Method for monitoring the voltage of a battery element of a vehicle battery and corresponding control unit

Abstract

The invention relates to a method for monitoring the voltage of a battery element (Zk) of a battery (101), in particular a vehicle battery, by means of a voltage monitoring circuit (102), wherein the voltage monitoring circuit is connected to a positive pole by a first measurement connection (Wk+1) and to a negative pole of the battery element (Zk) by a second measurement connection (Wk & 105). The method comprises the following steps: determining a voltage value (Uk), which is indicative of a battery element voltage between the two poles, using the voltage monitoring circuit (102); determining a resistance value (R) of a section of a connecting element (105), the connecting element (105) connecting the battery element (Zk) to an adjacent battery element (Zk-1) and one of the two measurement connections (Wk & 105, Wk+1) containing the section of the connecting element (105); and correcting the voltage value (Uk) on the basis of the resistance value (R). The invention also relates to a corresponding control device and to a computer program.

Description

[0001] DESCRIPTION

[0002] Method for voltage monitoring of a battery element of a vehicle battery and corresponding control unit

[0003] TECHNICAL AREA

[0004] The present disclosure relates to methods and control devices for monitoring the voltage of battery elements of a vehicle battery, for example battery cells.

[0005] BACKGROUND OF THE INVENTION

[0006] Batteries in vehicle powertrains typically consist of a number of battery cells connected in series and, if necessary, in parallel. For safety reasons, such as preventing thermal damage and excessive aging, these cells must only be operated within specific cell voltage limits, which are usually specified by the battery manufacturer. The upper cell voltage limit restricts the current during battery charging, for example, when charging from the mains or during regenerative braking in ferry operation, while the lower cell voltage limit restricts the current during battery discharge, for example, during acceleration in ferry operation. The cell voltages are measured using monitoring electronics, which use measuring leads to detect the potentials above and below each cell and calculate the cell voltage from the difference in voltage.For this purpose, one or more battery monitoring ICs (Bat-Mon ICs) are often used, each with multiple input channels for the individual cell voltages. The cell voltages can then be determined from the Bat-Mon IC readings, for example, in a battery control unit or within a vehicle or drive control unit. However, it has been shown that with conventional monitoring methods, at least some of the measured cell voltages exhibit systematic errors.

[0007] SUMMARY AND FORMS OF IMPLEMENTATION It is therefore an objective of the present disclosure to provide a particularly reliable and accurate method and control device for voltage monitoring of battery elements, in particular battery cells, taking into account systematic errors in the determination of at least some cell voltages.

[0008] This problem is solved by a method for monitoring the voltage of a battery cell, in particular a vehicle battery, as well as a control unit and a computer program according to the independent claims. Advantageous embodiments and further developments are described in the dependent claims, the following description, and the drawings.

[0009] According to a first aspect, a method for monitoring the voltage of a battery cell, particularly a vehicle battery, is provided using a voltage monitoring circuit. The voltage monitoring circuit is connected to a positive terminal and a negative terminal of the battery cell via a first measuring connection and a second measuring connection. The method comprises the following steps: determining, in particular measuring, a voltage value indicative of the battery cell voltage between the two terminals using the voltage monitoring circuit; determining the resistance value of a section of a connecting element, wherein the connecting element links the battery cell to an adjacent battery cell and wherein one of the two measuring connections includes the section of the connecting element; and correcting the voltage value based on the resistance value.The term "section" is used here in a general sense and can also refer to the entire connecting element.

[0010] According to another aspect, a control unit, in particular a battery management system, is provided which is configured to carry out the procedure described above. According to one embodiment, the control unit is or includes the voltage monitoring circuit. According to another aspect, a battery system is provided which includes the control unit described above, including the voltage monitoring circuit, the battery, and the first and second measuring connections between the voltage monitoring circuit and the battery.

