Method for charging at least one low-voltage battery by means of at least one high-voltage battery during operation of an electric vehicle

Abstract

The invention relates to a method for charging at least one low-voltage battery (14) by means of at least one high-voltage battery (16) during operation of an electric vehicle (10). At least the following steps are carried out: At least one high-voltage battery (16) is provided, which has a plurality (82) of series-connected battery cells (24), wherein each battery cell (24) supplies a single voltage value (58). A voltage tapping point (80) is arranged on the plurality (82) of the series-connected battery cells (24) in such a way that a number (84) of battery cells (24) remain below the voltage tapping point (80); and the at least one low-voltage battery (14) is connected to the voltage tapping point (80) via a charging switch (86). Thereafter, the charging of the at least one low-voltage battery (14) by the at least one high-voltage battery (16) is started by temporarily closing (90) the charging switch (86) for at least one defined period of time (96, 98), during which a minimum number (85) of battery cells (24) of the number (84) of battery cells (24) remains in a half-bridge or a full-bridge circuit (66, 72).

Description

[0001] R.416910

[0002] - 1 -

[0003] Description

[0004] title

[0005] Method for charging at least one low-voltage battery using at least one high-voltage battery during the operation of an electric vehicle

[0006] Technical field

[0007] The invention relates to a method for charging at least one low-voltage battery using at least one high-voltage battery during the operation of an electric vehicle. Furthermore, the invention relates to a battery system of an electric vehicle comprising at least one electric machine, at least one low-voltage battery, and at least one high-voltage battery, wherein the at least one high-voltage battery comprises at least one battery module with a plurality of battery cells. The invention also relates to the use of the method and the battery system in an electric vehicle with at least one low-voltage battery and at least one high-voltage battery.

[0008] State of the art

[0009] US 2022 / 0126724 A1 relates to a portable high-voltage charging system for remotely recharging an electric vehicle. The charging system comprises a housing and an array of battery cells forming a high-voltage battery located within the housing. A low-voltage battery is also located within the housing. These components can be connected to a vehicle charging station via a coupling arrangement, a cable, and a vehicle adapter. A switch arrangement allows the low-voltage battery to be charged, configured to be electrically connected to the high-voltage battery using the cable. This occurs in a first state, while discharge is possible in a second state. R.416910

[0010] - 2 -

[0011] US 2013 / 0154352 A1 relates to a system for disconnecting a high-voltage power source from the electrical system of an electric vehicle, employing at least one electrical connector. The high-voltage power source is electrically connected to the vehicle's electrical system when the electrical connector is in a closed state and is not electrically connected to the vehicle's electrical system when the electrical connector is in an open state. An additional system is provided that displays collision data supplied by a variety of impact sensors and emits an activation signal in response to displayed collision data.Finally, a pyrotechnic switch is provided which, in a pre-activated first state, forms a conductive path that allows the high-voltage source to be electrically connected to the vehicle's electrical system, and in a second state, disconnects the conductive path and prevents the high-voltage source from being connected to the vehicle's electrical system.

[0012] Disclosure of the invention

[0013] According to the invention, a method for charging at least one low-voltage battery using at least one high-voltage battery during the operation of an electric vehicle is proposed, comprising at least the following method steps:

[0014] a) Providing the at least one high-voltage battery comprising a plurality of battery cells connected in series, each battery cell representing an individual voltage value,

[0015] b) Arranging a voltage tap point on the majority of the battery cells connected in series such that a number of the battery cells remain below the voltage tap point,

[0016] c) Connecting at least one low-voltage battery to the voltage tap point via a charging switch,

[0017] d) Starting the charging of the at least one low-voltage battery by the at least one high-voltage battery by temporarily closing the charging switch for at least a defined period of time, during which a minimum number of battery cells remain in a half-bridge or full-bridge circuit, equal to the number of battery cells according to step b). R.416910

[0018] - 3 -

[0019] The solution according to the invention can provide a configuration in which a DC / DC circuit can be replaced by a simple switch, in this case the charging switch, using individual battery cell control. This enables a cost-effective downstream circuit for the at least one low-voltage battery.

