DC voltage converter, electric vehicle and method for operating a DC voltage converter

Abstract

A DC voltage converter having three DC voltage connections. The DC voltage converter can exchange electrical energy between the three DC voltage connections in any desired way. The DC voltage converter comprises a resonant circuit for resonant operation. In addition, a combination of an H-bridge circuit and a step-down converter is provided on at least one DC voltage converter connection.

Description

[0001] Description

[0002] title

[0003] DC-DC converter, electric vehicle and method for operating a DC-DC converter

[0004] Technical area

[0005] The present invention relates to a DC-DC converter and an electric vehicle with such a DC-DC converter. The present invention further relates to a method for operating a DC-DC converter. In particular, the present invention relates to a DC-DC converter with three DC voltage terminals.

[0006] State of the art

[0007] The electrical system of a fully or at least partially electrically powered vehicle typically comprises a high-voltage system and a low-voltage system. The high-voltage system typically has a direct current in the range of several hundred volts. The low-voltage system typically has a significantly lower direct current, for example, in the range of 12 to 14, 24, or 48 volts. Typically, the high-voltage system supplies the electric drive system of such a vehicle, as well as any other high-power consumers, from the high-voltage system. The low-voltage system typically supplies consumers such as lighting, control units, brake and steering actuators, or the vehicle's entertainment system.

[0008] The high-voltage network and the low-voltage network can be coupled together, for example, using a DC-DC converter. Using such a DC-DC converter, electrical energy can be exchanged between the high-voltage network and the low-voltage network. In this way, for example, electrical consumers in the low-voltage network can be supplied with electrical energy using electrical energy from a traction battery in the high-voltage network. For example, the publication DE 10 2014 210 283 A1 describes a method for operating a vehicle electrical system with at least two voltage levels that have different nominal voltages.

[0009] In addition, such an electric vehicle may be provided with a further voltage converter which converts an electrical voltage at the charging port of the vehicle into a direct voltage suitable for charging the traction battery of the electric vehicle.

[0010] Disclosure of the invention

[0011] The present invention provides a DC-DC converter, an electric vehicle, and a method for operating a DC-DC converter having the features of the independent patent claims. Further advantageous embodiments are the subject of the dependent patent claims.

[0012] Accordingly, it is provided:

[0013] A DC-DC converter with a transformer, a first H-bridge circuit, a second H-bridge circuit, a voltage converter circuit, and a resonant circuit. The transformer comprises a primary winding, a first secondary winding, and a second secondary winding. The first H-bridge circuit is connected to a first DC voltage terminal at external terminals. The center terminals of the first H-bridge circuit are electrically coupled to the primary winding of the transformer. The first resonant circuit is electrically arranged between the center terminals of the first H-bridge circuit and the primary winding of the transformer. The second H-bridge circuit is connected to a second DC voltage terminal at external terminals. The center terminals of the second H-bridge circuit are electrically coupled to the first secondary winding of the transformer. The voltage converter circuit comprises six semiconductor switching elements and an inductor.Here, a first semiconductor switching element is arranged between a first node and a first center terminal. A second semiconductor switching element is arranged between the first center terminal and a first outer terminal. A third semiconductor switching element is arranged between a second node and a second center terminal. A fourth semiconductor switching element is arranged between the second center terminal and the first outer terminal. A fifth switching element is arranged between a second outer terminal and the first node. A sixth switching element is arranged between the second outer terminal and the second node. The first outer terminal of the voltage converter circuit is electrically connected to a first connection point of a third DC voltage terminal.The inductance is arranged between the second outer terminal of the voltage converter circuit and a second connection point of the third DC voltage terminal. The first center terminal and the second center terminal of the voltage converter circuit are each electrically connected to terminals of the second secondary winding of the transformer.

[0014] Furthermore, it is planned:

[0015] An electric vehicle with a high-voltage electrical system, a low-voltage electrical system, and a DC-DC converter according to the invention. The second DC voltage connection of the DC-DC converter is electrically coupled to the high-voltage electrical system of the electric vehicle. The third DC voltage connection of the DC-DC converter is electrically coupled to the low-voltage electrical system of the electric vehicle. The first DC voltage connection of the DC-DC converter can further be configured to be connected to a charging port or charging circuit of the electric vehicle.

