On-board electrical system with at least two battery banks and method for charging battery banks of an on-board electrical system

Abstract

The invention proposes a method for efficiently complying with safety and EMC requirements during charging processes for charging at least two battery banks (U1, U2) of an on-board network (10) of a battery-electric vehicle, wherein a charging mode is selected during a charging process for charging the battery banks (U1, U2) depending on an asymmetry of the on-board network (10), and an on-board network (10) suitable for the method.

Description

The invention relates to a method for charging at least two battery banks of an electrical system of a battery-electric vehicle. Furthermore, the invention relates to an electrical system for a battery-electric vehicle. State of the art JP 2020 - 150 784 A describes an on-board electrical system with two 400 V battery banks that can be connected in series in an 800V configuration and in parallel in a 400V configuration. EP 1 928 070 A2 refers to solar battery technology and describes a power supply using a light-voltage battery. The generic document DE 10 2022 122 755 A1 relates to a vehicle electrical system with the possibility of charging the batteries at a charging station depending on the charging voltage, whereby the batteries can be connected in series or in parallel. DE 10 2018 106 304 A1 describes a direct current charging of an intelligent battery. Disclosure of the invention The electrical systems of battery-electric vehicles, especially fully electric vehicles, operate at the highest possible voltages for performance reasons. This makes safety requirements and electromagnetic compatibility (EMC) requirements particularly important, especially during charging. The object of the present invention is therefore to offer an improved method and a device that enable efficient charging and ensure safety and EMC requirements. The problem is solved first by a method for charging at least two battery banks of an on-board network of a battery-electric vehicle, wherein a charging mode is selected during a charging process for charging the battery banks depending on an asymmetry of the on-board network. This method enables an adaptive charging strategy that adjusts to the specific conditions of the vehicle's electrical system, thus ensuring an optimal balance between charging efficiency, safety and electromagnetic compatibility. In particular, asymmetry can be a measure that describes a degree of imbalance between a voltage positive with respect to ground (hereinafter: GND) and a voltage negative with respect to GND. As long as the asymmetry, particularly the imbalance, is sufficiently low to meet safety and / or electromagnetic compatibility (EMC) requirements, charging can proceed, especially using a high-power and / or high-voltage charging mode. If the asymmetry indicates risks regarding safety and / or EMC, a less risky charging mode or a temporary charging stop can be selected. This allows for at least partial or complete interruptions of charging, thereby improving overall charging efficiency while still meeting safety and EMC requirements. In particular, it can be leveraged that these requirements often permit the use of inexpensive Y-type interference suppression capacitors at low on-board voltages and / or eliminate the need for additional compensating measures such as symmetry monitoring. Overall, this results in an efficient yet safe way to charge the battery banks. The procedure can provide that symmetry monitoring is switched off when the on-board network voltage is 400 V. The symmetry monitoring system can be configured to monitor the degree of asymmetry. It can be configured to trigger when a limit value is exceeded. The vehicle's electrical system can be configured to stop a charging process, for example, when the symmetry monitoring system is triggered. By switching off the symmetry monitoring at low on-board voltages, for example of a maximum of 400 V, the EMC requirements can be handled more flexibly, which leads to simplified charging control. A 400 V charging mode or an 800 V charging mode can be selected. This can be understood as charging modes at voltages between 300 V and 500 V on the one hand, and between 700 V and 900 V on the other. Specifically, the voltages can be 0.4 kV on the one hand and 0.8 kV on the other. The ability to select between different charging modes increases the flexibility of the charging system. In particular, different options for meeting safety requirements may exist depending on the charging mode. For example, different types of interference suppression capacitors may be permitted or prohibited depending on the charging mode, and different additional protective measures may or may not be required. The charging mode can be selected while the vehicle is driving, allowing the charging mode to be proactively adjusted and a subsequent charging process to be started quickly yet safely. If the symmetry monitoring is triggered during a charging process, the charging process may be interrupted. This safety measure ensures that the charging process is stopped immediately in the event of critical asymmetries, in order to minimize potential risks. After the symmetry monitoring is triggered, it is also conceivable to use a 400 V charging mode until the next vehicle movement. This strategy can allow the charging process to continue under safe conditions, instead of completely aborting it. In particular, when the symmetry monitoring is triggered, a seamless switch from the 800 V charging mode to the 400 V charging mode can occur, thus avoiding charging pauses. This can further improve charging efficiency and user-friendliness. The invention also encompasses an electrical system for a battery-electric vehicle. The electrical system comprises at least two battery banks and at least three controllable switches. The electrical system is configured to selectively connect the at least two battery banks in parallel or in series using the switches, and is configured to implement the method described above. The vehicle electrical system provides the hardware basis for the flexible implementation of the various charging modes, thus enabling optimal adaptation to different charging conditions and requirements. The controllable switches allow the battery banks to be configured in series or parallel. This enables the vehicle's electrical system to be set up for single or double charging voltages, thus easily creating multiple charging modes. The vehicle electrical system can include symmetry monitoring to detect asymmetries, so that the sensor data required for the procedure can be provided directly by the electrical system. Alternatively or additionally, it is also conceivable to equip a charging station with such symmetry monitoring and, if necessary, to provide suitable data communication with the vehicle electrical system being monitored and / or to supply the necessary measuring points at an interface to the charging station. Further features and advantages of the invention will become apparent from the following detailed description of an embodiment of the invention with reference to the figures of the drawing, which show details essential to the invention, as well as from the claims. The individual features can be implemented individually or in any combination in various versions of the invention. The schematic drawing illustrates exemplary embodiments of the invention, which are explained in more detail in the following description. Brief description of the drawings Figure 1 shows a topology of a high-voltage (HV) electrical system with two battery banks, Figure 2 shows a high-voltage circuit with capacitive filtering and insulation monitoring, and Figure 3 shows a method for controlling an electrical system with at least two battery banks for a battery-electric vehicle. To facilitate understanding of the invention, the same reference numerals are used for corresponding elements in the following description of the figures. Embodiments of the invention Fig. 1 shows a topology of a direct current (DC) electrical system 10 for a battery-electric vehicle. The electrical system 10 comprises a first battery bank U1 and a second battery bank U2. The first battery bank U1 and the second battery bank U2 are designed for a nominal voltage of, for example, 400 V each. The on-board electrical system 10 includes at least three switches, which together enable a selection of different charging modes. Switch B1 is arranged in parallel with the first battery bank U1. Switch B2 is arranged in series between the first battery bank U1 and the second battery bank U2. Switch B0 connects the first battery bank U1 to the on-board electrical system 10. Switch B2 connects the second battery bank U2 to the on-board electrical system 10. Switches S1 and S2 connect a DC charging station 16 to the on-board electrical system 10 or disconnect them from each other in order to start or stop charging processes. The vehicle electrical system 10 also includes an HV component 14, which can represent, for example, an electric motor or other high-voltage consumers of the vehicle. By appropriately configuring switches B0, B1, B2, S1 and S2, the high-voltage electrical system 10 can be switched between a 400 V configuration and an 800 V configuration. In the 400 V configuration, for example, battery banks U1 and U2 can be used in parallel, while in the 800 V configuration, both battery banks U1 and U2 can be connected in series. This flexible configuration option allows the power supply to be adapted to different operating states of the vehicle, such as different charging modes or driving situations. Fig. 2 shows a high-voltage circuit with capacitive filtering and insulation monitoring. The circuit includes a positive voltage HV+, a negative voltage HV-, and a ground GND. A suppression capacitor Cy is arranged between the positive voltage HV+ and ground GND, and also between ground GND and the negative voltage HV. The high-voltage circuit shows a configuration that can also be implemented in the vehicle electrical system 10. The interference suppression capacitors Cy serve to ensure electromagnetic compatibility (hereinafter: EMC) and are subject to capacitive limits that depend on the applied voltage levels. These limits are defined by standards such as SAE J1772 to guarantee, for example, user safety during DC charging. Between the lines carrying the voltages HV+ and HV- and the ground GND, there are insulation resistances Riso+ and Riso-. The DC charging station 16 can be configured to monitor the insulation resistances Riso+ and Riso-. For example, the DC charging station 16 can induce asymmetries in the voltages HV+ and HV- to perform a measurement. Fig. 3 shows a method 1000 for controlling an on-board electrical system 10 with at least two battery banks U1, U2 for a battery-electric vehicle. The method 1000 comprises several steps for selecting a suitable charging mode and for charging the vehicle. The method 1000 is explained in more detail below with exemplary reference to the reference numerals introduced above. Procedure 1000 begins with step 1010, in which the asymmetry between HV+ and ground (GND) and between GND and HV- is measured. This measurement serves to monitor the symmetry of the vehicle electrical system. Following the measurement, a decision point 1020 is determined, at which it is determined whether the measured asymmetry exceeds a predefined limit. If the asymmetry exceeds the threshold, a 400 V charging mode is selected in step 1030. For this, switches B0 to B2 are set according to a parallel connection of battery banks U1 and U2. If the asymmetry does not exceed the limit, an 800V charging mode is selected. For this, switches B0 to B2 are set according to a series connection of battery banks U1 and U2. After selecting the charging mode, charging processes begin according to step 1050 in the 400V charging mode or according to step 1060 in the 800V charging mode. The procedure can be continued in a circular fashion, starting again with the measurement according to step 1010, until the battery banks U1, U2 are sufficiently charged or the charging process is otherwise interrupted, for example actively by a user of the vehicle. Reference symbol list 10 On-board electrical system 14 HV component 16 DC charging station 1000 Procedure 1010 Step 1020 Decision point 1030 Step 1040 Step 1050 Step B0 Switch B1 Switch B2 Switch Cy Interference suppression capacitor GND Ground HV+ Positive voltage HV- Negative voltage Riso+ Insulation resistance Riso- Insulation resistance S1 Switch S2 Switch U1 First battery bank U2 Second battery bank

