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) formed from at least two capacitors (C1, C2) connected in series and having a neutral point (N), an inverter (3), and a three-phase AC charging connection (6), wherein the three AC charging lines (L1-L3) are connected to an AC voltage filter (7), wherein the inverter (3) has three half-bridges (H1-H3), each half-bridge (H1-H3) being assigned a monolithic BIDFET (10), wherein the high-side transistors of the BIDFETs (10) are each connected to a center tap (M) of their assigned half-bridges (H1-H3), and the low-side transistors of the BIDFETs (10) are each 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 taps (M) of the half-bridges (H1-H3),where the DC / DC converter is designed as a galvanically isolated DC / DC converter.

Description

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

[0002] A typical traction network consists of a traction battery, an inverter, and an electric motor. Many different topologies exist for the configuration of the individual components of such a network. To reduce currents, attempts are made to operate at the highest possible voltages on the vehicle side. For example, traction networks are known where the nominal voltage of the traction battery is 800 V. This leads to problems with the voltage withstand capability of the semiconductor switches, so 3-level inverters have been proposed for such traction networks, as described, for example, in DE 10 2016 206 945 A1. Another problem is the inconsistent charging infrastructure, where both 400 V and 800 V DC charging stations are available. Depending on the topology used, the maximum charging power may not be fully utilized, or the circuit complexity may be very high.

[0003] Furthermore, there is often a desire for charging with alternating current (AC). In this case, a rectifier is installed between the AC charging port and the high-voltage battery, converting the AC voltage into a DC voltage. A DC / DC converter may also be included to adapt the rectified voltage to the voltage level of the high-voltage battery.

[0004] Another traction network is known from US 10 562 404 B1, which is designed to be charged from a single-, two- or three-phase alternating voltage source.

[0005] US patent 11 290 022 B2 discloses a galvanically isolated DC / DC converter which has two RF transformers forming a main and a secondary path.

[0006] From US patent 2019 / 0238062A1, a traction system for a motor vehicle is known, comprising at least one high-voltage battery, an intermediate circuit capacitor formed from at least two capacitors connected in series and having a neutral point, and an inverter. The inverter is designed as a 3-level T-type inverter, which can also be operated as a rectifier. The inverter can dynamically operate in 2-level or 3-level mode.

[0007] US Patent 9,718,374 B2 discloses a traction system for a motor vehicle that has a 3-phase AC charging connection, with rectification taking place via a 6-B bridge circuit of the inverter. A galvanically connected DC / DC converter is also arranged between the high-voltage battery and the inverter.

[0008] From WO 2021 / 074 661 A1 a power converter is known which has half-bridges which are connected to DC terminals of a battery, wherein the center taps of the half-bridges are led to non-insulated output terminals and to a transformer.

[0009] The invention is based on the technical problem of creating a traction network for a motor vehicle that has a three-phase AC charging connection, is compact in design and has galvanic isolation from the network.

[0010] The solution to the technical problem is achieved by a traction network with the features of claim 1. Further advantageous embodiments of the invention are set out in the dependent claims.

[0011] The traction network for a motor vehicle comprises at least one high-voltage battery, a DC / DC converter, an intermediate circuit capacitor formed from at least two capacitors connected in series and featuring a neutral point, an inverter, and a three-phase AC charging connection. The inverter has three half-bridges, each half-bridge being assigned a monolithic BIDFET. The high-side transistors of the BIDFETs are each connected to a center tap of their assigned half-bridge, and the low-side transistors of the BIDFETs are each connected to the neutral point of the intermediate circuit capacitor. Furthermore, the three AC charging lines are connected to, or can be connected to, the center taps of the half-bridges. The DC / DC converter is designed as a galvanically isolated DC / DC converter located between the high-voltage battery and the inverter.The BIDFETs can be integrated into a module housing of the inverter, preferably arranged on one or more circuit boards of the half-bridges. Using the bidirectional FETs, a PFC rectifier can be integrated into the inverter, eliminating the need for a separate rectifier. The integrated design results in a very compact form factor, which also facilitates cooling. Furthermore, the BIDFETs offer additional advantages, which will be described in more detail later. With a suitable bidirectional design of the integrated rectifier, vehicle-to-grid, vehicle-to-home, and vehicle-to-utility charging can be implemented, allowing the traction grid to also be used as a mobile charging station for other vehicles.

