Power supply device for providing a low-voltage on-board voltage in a low-voltage on-board network

Abstract

The power supply device (20) can be arranged in a low-voltage electrical system (10) which is coupled to the vehicle's high-voltage electrical system (5) via a high-voltage DC-DC converter (8). The power supply device (20) comprises a first energy storage device (22), a first DC-DC converter (23), and a second DC-DC converter (24). The first DC-DC converter (23) is configured as a bidirectional DC-DC converter and is designed to provide a higher power output than the second DC-DC converter (24). The second DC-DC converter (24) is connected in parallel to the first DC-DC converter (23).The second DC voltage converter (24) is designed to provide current for the low-voltage consumers (14) connected to the low-voltage on-board network (10) in a parked operating state of the vehicle, depending on the power demand of the low-voltage consumers (14) connected to the low-voltage on-board network (10).

Description

[0001] The invention relates to a power supply device for supplying a low-voltage electrical system of a vehicle. Furthermore, the invention relates to an electrical system.

[0002] To operate electrical devices, also known as loads, motor vehicles are equipped with low-voltage electrical systems containing one or more low-voltage batteries. Currently, there are efforts to eliminate low-voltage batteries, particularly 12V batteries, from these systems due to their high failure rate. This likely applies to both electric vehicles and vehicles with internal combustion engines.

[0003] Low-voltage batteries fulfill two main functions. Firstly, they supply power to low-voltage consumers when the vehicle is parked (key-off mode). Secondly, in electric vehicles, they are used to cover peak loads while driving when the power provided by a DC / DC converter, which converts the vehicle's high voltage to the low voltage of the vehicle's electrical system, is insufficient.

[0004] Modern vehicles, in particular, contain dynamic electrical consumers whose operation can cause a significant voltage drop, such as an anti-lock braking system (ABS) or an electric power steering system, as used in parking assist systems. These dynamic consumers are also activated while the vehicle is running, not just during the initial cold start or when the vehicle is switched off.

[0005] To absorb voltage spikes and dips and prevent disruptions to load behavior, several batteries, such as lead-acid batteries, are currently distributed throughout the low-voltage electrical system. These batteries can partially absorb voltage spikes and dips. However, for highly dynamic loads, the batteries react too slowly. Furthermore, the batteries are quite heavy.

[0006] The object underlying the invention is to provide a power supply device that contributes to ensuring that the supply of loads of a low-voltage on-board network can be provided reliably and / or cost-effectively and / or with a small installation space.

[0007] The problem is solved by the features of the independent patent claims. Advantageous embodiments are characterized in the subclaims.

[0008] According to a first aspect, the problem is solved by a power supply device for providing a low-voltage electrical system in a vehicle's low-voltage electrical system. The power supply device is arranged within the low-voltage electrical system, which is coupled to the vehicle's high-voltage electrical system via a high-voltage DC / DC converter. The power supply device comprises a first energy storage device, a first DC / DC converter, and a second DC / DC converter connected in parallel to the first DC / DC converter. The first DC / DC converter is designed as a bidirectional DC / DC converter. The first DC / DC converter is configured to provide a higher power output than the second DC / DC converter.

[0009] The first energy storage device includes a capacitor for energy supply. That is, the energy storage device is essentially formed by one or more capacitors.

[0010] The power supply device further comprises a voltage measuring arrangement and a low-voltage vehicle electrical system connection. The low-voltage vehicle electrical system connection serves to directly or indirectly connect the power supply device to one or more load branches of the low-voltage vehicle electrical system. The voltage measuring arrangement is arranged and configured to provide a first measurement signal for a control unit, which is representative of a voltage at the low-voltage vehicle electrical system connection, in particular of a voltage between the low-voltage vehicle electrical system connection and a reference potential.

[0011] The bidirectional first DC-DC converter has a first DC-DC terminal, a second DC-DC terminal, and a control terminal. The first DC-DC converter is connected to the first energy storage device via its first DC-DC terminal and to the low-voltage electrical system via its second DC-DC terminal. Depending on a control signal provided by the control unit based on the first measurement signal, the first DC-DC converter is configured to operate in either a buck or boost mode.

