DE102024001737A1 - Method for diagnosing a traction battery of a motor vehicle and diagnostic device for a method for diagnosing a traction battery - Google Patents

Abstract

The invention relates to a method for diagnosing a traction battery (10) of a motor vehicle, which has several cells (14) interconnected by means of a circuit (12), and a battery management system (16) by which at least one cell state variable can be detected for each of the cells (14), wherein at least one logical cell and/or at least one string can be formed by the circuit (12), comprising the steps:
- Recording at least one cell state parameter for each cell (14) by a diagnostic unit (20); (S1)
- Determining the respective influence value of each cell (14), of the at least one logical cell and/or of the at least one string on an achievability value of a battery parameter based on the recorded cell state variables; (S2) and
- Determining a circuit configuration based on the determined influence values and depending on the reachability value, wherein the circuit configuration specifies the circuit (12) through which the battery parameter assumes the reachability value. (S3)
Furthermore, the invention relates to a diagnostic unit (20) and a motor vehicle.

Description

The invention relates to a method for diagnosing a traction battery of a motor vehicle, wherein the traction battery comprises cells interconnected by means of a circuit, as well as a battery management system, according to claim 1. Furthermore, the invention relates to a diagnostic device, which is particularly configured to carry out a method for diagnosing a traction battery, according to claim 8, and to a motor vehicle according to claim 10.

Batteries, especially traction batteries, used to power at least partially electrically driven vehicles, comprise multiple battery cells or cells interconnected via a circuit, thereby forming, for example, logic cells or strings to provide the required power and/or capacity. With traction batteries, individual cells or cell connectors can fail, potentially rendering the battery unusable and/or causing malfunctions that reduce the usable energy and/or power.

During maintenance or repair of a traction battery in a workshop, it is difficult for workshop personnel to determine whether a cell is defective and should therefore be bypassed, and whether this would be beneficial. The workshop personnel decide whether cells should be bypassed based on measurements and visual inspection.

The JP 5 453 769 B2 This shows a vehicle battery diagnostic system. Furthermore, the JP 5 733 648 B2 a method for managing a battery system.

The object of the present invention is to provide a method for diagnosing a traction battery and a corresponding diagnostic unit as well as a motor vehicle, by which a particularly advantageous repair arrangement can be provided, by which a repair of the traction battery by workshop personnel can be realized in a particularly advantageous manner.

This problem is solved according to the invention by the subject matter of the independent claims. Advantageous embodiments and further developments of the invention are specified in the dependent claims, as well as in the description and in the drawings.

A first aspect of the invention relates to a method for diagnosing a traction battery which has several cells interconnected by means of a circuit, and a battery management system by which at least one cell state variable can be detected for each of the cells, wherein at least one logical cell and/or at least one string can be formed by the circuit.

A traction battery is specifically designed to supply energy to an electric powertrain for propelling a vehicle. Therefore, a traction battery is typically a high-voltage storage device with exceptionally high power output and accordingly comprises a large number of cells that can be interconnected via a circuit. The method described here is particularly advantageous for traction batteries, as they can have a complex circuit with many cells. For conventional batteries, which contain only a few cells, the added value of the method is less pronounced; however, the method can still be useful for conventional batteries. The individual cells can be lithium-ion and/or sodium-ion cells. The circuit connects the cells according to a circuit diagram. Several cells can be connected in parallel, forming so-called logic cells. Several cells connected in series via the circuit form a string. Multiple strings can be connected in series and/or parallel, thus characterizing the battery or traction battery.

• In einem ersten Schritt wird die wenigstens eine Zellzustandsgröße für jede Zelle durch eine Diagnoseeinheit erfasst beziehungsweise ausgelesen.
• In einem zweiten Schritt wird ein jeweiliger Einflusswert der jeweiligen Zelle, der wenigstens einen logischen Zelle und/oder des wenigstens einen Strangs auf einem Erreichbarkeitswert eines Batterieparameters anhand der erfassten Zellzustandsgrößen ermittelt beziehungsweise bestimmt.

The method according to the invention comprises the following steps:

• In a first step, at least one cell state parameter for each cell is recorded or read out by a diagnostic unit.
• In a second step, a respective influence value of the respective cell, the at least one logical cell and/or the at least one string on an achievability value of a battery parameter is determined or calculated based on the recorded cell state variables.

