Method for charging a high-voltage battery of a motor vehicle at a stationary charging station and motor vehicle

Abstract

The invention relates to a method for charging a high-voltage battery (10) of a motor vehicle at a stationary charging station (90). The invention further relates to a motor vehicle for carrying out the method.The motor vehicle has a high-voltage electrical system, wherein the high-voltage electrical system is connected to the high-voltage battery (10), wherein the high-voltage battery (10) has at least two battery banks (11, 12), wherein the at least two battery banks (11, 12) are connected in series in a first switching state of the battery banks (11, 12) and are connected in parallel in a second switching state of the battery banks (11, 12), such that a voltage level in the high-voltage electrical system is higher in the first switching state than in the second switching state, wherein the motor vehicle has a drive system (20) connected to the high-voltage electrical system, wherein components of the drive system (20) contain Cy capacities, wherein the drive system (20) can be operated in a heating mode, wherein in the heating mode, without generating a drive torque, the high-voltage battery (10) is heated.

Description

[0001] The invention relates to a method for charging a high-voltage battery of a motor vehicle at a stationary charging station. The invention further relates to a motor vehicle for carrying out the method.

[0002] To comply with electromagnetic compatibility (EMC) limits for electrically or partially electrically powered vehicles, appropriate EMC filters are typically used. These EMC filters are provided, for example, by so-called Cy capacitances, such as DC link capacitances. However, the charging standard SAE J1772 limits the permissible total Cy capacitance to protect the user during DC charging. High-performance components, such as drive systems, especially pulse inverters, often exhibit a high total Cy capacitance. One way to comply with the total capacitance limits during charging is to disconnect the drive system(s) from the high-voltage electrical system. This renders the corresponding Cy capacitances inactive, and they do not need to be considered in the charging budget according to the SAE J1772 standard.Typically, drive systems are therefore disconnected from the vehicle's high-voltage electrical system during or before the charging process.

[0003] DE 10 2021 003 844 A1 discloses a motor vehicle comprising at least one high-voltage battery for providing a positive potential and a negative potential, and at least one high-voltage consumer, wherein an insulation monitor is provided for monitoring insulation resistances to a vehicle ground galvanically isolated from the vehicle electrical system, wherein a Cy capacitance is provided between the positive potential and the vehicle ground and between the negative potential and the vehicle ground, and wherein a voltage center tap present in the vehicle electrical system or in a component of the vehicle electrical system is connected to the vehicle ground between the positive potential and the negative potential by means of an ohmic coupling resistor.

[0004] For optimizing the charging process, for example, to achieve a particularly short charging time, it is often advantageous to additionally heat the high-voltage battery, since lower charging currents can be accepted by a cold high-voltage battery. Therefore, by additionally heating the high-voltage battery until a threshold temperature is reached, the charging time can be shortened. Prior art reveals a method for heating a high-voltage battery by operating a drive system at operating points where no drive torque is applied but losses are generated. This eliminates the need for a separate heater. Such designs are known, for example, from DE 10 2022 207 314 B4, US 2006 / 0 290 325 A1, and US 2002 / 0 070 710 A1, the disclosures of which are hereby incorporated into this application.DE 10 2019 121 277 A1 and DE 10 2009 000 718 B4 each disclose a method for charging a high-voltage battery of a motor vehicle at a stationary charging station. The subsequently published DE 10 2023 121 336 A1 discloses a method for charging a high-voltage battery of a motor vehicle, wherein the motor vehicle has a high-voltage electrical system, the high-voltage electrical system comprising the high-voltage battery and at least a first and a second supply circuit.

[0005] A problem with heating the high-voltage battery using a drive system is that, for reasons of compliance with limits regarding the total capacity during the charging process, the drive system must be disconnected from the high-voltage electrical system, especially to meet the charging standard SAE J1772.

[0006] Therefore, the object of the invention is to provide a method that overcomes the aforementioned disadvantages. Furthermore, the object of the invention is to provide a motor vehicle for carrying out the method.

[0007] These tasks are solved by the subject matter of the independent claims. The dependent claims concern advantageous further developments.

[0008] The method according to the invention is a method for charging a high-voltage battery of a motor vehicle at a stationary charging station.

[0009] The charging equipment is, in particular, a charging station. The high-voltage battery is charged at the stationary charging equipment, in particular, using direct current. The motor vehicle is, in particular, an electrically or partially electrically powered motor vehicle.

