Method and device for operating an on-board electrical system

Abstract

Method for operating an on-board network (BN) comprising a first energy storage device (BAT_1) and a second energy storage device (BAT_2), wherein both energy storage devices are connected in parallel, in which - Key performance indicators (kW) of the first energy storage unit (BAT_1) and / or the second energy storage unit (BAT_2) are recorded, - depending on the recorded parameters (KW), a regeneration phase (RP) of the first energy storage device (BAT_1) is carried out, in which an initial operating voltage (V_1) is specified and provided by means of a generator (G) such that it contributes to the second energy storage device (BAT_2) having a higher open-circuit voltage than the first energy storage device (BAT_1) after a specified period of time, whereby the regeneration continues when the generator (G) is switched off, by further charging the first energy storage device (BAT_1) from the second energy storage device (BAT_2) until an equilibrium voltage is established between both energy storage devices (BAT_1, BAT_2).

Description

[0001] The invention relates to a method for operating an on-board electrical system having a first energy storage device and a second energy storage device.

[0002] Vehicle electrical systems usually have an energy storage device in the form of a lead-acid battery. However, the lead-acid battery often requires regeneration. This regeneration can take up to 24 hours. Since normal vehicle operation does not take that long, regeneration is usually carried out over several driving cycles.

[0003] DE 10 2010 062 116 A1 discloses an energy storage device for a motor vehicle with a first electrical energy store, having a first voltage characteristic curve which determines the open-circuit voltage of the first electrical energy store as a function of its relative state of charge, and a first resistance characteristic curve which determines the internal resistance of the first electrical energy store relevant for a charging process of the first electrical energy store as a function of its relative state of charge, and with a second electrical energy store connected in parallel to the first electrical energy store, having a second voltage characteristic curve which determines the open-circuit voltage of the second electrical energy store as a function of its relative state of charge, and by a second resistance characteristic curve,which determines the internal resistance of the second electrical energy storage device relevant for a charging process of the second electrical energy storage device as a function of its relative state of charge, in which the voltage value range covered by the first voltage characteristic curve and the voltage value range covered by the second voltage characteristic curve partially overlap and the first resistance characteristic curve and the second resistance characteristic curve have exactly one intersection point.

[0004] DE 10 2009 053 690 A1 discloses an on-board electrical system for a motor vehicle, comprising an energy storage device and a voltage source that can be electrically coupled to the energy storage device. The voltage source is configured to provide a predetermined first voltage and a predetermined second voltage. The second voltage represents a regeneration voltage of the energy storage device and is greater in magnitude than the first voltage. Furthermore, the on-board electrical system comprises a decoupling unit that can be electrically coupled to the energy storage device and the at least one first electrical consumer. The decoupling unit has a voltage converter that is electrically coupled to the input terminal on the input side and to the output terminal on the output side.The decoupling unit also comprises a switching element electrically coupled in parallel to the voltage converter and is designed to provide approximately the first voltage on the output side while the first or second voltage is applied on the input side.

[0005] US 2002 / 0145404 A1 discloses an electrical storage device for storing electrical energy and supplying a drive motor with electrical energy at different power levels. The electrical storage device has an energy battery connected to a power battery. The energy battery has a higher energy density than the power battery. However, the power battery can supply the electric motor with electrical energy at different power levels, ensuring that the motor has sufficient power and current when needed. The power battery is continuously recharged by the energy storage battery. In this way, the power battery temporarily stores the electrical energy received from the energy battery and provides the electrical energy at different power levels as needed by the motor.The energy storage unit can be detachably connected to an external power source to charge both batteries. Both batteries can be charged independently to optimize the charging and service life characteristics of the batteries.

[0006] The object underlying the invention is to create a method or a device that contributes to the regeneration of an energy storage device of an on-board electrical system.