Finally, in a third step, a switch configuration is determined based on the identified influence values and depending on the reachability value, whereby the circuit configuration specifies the circuit or a connection that can be realized by means of the circuit, through which the battery parameter assumes the reachability value.

The diagnostic unit can be designed as a component of the battery management system or as an additional component within the traction battery. Alternatively, or in addition, the diagnostic unit can be designed as an external device that can be connected to the traction battery or its battery management system. The respective cell state parameter can be a measured value, such as voltage, and/or a code number for identifying malfunctions, a so-called "diagnostic trouble code" (DTC).

The respective cell state parameter thus describes, in particular, the state of the respective cell. This state influences the battery parameter, with the influence value describing a change in the battery parameter. Based on the respective influence value, it can be determined how the battery parameter changes when the corresponding cell is present in the circuit or is bypassed via the circuit configuration. The battery parameter can be, for example, the total capacity or usable capacity and/or the energy of the battery. In the case of capacity, the achievable value can, for example, describe the maximum capacity achievable based on the realizable circuits, taking the cell states into account. The circuit configuration can thus, in particular, represent a bypass map that specifies which cells should be bypassed or removed from the circuit to achieve the achievable value of the battery parameter. Thus, the bypass map or the circuit configuration specifies which cells are to be removed from the circuit to influence the battery parameter in such a way that it reaches the desired achievable value.

In other words, the procedure offers a diagnostic service, particularly for workshop personnel, whereby the circuit configuration can, for example, generate a list of cells to be bypassed and output to a display. This allows for a simple decision as to whether a corresponding repair measure on the traction battery is economically viable. Based on the recorded condition values or cell state parameters, cells that could potentially be bypassed to improve the battery's condition can be identified, thus enabling a change in the battery's condition through a bypass scenario.

Through an algorithm, primarily internal, provided and executed by the diagnostic unit, a battery diagnosis can be performed. This determines which cells should be bypassed to set the desired or optimal value—the reachability value—of the battery parameter. The reachability value can be used to restore operational capability. Furthermore, the usable energy and/or capacity of the battery can be improved based on the reachability value, with the potential energy or capacity gain also being determined and displayed. Additionally or alternatively, the battery's performance can be improved, with the potential performance gain also being displayed as a key performance indicator. Finally, the self-discharge rate can be determined as a battery parameter, allowing for its improvement, with the potential reduction also being displayed as a key performance indicator.

For this process, it is particularly useful and advantageous if, for example, the battery management system or diagnostic unit provides relevant information, such as the circuit configuration, via a communication interface or means like CAN, LIN, and/or Ethernet. This allows workshop personnel to read this information directly from the battery and thus implement measures to repair the battery and achieve the desired operating range. A workshop diagnostic tool connected to the diagnostic unit can read this information directly from the battery, allowing, for example, the display of the potentially achievable operating range in addition to the circuit configuration.

The method according to the invention offers the advantage that, in particular, costs for troubleshooting and/or repair can be reduced or made significantly lower. Furthermore, the vehicle owner can be informed about repair costs very quickly. In addition, a prediction of the potential benefit of the repair can be generated, thus enabling an informed decision regarding the feasibility of the repair.

In an advantageous embodiment of the invention, the battery parameter describes operational capability, energy, capacity, performance, and/or self-discharge rate. In other words, the battery parameter characterizes the state of the entire battery, in particular whether it is operational and thus functional. Additionally or alternatively, the battery parameter describes energy or energy quantity of the battery and/or capacity, as well as power that can be provided by the battery. Furthermore, the self-discharge rate can describe the self-discharge of the battery over time. The associated achievability value, for example, for operational capability, can indicate whether battery operation can be restored or not. Thus, the achievability value itself can be determined. Therefore, in the event of battery failure due to cell damage, the achievability value is used to assume battery operation, and a circuit is optimized based on this so that the battery is at least usable again.

Furthermore, accessibility can describe usable energy or capacity, maximum performance, or minimum self-discharge rate. Thus, depending on the type of battery parameter, the accessibility value specifies the most advantageous circuit configuration. The ability of the battery to describe various battery properties offers the advantage that the method is particularly useful for various diagnostic applications. Additionally, the traction battery's operational capability can be restored simply and cost-effectively by directly selecting the appropriate cells for the circuit configuration or based on the circuit configuration.

