Method for operating an electric drive system for a vehicle

Abstract

The present invention relates to an operating method of an electric drive system (1) for a vehicle, wherein the electric drive system comprises at least a three-phase AC motor (2), a battery (3) for supplying power to the three-phase AC motor (2), and an inverter (4) for electrically connecting or electrically connecting the three-phase AC motor (2) to the battery (3), wherein a star point (7) of the three-phase AC motor (2) is electrically connected or electrically connectable to a positive terminal (8) of a DC charging interface of the electric drive system (1), and a negative potential wire (6) of the battery (3) is electrically connected or electrically connectable to a negative terminal (9) of the DC charging interface of the electric drive system (1). In this case, the star point (7) of the three-phase AC motor (2) is electrically connected or can be electrically connected to the positive terminal (8) of the DC charging interface of the electric drive system (1) via a first switch (S1), the negative potential line (6) of the battery (3) is electrically connected or can be electrically connected to the negative terminal (9) of the DC charging interface of the electric drive system (1) via a second switch (S2), and the positive terminal (8) of the DC charging interface of the electric drive system (1) is electrically connected or can be electrically connected to the tap of the intermediate circuit capacitor (C1) via a third switch (S3) and is thereby electrically connected or can be electrically connected to the positive potential line (5).

Description

[0001] The invention relates to a method for operating an electric drive system for a vehicle.

[0002] The prior art, such as that described in DE 10 2018 000 488 A1, discloses an electric drive system for a vehicle and a method for operating the same. The electric drive system includes at least a three-phase AC motor and a battery for powering the three-phase AC motor. The three-phase AC motor can be electrically connected to the battery via an inverter. The star point of the three-phase AC motor can be electrically connected to the positive terminal of a DC charging interface of the electric drive system, and the negative terminal of the battery can be electrically connected to the negative terminal of the DC charging interface of the electric drive system.

[0003] Furthermore, DE 10 2018 124 789 A1 discloses a charging device for charging a battery of a motor vehicle having an electric drive motor, comprising an inductor and a drive inverter. The drive inverter converts the battery DC voltage to drive the electric drive motor during vehicle operation, wherein the inductor, together with the drive inverter, serves as a voltage booster during battery charging operation. Furthermore, a switching unit is provided in the charging device to connect the charging power source to the battery during charging operation, either directly or via the voltage booster.

[0004] The object of the present invention is to specify a method for operating an electric drive system for a vehicle which is improved compared to the prior art.

[0005] According to the invention, this object is achieved by a method for operating an electric drive system for a vehicle.

[0006] Advantageous embodiments of the invention are described in the description.

[0007] An electric drive system for a vehicle comprises at least a three-phase AC motor, a battery for powering the three-phase AC motor, and an inverter that electrically connects the three-phase AC motor to the battery, wherein the star point of the three-phase AC motor is electrically connectable to the positive terminal of a DC charging interface of the electric drive system, and the negative potential wire of the battery is electrically connectable to the negative terminal of the DC charging interface of the electric drive system.

[0008] The star point of the three-phase AC motor can be electrically connected or electrically connected to the positive terminal of the DC charging interface of the electric drive system through a first switch, the negative potential wire of the battery can be electrically connected or electrically connected to the negative terminal of the DC charging interface of the electric drive system through a second switch, and the positive terminal of the DC charging interface of the electric drive system can be electrically connected or electrically connected to the tap of the intermediate circuit capacitor through a third switch and thereby can be electrically connected or electrically connected to the positive potential wire.

[0009] In the operating method of the electric drive system according to the present invention, when the battery should not be charged at an off-vehicle DC power supply, all three switches are opened; and in order to charge the battery at an off-vehicle DC power supply whose provided DC voltage corresponds to the battery rated voltage, the first switch and the second switch are closed and the third switch is opened; and in order to charge the battery at an off-vehicle DC power supply whose provided DC voltage is less than the battery rated voltage, all three switches are closed.

[0010] This solution allows the battery to be charged via the inductance of the three-phase AC motor. In this case, the battery can be charged both from an off-board DC power supply that provides a DC voltage corresponding to the battery nominal voltage, for example, 800 V, and from an off-board DC power supply that provides a DC voltage less than the battery nominal voltage, for example, 800 V, such as only 400 V. This solution requires only minimal expenditure and can therefore be implemented cost-effectively.

