Diagnostic method for battery pack

Abstract

The battery comprises a plurality of battery cells (Zk + 1, Zk, Zk-1) which are connected in series and are each connected to a battery cell monitoring unit via a connection line (Wk + 1, Wk-1) in a fault-free state. In the case of a diagnostic method, a first cell voltage difference between a first battery cell and a second battery cell is determined on the basis of a provided first signal representing a cell voltage of the first battery cell at a first point in time and a provided second signal representing a cell voltage of the second battery cell at the first point in time. Furthermore, a second cell voltage difference between the first battery cell and the second battery cell is determined on the basis of a further first signal provided which represents the cell voltage of the first battery cell at the second point in time and a further second signal provided which represents the cell voltage of the second battery cell at the second point in time, wherein the second time point lies in a predetermined time interval ([delta] t) after the first time point. A change in the battery voltage difference # imgabs0 # is determined and the change in the battery voltage difference # imgabs1 # is compared with a threshold value (THconst, TH).

Description

Technical Field

[0001] A diagnostic method and a diagnostic control unit for a battery pack are described. Furthermore, a battery pack system, a computer program and a computer program product are described. Background Art

[0002] Lithium-ion batteries have a very high power density. Therefore, lithium-ion batteries can be often found, especially in automotive applications. However, the chemically unstable behavior of lithium-ion battery cells under critical conditions requires lithium-ion batteries to be treated with care.

[0003] A battery pack usually consists of a plurality of battery modules, which in turn have a plurality of battery cells, for example 16 battery cells. In order to monitor the state of the battery pack and ensure safe operation, a battery management system with a battery cell controller is used in most cases. The battery cell controller is used to eliminate or at least reduce safety risks by precisely monitoring the key characteristics of the lithium-ion battery cells (voltage, temperature, current) and providing embedded compensation functions together with comprehensive system diagnostics.

[0004] Furthermore, each battery cell is usually connected to a battery cell controller in order to balance the battery cells. Such an arrangement can be disadvantageous, which can lead to imbalances in the battery modules, in particular during charging, discharging or balancing of the battery modules. This in turn can cause the battery module as a whole to be damaged. Furthermore, it is possible that in this case, erroneous measured values ​​of the cell voltage can be used for monitoring the cell voltage limits, and thus excessively high or too low cell voltages cannot be detected, which can likewise lead to damage to the battery. Summary of the invention

[0005] The object to be achieved is to specify a diagnostic method for a battery which allows reliable and cost-effective detection of faults in the connection between a battery cell and a battery cell monitoring unit.

[0006] This object is achieved by the features of the independent patent claim. Advantageous embodiments are indicated in the dependent claims.

[0007] According to a first aspect, the above object is achieved by a diagnostic method for a battery pack, wherein the battery pack has a plurality of battery cells which are connected in series. In a fault-free state, the battery cells are each connected to a battery cell monitoring unit via a connecting line, and the battery cell monitoring unit has a capacitor for cell voltage detection which is connected in parallel with the connected battery cells.

[0008] The battery cell may be constructed as a single cell. Alternatively, the battery cell may include a battery cell complex in which all single cells are connected in parallel.

[0009] The battery cell monitoring unit preferably comprises one or more integrated circuits ("chips") for battery cell monitoring. The capacitor of the battery cell monitoring unit is part of the battery cell monitoring unit, but is preferably arranged outside the chip. For the battery, it is also possible to use a plurality of separate battery cell monitoring units, which are each assigned to a part of the battery.

[0010] In the case of the diagnostic method, a first cell voltage difference between the first battery cell and the second battery cell is determined based on a first signal representing the cell voltage of the first battery cell at a first point in time and a second signal representing the cell voltage of the second battery cell at the first point in time.

[0011] Furthermore, a second battery voltage difference between the first battery cell and the second battery cell is determined based on another first signal representing the battery voltage of the first battery cell at the second time point and another second signal representing the battery voltage of the second battery cell at the second time point. In this case, the second time point is in a predetermined time interval after the first time point. It should be noted in this case that the first signal and the second signal are preferably detected simultaneously. However, the first time point and the second time point can each have a predetermined tolerance time range. However, the corresponding tolerance time range is smaller than the time interval. In particular, the tolerance time range includes less than 10% of the time interval. The time interval can also be referred to as a diagnostic time interval.

[0012] The first and the second battery cell are preferably directly adjacent and have a common connecting line to the battery cell monitoring unit.