In an advantageous embodiment of the invention, at least one cell state parameter is a capacitance, a voltage, a resistance, a connectivity parameter (characterizing, for example, detached cell connectors), and/or a diagnostic trouble code (DTC) for the respective cell. In other words, the cell state parameter, which can be acquired as a measured value, for example, by a sensor for the respective cell of the battery management system, describes the state of the respective cells. The DTC can, for example, describe or characterize a detached voltage sensor. Based on these parameters, a malfunction of the respective cell can be advantageously detected. This offers the advantage that the respective influence on the battery parameter can be determined particularly efficiently.

In a further advantageous embodiment of the invention, a list of cells to be bypassed is generated based on the circuit configuration. These cells must be bridged in the circuit to achieve the required level. In other words, a list identifying the relevant cells can be derived from the circuit configuration to provide workshop personnel with easier access for repairs. This offers the advantage that the method can be used particularly effectively for repairing traction batteries.

In a further advantageous embodiment of the invention, the diagnostic unit has an output device and/or is connected to, or is connected to, a display device, so that the list and/or further information is output at the output device. In other words, the diagnostic unit is designed such that the list can be output at an output device, and this list can be combined with further information. For example, such information can be used to determine what effect bridging a particular cell has on the achievability value of the battery parameter. For example, a ranking can also be created showing which cells or combinations of cells can be bridged to achieve corresponding achievability values. A comparison can also be made, for example, so that it is clear what bridging one cell has on the achievability value of the capacity and bridging other cells has on the achievability value of the performance. This has the advantage that the method enables particularly efficient repair and maintenance of the traction battery.

In a further advantageous embodiment of the invention, based on the respective cell state variable, a current circuit, i.e., based on which cells are already bridged, the following is carried out for each strand of the For at least one string, and in particular for multiple strings, the attainability value of the battery parameter is determined. In other words, if the traction battery has several strings, especially those connected in parallel, an attainability value of the battery parameter or an attainability value of the respective string parameter is calculated for each string, so that the battery parameter or its attainability value can be determined, particularly easily, based on these values. This offers the advantage that the method can be carried out with particular efficiency.

In a further advantageous embodiment of the invention, multi-factor optimization is performed for several operating parameters and their respective achievability values. In other words, when determining an achievability value, the influence of a circuit configuration determined for this purpose on other battery parameters is taken into account. Thus, changes in several parameters for a corresponding bridging scenario are considered, so that, for example, a circuit configuration may become less attractive. This offers the advantage that, in particular, a global recommendation for a circuit configuration can be made depending on several mutually influencing battery parameters.

A second aspect of the invention relates to a diagnostic unit which is designed to perform a method according to the first aspect of the invention.

Advantageous embodiments and further developments, as well as advantages of the first aspect of the invention, are to be regarded as advantageous embodiments and further developments, as well as advantages of the second aspect of the invention, and vice versa.

In an advantageous embodiment of the invention, the diagnostic unit is configured as a component of a traction battery for a motor vehicle. In other words, the diagnostic unit, which is specifically configured to execute an algorithm by which the steps of the method according to the first aspect of the invention can be carried out, is a component and thus an integral part of the traction battery. The diagnostic unit can, in particular, be a component of the traction battery's battery management system. This offers the advantage that the traction battery itself can perform the method, and thus, upon arrival at a workshop, all data for a repair can be readily available via a suitable interface.

A third aspect of the invention relates to a motor vehicle which is designed to perform a method according to the first aspect of the invention and/or which has a diagnostic unit according to the second aspect of the invention.

Advantageous embodiments and further developments, as well as advantages of the first aspect of the invention, are to be regarded as advantageous embodiments and further developments, as well as advantages of the second aspect and/or third aspect of the invention, and vice versa.

Further advantages, features, and details of the invention will become apparent from the following description of a preferred embodiment and from the drawing. The features and combinations of features mentioned above in the description, as well as those mentioned below in the figure description and/or shown in the figures alone, can be used not only in the combinations specified, but also in other combinations or individually, without departing from the scope of the invention.

