Controller for a battery module, computer-implemented method, computer program and non-volatile data carrier

Abstract

A battery module (200) containing a plurality of battery cells (101, 102, 103) is monitored by a controller (120) that repeatedly obtains performance characteristics of the battery cells. The controller (120) obtains two consecutively registered voltage values (V11(t), V11(t+t')) over each battery cell (101, 102, 103), which voltage values represent a previous and a recent performance characteristic respectively for the battery cell. The controller (120) compares the obtained voltage values (V11(t), V11(t+t')) for a battery cell (101) with one another; and if the voltage values differ by more than a threshold quantity, the controller (120) sets an alarm indicator (A) in respect of the battery cell (101).

Description

[0001] Controller for a Battery Module, Computer-Implemented Method, Computer Program and Non-Volatile Data Carrier

[0002] TECHNICAL FIELD

[0003] The present invention relates generally to battery based storage of electric energy. Especially, the invention relates to a controller according to the preamble of claim 1 and a corresponding computer-implemented method. The invention also relates to a computer program and a non-volatile data carrier storing such a computer program.

[0004] BACKGROUND

[0005] The recent dramatic increase of renewable energy resources has resulted in a high demand for efficient battery solutions because many of the renewable energy resources, for instance those being solar, wind or wave based have an uncontrollable production of electric energy. Therefore, to meet the varying demand on the consumer side, an intermediate storage is needed, typically in the form of an electric battery. In general, these type of batteries accumulate large amounts of electric power. For safety reasons, it is therefore of utmost importance that the battery is not tampered with, for example by a consumer. Namely, there is a risk of catastrophic consequences if a battery cell with mis-matched characteristics is connected to a system of battery cells. To prevent such incidents, it is necessary to have an intrusion protection system that is capable of detecting and preventing any unauthorized access to the battery system.

[0006] US 6,049, 145 shows an electronic device that includes electrical circuitry, a housing in which the electronic circuitry is situated, a cover for enclosing the electrical circuitry within the housing, and a tamper proof safety circuit coupled to the electrical circuitry for rendering the electronic device inoperable when the housing and cover are disassembled. US 2022 / 0330422 discloses a system for detecting access to a pre-defined area on a Printed Circuit Board. The system comprises: the Printed Circuit Board comprising, on at least one of its external surfaces, at least one pre-defined area comprising electrical components. A potting material is arranged over at least the pre-defined area, wherein the potting material comprises a first layer of transparent material configured to allow light to pass through. A second layer of opaque material is arranged so that it completely blocks light towards the first layer. The first layer is arranged between the Printed Circuit Board and the second layer and extends at least over the pre-defined area. At least one photo-sensor is arranged within the first layer of transparent material and configured to generate a tamper signal upon detection of light in the first layer.

[0007] US 8,395,519 describes a battery pack, which includes at least one battery cell that expands and contracts in relation to the chemical conditions of the battery cell. A substrate is configured to contact the at least one battery cell. A sensor is attached to the substrate and the sensor produces a signal indicative of the displacement of the substrate. A controller is communicatively connected to the sensor such that the controller receives the signal from the sensor. The controller processes the signal to produce an indication of a status of the battery cell. A method of monitoring battery safety includes movably securing a substrate across at least one cell of a battery. A displacement of the substrate is measured. The measured displacement is processed with a controller to identify a safety status of the at least one cell. An output device is operated with a controller to provide an indication of the safety status of the at least one cell of the battery.

[0008] US 2007 Z0229026 reveals a battery pack with a current cut-off device connected in series with batteries, a tamper detector to detect tampering and issue a tamper signal, and a control circuit connected to the tamper detector. If the tamper detector detects tampering with the battery pack, the control circuit switches the current cut-off device off to shut. Thus various solutions exist for preventing unauthorized access to electronic / electric systems, inter alia battery systems. However, there is room for improvement, for example in terms of reliability and power-efficiency of the monitoring.

[0009] SUMMARY

[0010] The object of the present invention is therefore to offer a solution that mitigates the above problems, and enables reliable and efficient surveillance of a battery module.

