Traction system for 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) which is formed by at least two capacitors (C1, C2) connected in series and has a neutral point (N), an inverter (3) and a three-phase AC charging interface (6), the three AC charging lines (L1-L3) being connected to an AC voltage filter (7), the inverter (3) having three half-bridges (H1-H3), wherein each half-bridge (H1-H3) is associated with a monolithic BIDFET (10), the high-voltage-side transistors of the BIDFET (10) are each connected to the center tap (M) of the associated half-bridge (H1-H3) and the low-voltage-side transistors of the BIDFET (10) are each connected to the neutral point (N) of the intermediate circuit capacitor (C), and wherein three AC charging lines (L1-L3) are connected to the center taps (M) of the half-bridges (H1-H3).

Description

Technical Field

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

[0002] The typical structure of a traction grid consists of a traction battery, an inverter and an electric motor. A variety of different topologies are known for constructing the individual components of such a traction grid. In order to reduce the current, efforts are made to operate at the highest possible voltage on the vehicle side. For example, traction grids are known in which the rated voltage of the traction battery is 800V. This leads to problems in the dielectric strength of the semiconductor switches, so that a 3-level inverter is proposed for this type of traction grid, as described, for example, in DE 10 2016206 945 A1. Another problem is the non-uniform charging infrastructure, in which there are both 400V DC charging posts and 800V DC charging posts. Depending on the topology used, the maximum charging power cannot be fully utilized here, or the circuit complexity is very high.

[0003] Furthermore, there is usually a desire to also charge using AC voltage. 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. In addition, a DC / DC converter can be provided to adapt the rectified voltage to the voltage level of the high-voltage battery.

[0004] DE 10 2019 106 485 A1 discloses a Weissach rectifier arrangement which can be adapted to different configurations on the AC voltage charging side.

[0005] A further traction network is known from US Pat. No. 10,562,404 B1, which is designed to be charged from a single-phase, two-phase or three-phase AC voltage source.

[0006] The technical problem posed here is to design the traction electrical system as compactly as possible and with as few components as possible. Summary of the invention

[0007] The technical problem underlying the invention is to create a more compact traction network.

[0008] The solution to this technical problem is achieved by the traction network according to the invention.

[0009] The traction grid 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. Here, three AC charging lines are connected to an AC voltage filter. The inverter has three half-bridges, wherein each half-bridge is associated with a monolithic BIDFET, wherein the high-voltage side transistor of the BIDFET is respectively connected to the center tap (Mittelabgriff) of its associated half-bridge, and the low-voltage side transistor of the BIDFET is respectively connected to the neutral point of the intermediate circuit capacitor. In addition, the three AC charging lines are connected or can be connected to the center tap of the half-bridge. Here, the BIDFET can be integrated into the module housing of the inverter, wherein the BIDFET is preferably arranged on one or more circuit boards of the half-bridge. With the help of a bidirectional FET, the PFC rectifier can be integrated into the inverter, thereby eliminating a separate rectifier, wherein the design is very compact through the arrangement scheme in the inverter, which also simplifies cooling in addition. In addition, the BIDFET realizes other advantages that will be described in more detail later. In this way, in a corresponding bidirectional design of the integrated rectifier, vehicle-to-grid, vehicle-to-home and vehicle-to-public charging is possible, so that the traction grid can also be used as a mobile charging station for other motor vehicles.

[0010] In one embodiment, the DC / DC converter is designed as a bidirectional step-up / step-down chopper. This allows for maximum freedom. Thus, for example, different charging facilities (400 V or 800 V) can be used and the desired voltage for the optimum operating point of the electric machine can be set at the inverter, even if the voltage of the high-voltage battery drops significantly. Thus, the high-voltage battery can then be composed of Na / sodium battery cells, which have a larger voltage fluctuation than lithium-ion battery cells.

[0011] In addition, the DC / DC converter can also be configured as a two-phase, three-phase or multi-phase interleaved DC / DC converter, wherein the DC / DC converter can also be configured as an asymmetric interleaved DC / DC converter. The advantage of the interleaved DC / DC converter is that the power can be divided, so that lower requirements must be placed on the individual structural elements, but the number of structural elements increases. Another advantage of the asymmetric interleaved DC / DC converter is that the losses in the low power range can be reduced.