[0011] To charge the battery from an off-board DC power supply providing a DC voltage corresponding to the battery's rated voltage, the first and second switches are closed, and the third switch is opened, as described above. The closed first switch connects the star point to the positive terminal of the DC charging interface and, therefore, electrically connects it to the positive terminal when the off-board DC power supply is connected. The closed second switch connects the negative potential line to the negative terminal of the DC charging interface and, therefore, electrically connects it to the negative terminal when the off-board DC power supply is connected. When an off-board DC power supply providing a DC voltage corresponding to the battery's rated voltage is connected to the DC charging interface, the star point and the negative potential line are thus electrically connected to the off-board DC power supply. Furthermore, all transistors in one region of the inverter, particularly the upper region, are permanently turned on to electrically connect the battery directly to the off-board DC power supply. The battery is thus charged with a DC voltage provided by the off-board DC power supply corresponding to the battery's rated voltage.

[0012] To charge the battery from an external DC power supply that provides a DC voltage lower than the battery's rated voltage, for example, only 400V, all three switches are closed as described above. The star point and the negative potential line are therefore electrically connected to the DC charging port and, therefore, to it when the external DC power supply is connected. All transistors of the inverter are operated in pulse-width modulation and, in combination with the inductance of the three-phase AC motor, form a voltage booster to boost the low DC voltage provided by the external DC power supply to the battery voltage level (i.e., its rated voltage of, for example, 800V). Alternatively, transistors in other areas of the inverter, particularly the lower area, can also be clocked, so that the current flows not through the transistors in the upper area of the inverter, but through the freewheeling diodes in the upper area. Furthermore, as described above, the intermediate circuit capacitor is advantageously designed as a two-piece structure. This arrangement allows the capacitor's midpoint to be connected parallel to the input of the DC voltage provided by the external DC power supply to stabilize it. Therefore, a separate input capacitor for charging is not required.

[0013] In one possible embodiment, two intermediate circuit capacitors are provided which are electrically connected in series.

[0014] The embodiments of the present invention will be explained in detail below with reference to the drawings, wherein:

[0015] Figure 1 schematically shows an electric drive system for a vehicle in a first switching state,

[0016] Figure 2 schematically shows the electric drive system in a second switching state,

[0017] Figure 3 The electric drive system is schematically shown in a third switching state.

[0018] Corresponding parts are provided with the same reference numerals in all the figures.

[0019] Figure 1-3 The schematic diagram shows an electric drive system 1 for a vehicle in three different switching states.

[0020] The electric drive system 1 comprises a three-phase AC motor 2, a battery 3 for supplying power to the three-phase AC motor 2 and a battery for electrically connecting the three-phase AC motor 2 (e.g. Figure 1-3 As shown) or an inverter 4 that can be electrically connected to the battery 3. To this end, the inverter 4 is electrically connected via a positive potential wire 5 and a negative potential wire 6 (as shown) Figure 1-3 As shown) or can be electrically connected to the battery 3, and can be electrically connected or electrically connected to the three-phase AC motor 2 through the phase conductors P1, P2, P3.

[0021] The inverter 4 includes a series circuit including two transistors T11, T12, T21, T22, T31, and T32 and two freewheeling diodes D11, D12, D21, D22, D31, and D32, which are electrically connected in parallel and are each electrically connected to a positive potential line 5 and a negative potential line 6. Phase conductors P1, P2, and P3 are each electrically connected to the three-phase AC motor 2 and connecting lines between a pair of transistors T11, T12, T21, T22, T31, and T32 connected in series and a pair of freewheeling diodes D11, D12, D21, D22, D31, and D32 connected in series. Transistors T11, T21, and T31, arranged on one side of the connection point of phase conductors P1, P2, and P3, and freewheeling diodes D11, D21, and D31, form what is here referred to as an upper inverter region OB. Transistors T12, T22, and T32, arranged on the other side of the connection point of phase conductors P1, P2, and P3, and freewheeling diodes D12, D22, and D32, form what is here referred to as a lower inverter region UB. The freewheeling diodes D11, D12, D21, D22, D31, and D32 each point in a conductive direction toward the positive potential line 5.

[0022] Furthermore, the positive potential line 5 and the negative potential line 6 are electrically connected to two intermediate circuit capacitors C1, C2 which are electrically connected in series and are electrically connected in parallel with respect to the inverter 4. This means that the solution described here includes the intermediate circuit capacitor being divided into two intermediate circuit capacitors C1, C2.