[0012] In one embodiment, the DC / DC converter is designed as a bidirectional boost / buck converter. This allows for maximum flexibility. For example, different DC charging infrastructures (400 V or 800 V) can be used, and a desired voltage can be set at the inverter for an optimal operating point of the electric motor, even if the voltage of the high-voltage battery has dropped significantly. This also allows the high-voltage battery to be constructed from sodium / sodium battery cells, which can exhibit larger voltage dips than lithium-ion battery cells.

[0013] Furthermore, the DC / DC converter can also be designed as a two-, three-, or multi-phase interleaved DC / DC converter, and can also be designed as an asymmetrical interleaved DC / DC converter. The advantage of interleaved DC / DC converters is that the power can be distributed, thus reducing the demands placed on the individual components, although the number of components increases. Another advantage of an asymmetrical interleaved DC / DC converter is that losses in the lower power range can be reduced.

[0014] In one embodiment, the DC / DC converter is designed as an RF transformer or multiple RF transformers, enabling particularly low-loss voltage transformation. Several RF transformers can be used to enable interleaved operation (symmetrical or asymmetrical). An RF transformer circuit like the one described in US 11,290,022 B2 can also be employed. The RF transformers can be implemented as energy-dense cores wound with Litz wires or as transformers integrated on a PCB (printed circuit board).

[0015] In a further embodiment, the DC / DC converter has a switching device and a bypass line, wherein at least one switching element is arranged in the bypass line, wherein the DC / DC converter is designed such that the switching element is closed during driving operation, wherein half-bridges are connected to the at least one transformer via the switching device during AC charging operation and to inductors during driving operation.

[0016] In another embodiment, the DC / DC converter has two bypass lines, each with at least one switching element, wherein the DC / DC converter is designed to bypass the DC / DC converter via the bypass lines during driving operation.

[0017] This allows transistors with a lower current-carrying capacity to be used for the DC / DC converter, while still enabling feedback into the grid. During operation, the inverter transistors with their higher current-carrying capacity are used. The switching elements are preferably designed as relays.

[0018] In another embodiment, the controller is designed to drive the BIDFETs during operation in such a way as to generate a 3-level pulse pattern. This reduces the motor harmonics at the electric machine, thus reducing motor losses. The BIDFETs therefore serve as part of the rectifier during charging and as part of the inverter during driving.

[0019] In an alternative embodiment, the same gate drivers are assigned to the transistors of the half-bridges and the BIDFETs, with a switching device configured such that the gate drivers are assigned to the BIDFETs during AC charging and to the transistors of the half-bridges during driving. During AC charging, a unidirectional rectifier is formed using the freewheeling diodes of the transistors and the BIDFETs. This eliminates the need for six gate drivers, but then no longer allows for feedback into the grid or other components, and only a two-level pulse pattern can be set during driving.

[0020] In a further embodiment, a switching device is provided which is designed to disconnect an electric motor from the AC charging lines during AC charging operation. This allows the electric motor to be de-energized during AC charging operation, so that no unwanted drive torques are generated at the electric motor.

[0021] In another embodiment, an AC filter (alternating current filter) is arranged between the AC charging port and the inverter.

[0022] In another embodiment, the BIDFETs are designed as GaN BIDFETs, which can be operated with very low losses.

[0023] The transistors of the half-bridges are designed, for example, as SiC transistors, but can also be designed as GaN transistors.

[0024] The invention is explained in more detail below with reference to preferred embodiments. The figures show: Fig. 1 a traction network in a first embodiment, Fig. 2 a galvanically isolated DC / DC converter in a first embodiment, Fig. 3 another alternative DC / DC converter, Fig. 4 another alternative DC / DC converter, Fig. 5 another alternative DC / DC converter with two bypass lines, Fig. 6 a schematic circuit diagram for a high-voltage battery with low voltage, Fig. 7 a unidirectional DC / DC converter, Fig. 8 a schematic block diagram of a switching device, Fig. 9 a circuit arrangement of a bidirectional Vienna rectifier (state of the art) and Fig. 10 a circuit arrangement of a unidirectional Vienna rectifier (state of the art).