[0011] According to another aspect, a computer program is provided that includes instructions which, when executed by a computer, cause it to perform the procedure described above. In the context of this disclosure, a computer is defined, for example, as a device that processes data using programmable computational instructions. Computers can be embedded in everyday devices, such as the control units of motor vehicles.

[0012] According to another aspect, a storage medium is provided with a computer program, wherein the computer program includes instructions which, when the computer program is executed by a computer, cause it to carry out the procedure described above.

[0013] In the context of this disclosure, a battery is defined, for example, as a storage device for electrical energy, particularly on an electrochemical basis. In one embodiment, the battery is an accumulator, i.e., a rechargeable battery. The battery can contain several battery cells, which can be connected in series, at least partially, and in particular completely. The battery can contain several battery modules, wherein several battery cells are grouped together to form a battery module. Furthermore, the battery can contain several battery packs, wherein several battery modules are grouped together to form a battery pack. The battery is, for example, a lithium-ion accumulator. The battery can be a traction battery suitable for providing energy for a vehicle propulsion system. The battery can be a high-voltage battery.

[0014] In the context of this disclosure, a battery element is defined, for example, as a part of the battery comprising at least one battery cell. A battery element can be a single battery cell or an arrangement of a plurality of battery cells. The plurality of battery cells can, in particular, be connected in parallel. In the context of this disclosure, a battery cell can comprise an anode and a cathode, which are, in particular, separated by a conductive medium, for example, an electrolyte.

[0015] A battery element can also be or comprise a battery module or an arrangement of multiple battery modules and / or a battery pack or an arrangement of multiple battery packs. A battery module can comprise multiple battery cells, which can be connected in series and / or parallel. Within a battery module, the battery cells can be grouped in such a way that it is modularly replaceable. Similarly, a battery pack can comprise multiple battery modules.

[0016] In the context of the present disclosure, adjacent battery elements are defined, for example, as those battery elements that are directly electrically connected to one another, that is, without any other battery cells being interposed. According to one embodiment, adjacent battery elements are connected in series. For example, two battery cells that are directly connected and in series are adjacent to each other.

[0017] In the context of this disclosure, a connecting element is defined, for example, as an element that establishes an electrical connection between adjacent battery elements and / or between adjacent battery units, for example, between directly connected series-connected battery cells and / or between directly connected series-connected battery modules. A battery unit can be a battery module or a section of a battery module. For example, a connecting element is a module connector or a connector between adjacent sections of a battery module.

[0018] In the context of this disclosure, a measuring connection is defined, for example, as an electrical connection between the voltage monitoring circuit and one of the poles of a battery element, such as a battery cell. The measuring connection may include at least part of a connecting element between adjacent battery elements and / or a measuring lead between the voltage monitoring circuit and the connecting lead or the corresponding pole of the battery element. The term measuring lead therefore refers to the part of the measuring connection excluding the connecting element. The measuring lead may be directly connected to a pole of the battery element, that is, without an interposed connecting element.

[0019] In the context of this disclosure, a battery management system (BMS) is defined, for example, as a component associated with a battery that performs at least one of the following functions: monitoring, regulating, and protecting the battery. For example, the battery management system may implement voltage diagnostics, in particular cell voltage diagnostics, charge and discharge control, state-of-charge detection, temperature control, deep discharge protection, and / or overcharge protection. The battery management system may be configured to balance or symmetrize the different cells, in particular to ensure a more uniform electrical charge distribution among the different battery cells.

[0020] In multi-cell batteries, the battery management system can be configured to monitor and / or control individual cells. For this purpose, the battery management system can include a voltage monitoring circuit. The voltage monitoring circuit can be configured to measure the voltage between the first and second measurement connections, specifically by measuring it directly. Alternatively, the voltage monitoring circuit can be configured to measure the voltage indirectly, i.e., to determine the voltage from other measured quantities. The voltage monitoring circuit can be, or include, a battery monitoring IC.

