METHOD FOR OPERATING A BATTERY MODULE

Abstract

A method for operating a battery module, including multiple battery cells. The method includes: a) ascertaining cell voltages of the individual battery cells at a starting point in time; b) ascertaining at the starting point in time an average cell voltage from the cell voltages of the battery cells ascertained at the starting point in time; c) estimating the cell voltage of at least one battery cell at an operating point in time if the cell voltage of the battery cell is not measurable at the operating point in time, taking into account the cell voltage of the battery cell ascertained at the starting point in time, the average cell voltage ascertained at the starting point in time, and an average cell voltage ascertained at the operating point in time.

Claims

1-10. (canceled)

11. A method for operating a battery module, including multiple individual battery cells, the method comprising the following steps: a) ascertaining a cell voltage of each of the individual battery cells at a starting point in time; b) ascertaining an average cell voltage from the cell voltages ascertained at the starting point in time of the battery cells; c) estimating a cell voltage of at least one battery cell of the battery cells at an operating point in time when the cell voltage of the battery cell is no longer measurable at the operating point in time, wherein the cell voltage of the battery cell ascertained at the starting point in time, the average cell voltage ascertained at the starting point in time, and an average cell voltage ascertained at the operating point in time are taken into account when estimating the cell voltage of the battery cell at the operating point in time, and wherein the average cell voltage ascertained at the operating point in time is ascertained from the cell voltages of remaining ones of the battery cells measured at the operating point in time.

12. The method as recited in claim 11, wherein the following steps are carried out after step b): ascertaining an upper threshold value as a sum of the average cell voltage ascertained at the starting point in time and a tolerance value; ascertaining a lower threshold value as a difference of the average cell voltage ascertained at the starting point in time and a tolerance value; classifying those battery cells whose cell voltage at the starting point in time is higher than the upper threshold value, as good battery cells; classifying those battery cells whose cell voltage at the starting point in time is less than the lower threshold value, as bad battery cells; classifying those battery cells whose cell voltage at the starting point in time is less than the upper threshold value and higher than the lower threshold value, as neutral battery cells

13. The method as recited in claim 12, wherein the cell voltage of a good battery cell at the operating point in time is estimated as a sum of the average cell voltage ascertained at the operating point in time and a difference of the cell voltage of the good battery cell ascertained at the starting point in time and the average cell voltage ascertained at the starting point in time.

14. The method as recited in claim 13, wherein a charging of the good battery cell and/or of the battery module is omitted when the cell voltage of the good battery cell estimated at the operating point in time is greater than an upper threshold value.

15. The method as recited in claim 13, wherein the cell voltage of a bad battery cell at the operating point in time is estimated as a sum of the average cell voltage ascertained at the operating point in time and a difference of the cell voltage of the bad battery cell ascertained at the starting point in time and the average cell voltage ascertained at the starting point in time.

16. The method as recited in claim 15, wherein a discharging of the bad battery cell and/or of the battery module is omitted when the cell voltage of the bad battery cell estimated at the operating point in time is less than a lower limiting value.

17. The method as recited in claim 13, wherein the cell voltage of a neutral battery cell at the operating point in time is estimated as the average cell voltage ascertained at the operating point in time.

18. The method as recited in claim 17, wherein a charging of the neutral battery cell and/or of the battery module is omitted when the cell voltage of the neutral battery cell estimated at the operating point in time is greater than an upper limiting value and/or when the cell voltage of at least one good battery cell measured at the operating point in time is greater than the upper limiting value.

19. The method as recited in claim 17, wherein a discharging of the neutral battery cell and/or of the battery module is omitted, when the cell voltage of the neutral battery cell estimated at the operating point in time is less than a lower limiting value and/or when the cell voltage of at least one bad battery cell measured at the operating point in time is less than the lower limiting value.

20. The method as recited in claim 11, wherein the method is used in a battery module of a purely electric vehicle, or of a hybrid vehicle, or of a plug-in-hybrid vehicle, or of an e-bike.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Specific embodiments of the present invention are explained in greater detail with reference to the figures and to the description below.

[0038] FIG. 1 schematically shows a representation of a battery module including multiple battery cells.

[0039] FIG. 2 shows a diagram for representing cell voltages of the battery cells of the battery module at a starting point in time.

[0040] FIG. 3 schematically shows a representation of a method for operating a battery module, in accordance with an example embodiment of the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0041] In the following description of the specific embodiments of the present invention, identical or similar elements are identified by the same reference numerals, a repeated description of these elements in individual cases being omitted. The figures represent only schematically the subject matter of the present invention.

[0042] FIG. 1 schematically shows a representation of a battery module 5 including multiple battery cells 2. Battery cells 2 in the present case are electrically interconnected in series. Each battery cell 2 includes an electrode unit, which includes one anode and one cathode each. The anode of the electrode unit is connected to a negative terminal of battery cell 2. The cathode of the electrode unit is connected to a positive terminal of battery cell 2. To serially interconnect battery cells 2 of battery module 5, the negative terminal of a battery cell 2 is electrically connected in each case to the positive terminal of adjacent battery cell 2.

[0043] Battery module 5 also includes a measuring circuit 50. Measuring circuit 50 is used to measure cell voltages U of battery cells 2 of battery module 5 and to measure a total voltage UGes of battery module 5. Total voltage UGes of battery module 5 corresponds in the present case to the sum of cell voltages U of individual battery cells 2. Battery cells 2 are connected to measuring circuit 50 with the aid of measuring lines.

[0044] FIG. 2 shows a diagram for representing cell voltages US of battery cells 2 of battery module 5 represented in FIG. 1 at a starting point in time. Battery module 5 is intact at the starting point in time, in particular, none of the measuring lines are interrupted, and all cell voltages US of all battery cells 2 are measurable at the starting point in time.

