METHOD FOR OPERATING AN ELECTRIC DRIVE SYSTEM FOR A VEHICLE

Description

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

[0002] As described in DE 10 2018 000 488 A1, an electric drive system for a vehicle and a method for operating the same are known from the prior art. The electric drive system comprises at least one three-phase electric machine and a battery for supplying electrical energy to the three-phase electric machine. The three-phase electric machine is electrically coupled or can be electrically coupled to the battery via an inverter, wherein a star point of the three-phase electric machine is electrically coupled or can be electrically coupled to a positive terminal of a direct current charging port of the electric drive system, and a negative terminal of the battery is electrically coupled or can be electrically coupled to a negative terminal of the direct current charging port 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 equipped with an electric drive motor, comprising an inductor and a drive converter. During drive operation of the motor vehicle, the drive converter converts the DC voltage of the battery for the electric drive motor, whereby the inductor, together with the drive converter, serves as a boost converter for charging the battery. Furthermore, a switching unit is provided in the charging device to connect a charge source to the battery directly or via the boost converter during charging.

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

[0005] The object is achieved according to the invention by a method for operating an electric drive system for a vehicle having the features of claim 1.

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

[0007] An electric drive system for a vehicle has at least one three-phase electric machine, a battery for supplying electrical energy to the three-phase electric machine, and an inverter via which the three-phase electric machine is or can be electrically coupled to the battery, wherein a star point of the three-phase electric machine is or can be electrically coupled to a positive pole connection of a direct current charging connection of the electric drive system, and a negative potential line of the battery is or can be electrically coupled to a negative pole connection of the direct current charging connection of the electric drive system.

[0008] The star point of the three-phase electric machine can be or is electrically coupled to the positive pole connection of the direct current charging connection of the electric drive system via a first switch, the negative potential line of the battery can be or is electrically coupled to the negative pole connection of the direct current charging connection of the electric drive system via a second switch and the positive pole connection of the direct current charging connection of the electric drive system can be or is electrically coupled to a tap of an intermediate circuit capacitor and thus to the positive potential line via a third switch.

[0009] In the method according to the invention for operating the electric drive system, if the battery is not to be charged from a vehicle-external DC energy source, all three switches are opened; to charge the battery from a vehicle-external DC energy source whose provided DC voltage corresponds to a nominal voltage of the battery, the first switch and the second switch are closed and the third switch is opened; and to charge the battery from a vehicle-external DC energy source whose provided DC voltage is lower than the nominal voltage of the battery, all three switches are closed.

[0010] The described solution enables charging of the battery via inductances of the three-phase electric machine, whereby it is possible to charge the battery both from a vehicle-external DC energy source whose provided DC voltage corresponds to a nominal battery voltage of, for example, 800 V, and from a vehicle-external DC energy source whose provided DC voltage is lower than the nominal battery voltage of, for example, 800 V, for example, only 400 V. This solution requires only minimal effort, making it cost-effective to implement.

[0011] To charge the battery from an external DC power source whose supplied DC voltage corresponds to the nominal voltage of the battery, the first and second switches are closed, as described above, and the third switch is opened. The first switch is closed, electrically coupling the star point to the positive terminal of the DC charging port and thus, if a vehicle-external DC power source is connected to it, to its positive terminal. The second switch is closed, electrically coupling the negative potential line to the negative terminal of the DC charging port and thus, if a vehicle-external DC power source is connected to it, to its negative terminal.When an external DC power source is connected to the DC charging port, whose DC voltage corresponds to the nominal voltage of the battery, the star point and the negative potential line are electrically coupled to this external DC power source. In addition, all transistors in a section, particularly an upper section, of the inverter are permanently switched on to electrically couple the battery directly to the external DC power source. This charges the battery with the DC voltage provided by the external DC power source, which corresponds to the nominal voltage of the battery.

