Method and apparatus for inspecting a battery cell monitoring unit

Abstract

A method for testing a cell monitoring unit (CSC), wherein a corresponding cell voltage (Uz-i) is applied to the cell voltage terminals (ZSA-i) of the cell monitoring unit (CSC), and then a measurement is made on the operating cell monitoring unit (CSC) to determine whether a corresponding current (Imess) flows through at least one cell voltage terminal (ZSA-i), and if so, a fault message is output. A testing device (1) is used for testing the cell monitoring unit (CSC) and has at least one current measuring device (4) for measuring the current (Imess) at the cell voltage terminals (ZSA-i) of the cell monitoring unit (CSC), wherein the testing device (1) is configured to carry out the method. The invention can be used in particular advantageously for testing cell monitoring units of vehicles, in particular electric vehicles.

Description

Technical Field

[0001] The present invention relates to a method for testing a cell monitoring unit, wherein a corresponding cell voltage is applied to the cell voltage terminals of the cell monitoring unit. The present invention also relates to a testing device for testing a cell monitoring unit, which is configured to carry out the method. The present invention can be used in particular to advantage for testing cell monitoring units in vehicles, in particular electric vehicles. Background Art

[0002] Batteries for electric vehicles today typically include battery modules with multiple battery cells, such as lithium-ion batteries, and a cell monitoring unit (CMU) for monitoring the cells' fault-free state. If a battery is reported as faulty by a user, typically in about half the cases, the fault isn't with the battery cells themselves, but rather with the CMU (which can also be referred to as a CSC, or cell monitoring circuit) that monitors the cells. To check whether the CMU is faulty, the CMU was previously removed from the battery, sent to the manufacturer, and inspected there. This check typically involves manually measuring all cell voltages of a known, fault-free battery module, then connecting the CMU to the module, determining the individual cell discharge rates, and declaring the CMU faulty if an excessively high cell discharge rate is detected. This utilizes the knowledge that cell discharge is not permitted if the CMU is fault-free. Therefore, if a voltage drop is detected across at least one cell, this indicates a fault in the CMU. A disadvantage here is that, in order to reliably determine any voltage drops, the cell monitoring unit must remain connected to a fault-free battery module for a long period of time (approximately 24 to 48 hours), and the cell voltages present at all cells must then be measured again and compared with the values ​​before the cell monitoring unit was connected. Summary of the Invention

[0003] The object of the present invention is to at least partially overcome the disadvantages of the prior art and, in particular, to provide a simple and rapid option for detecting faults in a cell monitoring unit.

[0004] This object is achieved by a method for testing a battery cell monitoring unit, wherein:

[0005] - applying the corresponding cell voltage to the cell voltage terminal of the cell monitoring unit, and

[0006] - On the operating cell monitoring unit, measure whether a corresponding current flows at at least one cell voltage terminal and, if so,

[0007] - output fault notification,

[0008] In order to measure the current, a current measuring device is connected continuously to the current line leading to the voltage connection of the corresponding battery cell.

[0009] In order to connect the current measuring device to the current line,

[0010] - firstly connect the current measuring device in parallel to the current line, and then

[0011] - disconnecting the branch of the current line connected in parallel with the connection of the current measuring device.

[0012] This object is achieved by a method for testing a cell monitoring unit, wherein a corresponding cell voltage is applied to the cell voltage terminals of the cell monitoring unit and, when the cell monitoring unit is in operation, it is measured whether a corresponding current flows at at least one cell voltage terminal and, if this is the case, a fault message is output.

[0013] This method offers the advantage of being able to determine the status of the cell monitoring unit within minutes, since the cell voltage difference is no longer checked to monitor cell discharge. Instead, the current flowing through the cell voltage terminals is measured, corresponding to the actual battery module discharge current. This exploits the fact that even small currents can be reliably measured and, moreover, occur continuously while the cell voltage is applied. This in turn reduces the effort required to check the cell monitoring unit. This also reduces costs, as it is no longer necessary to measure the cell voltages of intact battery modules. This also offers the advantage of being able to perform the inspection even by personnel not trained to work with disconnected batteries. In particular, the cell monitoring unit can now be inspected in a workshop, if necessary, eliminating the need to ship it to the manufacturer and return it to the workshop.

