Traction network for a motor vehicle

Abstract

The invention relates to a traction network (1) for a motor vehicle, at least comprising a high-voltage battery (2), a DC / DC converter (11), an inverter (3) and an AC voltage charging interface (9), the traction network (1) being designed to convert an AC voltage of the AC voltage charging interface (9) into a DC voltage, the DC / DC converter (11) being connected to the high-voltage battery (2), the inverter (3) being connected to the high-voltage battery (2), and the inverter (3) being connected to the high-voltage battery (2). The DC / DC converter (11) is designed as an electrically isolated DC / DC converter (11), in which taps are arranged, which are connected to a charging circuit (14) for an on-board electrical system battery (15), the DC / DC converter (11) has at least two high-frequency transformers (HFT1, HFT2), the first high-frequency transformer (HFT1) forming a main supply path, and the second high-frequency transformer (HFT2) forming a second supply path. The first high-frequency transformer (HFT1) forms a secondary power supply path, and the second high-frequency transformer (HFT2) forms a secondary power supply path, the voltage across the secondary winding (SW1) of the first high-frequency transformer (HFT1) being several times higher than the voltage across the secondary winding (SW2) of the second high-frequency transformer (HFT2), these voltages being added in a correct sign by means of a circuit (19).

Description

Field of the Invention

[0001] The present invention relates to a traction network, which at least comprises a high-voltage battery, an electrically isolated DC / DC converter, an inverter and an AC voltage charging interface. Wherein, a tap is arranged in the DC / DC converter, and the tap is connected to a charging circuit for an on-board electrical network battery. Background Art

[0002] A traction network of the type according to the present invention is known from patent document US2018 / 0 222 333A1. In this patent document, the DC / DC converter is designed as a transformer having a primary winding and two secondary windings, and the two secondary windings are coupled by a common magnetic core. The first secondary winding is connected to the high-voltage battery through a half-bridge circuit, and the second secondary winding is connected to the on-board electrical network battery through a half-bridge circuit. Summary of the Invention

[0003] A technical problem of improving the efficiency of such a traction network is proposed, and additionally, a design as compact as possible with fewer components is sought.

[0004] The solution to this technical problem is given by the traction network according to the present invention. Other advantageous design solutions of the present invention are given in the description.

[0005] The traction network for a motor vehicle according to the invention at least comprises a high-voltage battery, a DC / DC converter, an inverter and an AC voltage charging interface. Here, the traction network is designed to convert the AC voltage of the AC voltage charging interface into a DC voltage, wherein the DC / DC converter is connected to the high-voltage battery, wherein the DC / DC converter is designed as an electrically isolated DC / DC converter, and wherein a tap is arranged in the DC / DC converter, and this tap is connected to the charging circuit for the on-board electrical network battery. Here, the DC / DC converter has at least two high-frequency transformers, wherein the first high-frequency transformer forms the main power supply path, and the second high-frequency transformer forms the secondary power supply path, wherein the voltage on the secondary winding of the first high-frequency transformer is several times higher than the voltage on the secondary winding of the second high-frequency transformer, and wherein these voltages are added together in the correct sign by a circuit. Thereby, a very energy-efficient traction network is obtained, wherein the first high-frequency transformer is operated in an energy-efficient full-load operation, and wherein the adjustment of the charging voltage is carried out by the second high-frequency transformer. Exactly two high-frequency transformers are preferably used. For example, for a 400V high-voltage battery, the maximum output voltage of the first high-frequency transformer is between 300 - 380V, and for an 800V high-voltage battery, the maximum output voltage of the first high-frequency transformer is between 600 - 720V, and the respectively required voltage difference is achieved by the second high-frequency transformer. It can also be provided here that the circuit for adding the voltages together in the correct sign also additionally regulates the output voltage of the second secondary winding and boosts it if necessary.

[0006] In one embodiment, the two high-frequency transformers have a common primary winding, and the primary and secondary windings are coupled by a common magnetic core. Thereby, the design becomes more compact.

