Energy supply device for providing low-voltage on-board electrical system voltage in low-voltage on-board electrical system

Abstract

The invention relates to an energy supply device (20) which can be arranged in a low-voltage on-board electrical system (10) which is coupled to a high-voltage electrical system (5) of a vehicle via a high-voltage DC-DC converter (8). The energy supply device (20) has a first energy storage unit (22), a first DC-DC converter (23) and a second DC-DC converter (24). The first DC-DC converter (23) is in the form of a bidirectional DC-DC converter and is designed to deliver higher power than the second DC-DC converter (24). The second DC-DC converter (24) is connected in parallel with the first DC-DC converter (23). The second DC-DC converter (24) is designed to provide current to the low-voltage loads (14) connected to the low-voltage on-board electrical system (10) based on power requirements of the low-voltage loads (14) connected to the low-voltage on-board electrical system (10) in a parking mode of operation of the vehicle.

Description

Technical Field

[0001] This invention relates to an energy supply device for supplying power to a low-voltage on-board electrical system of a vehicle. The invention also relates to an on-board electrical system. Background Technology

[0002] A low-voltage on-board electrical system, consisting of one or more low-voltage batteries, is provided in motor vehicles to operate electrical loads (also known as loads). Due to the high failure rate of low-voltage batteries (especially 12V batteries), there are currently attempts to eliminate them from low-voltage on-board electrical systems. This applies to both electric vehicles and vehicles with internal combustion engines.

[0003] These low-voltage batteries perform two main functions. First, they supply power to low-voltage loads in parking mode (engine off mode). Second, when the electric vehicle is in motion, these low-voltage batteries supply power to the peak loads of the electric vehicle when the power delivered by the DC-DC converter that converts the vehicle's high voltage to low voltage in the onboard electrical system is insufficient.

[0004] Especially in modern vehicles, there are dynamic electrical loads whose operation can cause severe voltage drops, such as those in anti-lock braking systems or electric power steering systems, as used in parking assist systems. In particular, these dynamic loads are activated not only during initial cold starts or parking, but also while the vehicle is in motion.

[0005] To absorb voltage spikes or sags and mitigate the adverse effects of load behavior, multiple batteries, such as lead-acid batteries, are currently used throughout low-voltage vehicle electrical systems. These batteries can suppress voltage spikes or sags to a limited extent. However, they are too slow to respond to highly dynamic loads. Additionally, these batteries are relatively heavy. Summary of the Invention

[0006] The purpose of this invention is to provide an energy supply device that helps to reliably and / or cost-effectively and / or with minimal installation space supply loads in low-voltage vehicle electrical systems.

[0007] This objective is achieved through the features of the independent claim. The advantageous configuration is characterized in the dependent claims.

[0008] According to a first aspect, this objective is achieved by an energy supply device for providing low-voltage on-board electrical system voltage in a vehicle's low-voltage on-board electrical system. The energy supply device can be disposed in the low-voltage on-board electrical system, which is coupled to the vehicle's high-voltage electrical system via a high-voltage DC-DC converter. The energy supply device includes a first energy storage unit, a first DC-DC converter, and a second DC-DC converter connected in parallel with the first DC-DC converter. The first DC-DC converter is in the form of a bidirectional DC-DC converter. The first DC-DC converter is designed to deliver higher power compared to the second DC-DC converter.

[0009] The first energy storage unit includes a capacitor for energy delivery. This means that the energy storage unit is essentially formed by one or more capacitors.

[0010] The energy supply device also includes a voltage measuring device and a low-voltage on-board electrical system connector. The low-voltage on-board electrical system connector is used to connect the energy supply device directly or indirectly to one or more load branches of the low-voltage on-board electrical system. The voltage measuring device is arranged and designed to allow the control unit to deliver a first measurement signal representing the voltage across the low-voltage on-board electrical system connector, particularly the voltage between the low-voltage on-board electrical system connector and a reference ground potential.

[0011] The bidirectional first DC-DC converter has a first DC-DC connector, a second DC-DC connector, and a control connector. The bidirectional first DC-DC converter is connected to the first energy storage unit via the first DC-DC connector and to the low-voltage vehicle electrical system connector via the second DC-DC connector.