[0013] In the case of this diagnostic method, a change in the battery voltage difference is then determined based on the first battery voltage difference and the second battery voltage difference, and the change in the battery voltage difference is compared with a threshold value. If the change in the battery voltage difference is greater than the threshold value, a fault is detected.

[0014] In at least one embodiment of the first aspect, detecting the fault comprises providing a fault signal which is designed to signal an interruption of a connecting line which, in the fault-free state, connects the first battery cell and the second battery cell to an input of the battery cell monitoring unit.

[0015] It is thus possible to detect very quickly and reliably that a connecting line or line connecting a battery cell to a battery cell monitoring unit is interrupted. Appropriate measures can thus be taken which, in particular during charging, discharging or balancing of the battery cells, reduce or prevent imbalances in the battery cells and thus prevent damage to the battery. Furthermore, it is possible to prevent erroneous measured values ​​of the cell voltage from being used for monitoring the cell voltage limit and thus excessively high or low cell voltages from being detected, which could likewise lead to damage to the battery.

[0016] In at least one configuration according to the first aspect, the threshold value has a predefined constant value.

[0017] In at least one design solution according to the first aspect, the threshold value is determined based on a change in the average cell voltage of at least a portion of the battery cells of the battery pack. The battery pack can be connected to a plurality of battery cell monitoring units. All or a portion of the cells of the battery pack, even cells that are not connected to the battery cell monitoring unit under consideration, can be used for the average value calculation.

[0018] In this case, the average cell voltage change is determined as a function of the cell voltage change of the respective battery cell between the first time point and the second time point. The greater the current gradient flowing through the battery cell and the greater the average internal resistance of the battery cell, the greater the average cell voltage change. This advantageously enables more reliable fault detection in high dynamics, in which the values ​​of the current gradient are very high, and at low battery cell temperatures, in which the internal resistance of the battery cells is high. Since a large change in the cell voltage difference considered between the first time point and the second time point results due to the high current gradient and / or the high battery cell internal resistance, fault detection of interrupted connecting lines in a fault-free system can be prevented in particular.

[0019] In at least one embodiment of the first aspect, the threshold value is determined as a function of the distribution of the internal cell resistances of the battery cells and / or as a function of a maximum temperature difference between consecutive battery cells and / or as a function of a charge state deviation between consecutive battery cells and / or aging of the battery cells.

[0020] In at least one design solution according to the first aspect, the threshold is determined according to a provided correction factor, and the threshold is represented by a linear function according to an average battery voltage variation at least section by section, wherein the slope of the linear function is related to the correction factor.

[0021] The correction factors are determined in particular as a function of the distribution of the internal cell resistances of the battery cells and / or as a function of a maximum temperature difference between consecutive battery cells and / or as a function of charge state deviations between consecutive battery cells and / or aging of the battery cells and are provided for the diagnostic method.

[0022] According to a second aspect, the above-mentioned task is solved by a diagnostic control unit for a battery pack, wherein the battery pack has a plurality of battery cells, the battery cells are connected in series, the battery cells are respectively connected to a battery cell monitoring unit via connecting lines in a fault-free state, the battery cell monitoring unit has a capacitor for battery voltage detection, the capacitor is connected in parallel with the connected battery cells, and the diagnostic control unit is constructed to perform a diagnostic method according to the first aspect.

[0023] According to a third aspect, the above object is achieved by a computer program which, when executed by a processor or a controller of a diagnostic control unit, causes the diagnostic unit to perform the diagnostic method according to the first aspect.

[0024] According to a fourth aspect, the above-mentioned object is achieved by a computer program product comprising the computer program according to the third aspect.

[0025] According to a fifth aspect, the above-mentioned object is achieved by a battery system for a motor vehicle, wherein the battery system has a battery, at least one battery cell monitoring unit and a diagnostic control unit according to the second aspect, and wherein the battery has a plurality of battery cells, which are connected in series and which are each connected to at least one battery cell monitoring unit via a connecting line in a fault-free state, and wherein the battery cell monitoring unit has a capacitor for cell voltage detection, which is connected in parallel with the connected battery cells. The at least one battery cell monitoring unit is further designed to provide a first signal, a further first signal, a second signal and a further second signal.

[0026] The battery may have one or more battery cell strings, each having a plurality of battery cells, wherein the battery cells of the respective battery string are connected in series. The battery cell strings may be connected partially in parallel or completely in parallel. The method may therefore be carried out for a part of a battery cell string or for the entire battery cell string or for more than one battery cell string in each case.