[0023] The neutral point 7 of the three-phase AC motor 2 is electrically connectable or electrically connected to the positive terminal 8 of the DC charging interface of the electric drive system 1 via a first switch S1 , in particular designed as a contactor, depending on whether the first switch S1 is open or closed.

[0024] The negative potential line 6 can be electrically connected to the negative terminal 9 of the DC charging interface of the electric drive system 1 via a second switch S2 , in particular designed as a contactor, depending on whether the second switch S2 is open or closed.

[0025] Furthermore, the positive terminal 8 of the DC charging interface of the electric drive system 1 can be electrically connected or electrically connected to the connecting lines of the two intermediate circuit capacitors C1 and C2 via a third switch S3, in particular designed as a contactor, depending on whether the third switch S3 is open or closed, and is therefore electrically connected to the positive potential line 5 via one of the two intermediate circuit capacitors C1 and C2, in this case via the first intermediate circuit capacitor C1, in the closed state of the third switch S3.

[0026] By means of the solution, the battery 3 can be charged via the inductors L1, L2, L3 of the three-phase AC motor 2, wherein in this case, the battery 3 can be charged not only at an off-board DC power supply (e.g., a DC voltage UDC provided corresponding to a rated voltage UBat of the battery 3, e.g., 800V) but also at an off-board DC power supply (e.g., Figure 2 As shown), it can also be charged at an off-vehicle DC power source where the DC voltage UDC provided is less than the rated voltage UBat of the battery 3 (as shown in FIG. Figure 3 ). This solution requires only a small outlay and can therefore be realized at low cost.

[0027] exist Figure 1 In Figure 1, all three switches S1, S2, and S3 are open. This switching state is advantageously always set when charging is not to occur or is not yet possible from an off-board DC power source. The open switches S1, S2, and S3 electrically isolate the positive and negative terminals 8 and 9 of the DC charging interface from the rest of the electric drive system 1, particularly the battery 3, inverter 4, and three-phase AC motor 2. This prevents the risk of human exposure to the high rated voltage UBat of the battery 3 through the DC charging interface, which could endanger human health. Even if a DC voltage UDC is already applied to the DC charging interface, for example because it is electrically connected to an off-board DC power source, battery 3 cannot be charged from the off-board DC power source if switches S1, S2, and S3 are open.

[0028] This switching state is also provided for the travel of the vehicle. During travel, the three-phase AC motor 2 is supplied with electrical energy by the battery 3 via the inverter 4.

[0029] exist Figure 2 In Figure 1, the first and second switches S1 and S2 are closed, and the third switch S3 is open. This switching state is configured for charging the battery 3 from an off-board DC power supply whose supplied DC voltage UDC corresponds to the rated voltage UBat of the battery 3, for example, 800V. With the closed first switch S1, the star point 7 is electrically connected to the positive terminal 8 of the DC charging interface and, therefore, to the positive terminal of the power supply when the off-board DC power supply is connected. With the closed second switch S2, the negative potential line 6 is electrically connected to the negative terminal 9 of the DC charging interface and, therefore, to the negative terminal of the power supply when the off-board DC power supply is connected. Therefore, when an off-board DC power supply whose supplied DC voltage UDC corresponds to the rated voltage UBat of the battery 3, for example, 800V, is connected to the DC charging interface, the star point 7 and the negative potential line 6 are electrically connected to the off-board DC power supply. Furthermore, all transistors T11, T21, and T31 in this region of the inverter 4, here, the upper region OB, are continuously turned on to directly connect the battery 3 to the off-board DC power supply. The battery 3 is thereby charged with a DC voltage UDC provided by an off-vehicle DC power supply and corresponding to the rated voltage UBat of the battery 3 .

[0030] exist Figure 3 In Figure 1, all three switches S1, S2, and S3 are closed. This switching state is intended for charging battery 3 from an off-board DC power supply whose supplied DC voltage UDC is less than the rated voltage UBat of battery 3, for example, 800V. For example, the DC voltage UDC provided by the off-board DC power supply is 400V. By closing the first switch S1, star point 7 is electrically connected to the positive terminal 8 of the DC charging interface and, therefore, to the positive terminal of the power supply when an off-board DC power supply is connected. By closing the second switch S2, the negative potential line 6 is electrically connected to the negative terminal 9 of the DC charging interface and, therefore, to the negative terminal of the power supply when an off-board DC power supply is connected. Furthermore, by closing the third switch S3, the positive terminal 8 of the DC charging interface and, therefore, to the positive terminal of the power supply when an off-board DC power supply is connected, is electrically connected to the connecting leads of the two intermediate circuit capacitors C1 and C2 and, therefore, to the positive potential line 5 via one of the two intermediate circuit capacitors C1 and C2, in this case, the first intermediate circuit capacitor C1.

