply potentials or output or input potentials. The input voltage can be provided between the potentials of the first series circuit and the output voltage can be provided between the potentials of the second series circuit. The opposite case is also possible, depending on the integration of the DC-DC converter into the rest of the vehicle electrical system.

As mentioned, an inductive connection is provided between the series circuits or between the different sides. This is formed by two working inductances. A first working inductance connects the first connection point of the first series circuit to the first connection point of the second series circuit. The second connection point of the first series circuit is connected to the second connection point of the second series circuit via a second working inductance. The first potential of the first side has the same sign as the first potential of the second side and the second potential of the first side has the same sign as the second potential of the second side. This results in the first connection point of the two series circuits being connected to the first potential of the respective side via the first transistor device. The second connection point of the series connection is connected to the second potential of the respective side via the associated third transistor device. Thus, the first connection point is to be assigned to the first potential and the second connection point is to be assigned to the second potential. The first working inductance can thus also be assigned to the first potential and the second working inductance has to be assigned to the second potential. This results in a symmetry between the working inductances based on the second transistor means or, if present, on their intermediate connection point.

The inductive connection formed by the working inductances between the series circuits of the different sides enables the first side to be shifted to the second side by clocking (in relation to their potentials), so that, for example, in the event of an asymmetry caused by a fault, a potential shift is caused by the clocking can be generated from the second side to the first side (or vice versa), in order to compensate for an asymmetry or to prevent a dangerous flow of current, in particular to a reference potential. In particular, between the first series connection and the second series connection, i. H. between the first and the second side only said inductive connection. There is therefore no direct, ohmic connection between the first and the second side.

According to one embodiment, the transistor devices are each individual transistors (equivalent to individual transistor elements). Individual transistors refer to individual transistor components, or which are composed of several transistor components (e.g. formed as a cascode circuit or as a Darlington transistor), but which are connected to one another in such a way that the plurality of transistor components are used together functionally as a single transistor. In this case, the first series circuit and the second series circuit can each be formed with a first, second and third transistor device, which are each formed as individual transistors. Furthermore, only the first, second and third transistor devices of the first series circuit or the second series circuit, but not both series circuits, can be embodied as individual transistors.

Regardless of the configuration of the transistor devices, each series circuit has two connection points (as defined above) and there are preferably (precisely) two working inductances provided, the first connecting the first connection points of the different series circuits and the second working inductance connecting the second connection points of the different series circuits with one another .

It can be provided that the transistor devices of the first series circuit or the second series circuit (in this case not both series circuits) are in each case individual transistors or individual transistor elements. In this case, the first and the third transistor device of the respective other series connection is preferably in the form of a single transistor, as in the first-mentioned series connection, but the second transistor device of the other series connection, which connects the first to the third transistor device, is a partial series connection of two individual ones Transistors (or transistor devices) connected to each other via an interconnection point.

It is also stated that this intermediate connection point (of the second transistor device) is connected to other components of the DC-DC converter as part of the DC-DC converter. Provision can thus be made for the three transistor devices in the first series connection to be in the form of individual transistors or as individual transistor elements, while the second series connection provides for the first and third transistor devices (i.e. the outer transistor devices) to be in the form of individual transistor elements, while the second transistor device is designed as a partial series connection. This can also be the other way around: It can be provided that the three transistor devices of the second series connection are each designed as individual transistors or transistor elements, while this only applies to the first and third transistor device in the first series connection, while the second, intermediate transistor device is part - Series connection of two individual transistors is performed. If one of the series circuits includes a partial series circuit of two individual transistors or transistor elements as the second transistor device, this series circuit results in a series circuit with the first transistor device, which is connected to the third transistor device via the two individual transistors or transistor elements of the partial series circuit , while the two individual transistors or transistor elements are formed between the first and third transistor devices as a series connection of (at least) two transistor elements.

