Method for fault detection in a battery system and control device

Abstract

The invention relates to a method for fault detection in a battery system (100), wherein the battery system (100) comprises: (i) a battery management system (102), (ii) a battery (101) having at least one battery cell (Zk) and (iii) at least two electrical connections (Wk, Wk+1) between the battery management system (102) and the battery (101), wherein a first (Wk+1) of the electrical connections connects the battery management system (102) to a positive pole of the battery cell (Zk) and a second (Wk) of the electrical connections connects the battery management system (102) to a negative pole of the battery cell (Zk). The method comprises the following steps: (a) closing (110) a switch (Sk) configured to connect the first and the second electrical connection (Wk, Wk+1) to one another; (b) measuring a voltage (Uk,mess, U2,k,mess) between the first and the second electrical connection (Wk, Wk+1); and (c) identifying that at least one of the two electrical connections (Wk, Wk+1) is faulty on the basis of an evaluation criterion which is based on the measured voltage (Uk,mess, U2,k,mess). The invention also relates to a corresponding control device and to a computer program.

Description

[0001] DESCRIPTION

[0002] Method for fault detection in a battery system and control unit

[0003] TECHNICAL FIELD

[0004] The present disclosure relates to methods and control devices for fault detection in a battery system, in particular for detecting faulty connections between a battery and a battery management system.

[0005] BACKGROUND OF THE INVENTION

[0006] Battery management systems, such as those used in electric or hybrid vehicles, typically include electrical circuits for monitoring, controlling, and protecting rechargeable batteries. For example, such systems can be configured to measure the battery voltage or the voltages of individual battery cells. Such measured values ​​can be used, for example, to determine the battery's state of charge or state of health, or the maximum available capacity.

[0007] In order to perform such tasks reliably, control lines are required that connect the battery management systems to the associated battery and, in particular, to individual battery cells.

[0008] SUMMARY AND EMBODIMENTS

[0009] It is therefore an object of the present disclosure to provide a simple and at the same time reliable method for fault detection in a battery system, in particular for detecting faulty connecting lines between the battery and the battery management system, as well as an associated control unit which is capable of carrying out such a method.

[0010] This problem is solved by a method for fault detection in a battery system and a control unit according to the independent patent claims. Advantageous embodiments and further developments emerge from the respective dependent claims, the following description, and the drawings.

[0011] Thus, according to a first aspect, a method for fault detection in a battery system is provided, wherein the battery system comprises: (i) a battery management system, (ii) a battery with at least one battery cell, and (iii) at least two electrical connections between the battery management system and the battery, wherein a first of the electrical connections connects the battery management system to a positive pole of the battery cell and a second of the electrical connections connects the battery management system to a negative pole of the battery cell. The method comprises the following steps: (a) closing a switch configured to connect the first and second electrical connections to one another; (b) measuring a voltage between the first and second electrical connections; and (c) detecting that at least one of the two connections is faulty based on an evaluation criterion based on the measured voltage.

[0012] According to a further aspect, a control device, in particular a battery management system, is provided which is configured to carry out the method described above.

[0013] According to a further aspect, a battery system is provided, which comprises the previously described battery management system, the battery, and the at least two electrical connections between the battery management system and the battery. According to a further aspect, a computer program is provided, which comprises instructions that, when executed by a computer, cause the computer to perform the previously described method.

[0014] According to a further aspect, a storage medium is provided with a computer program, wherein the computer program comprises instructions which, when the computer program is executed by a computer, cause the computer to carry out the method described above

[0015] According to a further aspect, a use of balancing switches of a battery system for detecting faulty connection lines between a battery of the battery system and a battery management system of the battery system is provided.

[0016] In the context of the present disclosure, a battery management system or BMS is defined, for example, as a component connected to an associated battery that fulfills at least one of the following functions: monitoring, regulating, and protecting the battery. For example, the battery management system can implement charge and discharge control, state of charge detection, temperature control, voltage diagnosis, in particular cell voltage diagnosis, deep discharge protection, and / or overcharge protection. For batteries with multiple cells, the battery management system can be configured to monitor and / or control the individual cells. The battery management system can be configured to balance or symmetrize the different cells, in particular to ensure a more even electrical charge distribution in different battery cells.

