Computer-implemented method for determining the hysteresis voltage state of a motor vehicle battery

Abstract

The invention relates to a computer-implemented method for determining the hysteresis voltage state of a motor vehicle battery, comprising the following steps: - Subdivision of a continuous period (5) into several segments (1; 2; 2'; 2''; 3); - Determining the change in the battery charge level for each of the segments (1; 2; 2'; 2''; 3); - Determination of the hysteresis voltage state using the determined changes.

Description

[0001] The present invention relates to a computer-implemented method for determining a hysteresis voltage state of a battery according to claim 1.

[0002] Methods for determining the hysteresis voltage state of a motor vehicle battery are known in the art. The hysteresis voltage state can be used, for example, in a simulation of battery behavior to model the battery's hysteresis voltage. It is also possible to use the hysteresis voltage state to determine the battery's state of charge. The state of charge can be determined, for example, using a Kalman filter or a particulate filter.

[0003] From DE 10 2018 125 486 A1 a method for estimating the state of charge of a battery is known, in which the amount of charge with which the battery is charged or discharged is used.

[0004] From DE 10 2022 123 466 A1, a method for determining the capacity of a traction battery whose open-circuit voltage (OCV) characteristic curve exhibits hysteresis is known. A first phase is induced and / or awaited, during which battery current flows exclusively in one direction or is detected. A first relaxation period is awaited, during which no battery current flows. A first open-circuit voltage of the battery is determined after the first relaxation period. A second phase is induced and / or awaited, during which battery current flows exclusively in the second direction or is detected. A second relaxation period is awaited, during which no battery current flows. A second open-circuit voltage of the battery is determined after the second relaxation period. The battery capacity is determined based on the first open-circuit voltage and the second open-circuit voltage.

[0005] In contrast, the present invention is based on the objective of being able to determine the hysteresis voltage state more accurately during transitions of the battery from a first state in which the battery is charged with energy to a second state in which the battery releases energy, and / or vice versa.

[0006] This problem is solved by a method according to claim 1 and a motor vehicle according to claim 9. Embodiments of the invention are specified in the dependent claims.

[0007] In this method, a continuous period of time is divided into several segments. For each segment, the change in the battery's state of charge (State of Charge) is determined. The State of Charge can be expressed, for example, in kWh, as a percentage, or as charge in Ah or Coulombs. The State of Charge can be determined, for instance, by measuring the battery's open-circuit voltage. The change in the State of Charge can also be referred to as the depth of discharge. Alternatively, the change in the State of Charge can be determined by measuring the charge used to charge or discharge the battery. The charge can be measured, for example, in Ah or Coulombs. The segments can, for instance, form a ring buffer. In a ring buffer, data can be continuously stored in a fixed-size memory. When the memory is full, the oldest data is overwritten.This means that the data is only available for a limited period. For example, it is possible to store only one value per segment, indicating the respective change in the state of charge. This results in a particularly small amount of data to be stored, making the process suitable for computer systems with relatively small storage capacities. The hysteresis voltage state is then determined using the observed changes.

[0008] The segments comprise a first segment and several second segments. The first segment comprises a first portion of the time period. The second segments each comprise a second portion of the time period. The first portion increases until it is equal to the size of each of the second portions. The second portion can also change; in particular, it can decrease. This embodiment is especially advantageous for dividing a particularly current time period into segments.

[0009] For example, the period can consist of the first and second segments if the first and second segments are each of equal size. If there are nine second segments, for instance, the first segment and the second segments can each be 10%. However, if the first segment is smaller than the second segments, a third segment can still be at least partially included in the period.

[0010] According to one embodiment of the invention, the time period can encompass the most recently elapsed seconds. Within the scope of this description, this can particularly mean that the time period is chosen to be as up-to-date as possible. In practice, the processing time required by the computer system to execute the process steps must, of course, be taken into account.

[0011] According to one embodiment of the invention, the period can include a transition of the battery from the first state, in which it is supplied with energy, to the second state, in which energy is drawn from it, and / or vice versa. The battery can be supplied, for example, by connecting the vehicle to an electrical energy source, e.g., a public power grid. In the second state, the battery can, for example, supply energy to the vehicle's drive system.