[0012] The first DC-DC converter is designed to use the control signal delivered by the control unit based on the first measurement signal as the basis for operation in buck or boost mode.

[0013] The energy supply device may include the control unit, or the control unit may be associated with the energy supply device. The control unit is specifically designed to determine the control signal based on the first measurement signal, and then deliver the control signal to the first DC-DC converter.

[0014] The second DC-DC converter includes a first connector connected to the energy storage unit and a second connector connected to the low-voltage vehicle electrical system connector. Therefore, the second DC-DC converter is connected in parallel with the first DC-DC converter.

[0015] The second DC-DC converter is designed to use the second connector of the second DC-DC converter in the vehicle's parking operation mode, particularly when the first DC-DC converter is deactivated, to provide current to the low-voltage loads connected to the low-voltage vehicle electrical system based on their power requirements.

[0016] The energy required by these low-voltage loads is preferably delivered solely by a high-voltage DC-DC converter and energy supply equipment. The low-voltage vehicle electrical system preferably does not have a separate low-voltage battery (e.g., a 12V battery) or a low-voltage battery integrated into the energy supply equipment.

[0017] Advantageously, the second DC-DC converter allows for a sufficiently long period of continuous power supply to these low-voltage loads in the low-voltage on-board electrical system during the vehicle's parking operation mode, characterized by the vehicle being turned off and in standby mode, in which most of these low-voltage loads are turned off or only briefly activated, such that only a few milliamps of current flow, for example, a maximum of 20 mA.

[0018] Advantageously, when the vehicle is in driving mode, if the high-voltage DC-DC converter does not provide sufficient power in this operating mode, the first DC-DC converter allows peak power to be delivered to these low-voltage loads.

[0019] Advantageously, when the vehicle is started and when the vehicle is in driving mode, the first DC-DC converter allows voltage spikes or voltage drops in the low-voltage on-board electrical system to be avoided, and thus prevents load behavior from adversely affecting the low-voltage on-board electrical system.

[0020] Using this high-voltage DC-DC converter and the first DC-DC converter, the energy storage unit of the energy supply device can be easily charged in parking operation mode.

[0021] In at least one advantageous configuration according to the first aspect, the capacitor comprises either a hybrid capacitor, a polymer capacitor, a polymer-hybrid capacitor, or a lithium-ion battery cell. Polymer-hybrid capacitors are characterized by particularly low equivalent series resistance (ESR) and high ripple current carrying capacity. These polymer-hybrid capacitors also provide high capacitance values ​​independent of voltage.

[0022] In at least one advantageous configuration according to the first aspect, the energy supply device includes a series circuit. The series circuit includes a current measuring device and a buffer capacitor connected in series. A first connection of the series circuit is connected to a low-voltage vehicle electrical system connection, which is intended to connect the energy supply device to the low-voltage vehicle electrical system, and a second connection of the series circuit is connected to a reference ground potential. The current measuring device is designed to deliver a second measurement signal to the control unit, the second measurement signal representing the current flowing in the series circuit.

[0023] The control unit is designed to additionally determine the control signal it delivers to the DC-DC converter based on the second measurement signal. The control signal may include control commands.

[0024] Assessing the current flowing into or out of the buffer capacitor allows for better stabilization of low-voltage onboard electrical systems and enables faster response times by predicting the desired mode (buck or boost). Switching from buck mode to boost mode and vice versa requires a certain amount of time. Current measurement and analysis of current gradients allow for very early detection of whether the DC-DC converter must provide boost or buck functionality, and the DC-DC converter can be actuated accordingly at an early stage.

[0025] Evaluating the current flowing into or out of the buffer capacitor also allows for improved voltage stabilization effectiveness because the thresholds used to detect overvoltage and undervoltage can be selected more closely. Pure voltage threshold detection has the following drawbacks for overvoltage and undervoltage: if the voltage threshold is set very close (due to early detection), the DC-DC converter will change operating modes very frequently, and the effectiveness of voltage support will be reduced.

[0026] On the other hand, if the voltage thresholds are set far apart from each other, this could cause the switching to take effect too late due to the time spent switching from buck mode to boost mode and vice versa, and it would no longer be possible to prevent voltage sags.

