A method and control arrangement for diagnosing an electric battery unit

Abstract

The present invention relates to a method and control arrangement for diagnosing an electric battery unit (300) comprising a plurality of electric battery cells (201_1, …, 201_n) and a plurality of electrical conductors (202) interconnecting the electric battery cells (201_1, …, 201_n). A first battery unit portion (300a) comprises a first subset of the electric battery cells (201_1, …, 201_n), and a second battery unit portion (300b) comprises a second subset of the electric battery cells (201_1, …, 201_n), wherein the first and second subsets of electric battery cells (201_1, …, 201_n) are non-overlapping. The method comprises: determining a first voltage (U1), being a voltage over the first battery unit portion (300a); determining a second voltage (U2), being a voltage over the second battery unit portion (300b); determining a current flowing through the battery unit (300); determining a difference in resistance (Rdiff) over the first battery unit portion (300a) and the second battery unit portion (300b) using a difference between the first and second voltages, and the current flowing through the battery unit (300).

Description

[0001] A METHOD AND CONTROL ARRANGEMENT FOR DIAGNOSING AN ELECTRIC BATTERY UNIT

[0002] Technical field

[0003] Aspects of the invention relate to a method and a control arrangement for diagnosing the electrical interconnection of a plurality of electric battery cells of a battery unit. Further, aspects of the invention relate to a computer program, a computer-readable medium and a vehicle comprising a control arrangement.

[0004] Background

[0005] The following background description does not necessarily constitute prior art.

[0006] An electric battery cell can be seen as a container chemically storing energy. The electric battery cells may come in various forms and shapes. Electric battery cells may be connected in series and in parallel, into an electric battery unit, which may be called an electric battery pack, in order to attain a desired total voltage and energy capacity. A conventional electric battery pack, or a plurality of battery packs, may form the complete enclosure or entity that delivers electric power to a product or equipment, for example an electric vehicle, such as a battery electric vehicle or a hybrid electric vehicle.

[0007] In general, a conventional electric battery pack includes or contains electric battery cells, a control or management system, which may be called a battery management system (BMS) and may, for example, be implemented partly as software, and often also a cooling and / or heating system. The electric battery cells of an electric battery pack may be arranged in two or more modules, where a conventional module may be a frame holding a plurality of electric battery cells, and a conventional electric battery pack may be assembled by interconnecting the modules.

[0008] The battery cells of a battery module may be interconnected using electrical conductors such as busbars to provide for current distribution between the battery cells, and such busbars may also be used to connect the battery cells to connector poles of the battery module, and also to interconnect battery modules, and finally also between the modules and the connectors of the battery pack.

[0009] Summary

[0010] It is an object of the invention to provide a method for diagnosing electrical conductors, such as busbars, being used in battery units, such as battery packs, so as to identify presence of non-properly functioning electrical connectors.

[0011] According to a first aspect of the invention, the aforementioned and further objects are achieved through a method, e.g., performed by a control arrangement, for diagnosing an electric battery unit, the electric battery unit comprising: a plurality of electric battery cells; a plurality of electrical conductors interconnecting the electric battery cells; a first battery unit portion comprising a first subset of the electric battery cells; a second battery unit portion comprising a second subset of the electric battery cells, wherein the first and second subsets of electric battery cells are nonoverlapping; the method comprising: determining a first voltage, being a voltage over the first battery unit portion; determining a second voltage, being a voltage over the second battery unit portion; determining a current flowing through the battery unit; determining a difference in resistance over the first battery unit portion and the second battery unit portion using a difference between the first and second voltages, and the current flowing through the battery unit. The plurality of battery cells may be connected in series.

[0012] As was mentioned above, electrical conductors such as busbars may be used in battery units such as, for example, battery packs, to provide for current distribution between the battery cells of the battery unit, and the connector poles of the battery pack. Also, electrical conductors may be used to interconnect battery units.

[0013] In order for the battery unit, to operate in a desired manner it is essential that the electrical conductors provide for solid electrical connections. However, electrical conductors such as busbars may be incorrectly mounted in the assembly of the battery unit, or such electrical conductors may become loose or otherwise faulty due to, e.g., vibrations or other conditions during vehicle operation. This may give rise to serious problems, in particular since loose / faulty connections may cause a comparatively high resistance over the connections. Increased resistance may lead to excessive heat when a current is flowing through the faulty connection during vehicle operation. The excessive heat, in turn, may lead to melting or, in worst case, fire.

[0014] The present invention provides a solution that may be used to avoid vehicles operating with faulty electrical connectors giving rise to high resistance. This is accomplished by a diagnostic method that may detect connections giving rise to excess resistance, e.g. caused by loose screws or other faults in the battery unit. However, the accomplishing of a robust measurement of the resistance over an electrical conductor such as a busbar may be difficult, and the resistance must also be able to be distinguished from the cell internal resistance which varies with temperature and cell aging.

[0015] Furthermore, in order to be able to estimate the electrical conductor resistance over a particular electrical conductor this would require a very precise measurement of the voltage over the electrical conductor. This is not only hard to achieve, but also requires at least two measurement points per electrical connector. A typical truck battery consists of a large number of serially connected battery cells, where a number of such cells are serially connected to form a battery unit, where the cells of a battery unit may be grouped in battery modules where several battery modules may be serially connected to form the battery unit. A vehicle such as a truck may, in addition, comprise a plurality of battery units, or packs. Every single connection may be realized using electrical connectors such as busbars or other cabling, and every such busbar / cable connection may become damaged / loosen. Hence, a measurement of each of these individual “sites of failure” would require one measuring point per serial connection. In a typical truck this may result in ~200 or more such measurement points.