[0011] According to one aspect of the invention, the object is achieved by a controller for monitoring a battery module that includes a plurality of battery cells. The controller is configured to repeatedly obtain at least one performance characteristic of each battery cell. Specifically, the controller is configured to obtain two consecutively registered voltage values over each battery cell in the battery module. The voltage values represent a previous and a recent performance characteristic respectively for the battery cell. The controller is further configured to compare the obtained voltage values with one another; and if the voltage values differ by more than a threshold quantity, the controller is configured to set an alarm indicator in respect of the battery cell.

[0012] This controller is advantageous because it detects any improperly substituted battery cell in a straightforward manner. Namely, provided that the threshold quantity is set to a suitable value, it is impossible to swap battery cells in the battery module without triggering the alarm indicator. The controller may thus be defined as a controller for monitoring a battery module and detecting any improperly substituted battery cell.

[0013] The controller may be configured to repeatedly obtain at least two performance characteristic of each battery cell.

[0014] For example, to conserve battery, the controller may obtain updates of each battery cell’s performance characteristic at a first update frequency during a first period after that the battery module has entered a standby mode. Then, after expiry of the first period, the controller may obtain such updates at a second update frequency, which is lower than the first update frequency.

[0015] According to one embodiment of this aspect of the invention, the threshold quantity is defined in relation to an absolute voltage difference, and / or a ratio between the two consecutively obtained voltage values. Thus, the criterion for setting the alarm indicator may be conveniently adjusted.

[0016] For energy efficiency, the threshold quantity may be adapted to only detect relatively large voltage deviations, say above 25 % of a nominal voltage for the battery cell.

[0017] According to another embodiment of this aspect of the invention, the at least one performance characteristic comprises a discharge profile and / or a charge profile. The discharge profile describes how a voltage over the battery cell varies as function of time while electric energy is output from the battery cell at a constant current and at a prevailing temperature in the battery module. The charge profile describes how a voltage over the battery cell varies as function of time while electric energy is input into the battery cell at a constant current and at a prevailing temperature in the battery module. Thereby, different temporal processes in the battery cells may be employed to determine whether a battery cell in the battery module has been substituted.

[0018] A discharge profile and a charge profile are examples of at least one performance characteristic that the controller according to the present disclosure is configured to repeatedly obtain. As a discharge profile and a charge profile describe how a voltage over the battery cell varies as a function of time during electric energy output or input, the skilled person understands that these profiles are constructed by obtained consecutively registrable voltage values as previously described. For example, the controller may be configured to determine a test measure based on a leastsquare method comparing the recently obtained performance characteristic to the previously obtained performance characteristic, and compare the test measure with the threshold similarity measure to check if the recently obtained performance characteristic deviates from the previously obtained performance characteristic by more than the threshold similarity measure.

[0019] According to one embodiment of this aspect of the invention, the controller is configured to consider that the recently obtained performance characteristic deviates from the previously obtained performance characteristic by more than the threshold similarity measure if the recently obtained performance characteristic was registered within a time window after registering the previous performance characteristic; and has a value outside of a predefined voltage range.

[0020] According to still another embodiment of this aspect of the invention, the controller is configured to set the time window and the predefined voltage range dynamically based on a value of the previously obtained performance characteristic. This allows for highly sensitive detection of any manipulation the battery cells in the battery module.

[0021] According to yet another embodiment of this aspect of the invention, the controller is configured to obtain its operating power from the plurality of battery cells both when the battery module is in an active mode and in a standby mode. Further, the controller is configured to set the alarm indicator for a battery cell irrespective of whether the battery module is in the active or the standby mode, if the obtained voltage values for the battery cell differ by more than the threshold quantity. Consequently, unauthorized battery cell swapping may be detected in any state of active operation battery module, as well as when the battery module is inactive.

[0022] According to a further embodiment of this aspect of the invention, in response to the alarm indicator being set, the controller is configured to disconnect the battery cell from the battery module in respect of which battery cell the alarm indicator is set. Additionally, in response to the alarm indicator being set, the controller may configured to also disable the battery module. As a result, there is no risk that a battery module is operated with an unauthorized battery cell.

