Electrical circuit for monitoring the voltage of a battery, method for fault diagnosis of measuring connections and corresponding control unit

Abstract

The invention relates to an electrical circuit for monitoring the voltage of a battery (101), wherein the battery (101) comprises a plurality of battery elements (Zk-1, Zk, Zk+1), the electrical circuit comprising: (i) a first measuring connection (Wk) configured to be connected to a positive terminal of a first battery element (Zk) of the plurality of battery elements (Zk-1, Zk, Zk+1); (ii) a second measuring connection (Wk-1) configured to be connected to a negative terminal of the first battery element (Zk); (iii) a measuring device configured to determine a voltage between the first measuring connection (Wk) and the second measuring connection (Wk-1); and (iv) a current source (Yk) electrically connected to at least one of the two measuring connections (Wk, Wk-1) and configured to provide a predetermined current (Itest,k), wherein the current source (Yk) is variable, in particular switchable.Furthermore, the invention relates to a corresponding method for fault diagnosis of measuring connections, a computer program and a control unit.

Description

TECHNICAL AREA

[0001] The present disclosure relates to electrical circuits for monitoring the voltage of a battery and to methods for diagnosing faults in measuring connections between the battery and a battery monitoring unit. Furthermore, the disclosure relates to corresponding computer programs and control units. BACKGROUND OF THE INVENTION

[0002] 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 to avoid excessive aging, these cells must only be operated within specific cell voltage limits, which are usually specified by the battery manufacturer. 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. This often involves the use of one or more battery monitoring ICs, each with multiple input channels for the individual cell voltages. The cell voltages are then determined from the measured values ​​of the battery monitoring ICs, for example, in a battery control unit or within a vehicle or powertrain control unit.

[0003] If, in the event of a fault, the measured cell voltages deviate from the actual cell voltages, it is no longer guaranteed that the permissible voltage ranges are being adhered to. Operating cells outside their permissible voltage range can be dangerous, for example, leading to a fire. Therefore, the measuring connections must be checked for faults that lead to an incorrectly measured voltage.

[0004] From US patent 2018 / 0043781A1, a battery management device is known in which a voltage sensing unit detects the terminal voltage of battery cells. An RC filter is electrically connected to the voltage sensing lines, and a status change unit causes an electrical status change with respect to the voltage sensing lines. A voltage fluctuation unit fluctuates the terminal voltage of the battery cells in response to the electrical status change. A microcomputer diagnoses the voltage sensing unit based on a detection result of the battery cell terminal voltage by the voltage sensing unit when the battery cell terminal voltage fluctuates due to the voltage fluctuation unit.

[0005] From US 2022 / 0021230A1, a battery protection circuit is known that includes a first pin, a second pin, a first sensing circuit, a first current source, a first enable circuit, and a first protection circuit. The first pin and the second pin are connected to two terminals of a first battery. The first sensing circuit, coupled between the first pin and the second pin, provides a first sensing signal and a second sensing signal. The first current source, coupled between the first pin and the second pin, provides a first current. The first enable circuit, coupled to the first sensing circuit and the first current source, generates a first enable signal corresponding to the first sensing signal. The first protection circuit is coupled to the first sensor circuit.When the first enable signal enables the first power source, the first protection circuit generates a first protection signal corresponding to a second detection signal that changes with the first current. SUMMARY AND FORMS OF EXECUTION

[0006] It is therefore a purpose of the present disclosure to provide electrical circuits for voltage monitoring and corresponding diagnostic procedures with which anomalies or faults in measuring connections can be detected.

[0007] This task is accomplished by an electrical circuit for monitoring the voltage of a battery, a method for fault diagnosis of measuring connections, a computer program, and a control unit according to the independent patent claims. Advantageous embodiments and further developments are described in the respective dependent claims, the following description, and the drawings.