[0016] According to the invention, instead, there is provided a solution that requires very few voltage measurements to diagnose a battery unit such as a battery pack. This is accomplished by determining a first voltage over a first battery unit portion comprising a first subset of the electric battery cells, where the battery unit portion may comprise part of a battery pack, such as one or more battery modules. Furthermore, a second voltage is determined over a second subset of the electric battery cells, wherein the first and second subsets of electric battery cells are non-overlapping, and where the second subset may comprise the remaining battery cells, such as the remaining battery modules, of the battery unit.

[0017] Furthermore, a current flowing through the battery unit is also determined. As was mentioned above, the battery cells of a battery unit are in general connected in series, while battery units may then be connected in parallel, and hence the same current will flow through all battery cells of a battery unit. A single measurement of the current is therefore sufficient. A difference in resistance over the first battery unit portion and the second battery unit portion is then determined using a difference between the determined first and second voltages, and the current flowing through the battery unit. For example, the difference in resistance can be determined as a difference in voltage divided by the current. As will be explained below, the overall voltage over the first and second battery unit portions, respectively, may be subtracted from each other in the determination, but additional calculations may also be carried out prior to dividing the voltage difference with the current to obtain a determination of the difference in resistance.

[0018] The first and / or second voltages may be determined using a voltage sensor.

[0019] The current flowing through the battery unit may be determined using a current sensor. The first and / or the second voltages and the current flowing through the battery unit may be determined by a first sensor. Since the first sensor determines both the voltages and the current it may be also be called a common or same sensor. The first sensor may be a voltage / current sensor capable of determining both voltages and currents.

[0020] The method may be performed during normal operation of the battery unit. With normal operation of the battery unit is herein meant that the battery unit is operated in its intended application. For example, if the battery unit is a battery pack of a propulsion battery for an electrified vehicle, the normal operation of the battery unit is when the battery unit is operating within the electrified vehicle, e.g. during driving of the vehicle or charging of the vehicle. Thereby the diagnosis can be performed during normal use of the battery unit which is advantageous since problems arising during operation can be immediately observed and notified to an operator. Thus, there is no need to analyse the battery unit in workshop or other facility. This reduces cost and time consumption for maintenance and thereby also increases the uptime of the battery unit.

[0021] The battery unit may comprise a busbar. The diagnosis may then be performed to determine any faults related to the busbar of the battery unit.

[0022] According to aspects of the invention a diagnosis of the electric battery unit is performed based on the difference in resistance.

[0023] In this way there is provided a solution that require very few measurements to still obtain a diagnosis of the overall status of the battery unit. In particular, there is provided a solution that does not make it necessary to measure the voltage over each electrical connector in order to determine whether one or more electrical connectors are faulty. Instead, a first voltage for a first part of the battery cells and a second voltage for a second part of the battery cells are determined, where these voltages are compared by the voltage difference, and where this voltage difference is used to determine a difference in resistance that may indicate a faulty connection giving rise to excess resistance.

[0024] According to aspects of the invention, the diagnosing of the electric battery unit comprises to compare the determined difference in resistance with a predetermined resistance limit and generate a signal when the difference in resistance exceeds the predetermined resistance limit. Hence, the signal may be utilized to indicate an abnormality, such as a fault, where the abnormality can be considered to be present due to the arisen increased difference in resistance.

[0025] According to aspects of the invention, the method further comprises to determine the difference in resistance regularly, continuously and / or at predetermined intervals to generate a plurality of determinations of the difference in resistance, and generate a signal when a filtered difference in resistance exceeds a predetermined value, the filtered difference in resistance taking into account the plurality of generated differences in resistance. It is to be understood that the difference in resistance may be very small, and therefore subject to, e.g., measurement errors, or other factors influencing the measurements. The use of a plurality of measurement values taken over a period of time that then are filtered may reduce the impact of undesired influence on the measurements.

[0026] According to aspects of the invention, the first voltage over the first portion of the battery unit and the second voltage over the second portion, respectively, may be determined using the same voltage sensor, where the voltage sensor may be configured to determine the first voltage over the first portion of the battery unit and the second voltage over the second portion concurrently or consecutively. For example, a sensor having multiple inlets to allow measurements of different voltages may be used, where the measurement may be carried out at the same time or after one another. Such sensors are known in the art, and even if the measurements are carried out consecutively the difference in time between the measurements is in general so small that a measurement of the current will be representative for both measurements even if the current is not measured precisely simultaneously with the voltage. In fact, according to aspects of the invention the voltage sensor is a voltage / current sensor, and also the current flowing through the battery unit is determined using the voltage / current sensor, concurrently or consecutively with the measuring of the first voltage and the second voltage. As was mentioned, even if the measurements are carried out consecutively, the difference in time is in general so small that the measurement of the current is representative for both voltages.

[0027] The use of a same sensor for measuring the voltages, and / or voltages and current, further has the advantage that internal sensor errors will be the same or similar for all measurements, and hence factors such as different internal measurement errors can be reduced or eliminated from the determination of the difference in resistance.

[0028] According to aspects of the invention, the first and second battery unit portions may be configured to comprise an equal number of battery cells. This has the advantage that the voltages over the battery unit portions will be directly comparative.

[0029] According to aspects of the invention the first and second battery unit portions are, instead, configured to comprise a different number of battery cells. A reason for this may, for example, be that the battery unit, e.g., comprises an uneven number of battery modules, where accessible measurement points are between battery modules. The reason may also be that this may allow use of an already present voltage sensor in the battery unit. In such cases the method may further comprise to compensate the first and / or second voltage by a compensation factor being dependent on a difference in the number of battery cells of the two battery unit portions, so as to obtain representations of the first and second voltages representing equal size battery unit portions. For, example, one or both of the voltages may be compensated by factor being such that the resulting compensated voltages represent an equal number of battery cells.