[0020] In an advantageous further development of the method proposed according to the invention, the at least one defined time period represents at least one recharging window, during which a voltage is kept stable at a charging voltage level of the at least one low-voltage battery at the voltage tap point.

[0021] In an advantageous further development, the method proposed according to the invention provides that the charging voltage level of the at least one low-voltage battery depends on the number of battery cells that remain below the voltage tap point.

[0022] In the method proposed according to the invention, the charging voltage level of the at least one low-voltage battery is applied to the at least one low-voltage battery when the charging switch is closed.

[0023] In the method proposed according to the invention, it is further provided that the majority of battery cells installed in battery modules each provide an individual voltage between 8 V and 2 V, preferably between 6 V and 3 V and particularly preferably between 5 V and 4 V.

[0024] In an advantageous further development of the method proposed according to the invention, a charging voltage level of 48 V for the at least one low-voltage battery is achieved by having a first switch closed on 12 battery cells in the half-bridge circuit and a second switch closed on the remaining eight battery cells. In a full-bridge circuit, 12 battery cells must be connected by placing diagonally arranged switches, and the remaining eight must be switched off by placing two switches arranged one above the other.

[0025] Furthermore, in the method proposed according to the invention, a charging voltage level of 12 V can be achieved for the at least one low-voltage battery by connecting a first R.416910 to three battery cells in the half-bridge circuit.

[0026] - 4 -

[0027] The switch is closed, and a second switch is closed on the remaining 17 battery cells.

[0028] In a full bridge circuit, three battery cells would have to be switched on by setting diagonally arranged switches, and the remaining 17 would have to be switched off by setting two switches arranged one above the other.

[0029] In an advantageous further development of the method proposed according to the invention, it is provided that the respective battery cells are varied or rotated from the number of battery cells below the voltage tap point, which represent the charging voltage level of the at least one low-voltage battery, in order to ensure a symmetrization of the load on the battery cells.

[0030] In the method proposed according to the invention, it is further provided that during the period during which the charging switch remains in the open state, either the output voltage is below 48 V or is so high that the eight or 17 battery cells respectively cannot be dispensed with.

[0031] In an advantageous further development of the method proposed according to the invention, it is also provided that the battery cells below the voltage tap point are designed with a higher capacity than those battery cells above the voltage tap point.

[0032] In the method proposed according to the invention, it is further provided that, in a three-phase voltage system, the charging switch performs a time-staggered charging of the at least one low-voltage battery via different phases.

[0033] Furthermore, the invention relates to a battery system of an electric vehicle comprising at least one electric motor, at least one low-voltage battery, and at least one high-voltage battery, wherein the at least one high-voltage battery comprises at least one battery module with a plurality of battery cells. A voltage tap and a charging switch are arranged such that a number of battery cells are separated from the plurality of battery cells and charged to a level corresponding to the charging voltage of the at least one low-voltage battery. R.416910

[0034] - 5 -

[0035] Finally, the invention relates to the use of the method and the battery system in an electric vehicle with at least one low-voltage battery and at least one high-voltage battery.

[0036] Advantages of the invention

[0037] The solution proposed according to the invention allows for a configuration in which a DC / DC circuit is replaced by a simple switch, namely the charging switch, and charging can be carried out by individual battery cell control. The solution proposed according to the invention eliminates the need for a DC / DC converter. A relatively inexpensive recharging circuit can be configured, which allows the charging of the at least one low-voltage battery via the at least one high-voltage battery during the operation of the electric vehicle.

[0038] Batteries with individually switchable cells offer the possibility of integrating inverter and charging functions into the battery. Furthermore, this technology offers the advantage of deactivating individual, defective cells, thus maintaining functionality even when individual cells are selected.

[0039] Furthermore, the solution proposed according to the invention provides a method that enables a highly symmetrical loading of the switchable battery cells. This prevents the battery cells from drifting apart in their properties and exhibiting inconsistent aging behavior.

[0040] Brief description of the drawings

[0041] Embodiments of the invention are explained in more detail with reference to the drawings and the following description.