[0008] According to a first aspect, a method for fault diagnosis of measuring connections is provided by means of an electrical circuit for voltage monitoring of a battery, wherein the battery comprises a plurality of battery cells. The electrical circuit has: (a) a first measuring connection, which is configured to be connected to a positive terminal of a first battery cell of the plurality of battery cells; (b) a second measuring connection, which is configured to be connected to a negative terminal of the first battery cell; (c) a measuring device, which is configured to determine a voltage between the first and the second measuring connection; and (d) a current source, which is electrically connected to at least one of the two measuring connections and which is configured to provide a predetermined, in particular constant, current, wherein the current source is variable, in particular switchable.The method comprises the following steps: (a) varying the current source, for example, changing the current of the current source from a first predetermined, in particular constant, current to a second predetermined, in particular constant, current; and (b) performing a fault diagnosis of at least one of the two measuring connections based on a first voltage between the first and the second measuring connection, determined using the measuring device before the variation, and a second voltage between the first and the second measuring connection, determined using the measuring device after the variation. Performing the fault diagnosis comprises: comparing a difference between the first and the second voltage with an expected voltage difference.A resistance drift of at least one of the measuring leads is determined based on the difference between the first and second voltages and the expected voltage difference.

[0009] According to one embodiment, the first and / or second measuring connection each include a filter resistor, which is specifically designed to filter the voltage signal to be measured between the two measuring connections. Therefore, fault diagnosis can also involve these filter resistors.

[0010] According to one embodiment, a battery system comprises the previously described electrical circuit for monitoring the voltage of a battery, as well as the plurality of battery elements, in particular the battery itself. The first measuring connection is connected to the positive terminal of the first battery element and / or the second measuring connection is connected to the negative terminal of the first battery element.

[0011] According to another aspect, a computer program is provided which includes instructions that, when executed by a computer, cause it to carry out the previously described procedure. In the context of the present 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 executed by a computer, cause it to carry out the procedure described above.

[0013] According to another aspect, a control unit, in particular a battery management system, is provided which is configured to carry out the previously described procedure. According to one embodiment, the control unit comprises the previously described electrical circuit for monitoring the voltage of a battery. According to another embodiment, the control unit, in particular the battery management system, comprises one or more battery monitoring units, in particular battery monitoring ICs, as well as a processing unit which is configured to receive and process signals from the one or more battery monitoring units, for example, to determine the voltage between the measuring connections.

[0014] 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, control, and protection of the battery. For example, the battery management system may implement charge and discharge control, state-of-charge detection, temperature control, voltage diagnostics, in particular cell voltage diagnostics, deep discharge protection, and / or overcharge protection. In the case of batteries with multiple cells and / or modules, the battery management system may be configured to monitor and / or control the individual cells or modules. The battery management system may be configured to balance or symmetrize the different cells, in particular to ensure a more uniform electrical charge distribution.The battery management system, or at least parts of the battery management system, can be located in a separate housing. Parts of the battery management system, such as one or more battery monitoring units, can be located on or inside the battery, particularly within a battery housing.

[0015] In the context of this disclosure, a measuring device is defined, for example, as a device configured to determine a voltage between measuring connections. The determined voltage may be representative of an associated actual cell voltage. The measuring device may include one or more analog-to-digital converters (ADCs). The measuring connections may connect corresponding inputs of the analog-to-digital converter to the terminals of the associated battery cell. The analog-to-digital converter may be part of a battery monitoring unit, for example, a battery monitoring IC. The measuring device may include a processing unit that processes voltage signals, for example, from an analog-to-digital converter. The measuring device may be configured to measure the voltage indirectly, i.e., to determine the voltage from other measured quantities.

[0016] In the context of this disclosure, a measuring connection can be an electrical connecting line. The electrical connecting line can include electrical components, for example, a resistor, in particular a filter resistor. Alternatively or additionally, the electrical connecting line can have a branch, for example, to a negative or positive terminal of different battery cells. The measuring connection can include electrical conductors within the battery, a battery monitoring unit, and / or the battery management system.

[0017] According to one embodiment, the measuring connections extend to the measuring inputs of the measuring device and / or a battery monitoring unit. Alternatively or additionally, the measuring connections extend to the positive or negative terminal of the battery unit.

[0018] In the context of the present 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 may be at least partially connected in series. The battery is, for example, a lithium-ion accumulator.

[0019] In the context of this disclosure, a current source is defined, for example, as an electrical component that provides a predetermined current, in particular a current that is at least approximately constant. The current source may have two electrical interfaces, for example, an input and an output. One of the interfaces is electrically connected to one of the two measuring connections. The other interface is electrically connected either to the other measuring connection or to ground.