[0007] In a further embodiment, the charging circuit for the on-board electrical network battery has a (third) secondary winding, a full-bridge circuit and a buck regulator (or chopper), and the secondary winding of the charging circuit is wound on a common magnetic core with the secondary windings of the first high-frequency transformer and / or the second high-frequency transformer. Thereby, the design becomes even more compact. The full-bridge circuit is used as a rectifier here, and the output voltage of the full-bridge circuit can be adjusted to the required voltage for the on-board electrical network battery by the buck regulator. Through the full-bridge circuit, the circuit is bidirectional. If a bidirectional circuit is not required, the full-bridge circuit can also be replaced by a simple rectifier, which consists, for example, only of passive diodes.

[0008] In a further embodiment, the traction network has switching elements by means of which the DC / DC converter can be bridged. Thereby, the DC / DC converter can be designed to achieve low power during AC voltage charging, wherein the DC / DC converter is deactivated during driving operation. The switching elements are preferably designed as relays.

[0009] In a further embodiment, the traction network has additional switching elements, wherein the full-bridge circuit of the second high-frequency transformer is selectively assigned to the charging circuit of the high-voltage battery or the on-board electrical system battery by means of these additional switching elements. This saves one full-bridge circuit. However, in this case, the high-voltage battery and the on-board electrical system battery cannot be charged simultaneously. Nevertheless, even during AC voltage charging, it is possible to briefly switch to the on-board electrical system battery one or more times in order to charge it, wherein it is only necessary to ensure that the on-board electrical system battery or the support capacitor is sufficiently charged in order to supply the necessary consumers.

[0010] In a further embodiment, the magnetic core is designed as an EE magnetic core, which enables a particularly compact design.

[0011] In a further embodiment, the traction network has an intermediate circuit capacitor, which consists of at least two capacitors connected in series and has a neutral point. Furthermore, the traction network has a three-phase AC voltage charging interface, wherein the inverter has three half-bridges, wherein each half-bridge is assigned an integral bidirectional field-effect transistor (BIDFET), wherein the high-side transistors of these bidirectional field-effect transistors are each connected to the center tap of the corresponding half-bridge, and the low-side transistors of these bidirectional field-effect transistors are each connected to the neutral point of the intermediate circuit capacitor, wherein three AC charging lines are connected to the center taps of the half-bridges. Thereby, the rectifier is integrated into the inverter, which saves components and enables an extremely compact design.

[0012] In a further embodiment, the traction network has a control device, which is designed to control the bidirectional field-effect transistors during driving operation such that a 3-level pulse pattern is generated, which enables a very efficient operation of the electric motor.

[0013] In an alternative embodiment, the transistors of the half-bridges and the bidirectional field-effect transistors are assigned the same gate driver, wherein there is a switching device, which is designed such that the gate driver is assigned to the bidirectional field-effect transistors during AC charging operation and to the transistors of the half-bridges during driving operation. In this case, additional components can be saved, wherein, however, only a conventional 2-level pulse pattern can be generated during driving operation.

[0014] In a further embodiment, at least the bidirectional field effect transistor is designed as a gallium nitride bidirectional field effect transistor. The advantage of a gallium nitride transistor is its high switching frequency. Therefore, preferably, the transistors in the DC / DC converter can also be designed as gallium nitride transistors. The transistors of the half-bridge can also be designed as gallium nitride transistors or silicon carbide transistors. Generally, wide bandgap transistors are preferably used. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention will be explained in more detail below on the basis of preferred embodiments. In the drawings:

[0016] Figure 1 A schematic diagram of a traction network is shown;

[0017] Figure 2 In a first embodiment, an electrically isolated DC / DC converter with a charging circuit for an on-vehicle electrical network battery is shown;

[0018] Figure 3 In a second embodiment, an electrically isolated DC / DC converter with a charging circuit for an on-vehicle electrical network battery is shown;

[0019] Figure 4 In a third embodiment, an electrically isolated DC / DC converter with a charging circuit for an on-vehicle electrical network battery is shown; and