[0021] The previously described method and / or control unit can be advantageous in order to enable particularly reliable and accurate voltage monitoring when resistances of connecting elements between battery elements are taken into account when determining the voltage.

[0022] For safety reasons and to increase battery lifespan, manufacturers typically specify voltage limits within which the batteries may be operated: an upper cell voltage limit for charging and a lower cell voltage limit for discharging. Extensive investigation has revealed that unaccounted-for resistances in the measuring connections can significantly shift these voltage limits. Specifically, due to the different current directions, the upper cell voltage limit for charging is shifted downwards, and the lower cell voltage limit for discharging is shifted upwards. Consequently, during discharge, the lower cell voltage limit is detected too quickly, leading to a reduction in the discharge current and thus an unnecessarily early reduction in power.Conversely, during charging, the charging power is unnecessarily limited even though the upper cell voltage limit has not yet been reached. This results in tighter voltage limits than are actually required for safety and battery aging. Furthermore, the charging and discharging behavior of the battery is generally limited by the weakest link, i.e., the battery cell with the least favorable characteristics. Therefore, a few high-resistance connecting elements can significantly impair the performance of the entire battery. By taking the resistance of connecting elements into account when determining the cell voltage, the voltage limits can be set more efficiently, thus utilizing a wider power range during both charging and discharging.

[0023] In other words, the corrected cell voltage allows for efficient utilization of the cell voltage limits with respect to the true cell voltage, i.e., without connectors. It is important to consider that, with identical specifications, the highest and lowest cell voltages limit the charging and discharging operations, respectively. This prevents the distorted cell voltages of a few cells, e.g., above connectors within battery modules, or, in the worst case, a single cell with particularly unfavorable conditions, from unnecessarily restricting the operating range of all cells in the battery. The benefit of improved cell voltage determination is thus multiplied across all cells in the battery.

[0024] The high-power charging and discharging range can therefore be extended, leading to faster charging times and improved acceleration during discharge in the lower state of charge (SOC) range. Furthermore, reducing the discharge power later on increases the vehicle's range. Even a voltage adjustment in the millivolt range can result in a significant increase in vehicle range with the same battery size, representing considerable added value for both the vehicle manufacturer and the end customer. Conversely, the battery size could be reduced while maintaining the same vehicle range. Since the battery accounts for a large portion of the costs in, for example, a battery-electric vehicle, this can have a substantial financial impact.

[0025] According to one embodiment, the method further comprises: determining the current value of a current through the connecting element, wherein the voltage value is corrected based on the determined current value, particularly in combination with the resistance value. For example, correction can be based on the product of the determined current value and the resistance value. Here and elsewhere, in the context of the disclosure, the term "based" does not preclude the use of values ​​or quantities other than those specifically mentioned. According to one embodiment, the current value is measured using a shunt.

[0026] According to one embodiment, the first and second measuring connections are also used to monitor the voltage of a battery cell adjacent to the respective battery cell. In other words, only one measuring connection is used between adjacent battery cells. This can be advantageous in terms of material savings and efficiency. According to another embodiment, at least partially different voltage corrections are applied for different battery cells. For example, a correction may be necessary for some of the battery cells in a battery, but not for others. This can depend on the resistance of the respective connecting elements between the battery cells.

[0027] According to one embodiment, the battery element is a battery cell or an arrangement of two or more battery cells connected in parallel, wherein the adjacent battery element is an adjacent battery cell or an adjacent arrangement of two or more battery cells connected in parallel. Such an embodiment can be advantageous because battery cells represent the smallest units of a battery that need to be monitored and because, as already explained, individual battery cells can, under certain circumstances, significantly influence the charging and discharging behavior of the entire battery.

[0028] According to one embodiment, the connecting element is a module connector between a battery module and an adjacent battery module of the battery, wherein the battery element belongs to the battery module and the adjacent battery element belongs to the adjacent battery module. Such an embodiment can be advantageous if module connectors have a greater resistance than cell connectors between battery cells of a module. This can be caused, for example, by module connectors being longer than cell connectors within a module, having a different cross-section, and / or being made of a different material.

