Method for operating an electric drive system for a vehicle - Patents.com

Abstract

The invention relates to a method for operating an electric drive system (1) for a vehicle, the electric drive system having at least one three-phase electric machine (2), a battery (3) for supplying electric energy to the three-phase electric machine (2), and an inverter (4), the three-phase electric machine (2) being electrically connectable or connected to the battery (3) via the inverter (4), a neutral point (7) of the three-phase electric machine (2) is electrically connectable or connected to a positive terminal (8) of a direct current charging terminal of the electric drive system (1); The negative potential line (6) of the battery (3) is electrically connectable or connected to the negative terminal (9) of the DC charging terminals of the electric drive system (1), where: the neutral point (7) of the three-phase electric machine (2) is electrically connectable or connected to the positive terminal (8) of the DC charging terminals of the electric drive system (1) via a first switch (S1), the negative potential line (6) of the battery (3) is electrically connectable or connected to the negative terminal (9) of the DC charging terminals of the electric drive system (1) via a second switch (S2), and the positive terminal (8) of the DC charging terminals of the electric drive system (1) is electrically connectable or connected to a tap of the intermediate circuit capacitor (C1) via a third switch (S3) and further to the positive potential line (5).

Description

[Technical field]

[0001] The present invention relates to a method for operating an electric drive system for a vehicle according to the preamble of claim 1. [Background technology]

[0002] An electric drive system for a vehicle and a method for operating the drive system are known from the prior art, such as that described in DE 10 200 43 33 A1. The electric drive system comprises at least one three-phase electric machine and a battery for supplying the three-phase electric machine with electric energy. The three-phase electric machine is electrically connectable or connected to the battery via an inverter, the neutral point of the three-phase electric machine is electrically connectable or connected to the positive terminal of a direct current charging terminal of the electric drive system, and the negative pole of the battery is electrically connectable or connected to the negative terminal of the direct current charging terminal of the electric drive system. Furthermore, from DE 10 200 03 133 A1 a charging device for charging a battery of a motor vehicle designed with an electric drive motor is known, which includes an inductor and a traction inverter. In the driving mode of the motor vehicle, the traction inverter converts the direct current voltage of the battery for the electric drive motor, the inductor being used together with the traction inverter as a boost converter for the charging operation of the battery. Furthermore, a switch unit is provided in the charging device, by means of which the charging source is connected to the battery directly or via the boost converter during the charging operation. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] DE102018000488A1 [Patent Document 2] DE102018124789A1 Summary of the Invention [Problem to be solved by the invention]

[0004] The problem on which the invention is based is to provide a method for operating an electric drive system for a vehicle, which is improved over the prior art. [Means for solving the problem]

[0005] This problem is solved according to the invention by a method for operating an electric drive system for a vehicle with the features of claim 1.

[0006] Advantageous embodiments of the invention are the subject of the dependent claims.

[0007] An electric drive system for a vehicle has at least one three-phase electric machine, a battery for supplying electric energy to the three-phase electric machine, and an inverter, through which the three-phase electric machine is electrically connectable or connected to the battery, a neutral point of the three-phase electric machine is electrically connectable or connected to a positive terminal of a direct current charging terminal of the electric drive system, and a negative potential line of the battery is electrically connectable or connected to a negative terminal of the direct current charging terminal of the electric drive system.

[0008] The neutral point of the three-phase electric machine is electrically connectable or connected to a positive terminal of a DC current charging terminal of the electric drive system via a first switch, the negative potential line of the battery is electrically connectable or connected to the negative terminal of the DC current charging terminal of the electric drive system via a second switch, and the positive terminal of the DC current charging terminal of the electric drive system is electrically connectable or connected to a tap of the intermediate circuit capacitor and further to a positive potential line via a third switch.

[0009] In the method according to the invention for operating an electric drive system, when the battery is not charged by a direct current energy source external to the vehicle, all three switches are open, when the battery is charged by a direct current energy source external to the vehicle supplying a direct current voltage corresponding to the rated voltage of the battery, the first switch and the second switch are closed and the third switch is open, and when the battery is charged by a direct current energy source external to the vehicle supplying a direct current voltage lower than the rated voltage of the battery, all three switches are closed.

[0010] The above-mentioned solution allows charging of the battery via the inductors of the three-phase electric machine, both in terms of a DC energy source external to the vehicle which supplies a DC voltage corresponding to the rated voltage of the battery, for example 800 V, and also in terms of a DC energy source external to the vehicle which supplies a DC voltage lower than the rated voltage of the battery, for example 400 V. This solution requires only a minimum of effort, so that it can be implemented cost-effectively.