[0016] Finally, it is planned:

[0017] A method for operating an inventive

[0018] DC-DC converter, wherein the method comprises one of the following

[0019] can carry out steps. In a first operating mode, the method can transmit electrical energy from the first DC voltage connection to the second DC voltage connection. In a second operating mode, electrical energy can be transmitted from the second DC voltage connection to the third DC voltage connection. In a third operating mode, electrical energy can be transmitted from the third DC voltage connection to the second DC voltage connection. In a fourth operating mode, electrical energy can be transmitted from the second DC voltage connection to the first DC voltage connection and to the third DC voltage connection. In a fifth operating mode, electrical energy can be transmitted from the first DC voltage connection to the first second DC voltage connection and to the third DC voltage connection.Furthermore, in a sixth operating mode, electrical energy can be transferred from the third, second DC voltage terminal to the first DC voltage terminal. In the first and sixth operating modes, the fifth and sixth switching elements of the voltage converter circuit can be open. In the second and third operating modes, the fifth and sixth switching elements of the voltage converter circuit are closed. In the fourth and fifth operating modes, the fifth and sixth switching elements of the voltage converter circuit are controlled as buck converters.

[0020] Advantages of the invention

[0021] The present invention is based on the realization that conventional electric vehicles can optionally be provided with multiple DC-DC converters. For example, electrical energy can be exchanged between a high-voltage vehicle electrical system and a low-voltage vehicle electrical system using one DC-DC converter. Furthermore, a further DC-DC converter can also be provided between an external energy source and internal vehicle electrical systems. This entails significant hardware complexity and associated costs. Therefore, one idea of ​​the present invention is to create a DC-DC converter that can exchange electrical energy between more than two connections. In particular, it is desirable to create a cost-effective and efficient DC-DC converter for exchanging energy between more than two DC voltage connections.

[0022] According to the invention, a DC-DC converter with three DC voltage connections is provided. The electrical energy can be exchanged between the individual DC voltage connections in almost any configuration. For example, a first DC voltage connection can be provided for connection to an external energy source, such as a charging connection of an electric vehicle. A DC voltage can either be provided directly at the charging connection, or alternatively, a provided AC voltage can be rectified by means of a rectifier, and the rectified voltage can then be provided at the first DC voltage connection. A second DC voltage connection can, for example, be designed for connection to a high-voltage electrical system of an electric vehicle.Such a high-voltage electrical system can, for example, comprise a traction battery, an electric drive system, and possibly other consumers. The high-voltage electrical system generally has an electrical voltage of several hundred volts, for example 400 V or 800 V. A third DC voltage connection of the rectifier can, for example, be designed to be connected to a low-voltage electrical system of an electric vehicle. Such a low-voltage electrical system can, for example, accommodate electrical consumers such as sensors, actuators, control units, components of comfort functions, an entertainment system, or the like. In addition, this low-voltage electrical system can also contain an electrical energy storage device in the form of a rechargeable battery. The low-voltage electrical system can have an electrical voltage that is significantly lower than the electrical voltage in the high-voltage system.

[0023] For example, the electrical voltage in the low-voltage vehicle electrical system can be 12 to 14 V, 24 V, or 48 V. The half-bridge circuits of the rectifier can, for example, comprise two half-bridges, each with two semiconductor switching elements. The semiconductor switching elements can be, for example, MOSFETs or bipolar transistors with an insulated gate connection (IGBT). A half-bridge comprises two semiconductor switching elements connected in series. The two semiconductor switching elements are electrically connected to one another at a center connection. The other connections, referred to here as outer connections, are connected to corresponding connection points of the respective DC voltage connections. The center connections are connected to the connections of the corresponding windings of the transformer either directly or via an oscillating circuit.

[0024] The resonant circuit can, for example, comprise a series-connected coil or inductor and a capacitor or capacitance. Alternatively, an inductance can be provided between a center terminal and a corresponding terminal of the transformer winding, and a capacitance can be provided between the further center terminal and the corresponding terminal of the transformer winding. Of course, any other resonant circuit configurations are also possible. If necessary, the resonant circuit can also consist of only a capacitance or an inductance.

[0025] The voltage converter circuit, located between the second secondary winding and the third DC voltage terminal, includes the components of an H-bridge, as well as two additional switching elements (a fifth and sixth switching element) and an inductor. These additional components enable the functionality of a buck converter.

[0026] This makes it possible to appropriately adjust the voltage at the third DC voltage terminal when transmitting electrical energy to the third DC voltage terminal through these components of the buck converter. This allows for efficient transmission of electrical energy between the three DC voltage terminals, with the voltage at each of the individual terminals being specifically adjustable or regulated.