An embodiment is also shown in which the second transistor device on both sides is in the form of a partial series connection of two individual transistor elements. In such a DC voltage converter, the first transistor device of each of the two series circuits is in the form of individual transistors or transistor elements. This also applies to the third transistor device. In other words, the transistor devices are in the form of individual transistors which are (directly) connected to the first or the second potential. In this embodiment, for each of the two series circuits, the second transistor device, which connects the first to the third transistor device, is a partial series circuit of two individual transistors. These two individual transistors of the second transistor device are connected to one another via an intermediate connection point. In other words, the outer transistor devices (first and third transistor device) can be embodied as individual transistors, while the middle transistor device (ie the second transistor device) is embodied as a partial series connection of two individual transistors. The transistors that form the second transistor device are preferably switched synchronously (in particular in operation without an insulation fault).

If one side has an intermediate connection point (namely the second transistor device), provision can be made for this connection point to be connected to a capacitor connection point of a two-part intermediate circuit capacitor device. Such an intermediate circuit capacitor device is connected to the potentials of that side to which the intermediate connection point also belongs. If one side has an intermediate connection point, this means that its second transistor device is in the form of a partial series connection which has the intermediate connection point. If the first side has an intermediate connection point, this is preferably connected to a capacitor connection point of a two-part intermediate circuit capacitor device on the first side. If the second side has an intermediate connection point, then this is connected to a capacitor connection point of a two-part intermediate circuit capacitor device, which is connected to the potentials of the second side. Thus, the intermediate connection point of one side is preferably connected to the capacitor connection point of the same side, i. H. with the capacitor connection point, which belongs to a two-part intermediate circuit capacitor device, which is connected to the potentials of this side. In particular, there is no connection between an intermediate connection point of a second transistor device on one side and the other side, in particular not with a capacitor connection point of an intermediate circuit capacitor device on the other side. The intermediate connection point or points are connected to the capacitor connection point on the same side and thus to the intermediate circuit capacitor device on the same side. As mentioned, there is only one inductive connection between the different sides, which is formed by the two working inductances.

Provision can be made for the connection points of the second series circuit to be connected to those ends of the working inductances which are remote from the connection points of the first series circuit. Alternatively, the working inductances are connected to the second side via a common-mode choke. However, a common-mode choke can also be provided between the working inductances and the first side. This can be combined with the previously placed common mode choke, or can be an alternative to it. The inductive connection between the two sides can thus be provided by the working inductances combined with a common mode choke. In this case, the working inductances are connected to the second side (or also to the first side) via the common-mode choke. In addition to the working inductances, the inductive connection can therefore have a common-mode choke which is connected upstream and/or downstream of the working inductances. Here too, no element, in particular no conductive or ohmic element, bridges the working inductances.

Furthermore, the inductive connection can have a smoothing capacitor. This is connected to the two working inductances. The smoothing capacitor thus connects the two working inductances (or potentials from the ends of the working inductances) with one another. In particular, the smoothing capacitor is connected to the ends of the working inductances and the common-mode choke, via which these are connected to one another. The two ends of the smoothing capacitor can be connected between the respective connection points between the common-mode choke and the respective working inductance. The smoothing capacitor thus connects the first connection point to the second connection point (for example the second series circuit) via the common-mode choke.

The DC-DC converter preferably includes a controller which is connected to the transistor devices of the DC-DC converter in a driving manner. The controller is set up to simultaneously drive the first and third of the transistor devices of the series connection into an on state (and also to simultaneously drive an off state in a converter state) in a converter state (or in a converter state free of insulation faults). Thus, the controller controls the first and third transistor devices synchronously. In other words, the outer transistors of the series connection are switched simultaneously in the same way. In the (insulation-fault-free) converter state of the controller, the second transistor device is driven in a manner that is complementary to the driving of the first and third transistor devices. This affects the first series connection, the second series connection, or both. The control of the first series circuit and the control of the second series circuit can have different duty cycles and/or clock frequencies. The activation of the first series connection can be coordinated in time with the activation of the second series connection, or vice versa.

The controller is preferably set up to drive the second transistor devices of each series connection on the one hand and the second and third transistor devices on the other hand alternately into an on state (and also into an off state) in the (insulation fault-free) converter state. Intermediate phases can also be provided, in which the three transistor devices of the series connection are open, in contrast to the otherwise alternating activation. The controller is designed for this.

The controller controls the transistor devices according to duty ratios, it being possible for the duty ratio for driving the second transistor devices to differ from the duty ratio with which the first and third transistor devices are driven.