[0012] To charge the battery from an external DC power source whose supplied DC voltage is lower than the nominal voltage of the battery, for example, only 400 V, all three switches are closed as described above. This means that the star point and the negative potential line are electrically coupled to the DC charging connection and, if a vehicle-external DC power source is connected to it, to the DC charging connection. All transistors of the inverter are operated with pulse width modulation and, in combination with the inductors of the three-phase electric machine, form a boost converter to increase the low DC voltage supplied by the vehicle-external DC power source to the voltage level of the battery, i.e., to its nominal voltage of 800 V, for example.Alternatively, only the transistors of the other section, particularly a lower section, of the inverter can be clocked, so that current flows not through the transistors of the upper section of the inverter, but rather through freewheeling diodes of the upper section of the inverter. In addition, the intermediate circuit capacitor, as described above, is advantageously designed in two parts. This arrangement allows the center point of the capacitor to be connected in parallel to the input of the DC voltage provided by the vehicle's external DC power source in order to stabilize it. A separate input capacitor for charging operation is therefore not required.

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

[0014] Embodiments of the invention are explained in more detail below with reference to drawings.

[0015] Showing: Fig. 1 schematically shows an electric drive system for a vehicle in a first switching state, Fig. 2 schematically shows the electric drive system in a second switching state, and Fig. 3 schematically shows the electric drive system in a third switching state.

[0016] Corresponding parts are provided with the same reference numerals in all figures.

[0017] The Figures 1 to 3 show schematic representations of an electric drive system 1 for a vehicle in three different switching states.

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

[0019] The inverter 4 comprises electrical series circuits of two transistors T11, T12, T21, T22, T31, T32 and two

[0020] Freewheeling diodes D11, D12, D21, D22, D31, D32 are electrically connected in parallel to one another and are each electrically coupled to the positive potential line 5 and the negative potential line 6. The phase conductors P1, P2, P3 are each electrically coupled to the three-phase electric machine 2 and a connecting line between a pair of the electrically series-connected transistors T11, T12, T21, T22, T31, T32 and the electrically series-connected freewheeling diodes D11, D12, D21, D22, D31, D32. The transistors T11, T21, T31 and freewheeling diodes D11, D21, D31 arranged on one side of these coupling points of the phase conductors P1, P2, P3 form an, here upper, inverter area OB and the transistors T12, T22, T32 and freewheeling diodes D12, D22, D32 arranged on the other side of these coupling points of the phase conductors P1, P2, P3 form an, here lower, inverter area UB.A forward direction of the freewheeling diodes D11, D12, D21, D22, D31, D32 is each aligned in the direction of the positive potential line 5.

[0021] The positive potential line 5 and the negative potential line 6 are also electrically coupled to two intermediate circuit capacitors C1, C2 connected in series, which are electrically connected in parallel to the inverter 4. This means that the solution described here comprises an intermediate circuit capacitor divided into two intermediate circuit capacitors C1, C2.

[0022] A star point 7 of the three-phase electric machine 2 can be or is electrically coupled to a positive pole connection 8 of a direct current charging connection of the electric drive system 1 via a first switch S1 designed as a contactor, depending on whether the first switch S1 is open or closed.

[0023] The negative potential line 6 can be or is electrically coupled to a negative pole connection 9 of the DC charging connection of the electric drive system 1 via a second switch S2 designed as a contactor, depending on whether the second switch S2 is open or closed.

[0024] The positive pole connection 8 of the DC charging connection of the electric drive system 1 is also electrically coupled or can be electrically coupled to a connecting line of the two intermediate circuit capacitors C1, C2 via a third switch S3 designed as a contactor, depending on whether the third switch S3 is open or closed, and thus, in the closed state of the third switch S3, is electrically coupled to the positive potential line 5 via one of the two intermediate circuit capacitors C1, C2, here via the first intermediate circuit capacitor C1.