[0020] In the context of this disclosure, a current source is defined as variable, for example, if it is configured to provide at least two different, predetermined current intensities. One of the predetermined current intensities may be a very small current or zero. In other words, the current source can be switched on and off. The current source may be configured to maintain the respective predetermined current intensity constant over a predetermined period. The current source may be configured to provide two or more predetermined discrete current intensities and / or a continuous spectrum of current intensities.

[0021] In the context of this disclosure, a battery element is defined, for example, as a component of the battery that has a positive terminal and a negative terminal. The battery element can be a single battery cell and / or a plurality of battery cells connected in parallel. The battery element can be a battery module that combines several battery cells connected in series and / or series-connected units of parallel battery cells.

[0022] The previously described electrical circuit and / or method can be advantageous for diagnosing anomalies or faults in measurement connections. Based on this, erroneous measured values ​​can be identified, thus ensuring compliance with operating limits, such as prescribed voltage ranges, for battery components, particularly battery cells. This can reduce the probability of thermal events, including fires or explosions.

[0023] Crucial for diagnosing measurement connections in this way is the variable current source. If varying the current source changes the current flow through the first and / or second measurement connection, an expected voltage change can be calculated. If the actually measured voltage change deviates from this expected change, an anomaly or fault in the measurement connections can be inferred. For example, resistances, such as a filter resistance or a line resistance, may have changed, for instance, due to wear or aging.

[0024] A diagnostic method based on the variation of current sources allows not only purely qualitative fault detection but also quantitative statements, such as the precise resistance change of one or more measuring connections. This enables, for example, the assessment of the extent of aging or wear and allows for the implementation of various countermeasures, such as decommissioning, replacement, or repair of affected measuring connections.

[0025] According to an alternative method, measurement errors can be detected using a redundant measurement circuit. The redundant measurement connection with a redundant analog-to-digital converter is compared against the primary measurement channel. If the deviation is too high, this is detected by software or hardware measures.

[0026] However, this method is disadvantageous compared to the previously described approach, leading, for example, to greater space requirements and costs. The previously described approach uses a variable current source to detect changes in the resistance of the measuring lead and any filter resistance.

[0027] This makes it possible to use only a single measurement path for safety-relevant measurements. A redundant measurement path is not required. Measurement errors are identified by changes in the resistance between the analog-to-digital converter and the cell. This approach requires fewer components at the PCB level and is therefore more cost-effective. The current sources can, for example, be implemented in battery monitoring ICs, which offers further cost advantages.

[0028] According to one embodiment, at least one of the following faults can be detected: an interrupted electrical connection, an electrical connection with altered line resistance, and a changed value of a filter resistance arranged in the electrical connection.

[0029] According to one embodiment, the electrical circuit has several current sources, each electrically connected to at least one measuring connection assigned to one of the battery cells. All measuring connections of the battery cells can be checked using these multiple current sources. The multiple current sources can be arranged and configured analogously to the current source described above, for example, according to the embodiments described below.

[0030] According to one embodiment, the power source is electrically connected to the first and second measuring connections. The power source can be connected between the measuring device, in particular an analog-to-digital converter of the measuring device, and the battery unit with the first and second measuring connections. It can also be connected between the measuring device, in particular an analog-to-digital converter of the measuring device, and a respective filter resistor with the first and / or second measuring connection. Such an embodiment can be advantageous because adjacent measuring connections can be tested simultaneously using a single power source.

[0031] According to one embodiment, the power source can be electrically connected to two, in particular adjacent, measuring connections of several battery cells by means of respective switches, each measuring connection being assigned to one battery cell of the plurality of battery cells. All measuring connections of the plurality of battery cells can be checked by means of the power source. Such an embodiment can be advantageous because only one power source is required to perform the diagnosis of all measuring connections sequentially.

[0032] According to one embodiment, the power source is electrically connected to the first measuring connection and to ground. Such an embodiment can be advantageous because it is easy to implement. Furthermore, a direct correlation of the measured error to the affected measuring connection is possible.

[0033] According to one embodiment, the power source is electrically connected to ground and can be electrically connected to multiple measuring connections via a respective switch, with each measuring connection being assigned to one of the multiple battery cells. All measuring connections of the multiple battery cells can be tested using the power source. Such an embodiment can be advantageous because only one power source is required to perform the diagnosis of all measuring connections sequentially.