[0029] According to one embodiment, the connecting element is a package connector between a battery pack and an adjacent battery pack, wherein the battery element belongs to the battery pack and the adjacent battery element belongs to the adjacent battery pack. Battery packs can combine multiple battery modules. The advantages are analogous to the embodiment described above. According to another embodiment, the connecting element is an electrical connecting conductor between a section and an adjacent section of a battery module, wherein the battery element belongs to the section and the adjacent battery element belongs to the adjacent section. For example, the electrical connecting conductor can connect two halves of a battery module.The two halves can be arranged in such a way, for example as stacks or rows placed side by side, that the electrical connecting line between the halves is longer than other connecting lines between battery cells of the same module.

[0030] Such an embodiment can be advantageous because it is difficult to compensate for the measurement inaccuracies resulting from the various connecting elements, for example, by using additional measuring leads. This is particularly true for connecting elements between sections of the same module, because from a hardware perspective, changing the configuration of modules is very complex and costly.

[0031] According to one embodiment, the method further comprises: determining a minimum absolute current limit for a current through the connecting element, wherein the voltage value is corrected based on the minimum absolute current limit. For example, a minimum absolute current value can be determined taking into account measurement inaccuracies such as manufacturing tolerances, aging, and / or possible undetected faults. The minimum absolute current limit can be reliably maintained under predefined safety requirements, for example, ASIL level. Such an embodiment can be advantageous because a correction of the voltage value is made while simultaneously ensuring that no overcorrection occurs.

[0032] According to one embodiment, the current through the connecting element is determined based on a battery current. The battery current can be measured by a battery controller or a vehicle control unit, particularly by means of a shunt, or measured or calculated using other control devices, such as an inverter. Current measurement via a shunt can be performed using a special IC for measuring high-voltage quantities, often referred to as a UIR IC for measuring voltages, currents, and resistances.

[0033] According to one embodiment, a lower resistance limit is determined for the resistance of the connecting element section, and the voltage value is corrected based on this lower resistance limit. For example, the lower resistance limit can be chosen as the minimum value of a tolerance range. The tolerance range can account for manufacturing and aging effects. Such an embodiment can be advantageous because, on the one hand, the battery's performance range is extended by correcting the voltage value, while on the other hand, it ensures that overcorrection is avoided. In other words, by using a minimum resistance value and, if necessary, an additional safety factor, a conservative estimate of the ohmic voltage drop can be made, so that the limits for the true cell voltage are reliably maintained during charging and discharging.

[0034] According to one embodiment, the resistance value is determined from a measurement and / or a theoretical derivation, particularly taking aging effects into account. For example, the resistance value can be determined based on a specification, in particular a specification of the connecting element and / or a higher-level unit containing the connecting element, such as a battery module. For this purpose, the material and / or the geometric dimensions, in particular length and cross-section, of the connecting element can be taken into account. Such an embodiment can be advantageous with regard to a particularly accurate correction of the stress value.

[0035] According to one embodiment, the resistance value is determined based on a temperature, in particular a temperature measured by a temperature sensor of the battery, especially near the battery cell and / or the adjacent battery cell. Such an embodiment can be advantageous in the case of a temperature dependency of the resistance value for a particularly precise correction of the voltage value and thus for a particularly efficient utilization of the battery's performance capacity.

[0036] According to one embodiment, the voltage value, corrected based on the resistance value and / or the current value, is reduced using a safety factor. For example, the safety factor can be a safety factor less than one and greater than zero, particularly less than 0.5, which is multiplied by the corrected voltage value, and / or a safety subtrahend greater than zero, which is subtracted from the corrected voltage value. Such an embodiment can be advantageous for meeting safety requirements, for example, a specified ASIL level.

[0037] According to one embodiment, the correction is performed depending on whether the battery is being charged or discharged. Such an embodiment can be advantageous in order to fully utilize the battery's performance capacity in both charging and discharging modes.

