JP7809586B2 - battery management device - Google Patents

Description

The present invention relates to technology for managing battery status.

In energy storage systems, electric vehicles, and other systems that use secondary batteries, technology that can quickly and accurately diagnose the performance of secondary batteries is important for long-term operation of the batteries. Furthermore, grading secondary batteries according to the battery performance and deterioration state obtained through the diagnosis can contribute to highly efficient system operation and prompt maintenance before failure.

Patent Document 1 below describes a technology for determining the degree of deterioration from the rate of increase in the battery's internal resistance and capacity retention rate, and selecting a secondary battery for replacement. Patent Document 2 below, related to the present application, describes a technology for estimating the SOH (State of Health) of a battery cell using the correspondence relationship between the time derivative of the output voltage during a battery cell's idle period and the battery temperature.

Japanese Patent Application Laid-Open No. 2021-044145 Japanese Patent Application Laid-Open No. 2021-060198

In addition to the battery capacity and internal resistance described in Patent Document 1, parameters used to diagnose the performance of secondary batteries may also include the battery voltage during the rest period after charging. However, depending on the type of secondary battery, these values may differ from battery to battery due to initial manufacturing variations, making it impossible to obtain differences sufficient to distinguish between battery performance.

The present invention was made in consideration of the above-mentioned problems, and aims to provide technology that can accurately diagnose the battery performance of secondary batteries, even when there are large individual differences in battery characteristics due to manufacturing variations.

The battery management device of the present invention identifies a rest period after charging a battery with a first charging current and then charging with a second charging current that is smaller than the first charging current, and evaluates the performance of the battery using the change in battery voltage during that rest period.

The battery management device of the present invention can accurately diagnose the battery performance of a secondary battery, even when there are large individual differences in battery characteristics due to manufacturing variations. Other issues, configurations, advantages, etc. of the present invention will become clear from the description of the following embodiments.

1 is a configuration diagram of a battery system according to a first embodiment. 10 is a diagram illustrating an example of variations in discharge current amount among individual batteries. 10A and 10B are diagrams illustrating variations in performance and discharge current amount for individual batteries. 3A and 3B are diagrams illustrating a method for diagnosing the performance of a secondary battery by the battery management device 1. FIG. 10 is a diagram showing how ΔVcha differs depending on the battery performance. FIG. 10 is a diagram illustrating a criterion for diagnosing battery performance based on ΔVcha. FIG. 7 is a diagram in which FIG. 3 and FIG. 6 are superimposed. 4 is a flowchart illustrating the operation of the battery management device 1. 10 is an example of a user interface provided by the battery management device 1. 10 is an example of a user interface provided by the battery management device 1. FIG. 10 is a diagram illustrating an example of a starting point of ΔVcha. 10A and 10B are diagrams illustrating examples of charging states in a first charging period and a second charging period; FIG. 10 is a diagram illustrating the length of a charging period. FIG. 10 is a diagram illustrating an example of the number of charging periods. FIG. 10 is a diagram showing the time-dependent fluctuation of the battery voltage during a rest period after the battery has performed a discharging operation. FIG. 10 is a diagram showing the time-dependent fluctuation of the battery voltage during a rest period after the battery has performed a charging operation. FIG. 10 is a schematic diagram showing an example of data describing the relationship between the time derivative of a battery voltage and the state of health of a battery. 18 is a flowchart illustrating a procedure in which the calculation unit 12 performs the operations described with reference to FIGS. 15 to 17. FIG. 10 is a diagram illustrating an example of a result of clustering individual batteries performed by the calculation unit 12. FIG. 1 is an overall configuration diagram of a battery system. FIG. 10 is a configuration diagram of a battery system according to a fourth embodiment. FIG. 10 is another configuration diagram of a battery system according to a fourth embodiment. 10 is an example of a GUI provided by the calculation unit 12. 10 is an example of a GUI provided by the calculation unit 12. FIG. 10 is another configuration diagram of a battery system according to a fourth embodiment.