[0034] According to one embodiment, the electrical circuit further comprises another variable, in particular switchable, current source, which is connected in parallel to the main current source and is configured to provide another predetermined current. The additional current source can be electrically connected analogously to the main current source. For example, according to the embodiment before last, the additional current source can be electrically connected to the first and second measuring connections, or according to the previous embodiment, it can be electrically connected to the first measuring connection and to ground. The additional current source can be arranged between the measuring device and filter resistors. The main current source and the additional current source can be variable independently of each other, for example, via associated switches. The additional predetermined current may, but need not, differ from the predetermined current.An additional power source can be advantageous to validate the diagnostic result obtained using the power source or to increase its accuracy.

[0035] In one embodiment, the current source is configured such that the measured voltage decreases when the current source is switched on. Alternatively, the current source is configured such that the measured voltage increases when the current source is switched on.

[0036] According to one embodiment, the battery elements are battery cells, several battery cells connected in parallel, or battery modules. Such an embodiment can be advantageous because monitoring battery cells and battery modules is safety-relevant, and therefore faulty voltage measurements should be detected.

[0037] According to one embodiment, the electrical circuit lacks a redundant measuring circuit for verifying the voltage measured between the first and second measuring connections. As previously explained, a redundant measuring connection, and in particular a redundant measuring circuit, is not required when diagnostics are performed using variable current sources. This eliminates the need for additional components, such as additional measuring connections and / or an additional ADC converter, and saves installation space.

[0038] According to one embodiment, varying the current source involves either switching the current source on with the predetermined current or switching it off. When switching it off, the current source may have previously provided the predetermined current. Such an embodiment can be advantageous because it is particularly easy to implement, for example, using a constant current source and a switching element connected in series.

[0039] According to the invention, the fault diagnosis process involves comparing the difference between the first and second voltages with an expected voltage difference. A measure of deviation can be determined based on the difference between the measured and expected voltage difference. This deviation can then be compared with a threshold value to obtain a diagnostic result.

[0040] According to one embodiment, the expected voltage difference is based on the specified current and the resistances of the measuring connections to which the power source is electrically connected. The resistance of a measuring connection can include a conductor resistance, determined, for example, by the length, cross-section, and / or material of the conductor, and / or a filter resistance located within the measuring connection. Furthermore, the resistance of the measuring connection can include the resistance of another component located within the measuring connection. The expected voltage difference can additionally be based on the resistance of the first battery cell. The expected voltage difference can be determined using Ohm's law based on the aforementioned quantities and possibly other quantities.

[0041] According to the invention, the resistance drift of at least one of the measuring leads is determined based on the difference between the first and second voltages and the expected voltage difference. The resistance drift can be determined based on a deviation of the difference between the first and second voltages from the expected voltage difference. Such an embodiment can be advantageous for quantifying deviations, for example, due to aging or wear. Thus, not only connection breaks but also, for example, connections with increased or decreased resistance can be diagnosed.

[0042] According to one embodiment, a fault is diagnosed if the deviation of the difference between the first and second voltages from the expected voltage difference exceeds a predetermined threshold. The predetermined threshold can be variable, for example, depending on the battery's operating time or on the total resistance relevant for calculating the expected voltage difference.

[0043] According to one embodiment, the method further includes initiating safety measures upon detection of a fault. The safety measures may include at least one of the following: disconnecting one or more loads from the battery; switching off one or more loads; placing the battery system and / or one or more loads into a safety mode; displaying a safety warning, for example, visually or audibly.

[0044] According to one embodiment, the method is carried out when the battery is disconnected from one or more consumers by means of one or more switches, in particular contactors, and / or when the vehicle is stationary. Such an embodiment can be advantageous because little current flows through the cells and therefore little disturbance of the cell voltages occurs.

[0045] According to one embodiment, the power source is implemented in a battery monitoring unit, for example in a battery monitoring IC. Alternatively, the power source can also be implemented separately from such a battery monitoring unit.

[0046] According to one embodiment, the battery system is part of a motor vehicle, in particular an electric vehicle or a hybrid vehicle, wherein the battery is a vehicle battery, in particular a high-voltage battery. However, the battery system can also be part of a stationary energy storage system. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Further advantages and beneficial designs and further developments of the method and the control unit result from the following exemplary embodiments shown in connection with the figures.

