Traction network for a motor vehicle

Abstract

The invention relates to a traction network (1) for a motor vehicle, comprising at least one high-voltage battery (2), a DC / DC converter (11), an intermediate circuit capacitor (C) consisting of at least two capacitors (C1, C2) connected in series and having a neutral point (N), an inverter (3) and a three-phase AC charging interface (6), the three AC charging lines (L1-L3) are connected to an AC voltage filter (7), the inverter (3) having three half-bridges (H1-H3), each half-bridge (H1-H3) being associated with a monolithic bidirectional field-effect transistor (10), the high-voltage-side transistor of the bidirectional field-effect transistor (10) being connected to the center tap (M) of the associated half-bridge (H1-H3), and the high-voltage-side transistor of the bidirectional field-effect transistor (10) being connected to the center tap (M) of the associated half-bridge (H1-H3). The DC / DC converter is characterized in that low-voltage side transistors of the bidirectional field effect transistors (10) are each connected to a neutral point (N) of an intermediate circuit capacitor (C), three AC charging lines (L1-L3) are connected to a center tap (M) of the half bridges (H1-H3), and the DC / DC converter is designed as an electrically isolated DC / DC converter.

Description

Technical Field

[0001] The invention relates to a traction network for a motor vehicle. Background Art

[0002] The typical structure of a traction network consists of a traction battery, an inverter and an electric motor. There are many different topologies known for how the individual components of such a traction network are constructed. In order to reduce the current, attempts are made to operate at the highest possible voltage on the vehicle side. For example, the following traction network is known, in which the rated voltage of the traction battery is 800V. This leads to problems with the voltage resistance of the semiconductor switches, so a 3-level inverter as described in patent document DE10 2016 206 945 A1 is recommended for such a traction network. Another problem is that the charging infrastructure is not unified, with both 400V DC charging stations and 800V DC charging stations. Depending on the topology used, the maximum charging power cannot be fully utilized here, or the complexity of the circuit is very high.

[0003] Furthermore, it is usually desirable to also be able to use AC voltage for charging. In this case, a rectifier is arranged between the AC voltage charging interface and the high-voltage battery, which converts the AC voltage into a DC voltage. A DC / DC converter (DC / DC-Wandler) can be additionally provided here, which adapts the rectified voltage to the voltage level of the high-voltage battery.

[0004] Another traction network is known from US Pat. No. 10,562,404 B1, which is designed for charging from a single-phase, two-phase or three-phase AC voltage source.

[0005] No. 11,290,022 B2 discloses a galvanically isolated DC / DC converter having two high-frequency transformers which form a main path and an auxiliary path. Summary of the invention

[0006] The object of the present invention is to provide a traction network for a motor vehicle, which has a three-phase AC voltage charging interface and is compact and electrically isolated from the power grid.

[0007] The solution to the technical problem is provided by a traction network. Other advantageous embodiments of the invention are provided by the description.

[0008] The traction network for a motor vehicle includes at least one high-voltage battery, a DC / DC converter, an intermediate circuit capacitor consisting of at least two capacitors connected in series and having a neutral point, an inverter, and a three-phase AC charging interface. The inverter has three half-bridges, wherein each half-bridge is correspondingly configured with an integral bidirectional field effect transistor (BIDFET), wherein the high-voltage side transistors of the bidirectional field effect transistors are respectively connected to the center taps of the half-bridges correspondingly assigned thereto, and the low-voltage side transistors of the bidirectional field effect transistors are respectively connected to the neutral point of the intermediate circuit capacitor. In addition, three AC charging lines are connected to the center taps of the half-bridges or can be connected to the center taps. The DC / DC converter is designed as an electrically isolated DC / DC converter, which is arranged between the high-voltage battery and the inverter. The bidirectional field effect transistors can be integrated into the module housing of the inverter, wherein these bidirectional field effect transistors are preferably arranged on one or more printed circuit boards of the half-bridges. The bidirectional field effect transistor makes it possible to integrate the PFC rectifier into the inverter, so that a separate rectifier can be omitted, wherein the arrangement in the inverter makes the design very compact, which also makes cooling easier. In addition, the bidirectional field effect transistor achieves other advantages, which will be described in detail later. In the case of a suitable bidirectional design of the integrated rectifier, vehicle-to-grid, vehicle-to-home and vehicle-to-public charging is thus possible, so that the traction network can also be used as a mobile charging station for other motor vehicles.