[0023] According to another aspect of the invention, the object is achieved by a computer-implemented method, which is performed in a processing unit in a controller arranged to monitor a battery module. The method involves obtaining, repeatedly, at least one performance characteristic of each battery cell in a plurality of battery cells comprised in the battery module. Specifically, the method involves obtaining two consecutively registered voltage values over each battery cell, which voltage values represent a previous and a recent performance characteristic respectively for the battery cell. The method further involves comparing the obtained voltage values with one another, and if the voltage values differ by more than a threshold quantity for a battery cell, set an alarm indicator in respect of the battery cell. The advantages of this method, as well as the preferred embodiments thereof, are apparent from the discussion above with reference to the proposed system.

[0024] This method is advantageous because it detects any improperly substituted battery cells. Namely, provided that the threshold quantity is set to a suitable value, it is impossible to swap battery cells in the battery module without triggering the alarm indicator.

[0025] According to a further aspect of the invention, the object is achieved by a computer program loadable into a non-volatile data carrier communicatively connected to a processing unit. The computer program includes software for executing the above method when the program is run on the processing unit.

[0026] According to another aspect of the invention, the object is achieved by a non-volatile data carrier containing the above computer program.

[0027] Further advantages, beneficial features and applications of the present invention will be apparent from the following description and the dependent claims.

[0028] BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The invention is now to be explained more closely by means of preferred embodiments, which are disclosed as examples, and with reference to the attached drawings.

[0030] Figures 1-2 schematically illustrate a battery module and a controller according to embodiments of the invention;

[0031] Figure 3 shows a diagram exemplifying discharge graphs according to one embodiment of the invention;

[0032] Figure 4 shows a diagram exemplifying charge graphs according to one embodiment of the invention; and

[0033] Figures 5-6 illustrate, by means of flow diagrams, methods according to embodiments of the invention.

[0034] DETAILED DESCRIPTION

[0035] Figure 1 schematically illustrates a battery module 200 and a controller 120 according to one embodiment of the invention.

[0036] The controller 120 is arranged to monitor the battery module 200 containing a plurality of battery cells. The controller 120 may be arranged partially outside of the battery module 200. However, it may equally well be implemented entirely inside the battery module 200. In Figure 1 , the battery cells are exemplified as 101 , 102 and 103. The controller 120 is configured to repeatedly obtain at least one performance characteristic of each battery cell in the plurality of battery cells 101 , 102 and 103 respectively. Specifically, this means that the controller 120 is configured to at least obtain two consecutively registered voltage values over each battery cell. In Figure 1 , Vn(t) and Vn(t+t’) designate such voltage values in respect of the battery cell 101 , which voltage values have been registered at a point in time t and a point in time t+t’ respectively. Analogously, Vi2(t) and Vi2(t+t’) designate such voltage values in respect of the battery cell 102, which voltage values have been registered at the points in time t and t+t’ respectively; and Vis(t) and Vi3(t+t’) designate such voltage values in respect of the battery cell 103, which voltage values have been registered at the points in time t and t+t’ respectively. The registered voltage values thus represent a previous and a recent performance characteristic respectively for each battery cell in the battery module 200.

[0037] The controller 120 is further configured to compare the obtained voltage values for each battery cell with one another, for example compare the voltage value Vn(t) with the voltage value Vn(t+t’) for the battery cell 101. If, for a particular battery cell, say 101 , the voltage values differ by more than a threshold quantity, the controller 120 is configured to set an alarm indicator A in respect of the battery cell in question, e.g. the battery cell 101 . The alarm indicator A may involve reversing a setting of a binary flag and / or emitting a message adapted to be read by a machine and / or a human.

[0038] In response to the alarm indicator A being set, according to one embodiment of the invention, the controller 120 is also configured to disconnect the battery cell, say 101 , from the battery module 200. In many implementations this means that the entire battery module 200 also becomes inoperable.

[0039] According to one embodiment of the invention, for safety reasons, the controller 120 is specifically configured to disable the battery module 200 in response to the alarm indicator A being set. Thereby, it is ensured that the battery module 200 cannot be operated, neither to receive electric energy nor to provide electric energy.