[0027] According to one embodiment, the first semiconductor switching element and the fifth semiconductor switching element are complementary semiconductor switching elements. Likewise, the second semiconductor switching element and the sixth semiconductor switching element are complementary semiconductor switching elements. The first, second, third, and fourth semiconductor switching elements can be identical or at least similar semiconductor switching elements. A complementary semiconductor switching element to an n-channel transistor is, for example, a p-channel transistor, and vice versa. In particular, complementary semiconductor switching elements have opposite blocking and forward directions in the open state. The semiconductor switching elements can be, for example, MOSFETs or insulated-gate bipolar transistors (IGBTs).In principle, mixed forms are also conceivable, in which, for example, the first to fourth semiconductor switching elements are designed as IGBTs and the fifth to sixth semiconductor switching elements are designed as MOSFETs.

[0028] According to one embodiment, the first H-bridge circuit and the second H-bridge circuit each comprise four semiconductor switching elements. The four semiconductor switching elements are designed in particular in the form of two half-bridges. In each case, a first semiconductor switching element is arranged between a first external terminal and a first center terminal of the respective H-bridge circuit. A second semiconductor switching element is arranged between the first external terminal and a second center terminal of the respective H-bridge circuit. A third semiconductor switching element is arranged between a second external terminal and the first center terminal of the respective H-bridge circuit. A fourth semiconductor switching element is arranged between the second external terminal and the second center terminal of the respective H-bridge circuit. According to one embodiment, the DC-DC converter comprises a second resonant circuit.The second resonant circuit is electrically arranged between the center terminals of the second H-bridge circuit and the first secondary winding of the transformer. Analogous to the first resonant circuit, the second resonant circuit can also comprise a capacitance and an inductance. For example, a series circuit comprising a capacitance and an inductance can be provided between a center terminal of the second H-bridge circuit and the corresponding terminal of the first secondary winding of the transformer. Alternatively, it is also possible to arrange a capacitance between the first center terminal of the second H-bridge circuit and the corresponding terminal of the first secondary winding of the transformer, and to arrange the inductance between the second center terminal and the corresponding terminal of the first secondary winding of the transformer.Alternatively, the second resonant circuit may also comprise only a capacitance which is arranged between a center terminal of the second H-bridge circuit and the corresponding terminal of the first secondary winding of the transformer.

[0029] According to one embodiment, the DC-DC converter comprises a control device. The control device is designed to control the semiconductor switching elements of the first H-bridge circuit, the second H-bridge circuit, and the voltage converter circuit in the DC-DC converter. In particular, the control can be carried out, for example, using pulse-width modulated control signals. The control device can be designed to adapt a frequency and / or phase of an electrical alternating voltage occurring at the primary winding and / or the first secondary winding of the transformer during resonant operation.

[0030] According to a further embodiment, the control device can be designed to control the fifth and / or the sixth semiconductor switching element of the voltage converter circuit in a buck converter mode.

[0031] According to one embodiment, the DC-DC converter is designed to transmit electrical energy from the first DC voltage terminal to the second DC voltage terminal in a first operating mode. For example, electrical energy can be transmitted from a power source connected to the first DC voltage terminal to a traction battery of an electric vehicle connected to the second DC voltage terminal in order to charge the traction battery. In particular, the DC-DC converter can be operated in a resonant mode corresponding to the resonant frequency of the first resonant circuit. Furthermore, the DC-DC converter can be designed to transmit electrical energy from the second DC voltage terminal to the third DC voltage terminal in a second operating mode.If a second resonant circuit is provided between the second H-bridge circuit and the first secondary winding of the transformer, the DC-DC converter can also be operated in a resonant operating mode. In this second operating mode, for example, electrical energy can be transferred from a traction battery of an electric vehicle connected to the second DC voltage connection to a low-voltage on-board network of the electric vehicle connected to the third DC voltage connection. In this case, the fifth and sixth switching elements of the voltage converter circuit can both be closed. Furthermore, the DC-DC converter can be designed to transfer electrical energy from the third DC voltage connection to the second DC voltage connection in a third operating mode. In this case, the fifth and sixth switching elements of the voltage converter circuit can be closed.In this third operating mode, for example, electrical energy can be transferred from the low-voltage electrical system of an electric vehicle to the high-voltage electrical system of the electric vehicle at the second DC voltage connection in order to charge an intermediate circuit in the high-voltage electrical system. Furthermore, the DC-DC converter can be designed to transfer electrical energy from the second DC voltage connection simultaneously to the first DC voltage connection and to the third DC voltage connection in a fourth operating mode. In this fourth operating mode, the fifth and sixth switching elements of the voltage converter circuit can be controlled together with the inductance of the voltage converter circuit as a step-down converter. In this way, both the electrical voltage at the first DC voltage connection and at the third DC voltage connection can be specifically adjusted to predetermined target values.Furthermore, the DC-DC converter can be configured to transfer electrical energy from the first DC voltage terminal to the second DC voltage terminal and simultaneously to the third DC voltage terminal in a fifth operating mode. In this case, the fifth and / or sixth switching element of the voltage converter circuit can be controlled as a buck converter. Finally, the DC-DC converter can be configured to transfer electrical energy from the second DC voltage terminal to the first DC voltage terminal in a sixth operating mode. In this case, both the fifth and sixth switching elements of the voltage converter circuit are closed.