[0009] In one embodiment, the DC / DC converter is designed as a bidirectional step-up / step-down regulator (or chopper). This allows for maximum freedom. This allows, for example, different DC charging infrastructures (400 V or 800 V) to be used, and even if the voltage of the high-voltage battery has dropped significantly, the desired voltage can be adjusted at the inverter to achieve the optimal operating point of the motor. As a result, the high-voltage battery can also be composed of sodium (Na) battery cells, which may have greater voltage disturbances than lithium-ion battery cells.

[0010] In addition, the DC / DC converter can also be designed as a two-phase, three-phase or multi-phase interleaved DC / DC converter, wherein the DC / DC converter can also be designed as an asymmetric interleaved DC / DC converter. The advantage of the interleaved DC / DC converter is that the power can be distributed, so that the requirements for each individual component must be reduced, but the number of components increases. Another advantage of the asymmetric interleaved DC / DC converter is that the losses in the low power range can be reduced.

[0011] In one embodiment, the DC / DC converter is designed as a high-frequency transformer (HF-Trafo) or is composed of a high-frequency transformer, by means of which the voltage can be converted particularly low-loss. A plurality of high-frequency transformers can here again (symmetrically or asymmetrically) realize staggered operation. A high-frequency transformer circuit such as that in patent document US11,290,022B2 can also be applied. When realizing a high-frequency transformer, a core with high energy density wound with Litz wire or a transformer integrated on a PCB (printed circuit board) is feasible.

[0012] In another embodiment, the DC / DC converter has a switching device and a bypass line, wherein at least one switching element (Schaltelement, or switching element) is arranged in the bypass line, wherein the DC / DC converter is designed so that the switching element is closed during driving operation, wherein the half bridge is connected to at least one transformer via the switching device during AC charging operation and to an inductor during driving operation.

[0013] In a further embodiment, the DC / DC converter has two bypass lines, each of which has at least one switching element, wherein the DC / DC converter is designed to bridge the DC / DC converter via the bypass lines during driving operation.

[0014] As a result, transistors with a lower current carrying capacity can be used for the DC / DC converter, while feedback to the grid is still possible, wherein inverter transistors with a higher current carrying capacity are used during driving operation. The switching element is preferably designed as a relay.

[0015] In another embodiment, the control device is designed to control the bidirectional field effect transistor in driving operation so as to generate a 3-level pulse pattern. As a result, the motor harmonics at the electric motor can be reduced, thereby reducing the motor losses. Therefore, in charging operation, the bidirectional field effect transistor is used as a component of the rectifier, and in driving operation, the bidirectional field effect transistor is used as a component of the inverter.

[0016] In an alternative embodiment, the transistors of the half-bridge and the bidirectional field effect transistors are respectively configured with the same gate driver, wherein there is a switching device, which is designed so that the gate driver is correspondingly assigned (or allocated) to the bidirectional field effect transistor in AC charging operation, and is correspondingly assigned to the transistor of the half-bridge in driving operation. In AC charging operation, a unidirectional rectifier is formed by means of the freewheeling diode of the transistor and the bidirectional field effect transistor. As a result, 6 gate drivers can be omitted, but feedback to the power grid or other components can no longer be performed, and only a 2-level pulse mode can be adjusted in driving operation.

[0017] In another embodiment, a switching device is provided, which is designed to disconnect the electric machine from the AC charging line during AC charging operation. As a result, the electric machine can be switched to no voltage during AC charging operation, so that no undesired drive torque is generated at the electric machine.

[0018] In another specific embodiment, an AC filter (AC voltage filter) is arranged between the AC charging interface and the inverter.

[0019] In another embodiment, the bidirectional field effect transistor is designed as a gallium nitride bidirectional field effect transistor capable of operating with very low losses.