[0038] According to one embodiment, during battery charging, the voltage value is corrected downwards, and during battery discharge, it is corrected upwards. The correction can depend on the direction of the electric current. Such an embodiment can be advantageous because it takes into account the different conditions during charging and discharging.

[0039] According to one embodiment, the current value through the connecting element and the voltage value are determined over time, and a time interval between the current and voltage values ​​is taken into account for correcting the voltage value. A temperature-dependent resistance value can also be determined over time and accordingly considered for correcting the voltage value. Such an embodiment can be advantageous for enabling precise correction, for example, when the current value is acquired via a UIR IC and the voltage value via a Bat-Mon IC. Transmitting the measured values ​​from the UIR IC and the Bat-Mon IC(s) to, for example, the microcontroller of a battery or vehicle drive control system via an interface can lead to significant delays, which should not impair the cell voltage correction.

[0040] According to one embodiment, the permissible operating range of the battery is assessed based on the corrected voltage and / or a battery diagnosis is performed based on the corrected voltage. Such an embodiment can be advantageous because it enables more efficient utilization of the battery's performance limits and / or more accurate battery diagnostics. When using the corrected cell voltage for diagnostics, the diagnostics can be performed more precisely, for example, because by differentiating between voltage drops within the cell and at connectors, such as those within the module, the calculated internal resistance of the cell exhibits higher accuracy.

[0041] BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Further advantages and beneficial designs and further developments of the method and the control unit result from the following exemplary embodiments shown in conjunction with the figures.

[0043] They show:

[0044] Figure 1 shows a battery system with a battery and a voltage monitoring circuit according to an embodiment of the present disclosure; Figure 2 shows aspects of a method for monitoring the voltage of a battery cell according to an embodiment of the present disclosure. Identical, similar, or similarly functioning elements are designated with the same reference numerals in the figures. In some figures, individual reference numerals have been omitted for clarity. The figures and the relative sizes of the elements shown in the figures are not to be considered to scale. Rather, individual elements may be exaggerated for better representation and / or clarity.

[0045] DETAILED DESCRIPTION OF EXAMPLES OF EXECUTION

[0046] Figure 1 shows a battery system 100 of a motor vehicle comprising the following elements: (i) a voltage monitoring circuit 102, which may, for example, be part of a battery management system, (ii) a rechargeable battery 101 with at least two battery cells Zk, Zk-1, which are connected via a connecting element 105, and (iii) at least two measuring lines Wk, Wk+1 between the voltage monitoring circuit 102 and the battery 101.

[0047] A first measuring lead Wk connects the voltage monitoring circuit 102 to the positive terminal of battery cell Zk-1 and, via the connecting element 105, to the negative terminal of battery cell Zk. A second measuring lead Wk+1 connects the voltage monitoring circuit 102 to the positive terminal of battery cell Zk. In the configuration shown, the measuring leads Wk each contact the positive terminal of the corresponding battery cell Zk-1 directly. Alternatively, the measuring leads could also each contact the negative terminal of the corresponding battery cells directly or a section of the respective connecting lead between adjacent battery cells.

[0048] The voltage monitoring circuit 102 includes a measuring device, for example, a so-called battery monitoring IC, with which the voltage Uk between the measuring leads Wk and Wk+1 is measured. To determine the actual voltage between the negative and positive terminals of battery cell Zk, the conductive connecting element 105 must be taken into account. This connects the negative terminal of cell Zk to the positive terminal of the adjacent cell Zk-1. Simultaneously, the connecting element 105 connects the negative terminal of battery unit 103 to the positive terminal of the adjacent battery unit 104, each of which comprises a plurality of battery cells Zk-2, Zk-1 and Zk, Zk+1, respectively. The connecting element 105 differs from the electrical connections between adjacent battery cells Zk-2, Zk-1 and Zk, Zk+1 within a battery unit 104, 103, particularly in that the connecting element 105 has a comparatively higher resistance.The battery units 103, 104 can, for example, be different battery modules or battery packs of the battery. In this case, the battery units 103, 104 are adjacent sections within a battery module, which are distinguished, for example, by a special geometric arrangement, such as adjacent stacks or rows of battery cells or a back-to-back arrangement.