[0025] In the Fig. Figure 1 shows a traction network 1 in a first embodiment. The traction network 1 includes a high-voltage battery 2, which, for example, has a nominal voltage of 400 V, 420 V, or 800 V. Furthermore, the traction network 1 includes an intermediate circuit capacitor C, which is formed from at least two capacitors C1 and C2 connected in series and has a neutral point N. The traction network 1 also includes an inverter 3, at the output of which an electric motor 4 with gearbox 5 is arranged. The traction network 1 further includes a three-phase AC charging connection 6, wherein the three charging lines L1-L3 are connected to an AC filter (or alternating voltage filter) 7. The outputs of the AC filter 7 are then connected to the three AC lines of the inverter 3. It is further shown that voltage measuring devices V are connected in parallel to the capacitors C1 and C2 of the intermediate circuit capacitor C.Furthermore, an active discharge circuit 9 for the intermediate circuit capacitor C is shown, consisting of a resistor between HV+ and HV- and a parallel circuit comprising another 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, with each transistor T1-T6 associated with a freewheeling diode D. The transistors T1-T6 are, for example, SiC transistors, and the freewheeling diodes D can be intrinsic diodes or separate, discrete diodes. Each half-bridge H1-H3 has a center tap M, with the charging lines L1-L3 connected to the center taps M. Each half-bridge H1-H3 is also associated with a monolithic BIDFET 10. The BIDFET 10 has a voltage input and a voltage output, as well as two control terminals.The high-side transistor of the BIDFETs 10 is connected to the respective center tap M of the associated half-bridge H1-H3. The low-side transistors of the BIDFETs 10 are connected to the neutral point N of the intermediate circuit capacitor C. The BIDFETs 10 are preferably designed as GaN BIDFETs. Finally, a galvanically isolated bidirectional boost / buck converter 12, acting as a DC / DC converter 11, is arranged between the high-voltage battery 2 and the intermediate circuit capacitor C. A control circuit 13 is also shown.

[0026] Before the circuit according Fig. 1. Further explanation will be given on Fig. Figure 9, which shows a bidirectional Vienna rectifier 14, is referenced. An inductor is arranged at each of the three AC voltage terminals, each of which is connected to a center tap of a half-bridge. Furthermore, each center tap is connected to a series connection of two MOSFETs wired in opposite directions. The three series connections are connected to a common neutral point.

[0027] This exact structure of a Vienna rectifier 14 is now replicated in the inverter 3 by the three BIDFETs 10, so that the rectifier is integrated into the inverter 3, whereby the intrinsic diodes are not present in the GaN transistors.

[0028] In AC charging mode, the controller 13 then controls the three half-bridges H1-H3 and the three BIDFETs 10 like a rectifier, and the high-voltage battery 2 is charged via the DC / DC converter 11. Since the rectifier is bidirectional, power can also be fed back from the high-voltage battery 2 into the grid.

[0029] During operation, the three half-bridges H1-H3 and the three BIDFETs 10 can then be controlled by the controller 13 in such a way that they generate a 3L pulse pattern.

[0030] The BIDFETs 10 are fully integrated into the inverter 3. If, for example, all three half-bridges H1-H3 are arranged on a single circuit board, the BIDFETs 10 are preferably also integrated onto the circuit board. If there are multiple circuit boards for the half-bridges H1-H3, the BIDFETs 10 are preferably arranged on the circuit board of the corresponding half-bridge H1-H3. This allows for a very compact design and simplifies cooling.

[0031] If feedback to the grid is unnecessary, the rectifier does not need to be bidirectional, but can be designed as a unidirectional Vienna rectifier 15, as in Fig. Figure 10 shows the following: As you can see, instead of the three half-bridges made of Fig. Figure 9 shows three half-bridges made of diodes with transistors. The circuit corresponds to the freewheeling diodes D of the half-bridges H1-H3 of inverter 3, where the three series circuits with the transistors polarized against each other are made of Fig. 10 corresponds to the BIDFETs 10 again. Therefore, transistors T1-T6 are not needed for AC charging.