[0017] According to one embodiment, the battery system, in particular the battery management system, has a voltmeter which is configured to measure the voltage between the first and the second electrical connection. The voltmeter can be configured to measure the voltage indirectly, i.e. to determine the voltage from other measured variables. In the context of the present disclosure, an electrical connection can be an electrical connecting line. The electrical connecting line can have electrical components, for example a resistor. Alternatively or additionally, the electrical connecting line can have a branch, for example to a negative or positive pole of different battery cells. The electrical connection can comprise regions within the battery and / or the battery management system, for example an RC filter of the battery management system.

[0018] According to one embodiment, the electrical connections extend to the switch. Alternatively or additionally, the electrical connections extend to the positive or negative pole of the battery cell.

[0019] In the context of the present disclosure, a battery is defined, for example, as a storage device for electrical energy, in particular on an electrochemical basis. In one embodiment, the battery is an accumulator, i.e., a rechargeable battery. The battery can contain a plurality of battery cells, which can be connected at least partially in series. The battery is, for example, a lithium-ion accumulator.

[0020] In the context of the present disclosure, a switch is defined, for example, as a component that enables or prevents a current flow along an electrical connection. The switch can be configured to establish or break an electrically conductive connection. The separation can be implemented mechatronically, in particular by means of an isolating gap, and / or electronically. The switch can be, for example, a transistor, a reed switch, a bimetallic switch, a relay, or a contactor. The switch can have two switching positions, in particular open and closed, or more than two switching positions, for example a continuum of switching positions. The switch can be configured to connect the two connecting lines to one another in the closed state and / or to separate the two connecting lines from one another in the open state.According to one embodiment, the switch serves at least one further purpose in addition to fault detection, for example, symmetrizing and / or balancing battery cells. The symmetrizing or balancing can be designed to compensate for differences in the states of the individual battery cells, for example, to equalize the electrical charge distribution of the individual battery cells.

[0021] The previously described method and / or control unit can be advantageous for ensuring proper functioning of the battery system. If one or more of the connecting lines between the battery management system and the battery are defective, the monitoring, control, and / or protection of the battery by the battery management system may be impaired. This can lead to undervoltages or overvoltages in battery cells, which in turn can cause a loss of cell capacity, irreversible damage, or even a fire due to overcharging.

[0022] Checking the functionality of the electrical connections between the battery management system and the battery by closing and / or opening switches can be advantageous because such measures are simple and cost-effective to implement. This is especially true if the switches are already installed in the battery management system for another purpose, such as cell balancing.

[0023] The fact that the evaluation criterion is based on a measured voltage between the connecting lines can be advantageous if such a voltage value is already available, for example, as the measured voltage of the corresponding battery cell. According to one embodiment, such voltage values ​​are collected anyway for monitoring the voltage of the battery cells.

[0024] In summary, the described procedure or the described

[0025] Control unit the error detection of an open cell connection in a battery pack to the battery management system, whereby a circuit is used which is usually already present for reasons of cell symmetry.

[0026] According to one embodiment, at least one of the following faults can be detected: an open electrical line, an electrical line with increased resistance and an open resistance in the electrical line.

[0027] According to one embodiment, the evaluation criterion queries whether the measured voltage drops below a predetermined minimum value after the switch is closed. Such an embodiment can be advantageous because, in the case of certain faults in the connecting lines, for example, a high-resistance connection, the increased resistance in at least one of the electrical connecting lines leads to a larger measured voltage drop. Such an increased voltage drop can be detected using the described evaluation criterion.

[0028] According to one embodiment, the battery system has two measurement paths. The voltage drop can vary in both measurement paths, for example, depending on whether the measurement path contains the switch or not. Accordingly, the predetermined minimum value can be adjusted depending on whether the measurement path in which the voltage is measured contains the switch. According to one embodiment, the voltage is measured in the measurement path without a switch.