First Embodiment
FIG. 1 is a configuration diagram of a battery system according to a first embodiment of the present invention. The battery system has a battery group consisting of one or more secondary battery modules, and the battery group is controlled by a battery management unit (BMU). The BMU is further controlled by a higher-level controller (Power Control System: PCS). The secondary battery module has one or more sub-modules, and each sub-module has one or more secondary battery cells. The sub-modules have sensors that measure the battery current, battery temperature, and battery voltage of the secondary battery cells. A battery management device 1 acquires measurements from these sensors via the BMU and uses the measurements to diagnose the battery performance of each battery cell/battery module/battery group.

The detection unit acquires detected values from each sensor. The detection unit can be located within a submodule. The battery management device 1 can also include a detection unit 11 that acquires detected values from each sensor from the BMU. The battery management device 1 can further include a calculation unit 12 that performs the diagnostic procedure described below.

Figures 2 and 3 are diagrams illustrating variations in the amount of discharge current for individual batteries. Depending on the type of secondary battery, the amount of discharge current from a full charge may vary for individual batteries, even immediately after manufacture, as shown in Figure 2. This variation has little correlation with the battery's health or performance, making it difficult to diagnose battery performance using the amount of discharge current. Similar variations also occur in the battery's internal resistance and battery voltage, so if these values vary, it is similarly difficult to diagnose battery performance using these values.

Figure 4 is a diagram illustrating a method by which the battery management device 1 diagnoses the battery performance of a secondary battery. In batteries that exhibit the variations described in Figures 2 and 3, the battery voltage may continue to decrease during the rest period after a charging operation, even after the fluctuations in the battery voltage over time have slowed down. In other words, the decrease in battery voltage may continue for a long period of time even after the inflection point in Figure 4. The inventor has discovered a method that can slow down this continuous decrease in battery voltage during the rest period after a charging operation.

Specifically, in this first embodiment, as shown in Figure 4, a two-stage charging current value is set. A high charging current value is used in the first charging period, and a low charging current value is used in the subsequent second charging period. The inventors have discovered that this two-stage charging operation can cause the battery voltage to gradually and continuously decrease over time during the rest period after the charging operation. Furthermore, as will be described later, it has been found that the difference ΔVcha between the battery voltage in the second charging period and the battery voltage at the inflection point varies significantly depending on the state of battery degradation.

The charging current during the first charging period is, for example, 400 A, and the charging current during the second charging period is, for example, 18 A (or approximately 1/5 to 1/10 of the charging current during the first charging period). Charging is performed using a constant current during both the first and second charging periods, and charging is performed using a constant voltage during the second charging period. Therefore, the starting point for calculating ΔVcha does not necessarily have to be the end of the second charging period, and can be any point during the second charging period.

The method shown in Figure 4 is able to suppress the continuous drop in battery voltage during rest periods because it does not capture sudden changes due to the battery's reverse reaction, thereby eliminating the battery's internal resistance and other external resistance factors specific to the battery, and obtaining a waveform that is close to the hysteresis response characteristics caused by manufacturing variations in the battery.

Figure 5 shows how ΔVcha varies depending on battery performance. The battery management device 1 acquires ΔVcha at the point when the battery voltage change during the idle period following the second charging period becomes available. At this point, as shown in Figure 5, (a) for the performance B category, where the proportion of batteries tending to deteriorate is high, ΔVcha is smaller than for the performance A category, where the proportion of normal batteries is high. (b) For the performance C category, where the proportion of significantly deteriorated batteries is high, ΔVcha is larger than for the performance A category, where the proportion of normal batteries is high. Therefore, the battery management device 1 can classify battery performance into three categories: performance A, performance B, and performance C, based on ΔVcha. As shown in Figure 5, the battery voltage change can be detected at or near the inflection point several seconds after the end of the second charging period, for example, 2 to 3 seconds later (within a predetermined range around the inflection point, for example, within 10 to 500 ms around the inflection point). In other words, differences that allow for classification into three categories - Performance A, Performance B, and Performance C - are clearly apparent at or near the inflection point, allowing battery performance to be quickly diagnosed. The rest period is determined after a predetermined time has passed and before the voltage change reaches saturation.