[0027] The optional design solutions of the first aspect may also exist in other aspects accordingly and have corresponding effects.

[0028] The computer program may be implemented as a computer-readable instruction code in any suitable programming language, such as JAVA, C++, etc. The computer program may be stored on a computer-readable storage medium (CD-ROM, DVD, Blu-ray disc, removable drive, volatile or non-volatile memory, built-in memory / processor, etc.). The instruction code may program a computer or other programmable device, such as a control device, in particular for a motor vehicle, so that the desired functions are performed. In addition, the computer program may be provided in a network such as the Internet, from which it may be downloaded by a user when necessary. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Exemplary embodiments of the invention are explained in more detail below with reference to the schematic drawings.

[0030] The description of the subject matter described here is not limited to each specific embodiment. As long as it is technically meaningful, the features of different embodiments can be combined with each other to form other embodiments. Unless otherwise specified, changes or modifications described in view of one of the embodiments may also be applied to other embodiments, for example.

[0031] Figure 1 shows an exemplary equivalent circuit diagram for connecting a battery cell to a battery cell monitoring unit,

[0032] Figure 2 shows an exemplary battery voltage variation process of two adjacent battery cells,

[0033] Figure 3 An exemplary graph showing a method for determining a threshold value for a diagnostic method for detecting an open connection line, and

[0034] Figure 4 An exemplary flow chart for a diagnostic procedure is shown. DETAILED DESCRIPTION

[0035] In the figures, the same reference numerals are used for elements having substantially the same function, but these elements are not necessarily identical in all details.

[0036] The details are set forth below to provide a more detailed explanation of the exemplary embodiments. However, it is apparent to those skilled in the art that the embodiments can be implemented without these specific details. The special or general values, design data, additions, and inclusions or exclusions of components are not intended to affect the scope of protection of the present invention.

[0037] In other instances, well-known structures and devices are shown in block diagram form or in schematic view, rather than in detail, in order to simplify understanding of the embodiments.

[0038] It is noted that when an element is referred to as being "connected" or "coupled" to another element, the element may be directly connected or coupled to the other element, or there may be intervening elements. Conversely, when an element is referred to as being "directly" "connected" or "coupled" to another element, there are no intervening elements. Other expressions used to describe the relationship between elements should be interpreted in a similar manner (e.g., "between" versus "directly between," "adjacent" versus "directly adjacent," etc.).

[0039] Figure 1 A plurality of battery cells Z of a battery pack are shown k+1 , Z k , Z k-1 The battery pack cells are connected in series. The battery pack is arranged in a vehicle, for example, in particular in a pure electric vehicle or a hybrid vehicle.

[0040] also, Figure 1 An exemplary equivalent circuit diagram for the input terminals of the battery cell monitoring unit 10 is shown. The battery cell monitoring unit preferably includes one or more integrated circuits ("chips") for performing battery cell monitoring (in Figure 1 Battery cell Z k+1 , Z k , Z k-1 Connected to the battery pack battery monitoring unit 10.

[0041] The input of the battery cell monitoring unit 10 is connected via the connecting line W k+1 , W k-1 With battery pack battery Z k+1 , Z k , Z k-1 connect.

[0042] The directly adjacent inputs of the battery cell monitoring unit 10 are each connected via a capacitor C k , C k-1 connected so that the capacitor C k , C k-1 Respectively with the battery pack battery Z k+1 , Z k , Z k-1 connected in parallel. In the absence of faults, the corresponding battery voltage U k , U k-1 Landing on capacitor C k , C k-1 Here, the leakage current I leak into an integrated circuit for battery monitoring, which is required in conjunction with the measurement of the cell voltage. In the event of a fault, if, for example, the battery cell Z k+1 , Z k , Zk-1 With an open connection line W to the battery monitoring unit 10 err , then the corresponding leakage current I leak Lead capacitor C k The charging of capacitor C k-1 The discharge of capacitor C k , C k-1 The voltage drop at each cell is different. However, in the battery pack, k+1 , Z k , Z k-1 Unbalanced connections may also cause such effects, but these effects are usually less severe than in an open circuit connection. err In the event of a fault.