[0029] According to one embodiment, if the measured voltage drops below the predetermined minimum value, it is concluded that there is increased resistance and / or an interruption in at least one of the electrical connections. In the case of a connection with increased resistance, the resistance can be at least twice as high as that of an intact connection, in particular at least three times as high, in particular at least ten times as high, in particular at least one hundred times as high, in particular at least one thousand times as high. Such an embodiment can be advantageous because deviations in the voltage measurement can occur in the case of increased resistance and an interrupted connection.According to one embodiment, if the measured voltage rises above a predetermined threshold and / or above a predetermined maximum value that is greater than the predetermined minimum value after the switch is reopened, it is concluded that the connection has increased resistance but is not completely interrupted. Alternatively or additionally, if the measured voltage remains below the predetermined threshold and / or below the predetermined maximum value after the switch is reopened, it is concluded that the connection is interrupted. The predetermined minimum and maximum values ​​can define a window for the smallest voltage value to which the measured voltage drops after the switch is closed, assuming both electrical connections are fault-free.

[0030] According to one embodiment, the method is performed when the motor vehicle is not moving and / or when there is no or only a low load on the battery. Under these circumstances, the measured voltage can be particularly stable, which can enable particularly accurate and reliable implementation of the method. Of course, the method can also be performed while the motor vehicle is moving, for example, to detect broken connecting lines in a timely manner.

[0031] According to one embodiment, the method further comprises opening the switch after closing the switch, wherein the evaluation criterion queries whether the measured voltage exceeds a predetermined threshold after opening the switch. According to one embodiment, the measured voltage is waited for before opening. Such a method has proven particularly robust and reliable for fault detection in the connecting lines.

[0032] According to one embodiment, if the voltage does not exceed the predetermined threshold value, it is concluded that there is an interruption in at least one of the two electrical connections. Such an embodiment can be advantageous for diagnosing interrupted connecting lines particularly reliably. According to one embodiment, the predetermined threshold value and / or the predetermined minimum value depend on at least one of the following parameters: a resistance of the switch, a capacitance arranged between the two connecting lines, and a period of time during which the switch is closed. All of these parameters can influence the voltage curve, which is why it can be advantageous to adjust the threshold value and / or the minimum value accordingly.

[0033] According to one embodiment, the switch is a balancing switch configured to compensate for differences between battery cells. The differences may, in particular, relate to a voltage and / or a remaining capacity of the battery cells.

[0034] The balancing switches can be designed for passive balancing, in which more highly charged battery cells are discharged to the level of the less highly charged battery cells, with the released energy being converted into heat. With active balancing, however, the energy released by the more highly charged battery cells would be utilized, specifically transferred to less highly charged battery cells. Balancing can be beneficial for enabling safe, efficient, and long-lasting battery operation.

[0035] Using the balancing switches for fault detection can be advantageous because no additional components are required. Instead, existing components used for other purposes are additionally used for fault diagnosis.

[0036] According to one embodiment, the battery management system has at least two measuring paths for voltage measurement, wherein one of the measuring paths has the switch, wherein the voltage is measured in a measuring path without a switch and / or in the measuring path with the switch. Such an embodiment can be advantageous because the measured voltage can be checked for plausibility via the additional measuring path. According to one configuration, the voltage is measured in the measuring path with a switch and checked for plausibility using the voltage in the measuring path without a switch. Such a configuration can be advantageous because the voltage drop in the measuring path with a switch can be more pronounced.

[0037] According to one embodiment, the voltage in the measurement path is measured without a switch. Such an embodiment can be advantageous because the voltage curve in the measurement path without a switch can be more stable, thus allowing a potential fault to be detected more reliably.

[0038] According to one embodiment, at least one of the measuring paths, in particular both measuring paths, can have an RC filter, for example to filter interference and / or reduce input peaks.

[0039] According to one embodiment, the battery has at least two battery cells connected in series and the battery system has at least three electrical connections between the battery and the battery management system, wherein for each battery cell a first of the electrical connections contacts a negative pole of the battery cell and a second of the electrical connections contacts a positive pole of the battery cell.

[0040] Such an embodiment may be advantageous because the method can be carried out for a plurality of battery cells and the respective switches in order to detect faults in the associated electrical connections of the battery cells.