[0027] Assessing the current flowing into or out of the buffer capacitor also allows for the prevention or at least reduction of unwanted additional oscillations in the power supply to be supported. If the supply voltage oscillates faster than or similarly to the switching speed of the DC-DC converter's operating mode due to the inductance of the power supply lines to the load and the energy storage unit of the low-voltage on-board electrical system, this will result in additional oscillations in the power supply to be supported.

[0028] In at least one advantageous configuration, the performance capability of the first DC-DC converter is 10 to 100 times or 20 to 100 times greater than that of the second DC-DC converter.

[0029] In at least one advantageous configuration according to the first aspect, the first DC-DC converter is designed to deliver at least a portion of the energy delivered by the high-voltage DC-DC converter coupled to the low-voltage vehicle electrical system at the second DC-DC connector of the first DC-DC converter at the first DC-DC connector of the first DC-DC converter in the vehicle's parking operation mode, to charge the energy storage unit.

[0030] In at least one advantageous configuration according to the first aspect, the control unit is designed to use the state of charge of the energy storage unit as the basis for sending a wake-up signal to the battery management control unit so that the high-voltage energy storage unit can deliver energy for charging the energy storage unit via the high-voltage DC-DC converter and the first DC-DC converter.

[0031] In at least one configuration according to the first aspect, the voltage measuring device has a voltage divider with voltage divider taps, and the voltage divider is connected to the control unit to deliver the first measurement signal.

[0032] In at least one configuration according to the first aspect, the energy supply device includes the control unit, and the control unit is designed to: - Read the delivered first measurement data, which represents the voltage present on the low-voltage vehicle electrical system connector, and determine the voltage value based on the first measurement data. - Read the delivered second measurement data, which represents the current flowing in the series circuit. - Determine the time current gradient based on this second measurement data. - Compare the determined current gradient with a predetermined gradient threshold, and if the absolute value of the determined current gradient exceeds the predetermined gradient threshold, check whether the determined voltage value is below the lower voltage limit or above the upper voltage limit. - If the determined voltage value is lower than the lower voltage limit, the first control signal is delivered in such a way that the first control signal causes the first DC-DC converter to operate in the boost mode, and - If the determined voltage value exceeds the upper voltage limit, the first control signal is delivered in such a way that the first control signal causes the first DC-DC converter to operate in the buck mode.

[0033] In at least one configuration according to the first aspect, the control unit is designed to adjust the current delivered by the first DC-DC converter at its second DC-DC connector in either boost or buck mode based on the second measurement data.

[0034] According to the second aspect, this objective is achieved by an on-board electrical system for a vehicle. The on-board electrical system includes a high-voltage electrical system and a low-voltage on-board electrical system. The high-voltage electrical system includes a high-voltage energy storage unit, and the low-voltage on-board electrical system includes an energy supply device according to the first aspect. The high-voltage electrical system has a high-voltage DC-DC converter coupled to the high-voltage electrical system and the low-voltage on-board electrical system.

[0035] In at least one advantageous configuration according to the second aspect, the low-voltage load in the low-voltage vehicle electrical system is supplied with energy only by means of the energy storage unit via the first DC-DC converter and the second DC-DC converter, and by means of the high-voltage electrical system via the high-voltage DC-DC converter.

[0036] In this case, the advantageous configuration of the first aspect also applies to the second aspect. Attached Figure Description

[0037] Exemplary embodiments of the present invention are explained below based on schematic diagrams. The description of the subjects specified herein is not limited to a single specific embodiment. To the extent technically reasonable, features of different exemplary embodiments may be combined with each other to form other exemplary embodiments. For example, unless otherwise indicated, variations or modifications to the description of one exemplary embodiment may also be applied to other exemplary embodiments.

[0038] In the attached diagram: Figure 1 An illustrative block diagram showing an exemplary embodiment of the vehicle's onboard electrical system. Figure 2 An illustrative block diagram showing an exemplary embodiment of an energy supply device, and Figure 3 An illustrative flowchart is shown for the procedure used to operate the energy supply equipment to stabilize the low-voltage on-board electrical system.

[0039] In the accompanying drawings, the same reference numerals are used for elements that have substantially the same function, but these elements need not be identical in all details. Detailed Implementation

[0040] It should be noted that if an element is described as "connected" or "coupled" to another element, then that element may be directly connected or coupled to the other element, or there may be intermediate elements. In contrast, if an element is described as "directly," "connected," or "coupled" to another element, then there are no intermediate elements. Other expressions used to describe relationships between elements should be interpreted in the same way (e.g., "between" and "directly between," "adjacent" and "directly adjacent," etc.).