[0043] Figure 1 A battery cell monitoring unit 10 having three terminals is shown by way of example, wherein the middle terminal has an open connection line W err , that is, the battery pack cell Z k This results in the measured cell voltage U of the battery cell with index k being k The measured cell voltage U of the battery cell with index k-1 increases over time. k-1 The voltage of the two batteries U k , U k-1 The battery voltage difference It also increases over time.

[0044] Figure 2 Two directly adjacent battery cells Z are shown k , Z k-1 The battery voltage U k , U k-1 In the absence of faults, the two batteries Z k , Z k-1 All have a constant voltage, for example 2 V. At time t_0, the connection lines connecting the first pole of the kth battery cell and the second pole of the (k-1)th battery cell to the corresponding input terminals of the battery cell monitoring unit 10 are interrupted. The corresponding leakage current I leak The battery voltage U of the kth battery is k Increase and the battery voltage U of the (k-1)th battery k-1 decline.

[0045] After a certain period of time, for example, after 100ms, the battery voltage difference is 400mV.

[0046] For fault detection, which can be performed continuously, the change or gradient of the battery voltage difference is evaluated. For example, the battery voltage difference is determined at a diagnostic time interval of, for example, 100 ms. The change in the battery voltage difference is determined and evaluated for the corresponding diagnostic time intervals

[0047] If the battery voltage difference changes or gradients Exceeding a certain threshold TH const , TH, then it can be assumed that the open circuit connection line W err Failure of form.

[0048] The following is an equation that can be used to calculate the change in battery voltage difference: And determine the threshold TH const ,TH, makes reliable fault detection possible.

[0049] The cell voltage for the kth battery cell is:

[0050] U k =U 0，k +I·R k (Charge I>0; discharge I<0) Equation (1),

[0051] Where R k is the battery internal resistance of the kth battery, I is the current flowing into the battery cell, and U 0,k is the open circuit voltage of the kth battery cell. In the case of battery charging, the current I is greater than zero, and in the case of battery discharging, the current I is less than zero.

[0052] Similarly applicable to adjacent battery cells are:

[0053] U k-1 =U 0，k-1 +I·R k-1 (Charging I>0; Discharging I<0) Equation (2)

[0054] And therefore what applies to the battery voltage difference is:

[0055]

[0056] For the purpose of diagnosis, the directly adjacent battery cells Z are evaluated at predetermined diagnostic time intervals. k , Z k-1 The change of battery voltage difference For this purpose, the battery voltage difference is determined at a first time and at a second time. The second time point is later than the first time by a predetermined time interval Δt. Therefore, the time interval Δt between the detections of the battery voltage corresponds to the diagnostic time interval. Therefore, it is applicable that:

[0057]

[0058] In determining the threshold TH const , TH, on the one hand, we can consider: the threshold TH const TH is selected to be smaller than the minimum change in the battery voltage difference during the diagnostic time interval Δt in the event of a fault. This allows reliable fault detection.

[0059] On the other hand, the threshold TH const TH must be large enough so that even with large current gradients, open connections are not falsely detected. err Failure of the battery pack due to Z k+1 , Z k , Z k-1 Different internal resistances may also result in changes in battery voltage differences.

[0060] Figure 3 is a diagram illustrating determination of threshold values.

[0061] Draw the battery cell Z along the first axis k+1 , Z k , Z k-1 The average battery voltage change ΔU cell，mean In determining the average battery voltage change ΔU cell，mean When all the battery cells Z of the battery pack can be considered k+1 , Z k , Z k-1 or battery pack Z k+1 , Z k , Z k-1 part of.

[0062] Average battery voltage change ΔU cell，mean Represents the average value of the battery voltage change during the corresponding diagnostic time interval.

[0063] The change in battery voltage for battery k during the diagnostic time interval is

[0064] ΔU k =U k，t -U k,t -Δt Equation (5)

[0065] The value applicable to the average battery voltage change during the diagnostic interval is

[0066]

[0067] Where N is the battery cell Z under consideration k+1 , Z k , Z k-1 The amount of current flowing through the battery pack cell Z during the diagnostic time interval, ΔI k+1 , Z k , Z k-1 The change of current I and R mean is the battery cell Z under consideration k+1 , Z k , Z k-1 The average battery resistance.

[0068] Along a second axis perpendicular to the first axis, two directly adjacent battery cells Z are plotted within the diagnostic time interval. k+1 , Z k , Z k-1 The change of battery voltage difference

[0069] The dashed straight line represents the minimum change in cell voltage difference under fault conditions for a battery cell with index k.