[0041] According to one embodiment, the battery comprises several strings of battery cells connected in series, with the strings connected in parallel. Fault diagnosis of the connecting lines can, for example, be performed separately for each string.

[0042] According to one embodiment, electrically connected

[0043] The negative poles and positive poles of adjacent battery cells are each contacted by a common electrical connection of the at least three electrical connections, in particular by only one common electrical connecting line. In the context of the present disclosure, battery cells can be defined as adjacent if they are connected in series and the positive pole of one cell is electrically connected, in particular directly connected, to the negative pole of the other cell. Such an embodiment can be advantageous in terms of an efficient design of the circuit with the smallest possible number and length of electrical connections.

[0044] According to one embodiment, adjacent electrical connections of the at least three electrical connections can be connected to one another by means of a respective switch. In the context of the present disclosure, connections can be defined as adjacent if they each contact the positive pole of two adjacent battery cells and / or if they each contact the negative pole of two adjacent battery cells and / or if they contact the positive pole and the negative pole of the same battery cell. Such an embodiment can be advantageous because such an arrangement of switches can enable fault diagnosis of all connection lines to the battery cells. Furthermore, the described switches can also be used as

[0045] Balancing switches can be used with the corresponding synergy effects in terms of component usage and circuit complexity.

[0046] According to one embodiment, the method further comprises measuring a respective voltage between adjacent connections, in particular using two measuring channels, one of which has the respective switch. According to one embodiment, the voltages are measured between all adjacent connections. The voltage measurement can be performed using one or more voltage measuring devices. A voltage measurement in two measuring paths can be advantageous, in particular with regard to verifying the plausibility of the measurement signal. A particularly precise voltage measurement may be required to detect a connection with increased resistance, as described above.According to one embodiment, the method is carried out successively for two adjacent switches and, if a fault is detected for one of the switches but not for the other, it is concluded that the common electrical connection of the two adjacent switches is intact and / or that the other connecting line of the switch for which a fault was detected is faulty.

[0047] According to one embodiment, the method is first performed for switches that are each spaced apart by an intermediate switch, and then for the intermediate switches. For example, the first-mentioned switches can all be closed and / or opened simultaneously, and the intermediate switches can all be closed and / or opened simultaneously at a later time. Such a procedure can be advantageous for checking all switches or the associated electrical connections in the shortest possible time, without being affected by the diagnosis of neighboring switches.

[0048] 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.

[0049] BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Further advantages and advantageous embodiments and further developments of the method and of the control device emerge from the following exemplary embodiments shown in conjunction with the figures.

[0051] They show:

[0052] Figure 1 shows a battery system with a battery and a battery management system according to an exemplary embodiment of the present disclosure; Figures 2 and 3 show aspects of a method for detecting faults in a battery system during proper operation and in the event of a fault, respectively, according to an exemplary embodiment of the present disclosure;

[0053] Figure 4 shows a battery system with battery and battery management system according to another embodiment of the present disclosure;

[0054] Figures 5 and 6 show aspects of a method for detecting faults in a battery system during proper operation and in the event of a fault, respectively, according to a further embodiment of the present disclosure.

[0055] Identical, similar, or functionally identical elements are provided 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 in the figures are not to scale. Rather, individual elements may be exaggerated for clarity and / or clarity.

[0056] DETAILED DESCRIPTION OF EMBODIMENTS

[0057] Figure 1 shows a battery system 100 of a motor vehicle, which comprises the following elements: (i) a battery management system 102, (ii) a rechargeable battery 101 with at least one battery cell Zk and (iii) at least two electrical connections Wk, Wk+1 between the battery management system 102 and the battery 101. A first of the electrical connections Wk connects the battery management system 102 to the positive pole of the battery cell Zk and a second of the electrical connections Wk+1 connects the battery management 102 to the negative pole of the battery cell Zk.

[0058] The two electrical connections Wk, Wk+1 each comprise a resistor Rfilt, k, Rfilt, k+1 within the battery management system. A capacitor Ck is arranged between the two electrical connections Wk, Wk+1, starting from the battery, behind the respective resistors Rfilt, k, Rfilt, k+1. The capacitor Ck, together with the resistor Rfilt, k+1, forms an RC filter, which can, for example, filter out interference or compensate for voltage peaks. A switch Sk is arranged between the connecting lines Wk, Wk+1, starting from the battery and behind the RC filter. When closed, this switch Sk connects the connecting lines Wk, Wk+1 to one another.