[0040] According to one embodiment of the invention, the threshold quantity is defined in relation to an absolute voltage difference between the two consecutively registered voltage values. This for instance means that each of the differences , respectively are determined and compared to a first value. If one or more of the differences exceed the first value, the controller 120 triggers the alarm indication A for the battery cells in respect of which the first value is exceeded.

[0041] In addition to, or as an alternative to the above, the threshold quantity may be defined in relation to a ratio between the two consecutively obtained voltage values. This means that for example the ratios and respectively are determined and compared to a second value. If one or more of the differences exceed the second value, the controller 120 triggers the alarm indication A for the battery cells in respect of which the second value is exceeded. It should be noted that the exemplified ratios presuppose a discharging scenario. In a charging scenario, the ratio must either be reversed, or a different second value must be selected.

[0042] To conserve energy, it is preferable if the controller 120 is configured to monitor the registered voltage values exclusively in relatively coarse steps. For example, the threshold quantity may be adapted to detect a voltage deviation of a battery cell, which voltage deviation is above 25 % of a nominal voltage for the battery cell. In other words, if the nominal battery cell voltage is 3.69 V, only deviations being larger than 1 V will be detected.

[0043] Figure 2 shows another schematic illustration of the controller 120 and the battery module 200 according to one embodiment of the invention. Here, the controller 120 is co-located with the battery module 200 and is configured to obtain at least one general performance characteristic for each battery cell in the battery module 200. In Figure 2, this is symbolized by means of a current value In and a voltage value Vn respectively of the battery cell 101 , which is presumed to be located at a position P(1 ,1 ) in a first row of a first column in an array of battery cells in the battery module 200. The battery cell 102 is presumed to be located at a position P(1 ,2) in the first row of a second column in the array of battery cells, and so on up to a battery cell 10n at a position P(1 ,n) in the first row. A battery cell 121 is located at a position P(1 ,2) in the first column of a second row of in total m rows in the battery module 200. A battery cell 1 m1 is located at a position P(1 ,m) in the first column of the m:th row. All rows are presumed to have n columns, and a particular battery cell is presumed to be located in each column position of all rows. Thus, the battery module 200 contains in total n >m battery cells, and a last battery cell 1 mn is located at a position P(m,n) in the m:th row of the n:th column.

[0044] According to one embodiment of the invention, the at least one performance characteristic includes a discharge profile and / or charge profile. Figure 3 contains a diagram illustrating examples of discharge graphs 310, 311 , 312, 313 and 314 respectively for different battery cells as functions of time T at a particular temperature @T, say 25 degrees Celsius. Figure 4 contains a diagram illustrating examples of charge graphs 410, 411 , 412, 413 and 414 respectively for different battery cells as functions of time T at a particular temperature @T, say 25 degrees Celsius.

[0045] Thus, each graph in Figure 3 reflects how a voltage V over the battery cell’s poles varies as function of time t while electric energy is being output from the battery cell at a constant current when the battery cell has the particular temperature @T.

[0046] Here, we assume that the battery cell 101 at position P(1 ,1 ) has a discharge profile defined by the graph 310. This means that the voltage of the battery cell’s 101 poles has a maximum value of Vmax, which will gradually decrease over time t as the battery cell 101 releases electric charges in the form of a constant current. For example, at a point in time to, the battery cell 101 has a certain voltage, and in a time window tw shortly after to, the battery cell 101 has a similar voltage. More precisely, due to the discharge profile defined by the graph 310, at points in time ti and t2 within the time window tw, the battery cell 101 is expected to have voltage values within a predefined voltage range VS3. This means that voltage values corresponding to discharge profiles being only slightly different from the graph 310 are acceptable, such as discharge profiles defined by the graphs 311 and 312 respectively. However, discharge profiles being more dissimilar to the graph 310 are not acceptable. Such profiles would namely suggest that the battery cell 101 at position P(1 , 1 ) has been replaced by another battery cell.