[0030] According to aspects of the invention the method further comprises to, when the current through the battery unit is below a first current, determine a low current voltage difference between the first portion of the battery unit and the second portion of the battery unit, and utilize the low current voltage difference as a voltage correction when determining the difference in resistance, where the low current voltage difference is subtracted from the difference between the first voltage and the second voltage when determining the difference in resistance.

[0031] As was mentioned above, use of a same sensor for measuring voltages and or currents may reduce or eliminate factors that may adversely affect the accuracy of the measurements. The determination of a low-current voltage difference may further reduce or eliminate such factors, since the low current will have only a very limited effect on voltage drops over faulty electrical connectors.

[0032] The low-current voltage difference may according to some aspects only be used as a voltage correction when determining the difference in resistance for a predetermined time interval. The time interval may be clocked or calculated from the time when the low-current difference was determined. When the time interval has elapsed the usage of the voltage correction may be discontinued, i.e. stopped, or it may be paused. When the time interval has elapsed the determination of the difference in resistance over the first battery unit portion and the second battery unit portion may be discontinued, i.e. stopped, or it may be paused. Thus, the method for diagnosing a battery unit may thereby be stopped when the time interval has elapsed.

[0033] The reason for stopping or pausing the usage of the method is that the sensor output may drift over time. Said in a different way, the error in the sensor measurement may vary with time. The voltage correction will therefore not be accurate anymore after a certain amount of time has elapsed, i.e. after the time interval above. The time interval may be in the order of seconds or minutes. The time interval may be between 20 seconds and 10 minutes, for example 20 seconds and 5 minutes, or 20 seconds and 2 minutes. The time interval may e.g. be 1 minute.

[0034] A new low-current voltage difference may be determined before the method to diagnose the battery unit is again performed. According to aspects of the invention the battery unit comprises means for measuring individual voltages over at least part of, or all of, the battery cells of each of the first and second battery unit portion, and an aggregated battery cell voltage of measured battery cell voltages of a battery unit portion is determined for each battery unit portion. A battery unit portion voltage difference is then determined for each battery unit portion, i.e. , the difference between the voltage over the battery unit portion and the aggregated voltage of the battery cells of the battery unit portion.

[0035] The difference in resistance over the first battery unit portion and the second battery unit portion may then be determined using these battery unit portion voltage differences instead of only the voltages over the battery unit portions, respectively, where the battery unit portion voltage differences can be subtracted from each other and divided by current flowing through the battery unit. This may provide for a more robust determination of the difference in resistance.

[0036] The greater the number of battery cell voltages used to determine the aggregated battery cell voltages the closer the battery unit portion voltages differences will correspond to the busbar voltages for each battery unit portions. Consequently, the greater the number of battery cell voltages used to determine the aggregated battery cell voltages the closer the difference in resistance over the first battery unit portion and the second battery unit portion will then correspond to the difference in resistance between the busbar in the first and second battery unit portions. That is to say, if a large number of cell voltages are used to determine the aggregated battery cell voltage of the first battery unit portion, then the battery unit portion voltage difference of the first battery unit portion will be close to the voltage over the busbar of the first battery unit portion. Similarly, if a large number of cell voltages are used to determine the aggregated battery cell voltage of the second battery unit portion, then the battery unit portion voltage difference of the second battery unit portion will be close to the voltage over the busbar of the second battery unit portion.

[0037] It follows that if all of the battery cell voltages are aggregated, or summed, then the aggregated battery cell voltages will correspond to the voltages of all the battery cells. When these voltages are subtracted from the voltages of the respective battery unit portion, then the remaining voltage will correspond to the voltage over the busbar of the respective battery unit portion. Thereby, using this method, the voltage and consequently the resistance of the busbar of the battery unit can be determined in a precise manner. An accurate diagnosis of the busbar of the battery unit can therefor be determined.

[0038] According to aspects of the invention, the battery unit comprising at least two battery modules, each battery module comprising a subset of the battery cells, the plurality of electrical conductors interconnecting, in addition, the at least two battery modules, where the first battery unit portion may comprise at least one of the at least two battery modules, and the second battery unit portion may comprise the remaining modules of the at least two battery modules.

[0039] According to aspects of the invention each battery module comprises a cell module controller (CMC), where the cell module controller may be configured to measure the individual voltage over at least a plurality of the battery cells of the battery module, and hence be utilized to obtain more robust measurement results as described above.

[0040] According to aspects of the invention the diagnosis is only carried out when the current through the battery unit exceeds a current threshold. It may, for example, be desirable to perform the diagnosis for high currents, since the higher the current, the higher will the voltage drop over a faulty electrical connector be.

[0041] According to aspects of the invention, the battery unit forming part of a battery arrangement comprising a plurality of battery units, and the method may comprise to perform determinations according to the above, for each battery unit, where a signal, e.g., indicating a fault, may be generated when the difference in resistance exceeds a first difference for any one of the battery units of the battery arrangement.

[0042] According to a further aspect, the invention relates to a control arrangement for diagnosing an electric battery unit. It will be appreciated that all the embodiments described for the method aspects of the invention are applicable also to control arrangement aspects of the invention. Thus, all the aspects described for methods according to the invention may be performed by the control arrangement, which may also be a control device, i.e. , a device. The control arrangement and its embodiments have advantages corresponding to the advantages discussed above with regard to the various aspects of methods according to the invention.

[0043] Further advantageous aspects of the method and the control arrangement according to the present invention and further advantages with the aspects of the invention emerge from the detailed description.