[0041] Figure 1 A block diagram illustrating an exemplary embodiment of a vehicle's onboard electrical system is shown. The onboard electrical system includes a high-voltage electrical system 5 and a low-voltage onboard electrical system 20 (LV onboard electrical system).

[0042] The high-voltage electrical system 5 includes a high-voltage energy storage unit 7. The high-voltage energy storage unit 7 is, for example, a traction battery for an electric vehicle. The high-voltage energy storage unit 7 may include: at least two energy storage units connected in series, or a series circuit containing at least two energy storage units. Alternatively, the high-voltage electrical system 5 may have redundant high-voltage energy storage units (…). Figure 1 (Not shown in the image), this redundant high-voltage energy storage unit can be connected to a high-voltage electrical system, especially in the event of a failure of the high-voltage energy storage unit.

[0043] The high-voltage electrical system 5 also includes a high-voltage DC-DC converter 8 (HVLV DC / DC). The HVLV DC / DC 8 has a high-voltage connector HV and a low-voltage connector LV. The high-voltage connector HV of the HVLV DC / DC 8 is connected to the high-voltage energy storage unit 7. The low-voltage connector LV is connected to the LV vehicle electrical system 10, for example, via contactors 4 for each of the high and low potentials. Therefore, the HVLV DC / DC 8 couples the HV vehicle electrical system 5 to the LV vehicle electrical system 10. The HVLV DC / DC 8 is designed to supply low-voltage power to the vehicle's LV vehicle electrical system 10 by converting power from the high-voltage energy storage unit 7. The HVLV DC / DC 8 includes, for example, a transformer and is therefore designed to electrically isolate the HV vehicle electrical system 5 from the LV vehicle electrical system 8.

[0044] For example, the HV vehicle electrical system 5 has other high-voltage loads 9. Preferably, the HV vehicle electrical system 5 has a motor. These contactors 4 can be used to isolate the high-voltage energy storage unit 7 from these other components.

[0045] For example, the LV vehicle electrical system 10 is a 12-volt low-voltage vehicle electrical system. Alternatively, the LV vehicle electrical system 10 can operate at, for example, 23 volts, 48 ​​volts, or another typical low-voltage electrical system.

[0046] The LV vehicle electrical system 10 includes an energy supply device 20 and one or more load branches 12 arranged in parallel with the energy supply device. The low-voltage output of the HVLV DC / DC converter is connected to one or more load branches 12. One or more low-voltage loads (LV loads) 14 may be arranged in the respective load branches 12. The LV loads 14 may have different associated requirements regarding functional safety. For example, the LV vehicle electrical system may have LV loads 14, each with associated functional safety requirements, such as those according to ISO 26262. For instance, these LV loads may each have one of the following associated requirements: ASIL A (Automotive Safety Integrity Level A), ASIL B, ASIL C, ASIL D, or QM.

[0047] For example, the HVLV DC / DC 8 delivers a rated voltage of 12 volts at the low-voltage connection LV. Alternatively, the HVLV DC / DC 8 can deliver a rated voltage of, for example, 23 volts, 48 ​​volts, or another typical low voltage of a low-voltage electrical system at the low-voltage connection LV.

[0048] The energy required by these LV loads 14 is preferably delivered solely by the high-voltage battery via the HVLV DC / DC 8 and by the energy supply device 20. The LV on-board electrical system 10 preferably does not have a separate low-voltage battery (e.g., a 12 V battery) or a low-voltage battery integrated into the energy supply device 20.

[0049] The energy supply device 20 is designed to supply energy to the LV load 14 in the LV on-board electrical system 10 for a predetermined period of time during the vehicle's parking operation mode, characterized in that the vehicle is turned off and in standby mode, in which most of the LV load 14 is turned off or only briefly activated, such that only a few milliamps of current flow, for example, a maximum of 20 mA.

[0050] The energy supply device 20 is also designed to deliver peak power to the LV load 14 when the vehicle is in driving mode if the power provided by the HV DC / DC 8 in this operating mode is insufficient.