[0020] The transistors of the half bridge are designed, for example, as silicon carbide transistors, but can also be designed as gallium nitride transistors. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention is described in more detail below based on preferred embodiments. In the accompanying drawings:

[0022] Figure 1 The traction network in the first embodiment is shown;

[0023] Figure 2 A galvanically isolated DC / DC converter in a first embodiment is shown;

[0024] Figure 3 Another alternative DC / DC converter is shown;

[0025] Figure 4 Another alternative DC / DC converter is shown;

[0026] Figure 5 Another alternative DC / DC converter having two bypass lines is shown;

[0027] Figure 6 A schematic circuit for a high voltage battery with a low voltage is shown;

[0028] Figure 7 A unidirectional DC / DC converter is shown;

[0029] Figure 8 shows a schematic block diagram of a switching device;

[0030] Fig. 9 A circuit arrangement of a bidirectional Vienna rectifier (prior art) is shown; and

[0031] Fig.10 The circuit arrangement of a unidirectional Vienna rectifier (prior art) is shown. DETAILED DESCRIPTION

[0032] exist Figure 1 , a traction network 1 of a first embodiment is shown. The traction network 1 has a high-voltage battery 2, which has a rated voltage of 400V-420V or 800V, for example. 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 an electric machine 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 the three AC voltage lines of the inverter 3. In addition, it is shown that the voltage measuring device V is connected in parallel with the capacitors C1, C2 of the intermediate circuit capacitor C. In addition, 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 consists of other resistors connected in series with the transistor. A current measuring device A in the HV- line is also shown. The inverter 3 has three half-bridges H1-H3, wherein the transistors T1-T6 are respectively configured with freewheeling diodes D. The transistors T1-T6 are designed as silicon carbide transistors, for example, wherein the freewheeling diode D can be designed as a built-in diode or 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. In addition, each half-bridge H1-H3 is correspondingly configured with an integral bidirectional field effect transistor 10. The bidirectional field effect transistor 10 has a voltage input terminal and a voltage output terminal and two control interfaces. The high-voltage side transistor of the bidirectional field effect transistor 10 is connected to the corresponding center tap M of the correspondingly 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, a galvanically isolated, bidirectional step-up / step-down 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.

[0033] In further elaborating on the Figure 1 The circuit before reference Fig. 9 , Fig. 9 A bidirectional Vienna rectifier 14 is shown. An inductor is arranged at each of the three AC voltage connections, which is connected to a center tap of the half bridge. In addition, each center tap is connected to a series circuit consisting of two MOSFETs (metal oxide semiconductor field effect transistors) connected in opposite directions to each other. The three series circuits are connected to a common neutral point.

[0034] In the inverter 3 , this structure of the Vienna rectifier 14 is simulated exactly by three bidirectional field effect transistors 10 , so that the rectifier is integrated into the inverter 3 , wherein no internal diode is present in the gallium nitride transistors.

[0035] In AC charging operation, the control device 13 operates the three half bridges H1-H3 and the three bidirectional field effect transistors 10 as a rectifier, and charges the high-voltage battery 2 through the DC / DC converter 11. Since the rectifier is bidirectional, the power of the high-voltage battery 2 can also be fed back to the grid.

[0036] In driving operation, the control unit 13 can control the three half bridges H1 - H3 and the three bidirectional field effect transistors 10 so that they generate a three-level pulse pattern.

[0037] The bidirectional field effect transistor 10 is completely 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 transistor 10 is preferably also integrated into the printed circuit board. If there are multiple printed circuit boards for half-bridges H1-H3, the bidirectional field effect transistor 10 is preferably arranged on the printed circuit board of the correspondingly assigned half-bridge H1-H3. This enables a very compact design and simplifies cooling.

[0038] If no grid feedback is required, the rectifier does not have to be bidirectional but can be Fig.10 The Vienna rectifier 15 is designed as a unidirectional rectifier. Fig. 9 In the three half-bridges with transistors, three half-bridges composed of diodes are shown. The circuit arrangement corresponds to the freewheeling diodes D of the half-bridges H1-H3 of the inverter 3, wherein: Fig.10 The three series circuits with transistors of opposite polarity in the embodiment again correspond to the bidirectional field effect transistor 10. Therefore, the transistors T1-T6 are not necessary for AC charging.

[0039] Therefore, it can be alternatively provided that the transistors T1-T6 are assigned the same gate driver as the bidirectional field effect transistor 10, wherein the gate driver is connected to the bidirectional field effect transistor 10 in the AC charging operation and the gate driver is connected to the transistors T1-T6 in the driving operation, so that only a 2-level pulse mode can be realized. The corresponding switching device for the gate driver is not shown here, but it is controlled by the control device 13.

[0040] The galvanic isolation from the grid and the traction network 1 , which in the prior art is usually integrated in a separate OBC (On-Board Charger), is moved to the DC / DC converter 11 .