[0012] The power supply device may include the control unit, or the control unit may be associated with the power supply device. The control unit is specifically configured to determine the control signal based on the first measurement signal and subsequently provide the control signal to the first DC-DC converter.

[0013] The second DC-DC converter comprises a first terminal connected to the energy storage device and a second terminal connected to the low-voltage electrical system. The second DC-DC converter is thus connected in parallel to the first DC-DC converter.

[0014] The second DC-DC converter is designed to provide current at the second terminal of the second DC-DC converter in a parked operating state of the vehicle, particularly when the first DC-DC converter is deactivated, for the low-voltage consumers connected to the low-voltage electrical system, depending on the power demand of the low-voltage consumers connected to the low-voltage electrical system.

[0015] The energy required by the low-voltage consumers is preferably provided exclusively by the high-voltage DC-DC converter and the power supply device. The low-voltage electrical system preferably does not have a separate low-voltage battery, such as a 12-V battery, or one integrated into the power supply device.

[0016] Advantageously, the second DC-DC converter enables the low-voltage consumers of the low-voltage on-board network to be supplied with energy for a sufficient time during a parking mode of the vehicle, wherein the parking mode of the vehicle is characterized in that the vehicle is switched off and is in a sleep mode in which most of the low-voltage consumers are switched off or are only briefly active, so that only a few milliamperes of current flow, e.g. a maximum of 20mA.

[0017] Advantageously, the first DC-DC converter makes it possible to provide a peak power supply to the low-voltage consumers during vehicle operation if the power provided by the high-voltage DC-DC converter in this operating state is insufficient.

[0018] Advantageously, the first DC-DC converter makes it possible to avoid voltage spikes or voltage dips in the low-voltage electrical system during vehicle start-up and driving, thus preventing impairments to the load behavior of the low-voltage electrical system.

[0019] The energy storage of the power supply device can be easily charged via the high-voltage DC converter and the first DC converter in the park operating state.

[0020] In at least one advantageous embodiment according to the first aspect, the capacitor comprises or is a hybrid capacitor, a polymer capacitor, a polymer-hybrid capacitor, or a lithium battery cell. Polymer-hybrid capacitors, in particular, are characterized by especially low equivalent series resistance (ESR) and high ripple current handling capacities. Furthermore, they offer high and voltage-independent capacitance values.

[0021] In at least one advantageous embodiment according to the first aspect, the energy supply device comprises a series circuit. The series circuit has a current measuring arrangement and a buffer capacitor connected in series. A first terminal of the series circuit is connected to the low-voltage vehicle electrical system connection, which is provided for connecting the energy supply device to the low-voltage vehicle electrical system, and a second terminal of the series circuit is connected to a reference potential. The current measuring arrangement is designed to provide a second measurement signal to the control unit, which is representative of a current flowing in the series circuit.

[0022] The control unit is designed to determine the control signal it provides to the DC-DC converter based on the second measurement signal. The control signal may include a control command.

[0023] Analyzing the current flowing into and out of the buffer capacitor allows for better stabilization of the low-voltage electrical system and a faster response time by predicting the required operating mode (buck or boost). Switching from buck to boost mode and vice versa takes time. Current measurement and analysis of the current gradient enable early detection of whether the DC-DC converter needs to provide boost or buck functionality, allowing the converter to be controlled accordingly.

[0024] Furthermore, by analyzing the current flowing into and out of the buffer capacitor, the effectiveness of voltage stabilization can be increased, as the thresholds for overvoltage and undervoltage detection can be set more narrowly. Pure voltage threshold detection for overvoltages and undervoltage has the disadvantage that if the voltage thresholds are set very narrowly (due to early detection), the DC-DC converter switches operating mode very frequently, and the effectiveness of the voltage support decreases.

[0025] If, on the other hand, the voltage thresholds are set far apart, this can lead to the switching occurring too late due to the changeover time from buck converter mode to boost converter mode and vice versa, and a voltage drop can no longer be prevented.

[0026] Furthermore, by analyzing the current flowing into and out of the buffer capacitor, unwanted additional oscillations in the supported voltage supply can be prevented or at least reduced. If the oscillations of the supply voltage, due to the inductances of the leads to the load and the energy storage of the low-voltage electrical system, are faster than or nearly as fast as the switching of the operating modes of the DC-DC converter, then the converter will cause additional oscillations in the supported voltage supply.