[0032] The above embodiments and developments can be combined with one another as desired, where appropriate. Further embodiments, developments, and implementations of the invention also include combinations of features of the invention not explicitly mentioned above or described below with respect to the exemplary embodiments. In particular, those skilled in the art will also add individual aspects as improvements or additions to the respective basic forms of the invention.

[0033] Short description of the drawings

[0034] Further features and advantages of the invention are explained below with reference to the figures. These show:

[0035] Fig. 1: a schematic representation of a basic circuit diagram for a DC-DC converter according to an embodiment;

[0036] Fig. 2: a schematic representation of a basic circuit diagram of an H-bridge circuit in a DC-DC converter according to one embodiment; Fig. 3: a schematic representation of a basic circuit diagram of a DC-DC converter according to another embodiment; and

[0037] Fig. 4: a flowchart underlying a method for operating a DC-DC converter according to an embodiment.

[0038] Description of the embodiments

[0039] Figure 1 shows a schematic representation of a basic circuit diagram of a DC-DC converter 1 according to one embodiment. The DC-DC converter 1 comprises three DC voltage connections G1, G2 and G3. If such a DC-DC converter 1 is used, for example, in an electric vehicle, an external energy source, for example a charging station, can be connected to the first DC voltage connection G1. If this charging station already provides a DC voltage, the provided charging voltage can be provided directly, if necessary via a suitable disconnect switch, to the first DC voltage connection G1. If a single-phase or multi-phase AC voltage is provided by the external energy source, this can be converted into a DC voltage via a rectifier or another suitable charging circuit 100, if necessary, and the DC voltage can be provided at the first DC voltage connection G1.

[0040] For example, a high-voltage electrical system 200 of an electric vehicle can be connected to the second DC voltage connection G2. Such a high-voltage electrical system 200 can include, for example, a traction battery, an electric drive system, or any other electrical consumers. The high-voltage electrical system typically has an electrical voltage of several hundred volts, for example, 350 to 400 V or 800 V.

[0041] For example, a low-voltage electrical system 300 of an electric vehicle can be connected to the third DC voltage connection G3. For example, electrical consumers such as control devices, sensors, actuators, components for comfort functions in an electric vehicle, an entertainment system, or the like can be connected to this low-voltage electrical system 300. An electrical energy storage device, such as a lead-acid battery or the like, can also be provided in this low-voltage electrical system 300. The low-voltage electrical system 300 generally has an electrical voltage that is significantly lower than the electrical voltage in the high-voltage electrical system 200. For example, the electrical voltage in the low-voltage electrical system 300 can be 12 to 14 V, 24 V, or 48 V.

[0042] DC-DC converter 1 is designed to exchange electrical energy between the three DC voltage terminals G1, G2, and G3. A transformer TR is provided in DC-DC converter 1. This allows the individual DC voltage terminals G1, G2, and G3 to be galvanically isolated from each other.

[0043] The transformer TR comprises a primary winding 11, a first secondary winding 12, and a second secondary winding 13. Furthermore, the DC-DC converter 1 comprises a first H-bridge circuit H1, a second H-bridge circuit H2, and a voltage converter circuit H3. The basic structure of an H-bridge circuit H1, H2 is explained in more detail below.

[0044] The two outer terminals A11, A12 of the first H-bridge circuit H1 are electrically connected to corresponding terminals of the first DC voltage terminal G1. The two center terminals M11, M12 of the first H-bridge circuit H1 are connected to the two terminals of the primary winding 11 via a first resonant circuit S1.