[0014] The cell monitoring unit typically has a voltage terminal (hereinafter referred to as "cell voltage terminal" without limiting the generality) which is connected to the respective battery cell during actual vehicle operation and measures its cell voltage. The cell voltage is a DC voltage.

[0015] In the method, applying the corresponding cell voltage to the cell voltage terminals includes, in particular, applying cell voltages corresponding to the cell voltages of the cells of the actual battery module to the cell voltage terminals. The cell monitoring unit to be checked in operation operates as in actual driving operation.

[0016] One improvement involves applying the cell voltage by connecting the cell monitoring unit to a known, fault-free battery module. This battery module can be used to power an electric vehicle and include cells, for example, in the form of lithium-ion cells. However, this eliminates the need for manual cell voltage measurement.

[0017] One development is to connect the cell voltage by connecting the cell voltage terminals to a respectively suitably set voltage source of the voltage generator. In the latter case, the cell monitoring unit is advantageously misled into thinking that it is connected to an actual battery module.

[0018] In principle, for example, by providing a corresponding number of current measuring devices, the discharge current flowing at each battery cell voltage terminal can be measured simultaneously. This has the advantage that the current measuring devices can remain in the electrical lines that potentially carry the discharge direct current.

[0019] One design option is to measure the current at each cell voltage terminal sequentially. This has the advantage that only one current measuring device is required, saving costs and space. Even in this case, the cell monitoring unit can be checked within a few minutes.

[0020] In particular, if the cell monitoring unit is configured to detect interruptions in the cell voltage and trigger an action in response thereto (e.g., outputting a fault message, decoupling the associated cell, etc.), one embodiment is to uninterruptively insert a current measuring device into an electrical line ("current line") leading to the corresponding cell voltage terminal, which may carry (discharge) current in the event of a fault. This has the advantage that any discharge current can be measured quickly and without interruption. "Uninterruptible" is to be understood as meaning that the current line leading to the cell monitoring unit is not interrupted in order to couple or insert the current measuring device into the line or current path and then remove it again.

[0021] A particularly reliable and cost-effective embodiment is to connect the current measuring device in parallel to the current line in order to insert the current measuring device into the current line and then to disconnect the branch of the current line connected in parallel to the connection of the current measuring device.

[0022] One embodiment provides for outputting a fault message if a corresponding current is still measured at at least one cell voltage terminal. This assumes that the cell monitoring unit does not permit discharge current in a fault-free state. Therefore, if a current Imess > 0 is measured at any cell voltage terminal, the cell monitoring unit is considered faulty.

[0023] One embodiment provides for outputting a fault message when a corresponding current is measured at at least one cell voltage terminal, which current is equal to or greater than a predefined threshold value, i.e., whether Imess ≥ Ith applies to at least one cell voltage terminal. This has the advantage that tolerances in the current measurement are taken into account and false fault messages regarding a fault state of the cell monitoring unit are not output. For example, the threshold value Ith can be between 2 and 10 mA.

[0024] One embodiment consists in additionally measuring the cell voltage applied to the cell voltage terminal. This advantageously allows for a check to determine whether the cell voltage measured by the cell monitoring unit deviates from the applied cell voltage. Such a deviation can also indicate a defective cell monitoring unit and, if necessary, trigger a fault message. A further development consists in also measuring the cell voltage sequentially, in particular directly before or after the current measurement at the same cell voltage terminal.

[0025] This object is also achieved by a testing device for testing a cell monitoring unit, the testing device having at least one current measuring device for measuring the current at a cell voltage terminal of the cell monitoring unit, wherein the testing device is configured to carry out the method described above. The testing device can be designed similarly to the method described and has the same advantages.