[0044] Brief Description of the Drawings

[0045] Aspects of the invention will now be illustrated, for exemplary purposes, in more detail by way of embodiments and with reference to the enclosed drawings, where similar references are used for similar parts, in which:

[0046] Fig. 1 illustrates an exemplary battery electric vehicle in which aspects of the invention may be utilized;

[0047] Fig. 2 illustrates an exemplary battery module of a battery unit being diagnosed according to aspects of the invention;

[0048] Fig. 3 illustrates a battery unit comprising a plurality of battery modules according to Fig.2;

[0049] Fig. 4A illustrates an exemplary method according to aspects of the invention;

[0050] Fig. 4B illustrates a further exemplary method according to aspects of the invention;

[0051] Fig. 5 schematically illustrates a control arrangement according to aspects of the invention. Detailed Description

[0052] With reference to Fig. 1 , an embodiment of a vehicle 100 according to aspects of the invention is schematically illustrated. The vehicle 100 is illustrated as a tractor vehicle. However, for other embodiments, the vehicle 100 may, for example, be of any other kind of heavy vehicle, such as a bus or a truck. The vehicle may also, e.g., be a passenger car. The vehicle may also be of other types of vehicles. Although not illustrated in Fig. 1 , the vehicle 100 may be equipped with a trailer. The vehicle 100 comprises a powertrain configured as an electric vehicle EV, for example a hybrid electric vehicle, HEV, or a battery electric vehicle, BEV.

[0053] The vehicle 100 may further, as illustrated, be a wheeled vehicle, i.e. , a vehicle 100 having wheels 102. Only the wheels 102 on the left-hand side of the vehicle 100 are visible in Fig. 1 . It is to be understood that the vehicle 100 may have fewer or more wheels than what is shown in Fig. 1 .

[0054] The powertrain comprises at least one electrical machine 101 configured to apply a propulsive power and / or a braking power to one or more of the wheels 102 of the vehicle 100. The at least one electrical machine 101 may be arranged essentially anywhere, for as long as power is provided to one or more of the wheels 102 of the vehicle 100. Various applicable examples exist in the art.

[0055] The vehicle 100 is configured to comprise a plurality of electric battery units 103, 104, 105, such as battery stacks, and may also comprise further nondisclosed battery units. Each battery unit may, individually or collectively, be diagnosed according to aspects of the invention. The battery units may form part of a battery arrangement 106 of the vehicle 100.

[0056] The components of the powertrain of the vehicle 100, as well as other components in the vehicle may be controlled by a vehicle control system forming part of a vehicle electrical system via a control arrangement 120. The control arrangement 120 may be distributed on several control units configured to control different parts of the vehicle 100. The control arrangement 120 may, e.g., include a control unit for controlling the applying of a propulsive power and / or regenerative brake power of the electrical machine 101 . The control arrangement may also comprise a control unit for diagnosing battery units, i.e. , a control unit arranged for performing the method steps of the disclosed invention as is explained further on. Such a control unit may, e.g., for part of a battery management system (BMS) that may be responsible for various other functions involving the battery. The control arrangement 120 will be schematically described in further detail in conjunction with Fig. 5.

[0057] The vehicle 100 may further include one or more sensors providing sensor data to the vehicle control system. For example, according to the invention, e.g., at least one voltage and / or current sensor is configured to measure voltages over battery unit portions and / or a current through a battery unit of one or more of the battery units of the vehicle.

[0058] As is realized, the vehicle 100 may comprise a large number of control units and sensors for controlling various part of the vehicle, as is known in the art. Fig. 1 , only illustrates units / devices / entities of the vehicle that are required for understanding the present invention.

[0059] Fig. 2 schematically illustrates an exemplary battery module 200, according to embodiments of the invention. The battery module 200 may form a battery unit, or a plurality of battery modules may form a battery unit such as a battery stack. The battery module 200 comprises a plurality of battery cells, n according to the present example, denoted 201_1 , 201_2, 201_3, ... , 201_n. The battery cells 201 _1 , ... , 201 _n are interconnected by means of electrical connectors, such as busbars 202. According to the illustrated example, the battery cells each comprises a cell fuse 204 in order to, for example, provide for a short-circuit and / or overvoltage protection. According to embodiments of the invention, no such cell fuses 204 are present.

[0060] The battery module 200 further comprises connectors 205, 206 to be connected, either to further battery modules of a battery pack and / or to the connection points of the battery pack, where the connections of the connectors to the battery cells may also be realized through the use of electrical connectors such as busbars. According to the illustrated example, the battery module 200 further comprises a cell management controller (CMC) 210. The cell management controller 210 may, inter alia, be utilized to monitor the battery cells of the battery module. For example, the cell management controller CMC 210 may be configured to individually measure the cell voltage over each individual battery cell of the battery module. The CMC 210 therefore comprises connections 211 to each pole of each battery cell 201 _1 , ... , 201_n of the battery module 200. According to embodiments of the invention, such individual cell voltage measurements may be used as part of the diagnosis according to the invention as will be further explained below.

[0061] Fig. 3 illustrates an exemplary battery unit 300 comprising a plurality of battery modules, e.g., according to the embodiment illustrated in fig. 2. In particular, the battery unit of Fig. 3 comprises six battery modules 301-306. The battery modules 301-306 of Fig. 3 are illustrated as being divided into two portions 300a, 300b, but it is to be understood that this division according to the example is for illustration purposes only, and no such division may be the actual case. Furthermore, the vehicle electrical system may be configured to electrically connect the battery unit 300, either alone or as forming part of a larger battery arrangement of the vehicle comprising a plurality of battery units, to the one or more electrical machines of the vehicle to provide power for propelling and braking the vehicle. The figure illustrates connection points 314, 315 for such purposes.