[0027] In at least one advantageous embodiment, the first DC-DC converter has a greater power output than the second DC-DC converter by a factor that has a value between 10 and 100 or between 20 and 100.

[0028] In at least one advantageous embodiment according to the first aspect, the first DC-DC converter is designed to provide, in a parking operating state of the vehicle, energy which is provided by the high-voltage DC-DC converter, which is coupled to the low-voltage vehicle electrical system, at the second DCDC terminal of the first DC-DC converter, at least partially at the first DCDC terminal of the first DC-DC converter for charging the energy storage device.

[0029] In at least one advantageous embodiment according to the first aspect, the control unit is designed to send a wake-up signal to a battery management control unit depending on a state of charge of the energy storage device in order to cause the high-voltage energy storage device to provide energy for charging the energy storage device via the high-voltage DC-DC converter and the first DC-DC converter.

[0030] In at least one embodiment according to the first aspect, the voltage measuring arrangement comprises a voltage divider with a partial voltage tap, which is connected to the control unit for providing the first measuring signal.

[0031] In at least one embodiment according to the first aspect, the energy supply device includes the control unit and the control unit is designed as follows: - read in the first measurement data provided, which are representative of a voltage applied to the low-voltage vehicle electrical system connection, and determine a voltage value depending on the first measurement data, - to read in the provided second measurement data, which are representative of a current flowing in the series circuit, - to determine a time-dependent current gradient depending on the second set of measurement data, - to compare the determined current gradient with a specified gradient threshold and, if the determined current gradient exceeds the specified gradient threshold, to check whether the determined voltage value falls below a lower voltage limit or exceeds an upper voltage limit, and - if the determined voltage value falls below the lower voltage limit, to provide the first control signal such that the first control signal causes the first DC-DC converter to operate in boost converter mode, and - if the determined voltage value exceeds the upper voltage limit, to provide the first control signal such that the first control signal causes the first DC-DC converter to operate in the step-down converter mode.

[0032] In at least one embodiment according to the first aspect, the control unit is designed to regulate a current that the first DC-DC converter provides at its second DCDC terminal in the boost converter mode or buck converter mode depending on the second measurement data.

[0033] According to a second aspect, the task is solved by an on-board electrical system for a vehicle. This system comprises a high-voltage network with a high-voltage energy storage device and a low-voltage network that includes a power supply device as described in the first aspect. The high-voltage network includes a high-voltage DC / DC converter that couples the high-voltage and low-voltage networks.

[0034] In at least one advantageous embodiment according to the second aspect, low-voltage consumers of the low-voltage on-board network are supplied with energy exclusively from the energy storage via the first DC-DC converter and second DC-DC converter and from the high-voltage network via the high-voltage DC-DC converter.

[0035] Advantageous features of the first aspect also apply to the second aspect.

[0036] Exemplary embodiments of the invention are explained below with reference to the schematic drawings. The description of the items mentioned here is not limited to the individual specific embodiments. Features of different exemplary embodiments can be combined with one another—where technically feasible—to form further exemplary embodiments. For example, variations or modifications described with regard to one of the exemplary embodiments may also be applicable to other exemplary embodiments, unless otherwise stated.

[0037] They show: Fig. 1 an exemplary block diagram of an embodiment of an on-board power system of a vehicle Fig. 2 an exemplary block diagram of an embodiment of a power supply device and Fig. 3 An exemplary flowchart for a program to operate the power supply device for stabilizing the low-voltage on-board network.

[0038] In the figures, the same reference symbols are used for elements with essentially the same function; however, these elements do not have to be identical in every detail.

[0039] It should be noted that when an element is described as "connected" or "coupled" to another element, the element may be directly connected or coupled to the other element, or intermediate elements may be present. Conversely, when an element is described as "directly" "connected" or "coupled" to another element, no intermediate elements are present. Other expressions used to describe the relationship between elements should be interpreted similarly (e.g., "between" versus "directly between," "adjacent" versus "directly adjacent," etc.).