[0045] An average cell voltage MS at a starting point in time is ascertained from all cell voltages US of all battery cells 2 of battery module 5 ascertained at the starting point in time. Average cell voltage MS at the starting point in time is ascertained in the present case as an arithmetic average value of all ascertained values of cell voltages US at the starting point in time of individual battery cells 2.

[0046] An upper threshold value SO is subsequently ascertained as the sum of ascertained average cell voltage MS at the starting point in time and a tolerance value T. A lower threshold value SU is also ascertained as the difference of ascertained average cell voltage MS at the starting point in time and a tolerance value T. In the present example, tolerance values T, which are used to ascertain upper threshold value SO and lower threshold value SU, are identical. Aforementioned tolerance value T is, predefined, for example, by a known measuring accuracy of measuring circuit 50.

[0047] Battery cells 2, whose cell voltage US at the starting point in time is higher than upper threshold value SO, are then classified as good battery cells 2. Similarly, battery cells 2, whose cell voltage US at the starting point in time is less than lower threshold value SU, are classified as bad battery cells 2. Battery cells 2, whose cell voltage US at the starting point in time is less than upper threshold value SO or equal to upper threshold value SO and higher than lower threshold value SU or equal to lower threshold value SU, are also classified as neutral battery cells 2. As is apparent from the diagram, eight battery cells 2 are classified in the present case as neutral battery cells 2, one battery cell 2 is classified as good battery cell 2, and one battery cell 2 is classified as bad battery cell 2.

[0048] A charging of a battery cell 2 is omitted if its measured cell voltage UB at an operating point in time is greater than a maximum allowable charging voltage CVL. A charging of a battery cell 2 is omitted if its estimated cell voltage UB at an operating point in time is greater than an upper limiting value GO. Upper limiting value GO is, for example, 90% of the maximum allowable charging voltage CVL. In this way, damage as a result of an overcharge of battery cell 2 is reliably prevented.

[0049] A discharging of a battery cell 2 is omitted if its measured cell voltage UB at an operating point in time is less than a minimum allowable charging voltage DVL. A discharging of a battery cell 2 is omitted if its estimated cell voltage UB at an operating point in time is less than a lower limiting value GU. The lower limiting value GU is, for example, 110% of the minimum allowable charging voltage DVL. In this way, damage as a result of a deep discharge of battery cell 2 is reliably prevented.

[0050] FIG. 3 schematically shows a representation of a method for operating a battery module 5, in accordance with an example embodiment of the present invention.

[0051] In a starting step 100, cell voltages US of battery cells 2 of battery module 5 are ascertained at a starting point in time. Average cell voltage MS at the starting point in time is ascertained from cell voltages US of battery cells 2 ascertained at the starting point in time. Similarly, upper threshold value SO is ascertained as the sum of average cell voltage MS at the starting point in time and tolerance value T. Lower threshold value SU is also ascertained as the difference of average cell voltage MS at the starting point in time and of tolerance value T.

[0052] In a following step 101, those battery cells 2, whose cell voltage US at the starting point in time is higher than upper threshold value SO, are classified as good battery cells 2. Those battery cells 2, whose cell voltage US at the starting point in time is less than lower threshold value SU, are also classified as bad battery cells 2. Similarly, those battery cells 2, whose cell voltage US at the starting point in time is less than upper threshold value SO or equal to upper threshold value SO and higher than lower threshold value SU or equal to lower threshold value SU, are classified as neutral battery cells 2.

[0053] In a next step 102, an error occurs at one operating point in time. For example, a measuring line of battery module 5 is interrupted. Because of this error, at least cell voltage UB of at least one battery cell 2 is no longer measurable at the operating point in time. In battery module 5 depicted in FIG. 1, an interruption of a measuring line may also cause cell voltages UB of two adjacent battery cells 2 to no longer be measurable at the operating point in time.

[0054] In a following step 103, the battery management system determines which type of error is present based on all available measuring values.

[0055] If, for example, a short-circuit is present in one of battery cells 2, then a short-circuit current flows in relevant battery cell 2, which causes a strong temperature increase of battery cell 2. The battery management system registers the temperature increase, deduces in step 103 a short-circuit in battery cell 2, and subsequently switches off battery module 5 in a step 109.

[0056] If, for example, a line interruption is present in battery module 5 between battery cells 2, then a total voltage UGes is no longer measurable, or the battery management system measures presumably a total voltage UGes of battery module 5 of approximately zero volts. The battery management system deduces in step 103 a line interruption in battery module 5 and subsequently switches off battery module 5 in a step 109.

[0057] After battery module 5 is switched off in step 109, the operation of battery module 5 and the driving operation of the vehicle then ends with a final step 110.

[0058] If no temperature increase indicating a short-circuit is measured, and if total voltage UGes of battery module 5 continues to be measurable and provides plausible measured values, then the battery management system deduces in step 103 an interruption of a measuring line between battery cells 2 and measuring circuit 50.

[0059] In this case, cell voltages UB of relevant battery cells 2, whose cell voltages UB are no longer measurable at the operating point in time due to the interruption of the measuring line, are estimated at the operating point in time in a subsequent step 104.

[0060] In a subsequent step 105, a further operation of battery module 5 takes place, as well as a further driving operation of the vehicle.

[0061] The operation of battery module 5 and the driving operation of the vehicle end at a later point in time with final step 110.

[0062] The present invention is not limited to the exemplary embodiments described herein and to the aspects highlighted therein. Instead, a multitude of modifications are possible within the scope of the present invention, which fall within the routine practice of those skilled in the art.