[0062] According to the invention, it is provided a method for diagnosing a battery unit such as battery unit 300 of Fig. 3. In particular it is provided a method for determining a difference in resistance between a first battery unit portion and a second battery unit portion, such as battery unit portions 300a, 300b in Fig. 3.

[0063] Fig. 4A illustrates a first exemplary method 400 according to aspects of the invention. The method starts in step 401 , where a voltage U1 over a first battery unit portion, such as battery unit portion 300a in Fig. 3. This determination is, according to the present example, carried out by means of a voltage sensor, 310, which may be any suitable kind of voltage sensor. The voltage sensor hence measures the aggregated voltage over the battery modules 301-303, including the busbars interconnecting the battery modules 303-303 and battery cells of the battery modules 301-303. In step 402, similarly, a voltage U2 over the battery unit portion 300b is determined using a voltage sensor 311 which may be the same voltage sensor as voltage sensor 310 or a separate voltage sensor. It may be advantageous that the voltage sensors 310, 311 form parts of a same voltage sensor, such as a voltage sensor having multiple inlets, and which may simultaneously measure the voltages, and / or switch between voltages currently being measured. This has the advantage that internal errors, or measurement inaccuracies of such sensors, will be the same for both voltage measurements, and hence not participate to factors that has an influence on differences in the measured voltage. However, according to aspects of the invention, different voltage sensors are used.

[0064] According to step 403, a current flowing through the battery unit 300 is measured. Since the battery cells of the battery modules, and the battery modules, are serially connected the same current will flow through all cells, and the current may therefore be measured at essentially any suitable location, where an exemplary measurement position is illustrated by current sensor 312. The current sensor 312 may also form part of a same sensor as voltage sensors 310, 311 , which sensor hence would be a voltage-current (III) sensor. This is schematically indicated by dotted box 313 representing a single III sensor 313. Again, this may be advantageous to reduce or cancel out measurement errors. The III sensor 313 may be configured to determine the voltages and the current sequentially, where still the determinations may be carried out very rapidly, and the determined current can therefore be considered to be representative for both voltage measurements. The measurements can be signalled to the control arrangement 120, which may then perform calculations according to the invention.

[0065] In step 404 a difference in resistance between the battery unit portions 300a and 300b is determined. This difference may be determined by dividing the voltage of the battery unit portions, respectively, with the determined current, to thereby obtain resistance measurements, and then subtract the resistance measurements for the two battery unit portions to obtain a difference in resistance Rdiff. The voltages may also first be subtracted from each other prior to dividing with the current to obtain the difference in resistance Rdiff. This difference in resistance Rdiff hence reflects a difference in resistance between the two battery unit portions. Ideally, when the battery unit portions comprise the same number of battery units and battery cells, the resistance that the battery unit portions exhibit would be the same, and hence the difference in resistance ideally would be zero.

[0066] The determined difference in resistance Rdiff therefore represents a measure that can be seen as an indication of a status of the battery unit, and a diagnosis of the battery unit may therefore be based on this difference in resistance. In case the difference in resistance is non-zero, this could be seen as a possible presence of a malfunction, such as a malfunctioning busbar. However, it is realized that some difference may still exist, e.g., due to measurement errors and manufacturing tolerances, while the battery unit is still operating properly. According to embodiments of the invention, therefore, the determined difference in resistance is compared with a predetermined resistance limit, which may, e.g., be determined empirically or be calculated using a model representation of the battery unit, and a signal, e.g., indicating a fault may be generated when the difference in resistance exceeds the predetermined resistance limit.

[0067] It is to be understood that the electrical system of a vehicle of the kind in Fig. 1 may configured for direct current voltages of relatively high magnitude. For example, the vehicle electrical system may be configured for a high voltage, such as a voltage above 60 V, for example 400 V or above, or 450 V or above, such as 650 V or above. The vehicle electrical system may be configured for even higher voltages. The electric power required to propel a vehicle, in particular a heavy vehicle, and thereby the voltage and / or current may be very high.

[0068] The battery unit 300 of Fig. 3 may hence represent a high voltage component, and / or be configured for high currents. This means that even very small resistances may generate heat that may cause problems, such as damage or fire. As was mentioned above, a fault in the battery unit causing increased resistance is highly undesirable but may be difficult to detect. This is because increases in resistance that may give rise to a problem such as overheating may be comparatively very small resistances, e.g., in the range of milliohms. Resistances of such magnitudes are difficult to measure. Still, resistances of these magnitudes may give rise to problems due to the high current.

[0069] The invention provides a solution that determines a difference in resistance between two battery unit portions, where this difference in resistance will reflect any possible faulty busbars in a case when the resistances over the battery unit portions are expected to be substantially equal. The invention hence does not identify the particular faulty connection, but still identifies an error so that, e.g., a notification that repair is required can be generated. It is to be understood that a battery unit according to, e.g., Fig. 3 may comprise a large number of electrical connectors such as busbars that may give rise to a fault, and, as mentioned above, it would require a large number of measurement devices in case these were to be individually diagnosed. The invention makes fault detection possible without such cumbersome diagnosis. In case the battery unit forms part of a battery arrangement comprising a plurality of battery units, the faulty battery unit may also be disconnected, so that the vehicle may continue operation, albeit at reduced battery capacity, pending repair.