[0026] In one embodiment, the testing device has one, in particular exactly one, current measuring device, a control device and, for each battery cell voltage terminal to be monitored:

[0027] a first switch, a first terminal of which is connected to the current line and a second terminal of which is connected to a first terminal of the current measuring device,

[0028] a second switch in the form of a changeover switch, a central terminal and a first contact terminal of the second switch being connected to the current line, a first contact terminal of the second switch being connected to the first terminal of the first switch, and a second contact terminal of the second switch being connected to the second terminal of the current measuring device, and

[0029] a third switch, which is inserted into the current path between the central terminal of the second switch and the first contact terminal,

[0030] The control means is configured to switch the switch in an initial position outside of a current measurement process such that

[0031] - the first switch is open,

[0032] - the middle terminal of the second switch is connected to the first contact terminal of the second switch, and

[0033] - the third switch is connected between the middle terminal of the second switch and the first contact terminal,

[0034] And the control device is configured for the current measurement process to:

[0035] - firstly, the first switch is switched on and the middle terminal of the second switch is connected to the second contact terminal of the second switch, and

[0036] - The third switch is then opened between the middle terminal of the second switch and the first contact terminal.

[0037] This design has the advantage that the current measuring device can be reliably inserted into the current line without interrupting the current line. In addition, the structure can be realized in a cost-effective and robust manner.

[0038] An advantageous development is that the switch is a relay, since the switch is particularly robust and, in addition, provides galvanic isolation in the blocked or open state. However, in principle, the switch can also be an electronic switch, such as a power semiconductor, for example a triac.

[0039] In the above embodiment, the cutoff switch does not allow current to flow through it. The cutoff switch can also be referred to as an open switch. Conversely, in its on state, the switch allows current to flow through it. A conducting switch can also be referred to as a closed switch.

[0040] In particular, the first switch and the third switch can be designed as on / off switches. In a further development, the on / off switch can be present as a changeover switch, in which the contact terminals are free terminals.

[0041] In the above embodiment, in particular, the first terminal of the third switch is connected to the first terminal of the first switch, and the second terminal of the third switch is connected to the middle terminal of the second switch. The second switch and the third switch can also be considered as switches present in parallel branches of the current path.

[0042] In one embodiment, the third switch is a changeover switch, which is connected with its center terminal to the first terminal of the first switch, with its first contact terminal to the center terminal of the second switch, and with its second contact terminal to the voltage tap. This advantageously allows the third switch to perform the dual functions of a switch for measuring the current of the i-th cell voltage terminal and a switch for measuring the voltage of the (i+1)-th cell voltage terminal, when the positive line of the i-th cell voltage terminal corresponds to the negative line of the (i+1)-th cell voltage terminal. This eliminates the need for separate switches for performing these functions, which enables a particularly cost-effective and compact design.

[0043] One development consists in that a plurality of cell voltage terminals are connected in such a way that the positive line of a cell voltage terminal corresponds, depending on the type of chain, to the negative line of the next cell voltage terminal.

[0044] The above-described characteristics, features and advantages of the present invention as well as ways and methods of achieving these characteristics, features and advantages become clearer and more clearly understandable in conjunction with the following schematic description of an embodiment, which is explained in more detail in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 A schematic diagram showing components of an inspection device for inspecting a battery cell monitoring unit;

[0046] Figure 2 An equivalent circuit diagram of a current measuring circuit for interposing a current measuring device into a current line leading to a battery cell voltage connection, the current line having a switch in a first switching position, is shown;

[0047] Figure 3 Show Figure 2 , wherein the switch is in the second switching position;

[0048] Figure 4 Show Figure 2 , wherein the switch is in a third switching position suitable for voltage measurement; and

[0049] Figure 5 An equivalent circuit diagram of two current measuring circuits of a testing device connected electrically in series is shown. DETAILED DESCRIPTION

[0050] Figure 1A schematic diagram shows the components of a testing device 1 for testing a cell monitoring unit CSC. The cell monitoring unit CSC has i=1, ..., n cell voltage terminals ZSA-i, where n can be, for example, 12, 16, 20, or more. The testing device 1 has a voltage source unit 2, such as a voltage generator or a fault-free battery module, whose j=1, ..., m (where m ≥ n) cell voltage supply terminals ZVA-j are connected to the respective cell voltage terminals ZSA-i via respective pairs consisting of a "positive" electrical line L+ at a first voltage level and a "negative" electrical line L- at a lower voltage level. The voltage difference between the lines L+ and L- of the cell voltage terminals ZSA-i corresponds to the respective cell voltage Uz-i. The individual cell voltages Uz-i can be different or the same.