[0020] Figure 5 A schematic side view of an EE core is shown. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] In Figure 1A first embodiment of a traction network 1 is shown. The traction network 1 has a high-voltage battery 2 which, for example, has a rated voltage of 400 V - 420 V or 800 V. The traction network 1 also has an intermediate circuit capacitor C which is composed of at least two capacitors C1, C2 connected in series and has a neutral point N. The traction network 1 also has an inverter 3, at the output of which a motor 4 with a transmission 5 is arranged. The traction network 1 also has a three-phase AC charging interface 6, wherein three charging lines L1 - L3 are connected to an AC filter (or AC voltage filter) 7. The output of the AC voltage filter 7 is connected to three AC voltage lines of the inverter 3. Furthermore, it is shown that a voltage measuring device V is connected in parallel with the capacitors C1, C2 of the intermediate circuit capacitor C. Furthermore, an active discharge circuit 9 for the intermediate circuit capacitor C is shown, which is composed of a resistor between HV+ and HV- and a parallel circuit which is composed of a further resistor in series with a transistor. A current measuring device A in the HV- line is also shown. The inverter 3 has three half-bridges H1 - H3, wherein a plurality of transistors T1 - T6 are each assigned a freewheeling diode D. The transistors T1 - T6 are, for example, designed as SiC transistors, wherein the freewheeling diode D can be designed as an internal diode or as a separate discrete diode. The half-bridges H1 - H3 each have a center tap M, wherein the charging lines L1 - L3 are connected to these center taps M. Furthermore, each half-bridge H1 - H3 is assigned an integral bidirectional field-effect transistor 10. The bidirectional field-effect transistor 10 has a voltage input and a voltage output and two control interfaces. The high-voltage side transistor of the bidirectional field-effect transistor 10 is hereby connected to the respective center tap M of the assigned half-bridge H1 - H3. The low-voltage side transistor of the bidirectional field-effect transistor 10 is connected to the neutral point N of the intermediate circuit capacitor C. The bidirectional field-effect transistor 10 is preferably designed as a gallium nitride bidirectional field-effect transistor. Finally, an electrically isolated bidirectional boost-buck regulator 12 is arranged as a DC / DC converter 11 between the high-voltage battery 2 and the intermediate circuit capacitor C. Finally, a control device 13 is also shown.

[0022] The structure of a Vienna rectifier is simulated by means of the bidirectional field-effect transistor 10 and the half-bridges H1 - H3, so that the rectifier is integrated into the inverter 3.

[0023] During AC charging operation, the control device 13 controls the three half-bridges H1 - H3 and the three bidirectional field-effect transistors 10 like a rectifier and charges the high-voltage battery 2 via the DC / DC converter 11. Since the rectifier is bidirectional, the power in the high-voltage battery 2 can also be fed back into the grid.

[0024] During driving operation, the control unit 13 can control three half-bridges H1 - H3 and three bidirectional field-effect transistors 10 such that they generate a three-level pulse pattern.

[0025] The bidirectional field-effect transistors 10 are fully integrated in the inverter 3. If, for example, all three half-bridges H1 - H3 are arranged on a printed circuit board, the bidirectional field-effect transistors 10 are preferably also integrated into this printed circuit board. In the case of multiple printed circuit boards for the half-bridges H1 - H3, the bidirectional field-effect transistors 10 are preferably arranged on the printed circuit boards of the correspondingly configured half-bridges H1 - H3. This enables a very compact design and simplifies cooling.

[0026] If there is no need to feed back to the grid, the rectifier does not have to be bidirectional but can be designed as a unidirectional Vienna rectifier. In this case, only the freewheeling diodes D of the transistors T1 - T6 and the bidirectional field-effect transistors are required. AC charging does not require the transistors T1 - T6.

[0027] Therefore, it can alternatively be specified that the same gate driver is configured for the transistors T1 - T6 as for the bidirectional field-effect transistors 10, where the gate driver is connected to the bidirectional field-effect transistors 10 during AC charging operation and to the transistors T1 - T6 during driving operation, so that only a two-level pulse pattern can be achieved. The associated switching device for the gate driver is not shown here, but it is controlled by the control device 13.

[0028] The electrical isolation from the grid and the traction network 1 is moved to the DC / DC converter 11, while this electrical isolation is usually integrated in a separate OBC (on-board charger) in the prior art.

[0029] Finally, a charging circuit 14 for the on-board electrical network battery 15 is also schematically shown, which is connected to the DC / DC converter 11. It should be noted here that the on-board electrical network battery does not necessarily have to be a battery but can also be other electrical energy storage devices.