[0047] In Figure 3, such an unacceptable voltage variation is illustrated by a battery cell having an original discharge profile defined by the graph 313, which at a point in time to’ has a voltage V03, and at a point in time ti’ shortly after to’ has a voltage V13. Here, the voltage leap between V03 and V13 is too large given the time frame and the discharge profile defined by the graph 313. The leap appears to suggest that the battery cell in question has been replaced between to’ and ti’, for example by a battery cell having a discharge profile defined by the graph 312.

[0048] Referring now to Figure 4, we assume that the battery cell 101 at position P(1 , 1 ) has a charge profile defined by the graph 410. This means that the voltage of the battery cell’s 101 poles has a minimum value of Vmin, which will gradually increase over time t as the battery cell 101 receives electric charges in the form of a constant current. For example, at a point in time to, the battery cell 101 has a certain voltage, and in a time window tw shortly after to, the battery cell 101 has a similar voltage. More precisely, due to the charge profile defined by the graph 410, at points in time ti and t2 within the time window tw, the battery cell 101 is expected to have voltage values within a predefined voltage range VS4. This means that voltage values corresponding to charge profiles being only slightly different from the graph 410 are acceptable, such as charge profiles defined by the graphs 41 1 and 412 respectively. However, charge profiles being more dissimilar to the graph 410 are not acceptable. Such profiles would namely suggest that the battery cell 101 at position P(1 ,1 ) has been replaced by another battery cell.

[0049] In Figure 4, such an unacceptable voltage variation is illustrated by a battery cell having an original charge profile defined by the graph 414, which at a point in time to’ has a voltage V04, and at a point in time ti ’ shortly after to’ has a voltage V14. Here, the voltage leap between V04 and V14 is too large given the time frame and the charge profile defined by the graph 414. The leap appears to suggest that the battery cell in question has been replaced between to’ and ti’, for example by a battery cell having a charge profile defined by the graph 410.

[0050] According to one embodiment of the invention, the controller 120 is configured to consider that the recently obtained performance characteristic deviates from the previously obtained performance characteristic by more than a threshold similarity measure if the recently obtained performance characteristic was registered within a time window tw after registering the previous performance characteristic; and the recently obtained performance characteristic has a value outside of a predefined voltage range, say VS3 or VS4. As a result, in such a case, the controller 120 is configured to trigger the alarm indication A.

[0051] For enhanced flexibility and sensitivity, according to one embodiment of the invention, the controller 120 is configured to set the time window tw and the predefined voltage range, e.g. VS3 and VS4, dynamically based on a value of the previously obtained performance characteristic, for example the discharge profile defined by the graph 310 or the charge profile defined by the graph 410.

[0052] As an alternative to the above, according to one embodiment of the invention, the controller 120 is configured to determine a test measure based on a least-square method that compares the recently obtained performance characteristic to the previously obtained performance characteristic. Further, the controller 120 is configured to compare the test measure with a threshold similarity measure to check if the recently obtained performance characteristic deviates from the previously obtained performance characteristic by more than the threshold similarity measure.

[0053] It is preferable if the controller 120 is configured to always obtain its operating power from the battery cells in the battery module 200, i.e. both when the battery module 200 is in an active mode and in a standby mode. Moreover, it is desirable that the controller 120 is configured to set the alarm indicator A for a battery cell, say 101 , in the plurality of battery cells irrespective of whether the battery module 200 is in the active or the standby mode if the obtained voltage values, say Vn(t) and Vn(t+t’) respectively, for the battery cell 101 differ by more than the threshold quantity. Thereby, any unauthorized attempt to replace a battery cell can be detected whenever such an attempt is made.

[0054] To conserve battery in the standby mode, according to one embodiment of the invention, the controller 120 is configured to obtain updates of the at least one performance characteristic of each battery cell at a first update frequency during a first period after that the battery module 200 has entered the standby mode. Then, after expiry of the first period, the controller 120 is configured to obtain updates of the at least one performance characteristic of each battery cell at a second update frequency, which is lower than the first update frequency, for instance 10 or 100 times lower.

[0055] It is generally advantageous if the controller 120 is configured to effect the above-described procedure in in an automatic manner by executing a computer program. Therefore, the controller 120 may include a memory unit 125, i.e. non-volatile data carrier, storing a computer program 123, which, in turn, contains software for making processing circuitry in the form of at least one processor 121 in the controller 120 execute the actions mentioned in this disclosure when the computer program 123 is run on the at least one processor 121 .