[0042] It shows: R.416910

[0043] - 6 -

[0044] Figure 1 shows a variant of a high-voltage battery connection in a delta configuration.

[0045] Figure 2 shows a stepped voltage curve contrasted with a quarter sine wave,

[0046] Figure 3 shows a single-cell interconnection using a half-bridge or a full bridge.

[0047] Figure 4 shows a structure of a battery module of a high-voltage battery, wherein the battery module comprises 80 battery cells, with a voltage tap point arranged, for example, between the 20th and 21st battery cell.

[0048] Figure 5 shows a stress distribution according to the invention,

[0049] Figure 6 shows a low-voltage battery with, for example, 12 battery cells and changeover switches between three battery modules, for example, containing 80 battery cells, of a high-voltage battery and

[0050] Figure 7 shows a charging configuration.

[0051] Embodiments of the invention

[0052] In the following description of embodiments of the invention, identical or similar elements are designated by the same reference numerals, and repeated descriptions of these elements are omitted in individual cases. The figures represent the subject matter of the invention only schematically.

[0053] Figure 1 shows a variant of a high-voltage battery connection in a delta configuration.

[0054] As can be seen from the representation in Figure 1, an electric vehicle 10, shown schematically here, comprises at least one electric machine 12. Furthermore, the electric vehicle 10 comprises at least one low-voltage battery 14 and at least one high-voltage battery 16. This can, for example, be an R.416910

[0055] - 7 -

[0056] The battery modules 18, 20, and 22 are connected in a triangle and comprise a first battery module 18, a second battery module 20, and a third battery module 22. Each of these battery modules 18, 20, and 22 includes a number of rechargeable battery cells 24. In the illustrated embodiment, the battery modules 18, 20, and 22 each comprise, for example, 30 battery cells 24. The individual battery modules 18, 20, and 22 could, of course, also comprise a larger or smaller number of rechargeable battery cells 24.

[0057] Furthermore, the illustration in Figure 1 shows that the at least one high-voltage battery 16 can be charged with a charging voltage 26. This can be, for example, 400 V, 800 V or 960 V.

[0058] The battery modules 18, 20, 22, connected in a delta configuration 34, are such that a voltage U 28 is applied along the first battery module 18, a voltage V 30 along the second battery module 20, and a voltage W 32 along the third battery module 22. The aforementioned battery modules 18, 20, 22 are connected in a delta configuration 34, which has a node L1 36, a node L2 38, and a node L3 40.

[0059] The schematic representation in Figure 1 further shows that the electric vehicle 10 comprises at least one electric machine 12, which is electrically connected, for example, by means of a three-phase supply line 42 to at least one high-voltage battery 16, also referred to as a traction battery. The electric machine 12 is driven via the three phases of the three-phase supply line 42, as shown in Figure 1.

[0060] The representation according to Figure 2 shows a step-shaped voltage curve of a quarter sine wave when the battery cells are individually controlled.

[0061] The representation in Figure 2 shows that along the step function 50, individual battery cells 24 each have a single-cell voltage 58 of approximately 4 V. Of course, other single-cell voltage values ​​58, such as 3 V, 5 V, or 6 V, would also be possible. The step function 50 represents a quarter-sine wave 52. A voltage profile 54 is plotted against a time axis 56. In the representation in Figure 2, the quarter-sine wave 52 has an amplitude of 100.

[0062] - 8 -

[0063] As shown in Figure 3, a rechargeable battery cell 24 can be connected via a half-bridge 66 or alternatively via a full bridge 72. The individual connections 60 of the rechargeable battery cell 24 according to Figure 3 show that, in the case of the individual cell connection 60 as a half-bridge circuit 66, a first switch 62 and a second switch 64 connected in parallel to it are used.

[0064] In contrast, the single-cell circuit 60, configured as a full-bridge circuit 72, uses a total of four switches: the first switch 62, the second switch 64, the third switch 68, and the fourth switch 70. In the given single-cell circuits 60 as shown in Figure 3, the full-bridge circuit 72 offers the advantage over the half-bridge circuit 66 that an inverted polarity can also be switched via the full-bridge circuit 72.