[0041] exist Figure 21 shows an electrically isolated DC / DC converter 11 of a first embodiment. The DC / DC converter 11 has two high-frequency transformers HFT1, HFT2, wherein an oscillating circuit is arranged on the primary and secondary sides of each high-frequency transformer HFT1, HFT2, and the oscillating circuit is composed of a series circuit of a capacitor and an inductor. The DC / DC converter 11 is connected to the high-voltage battery 2 (see FIG. 2 ) on the left side. Figure 1 ) connection. Two half-bridges are arranged between the high-frequency transformers HFT1, HFT2 and the interface connected to the high-voltage battery 2, respectively, which (in AC charging operation) rectify the AC voltage or convert the DC voltage of the high-voltage battery into an AC voltage when feedback is to be performed from the high-voltage battery 2 to the power grid. In addition, four half-bridges are arranged at the interface connected to the inverter 3, and smoothing capacitors are arranged in parallel with the half-bridges. In addition, the DC / DC converter 11 has a switching device 21 and a bypass line 22 with a switching element 23. Finally, the DC / DC converter 11 has four inductors, which are connected to the HV+ line of the high-voltage battery at one end. The other end is connected to the switching device 21. In AC charging operation or when feeding back to the power grid, the four half-bridges on the right are connected to the four interfaces for the two high-frequency transformers HFT1 and HFT2, wherein the switching element 23 is disconnected. The winding ratio of the primary side to the secondary side determines whether the DC / DC converter 11 works as a step-up regulator or a step-down regulator in AC charging operation. During driving operation, the switching element 23 is closed and the two high-frequency transformers HFT1 and HFT2 are disconnected by the switching device 21. Instead, four inductors are connected to the four half-bridges on the right, wherein the inductors are respectively connected to the center taps of the half-bridges. With the help of this circuit arrangement, the battery voltage of the high-voltage battery 2 can be increased or decreased. In the example shown, the half-bridge on the left is designed as a gallium nitride transistor and the half-bridge on the right is designed as a silicon carbide transistor, because silicon carbide transistors have a higher current carrying capacity, while gallium nitride transistors have lower losses and are only necessary in AC charging operation or when feeding back to the power grid. However, the following construction method is also feasible, in which all transistors use the same technology (silicon, silicon carbide or gallium nitride), wherein wide bandgap transistors are preferably used. It should also be noted that the circuit can also have more than two high-frequency transformers HFT1, HFT2, so that it can also have an interleaved operation with more than two phases for different maximum power designs.

[0042] exist Figure 3 An alternative embodiment is shown in FIG. 1 , which has two bypass lines 22 , 24 , each of which has a switching element 23 , 25 . With regard to the operating method for AC charging operation or feedback to the grid, reference is made here to the description of the Figure 2, wherein in AC charging operation, the two switching elements 23, 25 are open. In driving operation, the two switching elements 23, 25 are closed and the DC / DC converter 11 is turned off, so that the DC / DC converter is bridged via bypass lines 22, 24. In driving operation, the inverter is only supplied with the battery voltage of the high-voltage battery 2. The advantage of this circuit is that the transistors of the right half bridge in the DC / DC converter 11 only need to be designed for the current during AC charging. The switching device 21 and the inductor can be omitted.

[0043] exist Figure 4 and Figure 5 It is shown in Figure 2 and Figure 3 An alternative embodiment of a circuit variant of , in which the four half-bridges on the right are replaced by two staggered half-bridges. Here, the center taps of the two half-bridges are connected to the neutral point between the two smoothing capacitors.

[0044] exist Figure 6 FIG. 2 shows the left half bridge 26 of the DC / DC converter 11 when the DC / DC converter 11 is to work with a high-voltage battery of 400V instead of 800V.

[0045] It can be seen that only a slight change in the wiring is required to Figures 2 to 5 The DC / DC converter 11 shown can be adapted very easily to changing conditions.

[0046] exist Figure 7 , another embodiment of the DC / DC converter 11 is shown in FIG. 1 , in which the left half bridge 26 is replaced by a passive diode. With this circuit, no feedback to the grid is possible, but only a unidirectional AC charging operation is possible. In driving operation, the DC / DC converter is switched via a bypass line 22, 24 (see FIG. 1 ) with switching elements 23, 25 (not shown here). Figure 3 and Figure 5 )bridging.