[0010] The motor vehicle has a high-voltage electrical system, wherein the high-voltage electrical system is connected to the high-voltage battery, wherein the high-voltage battery has at least two battery banks, wherein the at least two battery banks are connected in series in a first switching state of the battery banks and are connected in parallel in a second switching state of the battery banks, such that a voltage level in the high-voltage electrical system is higher in the first switching state than in the second switching state, wherein the motor vehicle has a drive system connected to the high-voltage electrical system, wherein components of the drive system contain Cy capacities, wherein the drive system can be operated in a heating mode, wherein in the heating mode, without generating a drive torque, the high-voltage battery is heated, wherein the charging of the high-voltage battery at the stationary charging device depends on the temperature of the high-voltage battery, such thatthat if the high-voltage battery has a temperature that is lower than a threshold temperature: - the battery banks are connected in parallel, - the drive system in which heating mode is used to heat the high-voltage battery, where the high-voltage battery has a temperature greater than or equal to the threshold temperature: - the heating operation is stopped, - the drive system or at least components of the drive system are disconnected from the high-voltage electrical system, - the battery banks are connected in series.

[0011] Due to the inventive design of the method, the voltage level of the high-voltage battery is initially lowered by connecting the battery banks in parallel. This results in higher limits for the total capacity of the vehicle's Cy capacities, particularly with regard to the charging standard SAE J1772. Therefore, the drive system can remain connected to the high-voltage electrical system and thus be advantageously used to warm or heat the high-voltage battery. While this does limit the charging power of the charging device due to its current limiting, it has been shown that heating the high-voltage battery using the drive system reduces the overall charging time. This is because, once the threshold temperature is reached, the high-voltage battery can be charged at a higher power and thus more quickly.The additional heating allows the threshold temperature to be reached more quickly, thus reducing the overall charging time. Once the threshold temperature is reached, the drive system or its components, such as a pulse inverter, can be disconnected from the high-voltage electrical system. This also disconnects the Cy capacity(s) of these components from the high-voltage electrical system, meaning they do not need to be considered when determining the total capacity limits. The battery banks can then be connected in series, increasing the voltage level of the high-voltage electrical system. This higher voltage level allows for charging at a higher power output, specifically at the maximum possible charging power of the charging system.

[0012] It is considered particularly advantageous if the drive system includes an electric drive and a pulse inverter.

[0013] In a further advantageous design, it is provided that the pulse inverter is disconnected from the high-voltage electrical system when the threshold temperature is reached or exceeded. Pulse inverters typically have particularly high cylindricity capacities.

[0014] It is considered advantageous if the high-voltage battery is periodically subjected to a discharge current and a charging current during heating operation by means of a predetermined pulse pattern, wherein the predetermined pulse pattern is asymmetrical with respect to a current intensity.

[0015] In an advantageous further development, it is provided that if the high-voltage battery has a temperature that is lower than the threshold temperature, the charging of the high-voltage battery at the charging device takes place with a reduced charging power compared to a maximum possible charging power.

[0016] It is considered advantageous if the entire drive system is disconnected from the high-voltage electrical system when the threshold temperature is reached or exceeded.

[0017] In a preferred further development, it is provided that if the threshold temperature is exceeded, the drive system or at least components of the drive system are galvanically isolated from the high-voltage on-board network.

[0018] Galvanic isolation can be achieved, for example, by means of one or more power switches, in particular by means of one or more contactors.

[0019] Particularly against this background, it is considered advantageous if the drive system or components of the drive system are connected to the high-voltage electrical system via one or more contactors, whereby the disconnection of the drive system or the components of the drive system is effected by opening one or more contactors.

[0020] In a preferred further development, it is provided that the high-voltage battery is charged at the stationary charging station using direct current.

[0021] The motor vehicle according to the invention is an electrically or partially electrically powered motor vehicle. The motor vehicle has a high-voltage electrical system, wherein the high-voltage electrical system is connected to the high-voltage battery, wherein the high-voltage battery has at least two battery banks, wherein the at least two battery banks are connected in series in a first switching state of the battery banks and are connected in parallel in a second switching state of the battery banks, such that a voltage level in the high-voltage electrical system is higher in the first switching state than in the second switching state, wherein the motor vehicle has a drive system connected to the high-voltage electrical system, wherein components of the drive system contain Cy capacities, wherein the drive system can be operated in heating mode, wherein in heating mode, without generating a drive torque, the high-voltage battery is heated.wherein the motor vehicle has a control unit, wherein the control unit is configured to execute the method according to one of the preceding claims.