[0012] According to one embodiment of the invention, the first segment can comprise the most recently elapsed seconds.

[0013] According to one embodiment of the invention, the hysteresis voltage state can be determined using a sum. This sum can include changes in the state of charge. For example, the changes determined for the second segment can be weighted differently in the calculation of the sum than the changes determined for the third segment.

[0014] According to one embodiment of the invention, the change determined for the third segment can be weighted in total by a factor that is the difference between 1 and the ratio of the first component to the second component. Here, 1 can be, in particular, the minuend and the ratio of the first component to the second component the subtrahend. The factor can be described as a formula as follows: Td−T1Td This involves Td the entire period over which the change in the state of charge was stored, and T1 the time during which the data was stored in the first segment.

[0015] In this embodiment, the third segment is weighted less in the overall calculation as the first segment's share of the time period increases. When the first and second shares are equal, the third segment is no longer considered in the total. In this way, despite dividing the time period into segments, the elapsed time is continuously taken into account when determining the hysteresis voltage state. While the third segment is only excluded from the total calculation in the exceptional case where the first and second shares are equal, its weighting decreases progressively even before this exceptional case occurs. As the first share increases, the change in the state of charge determined for the first segment typically also increases. However, the weighting of the third segment in the total calculation decreases proportionally.

[0016] According to one embodiment of the invention, the hysteresis voltage state can be determined using a conversion table. The conversion table can, for example, also be referred to as a lookup table. The conversion table can, for example, take into account the hysteresis behavior of the battery's open-circuit voltage. This hysteresis behavior is particularly important for determining the hysteresis voltage state when the battery transitions from the first to the second state or vice versa.

[0017] According to one embodiment of the invention, a first term can be assigned to a first time period before the battery transition using the conversion table. A second term can be assigned to a second time period after the battery transition using the conversion table. The hysteresis voltage state can then be determined by weighting the first term and the second term respectively and adding them together.

[0018] The weighting of the summands can, for example, be proportional to the magnitude of the open-circuit voltage's dynamics in the respective time period. Thus, the greater the change in the open-circuit voltage per unit of time in the respective time period, the higher the weighting of the respective assigned summand can be.

[0019] Besides determining the hysteresis voltage state of the battery, the principle of the invention can also be applied to other areas, particularly in automotive engineering, where hysteresis occurs during a change of state. In particular, the accuracy of determining the state of charge of a battery, for example with a particulate filter or a Kalman filter, can be increased.

[0020] The motor vehicle according to claim 9 comprises a battery, an evaluation unit, and a drive unit. The battery is configured to provide electrical energy to the drive unit. The drive unit is configured to propel the motor vehicle. The evaluation unit is configured to perform a method according to an embodiment of the invention.

[0021] Further features and advantages of the present invention will become clear with reference to the following description of preferred embodiments and the accompanying figures. The same reference numerals are used for identical or similar components, features, or elements, and for components, features, or elements with identical or similar functions. Fig. 1 a schematic representation of the period divided into several segments according to an embodiment of the invention; and Fig. 2 a graphical representation of the open-circuit voltage of a silicon-based battery with a voltage curve in hysteresis form at a low state of charge.

[0022] The period 5 is divided into a first segment 1, several second segments 2, 2' and 2" and a third segment 3. For each of the segments 1, 2, 2', 2" and 3, a change in the battery's state of charge is determined. Since the procedure is preferably carried out several times in succession, in Fig. 1 also shows a fourth segment 4, which may have been used as the third, second or first segment of a different period in one of the previous versions of the procedure.

[0023] At the time of execution of the procedure with the segments according to Fig. The first component 6 of the first segment 1 in the period 5 is smaller than the respective second components 7 of the second segments 2, 2', and 2". To determine the hysteresis voltage state, a sum is calculated that includes the changes in the state of charge determined for the first segment 1 and for the second segments 2, 2', and 2". To account for the fact that the period 5 includes the first segment 1 with the first component 6 being smaller than the second component 7, the change in the state of charge determined for the third segment 3 is weighted by a factor less than 1, calculated as the difference between 1 and the ratio of the first component 6 to the second component 7. While this changes the duration of the period when the procedure is performed multiple times, since the first component 6 can vary, this is compensated for by the weighting of the third component 3.Thus, despite the division of the period 5 into several segments 1, 2, 2', 2" and 3, a reliable and consistent calculation method for the hysteresis voltage state of the battery is enabled.