[0051] In one development, the cell voltage supply connection ZVA-j and the cell voltage connection ZSA-i can be electrically connected in series or linked, in the sense that the positive line L+ of the cell voltage supply connection ZVA-j corresponds to the negative line L- of the next cell voltage supply connection ZVA-(j+1). This corresponds to the electrical connection of actual battery cells and advantageously serves to save electrical wiring.

[0052] Furthermore, the cell monitoring unit CSC has a current measuring module 3 which is configured to measure, for each cell voltage terminal ZSA-i, the current flowing through at least one of the associated lines L+, L− and to measure this current in particular successively for different cell voltage terminals ZSA-i.

[0053] If a fault of the cell monitoring unit CSC is detected, the testing device 1 can output a corresponding fault message.

[0054] Figure 2 The equivalent circuit diagram shows the circuit of the current measuring module 3 for interconnecting a current measuring device 4 into the positive line L+ leading from the cell voltage supply terminal ZVA-i to the cell voltage terminal ZSA-i. The circuit has a first switch R1, a second switch R2, and a third switch R3, which are switchable by means of a control unit 5 (e.g., a microcontroller).

[0055] The first switch R1 is shown here as an on / off switch, whose first terminal K1 is connected to the positive line L+ serving as a current line and whose second terminal K2 is connected to a first terminal of the current measuring device 4 .

[0056] The second switch R2 is in the form of a changeover switch, wherein the intermediate terminal COM and the first contact terminal L1 are connected to the positive line L+, its first contact terminal L1 is further connected to the first terminal K1 of the first switch R1, and its second contact terminal L2 is connected to the second terminal of the current measuring device 4.

[0057] The third switch R3 is shown here as an on / off switch, inserted into the positive line L+ between the first contact terminal L1 and the center terminal COM of the second switch R2. Thus, the first terminal K1 of the third switch is connected to the first terminal K1 of the first switch R1 and the first contact terminal L1 of the second switch R2, and the second terminal K2 of the third switch is connected to the center terminal COM of the second switch R2. Switches R2 and R3 can also be considered as switches in parallel branches of the positive line L+.

[0058] In the figure, the control device 5 switches the switches R1 to R3 so that they are in an initial position, in which the current measuring device 4 is decoupled from the positive line L+ and therefore cannot measure the current Imess. More precisely, the control device 5 switches the switches R1 to R3 so that the first switch R1 is open, the intermediate terminal COM of the second switch R2 is connected to its first contact terminal L1, and the third switch R3 is closed. Thus, if the battery cell monitoring unit CSC fails and generates a current Imess via the positive line L+, this current Imess is conducted in parallel through the second switch R2 and the third switch R3.

[0059] For the current measurement process, the control device 5 first switches the first switch R1 on and the second switch R2 on, so that the intermediate terminal COM is now conductively connected to the second contact terminal L2. The current measuring device 4 is thus connected in parallel with the third switch R3. During this switching, the cell voltage Uz-i to the cell voltage terminal ZSA-i is not interrupted because the third switch R3 is continuously on.

[0060] Figure 3 Show Figure 2 , in a switching position (also called “current measuring position”), which is assumed after the third switch R3 is opened in a temporally subsequent step, so that the current Imess now flows only through the current measuring device 4 via the positive line L+ (if it still flows) and can thus be reliably measured by it.

[0061] In order to measure the current Imess at all cell voltage terminals ZSA-i sequentially or temporally, the above steps are carried out in reverse order for the cell voltage terminal ZSA-i after the current measurement until the starting position is reached, and then similarly for the other cell voltage terminals ZSA-(i+1). If a current Imess>0 or Imess≥Ith is measured at only one of the cell voltage terminals ZSA-i, an error message is output, optionally with information about the measured cell voltage terminal ZSA-i.

[0062] To achieve sequential current measurement, n relays R1 belonging to all positive lines L+ can be connected in series to one terminal of the current measuring device 4 , and n relays R2 can be connected in series to another terminal of the current measuring device 4 .

[0063] Typically, the cell voltage Uz-i between the lines L+, L- can also be measured and compared, for example, with the cell voltage Uz-i measured by the cell monitoring unit CSC. The cell monitoring unit CSC thus checks for a further source of error, namely, faulty voltage measurements. In one variant, the cell voltages Uz-i are also measured sequentially, so a single voltage measuring device (above) is sufficient. A further development involves measuring the cell voltage Uz-i at the cell voltage terminals ZSA-i directly before or after the current measurement process.