[0065] The illustration in Figure 4 shows a structure according to the invention of one of the battery modules 18, 20, 22, as schematically indicated in Figure 1.

[0066] As shown in Figure 4, in this embodiment a battery module 18, 20, 22 contains a plurality 82 of battery cells 24. The plurality 82 of battery cells 24 can, for example, be 80, as indicated in Figure 4.

[0067] Between the 20th and 21st rechargeable battery cells 24, a voltage tap 80 is provided, as shown in Figure 4. A charging switch 86 is located in the tap line, which is shown in an open state 88 in Figure 4. The line extending from the voltage tap 80, in which the charging switch 86 is arranged, leads to a low-voltage battery 14, which in this case is a 48 V battery. Above the voltage tap 80, the plurality 82 of battery cells 24 comprise the rechargeable battery cells 21 to 80. Below the voltage tap point 80, however, the majority 82 of battery cells 24 comprises a number 84 of battery cells 24 or rechargeable battery cells 1 to 20. Provided that the individual cell voltage 58 of each of the battery cells 24 1R.416910

[0068] - 9 -

[0069] Up to 204 volts, 20 rechargeable battery cells 24, according to the number 84 of battery cells 24, provide the voltage of at least one low-voltage battery 14, namely 48 V. In an alternative embodiment, not shown in the drawing, for example, the rechargeable battery cells 241 to 4 represent a minimum number 85 of rechargeable battery cells 24, which could, for example, provide the voltage of a 12-volt low-voltage battery 14 of an electric vehicle 10. The number 84 of battery cells 24 located below the voltage tap point 80 is therefore dependent on the charging voltage of the low-voltage battery 14 to be charged. Furthermore, the total voltage UHV and the maximum voltage required in the battery system also influence the optimal position of the voltage tap point 80. Accordingly, the selection of 20 battery cells 24 below the voltage tap point 80 in this context is to be understood as exemplary.

[0070] Figure 5 shows a voltage curve that can be used to recharge at least one low-voltage battery 14 via at least one high-voltage battery 16 with individual cell control. The illustration in Figure 5 shows that with a current corresponding to a full sine wave 92, as shown in Figure 5, the charging switch 86 initially assumes its open state 88. As soon as the charging switch 86 transitions from its open state 88 to a closed state 90, a stable voltage of 48 volts is established at the voltage tap point 80 – as shown in Figure 4 – for a temporary period, for example, during a first recharging window 96 of the closing period 100.The voltage required to charge the 48-volt low-voltage battery 14 shown in Figure 4 is obtained in this case – assuming the rechargeable battery cells 24 supply a single-cell voltage 58 of 4 volts – whenever 12 of the rechargeable battery cells 24 below the voltage tap point 80 are actively connected. "Actively connected" in this context means that, for example, the first switch 62 is closed on 12 battery cells 24 connected in series below the voltage tap point 80 – assuming a half-bridge circuit 66 is present – ​​and the second switch 64 is closed on the remaining eight rechargeable battery cells 24 (84 total) below the voltage tap point 80.This switching state is kept constant for a specific period of time, namely during the first reload window 96 or the closing period 100, as shown in Figure 5. In this way, R.416910.

[0071] - 10 -

[0072] the first recharging window 96 for the at least one low-voltage battery 14 as shown in Figure 4 is generated

[0073] As soon as the charging switch 86 is closed, in addition to the low-voltage battery 14 being connected to the electric machine 12, a recharge from the rechargeable battery cells 24 below the voltage tap point 80 will also take place in parallel, in the direction of the battery 14, which is shown here as a 48 V low-voltage battery. The necessary overall voltage change is thus achieved by connecting further cells between the rechargeable battery cell 21 and the rechargeable battery cell 24 at position 80. After the closing period 100 has elapsed and towards the end of the first recharge window 96, the charging switch 86 returns to its open state 88. The voltage curve 94, shown here as a dotted line and semicircle in Figure 5, is thus established within the opening period 102 between the end of the first recharge window 96 and the beginning of a second recharge window 98.At the beginning of the second charging window 98, the charging switch 86 is transferred from its open state 88 back to the closed state 90, resulting in the second charging window 98, during the duration of which, i.e., during the duration of the closing period 100 of the charging switch 86, the charging voltage level of essentially 48 volts is again stabilized.