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

[0008] The invention is characterized by a method and a device for operating an on-board electrical system. The on-board electrical system has a first energy storage device and a second energy storage device. The two energy storage devices are connected in parallel. Characteristic values ​​of the first and / or the second energy storage device are recorded. Depending on the recorded characteristic values, a regeneration phase of the first energy storage device is carried out. During the regeneration phase, a first operating voltage is predetermined and provided by a generator in such a way that it contributes to the second energy storage device having a higher open-circuit voltage than the first energy storage device after a predetermined period of time. The regeneration is continued when the generator is switched off by the first energy storage device continuing to be charged by the second energy storage device until an equilibrium voltage is established between the two energy storage devices.

[0009] By connecting the two energy storage units in parallel, it is possible for the first energy storage unit to continue charging as soon as the second energy storage unit has a higher open-circuit voltage, even when the generator is no longer running. This makes it possible for the first energy storage unit to continue regenerating even after a vehicle's driving cycle has ended. By executing the regeneration phase based on specific parameters, it is also possible for regeneration to only be performed when it makes sense, for example, when the first energy storage unit's battery temperature reaches a certain predefined temperature.

[0010] According to an advantageous embodiment, after a predetermined charge level of the second energy storage device has been reached, a second predetermined operating voltage is provided by the generator, which contributes to charging the first energy storage device and ensuring that the second energy storage device approximately maintains its charge level. This allows, for example, a higher first predetermined operating voltage to charge the second energy storage device more quickly, and, for example, at a charge level of 90% capacity, setting the second predetermined operating voltage can contribute to further charging the first energy storage device.

[0011] According to a further advantageous embodiment, characteristic values ​​of the first energy storage device are monitored during the regeneration phase. This allows regeneration to be checked and, for example, terminated if the characteristic values ​​fall below or exceed specified thresholds.

[0012] According to a further advantageous embodiment, the vehicle electrical system has a switch that allows the first energy storage device to be galvanically separated from the second energy storage device. This increases the safety of the vehicle electrical system, as it is possible to galvanically separate the two energy storage devices from each other, for example, if one of the two energy storage devices is defective.

[0013] According to a further advantageous embodiment, the first energy storage device comprises a lead-acid battery. This is a robust and cost-effective energy storage device, especially in vehicle electrical systems.

[0014] According to a further advantageous embodiment, the second energy storage device comprises a lithium-ion battery. This battery is characterized by its rapid charging capability and, when suitably configured, a higher open-circuit voltage than a lead-acid battery.

[0015] According to a further advantageous embodiment, if there is no or only a predetermined low charge flow between the first and second energy storage devices, a check is carried out based on the recorded characteristic values ​​to determine whether the regeneration phase was successful. This allows, for example, if the regeneration phase was not yet successful, the information that a further regeneration phase is necessary, for example, during the next driving operation to be stored. Alternatively or additionally, if the regeneration phase was successful, the information that the regeneration was successfully completed can be stored.

[0016] Embodiments of the invention are explained in more detail below with reference to the schematic drawings. They show: Fig. 1 a circuit diagram of an on-board network with two energy storage units, Fig. 2 a flowchart of a program for carrying out a regeneration phase and Fig. 3 different voltage curves of energy storage devices.

[0017] Elements of the same design and function are marked with the same reference symbols throughout the figures.

[0018] Fig. Figure 1 shows a circuit diagram of an on-board electrical system BN. The on-board electrical system BN includes a starter S and a generator G. The on-board electrical system BN also includes several loads L. Furthermore, the on-board electrical system BN includes a first energy storage device BAT_1 with a battery sensor BS and a second energy storage device BAT_2 with a battery sensor BS.

[0019] Operating voltages can be provided by means of the generator G, whereby it is possible for a voltage converter to be connected downstream of the generator G in order to set a predetermined operating voltage.

[0020] The first energy storage device BAT_1 is, for example, a lead-acid battery. The second energy storage device BAT_2 is, for example, a lithium-ion battery, such as a lithium iron phosphate battery (LiFePO4) and / or a lithium nickel manganese cobalt battery (Li-NMC) and / or another lithium-ion battery and / or a nickel metal hydride battery.

[0021] The battery sensors BS are designed to detect characteristic values ​​KW of the respective energy storage device, such as the respective temperature, the applied voltage, the state of charge, the charge throughput, and / or the energy throughput. The determination of these characteristic values ​​can be time-dependent.