[0048] They show: Fig. 1. A battery system with battery and battery management system for comparison; Fig. 2 a battery system comprising a battery and battery management system according to a first embodiment of the present disclosure, wherein power sources are each connected to two adjacent measuring connections; Fig. 3 a battery system comprising a battery and battery management system according to a second embodiment of the present disclosure, wherein each power source is connected to a measuring connection and ground; Fig. 4 a course of a voltage between two adjacent measuring connections in response to a variation of a current source for evaluation in a method for fault diagnosis according to an embodiment of the present disclosure.

[0049] Identical, similar, or similarly effective elements are marked with the same reference symbols in the figures. In some figures, individual reference symbols have been omitted for clarity. The figures and the relative sizes of the elements depicted within them are not to be considered to scale. Rather, individual elements may be exaggerated for better representation and / or comprehensibility. DETAILED DESCRIPTION OF EXAMPLES OF EXECUTION

[0050] Fig. 2 and Fig. Figure 3 shows battery systems 100 of a motor vehicle, each comprising the following elements: (i) a battery management system 102, (ii) a rechargeable battery 101 with at least one battery cell Zk having a voltage Uk, and (iii) at least two measuring connections Wk, Wk-1 between the battery 101 and a measuring device (indicated here by the measured voltages Umess,k and Umess,k-1), in particular an analog-to-digital converter of the measuring device. A first of the measuring connections Wk connects the measuring device of the battery management system 102 to the positive terminal of the battery cell Zk, and a second of the measuring connections Wk-1 connects the measuring device to the negative terminal of the battery cell Zk. The measuring device allows the voltages Umess,k and Umess,k-1 between adjacent measuring connections Wk-1, Wk and Wk-2, Wk-1, respectively, to be determined.

[0051] Within the battery management system 102, the two electrical connections Wk, Wk-1 each include a filter resistor Rfilt,k, Rfilt,k-1. The filter resistors Rfilt,k, Rfilt,k-1, together with a capacitor arranged between the two electrical connections Wk, Wk-1, can form an RC filter that can filter out interference or compensate for voltage spikes.

[0052] The battery includes further battery cells, of which in Fig. 2 and Fig. Figure 3 shows, as an example, the two battery cells Zk-1 and Zk+1 with voltages Uk-1 and Uk+1, respectively. Cells Zk-1, Zk, Zk+1, arranged in series, are usually numbered consecutively from lowest to highest potential, i.e., from the negative to the positive side of the battery. In this case, the term "cell" can also refer to several cells connected in parallel. The positive and negative terminals of the other battery cells Zk-1 and Zk+1 are connected via corresponding electrical connections Wk-2, Wk-1 and Wk, Wk+1, respectively (the latter in Fig. 2 and Fig. 3 (not shown) is connected to the measuring device of the battery management system 102. The electrical connections Wk-2, Wk-1, Wk, Wk+1 have resistances Rfilt,k-2, Rfilt,k-1, Rfilt,k and Rfilt,k+1 respectively (the latter in Fig. 2 and Fig. 3 not shown). Capacitors can be placed between any two adjacent electrical connections Wk-2, Wk-1, Wk, Wk+1 (in Fig. 2 and Fig. 3 (not shown) are arranged, which together with the previously described resistors Rfilt,k-2, Rfilt,k-1, Rfilt,k and Rfilt,k+1 form RC elements.

[0053] For each measurement connection Wk, Wk-1, Wk-2 from the measuring device to cell Zk, Zk-1, Zk-2, a variable or activatable current source Yk, Yk-1, Yk-2 is implemented. This current source Yk, Yk-1, Yk-2 generates a voltage drop in the circuit, which also changes the measured voltage Umess,k, Umess,k-1, Umess,k-2. This change depends on the current Itest,k, Itest,k-1, Itest,k-2 of the current source Yk, Yk-1, Yk-2 and the resistances in the circuit. Connection and filter resistances play an important role in determining the expected voltage change. If these resistances change due to faults or aging, this causes an error in the cell voltage measurement.

[0054] If the measured voltage Umess,k, Umess,k-1, Umess,k-2 does not change as expected, it must be assumed that the measured voltage Umess,k, Umess,k-1, Umess,k-2 is also faulty without an active current source Yk, Yk-1, Yk-2, and safety procedures can be initiated. The current source Yk, Yk-1, Yk-2 can also be configured as a current sink. The expected voltage change will then reverse its sign. The current source Yk, Yk-1, Yk-2 can also be implemented as a variable or switchable current source to create different test conditions.