[0045] The first resonant circuit S1 can, for example, comprise a first capacitance CI and a first inductance II. For example, the first capacitance CI can be provided between a first center terminal Mil of the first H-bridge circuit H1 and a corresponding terminal of the primary winding 11. Furthermore, the first inductance II can be provided between the second center terminal M12 of the first half-bridge H1 and the further terminal of the primary winding 11. Alternatively, it is also possible to provide a series circuit comprising the first capacitance CI and the first inductance II between a center terminal Mil, M12 of the first half-bridge H1 and a terminal of the primary winding 11. Furthermore, other suitable arrangements of resonant components for the first resonant circuit S1 are also possible if necessary.

[0046] The second H-bridge circuit H2 is electrically connected to the two outer terminals of the second DC voltage terminal G2 by corresponding terminals. The two center terminals of the second H-bridge circuit H2 are connected to the two terminals of the first secondary winding 12 of the transformer TR. If necessary, additional resonant components can also be provided between the terminals of the first secondary winding 12 of the transformer TR and the center terminals of the second H-bridge circuit H2. This will be explained in more detail below.

[0047] The voltage converter circuit H3 is arranged between the third DC voltage terminal G3 and the second secondary winding 13 of the transformer TR. The voltage converter circuit H3 comprises six semiconductor switching elements T1 to T6 and an inductor L. If necessary, a (parasitic) inductance of the second secondary winding 13 of the transformer TR can also be used in addition to or as an alternative to this discrete inductance.

[0048] A first semiconductor switching element T1 is arranged between a first node K1 and a first center connection M1 of the voltage converter circuit H3. The second switching element T2 is arranged between the first center connection M1 and a first external connection A1 of the voltage converter circuit H3. A third switching element T3 is arranged between a second node K2 and a second center connection M2 of the voltage converter circuit H3. A fourth switching element T4 is arranged between the second center connection M2 and the first external connection A1. Furthermore, a fifth semiconductor switching element T5 is arranged between a second external connection A2 and the first node K1 of the voltage converter circuit H3. Finally, a sixth semiconductor switching element T6 is arranged between the second external connection A2 and the second node K2.

[0049] The first external terminal A1 is electrically connected to a first connection point of the third DC voltage terminal G3. The inductance L is arranged between the second external terminal A2 of the voltage converter circuit H3 and the second connection point of the DC voltage terminal G3.

[0050] In this way, the voltage converter circuit H3 forms a combination of a third H-bridge circuit 31 and a buck converter 32.

[0051] The switching elements T1 to T6 of the voltage converter circuit H3 as well as the switching elements of the first half-bridge circuit H1 and the second half-bridge circuit H2 can be suitably controlled by a control device 20. In this way, electrical energy can be exchanged between the DC voltage terminals G1, G2, and G3 in almost any desired manner. To regulate the energy transfer, current and / or voltage sensors (not shown) can optionally be provided in the DC-DC converter 1. The sensor values ​​of these current or voltage sensors can be provided to the control device 20. The control device 20 then generates control signals for the switching elements in the first half-bridge circuit H1, the second half-bridge circuit H2, and the voltage converter circuit H3 using a setpoint value for the energy transfer and the output voltages to be set.These control signals can, if necessary, be provided to the corresponding switching elements via suitable driver stages.

[0052] Figure 2 shows a schematic representation of a basic circuit diagram of a half-bridge circuit, such as can be used, for example, as the first half-bridge circuit H1 or the second half-bridge circuit H2 in a rectifier 1 according to the invention. Even if the explanations below are described in connection with the first half-bridge circuit H1, they also apply analogously to the second half-bridge circuit H2.

[0053] As shown in Figure 2, the first half-bridge circuit H1 comprises two half-bridges, each with two semiconductor switching elements TU to T14 connected in series. A first semiconductor switching element TU is arranged between a first external terminal A11 and a first center terminal M11. A second semiconductor switching element T12 is arranged between the first center terminal M11 and a second external terminal A12. A third semiconductor switching element T13 is arranged between the first external terminal A11 and a second center terminal M12. A fourth semiconductor switching element T14 is arranged between the second center terminal M12 and the second external terminal A12. The two external terminals A11 and A12 are connected to the corresponding terminals of the primary winding 11 of the transformer TR via the first resonant circuit S1.

[0054] The second half-bridge circuit H2 is constructed analogously to the circuit principle described above with the four semiconductor switching elements T21 to T24. The semiconductor switching elements T21 to T24 are therefore arranged between the outer terminals A21 and A22 and the center terminals M21 and M22.