[0059] The battery comprises further battery cells, of which the two battery cells Zk-1 and Zk+1 are shown as examples in Figure 1. The positive and negative poles of the further battery cells Zk-1, Zk+1 are connected to the battery management system 102 via corresponding electrical connections Wk-1, Wk and Wk+1, Wk+2 (not shown in Figure 1). The electrical connections Wk-1, Wk, Wk+1, Wk+2 have resistors Rfilt,k-1, Rfilt,k, Rfilt,k+1 and Rfilt,k+2 (not shown in Figure 1). Between each two adjacent electrical connections Wk-1, Wk, Wk+1, Wk+2, capacitors Ck-1, Ck, and Ck+1 (not shown in Fig. 1) are arranged, which, together with the previously described resistors Rfilt,k-1, Rfilt,k, Rfilt,k+1, and Rfilt,k+2, form RC elements. Furthermore, between each two adjacent electrical connections Wk-1, Wk, Wk+1, Wk+2, the switches Sk-1, Sk, and Sk+1 (in Fig.1 not shown) which, when closed, electrically connect the respective connections to each other.

[0060] The battery management system 102 also has one or more measuring devices with which the voltages Uk-1,mess, Uk,mess between adjacent connecting lines Wk-1, Wk, or Wk, Wk+1 can be determined. Using an evaluation criterion based on the measured voltages Uk-1,mess, Uk,mess, it can be examined whether at least one of the electrical connections Wk-1, Wk, or Wk, Wk+1 is faulty.

[0061] Figures 2 and 3 illustrate the application of such an evaluation criterion, with Figure 3 showing the fault case and Figure 2 showing proper operation. Both figures plot the measured voltage Uk,mess over time t. The actual voltage llk of the battery cell Zk, a minimum possible or minimum permissible cell voltage Ukmin,THD of the battery cell Zk, and a predefined threshold value Ukow,THD are plotted as comparison values ​​along the U-axis.

[0062] At a predetermined time 110, the switch Sk is closed, whereupon, both in the event of a fault and during proper operation, the measured voltage Uk,mess drops to a value greater than or equal to the minimum cell voltage Ukmin,THD and approximately stabilizes. Upon subsequent opening 111 of the switch, the measured voltage rises again above the threshold value Ukow,THD during proper operation and approximately reaches the actual voltage value llk again (Figure 2). In contrast, in the event of a fault, after the opening 111 of the switch Sk, the measured voltage Uk,mess no longer exceeds the threshold value Ukow,THD (Figure 3). From this, it is deduced that at least one of the electrical connections Wk, Wk+1 is faulty.

[0063] In other words, switching the cell balancing switch Sk discharges the capacitor Ck. The measured voltage Uk,mess then drops rapidly. A software component evaluates the measured cell voltage Uk,mess after the switch Sk has been closed 110 and opened again 111, to see if it falls below a defined limit Ukow,THD. In the event of a fault, the voltage remains close to zero after the switch Sk has been opened 111. If there is no fault, Uk = Uk,mess is immediately established and the limit Ukow,THD is not fallen below. To rule out interaction between neighboring cells, it is advisable to first control all switches Sk with even k and then all switches Sk with odd k in order to check the corresponding electrical connections Wk, Wk+1 using the evaluation criterion.

[0064] This check is implemented by software control of the hardware switches. The measured voltage values ​​are provided by an analog-to-digital converter. It can potentially be used in any battery with a cell balancing circuit and cell voltage measurement, particularly if both use the same connection to the cell. The embodiment in Figure 4 shows the battery system 100 from Figure 1, which, in addition to the measurement path Uk,mess, Uk-1,mess shown in Figure 1, has a second measurement path U2,k,mess, U2,k-1,mess. Viewed from the battery, the second measurement path branches off before the RC elements of the first measurement path and likewise contains RC elements formed from corresponding resistors R2,filt,k-1 , R2,filt,k , R2,filt,k+1 and capacitors C2,k , C2,k-1. The second measuring path U2,k,mess, U2,k-1 ,mess is therefore constructed analogously to the first measuring path Uk,mess, Uk-1 ,mess, but does not contain switches Sk, Sk+1.The electrical connections Wk-1 , Wk, Wk+1 each comprise a branch leading to the two measuring paths.