[0040] Fig. Figure 1 shows a block diagram of an exemplary embodiment of a vehicle electrical system. The electrical system comprises a high-voltage network 5 and a low-voltage network 20 (LV electrical system).

[0041] The high-voltage network 5 comprises a high-voltage energy storage device 7. The high-voltage energy storage device 7 is, for example, a traction battery of an electric vehicle. The high-voltage energy storage device 7 can comprise a series connection of at least two energy storage devices or a series connection of at least two energy storage devices. Alternatively, the high-voltage network 5 can comprise a redundant high-voltage energy storage device (not shown in Fig. 1) exhibit, which can be connected to the high-voltage network, particularly in the event of a fault in the high-voltage energy storage system.

[0042] The high-voltage network 5 also includes a high-voltage DC / DC converter 8 (HVLV-DC / DC). The HVLV-DC / DC 8 has a high-voltage connection HV and a low-voltage connection LV. The high-voltage connection HV of the HVLV-DC / DC 8 is connected to the high-voltage energy storage device 7. The low-voltage connection LV is connected to the LV electrical system 10, for example, for the high potential and the low potential, each via a contactor 4. The HVLV-DC / DC 8 thus couples the HV electrical system 5 with the LV electrical system 10. The HVLV-DC / DC 8 is designed to supply a low-voltage voltage to the LV electrical system 10 of the vehicle by converting power from the high-voltage energy storage device 7. The HVLV-DC / DC 8, for example, has a transformer and is thus designed to galvanically isolate the HV on-board power supply 5 from the LV on-board power supply 8.

[0043] The HV electrical system 5 includes, for example, additional high-voltage consumers 9. Preferably, the HV electrical system 5 includes an electric motor. The high-voltage energy storage device 7 can be isolated from these additional components using the contactors 4.

[0044] The LV electrical system 10, for example, is a 12-volt low-voltage electrical system. Alternatively, the LV electrical system 10 can be operated with 23 volts, 48 ​​volts, or another typical low-voltage voltage of a low-voltage system.

[0045] The low-voltage electrical system 10 comprises a power supply device 20 and one or more load branches 12 arranged in parallel. The low-voltage output of the high-voltage low-voltage DC / DC converter is connected to the load branch 12 or branches 12. One or more low-voltage loads (LV loads) 14 can be arranged in each load branch 12. Different functional safety requirements can be assigned to the LV loads 14. For example, the LV electrical system can have LV loads 14, each of which is assigned a functional safety requirement, for example, according to the ISO 26262 standard. For example, each LV load can be assigned one of the following requirements: ASIL A (Automotive Safety Integrity Level A), ASIL B, ASIL C, ASIL D, or QM.

[0046] The HVLV-DC / DC 8 provides a nominal voltage of 12 volts at the low-voltage connection LV, for example. Alternatively, the HVLV-DC / DC 8 can provide a nominal voltage of, for example, 23 volts, 48 ​​volts, or another typical low-voltage voltage of a low-voltage network at the low-voltage connection LV.

[0047] The energy required by the LV loads 14 is preferably supplied exclusively by the high-voltage battery via the HVLV-DCDC converter 8 and the power supply unit 20. The LV electrical system 10 preferably does not have a separate low-voltage battery, for example a 12 V battery, nor does it have a low-voltage battery integrated into the power supply unit 20.

[0048] The energy supply device 20 is designed to supply the LV consumers 14 of the LV electrical system 10 with energy for a predetermined time during a parking operating state of the vehicle, wherein the parking operating state of the vehicle is characterized by the fact that the vehicle is switched off and is in a sleep mode in which most of the LV consumers 14 are switched off or are only briefly active, so that only a few milliamperes of current flow, e.g. a maximum of 20mA.

[0049] Furthermore, the energy supply device 20 is designed to provide a peak power supply to the LV loads 14 during driving operation of the vehicle if the power provided by the HV-DCDC 8 in this operating state is insufficient.

[0050] Furthermore, the energy supply device is designed to avoid voltage peaks or voltage dips in the LV on-board network 10 during starting of the vehicle and during driving operation and thus to avoid impairments of the load behavior on the LV on-board network 10.

[0051] Fig. Figure 2 shows an exemplary block diagram of an embodiment of the power supply device 20.