[0070] As was mentioned, the magnitude of a resistance that may give rise to serious problems may be very low and difficult to measure. According to embodiments of the invention, therefore, the difference in resistance may be configured to be determined regularly, continuously and / or at predetermined intervals so as to generate a plurality of determinations of the difference in resistance. The plurality of measurements of the difference in resistance may then be filtered using any suitable filter, where such filtering of signals is common and known per se, and a signal may be generated, e.g., when a filtered difference in resistance exceeds a predetermined resistance limit as above. In this way a plurality of generated differences in resistance are taken into account in the filtering, and possibly erroneous / noisy measurement values may be cancelled out during the filtering. This may provide for a more robust diagnosis of the battery unit.

[0071] Furthermore, according to the illustrated example, the diagnosing of the battery units 300 has been illustrated as being carried out for two equal size battery unit portions, that is, battery unit portions comprising the same number of battery cells. This has the advantage that the determined resistances of the two battery unit portions will be directly comparable, so that the difference in resistance obtained by subtracting the two voltages / resistances from each other will directly reflect a difference between battery unit portions that otherwise are expected to exhibit the same resistance. This provides for straight forward manner of comparing the two battery unit portions.

[0072] A comparison of this kind, i.e. , of two equal size battery unit portions, may not always be possible. According to aspects of the invention the battery unit portions comprise a non-equal number of battery cells. This may be a result of, e.g., design constraints. For example, a battery unit may comprise an uneven number of battery modules where it may be preferable, or even necessary, e.g., for design reasons, to arrange the voltage sensor in a manner such that the voltage is measured over a number of entire battery modules. There may also already exist a voltage sensor measuring voltages over different parts of the battery unit that differ in size. The invention hence allows use of such already present sensors.

[0073] For example, in case the battery unit comprises five battery modules it may be required to measure the voltages in such a manner that the first voltage is measured over two or three battery modules, while the other voltage is measured over the remaining three or two battery modules. The resulting resistance over these two non- evenly sized battery unit portions may not be directly comparable given the difference in size of the battery portions and thereby, e.g., difference in number of busbars and battery cells. Hence a difference in resistance determined from these two measurements may not be used to directly determine whether a fault has occurred. According to aspects of the invention, therefore, one or the other of these two voltages is compensated by a compensation factor being dependent on the difference in the number of battery cells of the two battery unit portions.

[0074] For example, with regard to the example comprising five battery modules a voltage measured over two battery portions modules may be multiplied by 3 / 2, or a voltage measured over three modules may be multiplied by 2 / 3. In this way representations of the first and second voltages representing equal size battery unit portions is obtained.

[0075] Furthermore, it is to be realized that even in the case when voltage measurements are performed for equal size battery unit portions, or voltage measurements over non-equal size battery unit portions are compensated, there may still exist and inherent difference in resistance, e.g., due to manufacturing tolerances and other factors having the result that the battery unit portions are not perfectly equal. Also, as was mentioned above, there may exist differences in measurement accuracy in particular if different voltage sensors are used for the two voltage measurements. Furthermore, each sensor may exhibit measurement errors, which may vary in time.

[0076] According to aspects of the invention, therefore, a voltage correction factor can be calculated to account for such differences. This voltage correction factor is determined by performing voltage measurements over the battery unit portions, i.e. measurements according to the above, in a situation when the current through the battery unit is below some threshold current. When the current is low the influence of resistances will be considerable smaller, and using voltage measurements in such a situation allows that a low current voltage difference between the battery unit portions can be determined. This low-current voltage difference can thereby be seen as a difference caused by, e.g. differences in manufacturing tolerances, and / or measurement accuracy. The voltage difference that is measured during high-current conditions to determine the difference in resistance over the battery unit portions can then be compensated by using the low-current voltage difference as a voltage correction factor by subtracting the low-current voltage difference from the difference between the first voltage and the second voltage when determining difference in resistance to remove irregularities that are not caused by a difference in resistance but by other factors.

[0077] As has been described above, the sensor measurement error may vary in time. Therefore the method of diagnosing the battery unit may be stopped or paused after a certain time period has elapsed, i.e. the method is only performed during a certain time interval, whereafter the method is stopped or paused. A new voltage correction factor may then need to be determined during low-current conditions before the diagnosis of the battery unit is performed again. The time interval may be in the order of minutes, as have been described above.

[0078] Fig. 4B illustrates a further exemplary method 410 according to aspects of the invention. The features that have been exemplified with reference to the method according to Fig. 4A are equally valid for the method according to Fig. 4B, but where Fig. 4B provides a solution that may further increase the robustness of the measurements. Method steps 411-413 are similar to steps 401-403 of Fig. 4A. That is, voltages are determined over the battery unit portions, respectively, and a current through the battery unit is also determined. However, in difference to the method of Fig. 4A, voltages over individual battery cells are also determined, step 414.

[0079] As was described above with reference to Fig. 3, a battery module may comprise a cell module controller CMC that may be equipped with measurement means for measuring individual battery cell voltages of battery cells of the battery module.

[0080] According to aspects of the invention, the individual battery cell voltage is measured for all battery cells of the battery unit in step 414. A difference in resistance is then determined in step 415 in a manner similar to what has been described above, however with the difference that instead of only taking the voltage difference between the voltage over the first battery unit portion and the second battery unit portion, respectively, the accumulated individual cell voltages of a battery unit portion is first subtracted from the voltage measured over the battery unit portion, respectively. That is, the battery unit voltage being used when determining the difference in resistance will, for each battery unit portion, only be the remaining voltage that does not constitute a battery cell voltage. This remaining voltage then corresponds to the busbar resistance. The two voltages that are then being used to calculate the difference in resistance will be much smaller. This, in turn, may increase the robustness of the measurements, since the busbar resistance is partly or fully separated from the internal resistance of the battery cells. The resulting difference in resistance may then be used as described above. Through this method, then, the busbar resistance is determined quite precisely whereby a fault related to the busbar can be diagnosed with good accuracy. Furthermore, according to aspects of the invention battery cell voltages need not be measured for all battery cells of a battery unit portion, but only for part of the battery cells. For as long as voltage is measured for a similar number of battery cells for both battery unit portions this may still increase the robustness of the measurements.