Claims

Method for charging at least two battery banks (U1, U2) of an on-board electrical system (10) of a battery-electric motor vehicle, characterized in that during a charging process for charging the battery banks (U1, U2) a charging mode is selected depending on an asymmetry of the on-board electrical system (10). Method according to claim 1, wherein a symmetry monitoring is switched off or left switched off at a system voltage of 400 V. Method according to one of the preceding claims, characterized in that the charging mode is selected between a 400 V charging mode and an 800 V charging mode. Method according to one of the preceding claims, characterized in that the selection of the charging mode takes place during a journey of the motor vehicle. Method according to one of the preceding claims, characterized in that the charging process is interrupted when the symmetry monitoring is triggered during a charging process. Method according to one of the preceding claims, characterized in that after triggering the symmetry monitoring, the 400 V charging mode is used until the next vehicle movement. Method according to one of the preceding claims, characterized in that when the symmetry monitoring is triggered, an uninterrupted switchover from the 800 V charging mode to the 400 V charging mode takes place. On-board electrical system (10) for a battery-electric motor vehicle, comprising at least two battery banks (U1, U2) and at least three controllable switches (B0, B1, B2), wherein the on-board electrical system (10) is configured to selectively connect the at least two battery banks (U1, U2) in parallel or in series using the switches (B0, B1, B2), wherein the on-board electrical system (10) is configured to implement the method according to one of the preceding claims. On-board network according to the preceding claim, further comprising a symmetry monitoring system for monitoring an asymmetry of the on-board network (10).

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