[0052] The power supply device 20 has a low-voltage on-board power supply connection A.

[0053] The power supply device 20 comprises an energy storage device 22, a first DC-DC converter 23 configured as a bidirectional DC-DC converter, and a second DC-DC converter 24 connected in parallel to the first DC-DC converter 23. The second DC-DC converter 24 is preferably configured as a boost converter. The first DC-DC converter 23 is configured to provide higher power than the second DC-DC converter 24. For example, the first DC-DC converter 23 has a power output 20 to 100 times higher than that of the second DC-DC converter.

[0054] The energy storage device 22 comprises at least one capacitor. The capacitor stores all or a substantial portion of the energy of the energy storage device 22. The capacitor preferably has an energy storage capacity greater than 10 Wh, ideally greater than 20 Wh. The capacitor is preferably designed as a polymer hybrid capacitor. This enables the energy storage device 22 to maintain the supply for approximately 200 hours and 100 hours, respectively, if the low-voltage consumers 14 of the low-voltage electrical system 10 require an average of approximately 10 mA in the vehicle's standby mode and approximately 20 mA in the worst-case scenario.

[0055] The capacitor provides, for example, 8 Ah at 4.2 V. This corresponds to approximately 11000 F.

[0056] The bidirectional first DC-DC converter 23 has a first DC-DC terminal DC1, a second DC-DC terminal DC2, and a control terminal Ctrl. The first DC-DC converter 23 is directly or indirectly connected to a first supply terminal of the first energy storage device 22 via the first DC-DC terminal DC1. The second terminal of the DC-DC converter DC2 is directly or indirectly connected to at least one load branch 12. The control terminal Ctrl of the first DC-DC converter 23 is connected to a control unit 25. The power supply device 20 can include the control unit 25. Alternatively, the control unit 25 can be assigned to the power supply device 20. The first DC-DC converter 23 can be activated or deactivated as needed by means of the control unit 25.

[0057] The second DC voltage converter 24 has a first terminal T1 and a second terminal T2.

[0058] The arrangement allows current to flow from the LV electrical system 10 via the first DC-DC converter 23 when the voltage level is high or when there is excess energy (or a high state of charge). Furthermore, current can flow in the opposite direction when the LV electrical system 10 has a low voltage level. A high voltage level is defined as a voltage that is above a predefined upper limit. A low voltage level is defined as a voltage that is below a predefined lower limit.

[0059] The second DC-DC converter 24 is designed to provide lower power levels, for example, less than 5W. Therefore, activating and deactivating the second DC-DC converter 24, as well as intensive monitoring of the second DC-DC converter 24, are not required. This means that the second DC-DC converter 24 can be continuously in operation or active. This has the advantage that additional control via a controller is not required.

[0060] The power supply device 20 is thus configured to provide power to the low-voltage (LV) consumers 14 of the LV electrical system 10 from the energy storage device 22 via the second DC-DC converter 24 during a parking operation of the vehicle. The second DC-DC converter 24 is configured, during a parking operation mode of the vehicle when the first DC-DC converter 23 is deactivated, to make available at the second terminal T2, which is directly or indirectly connected to the at least one load branch 12, energy which it receives from the energy storage device 22 of the power supply device 20, in particular to make available at the second terminal T2 of the second DC-DC converter 24 a predetermined current for the LV consumers 14 connected to the LV electrical system 10.

[0061] While the vehicle is parked, energy storage device 22 can be recharged. As described, energy storage device 22 can be discharged after approximately 100 hours and must be recharged. For example, control unit 25 is configured to send a wake-up signal to a battery management system during parked operation. The battery management system (BMS) then couples high-voltage energy storage device 7 to the HVLV-DC / DC 8, for example, by closing contactors 4. Furthermore, the BMS activates or starts the HVLV-DC / DC 8. The HVLV-DC / DC 8 and the first DC-DC converter 23 transfer the energy to energy storage device 22. Once energy storage device 22 is charged, the vehicle returns to sleep mode; in particular, the high-voltage battery 7 is disconnected again.