In general, the first and third transistor devices on the one hand and the second transistor device on the other hand are driven by the controller with different clock signals when the converter is in the (insulation-fault-free) converter state, but these are linked to one another in such a way that all three transistor devices (on one or both sides) are never switched off in the converter state of the controller. are in the on state at the same time. However, the three transistor devices of a series circuit can be in the off state at the same time, even in the converter state of the controller. This does not necessarily result in a complementary ratio of the driving of the second transistor device to the driving of the first and third transistor devices.

In order in particular to specifically generate asymmetrical potential shifts which, for example, counteract error-induced potential shifts (or to at least partially compensate for an asymmetry with respect to the reference potential), the third transistor can be driven with a different clock signal than the first transistor. As a result, the potential of the second connection point shifts as a function of the clock signal of the second and third transistor device. In the same way, a potential asymmetry (relative to the reference potential) for the first connection point can be generated in a targeted manner by clocking the first and second transistor devices accordingly, but not clocking the first transistor device like the third transistor device. An insulation fault operation can provide that, as mentioned, different clock signals are used for the first and the third transistor device. An operation in which there is insufficient insulation between the reference potential and one of the two potentials (one of the sides) is referred to as insulation fault operation.

If the insulation fault exists between the first potential and the reference potential, then the first transistor device (i.e. that which is directly connected to the insulation-faulty potential) can be placed in a permanently on state (to avoid a voltage between the reference potential and the first potential ), and the first and second transistor devices are switched in a clocked manner, preferably alternately on and off. If the insulation fault exists between the second potential and the reference potential, then the third transistor device (i.e. the one which is directly connected to the potential which is affected by the insulation fault) can be put into a permanent on state (in order to avoid a voltage between the reference potential and the second potential ), and the second and third transistor devices are switched in a clocked manner, preferably alternately on and off. Provision can be made for the relevant transistor devices to be partially driven alternately and for both to be in the off state. The transistor devices concerned (i.e. those not directly connected to an insulation-defective potential) are preferably switched in a clocked manner. Furthermore, the transistor device directly connected to the insulation-defective potential can be driven with a higher duty cycle (maximum: duty cycle of 1) than the transistor device directly connected to the other potential (same side) or with a higher one duty cycle as the second transistor device. If there is an insulation fault between a potential (one side) and the reference potential, such as earth or ground, then the transistor device directly connected to this potential can be driven with a duty cycle that is suitable for the magnitude of the voltage between the potential with the insulation fault and ground is below a predetermined limit, which characterizes, for example, a contact voltage that is still permissible. The limit can correspond to a maximum permissible touch voltage, possibly reduced by a safety margin. In this way, despite an insulation fault, touch voltages can be kept below a (permissible) limit, while the converter (within limits) continues to convert a voltage and thus provides a voltage for supplying vehicle components. This enables a limp home functionality, for example.

When the first and third transistor devices are driven synchronously, however, potentials result for the first and second connection points which are symmetrical to one another, based on a reference potential such as ground, for example.

In the (insulation fault-free) converter state, the second transistor device on the one hand and the first and third transistor devices on the other hand are driven alternately, with neither all three transistor devices being in the on state at the same time, nor the first and third transistor devices being driven differently.

The control for an insulation error state is designed for targeted potential shifting, for example to compensate for an insulation error (compared to a reference potential) or to reduce touch voltages. If an insulation fault occurs, i. H. an isolation fault condition is provided for the controller, then the first (or third) transistor means may be permanently on while the other two transistors are alternately on.

In particular in the event of an insulation fault between the first potential of the first or second side on the one hand and a reference potential, for example earth, on the other hand, the first transistor device can be driven permanently in an on state. In this case, in particular that transistor device which is connected to the potential which has the insulation defect is permanently driven in the on state. Furthermore, in this case the third transistor device and the second transistor device are switched alternately, i. H. non-simultaneously, driven to an on-state, preferably according to pulse width modulation (and related duty cycle). In this case, the transistor device, which is directly connected to the faulty potential, is driven to permanently go into an on state. Alternatively or preferably in combination with this, the controller can be set up to drive the third transistor (of the first series connection) permanently into an on state in the event of an insulation fault between the second potential on the first side and a reference potential, as well as the first and the second transistor of this series connection alternately drive according to an on-state. Here, too, the transistor device, which is directly connected to the potential with the insulation defect, is permanently switched on, and the subsequent, second transistor device and the transistor device, which is directly connected to the other potential, are controlled in a clocked manner, namely alternately in an on state ( and an off state). Alternate driving here can mean that the driving signals are directly complementary to each other, or that one transistor is turned off when the other is in an on state, but both transistors can be turned off at the same time.