[0074] Towards the end of the second charging window 98, the charging switch 86 is opened again and the charging of the at least one low-voltage battery 14, for example designed as a 48 V low-voltage battery 14, is terminated.

[0075] It should be noted that, for example, the 12 actively connected rechargeable battery cells 24 mentioned here, each having a single-cell voltage 58 of 4 volts and arranged below the voltage tap point 80, can be varied or rotated to achieve a symmetrization of the load on the rechargeable battery cells 24 within the battery modules 18, 20, 22. Rechargeable battery cells 24, which, in addition to recharging the at least one low-voltage battery 14, also contribute to controlling the electric machine 12 of the electric vehicle 10, are subjected to a higher load during this period than those of the rechargeable battery cells 24 located above the voltage tap point R.416910.

[0076] - 11 -

[0077] 80 are located, in the present example (see Figure 4) the rechargeable battery cells 24 21 to 80.

[0078] During the time windows in which the charging switch 86 is open, i.e., in its open state 88, the rechargeable battery cells 24 from the plurality 82 of battery cells 24 are preferably used to achieve a uniform electrical load on the battery cells 24. Alternatively, the 20 battery cells 24, namely the number 84 of battery cells located below the voltage tap point 80, can also be designed with a higher capacity than the rechargeable battery cells 2421 to 2422. This also allows the state of charge to be kept essentially constant even with uneven current loads. Of course, it is also possible to arrange the voltage tap point 80 differently than shown in Figure 4, namely between the rechargeable battery cell 2420 and the rechargeable battery cell 2421.It is helpful to choose a plurality 82 of battery cells 24 where a rotation principle is possible during recharging. This means that a number of 12 or more rechargeable battery cells 24 should be arranged below the voltage tap point 80. Furthermore, it is preferred not to choose the number of rechargeable battery cells 24 too high in order to maintain a sufficiently wide window for recharging in all possible operating conditions.

[0079] As shown in Figure 6, a low-voltage battery 14, for example, has 12 battery cells 24. A changeover switch 110 is provided between the first battery module 18, the second battery module 20, and the third battery module 22 of the high-voltage battery 16 of the electric vehicle 10, as shown here. Each of the battery modules 18, 20, 22 comprises a plurality 82 of battery cells 24, exactly 80 in total. By means of the changeover switch 110, each of the battery modules 18, 20, 22 can be used to recharge the at least one low-voltage battery 14.

[0080] The representation according to Figure 7 schematically shows that the batteries of the electric vehicle 10 are connected in series 116, namely the at least one low-voltage battery 14 and the three first, second and third battery modules 18, 20, 22 connected in series, each of which 80R.416910

[0081] - 12 -

[0082] have rechargeable battery cells 24 and which constitute at least one high-voltage battery 16, and can be connected to a power supply network 114 for charging via a charging port 112.

[0083] In the event that a three-phase system with a three-phase supply line 42 is used to supply the at least one electric machine 12 of the electric vehicle 10, it can be provided that the charging switch 86 includes three separate sub-switches, which allows for staggered recharging of the at least one low-voltage battery 14 from three different phases.

[0084] The invention is not limited to the embodiments described here and the aspects highlighted therein. Rather, within the scope specified by the claims, a multitude of modifications are possible that fall within the bounds of what is considered skilled in the art.

Claims

R.416910 - 13 - Claims 1. Method for charging at least one low-voltage battery (14) using at least one high-voltage battery (16) during the operation of an electric vehicle (10) comprising at least the following method steps: a) Providing the at least one high-voltage battery (16) comprising a plurality (82) of battery cells (24) connected in series, each battery cell (24) representing an individual voltage value (58), b) Arranging a voltage tap point (80) on the plurality (82) of the battery cells (24) connected in series such that a number (84) of the battery cells (24) remain below the voltage tap point (80), c) Connecting the at least one low-voltage battery (14) to the voltage tap point (80) via a charging switch (86), d) Starting the charging of the at least one low-voltage battery (14) by the at least one high-voltage battery (16) by temporarily closing (90) the charging switch (86) for at least a defined period of time (96, 98), during which a minimum number (85) of battery cells (24) of the number (84) of battery cells (24) according to process step b) remains in a half-bridge or full-bridge circuit (66, 72).