[0022] For example, a switch can be installed between the first energy storage device BAT_1 and the second energy storage device BAT_2, allowing the two energy storage devices to be electrically isolated. This can be used, for example, to separate the energy storage devices from each other if one of them is defective.

[0023] The on-board network BN is located, for example, in a vehicle. The vehicle in which the on-board network BN is located has, for example, a device that includes a computing unit, a program and data memory, and a communications interface. The computing unit and / or the data memory can be implemented in a single unit or distributed across multiple units.

[0024] To operate the on-board power supply system BN, a program is preferably stored in the program and data memory of the device, which can be executed during operation of the on-board power supply system BN. The program is described below using the flow chart of the Fig. 2 is explained in more detail.

[0025] The program is started in a step S1 in which variables can be initialized if necessary.

[0026] In a subsequent step S2, characteristic values ​​KW of the first energy storage device BAT_1 and / or characteristic values ​​KW of the second energy storage device BAT_2 are recorded. The characteristic values ​​KW are recorded, for example, by the respective battery sensor BS.

[0027] In a subsequent step S3, the recorded characteristic values ​​KW are checked, for example, by comparing them with predefined threshold values. For example, the temperature of the respective energy storage device can be checked, since regeneration is advantageous in certain temperature ranges. The charge absorption of the first energy storage device BAT_1 may improve in a certain temperature range, thereby potentially shortening the required time. Particularly when BAT_1 is designed as a lead-acid battery, regeneration is advantageous at elevated lead-acid battery temperatures.

[0028] Alternatively or additionally, the cycle count of the first energy storage device BAT_1 can be compared with a threshold value, so that regeneration is performed after a specified number of cycles. Alternatively or additionally, other parameters such as dwell time and / or charging conversion can be checked.

[0029] If, based on the recorded KW parameters, it is determined that regeneration is advisable, the program continues to step S5. If it is determined that regeneration is not advisable, the program continues to step S2.

[0030] In step S5, the regeneration phase RP is started. For this purpose, a first operating voltage V_1 is specified and provided by the generator G in such a way that it contributes to the second energy storage device BAT_2 having a higher open-circuit voltage than the first energy storage device BAT_1 after a specified period of time.

[0031] If the second energy storage device BAT_2 has a higher open-circuit voltage than the first energy storage device BAT_1, it is possible that regeneration will continue when the generator G is shut down. In such a case, the first energy storage device BAT_1 will continue to be charged by the second energy storage device BAT_2 until an equilibrium voltage is established between the two energy storage devices.

[0032] In an optional step S7 following step S5, after a predetermined charge level of the second energy storage device BAT_2 has been reached, a second predetermined operating voltage V_2 is provided by the generator G. This second predetermined operating voltage V_2 contributes to charging the first energy storage device BAT_1 and ensuring that the second energy storage device BAT_2 approximately maintains its charge level. This makes it possible to charge the second energy storage device BAT_2 and / or the first energy storage device BAT_1 more quickly, if necessary.

[0033] If the equilibrium voltage is established, i.e. no or only a predetermined low charge flow flows between the first energy storage device BAT_1 and the second energy storage device BAT_2, further characteristic values ​​KW are recorded in a step S9, such as a voltage applied to the first energy storage device BAT_1.

[0034] In a subsequent step S11, a check is carried out to determine whether the regeneration phase RP was successful, depending on the recorded characteristic values ​​KW. This is checked, for example, using the recorded voltage. If the recorded voltage is, for example, above a predetermined threshold value, or if another characteristic value KW indicates that the regeneration phase RP was successful, the program continues in a step S14. If it is, for example, below this threshold value, or if another characteristic value KW indicates that the regeneration phase RP was unsuccessful, the program continues in a step S13. The characteristic values ​​KW, for example, alternatively or additionally indicate the duration of the regeneration phase RP. For example, if a predetermined duration of the regeneration phase RP is reached, the regeneration phase RP can be designated as successful, whereby the duration of the regeneration phase can vary, for example, depending on the type of energy storage device.