• 1 ein schematisches Ablaufdiagramm für ein Verfahren zur Diagnose einer Traktionsbatterie eines Kraftfahrzeugs; und
• 2 eine schematische Ansicht der Traktionsbatterie, an welcher das Diagnoseverfahren durchgeführt werden kann.

This shows:

• 1 a schematic flowchart for a procedure for diagnosing a traction battery of a motor vehicle; and
• 2 a schematic view of the traction battery on which the diagnostic procedure can be performed.

1 Figure 1 shows a schematic flowchart for a method for diagnosing a traction battery 10 of a motor vehicle, which comprises several cells 14 connected by a circuit 12 and a battery management system 16. Through the battery management system 16, and in particular the sensors of the respective cell 14 connected to it, at least one Cell state parameters, such as voltage and/or a fault identification code, are recorded.

Circuit 12 can, for example, form at least one logic cell, which represents a parallel connection of at least two cells 14. Additionally or alternatively, at least one string can be formed, which is created by a series connection of cells 14 and/or logic cells. Several of these strings can be connected in series and/or parallel.

In the traction battery 10, individual cells 14, which are primarily lithium-ion and/or sodium-ion cells, may become defective over time. Furthermore, cell connectors 18, which primarily implement the circuit 12, may also become defective and, for example, break, which can lead to the traction battery 10 becoming inoperable.

Furthermore, the capacity or self-discharge of the traction battery 10 can change over time, for example, due to individual cells 14. This can make repair or maintenance advantageous. To enable workshop personnel to carry out repairs or maintenance particularly efficiently, it would be desirable for the procedure presented here, which comprises steps S1 to S3 below, to provide workshop personnel with a particularly advantageous diagnostic tool, thus simplifying the repair process.

In the first step S1, at least one cell state parameter for each cell 14 is recorded by a diagnostic unit 20.

In the second step S2, the influence of each cell 14, at least one logical cell, and/or at least one string on the attainability value of a battery parameter is determined based on the recorded cell state variables. In other words, the cell state variable characterizes the respective state of the cell, which influences the battery parameter. The battery parameter can, for example, represent total capacity or usable capacity, energy or usable energy, operational capability, battery performance, or battery self-discharge rate. That is, the state of the respective cell influences the battery parameter, with the magnitude of the influence being determined based on the influence value in the second process step S2.

In a third step S3, a circuit configuration is determined based on the determined influence values and depending on the reachability value, whereby the circuit configuration specifies the circuit through which the battery parameter assumes the reachability value.

It should be noted that, in addition to the procedure presented here, the diagnostic unit 20 is also introduced. The diagnostic unit 20 is configured to perform the steps of the procedure, for example, by means of a suitable algorithm of an electronic computing device or an integrated circuit. Advantageously, the diagnostic unit 20 is a component of the traction battery 10 and, in particular, also a component of the battery management system 16, or communicates with it via a communication interface. The diagnostic unit 20 can be connected to an output device 22 via another communication interface, such as a CAN bus or the like. Furthermore, a motor vehicle is also presented here, which is configured to perform the procedure and/or includes a diagnostic unit 20.

A diagnostic service is provided, allowing workshop personnel, for example via output device 22, to view a circuit configuration. This configuration indicates which cells 14 need to be bridged to influence the battery parameters, particularly to a beneficial degree. Advantageously, a list is derived from the circuit configuration, so that the workshop personnel can directly view a list of the cells 14 to be bridged. This list can be further enhanced with information to help workshop personnel decide which repair or maintenance measure for the traction battery 10 is most appropriate.

The following is an example list of additional information: priority Cell number Reason for bridging Cumulative gain in available battery energy in % 1 85 Improve usable energy/capacity of the battery 10% 2 8 Improve usable energy/capacity of the battery 12% 3 102 Improve usable energy/capacity of the battery 13%

The following section presents a possible embodiment of the diagnostic algorithm and the diagnostic unit 20 for each type of battery parameter. The respective algorithm essentially performs the steps according to... 1 provided.

• Hierzu werden Fehlerzustände des Batteriemanagementsystems, beispielsweise mit einer Liste, anhand welcher die Fehlzustände beziehungsweise deren zugehörige DTC-Nummer auf einzelner und/oder logischer Zellen zurückzuführen sind, und durch Überbrücken behoben werden können, abgeglichen.