[0055] In Fig. 2. The current source Yk connects the two electrical connections Wk and Wk-1 from the battery downstream of the filter resistors Rfilt,k and Rfilt,k-1. The current source Yk is configured to provide a predetermined current Itest,k of an electric current flowing through the electrical connections Wk and Wk-1 and through the battery cell Zk (indicated by the arrows). A current source Yk-1 is arranged and configured analogously between the two electrical connections Wk-2 and Wk-1.

[0056] In Fig. In contrast, power source Yk connects electrical connection Wk to ground 103. The current supplied by power source Yk, with current strength Itest,k, flows accordingly through electrical connection Wk and then through the series-connected battery cells Zk, Zk-1, ... to ground 103. With respect to electrical connections Wk-1 and Wk-2, power sources Yk-1 and Yk-2 are arranged and configured analogously.

[0057] In the circuit according to Fig. 2. An anomaly or fault in one of the two measurement connections Wk-1, Wk is detected by analyzing the voltage curve Umess,k when the current source Yk is varied. An analysis of the voltage curves Umess,k-1 and Umess,k+1 then allows, if necessary, a more precise assignment of the fault to the measurement connection Wk-1 or Wk. For example, if the voltage curve Umess,k indicates a fault, while the voltage curve Umess,k-1 is normal, then the cause of the fault can be assigned to connection Wk.

[0058] In Fig. Figure 2 represents an active current source Yk with current flowing through resistor Rfilt,k, the connection Wk, the cell Zk, and back through Wk-1 and Rfilt,k-1. Activating this current source should produce a voltage change ΔUk according to the following equation. ΔUk=Itest,k*(Rfilt,k+RW,k+RZ,k+RW,k−1+Rfilt,k−1), where RW,k and RW,k-1 are the respective line resistances and RZ,k is the cell resistance of cell Zk.

[0059] The voltage Umess,k can be measured before and after activating the current source Umess,k,v or Umess,k,n. From this, a measured voltage change ΔUmess,k can be calculated. ΔUmess,k=Umess,k,n−Umess,k,v.

[0060] The measured voltage change can now be compared to the expected voltage change using software or a hardware circuit. If the change is not sufficient, a safety response is initiated, such as switching off the battery.

[0061] In contrast, the circuit according to Fig. 3. An anomaly or error detected by analyzing the voltage waveform Umess,k when varying the current source Yk can be directly attributed to the measuring connection Wk. Thus, the current source Yk causes a current flow through resistance Rfilt,k, the connection Wk, and cell Zk to ground. Activating this current source should cause a voltage change of Umess,k by ΔUk according to the following equation. ΔUk=Itest,k*(Rfilt,k+RW,k+RZ,k), where N is the number of cells between W K and ground. Here again, software can be used to compare the measured voltage change against the expected voltage change. The measured voltage Umess,k-1 will also change by Itest,k * Rk-1, for example in the range of mΩ.

[0062] Fig. Figure 4 shows a voltage curve Umess,k, as it appears when varying the current source Yk in a circuit according to Fig. 2 as well as according to Fig. 3. The voltage Umess,k changes from a measured value Umess,k,v to a measured value Umess,k,n when current source Yk is switched on (110). Both before and after the change, the voltage Umess,k is subject to fluctuations, but these are much smaller than the described voltage change. After switching off current source Yk (111), the voltage value Umess,k drops again. The voltage change is only reflected in the measured voltage Umess,k. It is assumed that the actual cell voltage Uk of cell Zk remains constant throughout the entire process. This value Uk is close to the voltage Umess,k,v measured before the current source Yk was changed. Based on the voltage change from Umess,k,v to Umess,k,n, the previously described diagnosis of the measuring leads can be performed.

[0063] Fig.Figure 1 shows a comparison arrangement with a redundant measurement channel. From each of the measurement connections Wk, Wk-1, and Wk-2, a redundant measurement connection branches off from battery 101 upstream of the corresponding filter resistor Rfilt,k, Rfilt,k-1, and Rfilt,k-2. In this redundant connection, the respective redundant filter resistors Rfilt,red,k, Rfilt,red,k-1, and Rfilt,red,k-2 are arranged. With a redundant measuring device that includes a redundant analog-to-digital converter, redundant voltages Umess,red,k and Umess,red,k-1 can be measured. The original voltages Umess,k and Umess,k-1 from the primary measurement channel can be checked in this way. However, for example, anomalies or faults in a measurement connection upstream of the branch of the redundant measurement connection cannot be detected.