[0056] It should be noted that the controller 120 may be implemented in many different ways according to the invention. For example, the controller 120 may be housed in a single unit co-located with the battery module 200. Alternatively, a part of the controller 120 may be arranged outside of the battery module 200, either remote from or physically near the same. Moreover, the controller 120 may be a distributed resource, where for example one portion of its functionality is realized in the battery module 200, another portion of the functionality is implemented locally outside of the battery module 200, and yet another portion of the controller functionality is implemented in a server being communicatively connected to the other functionality portions via one or more networks, such as the Internet.

[0057] In order to sum up, and with reference to the flow diagrams in Figures 5 and 6, we will now describe embodiments of the computer-implemented method performed in the at least one processor 121 of the controller 120.

[0058] In Figure 5, in a first step 510, a first voltage value is obtained, which first voltage value represents a performance characteristic of a battery cell in a plurality of battery cells.

[0059] In a step 520 thereafter, a second voltage value is obtained, which second voltage value also represents a performance characteristic of the battery cell referred to in step 510.

[0060] A subsequent step 530 compares the first and second voltage values to one another, and checks if a difference between these voltage values exceeds a threshold quantity. If the difference exceeds the threshold quantity, a step 540 follows; and otherwise the procedure loops back to step 510.

[0061] In step 540, an alarm indicator is set in respect of the battery cell. Thereafter, the procedure ends and the battery module in which the battery cell is included is disabled. Alternatively, after step 540, the procedure continues to check additional battery cells in the battery module.

[0062] In Figure 6, in a first step 610, a first performance characteristic of a battery cell in a plurality of battery cells is obtained to represent a previous performance characteristic.

[0063] In a step 630 thereafter, a second performance characteristic is obtained, which second voltage value represents a recent performance characteristic of the battery cell referred to in step 610. A subsequent step 630 derives a similarity measure between the first and second performance characteristics, e.g. based on a least-square method, and checks if the similarity measure exceeds a threshold similarity measure. If the similarity measure exceeds the threshold similarity measure, a step 640 follows; and otherwise the procedure loops back to step 610.

[0064] In step 640, an alarm indicator is set in respect of the battery cell. Thereafter, the procedure ends and the battery module in which the battery cell is included is disabled. Alternatively, after step 640, the procedure continues to check additional battery cells in the battery module

[0065] The process steps described with reference to Figures 5 and 6 may be controlled by means of a programmed processor. Moreover, although the embodiments of the invention described above with reference to the drawings comprise processor and processes performed in at least one processor, the invention thus also extends to computer programs, particularly computer programs on or in a carrier, adapted for putting the invention into practice. The program may be in the form of source code, object code, a code intermediate source and object code such as in partially compiled form, or in any other form suitable for use in the implementation of the process according to the invention. The program may either be a part of an operating system, or be a separate application. The carrier may be any entity or device capable of carrying the program. For example, the carrier may comprise a storage medium, such as a Flash memory, a ROM (Read Only Memory), for example a DVD (Digital Video / Versatile Disk), a CD (Compact Disc) or a semiconductor ROM, an EPROM (Erasable Programmable Read-Only Memory), an EEPROM (Electrically Erasable Programmable Read-Only Memory), or a magnetic recording medium, for example a floppy disc or hard disc. Further, the carrier may be a transmissible carrier such as an electrical or optical signal which may be conveyed via electrical or optical cable or by radio or by other means. When the program is embodied in a signal, which may be conveyed, directly by a cable or other device or means, the carrier may be constituted by such cable or device or means. Alternatively, the carrier may be an integrated circuit in which the program is embedded, the integrated circuit being adapted for performing, or for use in the performance of, the relevant processes.