[0025] The described solution enables charging of the battery 3 via inductances L1, L2, L3 of the three-phase electric machine 2, whereby it is possible to charge the battery 3 both from a vehicle-external DC energy source, the DC voltage UDC of which corresponds to a nominal voltage UBat of the battery 3 of, for example, 800 V, as in Figure 2 shown, as well as to charge it from a vehicle-external DC energy source whose provided DC voltage UDC is lower than the nominal voltage UBat of battery 3, as shown in Figure 3 This solution requires minimal effort, making it cost-effective to implement.

[0026] In Figure 1All three switches S1, S2, and S3 are open. This switching state is advantageously always provided when no charging is to take place or has not yet been carried out using a DC energy source external to the vehicle. With switches S1, S2, and S3 open, both the positive terminal 8 and the negative terminal 9 of the DC charging connection are electrically decoupled from the rest of the electric drive system 1, in particular from the battery 3, the inverter 4, and the three-phase electric machine 2, so that there is no danger of a person coming into contact with the high and therefore hazardous nominal voltage UBat of the battery 3 via the DC charging connection.If a DC voltage UDC is already present at the DC charging connection, for example because it is already electrically coupled to the vehicle-external DC energy source, battery 3 will not be charged using the vehicle-external DC energy source when switches S1, S2, S3 are open.

[0027] This switching state is also intended for driving the vehicle. During driving, the three-phase electric motor 2 is supplied with electrical energy from the battery 3 via the inverter 4.

[0028] In Figure 2the first switch S1 and the second switch S2 are closed and the third switch S3 is open. This switching state is intended for charging the battery 3 from a vehicle-external direct current energy source whose provided direct voltage UDC corresponds to the nominal voltage UBat of the battery 3 of, for example, 800 V. Via the closed first switch S1, the star point 7 is electrically coupled to the positive pole connection 8 of the direct current charging connection and thus, if a vehicle-external direct current energy source is connected to it, to its positive pole. Via the closed second switch S2, the negative potential line 6 is electrically coupled to the negative pole connection 9 of the direct current charging connection and thus, if a vehicle-external direct current energy source is connected to it, to its negative pole.When a vehicle-external DC power source is connected to the DC charging port, the DC voltage UDC of which corresponds to the nominal voltage UBat of battery 3, for example, 800 V, the star point 7 and the negative potential line 6 are electrically coupled to this vehicle-external DC power source. Additionally, all transistors T11, T21, and T31 of one section, here the upper section OB, of inverter 4 are permanently switched on to electrically couple battery 3 directly to the vehicle-external DC power source. As a result, battery 3 is charged with the DC voltage UDC provided by the vehicle-external DC power source, which corresponds to the nominal voltage UBat of battery 3.

[0029] In Figure 3all three switches S1, S2, S3 are closed. This switching state is intended for charging the battery 3 from a vehicle-external direct current energy source whose provided direct voltage UDC is lower than the nominal voltage UBat of the battery 3 of, for example, 800 V. For example, the direct voltage UDC provided by the vehicle-external direct current energy source is 400 V. Via the closed first switch S1, the star point 7 is electrically coupled to the positive pole connection 8 of the direct current charging connection and thus, if a vehicle-external direct current energy source is connected to it, to its positive pole. Via the closed second switch S2, the negative potential line 6 is electrically coupled to the negative pole connection 9 of the direct current charging connection and thus, if a vehicle-external direct current energy source is connected to it, to its negative pole.In addition, the positive pole connection 8 of the DC charging connection and thus, when a vehicle-external DC energy source is connected to it, its positive pole is electrically coupled to the connecting line of the two intermediate circuit capacitors C1, C2 and thus via one of the two intermediate circuit capacitors C1, C2, here via the first intermediate circuit capacitor C1, to the positive potential line 5 via the closed third switch S3.