[0011] In order to charge the battery in a direct current energy source external to the vehicle that supplies a direct current voltage corresponding to the rated voltage of the battery, the first switch and the second switch are closed and the third switch is opened as described above. Through the closed first switch, the neutral point is electrically connected to the positive terminal of the direct current charging terminal, and therefore, when a direct current energy source external to the vehicle is connected to this positive terminal, is electrically connected to the positive pole of the direct current energy source external to the vehicle. Through the closed second switch, the negative potential line is electrically connected to the negative terminal of the direct current charging terminal, and therefore, when a direct current energy source external to the vehicle is connected to this negative terminal, is electrically connected to the negative pole of the direct current energy source external to the vehicle. Thus, when a direct current energy source external to the vehicle that supplies a direct current voltage corresponding to the rated voltage of the battery is connected to the direct current charging terminal, the neutral point and the negative potential line are electrically connected to this direct current energy source external to the vehicle. Furthermore, all the transistors in one region of the inverter, particularly the upper region, are permanently turned on, so that the battery is directly electrically connected to a direct current energy source external to the vehicle, whereby the battery is charged by a direct current voltage corresponding to the rated voltage of the battery, which is supplied from the direct current energy source external to the vehicle.

[0012] To charge the battery with a direct current energy source external to the vehicle that supplies only a DC voltage lower than the rated voltage of the battery, for example a DC voltage of 400 V, all three switches are closed, as described above. The neutral point and the negative potential line are therefore electrically connected to the DC charging terminal and thus to the external DC energy source, if such a source is connected to the DC charging terminal. All the transistors of the inverter operate in a pulse-width modulated manner and, in combination with the inductors of the three-phase electric machine, form a boost converter, by which the low DC voltage supplied by the external DC energy source is boosted to the voltage level of the battery, i.e., for example, to the rated voltage of the battery, which is 800 V. Alternatively, only the transistors of the other region of the inverter, here the lower region, can be clocked, so that the current does not flow through the transistors of the upper region of the inverter but through the flywheel diodes of the upper region of the inverter. Additionally, the intermediate circuit capacitor is preferably designed to have two parts, as described above. This arrangement allows the midpoint of the capacitor to be connected in parallel with the input of the DC voltage provided by a DC current energy source external to the vehicle, thereby stabilizing the DC voltage, so that a separate input capacitor for the charging operation is not required.

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

[0014] In the following, an embodiment of the present invention will be explained in detail with reference to the drawings. [Brief description of the drawings]

[0015] [Figure 1] 1 shows a schematic diagram of an electric drive system for a vehicle in a first circuit state. [Diagram 2] 2 illustrates a schematic of an electric drive system in a second circuit state. [Diagram 3] 2 illustrates a schematic of an electric drive system in a third circuit state. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] In all the drawings, the same reference numerals are used to designate corresponding parts.

[0017] 1 to 3 show schematic diagrams of an electric drive system 1 for a vehicle in three different circuit states.

[0018] The electric drive system 1 comprises a three-phase electric machine 2, a battery 3 for supplying electric energy to the three-phase electric machine 2, and an inverter 4, via which the three-phase electric machine 2 can be electrically connected to the battery 3 or as shown in Figures 1 to 3. For this purpose, the inverter 4 can be electrically connected to the battery 3 or as shown in Figures 1 to 3 via a positive potential line 5 and a negative potential line 6, and can be electrically connected to the three-phase electric machine 2 or as shown in Figures 1 to 3 via phase conductors P1, P2, P3.

[0019] The inverter 4 has an electrical series circuit of two transistors T11, T12, T21, T22, T31, T32 and an electrical series circuit of two flywheel diodes D11, D12, D21, D22, D31, D32, which are electrically connected in parallel with each other and are electrically connected to a positive potential line 5 and a negative potential line 6. The phase conductors P1, P2, P3 are electrically connected to the three-phase electric machine 2 and are electrically connected to the connection lines between the pairs of the electrically series-connected transistors T11, T12, T21, T22, T31, T32 and the pairs of the electrically series-connected flywheel diodes D11, D12, D21, D22, D31, D32. The transistors T11, T21, T31 and the flywheel diodes D11, D21, D31 arranged on one side of the connection points of the phase conductors P1, P2, P3 form an inverter area, here an upper inverter area OB, and the transistors T12, T22, T32 and the flywheel diodes D12, D22, D32 arranged on the other side of the connection points of the phase conductors P1, P2, P3 form an inverter area, here a lower inverter area UB. The conduction directions of the flywheel diodes D11, D12, D21, D22, D31, D32 are each directed toward the positive potential line 5.