For the first embodiment, the operational capability can be determined as the reachability value in the event of battery failure:

• For this purpose, fault conditions of the battery management system are compared, for example with a list which indicates that the fault conditions or their associated DTC number can be traced back to individual and/or logical cells and can be rectified by bridging.

Examples of corresponding faults of cells 14 that can affect operability include broken cell connectors 18 and broken voltage sensors of cell 14, which are assigned to the battery management system 16. Furthermore, the resistance of a cell 14 may be above a critical value and/or the capacity of a cell 14 may be below a critical value. The battery management system 16 can determine the fault codes for the respective cell 14, and instructions for the affected cell 14, as well as for plausibility checks and repairs, in particular for bypassing the respective cell 14 based on the circuit configuration, can be output at the output device 22.

In the second embodiment, the battery parameter energy or capacity, or the associated reachability value, is determined as the usable energy or the usable capacity of the traction battery 10:

• 1. Die Liste wird nach aufsteigender Kapazität k(0)...k(n-1), wobei k(0)=min(k) ist, geordnet
• 2. Es wir die aktuell verfügbare Energie der Batterie E(0) berechnet wobei : $$E\left(0\right)=k\left(0\right)*n*{\displaystyle {\int }_{SOCMin}^{SOCMax}U\left(SOC\right)dSOC\cong k\left(0\right)*n*U_{celldischarge}}*$$
• 3. Optimierungsoptionen:
  • (wobei Option1 die bevorzugte Variante ist da sie eine höhere Wahrscheinlichkeit hat das Optimum zu finden und Option 2 weniger Rechenzeit benötigt, aber Anfällig für die Anzeige einer zu kleinen Zahl an zu überbrückenden Zellen ist)
    1. 1. In einer Schleife wird solange die maximal entnehmbare Energie nach Überbrücken einer weiteren Zelle bestimmt, bis eine maximale Anzahl zu überbrückender Zellen j_max erreicht ist. Zusätzlich kann in derselben Schleife auch die Berechnung der Leistungswerte vorgenommen werden, um so den Einfluss der Reparaturmaßname auf diesen Batterieparameter mit in der Liste möglicher Reparaturmaßnamen auszugeben. j=0; while j<j_max; j=j+1
  $$E\left(j\right)=k\left(j\right)*\left(n-j\right)*{\displaystyle {\int }_{SOCMin}^{SOCMax}U\left(SOC\right)dSOC\cong k\left(j\right)*n*U_{celldischarge}}*$$ end Anschließend werden alle Werte verworfen, die nach dem Eintrag mit maximaler entnehmbarer Energie kommen.
• 2. In einer Schleife wird solange die maximal entnehmbare Energie nach Überbrücken einer weiteren Zelle 14 bestimmt, bis diese zum ersten Mal kleiner als E(0) plus einem Schwellwert ks**, welcher größer gleich oder kleiner als 0 sein kann, ist. Zusätzlich kann in derselben Schleife auch die Berechnung der Leistungswerte vorgenommen werden, um so den Einfluss der Reparaturmaßname auf diesen Batterieparameter mit in der Liste möglicher Reparaturmaßnamen auszugeben. j=0; while or(j<1, E(l)≤E(0) + ks); j=j+1 $$E\left(j\right)=k\left(j\right)*\left(n-j\right)*{\displaystyle {\int }_{SOCMin}^{SOCMax}U\left(SOC\right)dSOC\cong k\left(j\right)*n*U_{celldischarge}}*$$ end
• 4. Nun wird eine Liste der Zellpositionen der Zellen bis j -1 zusammen mit dem Wert E(l), (E(l)-E(0)) bzw. (E(l)-E(0))/E(0) zwischengespeichert oder direkt ausgegeben, wobei E(I) der Energie entspricht bis zu der die Batterie potenziell verbessert werden kann (E(l)-E(0)), dem Betrag der potenziellen Verbesserung und (E(l)-E(0))/E(0) der prozentualen Verbesserung wenn alle Zellen 14 bis zu diesem Eintrag überbrückt werden.
• 5. Falls der Wert vorberechnet und gespeichert wurde, wird er auf Anforderung per Diagnose ausgegeben, ansonsten live berechnet.