[0051] The energy supply equipment is also designed to prevent voltage spikes or voltage drops in the LV vehicle electrical system 10 when the vehicle is started and when the vehicle is in driving mode, and thus prevent load behavior from adversely affecting the LV vehicle electrical system 10.

[0052] Figure 2 An illustrative block diagram of an exemplary embodiment of the energy supply device 20 is shown.

[0053] The energy supply device 20 has a low-voltage vehicle electrical system connector A.

[0054] The energy supply device 20 includes an energy storage unit 22, a first DC-DC converter 23 in the form of a bidirectional DC-DC converter, and a second DC-DC converter 24 connected in parallel with the first DC-DC converter 23. The second DC-DC converter 24 is preferably in the form of a boost converter. The first DC-DC converter 23 is designed to deliver higher power than the second DC-DC converter 24. The performance capability of the first DC-DC converter 23 is, for example, 20 to 100 times higher than that of the second DC-DC converter.

[0055] The energy storage unit 22 includes at least one capacitor. The capacitor stores all or most of the energy of the energy storage unit 22. The capacitor preferably has an energy storage capacity of more than 10 Wh, more preferably more than 20 Wh. The capacitor is preferably in the form of a polymer hybrid capacitor. This ensures that if the LV load 14 in the LV vehicle electrical system 10 requires an average of about 10 mA in the vehicle's standby mode and about 20 mA in the worst case, the energy storage unit 22 can maintain power supply for about 200 hours and 100 hours, respectively.

[0056] For example, a capacitor delivers 8 Ah at 4.2 V. This is equivalent to approximately 11,000 F.

[0057] The bidirectional first DC-DC converter 23 has a first DC-DC connector DC1, a second DC-DC connector DC2, and a control connector Ctrl. The first DC-DC converter 23 is directly or indirectly connected to a first power supply connector of the first energy storage unit 22 via the first DC-DC connector DC1. The second connector of the DC-DC converter DC2 is directly or indirectly connected to at least one load branch 12. The control connector Ctrl of the first DC-DC converter 23 is connected to a control unit 25. The energy supply device 20 may include the control unit 25. Alternatively, the control unit 25 may be associated with the energy supply device 20. The first DC-DC converter 23 can be activated or deactivated as needed by means of the control unit 25.

[0058] The second DC-DC converter 24 has a first connector T1 and a second connector T2.

[0059] This arrangement ensures that a high voltage level or excess energy (or high state of charge) in the LV on-board electrical system 10 will cause current to flow out of the LV on-board electrical system 10 via the first DC-DC converter 23. If the LV on-board electrical system 10 has a low voltage level, the current can also flow in the opposite direction. A high voltage level refers to a voltage above a predetermined upper limit. A low voltage level refers to a voltage below a predetermined lower limit.

[0060] The second DC-DC converter 24 is designed to deliver lower power, for example, less than 5 W. Therefore, the activation and deactivation of the second DC-DC converter 24, as well as its intensive monitoring, can be eliminated. This means that the second DC-DC converter 24 can operate continuously or remain active. The advantage of this is that it eliminates the need for additional control via a controller.

[0061] Therefore, the energy supply device 20 is designed to deliver power from the energy storage unit 22 to the LV load 14 of the LV vehicle electrical system 10 via the second DC-DC converter 24 when the vehicle is in parking mode. The second DC-DC converter 24 is designed to provide the energy drawn from the energy storage unit 22 of the energy supply device 20 at the second connection T2 (which is directly or indirectly connected to at least one load branch 12) during the vehicle's parking operation mode, when the first DC-DC converter 23 is deactivated, and in particular, to provide a predetermined current to the LV load 14 connected to the LV vehicle electrical system 10 at the second connection T2 of the second DC-DC converter 24.

[0062] Energy storage unit 22 can be recharged while the vehicle is in parking mode. As described, energy storage unit 22 may be depleted and require recharging after approximately 100 hours. For example, control unit 25 is designed to send a wake-up signal to battery management system (BMS) when the vehicle is in parking mode. The BMS then couples high-voltage energy storage unit 7 to HVLV DC / DC 8, for example, via closing contactor 4. The BMS also activates or starts HVLV DC / DC 8. HVLV DC / DC 8 and first DC-DC converter 23 transfer energy to energy storage unit 22. When energy storage unit 22 is fully charged, the vehicle switches back to sleep mode, specifically, high-voltage battery 7 is disconnected again.