The DC-DC converter mentioned here can not only be used generally for the transmission of power, but also allows, in addition to voltage adjustment, a potential shift of the potentials on the second side compared to those on the first side or vice versa. The controller can also be set up, the voltage and / or a potential on the second side according to a first specification and the voltage between the first and second connection point of the first series circuit and / or a potential of the first or second connection point of the first series circuit according to a second set default. In other words, the controller can be set up, on the one hand, to set the output voltage of the second side according to the first specification if the first side is used as the input side (or vice versa). In addition, the controller is also set up to adjust the voltage between the connection points of the first series connection. In addition, the controller can set a potential offset of the second side with respect to a reference potential. It is therefore possible to set the output voltage and the voltage on the input side by means of the controller as two different adjustable variables, i. H. the voltage delivered to the working inductors (corresponding to the voltage between the first and second connection points). These quantities can be adjusted separately from each other because when a certain voltage is defined on the first side (between the connection points there) the transistor devices of the second side adjust to adjust the voltage on the second side (according to the first specification). This allows the two series circuits to be operated at an optimized operating point, even if the input voltage and the output voltage are each already defined. The potential offset between the side used as the output side and a reference potential can be set as a further variable that can be set, for example if there is an insulation fault with respect to it, as is shown below.

The controller can be set up to also set a potential of the first or second connection point of the first series connection according to a further specification. As a further variable, it is therefore possible to set the potential and thus the voltage of the first or second connection point in relation to a reference potential according to a specification. The second specification therefore specifies whether and how strong a potential shift between between the first two pages or between the output page and the reference potential. In particular, in the event of an insulation fault or an otherwise justified asymmetry of the potentials with respect to a reference voltage, this can be used to set at least one potential on one side with respect to the reference voltage in such a way that no dangerous touch voltage occurs there or the voltage with respect to the reference potential is zero or below a danger limit such as for example 60V, 40V, 20V or 10V. In other words, the controller is also set up, when using one of the two sides as an input stage, to clock the other side in such a way that a desired (small) potential difference between one of the potentials and a reference potential occurs there. This can also be set independently of a desired transmission ratio, in particular independently of a voltage that is delivered to the working inductances at the input stage, or also independently of the output voltage of the side that is used as the output stage.

the 1 and 2 show circuits that serve to explain the embodiments described here.

In both figures, a galvanically coupling DC-DC converter is provided with a first side A1 and a second side A2. Each side has a first potential and a second potential. The first potential is positive, the second potential is negative. In this case, the potential U+ is the first potential on the first side and V+ is the first potential on the second side. The second potential of the first side is the potential U- and the second potential of the second side is the potential V-. The DC-DC converter has a first and a second series connection R1, R2 of transistor devices. the 1 and 2 show embodiments in which the series circuits are mirrored to one another, in particular in which they have the same number of transistor elements or transistor devices. With regard to the number of transistor devices or transistor elements per series connection, the first series connection (ie the series connection on the first side) can differ from the second series connection (ie the series connection on the second side A2).

In 1 and 2 the series circuits each have a first, second and third transistor device. These are connected in series, with the ends of the series connection being connected between the first and second potential of the relevant side. The outer transistor devices are thus connected to the first and second potential of the relevant side. In the illustrated circuits, the second transistor device is located between the first and third transistor devices, resulting in a first connection point VP1 (between the first and second transistor devices) and a second connection point VP2 (between the second and third transistor devices). For the first side, the connection points of the series connection R1 have the designations VP1, VP2 and for the second side A2 the connection points have the reference symbols VP1' and VP2' within the second series connection R2.