[0022] The explanations regarding the advantages and advantageous further developments of the method according to the invention apply accordingly to the motor vehicle and vice versa.

[0023] The following figures explain the invention in more detail using one exemplary embodiment, without being limited to this embodiment. They show: Fig. 1. A schematic topology of a high-voltage electrical system of a motor vehicle. Fig. 2. A diagram showing the temporal development of heating power and temperature. Fig. 3 a diagram relating to the temporal development of a voltage, Fig. 4 a diagram concerning the temporal development of a charging power.

[0024] The Fig. Figure 1 shows a system circuit diagram. The system circuit diagram schematically depicts the components relevant for the charging process of a high-voltage battery 10 at a stationary charging device 90, which are relevant for understanding the present invention. The motor vehicle is designed as an electrically or partially electrically powered vehicle. The motor vehicle has a high-voltage electrical system, which is connected to the high-voltage battery 10. The high-voltage battery 10 has two battery banks 11, 12. In a first switching state, the two battery banks 11, 12 are connected in series, and in a second switching state, they are connected in parallel, such that the voltage level in the high-voltage electrical system is higher in the first switching state than in the second switching state.The vehicle has an auxiliary consumer 80 connected to the high-voltage electrical system and a drive system 20 connected to the high-voltage electrical system. Components of the drive system 20 contain relatively large Cy capacities. The drive system 20 comprises a pulse inverter 21 and an electric drive 22. The drive system 20 can be operated in heating mode, whereby, in heating mode, the high-voltage battery 10 is heated without generating a drive torque.

[0025] To optimize the charging process, the charging of the high-voltage battery 10 at the stationary charging station 90 depends on the temperature of the high-voltage battery 10. It is provided that two different charging modes are possible: a first charging mode with maximum charging power and a second charging mode with reduced charging power compared to the maximum charging power.

[0026] When the high-voltage battery 10 reaches a temperature below a threshold temperature, charging begins in the first charging mode. The first charging mode is designed to: - battery banks 11 and 12 are connected in parallel, - the drive system 20 in which heating mode is operated to heat the high-voltage battery 10, - the charging power of the charging device is reduced compared to a maximum charging power due to a reduced charging voltage.

[0027] When the high-voltage battery 10 reaches a temperature greater than or equal to the threshold temperature, charging begins in the second charging mode. This requires that: - the heating operation is stopped, - the drive system 20 or at least components of the drive system 20 are disconnected from the high-voltage electrical system, - battery banks 11 and 12 are connected in series - the high-voltage battery 10 is charged with a higher charging voltage compared to the reduced charging voltage.

[0028] Contactors 50 are provided for connecting the battery banks 11, 12, for connecting and disconnecting the charging device 90 and for connecting and disconnecting the drive system 10 with the high-voltage electrical system of the motor vehicle; these contactors can be controlled by a control unit of the motor vehicle.

[0029] The Fig. Figure 2 shows in a diagram the temporal development of the heating power generated by the drive system 20 (curve 2) and a temporal development of the temperature of the high-voltage battery (curve 1) during the execution of the procedure described above.

[0030] The Fig. Figure 3 shows in a diagram the temporal development of the voltage in the high-voltage on-board network (curve 3) during the execution of the procedure described above.

[0031] The Fig.Figure 4 shows in a diagram the temporal development of the charging power of the charging device (curve 4) during the execution of the procedure described above.

[0032] The time TS at which the threshold temperature is reached is indicated by the vertical line (line 5). Until time TS, the temperature of the high-voltage battery 10 is below the threshold temperature, and charging therefore takes place in the first charging mode, thus at a relatively low initial voltage level. Despite the Cy capacities of the drive system 20, the limits for the total Cy capacity are still met due to the lower initial voltage level. Furthermore, in the first charging mode, suitable control of the drive system 20 generates heating power in the high-voltage battery 10, leading to additional heating of the high-voltage battery 10 and thus to a rapid increase in its temperature. The charging power of the charging device 90 is reduced in the first charging mode due to the current limiting of the charging device 90 and the relatively low voltage level of the high-voltage electrical system.