Figure 6 is a diagram explaining the criteria for diagnosing battery performance based on ΔVcha. (a) If ΔVcha is greater than the threshold Border_a, the battery is classified as performance C, meaning that the proportion of significantly degraded batteries is high; (b) if ΔVcha is smaller than the threshold Border_b, the battery is classified as performance B, meaning that the proportion of batteries tending to deteriorate is high; and (c) if ΔVcha is between these two thresholds, the battery can be diagnosed as performance A, meaning that the proportion of normal batteries is high. However, even for normal batteries, the smaller ΔVcha is, the more relatively deteriorated they are considered to be. Each threshold can be used as an evaluation index when evaluating battery performance based on ΔVcha.

Figure 7 is a diagram that overlaps Figure 3 and Figure 6. Generally, normal batteries have a large discharge current, so batteries ID1, 3, and 6 shown in Figure 7 appear normal from the perspective of discharge current. On the other hand, according to ΔVcha, batteries ID1 and 4 are degraded. Therefore, although battery ID1 appears normal from the perspective of discharge current, it can be seen through diagnosis using ΔVcha that it is actually degraded.

Figure 8 is a flowchart explaining the operation of the battery management device 1. This flowchart is executed by the calculation unit 12. The calculation unit 12 acquires the battery voltage via the detection unit 11 and also acquires ΔVcha at the time described in Figure 5. The calculation unit 12 diagnoses the battery's performance (A to C) according to the following criteria: (a) if ΔVcha is greater than the threshold Border_a, it is considered to be performance C; (b) if ΔVcha is equal to or less than Border_a and greater than Border_b, it is considered to be performance A; (c) if ΔVcha is equal to or less than Border_b, it is considered to be performance B.

Figures 9 and 10 are examples of user interfaces provided by the battery management device 1. The calculation unit 12 generates and provides a GUI (Graphical User Interface) such as the one shown in Figure 9. The GUI presents, for example, for each battery cell, changes in battery voltage over time, the results of battery performance diagnosis, and the results of health diagnosis (described below). The diagnosis using the procedure described in Figures 5 to 8 classifies the battery into performance A, performance B, or performance C, and this will be referred to as performance diagnosis. The calculation unit 12 further classifies the degree of health in more detail within each classification. This will be referred to as health diagnosis. The GUI also presents detailed information for each battery cell (Figure 10).

<Second Embodiment>
In a second embodiment of the present invention, a description will be given of a variation of the charging period and the like in the first embodiment. The configuration of the battery management device 1 and the procedure for diagnosing battery performance are the same as those in the first embodiment, so the following description will mainly focus on the differences from the first embodiment.

Figure 11 is a diagram illustrating an example of the starting point for calculating ΔVcha. The starting point for calculating ΔVcha may be, for example, the end of the second charging period, or any point during the second charging period as long as the battery voltage during the second charging period is sufficiently stable.

Figure 12 is a diagram illustrating the state of charge during the first and second charging periods. When the battery management device 1 diagnoses battery performance using the procedure described in embodiment 1, it is desirable to fully charge the batteries during the first and second charging periods (solid lines in the lower part of Figure 12), but this is not limited to this. If the performance differences between individual batteries (Performance A/Performance B/Performance C) are sufficiently reflected in ΔVcha, the battery may enter the rest period at a state of charge (SOC: State of Charge) lower than full charge. The dotted and dashed lines in the lower part of Figure 12 show an example. For example, each battery may be charged during the first and second charging periods until the difference between ΔVcha for a battery classified as Performance B and ΔVcha for a battery classified as Performance A is equal to or greater than a threshold value.