[0062] The power supply device 20 is designed to stabilize the supply voltage for the low-voltage electrical system 10 during vehicle start-up. In particular, the power supply device 20 is designed to prevent voltage spikes or dips in the low-voltage electrical system 10 during vehicle start-up, thereby preventing any impairment of the load behavior of the low-voltage electrical system 10. During start-up, when a higher power than, for example, 5 W is required, the power for the loads of the low-voltage electrical system 10 is supplied by the hybrid capacitor(s) via the first DC-DC converter 23.

[0063] The power supply device 20 is further designed to provide a peak power supply to the LV consumers 14 during vehicle operation if the power provided by the HV-DCDC 8 in this operating state is insufficient.

[0064] Stabilizing the supply voltage during driving and starting requires special operation of the first DC-DC converter 23. The power supply device 20 therefore includes a voltage measurement arrangement 26, which is designed and configured to provide a first measurement signal to the control unit 25, representing a voltage at the low-voltage on-board power supply connection A. The first measurement signal represents the sum of the voltage drop across the load branch 12 and the voltage drop along the supply line to the load branch 12 due to line inductances 19.

[0065] The voltage measurement arrangement 26, for example, includes a voltage divider arranged in parallel to the load branch 12 or the low-voltage terminal LV of the HVLV-DC / DC converter 8. The voltage divider has a first terminal, a second terminal, and a partial voltage tap. The voltage divider is connected, for example, at its first terminal to the second DC-DC terminal DC2 of the first DC-DC converter 23 and at its second terminal to a reference potential, for example, ground. The partial voltage tap is connected, for example, to the control unit 25, in particular to an analog-to-digital converter of the control unit 25.

[0066] In an optional embodiment, the power supply device 20 includes a current measuring arrangement and a buffer capacitor 28. The current measuring arrangement 27 and the buffer capacitor 28 are connected in series. This series connection is arranged in a branch that is parallel to the at least one load branch 12.

[0067] The current measuring arrangement 27 is configured to provide a second measuring signal that is representative of a current flowing into or out of the buffer capacitor 28. The current measuring arrangement 27 includes, for example, a shunt resistor.

[0068] The first DC voltage converter 23 is designed to operate in a buck converter mode or a boost converter mode, depending on a control signal provided by the control unit 25 in relation to the second measurement signal.

[0069] Fig.Figure 3 shows an example flowchart for a program to operate the power supply device 20 for stabilizing the LV electrical system 10. The program is executed, for example, by a control computer of the power supply device 20. The control computer comprises, for example, a microcontroller or a microprocessor and program memory. The microcontroller and / or the microprocessor may have one or more integrated analog-to-digital converters. The control computer may be part of the control unit or the control unit itself.

[0070] The program starts in step S01. In step S01, variables are initialized, for example.

[0071] In step S03, initial measurement data, provided, for example, by another analog-to-digital converter of the control unit 25, is read in. This initial measurement data is representative of a voltage in the vehicle electrical system 10, specifically a voltage present at the low-voltage electrical system connection A (with respect to the reference potential GND). In step S03, a voltage value is also determined based on this initial measurement data.

[0072] In step S05, second measurement data, provided, for example, by another analog-to-digital converter of the control unit 25, are read in. This second measurement data is representative of a current flowing into or out of the buffer capacitor 28. Furthermore, in step S05, a current gradient over time is determined based on the previously determined current value and the currently determined current value.

[0073] Steps S03 and S05 can be performed simultaneously or sequentially and also in reverse order.

[0074] In step S07, the determined current gradient is compared with a predefined gradient threshold, for example, 50 A / ms. If the determined current gradient exceeds the predefined threshold, a check is performed in step S09 to determine whether the determined voltage value falls below a lower voltage threshold or exceeds an upper voltage threshold.

[0075] If the measured voltage value falls below the lower voltage limit, for example 13.5 V, in step S11, a first current to be supplied by the first DC-DC converter 23 to the LV electrical system 10 is determined, depending on the current gradient and / or the currently measured current value. Furthermore, in step S11, a first control signal is provided for the first DC-DC converter 23, which causes the first DC-DC converter 23 to operate in boost converter mode and supply the measured first current.

[0076] If the determined voltage value exceeds the upper voltage limit, for example 15 V, a second current to be supplied by the first DC-DC converter 23 to the LV electrical system 10 is determined in step S13, depending on the current gradient and / or the currently determined current value. Furthermore, in step S12, a second control signal is provided for the first DC-DC converter 23, which causes the first DC-DC converter 23 to operate in a buck converter mode and supply the determined second current.