[0012] In an alternative embodiment, the DC / DC converter is configured as a step-down chopper, which converts the higher voltage at the inverter down to the lower voltage of the high-voltage battery. Here, the step-down chopper can also be configured bidirectionally, thereby increasing the lower voltage of the high-voltage battery during driving operation.

[0013] In one embodiment, the DC / DC converter is designed as a unidirectional step-down converter, wherein at least one bypass line with at least one switching element is arranged between the high-voltage battery and the intermediate circuit capacitor, wherein the DC / DC converter is bridged in the closed state of one or more switching elements. As a result, components with a lower current carrying capacity can be used, since they only have to carry the charging current, whereas the larger driving current is conducted via the bypass line. This saves costs.

[0014] In another specific embodiment, the control device is designed such that the BIDFET is controlled in driving mode in such a way that a 3-level pulse pattern is generated. As a result, the motor harmonics at the electric machine are reduced, so that the motor losses are reduced. The BIDFET is thus used as a component of the rectifier in charging mode and as a component of the inverter in driving mode.

[0015] In an alternative embodiment, the transistors and BIDFETs of the half-bridge are associated with the same gate driver, wherein a switching device is present which is designed such that the gate driver is associated with the BIDFET in AC charging operation and with the transistors of the half-bridge in driving operation. In this case, a unidirectional rectifier is formed in AC charging operation by means of the freewheeling diode of the transistor and the BIDFET. This saves six gate drivers, but then feedback to the power grid or other components is no longer possible, and only a 2-level pulse mode can be set in driving operation.

[0016] In another embodiment, a switching device is provided, which is designed so that the electric machine is disconnected from the AC charging line during AC charging operation. Thus, the electric machine can be switched to a voltage-free state during AC charging operation, so that no undesirable drive torque is generated at the electric machine.

[0017] In another specific embodiment, an AC filter (alternating current filter) and an active residual current filter are arranged between the AC charging interface and the inverter, the latter being used in particular for contact protection.

[0018] In another specific embodiment, the BIDFET is designed as a GaN BIDFET, which can be operated with very low losses.

[0019] The transistors of the half bridge are designed, for example, as SiC transistors, but can also be designed as GaN transistors. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention is explained in more detail below based on preferred embodiments.

[0021] Figure 1 shows a traction network in a first embodiment,

[0022] Figure 2 shows an alternative step-up-down chopper,

[0023] Figure 3 Another alternative step-up / step-down chopper is shown.

[0024] Figure 4 A traction grid with a bidirectional step-down chopper is shown.

[0025] Figure 5 shows a traction grid with a bypass line,

[0026] Figure 6 shows a schematic block diagram of a switching device,

[0027] FIG. 7 shows a circuit arrangement of a bidirectional Vienna rectifier (prior art), and

[0028] FIG. 8 shows a circuit arrangement of a unidirectional Vienna rectifier (prior art). DETAILED DESCRIPTION

[0029] exist Figure 1, a traction grid 1 in a first embodiment is shown. The traction grid 1 has a high-voltage battery 2, which has a rated voltage of 400 V-420 V, for example. In addition, the traction grid 1 has an intermediate circuit capacitor C, which is formed by at least two capacitors C1, C2 connected in series and has a neutral point N. In addition, the traction grid 1 has an inverter 3, at the output of which an electric machine 4 with a transmission 5 is arranged. The traction grid 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, after which an active leakage current filter 8 is arranged. The output of the leakage current filter 8 is connected to the three AC voltage lines of the rectifier 3. In addition, a voltage measuring device V is shown 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 consists of a resistor between HV+ and HV- and a parallel circuit consisting of another resistor connected in series with a transistor. In addition, a current measuring device A in the HV-line is shown. The inverter 3 has three half-bridges H1-H3, wherein the transistors T1-T6 are respectively associated with a freewheeling diode D. The transistors T1-T6 are configured as SiC transistors, for example, wherein the freewheeling diode D can be configured as an intrinsic 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 the center tap M. In addition, each half-bridge H1-H3 is associated with a monolithic BIDFET 10. The BIDFET 10 has a voltage input and a voltage output and two control interfaces. Here, the high-voltage side transistor of the BIDFET 10 is connected to the corresponding center tap M of the associated half-bridge H1-H3. The low-voltage side transistor of the BIDFET 10 is connected to the neutral point N of the intermediate loop capacitor C. Preferably, the BIDFET 10 is configured as a GaN-BIDFET. Finally, a bidirectional step-up / step-down chopper 12 is arranged between the high-voltage battery 2 and the intermediate circuit capacitor C as a DC / DC converter 11. Here, 3x indicates that the DC / DC converter 11 is constructed as an interleaved three-phase interleaved DC / DC converter 11, which can also be asymmetrical, that is, one phase is designed for a smaller current than the other two phases. As a result, the DC / DC converter 11 can be operated with lower losses when the power requirement is lower. Here, the transistors of the DC / DC converter 11 are constructed as SiC transistors (with intrinsic diodes), for example. At the output of the DC / DC converter 11 on one side of the intermediate circuit capacitor C, two smoothing capacitors are shown. Finally, a control device 13 is also shown.