[0032] Therefore, an alternative approach is to assign the same gate drivers to transistors T1-T6 as to BIDFETs 10, whereby in AC charging mode the gate drivers are connected to BIDFETs 10 and in driving mode to transistors T1-T6, so that only a 2-level pulse pattern is possible. The associated switching device for the gate drivers is not shown, but is controlled by the controller 13.

[0033] The galvanic isolation from the mains and traction network 1 has been moved to the DC / DC converter 11, whereas in the prior art this is typically integrated in the separate OBC (onboard charger).

[0034] In the Fig. Figure 2 shows a galvanically isolated DC / DC converter 11 in a first embodiment. The DC / DC converter 11 has two RF transformers HFT1, HFT2, each RF transformer HFT1, HFT2 having a resonant circuit consisting of a series connection of a capacitor and an inductor arranged on both its primary and secondary sides. The DC / DC converter 11 is shown on the left with the high-voltage battery 2 (not shown) (see Figure 2). Fig. 1) connected. Between the RF transformers HFT1, HFT2 and the connections to the high-voltage battery 2, two half-bridges are arranged, which rectify the AC voltage (in AC charging mode) or convert the DC voltage of the high-voltage battery into AC voltage when power is to be fed back into the grid from the high-voltage battery 2. Furthermore, four half-bridges are arranged at the connection to the inverter 3, to which smoothing capacitors are connected in parallel. The DC / DC converter 11 also has a switching device 21 and a bypass line 22 with a switching element 23. Finally, the DC / DC converter 11 has four inductors, one end of which is connected to the HV+ line of the high-voltage battery. The other ends are connected to the switching device 21.During AC charging or grid feed-in, the four half-bridges on the right are connected to the four terminals for the two high-frequency transformers HFT1 and HFT2, with the switching element 23 open. The primary-to-secondary winding ratio determines whether the DC / DC converter 11 operates as a boost or buck converter during AC charging. During operation, the switching element 23 is closed, and the two high-frequency transformers HFT1 and HFT2 are disconnected by the switching device 21. Instead, the four inductors are connected to the four half-bridges on the right, with each inductor connected to a center tap of a half-bridge. This configuration allows the battery voltage of the high-voltage battery 2 to be boosted or boosted.In the example shown, the half-bridges on the left are implemented as GaN transistors and those on the right as SiC transistors, since the latter have a higher current-carrying capacity, whereas the GaN transistors are lower-loss and are only required for AC charging or for feeding power back into the grid. However, configurations are also possible where all transistors are of the same technology (Si, SiC, or GaN), with widebandgap transistors being preferred. Furthermore, it should be noted that the circuit can also have more than two RF transformers, HFT1 and HFT2, so that interleaved operation with more than two phases can be designed for different maximum power levels.

[0035] In the Fig. Figure 3 shows an alternative embodiment comprising two bypass lines 22, 24, each with a switching element 23, 25. Regarding the functionality for AC charging and / or feeding power back into the grid, the explanations in section 3 are entirely applicable. Fig. 2 is referenced, whereby both switching elements 23, 25 are open during AC charging. During driving, both switching elements 23, 25 are closed and the DC / DC converter 11 is deactivated, so that it is bypassed via the bypass lines 22, 24. During driving, the inverter is supplied only with the battery voltage of the high-voltage battery 2. The advantage of this circuit is that the transistors of the right half-bridges in the DC / DC converter 11 then only need to be designed for the currents during AC charging. The switching device 21 and the inductors can be omitted.

[0036] In the Fig. 4 and Fig. 5 are alternative embodiments of the circuit variants according to Fig. 2 and Fig. Figure 3 shows the four half-bridges on the right side being replaced by two staggered half-bridges. The center taps of the two half-bridges are connected to a neutral point between the two smoothing capacitors.

[0037] In the Fig. Figure 6 shows the left half-bridges 26 of the DC / DC converter 11 when, for example, it is to work with a 400 V high-voltage battery instead of an 800 V battery.