[0077] For this purpose, the control unit 25 can include a PID controller. The PID controller can be implemented as a software module, a hardware module, or a hybrid software and hardware module. The input variable of the PID controller is the current flowing into the buffer capacitor 28, determined from the initial measurement data. The PID controller controls the first DC-DC converter 23 such that the first DC-DC converter 23 provides a boost current or buck current, thus regulating the output current or input current of the buffer capacitor 28 towards zero. The PID controller is deactivated, for example, as soon as the lower voltage limit plus a hysteresis value of, for example, 0.25 V is exceeded, or as soon as the upper voltage limit minus a hysteresis value of, for example, 0.25 V is exceeded.

[0078] The program terminates in step S13. It is advantageous if the first and second measurement data are continuously recorded and evaluated during vehicle operation.

[0079] Because the current measuring arrangement 27 is located in the same branch as the buffer capacitor 28, a change in current caused by an overvoltage or undervoltage can be detected very quickly and early, and the DC voltage converter can be controlled appropriately.

[0080] The evaluation of the current change has the advantage that the hysteresis for the voltage evaluation can be very narrow, and thus the first DC voltage converter 23 can be controlled very quickly and early, i.e., the correct mode and the current that must be provided by the first DC voltage converter 23 can be set.

[0081] It should be noted that embodiments of the invention have been described with reference to different subject matter. In particular, some embodiments of the invention are described by means of method claims and other embodiments of the invention by means of apparatus claims. However, it will be immediately clear to the person skilled in the art upon reading this application that, unless explicitly stated otherwise, in addition to a combination of features belonging to one type of subject matter, any combination of features belonging to different types of subject matter is also possible. List of reference symbols 1 on-board power system 4 contactor 5 High-voltage network 7 high-voltage energy storage units 8 high-voltage DC converters 9 high-voltage consumers 10 Low-voltage electrical system 12 load branch 14 consumers 19 Line inductance 20 Device 22 first energy storage 23 first DC-DC converter 24 second DC-DC converter 25 Control unit 26 Voltage measurement setup 27 Current measuring arrangement 28 Buffer capacitor A low-voltage electrical system connection QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited non-patent literature

[0000] ISO 26262

[0045]