[0047] exist Figure 8 , a switching device 19 controlled by the control device 13 is shown. In AC charging operation, the AC charging lines L1-L3 are connected to the inverter 3 by means of the switching device 19 controlled by the control device 13, wherein the motor 4 is disconnected. In driving operation, the AC charging lines L1-L3 are disconnected and the inverter 3 is connected to the motor 4.

[0048] Reference numerals list

[0049] 1 Traction network

[0050] 2 High voltage battery

[0051] 3 Inverter

[0052] 4 Motor

[0053] 5 Transmission

[0054] 6 AC charging port

[0055] 7 AC filter (AC voltage filter)

[0056] 9 Discharge circuit

[0057] 10 Bidirectional Field Effect Transistor

[0058] 11 DC / DC Converter

[0059] 12 Boost-Buck Regulator

[0060] 13 Control Devices

[0061] 14 Vienna Rectifier

[0062] 15 Vienna Rectifier

[0063] 18 Switching elements

[0064] 19 Switching device

[0065] 21 Switching device

[0066] 22 Bypass line

[0067] 23 Switching element

[0068] 24 Bypass line

[0069] 25 Switching element

[0070] 26 Half Bridge

[0071] M Center tap

[0072] N Neutral point

[0073] C Intermediate circuit capacitor

[0074] C1, C2 capacitors

[0075] L1-L3 charging line

[0076] H1-H3 Half Bridge

[0077] T1-T6 transistors

[0078] A Current measuring device

[0079] D Freewheeling diode

[0080] V Voltage measurement device

[0081] HFT1, HFT2 High Frequency Transformer

Claims

1. A traction network (1) for a motor vehicle, comprising at least one high-voltage battery (2), a DC / DC converter (11), an intermediate circuit capacitor (C) formed by at least two capacitors (C1, C2) connected in series and having a neutral point (N), an inverter (3) and a three-phase AC charging interface (6), wherein: Three AC charging lines (L1-L3) are connected to an AC voltage filter (7), 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 the bidirectional field effect transistor (10) are respectively connected to the center tap (M) of the corresponding half bridge (H1-H3), and the low-voltage side transistors of the bidirectional field effect transistor (10) are respectively connected to the neutral point (N) of the intermediate circuit capacitor (C), wherein the three AC charging lines (L1-L3) are connected to the center tap (M) of the half bridge (H1-H3), and wherein the DC / DC converter is designed as an electrically isolated DC / DC converter.

2. The traction network according to claim 1, characterized in that: The DC / DC converter (11) is designed as a bidirectional step-up / step-down regulator (12).

3. Traction network according to any one of the preceding claims, characterized in that The DC / DC converter (11) has at least one high-frequency transformer (HFT1, HFT2).

4. The traction network according to claim 3, characterized in that: The DC / DC converter (11) has a switching device (21) and a bypass line (22), wherein at least one switching element (23) is arranged in the bypass line (22), wherein the DC / DC converter (11) is designed so that the switching element (23) is closed during driving operation, wherein the half bridge is connected to a high-frequency transformer (HFT1, HFT2) via the switching device (21) during AC charging operation and is connected to an inductor during driving operation.

5. The traction network according to claim 3, characterized in that: The DC / DC converter (11) has two bypass lines (22, 24), each of which has at least one switching element (23, 25), wherein the DC / DC converter (11) is designed to bridge the DC / DC converter (11) during driving operation.

6. Traction network according to any of the preceding claims, characterized in that The control device (13) is designed to actuate the bidirectional field effect transistor (10) during driving operation so that a three-level pulse pattern is generated.

7. The traction network according to any one of claims 1 to 5, 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 assigned to the bidirectional field effect transistor (10) in AC charging operation and is correspondingly assigned to the transistors (T1-T6) of the half bridge (H1-H3) in driving operation.

8. Traction network according to any one of the preceding claims, characterized in that A switching device (19) is provided, which is designed to disconnect the electric machine (4) from the AC charging line during AC charging operation.

9. Traction network according to any one of the preceding claims, characterized in that An AC voltage filter (7) is arranged between the AC charging interface (6) and the inverter (3).

10. Traction network according to any of the preceding claims, characterized in that The bidirectional field effect transistor (10) is designed as a gallium nitride bidirectional field effect transistor.

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