[0065] Figures 5 and 6 illustrate the application of a further evaluation criterion, which can be queried alternatively or in addition to the evaluation criterion in Figures 2 and 3. Figure 5 shows proper operation, and Figure 6 shows a fault. A voltage Uk,mess, U2,k,mess is again measured between two electrical connections Wk, Wk+1. As shown in Figures 5 and 6, the voltage U2,k,mess measured in the second measurement path is considered for the further evaluation criterion. However, an analogous diagnosis could also be performed based on the voltage Uk,mess measured in the first measurement path.

[0066] The further evaluation criterion examines whether the measured voltage U2,k,mess drops below a predetermined minimum value Uk,OK,min after the switch Sk is closed 110, in particular before the subsequent opening 111 of the switch Sk. If this is the case, it is concluded that at least one of the electrical connections Wk,Wk+1 is faulty. The fault being investigated consists in at least one of the electrical connections having an increased resistance or a high-impedance connection. The increased resistance can be higher than during normal operation, for example by at least twice, three times, five times, ten times, one hundred times, or a thousand times. If the measured voltage Uk,mess from the first measuring path is analyzed, a different predetermined minimum value can, but does not have to, be selected because the measuring paths typically react differently to the closing of the switch Sk.

[0067] In other words, a high-impedance connection between the battery management system and the battery pack should be detected. For this purpose, a second measuring path and a cell balancing circuit in the first measuring path are used. Such a high-impedance connection is critical because it can lead to incorrect measured values. Closing the cell balancing switch Sk allows a current to flow through the connection. This current leads to a drop in the voltage U2,k,mess. This voltage drop is increased when the resistance between the battery pack and the battery management system is increased. The measured values ​​are provided by an analog-to-digital converter and can be compared against the limit values ​​using software. In a good case, values ​​between Uk,OK,max and Uk,OK,min are expected. With a poor connection, the value U2,k,mess will be below Uk,OK,min.

[0068] The invention is not limited to the embodiments described herein. Rather, the invention encompasses any novel feature and any combination of features, including, in particular, any combination of features in the embodiments and claims.

[0069] REFERENCE SYMBOL

[0070] 100 battery system

[0071] 101 Battery

[0072] 102 Battery management system

[0073] 110 Closing the switch

[0074] 111 Opening the switch

[0075] Zk battery cell

[0076] Wk electrical connection to the negative pole of the battery cell Zk

[0077] Werr faulty electrical connection

[0078] Rfiit.k filter resistance

[0079] Ck capacitor

[0080] Sk switch

[0081] I current

[0082] Uk voltage of the battery cell Zk

[0083] Uk ,mess measured voltage

[0084] R2,fiit,k filter resistance of the additional measuring channel

[0085] C2,k capacitor in the further measuring channel

[0086] U2 ,k,mess measured voltage in the further measuring channel t time

[0087] U voltage

[0088] Ukow.THD specified threshold (interrupted electrical line)

[0089] Ukmin.THD minimum cell voltage

[0090] Uk , OK, max specified maximum value (high-resistance electrical line)

[0091] Uk,oK,min specified minimum value (high-resistance electrical line)

Claims

PATENT CLAIMS 1. A method for fault detection in a battery system (100), wherein the battery system (100) comprises: a battery management system (102), a battery (101 ) with at least one battery cell (Zk) and at least two electrical connections (Wk, Wk+1 ) between the battery management system (102) and the battery (101 ), wherein a first (Wk+1 ) of the electrical connections connects the battery management system (102) to a positive pole of the battery cell (Zk) and a second (Wk) of the electrical connections connects the battery management system (102) to a negative pole of the battery cell (Zk), the method comprising the following steps: - closing (110) a switch (Sk) which is arranged to connect the first and the second electrical connection (Wk, Wk+1 ) to one another; - measuring a voltage (Uk,mess, U2,k,mess) between the first and the second electrical connection (Wk, Wk+1 ); and - Detecting that at least one of the two electrical connections (Wk, Wk+1 ) is faulty, based on an evaluation criterion based on the measured voltage (Uk,mess, U2,k,mess).