[0033] After time TS, the system switches to the second charging mode by first ending the heating operation, then disconnecting the drive system 20 from the high-voltage electrical system, and subsequently connecting battery banks 11 and 12 in series. This increases the voltage level in the high-voltage electrical system to a higher level compared to the relatively low voltage level. This then allows the charging voltage and thus the charging power of the charging unit 90 to be increased. Despite the higher voltage level, the limits for the total Cy capacity are still met, as the Cy capacities do not contribute to the total Cy capacity in the second charging mode.

Claims

[1] Method for charging a high-voltage battery (10) of a motor vehicle at a stationary charging device (90), wherein the motor vehicle is designed as an electrically or partially electrically powered motor vehicle, wherein the motor vehicle has a high-voltage electrical system, wherein the high-voltage electrical system is connected to the high-voltage battery (10), wherein the high-voltage battery (10) has at least two battery banks (11, 12), wherein the at least two battery banks (11, 12) are connected in series with each other in a first switching state of the battery banks (11, 12) and are connected in parallel with each other in a second switching state of the battery banks (11, 12) such that a voltage level in the high-voltage electrical system is higher in the first switching state than in the second switching state, wherein the motor vehicle has a drive system (20) connected to the high-voltage electrical system, wherein components of the drive system (20) contain Cy capacities,wherein the drive system (20) can be operated in a heating mode, wherein in the heating mode without generating a drive torque the high-voltage battery (10) is heated, wherein the charging of the high-voltage battery (10) at the stationary charging device (90) takes place depending on the temperature of the high-voltage battery (10), such that, when the high-voltage battery (10) has a temperature that is less than a threshold temperature: - the battery banks (11, 12) are connected in parallel, - the drive system (20) in which heating mode is operated to heat the high-voltage battery (10), where the high-voltage battery (10) has a temperature greater than or equal to the threshold temperature: - the heating operation is stopped, - the drive system (20) or at least components of the drive system (20) are disconnected from the high-voltage electrical system, - the battery banks (11, 12) are connected in series. [2] Method according to claim 1, wherein the drive system (20) comprises an electric drive (22) and a pulse inverter (21). [3] Method according to claim 1 or 2, wherein the high-voltage battery (10) is periodically supplied with a discharge current and a charging current by means of a predetermined pulse pattern during heating operation, wherein the predetermined pulse pattern is asymmetrical with respect to a current intensity. [4] Method according to one of the preceding claims, wherein, when the high-voltage battery (10) has a temperature which is less than a threshold temperature, the charging of the high-voltage battery (10) at the charging device (90) is carried out with a reduced charging power compared to a maximum possible charging power. [5] Method according to one of the preceding claims, wherein when the threshold temperature is reached or exceeded the entire drive system (20) is disconnected from the high-voltage on-board network. [6] Method according to one of the preceding claims, wherein, upon reaching or exceeding the threshold temperature, the drive system (20) or at least components of the drive system (20) are galvanically isolated from the high-voltage electrical system. [7] Method according to one of the preceding claims, wherein the drive system (20) or components of the drive system (20) are connected to the high-voltage electrical system via one or more contactors (50), wherein the disconnection of the drive system (20) or the components of the drive system (20) is carried out by opening one or more contactors (50). [8] Method according to one of the preceding claims, wherein the charging of the high-voltage battery (10) at the stationary charging device (90) is carried out with direct current. [9] Motor vehicle, wherein the motor vehicle is designed as an electrically or partially electrically powered motor vehicle, wherein the motor vehicle has a high-voltage electrical system, wherein the high-voltage electrical system is connected to the high-voltage battery (10), wherein the high-voltage battery (10) has at least two battery banks (11, 12), wherein the at least two battery banks (11, 12) are connected in series with each other in a first switching state of the battery banks (11, 12) and are connected in parallel with each other in a second switching state of the battery banks (11, 12) such that a voltage level in the high-voltage electrical system is higher in the first switching state than in the second switching state, wherein the motor vehicle has a drive system (20) connected to the high-voltage electrical system, wherein components of the drive system (20) contain Cy capacities, wherein the drive system (20) is operable in a heating mode,wherein in the heating operation without generating a drive torque the high-voltage battery (10) is heated, wherein the motor vehicle has a control unit, wherein the control unit is configured to execute the method according to one of the preceding claims.

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