[0063] The energy supply device 20 is designed to stabilize the supply voltage of the LV on-board electrical system 10 during vehicle startup. Specifically, the energy supply device 20 is designed to prevent voltage spikes or drops in the LV on-board electrical system 10 during vehicle startup, and thus prevent load behavior from adversely affecting the LV on-board electrical system 10. During startup (when the required power is higher than, for example, 5 W), the power for the loads in the LV on-board electrical system 10 is delivered by one or more hybrid capacitors via a first DC-DC converter 23.

[0064] The energy supply device 20 is also designed to deliver peak power to the LV load 14 when the vehicle is in driving mode if the power provided by the HV DC / DC 8 in this operating mode is insufficient.

[0065] Maintaining a stable supply voltage in driving mode and during startup requires special operation of the first DC-DC converter 23. Therefore, the energy supply device 20 includes a voltage measuring device 26, which is designed and arranged so that the control unit 25 delivers a first measurement signal representing the voltage at the low-voltage vehicle electrical system connection A. This first measurement signal represents the sum of the voltage drop across the load branch 12 and the voltage drop along the power supply line leading to the load branch 12 due to line inductance 19.

[0066] For example, the voltage measuring device 26 has a voltage divider arranged in parallel with the low-voltage connection LV of the load branch 12 or the HVLV DC / DC 8. The voltage divider has a first connection, a second connection, and a voltage divider tap. For example, the first connection of the voltage divider is connected to the second DC-DC connection DC2 of the first DC-DC converter 23, and the second connection of the voltage divider is connected to a reference ground potential, such as ground. For example, the voltage divider tap is connected to the control unit 25, and in particular to the analog-to-digital converter of the control unit 25.

[0067] In an optional configuration, the energy supply device 20 includes a current measuring device 27 and a buffer capacitor 28. The current measuring device 27 and the buffer capacitor 28 are connected in series. This series circuit is arranged in a branch connected in parallel with at least one load branch 12.

[0068] The current measuring device 27 is designed to deliver a second measurement signal representing the current flowing into or out of the buffer capacitor 28. For example, the current measuring device 27 includes a shunt resistor.

[0069] The first DC-DC converter 23 is designed to use the control signal delivered by the control unit 25 based on the second measurement signal as the basis for operation in buck mode or boost mode.

[0070] Figure 3 An illustrative flowchart is shown of a procedure for operating the energy supply device 20 to stabilize the LV vehicle electrical system 10. For example, this procedure is executed by a control computer of the energy supply device 20. For example, the control computer has a microcontroller or microprocessor and program memory. The microcontroller and / or microprocessor may have one or more integrated analog-to-digital converters. The control computer may be part of a control unit or may be a control unit itself.

[0071] The program starts in step S01. For example, variables are initialized in step S01.

[0072] In step S03, first measurement data is read, for example, delivered by another analog-to-digital converter of control unit 25. The first measurement data represents the voltage in the vehicle electrical system 10, particularly the voltage present on the low-voltage vehicle electrical system connector A (relative to the reference ground potential GND). In step S03, the voltage value is also determined based on the first measurement data.

[0073] In step S05, second measurement data is read, for example, delivered by another analog-to-digital converter of control unit 25. The second measurement data represents the current flowing into or out of buffer capacitor 28. In step S05, the time current gradient is also determined based on the previously determined current value and the currently determined current value.

[0074] Steps S03 and S05 can be performed simultaneously or sequentially, or in reverse order.

[0075] In step S07, the determined current gradient is compared with a predetermined gradient threshold, for example, 50 A / ms. If the determined current gradient exceeds the predetermined threshold, a check is performed in step S09 to determine whether the determined voltage value is below the lower voltage limit or above the upper voltage limit.

[0076] If the determined voltage value is lower than, for example, a lower voltage limit of 13.5 V, then in step S11, a first current to be delivered by the first DC-DC converter 23 to the LV vehicle electrical system 10 is determined based on the current gradient and / or the currently determined current value. In step S11, a first actuation signal is also delivered to the first DC-DC converter 23, and this signal causes the first DC-DC converter 23 to operate in boost mode and deliver the determined first current.