Claims

[1] Energy supply device (20) for providing a low-voltage vehicle electrical system voltage in a low-voltage vehicle electrical system (10) of a vehicle, wherein - the energy supply device (20) can be arranged in the low-voltage on-board network (10), which is coupled to a high-voltage network (5) of the vehicle via a high-voltage DC converter (8), - the energy supply device (20) has a first energy store (22), a first DC-DC converter (23) and a second DC-DC converter (24), and the first DC-DC converter (23) is designed as a bi-directional DC-DC converter, - the first DC-DC converter (23) is designed to provide a higher power than the second DC-DC converter (24), - the first energy storage device (22) comprises a capacitor for providing energy, - the energy supply device (20) further comprises a voltage measuring arrangement (26) and a low-voltage vehicle electrical system connection (A) for directly or indirectly connecting the energy supply device (20) to one or more load branches (12) of the low-voltage vehicle electrical system (10), - the bi-directional first DC-DC converter (23) has a first DCDC connection (DC1), a second DCDC connection (DC2) and a control connection (Ctrl), and the bi-directional first DC-DC converter (23) is connected to the first energy store (22) via the first DCDC connection (DC1) and to the low-voltage vehicle electrical system connection (A) via the second DCDC connection (DC2), - the voltage measuring arrangement (26) is arranged and designed to provide a first measuring signal for a control unit (25) which is representative of a voltage at the low-voltage vehicle electrical system connection (A), - the first DC-DC converter (23) is designed to operate in a step-down converter mode or a step-up converter mode depending on a control signal provided by the control unit (25) in dependence on the first measurement signal, - the second DC-DC converter (24) has a first connection (T1) which is connected to the energy store (22), and a second connection (T2) which is connected to the low-voltage vehicle electrical system connection (A), and the second DC-DC converter (24) is designed to provide a current for the low-voltage consumers (14) connected to the low-voltage vehicle electrical system (10) at the second connection (T2) of the second DC-DC converter (24) in a parked operating state of the vehicle, depending on a power requirement of the low-voltage consumers (14) connected to the low-voltage vehicle electrical system (10). [2] The power supply device (20) of claim 1, wherein the capacitor comprises or is a hybrid capacitor or a polymer capacitor or a polymer hybrid capacitor or a lithium battery cell. [3] Energy supply device (20) according to claim 1 or 2, wherein - the power supply device (20) comprises a series circuit having a current measuring arrangement (27) and a buffer capacitor (28) connected in series, - the series circuit has a first terminal and a second terminal, and the first terminal is connected to the low-voltage vehicle electrical system connection (A) and the second terminal is connected to a reference potential (GND), - the current measuring arrangement (27) is designed to provide a second measuring signal for the control unit (25), which is representative of a current flowing in the series circuit, and the control unit (25) additionally provides the control signal for setting the step-down converter mode or the step-up converter mode of the first DC-DC converter (23) as a function of the second measuring signal. [4] Power supply device (20) according to one of the preceding claims, wherein the first DC-DC converter (23) has a power capability greater than the second DC-DC converter (24) by a factor having a value between 20 and 100. [5] Energy supply device (20) according to one of the preceding claims, wherein the first DC-DC converter (23) is designed, in a parking operating state of the vehicle, to provide energy, which is provided by the high-voltage DC-DC converter (8), which is coupled to the low-voltage vehicle electrical system (10), at the second DCDC terminal (DC2) of the first DC-DC converter (23), at least partially at the first DCDC terminal (DC1) of the first DC-DC converter (23) for charging the energy storage device (22). [6] Energy supply device (20) according to one of the preceding claims, wherein the control unit (25) is designed, in the parking operating state of the vehicle, to send a wake-up signal to a battery management control unit depending on a state of charge of the energy storage device in order to cause the high-voltage energy storage device (7) to provide energy for charging the energy storage device (22) via the high-voltage DC-DC converter (8) and the first DC-DC converter (23). [7] Energy supply device (20) according to one of the preceding claims, wherein the voltage measuring arrangement (26) comprises a voltage divider with a partial voltage tap which is or can be connected to the control unit (25) for providing the first measuring signal. [8] Energy supply device (20) according to one of the preceding claims 3 to 7, wherein the energy supply device comprises the control unit (25), and the control unit (25) is designed, - read in the first measurement data provided, which are representative of a voltage applied to the low-voltage vehicle electrical system connection, and determine a voltage value depending on the first measurement data, - read in the second measurement data provided, which are representative of a current flowing in the series circuit, - to determine a temporal current gradient depending on the second measurement data, - to compare the determined current gradient with a specified gradient threshold and, if the determined current gradient exceeds the specified gradient threshold, to check whether the determined voltage value falls below a lower voltage limit or exceeds an upper voltage limit, and - if the determined voltage value falls below the lower voltage limit, to provide the first control signal such that the first control signal causes the first DC-DC converter (23) to operate in the boost converter mode, and - if the determined voltage value exceeds the upper voltage limit, to provide the first control signal such that the first control signal causes the first DC-DC converter (23) to operate in the step-down converter mode. [9] Energy supply device (20) according to claim 8, wherein the control unit is designed to regulate a current which the first DC-DC converter (23) provides at its second DCDC terminal (DC2) in the boost converter mode or buck converter mode, depending on the second measurement data. [10] On-board power system for a vehicle comprising: - a high-voltage network (5) with a high-voltage energy storage device (7) and - a low-voltage vehicle electrical system (10) comprising a power supply device (20) according to one of claims 1 to 9, wherein the high-voltage vehicle electrical system has a high-voltage DC-DC converter (8) which couples the high-voltage vehicle electrical system (5) and the low-voltage vehicle electrical system (10). [11] On-board power system according to claim 10, wherein low-voltage consumers (14) of the low-voltage on-board power system (10) are supplied with energy exclusively from the energy store (22) via the first DC-DC converter (23) and second DC-DC converter (24) and from the high-voltage network via the high-voltage DC-DC converter (8).

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