[0055] Figure 3 shows a schematic representation of a basic circuit diagram of a DC-DC converter 1 according to a further embodiment. All statements made previously in connection with Figures 1 and 2 apply here, where applicable. The DC-DC converter 1 according to Figure 3 differs in particular in that a second resonant circuit S2 is provided between the first secondary winding 12 of the transformer TR and the second half-bridge circuit H2. This resonant circuit can, for example, comprise a second capacitor C2 and a second inductor 12. For example, a series circuit comprising the second capacitor C2 and the second inductor 12 can be provided between a connection point of the first secondary winding 12 of the transformer TR and a center connection of the second half-bridge circuit H2.Alternatively, the second capacitor C2 can also be provided between a terminal of the first secondary winding 12 of the transformer TR and a first center terminal of the second half-bridge H2, and the second inductor 12 can be provided between another terminal of the first secondary winding 12 of the transformer TR and a second center terminal of the second half-bridge H2. If necessary, only a capacitor C2 between a terminal of the first secondary winding 12 of the transformer TR and a center terminal of the second half-bridge circuit H2 is also possible as the second resonant circuit S2.

[0056] To transmit electrical energy between the DC voltage terminals G1, G2, and G3, the switching elements of the first half-bridge circuit H1 and the second half-bridge circuit H2 can be controlled such that an electrical alternating voltage is applied to the windings of the transformer TR, wherein the frequency and / or phase of these alternating voltages can be adjusted taking into account a resonant frequency of the first resonant circuit S1 and / or the second resonant circuit S2. In this way, a resonant operating mode can be set in the DC-DC converter 1. However, since the basic principle of such resonant operation is considered to be known, a more detailed explanation is omitted here.

[0057] Various operating modes are possible for the exchange of electrical energy between the DC voltage terminals G1, G2, and G3. Some exemplary operating modes are explained in more detail below with reference to the inventive method for operating a DC-DC converter 1.

[0058] Figure 4 shows a flowchart of how a method for operating a DC-DC converter 1, in particular one of the previously described DC-DC converters 1, can be based according to one embodiment. To operate the DC-DC converter 1, the control device 20 can control the switching elements in the H-bridge circuits H1, H2 and / or in the voltage converter circuit H3 in a suitable manner. For this purpose, pulse-width modulation can be used, for example, to set the desired electrical voltage in terms of amplitude, frequency, and phase at the respective primary or secondary windings 11, 12, 13.

[0059] In a first operating mode B1, for example, electrical energy can be transferred from the first DC voltage terminal G1 to the second DC voltage terminal G2. In this case, the fifth switching element T5 and the sixth switching element T6 of the voltage converter circuit H3 can be open. In this way, the third DC voltage terminal G3 is electrically separated from the second secondary winding 13 of the transformer TR. To transfer energy from the first DC voltage terminal G1 to the second DC voltage terminal G2, an electrical alternating voltage can be generated in a resonant operating mode, the frequency and / or phase of which is adjusted taking into account a resonant frequency of the first resonant circuit S1.In such a first operating mode Bl, for example, electrical energy can be transferred from an energy source connected to the first DC voltage terminal Gl to a traction battery connected to the second DC voltage terminal G2, for example to charge the traction battery.

[0060] In a second operating mode B2, for example, electrical energy can be transferred from the second DC voltage connection G2 to the third DC voltage connection G3. This allows, for example, electrical energy to be transferred from a traction battery in the high-voltage network of an electric vehicle to a low-voltage network of the electric vehicle. If a second resonant circuit S2 is provided between the second half-bridge circuit H2 and the first secondary winding 12 of the transformer TR, resonant operation can also be set here, taking into account the resonant frequency of the second resonant circuit S2. For the transmission of electrical energy from the second DC voltage connection G2 to the third DC voltage connection G3, the fifth switching element T5 and the sixth switching element T6 are both closed.

[0061] In a third operating mode B3, electrical energy can be transferred from the third DC voltage connection G3 to the second DC voltage connection G2. This can, for example, charge an intermediate circuit located in the high-voltage vehicle electrical system that is connected to the second DC voltage connection G2. Here, too, both the fifth switching element T5 and the sixth switching element T6 are closed. To transfer the electrical energy from the third DC voltage connection G3 to the second DC voltage connection G2, the switching elements T1 - T4 in an H-bridge circuit 31 of the voltage converter circuit H3 can be controlled, for example, according to the principle of a dual active bridge. Since this switching principle is also considered to be known, further details will not be discussed here.