[0024] This is in Fig. 1 For better understanding, the third segment is only partially shown as belonging to period 5, as it is weighted to a lesser extent in the calculation of the sum.

[0025] Dividing the time period into segments 1, 2, 2', 2" and 3 is advantageous in order to save storage space, since only one value needs to be stored per segment 1, 2, 2', 2" and 3, which includes an indication of the change in the state of charge determined for the respective segment 1, 2, 2', 2" and 3.

[0026] Period 5 comprises a first period in which the battery was charged and a second period in which the battery was used as an energy source. Each period is assigned some of the segments 1, 2, 2', 2" and 3. For each period, the changes of the segments 1, 2, 2', 2" and 3 assigned to that period are summed. The change determined for the third segment, 3, is added only after being weighted by the factor mentioned above.

[0027] In Fig.Figure 2 shows the battery's open-circuit voltage on the Y-axis and the state of charge on the X-axis. A first curve, 8, depicts the open-circuit voltage as a function of the state of charge during a battery charging process. A second curve, 9, depicts the open-circuit voltage as a function of the state of charge during a battery discharging process. As can be seen, curves 8 and 9 are not identical. This is due to the battery's hysteresis behavior.

[0028] As mentioned previously, during period 5 the battery transitioned from its first state, in which it was being charged, to a second state, in which it was being discharged, or vice versa. To determine the hysteresis voltage state as accurately as possible, the state of charge determined for the first time period is multiplied by a first weighting factor, and the state of charge determined for the second time period is multiplied by a second weighting factor. Both the first and second weighting factors depend on the dynamics of the state of charge during the respective time period. The greater the dynamics of the state of charge in a given time period, the higher the weighting of the sum determined for that period.

[0029] The charge states, multiplied by their respective weighting factors, are added together as the first and second summands. The hysteresis voltage state 10 of the battery is then determined from the result.

Claims

[1] Computer-implemented method for determining the hysteresis voltage state of a motor vehicle battery, comprising the following steps: - Subdivision of a continuous period (5) into several segments (1; 2; 2'; 2''; 3); - Determining the change in the battery charge level for each of the segments (1; 2; 2'; 2''; 3); - Determination of the hysteresis voltage state using the determined changes; characterized by , that the segments (1; 2; 2'; 2''; 3) comprise a first segment (1) and several second segments (2; 2'; 2''), wherein the first segment (1) comprises a first share (6) of the period, wherein the second segments (2; 2'; 2'') each comprise a second share (7) of the period, wherein the first share (6) increases until it is equal to the size of each of the second shares (7). [2] Method according to claim 1, characterized by, that the period (5) comprises the last elapsed seconds. [3] Method according to any one of the preceding claims, characterized by , that the period (5) includes a transition of the battery from a first state in which it is supplied with energy to a second state in which energy is taken from it, and / or vice versa. [4] Method according to any one of the preceding claims, characterized by , that the first segment (1) comprises the most recently elapsed seconds. [5] Method according to any one of the preceding claims, characterized by , that the state of charge is determined using a sum, where the sum includes the changes. [6] Method according to the previous claim, characterized by , that the change determined for a third segment (3) of the segments is weighted in the sum by a factor, where the factor is the difference between 1 and the ratio of the first share (6) to the second share (7). [7] Method according to any one of the previous three claims, characterized by that the state of charge is determined using a conversion table. [8] Method according to the previous claim characterized by , that a first summand is assigned to a first time period (5) before the battery transition using the conversion table, wherein a second summand is assigned to a second time period (5) after the battery transition using the conversion table, wherein the state of charge is determined by weighting the first summand and the second summand respectively and adding them together. [9] Motor vehicle comprising a battery, an evaluation unit and a drive, wherein the battery is configured to provide electrical energy to the drive, wherein the drive is configured to propel the motor vehicle and wherein the evaluation unit is configured to perform a method according to any of the preceding claims.

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