[0081] Furthermore, even though the invention mainly has been illustrated using battery units divided into modules above it is to be understood that the battery unit may consist of a single unit comprising a plurality of battery cells.

[0082] According to an aspect of the invention, a control arrangement 120 for diagnosing a battery unit is provided.

[0083] The control arrangement 120, includes a control unit 121 arranged to provide for measuring voltages over battery unit portions, and a current flowing through a battery unit, and determine a difference in resistance over the battery unit portions using the measurements. The control arrangement 120, e.g., a device or a control device, according to the invention may be configured to perform all aspects that have been described with regard to methods of the invention.

[0084] Hence the control arrangement 120 is provided with the above-described advantages for the various aspects of the invention. The invention also relates to a vehicle 100 including the control arrangement 120.

[0085] Fig. 5 illustrates a control arrangement 500 / 120, which may be utilized to carry out the invention. The control arrangement 500 / 120 may comprise a computing unit 501 , which can be constituted by essentially any suitable type of computer, where a computer may be any hardware or hardware / firmware device implemented using processing circuity such as, but not limited to, a processor, Central Processing Unit (CPU), a controller, an arithmetic logic unit (ALU), a digital signal processor, a microcomputer, a field programmable gate array (FPGA), a System-on-Chip (SoC), a programmable logic unit, a microprocessor, an application-specific integrated circuit, or any other device capable of electronically performing operations in a defined manner. The computing unit 501 is connected to a memory unit 502 arranged in the control arrangement 500 / 120, which memory unit provides the computing unit 501 with, e.g., the stored program code and / or the stored data which the computing unit 501 requires to be able to perform computations. The computing unit 501 is also arranged to store partial or final results of computations in the memory unit 502.

[0086] In addition, the control arrangement 500 / 120 is provided with devices 511 , 512, 513, 514 for receiving and transmitting input and output signals. These input and output signals can contain waveforms, impulses, or other attributes which, by the devices 511 , 513 for the reception of input signals, such as signals from a III sensor, can be detected as information and can be converted into signals which can be processed by the computing unit 501 . These signals are then made available to the computing unit 501 . The devices 512, 514 for the transmission of output signals are arranged to convert signals received from the computing unit 501 in order to create output signals by, e.g., modulating the signals, which can be transmitted to other parts of and / or systems in the vehicle 100.

[0087] Each of the connections to the devices for receiving and transmitting input and output signals can be constituted by one or more of a cable; a data bus, such as a Controller Area Network CAN bus, a Media Orientated Systems Transport MOST bus, or some other bus configuration; or by a wireless connection. A person skilled in the art will appreciate that the above-stated computer can be constituted by the computing unit 501 and that the above-stated memory can be constituted by the memory unit 502.

[0088] Control systems in modern vehicles commonly comprise communication bus systems consisting of one or more communication buses for linking a number of electronic control units, ECU's, or controllers, and various components located on the vehicle. Such a control system can comprise a large number of control units and the responsibility for a specific function can be divided amongst more than one control unit. Vehicles of the shown type thus often comprise significantly more control units than are shown in Figs. 1 and 5, which is well known to the person skilled in the art within this technical field. The invention may be implemented by one or more such control units. The invention can also, however, be implemented wholly or partially in one or more other control units being present in the vehicle 100, or in one or more control unit dedicated to the invention. Here and in this document, units are often described as being arranged for performing steps of the method according to the invention. This also includes that the units are designed to and / or configured to perform these method steps.

[0089] The control units of the vehicle may be logically separated but physically implemented in the same unit or can be both logically and physically arranged separately or together. These units may, e.g., correspond to groups of instructions, which can be in the form of programming code, that are input into, and are utilized by a processor / computing unit 501 when the units are active and / or are utilized for performing its method step, respectively.

[0090] The person skilled in the art will appreciate that the embodiments described herein for diagnosing a battery unit may also be implemented in a computer program, which, when it is executed in a computer, instructs the computer to execute the method. The computer program is usually constituted by a computer program product 503 stored on a computer-readable medium. In some embodiments, the computer-readable medium may be a non-transitory computer-readable medium, such as a tangible electronic, magnetic, optical, infrared, electromagnetic, and / or semiconductor system, apparatus, and / or device. The computer-readable medium comprises a suitable memory, such as, e.g.: Read-Only Memory ROM, Programmable Read-Only Memory PROM, Erasable PROM EPROM, Flash memory, Electrically Erasable PROM EEPROM, a hard disk unit, etc.

[0091] The invention is not limited to the above-described aspects. Instead, the invention relates to, and encompasses all different aspects being included within the scope of the independent claims.

Claims

Claims1. A method for diagnosing an electric battery unit (300), the electric battery unit (300) comprising: a plurality of electric battery cells (201_1 , 201_n); a plurality of electrical conductors (202) interconnecting the electric battery cells (201_1 , ... , 201_n); a first battery unit portion (300a) comprising a first subset of the electric battery cells (201_1 , ... , 201_n); a second battery unit portion (300b) comprising a second subset of the electric battery cells (201 _1 , , 201 _n), wherein the first and second subsets of electric battery cells (201 _1 , ... , 201 _n) are non-overlapping; the method comprising: determining a first voltage (U1 ), being a voltage over the first battery unit portion (300a); determining a second voltage (U2), being a voltage over the second battery unit portion (300b); determining a current flowing through the battery unit (300); determining a difference in resistance (Rdiff) over the first battery unit portion (300a) and the second battery unit portion (300b) using a difference between the first and second voltages, and the current flowing through the battery unit (300).