Using a list which corresponds to the state of the respective cell 14, for example whether it is already bridged or not, the number of unbridged cells n and their estimated capacity k _i, the following algorithm can be implemented for each string of the traction battery 10 (with SOC _Max = maximum permissible state of charge, SOC _Min = minimum permissible state of charge, SOC _ref = reference state of charge to specify a performance characteristic):

• 1. The list is ordered according to ascending capacity k(0)...k(n-1), where k(0)=min(k).
• 2. The currently available energy of the battery E(0) is calculated where: $$E\left(0\right)=k\left(0\right)*n*{\displaystyle {\int }_{SOCMin}^{SOCMax}U\left(SOC\right)dSOC\cong k\left(0\right)*n*U_{celldischarge}}*$$
• 3. Optimization options:
  • (where Option 1 is the preferred option because it has a higher probability of finding the optimum, and Option 2 requires less computing time but is prone to displaying too few cells to bridge)
    1. 1. In a loop, the maximum extractable energy after bridging another cell is determined until a maximum number of cells to be bridged, j_{_max,} is reached. Additionally, the power values can also be calculated in the same loop to determine the influence of the bridging process. The repair measure should include this battery parameter in the list of possible repair measures. j=0; while j<j _max ; j=j+1
  $$E\left(j\right)=k\left(j\right)*\left(n-j\right)*{\displaystyle {\int }_{SOCMin}^{SOCMax}U\left(SOC\right)dSOC\cong k\left(j\right)*n*U_{celldischarge}}*$$ Finally, all values that follow the entry with maximum extractable energy are discarded.
• 2. In a loop, the maximum extractable energy after bridging another cell 14 is determined until it is first less than E(0) plus a threshold value ks**, which can be greater than or equal to, or less than, 0. Additionally, the power values can also be calculated in the same loop to output the effect of the repair measure on this battery parameter in the list of possible repair measures. j=0; while or(j<1, E(l)≤E(0) + ks); j=j+1 $$E\left(j\right)=k\left(j\right)*\left(n-j\right)*{\displaystyle {\int }_{SOCMin}^{SOCMax}U\left(SOC\right)dSOC\cong k\left(j\right)*n*U_{celldischarge}}*$$ end
• 4. Now, a list of the cell positions of the cells up to j -1 is temporarily stored or directly output along with the value E(l), (E(l)-E(0)) or (E(l)-E(0))/E(0), where E(l) corresponds to the energy up to which the battery can potentially be improved (E(l)-E(0)), the amount of the potential improvement, and (E(l)-E(0))/E(0) the percentage improvement if all cells 14 up to this entry are bridged.
• 5. If the value has been pre-calculated and saved, it will be output on request via diagnostics; otherwise, it will be calculated live.

This means: * The degree of simplification is application-specific. ** ks can either be fixed or dynamically scaled with the accuracy of the cell capacity estimates. Thus, ks can also be a vector of length n.