[0020] The positive potential line 5 and the negative potential line 6 are further electrically connected to two intermediate circuit capacitors C1, C2 which are electrically connected in series, and these two intermediate circuit capacitors C1, C2 are electrically connected in parallel to the inverter 4. That is to say, the solution described here comprises an intermediate circuit capacitor which is split into two intermediate circuit capacitors C1, C2.

[0021] A neutral point 7 of the three-phase electric machine 2 is electrically connectable or connected via a first switch S1, in particular formed as a contactor, to a positive terminal 8 of a direct current charging terminal of the electric drive system 1 depending on whether the first switch S1 is open or closed.

[0022] The negative potential line 6 can be electrically connected or is connected to the negative terminal 9 of the DC charging terminal of the electric drive system 1 via a second switch S2, in particular formed as a contactor, depending on whether the second switch S2 is open or closed.

[0023] Furthermore, the positive terminal 8 of the DC current charging terminal of the electric drive system 1 can be or is electrically connectable to the connection line of the two intermediate circuit capacitors C1, C2 via a third switch S3, in particular formed 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, C2, here via the first intermediate circuit capacitor C1, when the third switch S3 is closed.

[0024] The above-described solution allows charging of the battery 3 via the inductors L1, L2, L3 of the three-phase electric machine 2, both in a direct current energy source external to the vehicle, which supplies a direct current voltage UDC corresponding to the rated voltage UBat of the battery 3, for example 800 V, as shown in figure 2, and also in a direct current energy source external to the vehicle, which supplies a direct current voltage UDC lower than the rated voltage UBat of the battery 3, as shown in figure 3. Here, this solution requires only a minimum of effort, so that it is implemented cost-effectively.

[0025] In Fig. 1, all three switches S1, S2, S3 are open. This circuit state is advantageously always provided when charging is not or has not yet been performed in a direct current energy source external to the vehicle. With the switches S1, S2, S3 open, both the positive terminal 8 and the negative terminal 9 of the direct current charging terminal are electrically isolated from the rest of the electric drive system 1, in particular the battery 3, the inverter 4 and the three-phase electric machine 2, so that there is no risk of a person coming into contact with the potentially health-threatening high rated voltage UBat of the battery 3 via the direct current charging terminal. Even if a direct current voltage UDC is already applied to the direct current charging terminal, for example because the direct current charging terminal is already electrically connected to a direct current energy source external to the vehicle, charging of the battery 3 with a direct current energy source external to the vehicle does not yet take place when the switches S1, S2, S3 are open.

[0026] This circuit state is also provided for driving operation of the vehicle. During driving operation, the three-phase electric machine 2 is supplied with electrical energy from the battery 3 via an inverter 4.

[0027] In Fig. 2, the first switch S1 and the second switch S2 are closed, and the third switch S3 is open. This circuit state is provided for charging the battery 3 with a direct current energy source external to the vehicle, which supplies a direct current voltage UDC corresponding to a rated voltage UBat of the battery 3, for example, 800V. Via the closed first switch S1, the neutral point 7 is electrically connected to the positive terminal 8 of the direct current charging terminal, and thus, when a direct current energy source external to the vehicle is connected to this positive terminal 8, is electrically connected to the positive pole of the direct current energy source external to the vehicle. Via the closed second switch S2, the negative potential line 6 is electrically connected to the negative terminal 9 of the direct current charging terminal, and thus, when a direct current energy source external to the vehicle is connected to this negative terminal 9, is electrically connected to the negative pole of the direct current energy source external to the vehicle. Therefore, when a DC current energy source outside the vehicle that supplies a DC voltage UDC corresponding to the rated voltage UBat of the battery 3 of, for example, 800 V is connected to the DC current charging terminal, the neutral point 7 and the negative potential line 6 are electrically connected to this DC current energy source outside the vehicle. Furthermore, all the transistors T11, T21, and T31 in one region of the inverter 4, here the upper region OB, are permanently turned on, so that the battery 3 is directly electrically connected to the DC current energy source outside the vehicle. As a result, the battery 3 is charged by the DC voltage UDC corresponding to the rated voltage UBat of the battery 3 that is supplied from the DC current energy source outside the vehicle.