[0066] Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

[0067] The term “comprises / comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components. The term does not preclude the presence or addition of one or more additional elements, features, integers, steps or components or groups thereof. The indefinite article "a" or "an" does not exclude a plurality. In the claims, the word “or” is not to be interpreted as an exclusive or (sometimes referred to as “XOR”). On the contrary, expressions such as “A or B” covers all the cases “A and not B”, “B and not A” and “A and B”, unless otherwise indicated. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

[0068] It is also to be noted that features from the various embodiments described herein may freely be combined, unless it is explicitly stated that such a combination would be unsuitable.

[0069] The invention is not restricted to the described embodiments in the figures, but may be varied freely within the scope of the claims.

Claims

Claims1. A controller (120) for monitoring a battery module (200) comprising a plurality of battery cells (101 , 102, 103, 121 , 10n, 121 , 1 m1 , 1 mn), which controller (120) is configured to: repeatedly obtain at least one performance characteristic of each battery cell in said plurality of battery cells, characterized in that the controller (120) is configured to: obtain two consecutively registered voltage values (Vn(t), Vn(t+t’)) over each battery cell, which voltage values represent a previous and a recent performance characteristic respectively for the battery cell; compare the obtained voltage values (Vn(t), Vn(t+t’)) for a battery cell (101 ) with one another; and if the voltage values differ by more than a threshold quantity set an alarm indicator (A) in respect of the battery cell (101 ).

2. The controller (120) according to claim 1 , wherein the threshold quantity is defined in relation to at least one of: an absolute voltage difference, and a ratio between the two consecutively obtained voltage values (Vn(t), Vii(t+t’)).

3. The controller (120) according to any of claims 1 or 2, wherein the threshold quantity is adapted to detect a voltage deviation of a battery cell in said plurality of battery cells, which voltage deviation is above 25 % of a nominal voltage for the battery cell.

4. The controller (120) according to claim 1 , wherein the at least one performance characteristic comprises at least one of: a discharge profile (310, 311 , 312, 313, 314), which at a prevailing temperature (@T) in the battery module (200), describes how a voltage (V) over the battery cell varies as function of time (t) while electric energy is output from the battery cell at a constant current; and a charge profile (410, 411 , 412, 413, 414), which at a prevailing temperature (@T) in the battery module (200), describeshow a voltage (V) over the battery cell varies as function of time while electric energy is input into the battery cell at a constant current.

5. The controller (120) according to claim 4, wherein the controller (120) is configured to: determine a test measure based on a least-square method comparing the recently obtained performance characteristic to the previously obtained performance characteristic; and compare the test measure with the threshold similarity measure to check if the recently obtained performance characteristic deviates from the previously obtained performance characteristic by more than the threshold similarity measure.

6. The controller (120) according claim 5, wherein the controller (120) is configured to consider that the recently obtained performance characteristic deviates from the previously obtained performance characteristic by more than the threshold similarity measure if the recently obtained performance characteristic: was registered within a time window (tw) after registering the previous performance characteristic; and has a value outside of a predefined voltage range (VS3j VS4).

7. The controller (120) according claim 6, wherein controller (120) is configured to set the time window (tw) and the predefined voltage range (VS3j VS4) dynamically based on a value of the previously obtained performance characteristic (310; 410).

8. The controller (120) according to any of the preceding claims, wherein the controller (120) is configured to: obtain operating power from the plurality of battery cells when the battery module (200) is in an active mode and in a standby mode, and set the alarm indicator (A) for a battery cell (101 ) in the plurality of battery cells irrespective of whether the battery module (200) is in the active or the standby mode if the obtained voltagevalues (Vn(t), Vn(t+t’)) for the battery cell (101 ) differ by more than the threshold quantity.

9. The controller (120) according to any one of the preceding claims, wherein, in response to the alarm indicator (A) being set, the controller (120) is further configured to: disconnect the battery cell (101 ) from the battery module (200) in respect of which battery cell (101 ) the alarm indicator (A) is set.

10. The controller (120) according to any of the preceding claims, wherein in response to the alarm indicator (A) being set, the controller (120) is further configured to: disable the battery module (200).

11. The controller (120) according to any of the preceding claims, wherein the controller (120) is configured to: obtain updates of the at least one performance characteristic of each battery cell in said plurality of battery cells at a first update frequency during a first period after that the battery module (200) has entered a standby mode, and after expiry of the first period obtain updates of the at least one performance characteristic of each battery cell in said plurality of battery cells at a second update frequency being lower than the first update frequency.