[0035] In step S13, since the regeneration phase RP was not successful, it is stored, for example, that a further regeneration phase RP is necessary, which can be carried out, for example, during the next driving operation.

[0036] In step S14, since the regeneration phase RP is successful, it is stored, for example, that the regeneration was successful and / or, for example, a cycle counter or trigger counter is reset.

[0037] In a step S15 following step S13 or S14, the program is terminated and can, if necessary, be started again in step S1.

[0038] Fig. Figure 3 shows various combinations of energy storage devices in an on-board electrical system. The capacity KAP of each energy storage combination is plotted at an open-circuit voltage LLV. The diagram shows voltage curves for a single lead-acid battery PB and for three different combinations of lead-acid batteries and lithium-ion batteries: PBLI_1, PBLI_2, and PBLI_3.

[0039] The intersection point of the two axes in Fig.3 is normalized with respect to the x-axis for the combinations shown to the fully charged lead-acid battery. This state is considered ideal for the lead-acid battery. Charge states of the combination of the two batteries that are above the maximum charge of the lead-acid battery and that arise from electrochemical energy stored in the lithium-ion battery are plotted along the negative x-axis. The illustration shows that by combining the two batteries, even without current generator operation, a state of the combination of the two batteries can be set that is above the full charge state of the lead-acid battery in relation to the open-circuit voltage (y-axis). This effect can be used to fully charge the lead-acid battery as part of its regeneration. List of reference symbols BN on-board network S Starter G Generator L Consumer BAT_1 first energy storage BAT_2 second energy storage BS battery sensor KW characteristics RP regeneration phase V_1 first operating voltage V_2 second operating voltage LLV open circuit voltage CAP capacity PB voltage curve lead-acid battery PBLI_1 Voltage curve of the first energy storage combination PBLI_2 Voltage curve of the second energy storage combination PBLI_3 Voltage curve of the third energy storage combination

Claims

[1] Method for operating an on-board network (BN) which has a first energy storage device (BAT_1) and a second energy storage device (BAT_2), both energy storage devices being connected in parallel, in which - Characteristic values (KW) of the first energy storage device (BAT_1) and / or the second energy storage device (BAT_2) are recorded, - depending on the recorded characteristic values (KW), a regeneration phase (RP) of the first energy storage device (BAT_1) is carried out, in which a first operating voltage (V_1) is predetermined and provided by means of a generator (G) in such a way that it contributes to the second energy storage device (BAT_2) having a higher open-circuit voltage than the first energy storage device (BAT_1) after a predetermined period of time, wherein the regeneration is continued when the generator (G) is switched off by the first energy storage device (BAT_1) continuing to be charged by the second energy storage device (BAT_2) until an equilibrium voltage is established between the two energy storage devices (BAT_1, BAT_2). [2] Method according to claim 1, wherein after reaching a predetermined state of charge of the second energy storage device (BAT_2), a second predetermined operating voltage (V_2) is provided by means of the generator (G), which contributes to the charging of the first energy storage device (BAT_1) and the approximately maintenance of its state of charge of the second energy storage device (BAT_2). [3] Method according to claim 1 or 2, wherein during the regeneration phase (RP) characteristic values (KW) of the first energy storage device (BAT_1) are monitored. [4] Method according to claim 1, 2 or 3, wherein the on-board electrical system (BN) has a switch by means of which the first energy storage device (BAT_1) can be galvanically separated from the second energy storage device (BAT_2). [5] Method according to one of the preceding claims, wherein the first energy storage device (BAT_1) comprises a lead-acid battery. [6] Method according to one of the preceding claims, wherein the second energy storage device (BAT_2) comprises a lithium-ion accumulator. [7] Method according to one of the preceding claims, in which, if there is no or only a predetermined low charge flow between the first energy storage device (BAT_1) and the second energy storage device (BAT_2), it is checked depending on the recorded characteristic values (KW) whether the regeneration phase (RP) was successful. [8] Device for operating an on-board network (BN) which has a first energy storage device (BAT_1) and a second energy storage device (BAT_2), wherein both energy storage devices are connected in parallel, which device is designed to carry out a method according to one of claims 1-7.

Images