There is a reference potential M, which is located in the middle between the potentials U+, U- in error-free operation. In particular, the reference potential M is electrically isolated from the first and the second potential U+, U− (and also from V+, V−) during error-free operation. The voltage UHV1 exists between the potentials U+, U- and the potential UHV2 exists between the potentials V+, V-. The DC-DC converter is set up to convert the voltage UHV1 into the voltage UHV2. The potential UHV1P exists between the positive potential U+ on the first side A1 and the reference potential M, and the voltage UHV1M exists between the second potential U− on the first side A1 and the reference potential M. In error-free operation, the two voltages are the same; the first and the second potential are symmetrical to the reference potential M.

The voltage UHV2P exists between the first potential V+ and the reference potential M on the second side A2, and the voltage UHV2M exists between the second potential V− of the second side A2 and the reference potential M. These are also the same size in error-free operation. If there is a one-sided insulation fault, then the reference of the potentials U+, U- in relation to the potential M shifts or the potential level of the potentials V+, V- in relation to the reference potential M shifts.

Between the two sides A1, A2 is located in the circuits of 1 and 2 an inductive connection. This includes a first working inductance L1, via which the first connection point VP1 of the first series circuit R1 is connected to the first connection point VP1' of the second series circuit R2. Furthermore, the inductive connection includes a second working inductance L1′, via which the second connection point VP2 of the first series circuit R1 is connected to the second connection point VP2′ of the second series circuit R2. In both figures, a common-mode choke L2, L2' is also provided within the inductive connection. This connects the working in both exemplary circuits shown inductors L1, L1' to the connection points VP1', VP2' of the second series circuit R2. There is also a smoothing capacitor C3 between the ends of the first and second working inductors L1, L1' that are remote from the connection points VP1, VP2 (of the first series circuit R1). One end of the first working inductance L1 is connected to the first potential U+ on the first side A1 via the first transistor device S1 in the first series circuit R1. One end of the second working inductance L1' is connected to the second potential U− on the first side A1 via the third transistor device S3 or S4 of the first series circuit R1. The opposite end of the first working inductor L1 is connected (via the common mode choke) to the first connection point VP1' of the second series connection and thus to the first potential V+ of the second side A2 via the first transistor device of the second series connection R2. The opposite end of the second working inductance is connected (via the common mode choke F) to the second potential V- of the second side A2 via the third transistor device of the second series connection.

A controller C is drivingly connected to the transistor devices S1 to S6 or S1 to S8, as shown by the double arrows. This is set up to switch the third and first transistor devices of the series circuits on and off synchronously in an operating state, for example in the normal operating state (i.e. in an operating state free of insulation faults). Furthermore, it is set up not to turn on the second transistor devices and the first and third transistor devices of the same series connection at the same time. When the first and third transistors are off, the controller C turns the second transistor devices S on. The controller C is set up, for example, to set a target voltage across the smoothing capacitor C3 or between the ends of the working inductances L1, L1' that face away from the first side, according to a target voltage. For this purpose, the second transistor device on the one hand and the first and third transistor devices on the other hand are switched on and off alternately in order to achieve a conversion effect via the working inductances. The controller C is also set up to alternately switch on and off the second transistor device of the second series connection R2 on the one hand and the first and third transistor device of the second series connection R2 in order to achieve a voltage between the potentials V+, V- according to a target voltage. The controller C is also set up to alternately switch on and off the second transistor device of the second series circuit R2 on the one hand and the first transistor device of the second series circuit R2 in order to generate a voltage between the potentials V+, V- according to a target voltage. In this case, too, there is a converter effect based on the voltage that lies between the ends of the two working inductances L1, L1', which face away from the first series circuit R1.

In addition, the first and the third transistor devices can be driven differently by means of the controller C, resulting in a potential shift. This affects the potentials at the points VP1, VP2, VP1', VP2' as well as V+, V- and/or U+, U-. This is carried out in particular with a fault in which a (one-sided) insulation fault between one of the potentials U+, U-, V+, V- and the reference potential M occurs. As a result, the voltage of the potential with the insulation fault and the reference potential M can be summed or set to zero in order to avoid dangerous contact voltages on parts that are connected to the reference potential M. This concerns the minimization of one of the voltages UHV1 P, UHV1 M, UHV2P or UHV2M. The first side A1 can serve as the input side, while the second side serves as the output of the DC/DC converter, so that the voltage UHV2 is set by the controller C. However, the voltage UHV2 can also be converted into a desired voltage UHV1 in accordance with a voltage specification during a feedback process.