[0030] In Figure 2A first embodiment of a DC / DC converter 11 is shown. The DC / DC converter 11 has a first full-bridge circuit 16 on the input side, and two series-connected filter capacitors are connected in parallel with the first full-bridge circuit. The DC / DC converter 11 also has a first high-frequency transformer HFT1 and a second high-frequency transformer HFT2. These two high-frequency transformers HFT1, HFT2 are connected to the center tap of the full-bridge circuit 16, and additionally, LC resonance circuits are arranged in the connections respectively. Similarly, each of the high-frequency transformers HFT1, HFT2 is also correspondingly configured with an LC resonance circuit on the output side (i.e., in the direction of the high-voltage battery 2). Then, two full-bridge circuits 17, 18 are arranged on the output side respectively to rectify the corresponding AC voltage. The high-frequency transformers HFT1, HFT2 with LC resonance circuits can also be referred to as resonance converters.

[0031] Since the DC / DC converter 11 is designed to be bidirectional, the input and output sides are only used for description here. For example, if energy is fed back from the high-voltage battery 2 to the power grid, the full-bridge circuits 17, 18 convert the DC voltage of the high-voltage battery 2 into an AC voltage for the high-frequency transformers HFT1, HFT2. A circuit 19 is also shown, which adds the two output voltages on the full-bridge circuits 17, 18 with the correct signs.

[0032] Here, the first high-frequency transformer HFT1 constitutes the main power supply path, and the second high-frequency transformer HFT2 constitutes the secondary power supply path, that is, the output voltage of the first high-frequency transformer HFT1 is several times greater than the output voltage of the second high-frequency transformer HFT2. The center tap of the full-bridge circuit 16 on the input side is also connected to the charging circuit 14 of the on-vehicle power grid battery. The charging circuit 14 has another transformer HFT3, a full-bridge circuit 20, and a buck regulator 21. In addition, switch elements 22-24 are provided, and through these switch elements, the DC / DC converter 11 can be bridged and disconnected during driving operation. The electrical isolation line with respect to the AC voltage network is represented by a dashed box.

[0033] In Figure 3 an alternative embodiment is shown, in which all three transformers HFT1-HFT3 have a common primary winding PW, and the primary winding PW and the three secondary windings SW1-SW3 are coupled through a common magnetic core 25. This is shown in Figure 5 for the EE magnetic core 26. Here, the number of turns of the primary winding PW and the first secondary winding SW1 is greater than the number of turns of the other two secondary windings SW2, SW3.

[0034] Finally, in Figure 4Further alternative embodiments are shown here. Here, the first high-frequency transformer HFT1 and the second high-frequency transformer HFT2 again have a common primary winding. Conversely, the charging circuit 14 does not have a transformer. For this purpose, additional switching elements 27 - 30 are provided, by means of which the full-bridge circuit 18 can be selectively assigned to the charging circuit 14 or the high-voltage battery 2. If the full-bridge circuit 18 is to be assigned to the charging circuit 14, the switching elements 27, 28 are closed and the switching elements 29, 30 are opened. If the full-bridge circuit 18 is to be assigned to the high-voltage battery 2, the switching elements 27, 28 are opened and the switching elements 29, 30 are closed. Overall, this saves one full-bridge circuit and one secondary winding.