[0062] In a fourth operating mode B4, for example, electrical energy can be transmitted from the second DC voltage terminal G2 to the first DC voltage terminal G1 and simultaneously to the third DC voltage terminal G3. In a resonant operating mode, the DC-DC converter 1 is operated such that an electrical DC voltage to be adjusted is present at the first DC voltage terminal G1. The fifth switching element T5 and the sixth switching element T6, as well as the inductance L of the voltage converter circuit H3, form a buck converter 32. Thus, by appropriately controlling the fifth switching element T5 and the sixth switching element T6 of this buck converter circuit 32, the control device 20 can adjust the electrical voltage at the third DC voltage terminal G3 according to a predetermined target value.

[0063] In a fifth operating mode B5, electrical energy can be transferred from the first DC voltage terminal G1 to the second DC voltage terminal G2 and simultaneously from the first DC voltage terminal G1 to the third DC voltage terminal G3. Here, too, in a resonant operating mode, the electrical voltage at the second DC voltage terminal G2 is first adjusted according to a setpoint. Furthermore, here, too, the electrical voltage at the third DC voltage terminal G3 can be adjusted by appropriately controlling the fifth switching element T5 and the sixth switching element T6 in the buck converter circuit 32 of the voltage converter circuit H3.

[0064] Finally, in a sixth operating mode B6, electrical energy can be transferred from the second DC voltage terminal G2 to the first DC voltage terminal G1 and simultaneously to the third DC voltage terminal (G3). A resonant operating mode can also be selected here if necessary. In this case, the fifth switching element T5 and the sixth switching element T6 of the voltage converter circuit H3 are open.

[0065] In summary, the present invention relates to a DC-DC converter with three DC voltage terminals. Electrical energy can be exchanged between the three DC voltage terminals in virtually any manner. The DC-DC converter includes an oscillating circuit for resonant operation. Furthermore, a combination of an H-bridge circuit and a buck converter is provided at at least one DC-DC converter terminal.

Claims

Claims 1. A DC-DC converter (1), comprising: a transformer (TR) having a primary winding (11), a first secondary winding (12), and a second secondary winding (13); a first H-bridge circuit (H1) connected at external terminals (A11, A12) to a first DC voltage terminal (G1) and electrically coupled at center terminals (M11, M12) to the primary winding (11) of the transformer (TR); a first resonant circuit (S1) electrically arranged between the center terminals (M11, M12) of the first H-bridge circuit (H1) and the primary winding (11) of the transformer (TR); a second H-bridge circuit (H2) connected at external terminals to a second DC voltage terminal (G2) and electrically coupled at center terminals to the first secondary winding (12) of the transformer (TR);and a voltage converter circuit (H3), wherein a first semiconductor switching element (T1) is arranged between a first node (K1) and a first center terminal (M1), a second semiconductor switching element (T2) is arranged between the first center terminal (M1) and a first external terminal (A1), a third semiconductor switching element (T3) is arranged between a second node (K2) and a second center terminal (M2), a fourth semiconductor switching element (T4) is arranged between the second center terminal (M2) and the first external terminal (A2), a fifth switching element (T5) is arranged between a second external terminal (A2) and the first node (K1), a sixth switching element (T6) is arranged between the second external terminal (A2) and the second node (K2), and; wherein the first external terminal (A1) is electrically connected to a first connection point of a third DC voltage terminal (G3), an inductance (L) is arranged between the second external terminal (A2) and a second connection point of the third DC voltage terminal (G3), and the first center terminal (M1) and the second center terminal (M2) are each electrically connected to terminals of the second secondary winding (13) of the transformer (TR).

2. DC-DC converter (1) according to claim 1, wherein the first semiconductor switching element (T1) and the fifth semiconductor switching element (T5) of the voltage converter circuit (H3) are complementary semiconductor switching elements, and the second semiconductor switching element (T2) and the sixth semiconductor switching element (T6) of the voltage converter circuit (H3) are complementary semiconductor switching elements.