[0049] The voltage monitoring circuit 102 is designed to perform a method for monitoring the voltage of a battery element Zk of a battery 101, in particular a vehicle battery. The voltage monitoring circuit 102 is connected to a positive terminal of the battery element Zk via a first measuring connection Wk+1 and to a negative terminal of the battery element Zk via a second measuring connection Wk & 105.The procedure comprises the following steps: (i) determining a voltage value llk, which is indicative of a battery cell voltage between the two poles, using the voltage monitoring circuit 102; (ii) determining a resistance value R of a section of a connecting element 105, wherein the connecting element 105 connects the battery cell Zk to an adjacent battery cell Zk-1 and wherein one of the two measuring connections Wk & 105, Wk+1 includes the section of the connecting element 105; and correcting the voltage value llk based on the resistance value R.

[0050] Cells Zk-2, Zk-1, Zk, Zk+1, arranged in series, are typically numbered sequentially from lowest to highest potential, i.e., from the negative to the positive side of the battery. In this context, the term "cell" can also refer to several cells connected in parallel. Cells Zk-2, Zk-1, Zk, Zk+1 are often grouped into battery modules, which can be replaced in case of a fault. The specified cell voltage limits refer to the cell itself, not to any connecting elements 105 that may be present between the cells. The latter can exhibit a significant ohmic voltage drop during operation. This applies particularly to the connections between modules, so-called module connectors.Therefore, the ohmic voltage drop across module connectors is generally avoided when determining cell voltage by either using separate measuring leads above and below a module connector (in particular, ensuring that the corresponding input channel of a battery monitoring IC is not used for cell voltage measurement) or by assigning separate battery monitoring ICs to the cells above and below a module connector. In both cases, measuring leads are available on both sides of the module connector for cell voltage determination.

[0051] A comprehensive root cause analysis revealed that significant ohmic resistances can still occur within the battery modules at connecting elements 105 or connectors, for example, at the connection between two halves 103, 104 of a battery module in which two rows of cells Zk-2, Zk-1 and Zk, Zk+1 are arranged back-to-back (shown differently in Figure 1 for clarity). Using separate measuring leads on both sides of the connection within the module would entail considerable additional costs. For example, if, in such a ten-cell module, one measuring lead Wk is placed above the fifth cell Zk-1 of the module, and the next measuring lead Wk+1 is placed above the sixth cell Zk, then the differential voltage of these measuring leads, which is used for the cell voltage of the sixth cell Zk of the module, also includes the ohmic voltage drop at the connector 105 between the two module halves.

[0052] This reduces the apparent voltage of the sixth cell Zk during discharge. The control unit or voltage monitoring circuit 102 therefore incorrectly detects that the lower cell voltage limit has been reached, leading to a reduction in the discharge current and thus an unnecessarily early reduction in power. Conversely, this increases the apparent voltage of the sixth cell Zk during charging, unnecessarily limiting the charging power. Since the discharge power cannot be arbitrarily reduced while driving, this also limits the usable energy content of the battery 101, which is crucial for the vehicle's range.

[0053] The influence of connections within modules on cell voltage measurement can either be accepted to avoid additional costs, or connections within the modules with significant ohmic resistance must also be placed on a separate measurement channel of a Bat-Mon-IC or between Bat-Mon-ICs, with the corresponding additional effort for the measurement lines and the monitoring electronics, e.g. more Bat-Mon-ICs with a limited maximum number of channels per Bat-Mon-IC.