[0035] List of reference numerals

[0036] 1) Traction network

[0037] 2) High-voltage battery

[0038] 3) Inverter

[0039] 4) Electric motor

[0040] 5) Transmission

[0041] 6) Charging interface

[0042] 7) AC voltage filter

[0043] 9) Discharge circuit

[0044] 10) Bidirectional field-effect transistor

[0045] 11) DC / DC converter

[0046] 12) Buck regulator

[0047] 13) Control device

[0048] 14) Charging circuit

[0049] 15) On-board electrical system battery

[0050] 16) Full-bridge circuit

[0051] 17) Full-bridge circuit

[0052] 18) Full-bridge circuit

[0053] 19) Switch

[0054] 20) Full-bridge circuit

[0055] 21) Buck regulator

[0056] 22) Switching element

[0057] 23) Switching element

[0058] 24) Switching element

[0059] 25) Magnetic core

[0060] 26) EE magnetic core

[0061] 27) Switching element

[0062] 28) Switching element

[0063] 29) Switching element

[0064] 30) Switching element

[0065] A) Current measuring device

[0066] C) Intermediate circuit capacitor

[0067] C1, C2) Capacitor

[0068] D) Freewheeling diode

[0069] H1 - H3) Half - bridge

[0070] HFT1) High - frequency transformer

[0071] HFT2) High - frequency transformer

[0072] HFT3) High - frequency transformer

[0073] L1 - L3) Charging line

[0074] M) Center tap

[0075] N) Neutral point

[0076] PW) Primary winding

[0077] SW1 - SW3) Secondary winding

[0078] T1 - T6) Transistor

[0079] V) Voltage measuring device

Claims

1. A traction network (1) for a motor vehicle, comprising at least a high-voltage battery (2), a DC / DC converter (11), an inverter (3) and an AC voltage charging interface (9), wherein: The traction network (1) is designed to convert an AC voltage of an AC voltage charging interface (9) into a DC voltage, wherein a DC / DC converter (11) is connected to a high-voltage battery (2), wherein the DC / DC converter (11) is designed as an electrically isolated DC / DC converter (11), wherein a tap is arranged in the DC / DC converter (11) and is connected to a charging circuit (14) for an onboard power supply battery (15), It is characterized in that The DC / DC converter (11) has at least two high-frequency transformers (HFT1, HFT2), wherein the first high-frequency transformer (HFT1) forms a main power supply path and the second high-frequency transformer (HFT2) forms a secondary power supply path, wherein the voltage on the secondary winding (SW1) of the first high-frequency transformer (HFT1) is several times higher than the voltage on the secondary winding (SW2) of the second high-frequency transformer (HFT2), wherein these voltages are added with the correct sign via a circuit (19).

2. The traction network according to claim 1, characterized in that: Two high-frequency transformers (HFT1, HFT2) have a common primary winding (PW), wherein the primary and secondary windings (PW, SW1, SW2) are coupled via a common magnetic core (25).

3. The traction network according to claim 1 or 2, characterized in that: A charging circuit (14) for an onboard power supply battery (15) comprises a secondary winding (SW3), a full bridge circuit (20) and a buck regulator (21), wherein the secondary winding (SW3) of the charging circuit (14) and the secondary winding (SW1) of a first high-frequency transformer (HFT1) and / or a second high-frequency transformer (HFT2) are wound on a common magnetic core (25).

4. Traction network according to any of the preceding claims, characterized in that The traction network (1) has switching elements (22-24) by means of which the DC / DC converter (11) can be bridged.

5. Traction network according to any of the preceding claims, characterized in that The traction network (1) has further switching elements (27-30), wherein the full bridge circuit (18) of the second high-frequency transformer (HFT2) is selectively assigned to the charging circuit (14) of the high-voltage battery (2) or the onboard power supply battery (15) via these further switching elements (27-30).

6. The traction network according to any one of claims 2 to 5, characterized in that The magnetic core (25) is designed as an EE magnetic core (26).

7. Traction network according to any of the preceding claims, characterized in that The traction network (1) has an intermediate circuit capacitor (C), which is composed of at least two capacitors (C1, C2) connected in series and has a neutral point (N), and the traction network has a three-phase AC voltage charging interface (9), wherein the inverter (3) has three half bridges (H1-H3), wherein each half bridge (H1-H3) is correspondingly configured with an integrated bidirectional field effect transistor (10), wherein the high-voltage side transistors of these bidirectional field effect transistors (10) are respectively connected to the center tap of the half bridge (H1-H3) correspondingly configured thereto, and the low-voltage side transistors of these bidirectional field effect transistors (10) are respectively connected to the neutral point (N) of the intermediate circuit capacitor (C), wherein three AC charging lines (L1-L3) are connected to the center taps of the half bridges (H1-H3).

8. The traction network according to claim 7, characterized in that The traction network (1) has at least one control device (13) which is designed to actuate the bidirectional field effect transistor (10) during driving operation in such a way that a three-level pulse pattern is generated.

9. The traction network according to claim 7, characterized in that: The transistors (T1-T6) of the half bridge (H1-H3) and the bidirectional field effect transistor (10) are respectively configured with the same gate driver, wherein a switching device is provided, which is designed so that the gate driver is correspondingly configured to the bidirectional field effect transistor (10) in AC charging operation and is correspondingly configured to the transistors (T1-T6) of the half bridge in driving operation.

10. A traction network according to any one of claims 7 to 9, characterized in that The bidirectional field effect transistor (10) is designed as a gallium nitride bidirectional field effect transistor.

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