[0031] Therefore, when an off-board DC power supply, whose supplied DC voltage UDC is less than the rated voltage UBat of battery 3 (e.g., 800V), is connected to the DC charging interface, star point 7 and negative potential line 6 are electrically connected to the off-board DC power supply. Positive potential line 5 is also electrically connected to the off-board DC power supply via connecting wires of the two intermediate circuit capacitors C1 and C2, and further via one of the two intermediate circuit capacitors C1 and C2, in this case, the first intermediate circuit capacitor C1. All transistors T11, T12, T21, T22, T31, and T32 of inverter 4 are operated in a pulse-width-modulated manner and, in combination with inductors L1, L2, and L3 of three-phase AC motor 2, form a voltage booster to boost the low DC voltage UDC provided by the off-board DC power supply to the voltage level of battery 3 (i.e., its rated voltage UBat (e.g., 800V). Alternatively, only the transistors T12, T22, and T32 of another region of the inverter 4, in this case the lower region UB, can be clocked, so that the current flows not through the transistors T11, T21, and T31 of the upper region OB of the inverter 4, but instead through the freewheeling diodes D11, D21, and D31 of the upper region OB of the inverter 4. Furthermore, as already explained, the intermediate circuit capacitor is designed to consist of two parts, namely, in the form of the two intermediate circuit capacitors C1 and C2. This arrangement allows the capacitor midpoint to be connected in parallel with the input of the DC voltage UDC provided by the off-board DC power supply to stabilize it. Therefore, a separate input capacitor for charging operation is not required.

[0032] Reference Signs List

[0033] 1. Drive system

[0034] 2 Three-phase AC motor

[0035] 3 Batteries

[0036] 4 Inverter

[0037] 5 Positive potential wire

[0038] 6 Negative potential wire

[0039] 7 stars

[0040] 8 Positive terminal

[0041] 9 Negative terminal

[0042] C1,C2 Intermediate circuit capacitors

[0043] D11, D12, D21, D22, D31, D32 freewheeling diodes

[0044] L1, L2, L3 inductors

[0045] OB, UB inverter area

[0046] P1, P2, P3 phase conductors

[0047] S1, S2, S3 switches

[0048] T11, T12, T21, T22, T31, T32 transistors

[0049] Rated voltage of UBat battery

[0050] UDC DC voltage of the DC power supply

Claims

1. A method for operating an electric drive system (1), the electric drive system comprising at least a three-phase AC motor (2), a battery (3) for supplying power to the three-phase AC motor (2), and an inverter (4) for electrically connecting or electrically connectable to the battery (3) the three-phase AC motor (2), wherein: The star point (7) of the three-phase AC motor (2) is electrically connected or can be electrically connected to the positive terminal (8) of the DC charging interface of the electric drive system (1). The negative potential wire (6) of the battery (3) is electrically connected or can be electrically connected to the negative terminal (9) of the DC charging interface of the electric drive system (1), and - the star point (7) of the three-phase AC motor (2) is electrically connected or can be electrically connected to the positive terminal (8) of the DC charging interface of the electric drive system (1) via a first switch (S1), - the negative potential wire (6) of the battery (3) is electrically connected or can be electrically connected to the negative terminal (9) of the DC charging interface of the electric drive system (1) via a second switch (S2), - the positive terminal (8) of the DC charging interface of the electric drive system (1) is electrically connected or can be electrically connected to a tap of the intermediate circuit capacitor (C1) via a third switch (S3) and thus electrically connected or can be electrically connected to the positive potential line (5), Its characteristics are: - if the battery (3) is not to be charged at an off-board DC power source, all three switches (S1, S2, S3) are opened, - in order to charge the battery (3) at an off-board DC power supply providing a DC voltage (UDC) corresponding to the rated voltage (UBat) of the battery (3), the first switch (S1) and the second switch (S2) are closed and the third switch (S3) is opened, In order to charge the battery (3) at an off-board DC power supply which provides a DC voltage (UDC) which is less than the rated voltage (UBat) of the battery (3), all three switches (S1, S2, S3) are closed.

2. The method according to claim 1, wherein: Two intermediate circuit capacitors (C1, C2) electrically connected in series are provided in the electric drive system (1).

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