[0064] Figure 4 Shown in one switching position (also called "voltage measuring position") Figure 2 and Figure 3 The equivalent circuit diagram of the switch position is occupied to measure the cell voltage Uz-i at the cell voltage terminal ZSA-i. To measure the voltage, the control device 5 switches the first switch R1, switches the second switch R2 so that the intermediate terminal COM is connected to its first contact terminal L1, and switches the third switch R3. The cell voltage Uz-i can now be measured, for example, between the second terminal K2 of the first switch R1 and the negative line L-. For this purpose, the voltage tap 6 can be connected to the second terminal of the first switch R1, for example.

[0065] One refinement consists in additionally providing a fourth switch R4 for voltage measurement, which is connected with its first terminal K1 to the negative line L- and with its second terminal K2 to the voltage tap 7. This provides the advantage that only one voltage measuring device (top figure) is required to measure all cell voltages Uz-i, which can be connected to the respective cell voltage terminal ZSA-i to be measured via switches R1 and R4. One refinement consists in using the current measuring device 4 as the voltage measuring device.

[0066] At the cell voltage connection ZSA-i, the current Imess can first be measured and then the cell voltage Uz-i, or vice versa.

[0067] Figure 5 An equivalent circuit diagram shows two current measuring circuits connected electrically in series for the battery cell voltage terminals ZSA-1 and ZSA-2, which are connected to the Figure 4 The current measurement circuit shown in FIG. 1 similarly uses four switches R1 to R4 or R3, R5 to R7 for current and voltage measurement. The cell voltage supply terminals ZSA-1 and ZSA-2 are electrically connected in series or linked, with the positive line L+ of the current measurement circuit for monitoring the first cell voltage terminal ZSA-1 corresponding to the negative line L- of the current measurement circuit for monitoring the second cell voltage terminal ZSA-2. This applies analogously to the other cell voltage terminals ZSA-i, where i ≥ 3.

[0068] The current measuring circuits R1 to R4 for monitoring the first cell voltage connection ZSA- 1 correspond functionally to Figure 4 The current measuring circuits R1 to R4 in FIG. 1 are also provided for voltage measurement.

[0069] The current measuring circuits R3, R5 to R7 for monitoring the second cell voltage connection ZSA-2 also correspond functionally to Figure 4 The current measuring circuits R1 to R4 in FIG. 1 are connected to the battery cell voltage terminal ZSA-1, with switches R5 to R7 taking over the functions of switches R1 to R3, and switch R3 taking over the function of switch R4 of the current measuring circuits R1 to R4 for monitoring the first cell voltage terminal ZSA-1. For this purpose, the third switch R3 is now designed as a changeover switch, wherein the intermediate terminal COM is connected to the first terminal K1 of the first switch R1, and its first contact terminal L1 is connected to the intermediate terminal COM of the second switch R2. The second contact terminal K2 of the third switch R3 is connected to the voltage tap 8.

[0070] In particular, for the temporally sequential measurement of the cell voltage Uz-1 and the current Imess at the first cell voltage terminal ZSA-1 and subsequently of the cell voltage Uz-2 and the current Imess at the first cell voltage terminal ZSA-2, the switching positions described in more detail below can be used. "0" represents an open on / off switch, 1 represents an open on / off switch:

[0071] Initial position

[0072] R1 R2 R3 R4 R5 R6 R7 0 COM-L1 COM-L1 0 0 COM-L1 COM-L1

[0073] On voltage taps 6 and 7 Voltage measurement Uz-1 at the first cell voltage terminal ZSA-1

[0074] R1 R2 R3 R4 R5 R6 R7 1 COM-L1 COM-L1 1 0 COM-L1 COM-L1

[0075] These switching positions are in particular envisaged starting from a starting position. After the voltage measurement, in particular a return to the starting position is possible.