2. Method according to the preceding claim, wherein the evaluation criterion queries whether the measured voltage (Uk,mess, U2,k,mess) drops below a predetermined minimum value (Uk,OK,min) after the switch (Sk) is closed (110).

3. Method according to the preceding claim, wherein, if the measured voltage (Uk,mess, U2,k,mess) falls below the predetermined minimum value (Uk,OK,min), it is concluded that there is an increased resistance and / or an interruption in at least one of the electrical connections (Wk, Wk+1).

4. Method according to one of the preceding claims, wherein the method further comprises opening (111) the switch (Sk) after closing (110) the switch (Sk) and wherein the evaluation criterion queries whether after the Opening (111) of the switch (Sk) the measured voltage (Uk,mess, U2,k,mess) exceeds a predetermined threshold value (Ukow,THD).

5. Method according to the preceding claim, wherein, if the measured voltage (Uk,mess, U2,k,mess) does not exceed the predetermined threshold value (Ukow,THD), it is concluded that there is an interruption in at least one of the two electrical connections (Wk, Wk+1).

6. Method according to one of the preceding claims, wherein the predetermined threshold value (Ukow,THD) and / or the predetermined minimum value (Uk,OK,min) depend on at least one of the following parameters: a resistance of the switch (Sk), a capacitance (Ck) arranged between the two connecting lines (Wk, Wk+1 ) and a time period during which the switch (Sk) is closed.

7. Method according to one of the preceding claims, wherein the switch (Sk) is a balancing switch which is designed to compensate for differences between battery cells (Zk-1, Zk, Zk+1).

8. The method according to one of the preceding claims, wherein the battery management system (102) has at least two measuring paths (Uk,mess, U2,k,mess) for voltage measurement, wherein one of the measuring paths (Uk,mess) has the switch (Sk), wherein the voltage (U2,k,mess) is measured in the measuring path (U2,k,mess) without the switch (Sk).

9. Method according to one of the preceding claims, wherein the battery (101 ) has at least two battery cells (Zk-1 , Zk, Zk+1 ) connected in series and the battery system (102) has at least three electrical connections (Wk-1 , Wk, Wk+1 ) between the battery (101 ) and the battery management system (102), wherein for each battery cell (Zk-1 , Zk, Zk+1 ) a first of the electrical connections (Wk-1 , Wk, Wk+1 ) contacts a negative pole of the battery cell (Zk-1 , Zk, Zk+1 ) and a second of the electrical connections (Wk-1 , Wk, Wk+1 ) contacts a positive pole of the battery cell (Zk-1 , Zk, Zk+1 ).

10. Method according to the preceding claim, wherein electrically connected negative poles and positive poles of adjacent battery cells (Zk-1, Zk, Zk+1) are each contacted by a common electrical connection of the at least three electrical connections (Wk-1, Wk, Wk+1).

11. Method according to the preceding claim, wherein adjacent electrical connections of the at least three electrical connections (Wk-1, Wk, Wk+1) can be connected to one another by means of a respective switch (Sk-1, Sk).

12. Method according to the preceding claim, wherein the method is carried out for two adjacent switches (Sk-1 , Sk) and, if a fault is detected for one of the switches (Sk-1 , Sk) but not for the other (Sk, Sk-1 ), it is concluded that the common electrical connection (Wk) of the two adjacent switches (Sk-1 , Sk) is intact and / or that the other connecting line (Wk-1 , Wk+1 ) of the switch (Sk-1 , Sk) for which a fault was detected is faulty.

13. Use of balancing switches of a battery system (100) for detecting faulty connecting lines (Wk, Wk+1) between a battery (101) of the battery system (100) and a battery management system (102) of the battery system (100).

14. Control device, in particular battery management system (102), which is configured to carry out the method according to one of claims 1 to 13.

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

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