[0030] In further explanation of Figure 1Before describing the circuit of the bidirectional Vienna rectifier 14, refer to FIG. 7, which shows a bidirectional Vienna rectifier 14. An inductor is arranged at each of the three AC voltage interfaces, and the inductor is connected to the center tap of the half bridge. In addition, each center tap is connected to a series circuit consisting of two MOSFETs connected in opposite directions to each other. The three series circuits are connected to a common neutral point.

[0031] This structure of the Vienna rectifier 14 is now exactly replicated in the inverter 3 by means of three BIDFETs 10 , so that the rectifier is integrated into the inverter 3 , wherein no intrinsic diode is present in the GaN transistors.

[0032] In AC charging operation, the control device 13 operates the three half bridges H1-H3 and the three BIDFETs 10 as 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 to the grid.

[0033] During driving operation, the three half bridges H1 - H3 and the three BIDFETs 10 can then be controlled by the control device 13 in such a way that they generate a 3L pulse pattern.

[0034] The BIDFET 10 is fully integrated in the inverter 3. For example, if all three half-bridges H1-H3 are arranged on one circuit board, the BIDFET 10 is preferably also integrated on the circuit board. In the case where multiple circuit boards are used for the half-bridges H1-H3, the BIDFET 10 is preferably arranged on the circuit board of the associated half-bridge H1-H3. This allows a very compact design and simplifies cooling.

[0035] If no feedback into the grid is required, the rectifier does not have to be bidirectional, but can be constructed as a unidirectional Vienna rectifier 15, as shown in FIG8. It can be seen that instead of the three half-bridges in FIG7 with transistors, three half-bridges composed of diodes are shown. Here, the connection corresponds to the freewheeling diodes D of the half-bridges H1-H3 of the inverter 3, wherein the three series circuits of transistors with opposite polarity in FIG8 again correspond to the BIDFET 10. Therefore, the transistors T1-T6 for AC charging are not required.

[0036] Therefore, it can be alternatively provided that the transistors T1-T6 are associated with the same gate driver as the BIDFET 10, wherein the gate driver is connected to the BIDFET 10 in AC charging operation and is connected to the transistors T1-T6 in driving operation, so that only a 2-level pulse mode is possible. Here, the associated switching device for the gate driver is not shown, but is controlled by the control device 13.

[0037] exist Figure 2, an alternative embodiment for a DC / DC converter 11 as a step-up / step-down converter 12 is shown, wherein the transistors are designed as GaN transistors, which have lower switching losses than SiC transistors.

[0038] exist Figure 3 Another alternative embodiment is shown in , which has even fewer inductors, thereby saving three inductors in the 3-phase interleaved DC / DC converter 11 .

[0039] exist Figure 4 An alternative traction network 1 is shown in FIG. Figure 1 The only difference between the traction grid 1 of FIG. 1 and FIG. 2 is the design of the DC / DC converter 11. Figure 1 In contrast, the DC / DC converter 11 is designed as a bidirectional step-down converter 16 , wherein it is assumed here that the voltage at the inverter 3 or at the intermediate circuit capacitor is always higher than the voltage of the high-voltage battery 2 .