Figure 13 is a diagram illustrating the length of a charging period. During each charging period, the charging current may fluctuate over time due to changes in the charging current. This fluctuation over time gradually stabilizes as the charging operation is performed continuously for a certain period of time. Therefore, the length of each charging period should be long enough so that the difference between the charging current value instructed by the charging device and the actual charging current value is less than the threshold value.

Figure 14 is a diagram illustrating the number of charging periods. There may be three or more charging periods in the charging operation. However, it is desirable to gradually decrease the charging current value. In Figure 14, a third charging period is provided after the second charging period, and the charging current value in the third charging period is even smaller than that in the second charging period. The charging voltage only needs to be constant during at least the charging period immediately preceding the pause period. In Figure 14, the voltage is constant only during the third charging period.

<Third Embodiment>
In a third embodiment of the present invention, a method for classifying battery performance (A to C) by the method described in the first embodiment and then further classifying the battery health state in each class will be described. The configuration of the battery management device 1 is the same as in the first and second embodiments.

Figure 15 shows the time variation of battery voltage during a rest period after the battery has performed a discharge operation. The time derivative of the battery voltage during the rest period after the discharge operation (ΔVdis/Δt2 in Figure 15) correlates with the battery health (see Patent Document 2). Therefore, the calculation unit 12 obtains this time derivative and estimates the battery health by referring to the relationship data described below.

Figure 16 shows the time variation of battery voltage during a pause period after a battery has performed a charging operation. The time derivative of battery voltage during a pause period after a charging operation (ΔVcha/Δt3 in Figure 16) correlates with the battery's state of health (see Patent Document 2). Therefore, the calculation unit 12 obtains this time derivative and estimates the battery's state of health by referring to the relationship data described below. Whether to use the pause period after a discharging operation or the pause period after a charging operation can be selected appropriately depending on the battery characteristics, etc.

The time derivatives in Figures 15 and 16 are preferably obtained when the rate of change of battery voltage over time during the rest period after charging/discharging has stabilized to below a threshold. Δt2 or Δt3 in Figures 15 and 16 may generally be shorter than Δt1, which is used to obtain ΔVcha in embodiment 1.

Figure 17 is a schematic diagram showing an example of data describing the relationship between the time derivative of battery voltage and the battery state of health. The battery management device 1 includes a memory unit 13, which stores the data shown in Figure 17. This data describes the relationship between the time derivative ΔVdis/Δt2 (or ΔVcha/Δt3) and SOH described in Figures 15 and 16. This data can be described as a function that approximates a plot of actual measurements obtained in advance by experiment, for example. The calculation unit 12 can estimate the SOH of the battery by referencing this data using the time derivative described in Figures 15 and 16.

Data describing the relationship between the time derivative and the battery internal resistance may be similarly stored in advance in the memory unit 13, and the calculation unit 12 may estimate the internal resistance by referencing this data using the time derivative. The SOH or internal resistance may be used as an index representing the battery's state of health. That is, in the state of health clustering described below, the SOH or internal resistance may be used as the battery's state of health.

Figure 18 is a flowchart illustrating the procedure by which the calculation unit 12 performs the operations described in Figures 15 to 17. The calculation unit 12 obtains the time derivative ΔVdis/Δt2 (or ΔVcha/Δt3) described in Figures 15 to 16, and uses this to refer to the data in Figure 17 to estimate a battery state of health index (e.g., SOH, internal resistance, etc.). The battery state of health is classified into, for example, three levels according to the estimated state of health. For example, for batteries diagnosed as performance A in embodiment 1, which includes many normal batteries, the procedure in Figure 18 can be performed to further classify the performance A batteries into three levels of state of health (A1/A2/A3).

