Electrical traction network for a motor vehicle and method for operating the same in a driving and a charging mode

Abstract

The invention relates to an electrical traction network (1) for a motor vehicle, comprising a separately excited synchronous machine (2), a pulse-controlled inverter (3), a high-voltage battery (4), a DC / DC converter (6) and a charger (5), wherein the charger (5) has a mains connection (9) for an external AC voltage network, wherein the charger (5) is connected to AC voltage outputs of the pulse-controlled inverter (3) via first switching elements (S1), wherein the AC voltage outputs of the pulse-controlled inverter (3) are connected to the phases of the synchronous machine (2) via second switching elements (S2), wherein the DC voltage connections (HV+_PWR, HV-_PWR) of the pulse-controlled inverter (3) and an output of the DC / DC converter (6) are connected to the high-voltage battery (4) via third switching elements (S3), wherein the inputs of the DC / DC converter (6) are connected to the DC voltage connections (HV+_PWR, HV-_PWR) of the pulse inverter (3),wherein fourth switching elements (S4) are arranged between the output of the DC / DC converter (6) and two half-bridges of the DC / DC converter (6), wherein the DC / DC converter (6) is connected to a rotor winding of the synchronous machine (2) via fifth switching elements (S5), and a method for operating such an electrical traction network.

Description

[0001] The invention relates to an electrical traction network for a motor vehicle and a method for operating such an electrical traction network in a driving and a charging mode.

[0002] The typical structure of an electric traction network consists of an electric motor, an inverter, and a high-voltage battery. The electric motor can generally be an asynchronous or synchronous motor, the latter being permanent or separately excited. The inverter is usually a pulse-controlled inverter. It is also common practice to provide a charger that can charge the high-voltage battery from an external AC power network. Increasingly, electrical components are being used, so attempts are being made to use at least some components for both driving and charging.

[0003] WO 2023 / 006726 A1 discloses an electric drive system for a vehicle comprising a three-phase electric motor, an electrical energy storage device, and an inverter. The inverter is preferably a 3-level T-type pulse-controlled inverter. A series circuit comprising two capacitors is provided as the intermediate circuit capacitor, with the connection point between the capacitors being connected to a center tap of the inverter. In a first switching state, in which a positive potential of a charging terminal is connected to the positive potential of the electrical energy storage device and a negative potential of the charging terminal is connected to the negative potential of the electrical energy storage device, the energy storage device can be charged via the charging terminal.In a second switching state, in which the positive potential of the charging connection is connected to the positive potential of the electrical energy storage device and the negative potential of the charging connection is connected to the center tap of the inverter, the energy storage device can be charged via the inverter. In a third switching state, the positive potential of the charging connection is applied to the center tap and the negative potential of the charging connection is connected to the negative potential of the energy storage device. The inverter is designed to charge the first capacitor and / or the second capacitor and to provide a sum of a first voltage of the first capacitor and a voltage of the second capacitor as an output voltage of the inverter for charging the electrical energy storage device. The inverter is therefore used for both driving operation and charging operation.

[0004] The invention is based on the technical problem of creating an electrical traction network with a separately excited synchronous motor, in which the components are effectively used for driving and charging. A further technical problem is to provide a method for operating such a traction network.

[0005] DE 10 2017 203 063 B3 shows a control unit, in particular for an electric drive of a vehicle, which comprises a power converter and a DC-DC converter. During driving operation, the DC side of the power converter can be directly connected to a (traction) battery via a contactor, while the AC side of the power converter can be directly connected to an electrical machine via an alternative circuit breaker. During charging operation, the alternative circuit breaker can disconnect the electrical machine from the power converter and instead connect a power source via inductors. At the same time, the direct connection to a (traction) battery on the DC side of the power converter is disconnected and connected via a DC-DC converter to provide a charging voltage.