[0054] Preferably, however, for cell voltages Uk that are significantly influenced by the ohmic resistances of connecting elements 105 or connectors, typically connectors within battery modules, a computational correction of the influence of the ohmic voltage drop of the connector 105 on the cell voltage Uk during charging and / or discharging is performed in the battery or vehicle control system. During charging, for example, the product of the resistance value R of the connector 105 and the magnitude of a battery current I is subtracted from the cell voltage Uk. During discharging, for example, the product of the resistance value R of the connector 105 and the magnitude of a battery current I is added to the cell voltage Uk.

[0055] The battery current I can be measured by the battery or vehicle control unit, for example using a shunt, or measured or calculated by other control units such as an inverter. During charging and discharging, a minimum current value can be used, taking into account measurement accuracy, particularly manufacturing tolerances, aging, and potential undetected faults, etc., which is reliably maintained under the relevant safety requirements, such as ASIL levels. Current measurement using a shunt can be performed via a special integrated circuit (IC) for measuring high-voltage quantities, often referred to as a UIR IC for measuring voltages, currents, and resistances.

[0056] The resistance value R can be determined using the specifications of the corresponding connector 105 or battery module. This can be done, in particular, based on a minimum value within a tolerance range to avoid overcompensation. The tolerance range can take manufacturing and aging effects into account. The minimum value can also be reduced by a safety factor, e.g., by a factor of 2, to cover any potential exceedance of the specified tolerances in the event of a fault. The resistance value R can also be stored as a function of temperature values, for example, as a function of a temperature measurement within the battery module, especially from a temperature sensor located near connector 105.The resistance value R can also be stored as a function of the operating time of the storage device or battery module in order to take into account the effects of aging, possibly considering a thermal profile of the operation.

[0057] The corrected cell voltage Uk can be used not only for regulating the charging and discharging current, but also for diagnostics, e.g., based on a calculated internal resistance of the cell, or for calculating the state of charge (SOC) or state of health (SOH) of the cell.

[0058] To enable precise timing of current I and cell voltage Uk, and thus accurate correction, the current I can be measured, for example, via a UIR IC, and the cell voltage Uk can be measured, synchronized via a Bat-Mon IC. This may be necessary because transmitting the measured values ​​from the UIR IC and the Bat-Mon IC(s) to, for example, the microcontroller of a battery or vehicle drive control system via an interface can lead to significant delays that should not affect the correction of the cell voltage Uk.

[0059] Figure 2 illustrates a method for voltage monitoring of a

[0060] Battery element Zk, as already explained in connection with Figure 1. The upper part shows the battery current or the current intensity I of a current through the connecting element 105. The lower part then shows corresponding voltage values ​​... , llk-1 , llk, llk+1 , ... of various battery cells ... , Zk-1 , Zk, Zk+1 , ... which depend on the current intensity I. Figure 2 thus shows the measured behavior of the cell voltages ... , llk-1 , llk, llk+1 , ... of a battery 101 during increasing discharge operation, i.e., increasingly negative current intensity I. In addition to a continuous scatter band of cell voltages llk-1 , llk+1 , ..., a group of cell voltages llk, ... can also be seen whose cell voltage decreases more sharply with increasing discharge operation than that of the other cells. In this case, these are precisely the cells Zk, ...which lie above half 104 of a battery module and thus include the voltage drop at the connector 105 between the two module halves 103, 104. These cell voltages llk, ... are limiting for discharge operation if no correction of the ohmic voltage drop at the connector 105 within the module takes place. The discrepancy between the measured cell voltages ... , llk-1 , llk, llk+1 , ... shown in Figure 2 was the starting point for determining the causes and finding a solution, as described in this disclosure.

[0061] The invention is not limited to the exemplary embodiments described therein. Rather, the invention encompasses every new feature as well as every combination of features, which in particular includes every combination of features in the exemplary embodiments and claims.