[0070] However, for a battery cell with index k, the minimum change in the cell voltage difference under fault conditions is is not constant, but also depends on the other battery cells Z k+1 , Z k , Z k-1 The battery voltage changes. If the battery pack of the battery Z k+1 , Z k , Z k-1 The battery voltage of the battery increases within the considered diagnostic time interval and thus the average battery voltage changes by ΔU cell，mean If a positive value is used, the minimum change in battery voltage difference The same becomes larger. If the battery pack battery Z k+1 , Z k , Z k-1 The battery voltage decreases (ΔU cell，mean <0), the minimum change in battery voltage difference Point A represents when the battery pack cell Z k+1 , Z k , Z k-1 The battery voltage does not change.

[0071] Preferably, the threshold TH is selected const, TH, so that the threshold is located at or stretched to represent the minimum change in battery voltage difference under fault conditions This ensures that open connections can be reliably detected. err .

[0072] In determining the threshold TH const , TH, it should also be noted that the current may change within the diagnostic interval. In particular, in the case of large current gradients, additional battery voltage differences may occur.

[0073] Therefore, the threshold TH const TH can preferably be selected to be greater than the maximum battery voltage change that occurs in a fault-free situation at high current gradients.

[0074] A second dashed line (dots and lines alternating) extending parallel to the first axis represents a constant threshold value TH used exemplarily. const , for example at 250mV.

[0075] However, it is shown that as the current change ΔI increases during the diagnostic time interval or as the average voltage change ΔU cell,mean Increase, the constant threshold TH const may be too low, which may result in an open circuit connection to the W err or line fault detection. Point P in the diagram represents such a fault detection, where the cell，mean = 800mV, the change in battery voltage difference of 260mV during the diagnostic time interval is determined

[0076] Therefore, if the threshold value TH is not predetermined as a fixed value, but is varied according to the average battery voltage ΔU cell，mean Being determined is beneficial.

[0077] To this end, the maximum change in the battery voltage difference is first estimated for a no-fault situation.

[0078] For this purpose, it is assumed that the battery internal resistance is around the average value R mean Changes by ±ΔR.

[0079] R k =R mean +ΔR

[0080] Equation (7)

[0081] R k-1 =R mean -ΔR Equation (8).

[0082] This assumption takes the worst-case scenario into account to some extent.

[0083] Under this assumption, it is applicable to two adjacent battery cells Z k+1 , Z k , Z k-1 The gradient of the battery voltage difference The ones are:

[0084]

[0085] Battery pack Z k+1 , Z k , Z k-1 The change of the battery internal resistance ΔR is assumed in a simplified manner according to the average battery internal resistance and the correction factor K

[0086] ΔR=K·R mean Equation (10).

[0087] For example, according to the battery cell Z k+1 , Z k , Z k-1 The initial cell internal resistance distribution and / or the distribution of the cell Z in successive battery packs k+1 , Z k , Z k-1 The maximum temperature difference between and / or between successive battery cells Z k+1 , Z k , Z k-1 The state of charge deviation between the battery cells Z and / or the battery pack according to the battery pack k+1 , Z k , Z k-1 The aging of the correction factor K is determined or specified. The correction factor can therefore be newly determined in each case during ongoing operation or can be selected and predefined as a fixed number, wherein the aforementioned influences under worst-case conditions are taken into account when selecting the correction factor.

[0088] In the worst case, this applies to two adjacent battery cells Z within the diagnostic interval. k+1 , Z k , Z k-1 The change of battery voltage difference Yes

[0089]

[0090] This means that the possible battery voltage change in a fault-free system can be estimated by means of the average battery voltage change within the diagnostic time interval taking into account the correction factor K. The threshold value TH selected according to equation (12) is Figure 3, a dotted straight line is shown in FIG. 1 , wherein a symmetrical profile of the threshold value TH is applied in the case of positive and negative mean battery voltage profiles.

[0091] In order to enable reliable fault detection, for example in the case of small current gradients, the threshold TH is chosen to be constant. However, once the gradient of the battery voltage difference according to equation (12) Beyond a constant threshold, a threshold is selected according to Equation 12.