[0006] US 9 718 374 B2 provides a charging system for an electric vehicle and an electric vehicle.The charging system includes: a power battery; a charge / discharge socket; a bidirectional DC / DC module having a first DC terminal connected to a first terminal of the power battery and a second DC terminal connected to a second terminal of the power battery; a bidirectional DC / AC module having a first DC terminal connected to the second terminal of the power battery and a second DC terminal connected to the first terminal of the power battery; a charge / discharge control module having a first terminal connected to the AC terminal of the bidirectional DC / AC module and a second terminal connected to the charge / discharge socket; and a control module connected to the charge / discharge control module and controlling the charge / discharge control module according to the current operating mode of the charging system.

[0007] DE 10 2018 209 139 A1 describes an AC charging device equipped with an AC connection, a controllable rectifier connected to it, a bidirectional DC-DC converter, and a battery connection. The DC-DC converter has a first side and a second side. The first side has an intermediate circuit capacitor. The second side is connected to the battery connection. The AC charging device has a changeover switch. This selectably connects the rectifier to the first side of the DC-DC converter or to the second side of the DC-DC converter.

[0008] DE 10 2020 209 806 A1 discloses an integrated electric drive system and a vehicle. The system comprises: an electric machine; an energy storage unit; a first conversion unit configured to convert an alternating voltage originating from an external power supply outside the vehicle or generated during regeneration by the electric machine into a direct voltage, or to convert a high direct voltage originating from the energy storage unit into an alternating voltage; a second conversion unit configured to increase or decrease a high direct voltage originating from the first conversion unit or the energy storage unit; a third conversion unit configured to convert a high direct voltage originating from the second conversion unit or the energy storage unit;and a control unit configured to selectively control the external power supply, the electric machine, the first, second, and third conversion units, and the energy storage unit to implement various operating modes of the system. The present disclosure further relates to an electric vehicle having such a system. The system and vehicle according to the present disclosure implement multifunctional power electronics and also reduce the manufacturing costs of a vehicle.

[0009] The solution to the technical problem is provided by an electric traction network having the features of claim 1 and a method having the features of claim 9 or 10. Further advantageous embodiments of the invention emerge from the subclaims.

[0010] The electrical traction network for a motor vehicle comprises a separately excited synchronous machine, a pulse-controlled inverter, a high-voltage battery, a DC / DC converter, and a charger. The charger has a mains connection for an external AC voltage network. The charger is connected to the AC voltage outputs of the pulse-controlled inverter via first switching elements. The AC voltage outputs of the pulse-controlled inverter are connected to the phases of the synchronous machine via second switching elements. The DC voltage terminals of the pulse-controlled inverter and an output of the DC / DC converter are connected to the high-voltage battery via third switching elements. The inputs of the DC / DC converter are connected to the DC voltage terminals of the pulse-controlled inverter.Fourth switching elements are arranged between the output of the DC / DC converter and two half-bridges of the DC / DC converter, with the DC / DC converter being connected to a rotor winding of the synchronous machine via fifth switching elements. This allows parts of the DC / DC converter to generate the rotor current during driving operation, while during charging operation the DC / DC converter adjusts the DC voltage generated by the pulse-controlled inverter to the voltage level of the high-voltage battery. Generally, the switching elements can be relays or transistors. These can be Si, SiC, and / or GaN-based.

[0011] In one embodiment, an AC voltage output of the pulse inverter is directly connected to a phase of the synchronous machine, so that a second switching element can be eliminated.

[0012] In another embodiment, the pulse-controlled inverter is designed as a 3-level T-type pulse-controlled inverter. Among other advantages, this allows for smaller mains filters in the charger. Furthermore, the leakage currents via Y capacitors at the DC voltage connection of the pulse-controlled inverter to ground are lower, as the voltage swings are smaller, thus also reducing the amplitudes of the AC voltage interference.

[0013] In a further embodiment, an EMC filter is arranged between the fifth switching elements and the rotor winding. This allows interference components in the rotor current due to the switching operations of the two half-bridges to be reduced.

[0014] In a further embodiment, the DC / DC converter has two inductances, wherein the fourth switching elements are arranged between the center taps of the half-bridges and the inductances, ie the inductances are not effective in generating the rotor current.

[0015] Alternatively, the inductors are connected to the half-bridges, with the fourth switching elements arranged between the inductors and an output capacitor. The inductors can dampen high-frequency interference.