3. DC-DC converter (1) according to claim 1 or 2, wherein the first H-bridge circuit (Hl) and the second H-bridge circuit (H2) each comprise a first semiconductor switching element (T11, T21) arranged between a first external terminal (A11, A21) and a first center terminal (M11, M21) of the respective H-bridge circuit (Hl, H2), a second semiconductor switching element (T12, T22) arranged between the first external terminal (A11, A21) and a second center terminal (M12, M22) of the respective H-bridge circuit (Hl, H2), a third semiconductor switching element (T13, T23) arranged between a second external terminal (A12, A22) and the first center terminal (M11, M21) of the respective H-bridge circuit (Hl, H2), and a fourth semiconductor switching element (T14, T24) arranged between the second external terminal (A12, A22) and the second center terminal (M12, M22) of the respective H-bridge circuit (Hl, H2).

4. DC-DC converter (1) according to one of claims 1 to 3, with a second resonant circuit (S2) which is electrically connected between the Center terminals (M21, M22) of the second H-bridge circuit (H2) and the first secondary winding (12) of the transformer (TR).

5. DC-DC converter (1) according to one of claims 1 to 4, with a control device (20) which is designed to control the semiconductor switching elements (T11-T14, T21-T24, T1-T6) of the first H-bridge circuit (H1), the second H-bridge circuit (H2) and the voltage converter circuit (H3), wherein the control device (20) is designed to adapt a frequency and / or a phase of an electrical alternating voltage which is established at the primary winding (11) and / or one of the secondary windings (12, 13) in a resonant operation.

6. DC voltage connection (1) according to claim 5, wherein the control device (20) is designed to control the fifth and / or the sixth semiconductor switching element (T5, T6) of the voltage converter circuit (A1) in a buck converter mode.

7. DC-DC converter (1) according to one of claims 1 to 6, wherein the DC-DC converter (1) is designed to transmit electrical energy from the first DC voltage terminal (G1) to the second DC voltage terminal (G2) in a first operating mode, to transmit electrical energy from the second DC voltage terminal (G2) to the third DC voltage terminal (G3) in a second operating mode, to transmit electrical energy from the third DC voltage terminal (G3) to the second DC voltage terminal (G2) in a third operating mode, in a fourth operating mode, to transmit electrical energy from the second DC voltage terminal (G2) to the first DC voltage terminal (G1) and to the third DC voltage terminal (G3), in a fifth operating mode, to transmit electrical energy from the first DC voltage terminal (G1) to the second DC voltage terminal (G2) and the third DC voltage terminal (G3), and in a sixth operating mode, to transmit electrical energy from the second DC voltage terminal (G3) to the first DC voltage terminal (B1); wherein the fifth and sixth switching elements (T5, T6) of the voltage converter circuit (H3) are open in the first and sixth operating modes, are closed in the second and third operating modes, and are controlled as buck converters in the fourth and fifth operating modes.Electric vehicle with a high-voltage electrical system (200); a low-voltage electrical system (300); and a DC-DC converter (1) according to one of claims 1 to 7; wherein the second DC voltage connection (G2) of the DC-DC converter (1) is electrically coupled to the high-voltage electrical system (2) of the electric vehicle, and the third DC voltage connection (G3) of the DC-DC converter. (1) is electrically coupled to the low-voltage electrical system (300) of the electric vehicle.

9. Electric vehicle according to claim 8, comprising a rectifier (100) which is designed to be coupled to a single-phase or multi-phase AC voltage source at an AC voltage input and which is electrically coupled to the first DC voltage terminal (Gl) of the DC-DC converter (1) at a DC voltage output.

10. A method for operating a DC-DC converter (1) according to one of claims 1 to 7, wherein one of the following steps is carried out during operation of the DC-DC converter (1): Transferring (Bl) electrical energy from the first DC voltage terminal (Gl) to the second DC voltage terminal (G2) in a first operating mode; Transferring (B2) electrical energy from the second DC voltage terminal (G2) to the third DC voltage terminal (G3) in a second operating mode; Transferring (B3) electrical energy from the third DC voltage terminal (G3) to the second DC voltage terminal (G2) in a third operating mode; Transferring (B4) electrical energy from the second DC voltage terminal (G2) to the first DC voltage terminal (G1) and to the third DC voltage terminal (G3) in a fourth operating mode; Transferring (B5) electrical energy from the first DC voltage terminal (G1) to the second DC voltage terminal (G2) G2 and to the third DC voltage terminal (G3) in a fifth operating mode; or Transferring (B6) electrical energy from the second DC voltage terminal (G2) to the first DC voltage terminal (G1) in a sixth operating mode; wherein the fifth and sixth switching elements (T5, T6) of the voltage converter circuit (H3) are open in the first and sixth operating modes, closed in the second and third operating modes, and controlled as buck converters in the fourth and fifth operating modes.

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