1. 1. Die Liste wird nach absteigendem Zellinnenwiderstand R(0)...R(n-1), wobei R(0)=max(R), geordnet
2. 2. Es wird die aktuell verfügbare Leistungsfähigkeit der Batterie P(0) berechnet zum Beispiel über folgende Formel : $$P_0=\frac{{\left(U\left(SO{C}_{ref}\right)-U_{min,lim}\right)}^3}{R_0}*n$$
3. 3. Optimierungsoptionen:
   • (wobei Option1 die bevorzugte Variante ist da sie eine höhere Wahrscheinlichkeit hat das Optimum zu finden und Option 2 weniger Rechenzeit benötigt, aber Anfällig für die Anzeige einer zu kleinen Zahl an zu überbrückenden Zellen ist)
     1. 1. In einer Schleife wird solange die verfügbare Leistungsfähigkeit nach Überbrücken einer weiteren Zelle bestimmt bis eine maximale Anzahl zu überbrückender Zellen j_max erreicht ist. j=0; while j<k; j=j+1 $$\text{P}\left(\text{I}\right)=\frac{{\left(U\left(SO{C}_{ref}\right)-U_{min,lim}\right)}^3}{R_j}*\text{n}-\text{j}$$ end Anschließend werden alle Werte verworfen, die nach dem Eintrag mit maximaler Leistungsfähigkeit kommen.
     2. 2. In einer Schleife wird solange die verfügbare Leistungsfähigkeit nach Überbrücken einer weiteren Zelle bestimmt, bis diese zum ersten Mal kleiner als P(0) plus einem Schwellwert ps**, welcher größer oder gleich 0 ist, ist. j=0; while or(j<1, P(l)≤P(0) + ps); j=j+1 $$\text{P}\left(\text{I}\right)=\frac{{\left(U\left(SO{C}_{ref}\right)-U_{min,lim}\right)}^3}{R_j}*\text{n}-\text{j}$$ end
4. 4. Nun wird eine Liste der Zellpositionen der Zellen l mit l =0 bis j -1 mit dem Wert P(l), (P(l)-P(0)) bzw. (P(l)-P(0))/P(0) zwischengespeichert oder direkt ausgegeben, wobei P(l) der Leistung entspricht bis zu der die Batterie potenziell verbessert werden kann (P(l)-P(0)), dem Betrag der potenziellen Verbesserung und (P(l)-P(0))/P(0) der prozentualen Verbesserung wenn alle Zellen bis zu diesem Eintrag überbrückt werden.
5. 5. Falls der Wert vorberechnet und gespeichert wurde wird er auf Anforderung per Diagnose ausgegeben, ansonsten live berechnet.

If the battery's performance is changed as a reachability value or associated battery parameter, the following algorithm can be carried out as a third example based on the performance at a reference state of charge:

1. 1. The list is ordered according to descending cell internal resistance R(0)...R(n-1), where R(0)=max(R).
2. 2. The currently available power of the battery P(0) is calculated, for example using the following formula: $$P_0=\frac{{\left(U\left(SO{C}_{ref}\right)-U_{min,lim}\right)}^3}{R_0}*n$$
3. 3. Optimization options:
   • (where Option 1 is the preferred option because it has a higher probability of finding the optimum, and Option 2 requires less computing time but is prone to displaying too few cells to bridge)
     1. 1. In a loop, the available processing power after bridging another cell is determined until a maximum number of cells to be bridged, j _{_max,} is reached. j_max = 0; while j<k;j_max = j + 1 $$\text{P}\left(\text{I}\right)=\frac{{\left(U\left(SO{C}_{ref}\right)-U_{min,lim}\right)}^3}{R_j}*\text{n}-\text{j}$$ Finally, all values that come after the entry with maximum performance are discarded.
     2. 2. In a loop, the available power after bridging another cell is determined until it is first less than P(0) plus a threshold value ps**, which is greater than or equal to 0. j=0; while or(j<1, P(l)≤P(0) + ps); j=j+1 $$\text{P}\left(\text{I}\right)=\frac{{\left(U\left(SO{C}_{ref}\right)-U_{min,lim}\right)}^3}{R_j}*\text{n}-\text{j}$$ end
4. 4. Now, a list of the cell positions of cells l with l = 0 to j - 1 with the value P(l), (P(l)-P(0)) or (P(l)-P(0))/P(0) is temporarily stored or directly output, where P(l) corresponds to the power up to which the battery can potentially be improved (P(l)-P(0)), the amount of the potential improvement and (P(l)-P(0))/P(0) the percentage improvement if all cells up to this entry are bridged.
5. 5. If the value has been pre-calculated and saved, it will be output via diagnostics on request; otherwise, it will be calculated live.

This means: * The degree of simplification is application-specific. ** ps can either be fixed or dynamically scaled with the accuracy of the cell internal resistance estimate. Thus, ps can also be a vector of length n.

1. 1. Die Liste wird nach absteigender Selbstentladung S(0)...S(n-1), wobei S(0)=max(S), geordnet
2. 2. Der aktuelle Balancing bedarf wird durch S(0) gegeben
3. 3. Nun wird die erste Zelle gesucht deren Selbstentladerate unter dem Schwellwert ss liegt. j=0; while or (j<1, S(j)<ss); j=j+1 end
4. 4. Nun wird eine Liste der Zellpositionen der Zellen l mit l =0 bis j -1 ausgegeben, welche überbrückt werden müssen, um die Selbstentladung auf ein akzeptables Niveau abzusenken.
5. 5. Falls der Wert vorberechnet und gespeichert wurde, wird er auf Anforderung per Diagnose ausgegeben, ansonsten live berechnet.