[0016] In a further embodiment, the DC / DC converter is designed as a buck converter.

[0017] Alternatively, the DC / DC converter is designed as a boost-buck converter, which requires more circuitry but provides greater flexibility.

[0018] The method for operating a traction network described above comprises the steps of opening the first switching elements during driving operation, closing the second switching elements, closing the third switching elements which connect the pulse inverter to the high-voltage battery, and opening the third switching element which connects the output of the DC / DC converter to the high-voltage battery, opening the fourth switching elements and closing the fifth switching elements.

[0019] During charging, the first switching elements are closed, the second switching elements are closed, the third switching elements, which connect the negative DC voltage terminal of the pulse inverter and the output of the DC / DC converter to the high-voltage battery, are closed and the third switching element, which connects the positive DC voltage terminal of the pulse inverter to the high-voltage battery, is opened, the fourth switching elements are closed and the fifth switching elements are opened.

[0020] The invention is explained in more detail below using preferred embodiments. The figures show: Fig. 1 a schematic block diagram of an electric traction network in a first embodiment and Fig. 2 an alternative embodiment of a device of the fourth and fifth switching elements.

[0021] In the Fig. Figure 1 shows a schematic block diagram of an electrical traction network 1. The electrical traction network 1 comprises a separately excited synchronous machine 2, a pulse-controlled inverter 3, a high-voltage battery 4, a charger 5, and a DC / DC converter 6, which is designed as a step-down converter 7. The pulse-controlled inverter 3 is designed as a 3-level T-type pulse-controlled inverter 8. The charger has a grid connection 9 for an external AC voltage network, with only the three phase inputs being shown schematically. The charger 5 has AC voltage network filters and a power factor correction filter, whose three inductors L1-L3 are shown schematically. The AC voltage network filter can have X and Y capacitors. The charger is connected to the AC voltage outputs of the pulse-controlled inverter 3 via first switching elements S1.The AC voltage outputs of the pulse-controlled inverter 3 are connected to the synchronous machine 2 via second switching elements S2, whereby a second switching element S2 could be omitted. On the DC voltage side of the pulse-controlled inverter 3, a series circuit comprising two capacitors C1, C2 is arranged as an intermediate circuit capacitor, the center tap of which is connected to the center tap M of the 3-level T-type pulse-controlled inverter 8. Third switching elements S3 are also provided, whereby the positive DC voltage connection HV+_PWR is connected to the positive pole of the high-voltage battery 4, the negative DC voltage connection HV-_PWR is connected to the negative pole of the high-voltage battery 4, and the output of the DC / DC converter 6 is connected to the positive pole of the high-voltage battery 4 via the third switching elements S3. The third switching elements S3 are arranged, for example, in a battery junction box 10. The DC / DC converter 6 has two half bridges, two inductors L4, L5 and an output capacitor C.The two inductors L4, L5 are connected on the side facing capacitor C. On the other side, inductors L4, L5 are each connected to a center tap of a half-bridge via fourth switching elements S4. Finally, the center taps of the half-bridges are connected to the rotor winding of synchronous machine 2 via fifth switching elements S5, with the arrow symbolizing the rotor current.

[0022] During driving, the first switching elements S1 and the fourth switching elements S4 are opened. The second switching elements S2 and the fifth switching elements S5 are closed. The third switching element S3, which connects the output of the DC / DC converter 6 to the positive terminal of the high-voltage battery 4, is opened, and the other two third switching elements S3 are closed. The pulse-controlled inverter 3 then generates the stator current for the synchronous machine 2, and the two half-bridges of the DC / DC converter 6 generate the rotor current.

[0023] During charging, the first switching elements S1 and the fourth switching elements S4 are closed, and the second switching elements S2 and the fifth switching elements S5 are opened. The third switching element S3, which connects the positive DC voltage terminal HV+_PWR of the pulse-controlled inverter 3 to the positive terminal of the high-voltage battery 4, is opened, and the other two third switching elements S3 are closed. The pulse-controlled inverter 3 then rectifies the AC mains voltage and feeds this DC voltage to the DC / DC converter 6, which then steps it down and supplies it to the high-voltage battery 4 as the charging voltage.