[0030] When a vehicle-external DC energy source is connected to the DC charging connection, the DC voltage UDC of which is less than the nominal voltage UBat of the battery 3 of, for example, 800 V, the star point 7 and the negative potential line 6 are electrically coupled to this vehicle-external DC energy source and, in addition, the connecting line of the two intermediate circuit capacitors C1, C2 and thus, via one of the two intermediate circuit capacitors C1, C2, here via the first intermediate circuit capacitor C1, the positive potential line 5 is electrically coupled to this vehicle-external DC energy source.All transistors T11, T12, T21, T22, T31, T32 of inverter 4 are operated with pulse width modulation and, in combination with the inductors L1, L2, L3 of the three-phase electric machine 2, form a boost converter to boost the low DC voltage UDC provided by the vehicle-external DC energy source to the voltage level of battery 3, i.e., to its nominal voltage UBat of, for example, 800 V. Alternatively, only the transistors T12, T22, T32 of the other section, here the lower section UB, of inverter 4 can be clocked, so that current flows not via the transistors T11, T21, T31 of the upper section OB of inverter 4, but via the freewheeling diodes D11, D21, D31 of the upper section OB of inverter 4. In addition, as already mentioned, the intermediate circuit capacitor is designed in two parts, in the form of the two intermediate circuit capacitors C1, C2.This arrangement allows the center point of the capacitor to be connected in parallel with the input of the DC voltage UDC provided by the vehicle's external DC power source to stabilize it. A separate input capacitor for charging is therefore not required. List of reference symbols

[0031] 1Drive system 2Three-phase machine 3Battery 4Inverter 5Positive potential line 6Minus potential line 7Star point 8Positive pole connection 9Minus pole connection C1, C2Intermediate circuit capacitor D11, D12, D21, D22, D31, D32Freewheeling diode L1, L2, L3Inductance OB, UBInverter section P1, P2, P3Phase conductors S1, S2, S3Switches T11, T12, T21, T22, T31, T32Transistor UBatNominal voltage of the battery UDCDirect voltage of the direct current energy source

Claims

1. A method for operating an electric drive system (1), which has at least one three-phase electric machine (2), one battery (3) for supplying electrical energy to the three-phase electric machine (2) and one inverter (4) via which the three-phase electric machine (2) is electrically coupled to the battery (3) via a positive potential line (5) and a negative potential line (6), wherein a star point (7) of the three-phase electric machine (2) can be electrically coupled to a positive pole connection (8) of a direct current charging connection of the electric drive system (1) and therefore to a direct current energy source connected thereto outside the vehicle for charging the battery (3) at the direct current energy source outside the vehicle, and the negative potential line (6) of the battery (3) can be electrically coupled to a negative pole connection (9) of the direct current charging connection of the electric drive system (1) and therefore to the direct current energy source connected thereto outside the vehicle for charging the battery (3) at the direct current energy source outside the vehicle, and - the star point (7) of the three-phase electric machine (2) can be electrically coupled to the positive pole connection (8) of the direct current charging connection of the electric drive system (1) via a first switch (S1) designed as a contactor - the negative potential line (6) of the battery (3) can be electrically coupled to the negative pole connection (9) of the direct current charging connection of the electric drive system (1) via a second switch (S2) designed as a contactor - the positive pole connection (8) of the direct current charging connection of the electric drive system (1) can be electrically coupled to a tap of an intermediate capacitor (C1) via a third switch (S3) designed as a contactor and to the positive potential line (5) via the intermediate capacitor (C1), characterized in that - if the battery (3) is not to be charged at the direct current energy source outside the vehicle, all three switches (S1, S2, S3) are open, - to charge the battery (3) at a direct current energy source outside the vehicle whose provided direct voltage (UDC) corresponds to a nominal voltage (UBat) of the battery (3), the first switch (S1) and the second switch (S2) are closed and the third switch (S3) is opened, - to charge the battery (3) from a direct current energy source outside the vehicle whose provided direct voltage (UDC) is lower than the nominal voltage (UBat) of the battery (3), all three switches (S1, S2, S3) are closed.

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