[0038] As can be seen, only minor changes to the wiring are required so that the DC / DC converters 11 shown can be used according to the Fig. 2 to Fig. 5. They can be adapted very easily to changing conditions.

[0039] In the Fig. Figure 7 shows another embodiment of a DC / DC converter 11, in which the left half-bridges 26 have been replaced by passive diodes. With this circuit, no feedback into the grid is possible, but only unidirectional AC charging. During driving operation, the DC / DC converter is then bypassed by means of bypass lines 22, 24 (not shown) with switching elements 23, 25 (see Figure 7). Fig. 3 and Fig. 5) bridged.

[0040] In the Fig. Figure 8 shows a switching device 19, which is controlled by the controller 13. By means of the switching device 19, which is controlled by the controller 13, the AC charging lines L1-L3 are connected to the inverter 3 during AC charging operation, whereby the electric machine 4 is disconnected. During driving operation, however, the AC charging lines L1-L3 are disconnected and the inverter 3 is connected to the electric machine 4. Reference symbol list 1 Traction network 2 high-voltage batteries 3 inverters 4 Electric machine 5 gearboxes 6 AC charging ports 7 AC filters (alternating current filters) 9 Discharge circuit 10 BIDFET 11 DC / DC converters 12 boost / decrement converters 13 Control 14 Vienna rectifier 15 Vienna rectifiers 18 switching element 19 Switching device 21 Switching device 22 Bypass line 23 Switching element 24 Bypass lines 25 switching element 26 Half-bridge M Center tap N Neutral point C Intermediate circuit capacitor C1,C2 capacitors L1-L3 charging lines H1-H3 half-bridges T1-T6 transistors A current measuring device D Freewheeling diode V Voltage measuring device HFT1, HFT2 RF transformer

Claims

[1] 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 from at least two series-connected capacitors (C1, C2) and having a neutral point (N), an inverter (3) and a three-phase AC charging connection (6), wherein the 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 assigned a monolithic BIDFET (10), wherein the high-side transistors of the BIDFETs (10) are each connected to a center tap (M) of their assigned half-bridges (H1-H3) and the low-side transistors of the BIDFETs (10) are each connected to the neutral point (N) of the intermediate circuit capacitor (C). are, with the three AC charging lines (L1-L3) connected to the center taps (M) of the half bridges (H1-H3),wherein the DC / DC converter is designed as a galvanically isolated DC / DC converter, wherein the traction network (1) has a controller (13) which is designed to control at least the BIDFETs (10) as rectifiers in an AC charging operation, wherein the DC / DC converter (11) has at least one HF transformer (HFT1, HFT2), a switching device (21) and a bypass line (22), wherein at least its switching element (23) is arranged in the bypass line (22), wherein the DC / DC converter (11) is designed such that the switching element (23) is closed in driving operation, wherein half-bridges are connected to the HF transformer (HFT1, HFT2) via the switching device (21) in AC charging operation and are connected to inductors in driving operation, which are connected at one end to an HV+ line of the high-voltage battery (2) and at the other end to the switching device (21) are connected., [2] Traction network according to claim 1, characterized bythat the DC / DC converter (11) is designed as a bidirectional boost-buck converter (12). [3] Traction network according to one of the preceding claims, characterized by that a controller (13) is designed to control the BIDFETs (10) during driving operation in such a way that a 3-level pulse pattern is generated. [4] Traction network according to one of claims 1 or 2, characterized by that the transistors (T1-T6) of the half-bridges (H1-H3) and the BIDFETs (10) are assigned the same gate drivers, wherein a switching device is provided which is designed such that the gate drivers are assigned to the BIDFETs (10) in AC charging mode and to the transistors (T1-T6) of the half-bridges (H1-H3) in driving mode. [5] Traction network according to one of the preceding claims, characterized by that a switching device (19) is provided which is designed to disconnect an electric machine (4) from the AC charging line in AC charging operation. [6] Traction network according to one of the preceding claims, characterized by that an AC voltage filter (7) is arranged between the AC charging connection (6) and the inverter (3). [7] Traction network according to one of the preceding claims, characterized by that the BIDFETs (10) are designed as GaN BIDFETs.

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