** ss kann entweder festgelegt sein, oder dynamisch mit der Genauigkeit der Schätzung der Selbstentladung skaliert werden. Somit kann ss auch ein Vektor der Länge n sein.As a further example, an algorithm is outlined which should enable a particularly low achievability value for the self-discharge rate as a battery parameter. Here, too, an algorithm is implemented for each string of the battery based on the list of cell states, the number of unbridged cells, and their estimated self-discharge:

1. 1. The list is ordered according to descending self-discharge S(0)...S(n-1), where S(0)=max(S).
2. 2. The current balancing requirement is given by S(0).
3. 3. Now, the first cell whose self-discharge rate is below the threshold value ss is sought. j=0; while or (j<1, S(j)<ss); j=j+1 end
4. 4. Now a list of the cell positions of cells l with l = 0 to j - 1 is output, which must be bridged to reduce the self-discharge to an acceptable level.
5. 5. If the value has been pre-calculated and saved, it will be output on request via diagnostics; otherwise, it will be calculated live.

** ss can either be fixed or dynamically scaled with the accuracy of the self-discharge estimate. Thus, ss can also be a vector of length n.

This reveals that bridging individual cells (14) has different effects on the respective battery parameters. Therefore, it would be advantageous to consider multiple battery parameters when determining the circuit configuration. A circuit configuration that benefits one battery parameter might negatively impact another, thus reducing its attractiveness. For example, the self-discharge rate can reduce capacity. Therefore, the lists or tables could either be directly enriched with the other predicted parameters, or a second diagnostic service could be offered that outputs the battery parameters energy, power, and voltage for a specific bridging scenario, or provides a global recommendation using multi-factor optimization.

The procedure presented here demonstrates a diagnostic tester with functionality for recommending repair measures on traction batteries 10.

Reference symbol list

10

Traction battery

12

circuit

14

cell

16

Battery management system

18

Cell connectors

20

Diagnostic unit

22

Output device

S1

First step

S2

Second step

S3

Third step

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• JP 5 453 769 B2 [0004]
• JP 5 733 648 B2 [0004]

Claims (10)

Method for diagnosing a traction battery (10) of a motor vehicle, comprising several cells (14) interconnected by means of a circuit (12), and a battery management system (16) by which at least one cell state variable can be detected for each of the cells (14), wherein at least one logic cell and/or at least one string can be formed by the circuit (12), comprising the steps: - Detect the at least one cell state variable for each cell (14) by a diagnostic unit (20); (S1) - Determine a respective influence value of the respective cell (14), the at least one logic cell and/or the at least one string on an attainability value of a battery parameter based on the detected cell state variables; (S2) and - Determine a circuit configuration based on the determined influence values and as a function of the attainability value, wherein the circuit configuration specifies the circuit (12) by which the battery parameter assumes the attainability value. (S3) Procedure according to Claim 1 characterized in that the battery parameter describes an operational capability, an energy, a capacity, a performance and/or a self-discharge rate. Procedure according to Claim 1 or 2 characterized in that the at least one cell state variable comprises a capacitance, a voltage, a resistance, a connectivity and/or a malfunction indicator for the respective cell (14). Method according to one of the preceding claims, characterized in that a list of cells (14) to be bridged is created based on the circuit configuration, which are to be bridged in the circuit (12) to achieve the reachability value. Procedure according to Claim 4 , characterized in that the diagnostic unit (20) has an output device (22) and/or is connected to an output device (22) at which the list and/or further information is output. Method according to one of the preceding claims, characterized in that the achievability value of the battery parameter is determined for each string based on the respective cell state variables of a current circuit (12). Method according to one of the preceding claims, characterized in that a multi-factor optimization is performed for several battery parameters and their respective reachability values. Diagnostic unit (20) which is designed to perform a procedure according to one of the preceding claims. Diagnostic unit (20) after Claim 8 , characterized in that the diagnostic unit (20) is designed as a component of a traction battery (10) for a motor vehicle. Motor vehicle which is designed to perform a method according to one of the preceding claims, and/or which has a diagnostic unit (20) according to Claim 8 or 9 exhibits.