[0076] Current measurement at the first cell voltage terminal ZSA-1

[0077] first

[0078] R1 R2 R3 R4 R5 R6 R7 1 COM-L2 COM-L1 0 0 COM-L1 COM-L1

[0079] Then

[0080] R1 R2 R3 R4 R5 R6 R7 1 COM-L2 COM-L2 0 0 COM-L1 COM-L1

[0081] After the current measurement, the device can return to the initial position.

[0082] On voltage taps 8 and 9 Voltage measurement Uz-2 of the second battery cell voltage terminal ZSA-2

[0083] R1 R2 R3 R4 R5 R6 R7 0 COM-L1 COM-L2 0 1 COM-L1 COM-L1

[0084] These switching positions are in particular envisaged starting from a starting position. After the voltage measurement, in particular a return to the starting position is possible.

[0085] Current measurement at the second cell voltage terminal ZSA-2

[0086] first

[0087] R1 R2 R3 R4 R5 R6 R7 0 COM-L1 COM-L1 0 1 COM-L2 COM-L1

[0088] Then

[0089] R1 R2 R3 R4 R5 R6 R7 0 COM-L1 COM-L1 0 1 COM-L2 COM-L2

[0090] After the current measurement, the device can return to the initial position.

[0091] This process can be carried out similarly for further cell voltage connections ZSA-i, where i≥3, wherein, similar to the switch R3, the changeover switch R7 is used both for the current path of the second cell voltage connection ZSA-2 and for the voltage measurement Uz-3 of the third cell voltage connection ZSA-3, etc.

[0092] One advantage is that, due to the dual functionality of the third switch R3 , the seventh switch R7 , etc., a particularly small number of switches is required, which enables a particularly inexpensive design.

[0093] For current measurement at the individual cell voltage terminals ZSA-i, only a single current measuring device 4 is required, which is connected via switches R1 and R2 , R5 and R6 , etc., into the corresponding current path.

[0094] For current measurement of the individual battery cell voltage terminals ZSA-i, only a single voltage measuring device is required, which can be connected sequentially via switches R4 , R3 , etc. to the corresponding negative line L−.

[0095] Since the negative line L− of the first cell voltage connection ZSA- 1 is at the lowest reference potential (also referred to as ground GND), a further current measuring device 11 can advantageously be present in this line, which measures the current fed back from the cell monitoring unit CSC.

[0096] Of course, the invention is not limited to the embodiments shown.

[0097] Therefore, the switches R1 , R5 etc. can also be designed as changeover switches with free or unoccupied contact terminals.

[0098] Generally, unless explicitly excluded, for example, by expressions such as “exactly one”, “a”, “an”, etc., “a”, “an”, etc. can be understood as singular or plural, especially in the sense of “at least one” or “one or more”, etc.

[0099] Quantity specifications may also include the stated quantity as well as the customary tolerance range, unless this is explicitly excluded.