2. A method according to claim 1 , further comprising: performing a diagnosis of the electric battery unit (300) based on the difference in resistance (Rdiff).

3. A method according to claim 1 or 2, the diagnosing of the electric battery unit (300) comprising: comparing the determined difference in resistance (Rdiff) with a predetermined resistance limit, and generating a signal when the difference in resistance (Rdiff) exceedsthe predetermined resistance limit.

4. A method according to any one of the claims 1 -3, further comprising: determining the difference in resistance (Rdiff) regularly, continuously and / or at predetermined intervals to generate a plurality of determinations of the difference in resistance (Rdiff), and generating the signal when a filtered difference in resistance (Rdiff) exceeds a predetermined value, the filtered difference in resistance (Rdiff) taking into account the plurality of generated differences in resistance (Rdiff).

5. A method according to any one of the claims 1 -4, wherein the first and second battery unit portions (300a, 300b) are configured to comprise an equal number of battery cells.

6. A method according to any one of the claims 1 -4, wherein the first and second battery unit portions (300a, 300b) are configured to comprise a different number of battery cells, the method further comprising: compensating the first (U1) and / or second voltage (U2) by a compensation factor being dependent on a difference in the number of battery cells of the two battery unit portions (300a, 300b), so as to obtain representations of the first and second voltages representing equal size battery unit portions (300a, 300b).

7. A method according to any one of the claims 1 -6, further comprising, when the current through the battery unit (300) is below a first current: determining a low current voltage difference between the first portion (300a) of the battery unit (300) and the second portion (300b) of the battery unit (300), and utilizing the low current voltage difference as a voltage correction when determining the difference in resistance (Rdiff), the low current voltage difference being subtracted from the difference between the first voltage (U1 ) and the second voltage (U2) when determining the difference in resistance(Rdiff).

8. A method according to any one of the claims 1 -7, further comprising: determining the first voltage (U1 ) over the first portion (300a) of the battery unit (300) and the second voltage (U2) over the second portion (300b), respectively, using a same voltage sensor, wherein the voltage sensor is configured to determine the first voltage (U1 ) over the first portion (300a) of the battery unit (300) and the second voltage (U2) over the second portion (300b), respectively, concurrently or consecutively.

9. A method according to claim 8, wherein the voltage sensor is a voltage / current sensor, the method further comprising: determining the current flowing through the battery unit (300) using the voltage / current sensor concurrently or consecutively with the measuring of the first voltage (U1 ) and second voltage (U2).

10. A method according to any one of the claims 1-9, wherein the battery unit (300) comprises means for measuring individual voltages over at least part of the battery cells of each of the first and second battery unit portions (300a, 300b), the method further comprising: for each battery unit portion (300a, 300b), determining an aggregated battery cell voltage of measured battery cell voltages of the battery unit portion (300a, 300b), and for each battery unit portion (300a, 300b), determining a battery unit portion voltage difference between the determined voltage over the battery unit portion (300a, 300b) and the aggregated battery cell voltage of the battery unit portion (300a, 300b), and determining the difference in resistance (Rdiff) over the first battery unit portion (300a) and the second battery unit portion (300b) using these battery unit portion voltage differences and the current flowing through the battery unit (300).11 . A method according to any one of the claims 1 -10, the battery unit (300) comprising at least two battery modules, each battery module comprising a subset of the battery cells, the plurality of electrical conductors (202) interconnecting, in addition, the at least two battery modules, wherein: the first battery unit portion (300a) comprises at least one of the at least two battery modules, and the second battery unit portion (300b) comprises remaining modules of the at least two battery modules.

12. A method according to claims 11 , wherein each battery module comprises a cell module controller (CMC), the cell module controller being configured to measure the individual voltage over at least a plurality of the battery cells of the battery module.

13. A method according to any one of the claims 1-12, the battery unit (300) forming part of a battery arrangement comprising a plurality of battery units, the method comprising, for each battery unit (300): determining a difference in resistance (Rdiff) between a first portion (300a) of the battery unit (300) and a second portion (300b) of the battery unit (300) using a difference in voltages over the first portion (300a) of the battery unit (300) and the second portion (300b) of the battery unit (300), and the current flowing through the battery unit (300); and generating a signal when the difference in resistance (Rdiff) exceeds a first difference for any one of the battery units of the battery arrangement.

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

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

16. A control arrangement (120; 500) for diagnosing an electric battery unit (300), the electric battery unit (300) comprising: a plurality of electric battery cells (201_1 , 201_n); a plurality of electrical conductors (202) interconnecting the electric battery cells (201_1 , ... , 201_n); a first battery unit portion (300a) comprising a first subset of the electric battery cells (201_1 , ... , 201_n); a second battery unit portion (300b) comprising a second subset of the electric battery cells (201 _1 , , 201 _n), wherein the first and second subsets of electric battery cells (201 _1 , ... , 201 _n) are non-overlapping; the control arrangement (120; 500) comprising: means for determining a first voltage (U1 ), being a voltage over the first battery unit portion (300a); means for determining a second voltage (U2), being a voltage over the second battery unit portion (300b); determining a current flowing through the battery unit (300); determining a difference in resistance (Rdiff) over the first battery unit portion (300a) and the second battery unit portion (300b) using a difference between the first and second voltages, and the current flowing through the battery unit (300).

17. A battery unit assembly comprising a battery unit (300) and control arrangement (120; 500) according to claim 16.

18. A vehicle (100) comprising a control arrangement (120; 500) according to claim 16.

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