[0064] 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. REFERENCE MARK 100 battery system 101 Battery 102 Battery Management System 103 mass 110 Switching on the power source Y k 111 Switching off the power source Y k Z k Battery cell R k Cell resistance of battery cell Z k W k electrical connection to the positive terminal of battery cell Z k or negative terminal of battery cell Z k+1 R filt,k Filter resistance of the connection W k R filt,red,k redundant filter resistor for connection W k Uk Battery cell voltage Z k U mess,k measured voltage U mess,red,k redundantly measured voltage Y k with connection W k connected power source I test,k from power source Y k provided test current t time U voltage U mess,k,v measured voltage before switching on the power source Y k U mess,k,n measured voltage after switching on the power source Y k

Claims

[1] Method for fault diagnosis of measuring connections (Wk-1, Wk) using an electrical circuit for voltage monitoring of a battery (101), wherein the battery (101) comprises a plurality of battery elements (Zk-1, Zk, Zk+1), wherein the electrical circuit has: - a first measuring connection (Wk) which is set up to be connected to a positive pole of a first battery element (Zk) of the plurality of battery elements (Zk-1, Zk, Zk+1); - a second measuring connection (Wk-1) which is set up to be connected to a negative pole of the first battery element (Zk); - a measuring device which is configured to determine a voltage between the first measuring connection (Wk) and the second measuring connection (Wk-1); and - a current source (Yk) which is electrically connected to at least one of the two measuring connections (Wk, Wk-1) and which is configured to provide a predetermined current strength (Itest,k), wherein the power source (Yk) is variable, in particular switchable, the procedure comprises the following steps: - Varying the power source (Yk); and - Performing a fault diagnosis of at least one of the two measuring connections (Wk-1, Wk) based on a first voltage (Umess,k,v) between the first and the second measuring connection (Wk-1, Wk) determined using the measuring device before variation, and a second voltage (Umess,k,n) between the first and the second measuring connection (Wk-1, Wk) determined using the measuring device after variation, where the fault diagnosis involves: comparing a difference between the first and second voltage (Umess,k,v, Umess,k,n) with an expected voltage difference, wherein a resistance drift of at least one of the measuring lines (Wk, Wk-1) is determined based on the difference between the first and second voltage (Umess,k,v, Umess,k,n) and the expected voltage difference. [2] Method according to the preceding claim, wherein varying the current source (Yk) is switching on the current source (Yk) with the predetermined current strength (Itest,k) or switching off the current source (Yk). [3] Method according to claim 1 or 2, wherein the expected voltage difference is based on the predetermined current (Itest,k) and resistances of those measuring connections (Wk, Wk-1 or Wk) to which the current source (Yk) is electrically connected. [4] Method according to one of the preceding claims, wherein a fault is diagnosed if the magnitude of a deviation of the difference between the first and the second voltage (Umess,k,v, Umess,k,n) from the expected voltage difference is greater than a predetermined threshold. [5] Method according to the preceding claim, further comprising: Initiating safety measures upon detection of an error. [6] Method according to one of the preceding claims, wherein the power source (Yk) is electrically connected to the first and second measuring connections (Wk, Wk-1). [7] Method according to any one of claims 1 to 5, wherein the current source (Yk) is electrically connected to the first measuring connection (Wk) and to ground (103). [8] Method according to one of the preceding claims, wherein the electrical circuit further comprises a further variable, in particular switchable, current source which is connected in parallel to the current source (103) and which is configured to provide a further predetermined current strength. [9] Method according to any of the preceding claims, wherein the battery elements (Zk-1, Zk, Zk+1) are battery cells, several battery cells connected in parallel or battery modules. [10] Method according to one of the preceding claims, wherein the electrical circuit does not have a redundant measuring circuit (Rfilt,red,k, Umess,red,k) by means of which the voltage (Umess,k) measured between the first and the second measuring connection (Wk, Wk-1) can be checked. [11] Computer program comprising instructions which, when executed by a computer, cause the computer to perform a method according to any one of claims 1 to 10. [12] Control unit, in particular battery management system (102), which is configured to carry out a method according to any one of claims 1 to 10.

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