Figure 19 is a diagram illustrating the results of clustering individual batteries performed by the calculation unit 12. The calculation unit 12 can diagnose battery performance using the voltage change ΔVcha after the second charging period described in embodiment 1. This allows individual batteries to be classified as performance A, performance B, or performance C. The results are shown on the horizontal axis of Figure 19. The calculation unit 12 can further classify the battery health for each battery performance (normal range/degraded state/severely degraded state) using a method that uses the time derivative of the battery voltage during the rest period after charging and discharging described in embodiment 3. For each of the performance A/performance B/performance C classifications, for example, three detailed classifications may be set, as described in Figure 18.

The calculation unit 12 may operate the battery system based on the clustering results. For example, as described below, it may assign priorities to each battery cell or battery group. Alternatively, it may determine operating procedures such as the timing of battery replacement based on the estimated health level. The health level estimation results may also be used in any other operating process.

Figure 20 is an overall configuration diagram of the battery system. As previously described, the battery management device 1 includes a detection unit 11, a calculation unit 12, and a memory unit 13. The detection unit 11 acquires the battery voltage, battery current, battery temperature, etc. of each battery via, for example, a battery controller (BMU). The calculation unit 12 uses these values to diagnose battery performance and battery health using the methods described in embodiments 1 to 3, and clusters each battery based on the results. The results of the diagnosis and clustering can be presented on the GUI described in embodiment 1.

<Fourth Embodiment>
FIG. 21 is a configuration diagram of a battery system according to a fourth embodiment of the present invention. The calculation unit 12 may evaluate the performance and health of a battery cell using the method described in the third embodiment, and assign priorities to battery cells or battery groups each composed of multiple battery cells based on the evaluation results. In FIG. 21, the performance of the battery cells is evaluated on three levels, from performance A to performance C, and the battery health is further divided into three levels for each performance level. A battery group having more battery cells with better performance is assigned a higher priority. The calculation unit 12 can efficiently operate the battery system by, for example, prioritizing the operation of battery groups in descending order of priority.

Figure 22 is another configuration diagram of a battery system according to the fourth embodiment. The calculation unit 12 evaluates the battery performance and battery health for each different battery system in the same manner as in Figure 21, and assigns priorities to the battery cells (or battery groups). The calculation unit 12 may select a battery cell (or battery group) with a high priority from each battery system, combine the power outputs from the selected battery cells (or battery groups), and provide them to the supply destination. This allows for efficient operation across multiple battery systems.

Figures 23 and 24 are examples of GUIs provided by the calculation unit 12. The calculation unit 12 may provide a GUI similar to that shown in Figures 9 and 10 for each battery group. This makes it possible to manage the performance and health of each battery group.

Figure 25 is another configuration diagram of a battery system according to the fourth embodiment. The battery management device 1 may implement the methods described in the above embodiments on a secondary battery mounted on an electrically powered device (e.g., an electric vehicle). For example, the detection unit 11 acquires measurement values such as battery voltage from the electrically powered device or a measuring instrument (e.g., an on-board diagnostic device) connected to the electrically powered device, and the calculation unit 12 uses the measurement values to diagnose the battery using the method of each embodiment.

<Modifications of the present invention>
The present invention is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

In the above embodiments, a battery system composed of battery cells (secondary batteries) connected in series or parallel has been described as an example. For example, LiB (lithium ion battery), lead acid battery or other solid-state battery, sodium battery, etc. can be used as the battery. In any case of battery, the method of the present invention can be applied using ΔVdis and ΔVcha.

In the above embodiments, the calculation unit 12 can be configured using hardware such as a circuit device that implements its functions, or it can be configured by a calculation device such as a CPU (Central Processing Unit) executing software that implements its functions.