[0092] For example, five areas can be distinguished:

[0093] Area I: f<ΔUcell, mean<e

[0094] Region II: e<ΔUcell,mean≤d

[0095] Region III: d<ΔUcell,mean≤c

[0096] Region IV: c<ΔUcell,mean≤b

[0097] Region V: b<ΔUcell,mean≤a

[0098] Therefore, the diagnostic thresholds applicable in the following areas are:

[0099] In regions I and II: TH II =-2·K·ΔU cell,mean

[0100] In Region III: TH III =const

[0101] In regions IV and V: TH IV =2·K·ΔU cell,mean

[0102] Therefore, assuming that the battery internal resistance is around the average value R mean ±ΔR changes can be expressed as ΔR = K·R mean As described below, the diagnostic thresholds in regions I, II, IV, and V correspond to changes in the battery voltage difference This corresponds to the worst-case scenario.

[0103] K is in this case a correction factor, for example according to the battery cell Z k+1 , Z k , Z k-1 The initial cell internal resistance distribution and / or the distribution of the cell Z in successive battery packs k+1 , Zk, Z k-1 The maximum temperature difference between and / or between successive battery cells Z k+1 , Zk , Z k-1 The state of charge deviation between the battery cells Z and / or the battery pack according to the battery pack k+1 , Z k , Z k-1 The correction factor is determined and specified by the aging.

[0104] In region I, safe fault detection or open circuit connection line W err Detection is not possible because the minimum cell voltage change in the event of a fault is below the selected diagnostic threshold. Area I describes the battery cell Z k+1 , Z k , Z k-1 Operating situations in which a high negative current gradient may be present in combination with a low battery temperature. Since such high dynamics usually only exist for a short time, the fault can usually be detected in a subsequent diagnostic step, in which a lower diagnostic threshold can then be applied. For example, the boundary between region I and region II can be determined with the aid of simulations. Region V accordingly describes operating situations with a high positive current gradient, in which safe fault detection is not possible, because here too, in the event of a fault, the minimum battery voltage change is below the selected diagnostic threshold.

[0105] The value f representing the lower end of region I is the theoretical minimum average battery voltage change ΔU within the diagnostic time interval that occurs when switching from “full charge” to “full discharge” within the diagnostic time interval. cell，mean，min This limit value is consistent with the battery pack cell Z k+1 , Z k , Z k-1 is related to the temperature.

[0106] Figure 4 A flow chart showing a computer program for diagnosing a battery pack. The computer program may be executed by a processor or microcontroller of a battery pack management system.

[0107] First, the program is started in step S01. In step S01, for example, program variables are initialized.

[0108] In step S03, a first battery voltage difference between the first battery cell and the second battery cell is determined based on a provided first signal representing the battery voltage of the first battery cell at a first time point and a provided second signal representing the battery voltage of the second battery cell at the first time point.

[0109] In step S05, a second battery voltage difference between the first battery cell and the second battery cell is determined based on another first signal provided representing the battery voltage of the first battery cell at a second time point and another second signal provided representing the battery voltage of the second battery cell at the second time point, wherein the second time point is within a predetermined time interval Δt after the first time point.

[0110] In step S07, the change of the battery voltage difference is determined according to the first battery voltage difference and the second battery voltage difference. And the change of battery voltage difference With a predetermined threshold value TH const , TH for comparison.

[0111] If the battery voltage difference changes in step S07 Greater than a pre-set threshold TH const , TH, this is recognized as a fault in step S09 and a command for outputting a fault signal is generated.

[0112] Especially for all battery packs of battery packs Z k+1 , Z k , Z k-1 The program is preferably executed repeatedly with a predetermined time step, so that continuous monitoring of the battery pack is possible. The predetermined time step can, for example, be equal to the diagnostic time interval. In particular, the time interval Δt between the detections of the battery voltage can correspond to the diagnostic time interval.

[0113] For example, when the vehicle is parked, the program ends in step S11.

[0114] Reference numerals list

[0115] 10 Battery Pack Battery Monitoring Unit

[0116] C k , C k-1 Capacitors

[0117] Δt time interval

[0118] ΔU cell，mean Average battery voltage change

[0119] The change or gradient of the battery voltage difference

[0120] I leak Compensation or leakage current

[0121] S01...S11 program steps

[0122] TH Threshold

[0123] TH const Constant Threshold

[0124] U k , U k-1 Battery voltage

[0125] Battery voltage difference

[0126] W err Open connection line

[0127] W k+1 , W k-1 Connection lines

[0128] Z k+1 , Z k , Z k-1 Battery pack batteries.