[0100] Reference Signs List

[0101] 1. Check the equipment

[0102] 2 Voltage source unit

[0103] 3 Current measurement module

[0104] 4 Current measurement device

[0105] 5 Control devices

[0106] COM intermediate connector

[0107] CSC Battery Cell Monitoring Unit

[0108] K1 First terminal of on / off switch

[0109] K2 Second connector for on / off switch

[0110] L1 first contact

[0111] L2 Second contact

[0112] L+ positive line

[0113] L- Negative circuit

[0114] R1 First switch

[0115] R2 Second switch

[0116] R3 Third switch

[0117] Uz-i Battery cell voltage at the i-th battery cell voltage connector

[0118] ZSA-1 First battery cell voltage connector

[0119] ZSA-i First battery cell voltage connector

[0120] ZSA-n Nth battery cell voltage connector

[0121] ZVA-1 First battery cell voltage supply connector

[0122] ZVA-j Voltage supply connector for the Jth battery cell

[0123] ZVA-m Voltage supply connector for the Mth battery cell

Claims

1. A method for inspecting a battery cell monitoring unit (CSC), wherein: - applying the corresponding cell voltage (Uz-i) to the cell voltage terminal (ZSA-i) of the cell monitoring unit (CSC), and - On an operating cell monitoring unit (CSC), it is measured whether a corresponding current (Imess) is flowing at at least one cell voltage terminal (ZSA-i) and, if so, whether - output fault notification, In order to measure the current (Imess), a current measuring device (4) is connected continuously to the current line (L+) leading to the corresponding battery cell voltage connection (ZSA-i). In order to connect the current measuring device (4) to the current line (L+), - Firstly, the current measuring device (4) is connected in parallel to the current line (L+), and then - disconnecting the branch of the current line (L+) connected in parallel with the connection of the current measuring device (4), In this case, a testing device provided for carrying out the method has, for each battery cell voltage connection (ZSA-i) to be monitored: a first switch (R1), a first terminal (K1) of which is connected to the current line (L+) and a second terminal (K2) of which is connected to a first terminal of the current measuring device (4), - a second switch (R2) in the form of a changeover switch, the central terminal (COM) and the first contact terminal (L1) of the second switch being connected to the current line (L+), the first contact terminal (L1) of the second switch being connected to the first terminal (K1) of the first switch (R1), and the second contact terminal (L2) of the second switch being connected to the second terminal of the current measuring device (4), and - a third switch (R3), which is connected to the current line (L+) between the central terminal (COM) of the second switch (R2) and the first contact terminal (L1), Among them, in order to measure the current (Imess), - firstly, the first switch (R1) is turned on and the middle terminal (COM) of the second switch (R2) is connected to the second contact terminal (L2) of the second switch, and - Then the third switch (R3) is opened between the middle terminal (COM) of the second switch (R2) and the first contact terminal (L1).

2. The method according to claim 1, wherein The current (Imess) is measured successively at the individual cell voltage terminals (ZSA-i).

3. The method according to claim 1 or 2, wherein: Measurement: Whether a corresponding current (Imess) is flowing at at least one battery cell voltage terminal (ZSA-i).

4. The method according to claim 1 or 2, wherein: Measurement: Whether a corresponding current (Imess) equal to or greater than a predefined threshold value flows at at least one cell voltage terminal (ZSA-i).

5. The method according to claim 1 or 2, wherein: In addition, the cell voltage (Uz-i) present at the cell voltage connection (ZSA-i) is measured.

6. A testing device (1) for testing a cell monitoring unit (CSC), the testing device comprising at least one current measuring device (4) for measuring a current (Imess) at a cell voltage terminal (ZSA-i) of the cell monitoring unit (CSC), wherein: The inspection device (1) is configured to carry out the method according to any one of claims 1 to 5, The testing device (1) comprises a control unit (5) and, for each battery cell voltage connection (ZSA-i) to be monitored: a first switch (R1), a first terminal (K1) of which is connected to the current line (L+) and a second terminal (K2) of which is connected to a first terminal of the current measuring device (4), - a second switch (R2) in the form of a changeover switch, the central terminal (COM) and the first contact terminal (L1) of the second switch being connected to the current line (L+), the first contact terminal (L1) of the second switch being connected to the first terminal (K1) of the first switch (R1), and the second contact terminal (L2) of the second switch being connected to the second terminal of the current measuring device (4), and - a third switch (R3), which is connected to the current line (L+) between the central terminal (COM) of the second switch (R2) and the first contact terminal (L1), The control device (5) is configured to switch the switches (R1-R3) in an initial position outside of a current measurement process so that: - the first switch (R1) is open, - the middle terminal (COM) of the second switch (R2) is connected to the first contact terminal (L1) of the second switch, and - the third switch (R3) is connected between the middle terminal (COM) of the second switch (R2) and the first contact terminal (L1), And the control device (5) is configured for the current measurement process to: - firstly, the first switch (R1) is turned on and the middle terminal (COM) of the second switch (R2) is connected to the second contact terminal (L2) of the second switch, and - Then the third switch (R3) is opened between the middle terminal (COM) of the second switch (R2) and the first contact terminal (L1).

7. The inspection device (1) for inspecting a battery cell monitoring unit (CSC) according to claim 6, wherein: Additionally, the cell voltage (Uz-i) present at the cell voltage terminal (ZSA-i) is measured, wherein the third switch (R3) is a changeover switch. - connected with its middle terminal (COM) to the first terminal (K1) of the first switch (R1), - is connected with its first contact terminal (L1) to the middle terminal (COM) of the second switch (R2), and - is connected with its second contact terminal (L2) to the voltage tap (8).

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