2. Method according to claim 1, characterized in that the at least one defined time period represents at least one recharging window (96, 98) during which a voltage (58) is kept stable at a charging voltage level of the at least one low-voltage battery (14) at the voltage tap point (80).

3. Method according to claims 1 and 2, characterized in that the charging voltage level of the at least one low-voltage battery (14) depends on the number (84) of battery cells (24) below the voltage tap point (80). R.416910 - 14 - 4. Method according to claims 1 to 3, characterized in that the charging voltage level of the at least one low-voltage battery (14) is applied to the at least one low-voltage battery (14) in the closed state (90) of the charging switch (86).

5. Method according to claims 1 to 4, characterized in that the plurality (82) of battery cells (24) which are installed in battery modules (18, 20, 22) each provide a single voltage (58) in the range between 8 V and 2 V, preferably between 6 V and 3 V and particularly preferably between 5 V and 4 V.

6. Method according to claims 1 to 5, characterized in that a charging voltage level of 48 V of the at least one low-voltage battery (14) is represented by having a first switch (62) closed on 12 battery cells (24) in the half-bridge circuit (66) and a second switch (64) closed on the remaining eight battery cells (24).

7. Method according to claims 1 to 5, characterized in that a charging voltage level of 12 V of the at least one low-voltage battery (14) is represented by having a first switch (62) closed on three battery cells (24) in the half-bridge circuit (66) and a second switch (64) closed on the remaining 17 battery cells (24).

8. Method according to claims 1 to 7, characterized in that those battery cells (24) from the number (84) of battery cells (24) below the voltage tap point (80) which provide the charging voltage level of the at least one low-voltage battery (14) are varied or rotated to ensure a symmetrization of the load on the battery cells (24).

9. Method according to claims 1 to 8, characterized in that during the periods during which the charging switch (86) remains in the open state (88), the battery cells (24) below the voltage tap point (80) do not represent the desired charging voltage for the at least one low-voltage battery (14). R.416910 - 15 - 10. Method according to claims 1 to 9, characterized in that the number (84) of the battery cells (24) below the voltage tap point (80) are designed with a higher capacity than the battery cells (24) above the voltage tap point (80).

11. Method according to claims 1 to 10, characterized in that, in a three-phase (42) voltage system, the charging switch (86) performs a time-staggered charging of the at least one low-voltage battery (14) from different phases of the three phases (42).

12. Method according to claims 1 to 5, characterized in that a charging voltage level of 48 V of the at least one low-voltage battery (14) is represented by having a first switch (62) and a second switch (64) closed on 12 battery cells (24) in the full bridge circuit (72) and having the switches (62, 68) or (64, 70) closed on the remaining eight battery cells (24).

13. Method according to claims 1 to 5, characterized in that a charging voltage level of 12 V of the at least one low-voltage battery (14) is represented by having a first switch (62) and a second switch (64) closed on three battery cells (24) in the half-bridge circuit (66) and having the switches (62, 68) or (64, 70) closed on the remaining 17 battery cells (24).

14. Battery system of an electric vehicle (10) with at least one electric machine (12), at least one low-voltage battery (14) and at least one high-voltage battery (16), wherein the at least one high-voltage battery (16) comprises at least one battery module (18, 20, 22) with a plurality (82) of battery cells (24), characterized in that a voltage tap (80) and a charging switch (86) are arranged such that a number (84) of battery cells (24) are separated from the plurality (82) of battery cells (24) of the respective battery module (18, 20, 22), which provide a charging voltage level for the at least one low-voltage battery (14) in order to charge it accordingly. R.416910 - 16 - 15. Use of the method according to any one of claims 1 to 13 and of the battery system according to claim 14 in an electric vehicle (10) with at least one low-voltage battery (14) and at least one high-voltage battery (16).

Images