[0040] exist Figure 5 Another traction grid 1 is shown in FIG. Figure 4 The traction grid 1 of FIG. 1 is similar to that of FIG. 2 . The only difference is that a bypass line 17 with at least one switching element 18 is arranged between the high-voltage battery 2 and the intermediate circuit capacitor C, both from the + side and from the - side, wherein in the closed state of the switching element 18, the DC / DC converter 11 is bridged. Here, the switching element 18 is closed during driving operation and is opened during AC charging operation, so that in AC charging operation, the transistors in the DC / DC converter 11 are designed for the lower current in AC charging operation. Then, in driving operation with a higher current, the DC / DC converter 11 is deactivated and bridged via the bypass line 17, wherein the control of the switching element 18 is again performed via the control device 13. As a result, costs can be saved. In this case, in principle, a bypass line 17 with a switching element 18 is sufficient.

[0041] exist Figure 6 , a switching device 19 controlled by the control device 13 is shown. By means of the switching device 19 controlled by the control device 13, the AC charging lines L1-L3 are connected to the inverter 3 in the AC charging operation, wherein the motor 4 is disconnected. Conversely, in the driving operation, the AC charging lines L1-L3 are disconnected, and the inverter 3 is connected to the motor 4.

[0042] Reference numerals list

[0043] 1 Traction grid

[0044] 2 High voltage battery

[0045] 3 Inverter

[0046] 4 Motor

[0047] 5 Transmission

[0048] 6 Charging port

[0049] 7AC filter (AC voltage filter)

[0050] 8 Leakage current filter

[0051] 9 Discharge circuit

[0052] 10BIDFET

[0053] 11DC / DC Converter

[0054] 12 Bidirectional step-up and step-down chopper

[0055] 13. Control Device

[0056] 14 Bidirectional Vienna rectifier

[0057] 15 One-way Vienna rectifier

[0058] 16 Bidirectional Buck Chopper

[0059] 17 Bypass line

[0060] 18 Switching elements

[0061] 19 Switching device

[0062] M Center tap

[0063] N Neutral point

[0064] C Intermediate circuit capacitor

[0065] C1, C2 capacitors

[0066] L1-L3 charging line

[0067] H1-H3 Half Bridge

[0068] T1-T6 transistors

[0069] D Freewheeling diode

[0070] V Voltage measuring device

[0071] A Current measuring equipment

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 associated with a monolithic BIDFET (10), wherein the high-voltage side transistors of the BIDFET (10) are respectively connected to the center tap (M) of the half bridge (H1-H3) associated therewith, and the low-voltage side transistors of the BIDFET (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).

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

3. The traction power grid according to claim 1, characterized in that: The DC / DC converter (11) is designed as a step-down chopper (16).

4. The traction power grid according to claim 3, characterized in that: At least one bypass line (17) having at least one switching element (18) is arranged between the high-voltage battery (2) and the intermediate circuit capacitor (C), wherein in the closed state of the switching element (18), the DC / DC converter (11) is bridged.

5. The traction network according to any one of the preceding claims, characterized in that The control device (13) is designed in such a way that, during driving operation, the BIDFET (10) is actuated in such a way that a three-level pulse pattern is generated.

6. The traction power grid according to any one of claims 1 to 5, characterized in that: The transistors (T1-T6) of the half bridge (H1-H3) and the BIDFET (10) are associated with the same gate driver, wherein a switching device is present which is designed such that the gate driver is associated with the BIDFET (10) in AC charging operation and is associated with the transistors (T1-T6) of the half bridge (H1-H3) in driving operation.

7. The traction network according to any one of the preceding claims, characterized in that A switching device (19) is provided, which is designed in such a way that the electric machine (4) is disconnected from the AC charging line (L1-L3) during AC charging operation.

8. The traction network according to any one of the preceding claims, characterized in that An alternating current voltage filter (7) and an active leakage current filter (8) are arranged between the AC charging interface (6) and the inverter (3).

9. The traction network according to any one of the preceding claims, characterized in that The BIDFET (10) is configured as a GaN-BIDFET.

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