[0077] If the determined voltage value exceeds, for example, a voltage upper limit of 15 V, then in step S13, a second current to be delivered by the first DC-DC converter 23 to the LV vehicle electrical system 10 is determined based on the current gradient and / or the currently determined current value. In step S12, a second actuation signal is also delivered to the first DC-DC converter 23, and this signal causes the first DC-DC converter 23 to operate in buck mode and deliver the determined second current.

[0078] For this purpose, control unit 25 may have a PID controller. The PID controller may be 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, which is determined in each case based on first measurement data. The PID controller actuates the first DC-DC converter 23 by delivering a boost or buck current, resulting in the output or input current of the buffer capacitor 28 being adjusted to zero. For example, the PID controller is deactivated once the lower voltage limit plus, for example, a hysteresis value of 0.25 V is exceeded, or once the upper voltage limit minus, for example, a hysteresis value of 0.25 V is exceeded.

[0079] In step S13, the program ends. Advantageously, the first and second measurement data are continuously captured and evaluated while the vehicle is running.

[0080] Since the current measuring device 27 is arranged in the same branch as the buffer capacitor 28, current changes caused by overvoltage or undervoltage can be identified very quickly and at an early stage, and the DC-DC converter can be actuated appropriately.

[0081] The advantage of assessing current changes is that the hysteresis of voltage assessment can be very narrow, and therefore the first DC-DC converter 23 can be actuated very quickly and appropriately at an early stage, i.e., the correct mode and the current that must be provided by the first DC-DC converter 23 can be set.

[0082] It should be noted that embodiments of the invention have been described with reference to different subjects of the invention. In particular, some embodiments of the invention are described by way of method claims, while others are described by way of device claims. However, it will be immediately apparent to those skilled in the art upon reading this application that, unless otherwise expressly stated, any combination of features associated with different types of subjects of the invention is possible, in addition to combinations of features associated with one type of subject matter of the invention. List of reference numerals 1. Vehicle electrical system 4 contactors 5. High-voltage electrical systems 7 High-voltage energy storage units 8 High-voltage DC-DC converter 9 High-voltage load 10 Low-voltage vehicle electrical systems 12 load branches 14 loads 19-line inductor 20 devices 22 First Energy Storage Unit 23 First DC-DC Converter 24 Second DC-DC Converter 25 control units 26 Voltage measuring device 27 Current measuring device 28 buffer capacitors A. Low-voltage vehicle electrical system connector.

Claims

1. An energy supply device (20) for providing low-voltage on-board electrical system voltage in a vehicle's low-voltage on-board electrical system (10), wherein - The energy supply device (20) can be arranged in the low-voltage vehicle electrical system (10), which is coupled to the high-voltage electrical system (5) of the vehicle via a high-voltage DC-DC converter (8). - The energy supply device (20) has a first energy storage unit (22), a first DC-DC converter (23), and a second DC-DC converter (24), and the first DC-DC converter (23) is in the form of a bidirectional DC-DC converter. - The first DC-DC converter (23) is designed to deliver higher power compared to the second DC-DC converter (24). - The first energy storage unit (22) includes a capacitor for energy delivery. - The energy supply device (20) also includes a voltage measuring device (26) and a low-voltage vehicle electrical system connector (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 bidirectional first DC-DC converter (23) has a first DC-DC connector (DC1), a second DC-DC connector (DC2) and a control connector (Ctrl), and the bidirectional first DC-DC converter (23) is connected to the first energy storage unit (22) through the first DC-DC connector (DC1) and connected to the low-voltage vehicle electrical system connector (A) through the second DC-DC connector (DC2). - The voltage measuring device (26) is arranged and designed to deliver a first measuring signal to the control unit (25), the first measuring signal representing the voltage on the low-voltage vehicle electrical system connector (A). - The first DC-DC converter (23) is designed to use the control signal delivered by the control unit (25) based on the first measurement signal as the basis for operation in buck mode or boost mode. - The second DC-DC converter (24) has a first connector (T1) connected to the energy storage unit (22) and a second connector (T2) connected to the low-voltage vehicle electrical system connector (A), and the second DC-DC converter (24) is designed to use the second connector (T2) of the second DC-DC converter (24) in the parking operation mode of the vehicle to provide current to the low-voltage loads (14) connected to the low-voltage vehicle electrical system (10) based on the power requirements of the low-voltage loads (14) connected to the low-voltage vehicle electrical system (10).