1: Battery management device 11: Detection unit 12: Calculation unit 13: Storage unit

Claims (14)

A battery management device for managing the state of a battery,
a detection unit that acquires a detected value of the voltage output by the battery and a detected value of the current output by the battery;
a calculation unit that estimates the state of the battery;
Equipped with
the calculation unit identifies a first pause period that occurs after the start of a second charging period in which the battery is charged with a second charging current that is smaller than the first charging current, the second charging period following a first charging period in which the battery is charged with a first charging current;
the first pause period is a period counted from a time when a predetermined time has elapsed since the start of the second charging period,
the calculation unit obtains a change in the voltage during the first pause period;
the calculation unit obtains an evaluation index for evaluating the performance of the battery based on the change;
the calculation unit evaluates the performance of the battery by comparing the change with the evaluation index and outputs the result ;
During the first rest period, the battery stops charging and discharging.
A battery management device characterized by: The battery management device according to claim 1, characterized in that the calculation unit acquires as the change in the voltage during the first rest period when the battery is charged with a constant current during the first charging period and when the battery is charged with a constant current and a constant voltage during the second charging period. The battery management device according to claim 1 , wherein the calculation unit acquires the change in the voltage at an inflection point after the second charging period or within a predetermined time range before and after the inflection point. The battery management device according to claim 1 , wherein the starting point of calculation is a point at which the second charging period ends. The starting point is:
When the battery is fully charged,
or
a time when the battery is charged to such an extent that the difference between the change in the battery and the change in another battery different from the battery becomes equal to or greater than a threshold value;
The battery management device according to claim 1 , a charging current for the battery varies over time during each of the first charging period and the second charging period;
the first charging period has a length of time sufficient for a difference between the charging current and the indicated value of the first charging current to be less than a threshold;
2. The battery management device according to claim 1, wherein the second charging period has a length of time sufficient for a difference between the charging current and the indicated value of the second charging current to be less than a threshold value. The battery management device according to claim 1, characterized in that the calculation starting point is determined to be a point after the start of a third charging period following the second charging period, in which the battery is charged with a third charging current smaller than the second charging current. the detection unit acquires detected values of an output voltage and an output current of a battery group constituted by a plurality of the batteries,
the calculation unit acquires the change in the output voltage of the battery group;
The battery management device according to claim 1 , wherein the calculation unit evaluates the performance of the battery group by comparing the acquired change in output voltage with a threshold value, and outputs the evaluation result. the calculation unit obtains a time derivative of the voltage during a second pause period after a charging operation or a discharging operation performed by the battery at a time point different from any of the first charging period, the second charging period, and the first pause period;
the calculation unit estimates the state of health by referring to data describing a correspondence relationship between the time differential and the state of health of the battery;
the calculation unit clusters the batteries based on the time differential and the state of health and outputs the clustering result ;
During the second rest period, the battery stops charging and discharging.
2. The battery management device according to claim 1. The data has the following correspondence relationship:
a function describing the relationship between the SOH of the battery and the time derivative;
or
a function describing the relationship between the internal resistance of the battery and the time derivative;
At least one of the following is described:
The battery management device according to claim 9 , wherein the calculation unit acquires at least one of the SOH and the internal resistance as the state of health by referring to the data using the time differentiation. the calculation unit estimates a state of health of the battery using a detection result by the detection unit;
The battery management device according to claim 1 , wherein the calculation unit manages the timing of battery replacement based on the estimated health state. the calculation unit estimates a state of health of the battery or the battery group using the detection result by the detection unit;
the calculation unit clusters the battery or the group of batteries based on the estimated state of health;
the calculation unit assigns priorities to the clustered batteries or battery groups based on the health levels;
The battery management device according to claim 8 , wherein the calculation unit operates the battery or the group of batteries in accordance with the priority. the calculation unit selects the battery or the battery group in descending order of priority;
The battery management device according to claim 12, wherein the calculation unit controls the battery or the group of batteries so as to combine the output from the selected battery or group of batteries with the output from a battery or group of batteries in another system and output the combined output to a supply destination. The battery management device according to claim 9, characterized in that the battery is mounted on an electrically powered device that operates using the output from the battery as power, and the calculation unit acquires the change from the electrically powered device or a measuring instrument connected to the electrically powered device.