In the 1 a voltage converter circuit is shown in which both sides A1, A2 have a series circuit R1, R2, which each includes only three transistor devices S1 to S6. In this case, S2 and S5 form the second transistor device, while S1 and S4 form the first transistor device and the devices S3 and S6 form the third transistor device. The third transistor device (in 1 : first side: S3, second side: S6) is directly connected to the negative potential (in 1 : first side: U-, second side: V-) of the respective side and the first transistor device (in 1 : first side: S1, second side: S4) with the positive potential (in 1 : first side: U+, second side: V+) of the respective side.

In the 1 an intermediate circuit capacitor device is also provided in the form of two parallel intermediate circuit capacitors C1′, C1 on the first side and two intermediate circuit capacitors C2, C2′ on the second side.

In contrast, in the 2 a circuit is shown in which the second transistor device consists of two transistor elements, namely the transistors S2 and S3 in the series circuit R1 and the transistors S6 and S7 in the series circuit R2. Here, the transistor devices S1, S5 are the first transistor devices, and the transistor devices S4 and S8 are the third transistor devices. The second transistor device of the first series connection R1 is formed from a series connection of the transistor elements S2 and S3, the connection point of which is referred to as the intermediate connection point ZP. In the same way, the series circuit R2 comprises, as the second transistor device, a series circuit of the transistor elements S6, S7, which are connected via an interconnection point ZP'.

Furthermore, the intermediate circuit capacitor devices are provided in two parts on each side in the form of two capacitors which are connected in series. The ends of this capacitor series circuit are connected to the respective first potential (U+, V+) and second potential (U-, V-) of the respective side A1, A2. The intermediate connection point ZP of the (second transistor device S2, S3) on the first side A1 is directly connected to the capacitor connection point KP on the first side A1. On the second side A2, the intermediate connection point ZP' (of the second transistor device S6, S7) is connected directly to the capacitor connection point KP', via which the capacitor elements of the intermediate circuit capacitor device are connected to one another in series. A neutral conductor connection can be connected to the intermediate connection point, for example a neutral conductor connection of a charging input, with preferably only the side of the converter used as the input side having this connection.

The points KP, KP' and ZP, ZP' each form a potential center. The potentials U+, U- are (in the case of no insulation faults) provided symmetrically with respect to the points KP and ZP. This also applies to the second side, in which the potentials V+, V- are provided symmetrically to the points KP', ZP'.

The number of transistor elements or transistors in the series circuit R1 can differ from the number of transistors or transistor elements in the series circuit R2. So is a circuit based on the 2 conceivable, with either the transistors S2 and S3 being replaced by a single transistor element, or the transistors S6, S7 being replaced by a single transistor element. On the side whose series connection is only a single element as the second transistor device, only a one-piece intermediate circuit capacitor device is preferably provided, ie one or more intermediate circuit capacitors whose ends are connected to both potentials of the relevant side. There is then also no connection between a capacitor connection point and an intermediate connection point, since these do not exist.

The dichotomy of the in 2 shown intermediate circuit capacitor devices is that two parts are provided, which are connected in series. This does not apply to the parallel connection of capacitor elements.

In the 1 and 2 For example, a polarized capacitor element and a non-polarized capacitor element connected in parallel can be regarded as a single capacitor element. For example, the parallel connection of C1 'and C1 of 1 be considered as a capacitor element or as an intermediate circuit capacitor. As mentioned, the two-piece design of the capacitors refers to the division of two capacitor elements connected in series.