2. The energy supply device (20) as described in claim 1, wherein, The capacitor may be a hybrid capacitor, a polymer capacitor, a polymer hybrid capacitor, or a lithium battery cell.

3. The energy supply device (20) as described in claim 1 or 2, wherein - The energy supply device (20) includes a series circuit, which includes a current measuring device (27) and a buffer capacitor (28) connected in series. - The series circuit has a first connector and a second connector, the first connector being connected to the low-voltage vehicle electrical system connector (A), and the second connector being connected to the reference ground potential (GND). - The current measuring device (27) is designed so that the control unit (25) delivers a second measuring signal representing the current flowing in the series circuit, and the control unit (25) additionally delivers a control signal for setting the buck mode or boost mode of the first DC-DC converter (23) based on the second measuring signal.

4. The energy supply device (20) as described in any one of the preceding claims, wherein, The performance capability of the first DC-DC converter (23) is 20 to 100 times greater than that of the second DC-DC converter (24).

5. The energy supply device (20) as described in any one of the preceding claims, wherein, The first DC-DC converter (23) is designed to deliver at least a portion of the energy delivered by the high-voltage DC-DC converter (8) coupled to the low-voltage vehicle electrical system (10) at the first DC-DC connector (DC1) of the first DC-DC converter (23) at the second DC-DC connector (DC2) of the first DC-DC converter (23) to charge the energy storage unit (22) in the vehicle's parking operation mode.

6. The energy supply device (20) as described in any one of the preceding claims, wherein, In the vehicle's parking operation mode, the control unit (25) is designed to use the state of charge of the energy storage unit as the basis for sending a wake-up signal to the battery management control unit so that the high-voltage energy storage unit (7) can deliver energy for charging the energy storage unit (22) via the high-voltage DC-DC converter (8) and the first DC-DC converter (23).

7. The energy supply device (20) as described in any one of the preceding claims, wherein, The voltage measuring device (26) has a voltage divider with a voltage divider tap, which is connected to or can be connected to the control unit (25) to deliver the first measurement signal.

8. The energy supply device (20) as described in any one of claims 3 to 7, wherein, The energy supply device includes the control unit (25), and the control unit (25) is designed to be - Read the delivered first measurement data, which represents the voltage present on the low-voltage vehicle electrical system connector, and determine the voltage value based on the first measurement data. - Read the delivered second measurement data, which represents the current flowing in the series circuit. - Determine the time current gradient based on this second measurement data. - Compare the determined current gradient with a predetermined gradient threshold, and if the absolute value of the determined current gradient exceeds the predetermined gradient threshold, check whether the determined voltage value is below the lower voltage limit or above the upper voltage limit. - If the determined voltage value is lower than the lower voltage limit, the first control signal is delivered in such a way that the first control signal causes the first DC-DC converter (23) to operate in the boost mode, and - If the determined voltage value exceeds the upper limit of the voltage, the first control signal is delivered in such a way that the first control signal causes the first DC-DC converter (23) to operate in the buck mode.

9. The energy supply device (20) as described in claim 8, wherein, The control unit is designed to adjust the current delivered by the first DC-DC converter (23) at its second DC-DC connector (DC2) in either boost or buck mode based on the second measurement data.

10. An on-board electrical system for a vehicle, the on-board electrical system comprising: - A high-voltage electrical system (5), which includes a high-voltage energy storage unit (7), and - A low-voltage vehicle electrical system (10), comprising an energy supply device (20) as described in any one of claims 1 to 9, wherein, The high-voltage electrical system has a high-voltage DC-DC converter (8) that couples the high-voltage electrical system (5) and the low-voltage vehicle electrical system (10).

11. The vehicle electrical system as claimed in claim 10, wherein, The low-voltage load (14) in the low-voltage vehicle electrical system (10) is supplied with energy only by means of the energy storage unit (22) via the first DC-DC converter (23) and the second DC-DC converter (24), and by means of the high-voltage electrical system via the high-voltage DC-DC converter (8).

Images