[0024] In the Fig. Figure 2 shows an alternative arrangement of the fourth switching elements S4 and fifth switching elements S5. The fourth switching elements S4 have been clearly shifted behind the inductors L4, L5, so that they are included in the circuit for the rotor current. Furthermore, an EMC filter 11 is arranged in the circuit. This EMC filter 11 can also be used in the embodiment according to Fig. 1 can be used. The inductances L4 and L5 can then reduce inductances in the EMC filter. List of reference symbols 1 traction network 2 synchronous machines 3 pulse inverters 4 high-voltage battery 5 Charger 6 DC / DC converters 7 buck converters 8 3-level T-type pulse inverters 9 Mains connection 10 Battery junction box 11 EMC filters S1-S5 switching element C1, C2 capacitor C capacitor L1-L5 inductors M center tap

Claims

[1] Electric traction network (1) for a motor vehicle, comprising a separately excited synchronous machine (2), a pulse inverter (3), a high-voltage battery (4), a DC / DC converter (6) and a charger (5), wherein the charger (5) has a mains connection (9) for an external AC power supply, wherein the charger (5) is connected via first switching elements (S1) to AC outputs of the pulse inverter (3), wherein the AC outputs of the pulse inverter (3) are connected via second switching elements (S2) to the phases of the synchronous machine (2), wherein the DC terminals (HV+_PWR, HV-_PWR) of the pulse inverter (3) and an output of the DC / DC converter (6) are connected via third switching elements (S3) to the high-voltage battery (4), wherein the inputs of the DC / DC converter (6) are connected to the DC terminals (HV+_PWR, HV-_PWR) of the pulse inverter (3) are connected,wherein fourth switching elements (S4) are arranged between the output of the DC / DC converter (6) and two half-bridges of the DC / DC converter (6), wherein the DC / DC converter (6) is connected to a rotor winding of the synchronous machine (2) via fifth switching elements (S5). [2] Electric traction network according to claim 1, characterized by , that an AC voltage output of the pulse inverter (3) is directly connected to a phase of the synchronous machine (2). [3] Electric traction network according to claim 1 or 2, characterized by , that the pulse inverter (3) is designed as a 3-level T-type pulse inverter (8). [4] Electric traction network with one of the preceding claims, characterized by , that an EMC filter (11) is arranged between the fifth switching elements (S5) and the rotor winding. [5] Electric traction network according to any of the preceding claims, characterized by, that the DC / DC converter (6) has inductors (L4, L5), wherein the fourth switching elements (S4) are arranged between the center taps of the half-bridges and the inductors (L4, L5). [6] Electric traction network according to one of claims 1 to 4, characterized by , that the inductors (L4, L5) are connected to the half-bridges, with the fourth switching elements (S4) being arranged between the inductors (L4, L5) and an output capacitor (C). [7] Electric traction network according to any of the preceding claims, characterized by , that the DC / DC converter (6) is designed as a buck converter (7). [8] Electric traction network according to any one of claims 1 to 6, characterized by , that the DC / DC converter (6) is designed as a boost-bubble converter. [9] Method for operating an electric traction network (1) with the features of claim 1, characterized by, that during driving operation the first switching elements (S1) are opened, the second switching elements (S2) are closed, the third switching elements (S3), which connect the pulse inverter (3) to the high-voltage battery (4), are closed, and the third switching element (S3), which connects the output of the DC / DC converter (6) to the high-voltage battery (4), is opened, the fourth switching elements (S4) are opened, and the fifth switching elements (S5) are closed. [10] Method for operating an electric traction network (1) with the features of claim 1, characterized by, that during charging operation the first switching elements (S1) are closed, the second switching elements (S2) are opened, the third switching elements (S3), which connect the negative DC voltage terminal (HV-_PWR) of the pulse inverter (3) and the output of the DC / DC converter (6) to the high-voltage battery (4), are closed, and the third switching element (S3), which connects the positive DC voltage terminal (HV+_PWR) of the pulse inverter (3) to the high-voltage battery (4), is opened, the fourth switching elements (S4) are closed, and the fifth switching elements (S5) are opened.

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