Claims (12)

Galvanically coupled DC-DC converter having a first side (A1) and a second side (A2), the first side (A1) and the second side (A2) each having a first potential (U+, V+) and a second potential (U-, V -) have, wherein the DC-DC converter has a first and a second series connection (R1, R2) each of a first, second and third transistor device (S1, S2, S3; S4, S5, S6), which via a first and a second connection point (VP1, VP2) are connected in series, the first series connection (R1) being provided between the potentials (U+, U-) of the first side (A1) and the second series connection (R2) being provided between the potentials (V+, V-,) the second side (A2), the first connection point (VP1) of the first series circuit (R1) being connected to the first connection point (VP1') of the second series circuit (R2) via a first working inductance (L1) and the second connection point ( VP2) of the first series connection is connected via a second working inductance (L1') to the second connection point (VP2') of the second series circuit. Galvanically coupled DC voltage converter claim 1 , wherein the transistor devices are each individual transistors (S1 - S3, S4 - S6). Galvanically coupled DC voltage converter claim 1 , wherein the transistor devices of the first series circuit (R1) or the second series circuit (R2) are each individual transistors (S1 - S3, S4 - S6) and the first and third transistor devices (S1, S4; S5, S8) of the respective other series circuit ( R2, R1) are each individual transistors (S1 - S3, S4 - S6), while the second transistor device (S1, S4; S5, S8) of this series circuit (R2, R1), wel which connects the first (S1, S4) to the third transistor device (S5, S8), is designed as a partial series connection of two individual transistors (S2, S3; S6, S7) which are connected via an intermediate connection point (ZP, ZP') are connected. Galvanically coupled DC voltage converter claim 1 , wherein the first and third transistor devices (S1, S4; S5, S8) of each of the series circuits (R2, R1) are each individual transistors (S1 - S3, S4 - S6), while the second transistor device (S1, S4; S5, S8 ), which connects the first (S1, S4) to the third transistor device (S5, S8), is designed as a partial series connection of two individual transistors (S2, S3; S6, S7), which is connected via an intermediate connection point (ZP, ZP ') are connected. Galvanically coupled DC voltage converter claim 3 or 4 , wherein the intermediate connection point or points (ZP, ZP') is connected to a capacitor connection point (KP) of a two-part intermediate circuit capacitor device (C1a - C2b') which is connected to the potentials (U+, U-; V+, V-) the same side (A1, A2) as that of the intermediate connection point (ZP, ZP') connected thereto. Galvanically coupling DC-DC converter according to one of the preceding claims, wherein the connection points (VP1', VP2') of the second series circuit are connected directly or via a common-mode choke (L2, L2') to those ends of the working inductances (L1, L1') which are connected to the connection points (VP1, VP2) facing away from the first series circuit (R1). Galvanically coupled DC voltage converter claim 6 , wherein a smoothing capacitor (C3) is connected to the ends of the working inductances (L1, L1') remote from the connection points (VP1, VP2) of the first series circuit (R1). Galvanically coupled DC-DC converter according to one of the preceding claims, having a controller (C) which is drivingly connected to the transistor devices (S1 - S6; S1 - S8) and is arranged, in a converter state, to switch the first and third transistor devices (S1, S3, S4 , S6; S1, S4, S5, S8) of each series circuit (R1, R2) simultaneously in an ON state. Galvanically coupled DC voltage converter claim 8 , wherein the controller (C) is set up, in the converter state, the second transistor devices (S2, S3; S2) of each series connection (R1, R2) on the one hand and the first and third transistor devices (S1, S3, S4, S6; S1, S4, S5, S8), on the other hand, to be driven in an ON state alternately. DC converter after claim 8 or 9 , wherein the controller (C) is set up, in the event of an insulation fault between the first potential (U+) of the first side (A1) or second side (A2) and a reference potential (M), the third transistor device (S3) is permanently in an ON state to drive and to drive the first transistor device (S1) and the second transistor device (S2) alternately in an ON state, and/or wherein the controller (C) is set up, in the event of an insulation fault between the second potential (U-) of the first side ( A1) and a reference potential (M) to drive the first transistor device (S1) permanently in an ON state and to drive the second transistor device (S2) and the third transistor device (S3) alternately in an ON state. DC converter after claim 8 , 9 or 10 , wherein the controller (C) is set up, the voltage and / or a potential on the second side (A2) according to a first specification and the voltage between the first and second connection point (VP1, VP2) of the first series circuit (R1) and / or to set a potential of the first or second connection point (VP1, VP2) of the first series circuit (R1) according to a second specification. Vehicle electrical system with at least two vehicle electrical system branches which have different nominal voltages, the vehicle electrical system having at least one DC-DC converter according to one of the preceding claims, which connects the two vehicle electrical system branches with different nominal voltages to one another in a voltage-converting manner.

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