[0028] In FIG. 3, all three switches S1, S2, and S3 are closed. This circuit state is provided for charging the battery 3 in a DC current energy source outside the vehicle that supplies a DC voltage UDC lower than the rated voltage UBat of the battery 3, for example, 800 V. For example, the DC voltage UDC supplied from the DC current energy source outside the vehicle is 400 V. Through the closed first switch S1, the neutral point 7 is electrically connected to the positive terminal 8 of the DC current charging terminal, and therefore, when a DC current energy source outside the vehicle is connected to this positive terminal 8, it is electrically connected to the positive pole of the DC current energy source outside the vehicle. Through the closed second switch S2, the negative potential line 6 is electrically connected to the negative terminal 9 of the DC current charging terminal, and therefore, when a DC current energy source outside the vehicle is connected to this negative terminal 9, it is electrically connected to the negative pole of the DC current energy source outside the vehicle. Additionally, via the closed third switch S3, the positive terminal 8 of the DC charging terminal and thus, in the case where a DC current energy source external to the vehicle is connected to this positive terminal 8, the positive pole of the DC current energy source external to the vehicle is electrically connected to the connecting line of the two intermediate circuit capacitors C1, C2 and thus electrically connected to the positive potential line 5 via one of the two intermediate circuit capacitors C1, C2, here the first intermediate circuit capacitor C1.

[0029] Thus, if the DC charging terminals are connected to a DC energy source external to the vehicle, which supplies a DC voltage UDC lower than the rated voltage UBat of the battery 3, for example 800 V, the neutral point 7 and the negative potential line 6 are electrically connected to this DC energy source external to the vehicle and additionally the positive potential line 5 is electrically connected to this DC energy source external to the vehicle via the connection lines of the two intermediate circuit capacitors C1, C2 and thus one of the two intermediate circuit capacitors C1, C2, here the first intermediate circuit capacitor C1. All transistors T11, T12, T21, T22, T31, T32 of the inverter 4 operate in pulse width modulation and form a boost converter in combination with the inductors L1, L2, L3 of the three-phase electric machine 2, by means of which the low DC voltage UDC supplied by the DC energy source external to the vehicle is boosted to the voltage level of the battery 3, i.e. for example to the rated voltage UBat of the battery 3, for example 800 V. Alternatively, it is also possible to clock only the transistors T12, T22, T32 of the other region of the inverter 4, here the lower region UB, so that the current does not flow through the transistors T11, T21, T31 of the upper region OB of the inverter 4, but through the flywheel diodes D11, D21, D31 of the upper region OB of the inverter 4. In addition, the intermediate circuit capacitor is designed as described above to have two parts in the form of two intermediate circuit capacitors C1, C2. With this arrangement, the midpoint of the capacitor can be connected in parallel to the input of the direct current voltage UDC, which is supplied from a direct current energy source external to the vehicle, so that the direct current voltage UDC is stabilized. A separate input capacitor for the charging operation is therefore not required. [Explanation of symbols]

[0030] 1. Drive system 2 three phase machine 3 Battery 4 Inverter 5 Positive potential line 6 Negative potential line 7 Neutral point 8 Positive terminal 9 Negative terminal C1, C2 Intermediate circuit capacitors D11, D12, D21, D22, D31, D32 Flywheel diodes L1, L2, L3 Inductors OB, UB inverter area P1, P2, P3 phase conductors S1, S2, S3, S4 Switches T11, T12, T21, T22, T31, T32 transistors UBat Battery Rated Voltage UDC DC voltage of DC current energy source

Claims

1. A method for operating an electric drive system (1), comprising: The system comprises at least one three-phase electric machine (2), a battery (3) for supplying electric energy to the three-phase electric machine (2), and an inverter (4), the three-phase electric machine (2) being electrically connectable or connected to the battery (3) via the inverter (4), a neutral point (7) of the three-phase electric machine (2) is electrically connectable or connected to a positive terminal (8) of a direct current charging terminal of the electric drive system (1); a negative potential line (6) of the battery (3) is electrically connectable or connected to a negative terminal (9) of the DC charging terminal of the electric drive system (1); the neutral point (7) of the three-phase electric machine (2) is electrically connectable or connected to the positive terminal (8) of the DC charging terminal of the electric drive system (1) via a first switch (S1); the negative potential line (6) of the battery (3) is electrically connectable or connected to the negative terminal (9) of the DC charging terminal of the electric drive system (1) via a second switch (S2); the positive terminal (8) of the DC charging terminal of the electric drive system (1) is electrically connectable or connected to a tap of an intermediate circuit capacitor (C1) and further to a positive potential line (5) via a third switch (S3), all three switches (S1, S2, S3) are open when the battery (3) is not being charged by a direct current energy source external to the vehicle; when charging the battery (3) by a direct current energy source external to the vehicle providing a direct current 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; the method, characterized in that all three of the switches (S1, S2, S3) are closed when the battery (3) is charged by a direct current energy source external to the vehicle supplying a direct current voltage (UDC) lower than the rated voltage (UBat) of the battery (3).

2. 2. The method according to claim 1, characterized in that in the electric drive system (1), two intermediate circuit capacitors C1, C2 are provided which are connected in series.

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