12. A computer-implemented method for monitoring a battery module (200), which method is performed in a processing unit (121 ) of a controller (120), the method comprising: obtaining, repeatedly, at least one performance characteristic of each battery cell in a plurality of battery cells (101 , 102, 103, 121 , 10n, 121 , 1 m1 , 1 mn) comprised in a battery module (200), characterized by obtaining two consecutively registered voltage values (Vn(t), Vn(t+t’)) over each battery cell, which voltage values represent a previous and a recent performance characteristic respectively for the battery cell;comparing the obtained voltage values (Vn(t), Vn(t+t’)) with one another, and if the voltage values differ by more than a threshold quantity for a battery cell (101 ) setting an alarm indicator (A) in respect of the battery cell (101 ).

13. The method according to claim 12, wherein the threshold quantity is defined in relation to at least one of: an absolute voltage difference, and a ratio between the two consecutively obtained voltage values (Vn(t), Vii(t+t’)).

14. The method according to any of claims 12 or 13, wherein the threshold quantity is adapted to detect a voltage deviation of a battery cell in said plurality of battery cells, which voltage deviation is above 25 % of a nominal voltage for the battery cell.

15. The method according to claim 12, wherein the at least one performance characteristic comprises at least one of: a discharge profile (310, 311 , 312, 313, 314), which at a prevailing temperature (@T)) in the battery module (200), describes how a voltage (V) over the battery cell varies as function of time (t) while electric energy is output from the battery cell at a constant current; and a charge profile (410, 411 , 412, 413, 414), which at a prevailing temperature (@T) in the battery module (200), describes how a voltage (V) over the battery cell varies as function of time while electric energy is input into the battery cell at a constant current.

16. The method according to claim 15, further comprising: determining a test measure based on a least-square method comparing the recently obtained performance characteristic to the previously obtained performance characteristic; and comparing the test measure with the threshold similarity measure to check if the recently obtained performance charac-teristic deviates from the previously obtained performance characteristic by more than the threshold similarity measure.

17. The method according claim 16, wherein the recently obtained performance characteristic is considered to deviate from the previously obtained performance characteristic by more than the threshold similarity measure if the recently obtained performance characteristic: was registered within a time window (tw) after registering the previous performance characteristic; and has a value outside of a predefined voltage range (VS3j VS4).

18. The method according claim 17, wherein method comprises: setting the time window (tw) and the predefined voltage range (VS3j VS4) dynamically based on a value of the previously obtained performance characteristic (310; 410).

19. The method according to any of claims 12 to 18, comprising: obtaining operating power from the plurality of battery cells in the controller (120) when the battery module (200) is in an active mode and in a standby mode, and setting the alarm indicator (A) for a battery cell (101 ) in the plurality of battery cells irrespective of whether the battery module (200) is in the active or the standby mode if the obtained voltage values (Vn(t), Vn(t+t’)) for the battery cell (101 ) differ by more than the threshold quantity.

20. The method according to any one of claims 12 to 19, wherein, in response to the alarm indicator (A) being set, the method comprises: disconnecting the battery cell (101 ) from the battery module (200) in respect of which battery cell (101 ) the alarm indicator (A) is set.21 . The method according to any one of claims 12 to 20, wherein, in response to the alarm indicator (A) being set, the methodcomprises: disabling the battery module (200).

22. The method according to any of claims 12 to 21 , comprising: obtaining updates of the at least one performance characteristic of each battery cell in said plurality of battery cells at a first update frequency during a first period after that the battery module (200) has entered a standby mode, and after expiry of the first period obtaining updates of the at least one performance characteristic of each battery cell in said plurality of battery cells at a second update frequency being lower than the first update frequency.

23. A computer program (123) loadable into a non-volatile data carrier (125) communicatively connected to a processing unit (121 ), the computer program (123) comprising software for executing the method according any of the claims 12 to 22 when the computer program (133) is run on the processing unit (121 ).

24. A non-volatile data carrier (125) containing the computer program (123) of the claim 23.

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