[0062] REFERENCE MARK

[0063] 100 battery system

[0064] 101 Battery

[0065] 102 Voltage monitoring circuit 103 First battery unit (e.g. section of a battery module)

[0066] 104 second battery unit (e.g. adjacent section of the battery module)

[0067] 105 Connecting element

[0068] Zk Battery cell Wk Measuring lead to the positive terminal of the battery cell Zk-i

[0069] I Current intensity

[0070] UK voltage of the battery cell Zk

[0071] R resistance of the connecting element t time

Claims

PATENT CLAIMS 1. Method for monitoring the voltage of a battery element (Zk) of a battery (101), in particular a vehicle battery, by means of a voltage monitoring circuit (102), wherein the voltage monitoring circuit is connected to a positive pole by a first measuring connection (Wk+1) and to a negative pole of the battery element (Zk) by a second measuring connection (Wk & 105), wherein the method comprises the following steps: - Determining a voltage value (llk) indicative of a battery cell voltage between the two poles using the voltage monitoring circuit (102); - Determining a resistance value (R) of a section of a connecting element (105), wherein the connecting element (105) connects the battery element (Zk) to an adjacent battery element (Zk-1) and wherein one of the two measuring connections (Wk & 105, Wk+1) includes the section of the connecting element (105); and - Correcting the voltage value (llk) based on the resistance value (R).

2. Method according to the preceding claim, wherein the battery element (Zk) is a battery cell or an arrangement of two or more battery cells connected in parallel and wherein the adjacent battery element (Zk-1) is an adjacent battery cell or an adjacent arrangement of two or more battery cells connected in parallel.

3. Method according to one of the preceding claims, wherein the connecting element (105) is a module connector between a battery module and an adjacent battery module of the battery (101) and wherein the battery element (Zk) belongs to the battery module and the adjacent battery element (Zk-1) belongs to the adjacent battery module.

4. Method according to claim 1 or 2, wherein the connecting element (105) is an electrical connecting line between a section (103) of a battery module and an adjacent section (104) of the same. battery module and wherein the battery element (Zk) belongs to section (103) and the adjacent battery element (Zk-1) belongs to the adjacent section (104).

5. Method according to one of the preceding claims, further comprising: determining a minimum absolute current limit for a current (I) through the connecting element (105), wherein the voltage value (llk) is corrected based on the minimum absolute current limit.

6. Method according to one of the preceding claims, wherein a lower resistance limit for the resistance of the section of the connecting element (105) is determined as the resistance value (R) and wherein the voltage value (llk) is corrected based on the lower resistance limit.

7. Method according to one of the preceding claims, wherein the resistance value (R) is determined from a measurement and / or a theoretical derivation, in particular taking into account aging effects.

8. Method according to one of the preceding claims, wherein the resistance value (R) is determined based on a temperature, in particular a temperature measured by a temperature sensor of the battery (101).

9. Method according to one of the preceding claims, wherein the voltage value (llk) corrected on the basis of the resistance value (R) is reduced using a safety value, in particular by multiplying by a safety factor less than one.

10. Method according to one of the preceding claims, wherein the correction is made depending on whether the battery (101) is being charged or discharged.

11. Method according to the preceding claim, wherein during the charging operation of the battery (101) the voltage value (llk) is corrected downwards in magnitude and during the discharging operation of the battery (101) the voltage value (llk) is corrected upwards in magnitude.

12. Method according to one of the preceding claims, wherein a current value (I) through the connecting element (105) and the voltage value (llk) are determined over time and a time interval between the current value (I) and the voltage value (llk) is taken into account for correcting the voltage value (llk).

13. Method according to one of the preceding claims, wherein a permissible operating range of the battery (101) is assessed based on the corrected voltage (llk) and / or a diagnosis of the battery (101) is performed based on the corrected voltage (llk).

14. Control unit, in particular battery management system, which is configured to carry out a method according to any one of claims 1 to 13.

15. Computer program comprising instructions which, when executed by a computer, cause the computer to perform the method according to any one of claims 1 to 13.

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