Claims

1. A diagnostic method for a battery pack, wherein the battery pack has a plurality of battery cells (Z k+1 , Z k , Z k-1 ), the battery cells are connected in series, the battery cells (Z k+1 , Z k , Z k-1 ) in a fault-free state via the connecting line (W k+1 , W k-1 ) is connected to a battery pack battery monitoring unit (10), wherein the battery pack battery monitoring unit (10) has a capacitor (C k , C k-1 ), the capacitor and the connected battery cell (Z k+1 , Z k , Z k-1 ) are connected in parallel, and the method comprises the following steps: - determining a first cell voltage difference between the first battery cell and the second battery cell based on a provided first signal representative of a cell voltage of the first battery cell at a first point in time and a provided second signal representative of a cell voltage of the second battery cell at the first point in time, - determining a second cell voltage difference between the first battery cell and the second battery cell based on a provided further first signal representing the cell voltage of the first battery cell at a second point in time and a provided further second signal representing the cell voltage of the second battery cell at a second point in time, wherein the second point in time is a predetermined time interval (Δt) after the first point in time, - determining a change in the battery voltage difference based on the first battery voltage difference and the second battery voltage difference - The battery voltage difference changes With threshold (TH const , TH) are compared, and if the battery voltage difference changes Greater than the threshold (TH const , TH), the fault is detected.

2. A diagnostic method according to claim 1, wherein detecting a fault includes providing a fault signal, wherein the fault signal is configured to signal an interruption of a connection between the first battery cell and the second battery cell and an input end of the battery cell monitoring unit (10) in a fault-free state.

3. The diagnostic method according to claim 1 or 2, wherein the threshold value (TH const ) has a predetermined constant value.

4. The diagnostic method according to claim 1 or 2, wherein the battery pack battery (Z k+1 , Z k , Z k-1 ) in at least a portion of the average battery voltage change (ΔU cell，mean ) determines the threshold value (TH), wherein the threshold value (TH) is determined according to the battery cell (Z) between the first time point and the second time point. k+1 , Z k , Z k-1 ) of the battery voltage change to determine the average battery voltage change (ΔU cell，mean ).

5. The diagnostic method according to any one of the preceding claims, wherein the battery cell (Z k+1 , Z k , Z k-1 ) of the battery internal resistance and / or according to the distribution of the battery internal resistance in the successive battery cells (Z k+1 , Z k , Z k-1 ) and / or according to the maximum temperature difference between successive battery cells (Z k+1 , Z k , Z k-1 ) and / or the state of charge deviation between the battery cells (Z k+1 , Z k , Z k-1 ) determines the threshold value (TH const , TH).

6. The diagnostic method according to claim 4 or 5, wherein the threshold value (TH) is determined according to a provided correction factor and the threshold value is determined at least section by section according to the average battery voltage change (ΔU cell，mean ) is represented by a linear function, wherein the slope of the linear function is related to the correction factor.

7. A diagnostic control unit for a battery pack, wherein the battery pack has a plurality of battery cells (Z k+1 , Z k , Z k-1 ), the battery cells are connected in series, the battery cells (Z k+1 , Z k , Z k-1 ) in a fault-free state via the connecting line (W k+1 , W k-1 ) is connected to a battery pack battery monitoring unit (10), wherein the battery pack battery monitoring unit (10) has a capacitor (C k , C k-1 ), the capacitor and the connected battery cell (Z k+1 , Z k , Z k-1 ) are connected in parallel and the diagnosis control unit is configured to execute a diagnosis method according to any one of claims 1 to 6.

8. A computer program which, when executed by a processor or a controller of a diagnosis control unit, causes the diagnosis unit to perform the diagnosis method according to any one of claims 1 to 6.

9. A computer program product comprising a computer program according to claim 8.

10. A battery system for a motor vehicle, comprising a battery, at least one battery cell monitoring unit (10) and a diagnostic control unit according to claim 7, wherein the battery comprises a plurality of battery cells (Z k+1 , Z k , Z k-1 ), the battery cells are connected in series, the battery cells (Z k+1 , Z k , Z k-1 ) in a fault-free state via the connecting line (W k+1 , W k-1 ) is connected to the at least one battery cell monitoring unit, wherein the battery cell monitoring unit (10) has a capacitor (C k , C k-1 ), the capacitor and the connected battery cell (Z k+1 , Z k , Z k-1 ) are connected in parallel, and the at least one battery cell monitoring unit (10) is configured to provide a first signal, another first signal, a second signal and another second signal.

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