JP2021197237A - Diagnostic system - Google Patents

Abstract

To diagnose a deterioration state of a secondary battery with high accuracy and to shorten charging/discharging time for diagnosis of the deterioration state.SOLUTION: A diagnostic system 10 includes: a storage unit 11 that stores a differential curve of a charging/discharging curve of a lithium ion battery; an obtaining unit 12 that obtains information on a temperature, a deterioration state, and a C rate as charging/discharging conditions related to charging/discharging control of the lithium ion battery; a specification unit 13 that specifies a differential curve that matches the obtained charging/discharging conditions among each differential curve; a charging/discharging rate determination unit 14 that determines a charging/discharging region important for diagnosing a deterioration state of the lithium ion battery to be a low-C rate charging/discharging region where charging/discharging is performed at a relatively low C rate on the basis of the specified differential curve, and determines the rest of regions to be a high-C rate charging/discharging region where the charging/discharging is performed at a higher C rate than the low-C rate charging/discharging region; and a charging/discharging control unit 15 that performs charging/discharging control of the lithium ion battery in accordance with the determined C rate.SELECTED DRAWING: Figure 1

Description

The present invention relates to a diagnostic system for a secondary battery.

As a method for diagnosing the deterioration state of the secondary battery, the differential characteristic of the charge / discharge curve of the secondary battery is obtained, and the SOH (State Of Health) indicating the deterioration state of the secondary battery is obtained from the information of the peak portion in the differential characteristic. A method for determining is known (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2017-227539

Here, in order to determine SOH with high accuracy, it is necessary to acquire the peak of the differential characteristic of the charge / discharge curve in an appropriate shape. In order to obtain the peak in an appropriate shape, it is necessary to charge and discharge at a relatively low C rate (that is, a low current). This is because when charging / discharging is performed at a relatively high C rate (that is, high current), the chemical structure of the secondary battery changes rapidly, the data sampling sensitivity of the charging / discharging curve is insufficient, and the peak is appropriate. This is because it cannot be obtained by shape. On the other hand, when charging / discharging is performed at a low C rate, the time required for charging / discharging becomes long, and the dead time of the product driven by the energy of the secondary battery becomes long. As described above, conventionally, it has been difficult to shorten the charge / discharge time while diagnosing the deteriorated state of the secondary battery with high accuracy.

The present invention has been made in view of the above circumstances, and an object of the present invention is to perform highly accurate diagnosis of a deteriorated state of a secondary battery and to shorten the charge / discharge time for diagnosing the deteriorated state.

The secondary battery diagnostic system according to one aspect of the present invention includes a storage unit that stores a differential curve of the charge / discharge curve of the secondary battery for each combination of temperature, deterioration state, and C rate, and charge / discharge of the secondary battery. The charge / discharge conditions related to the control match the charge / discharge conditions acquired by the acquisition unit from the acquisition unit that acquires temperature, deterioration state, and C rate information and each differential curve stored in the storage unit. A low C rate that charges and discharges at a relatively low C rate for the charge / discharge region that is important for diagnosing the deterioration state of the secondary battery based on the specific part that specifies the differential curve and the differential curve specified by the specific part. The charge / discharge rate determination unit determines the charge / discharge region, and the other regions are determined to be the high C rate charge / discharge region that charges / discharge at a higher C rate than the low C rate charge / discharge region, and the charge / discharge rate determination unit. A charge / discharge control unit that controls charge / discharge of the secondary battery according to the determined C rate is provided.

In the diagnostic system according to the present invention, a differential curve that matches the charge / discharge conditions (temperature, deterioration state, and C rate) related to charge / discharge control from the differential curve of the charge / discharge curve which is the tabletop data stored in advance. Is identified. Then, in the diagnostic system according to the present invention, the low C rate charge / discharge region is determined for the region important in the diagnosis of the deterioration state, and the high C rate charge / discharge region is determined for the other regions based on the specified differential curve. Then, charge / discharge control of the secondary battery is performed according to the determined C rate. According to such a configuration, based on the tabletop data prepared in advance, charge / discharge is performed at a low C rate for an important region in the diagnosis of the deterioration state to obtain an accurate charge / discharge curve, and other parts are obtained. For the region, charging / discharging can be performed at a high C rate to quickly obtain a charging / discharging curve. As described above, according to the diagnostic system according to the present invention, it is possible to diagnose the deteriorated state of the secondary battery with high accuracy and shorten the charge / discharge time for diagnosing the deteriorated state.

The charge / discharge rate determining unit may specify a peak location in the differential curve specified by the specific unit, and determine the peak location in the low C rate charge / discharge region. Information on the peak location (position, shape, etc.) on the differential curve is important information for diagnosing the deterioration state of the secondary battery. Therefore, since the peak portion in the differential curve is determined in the low C rate charge / discharge region, the deterioration state of the secondary battery can be diagnosed with higher accuracy.

According to the present invention, it is possible to diagnose the deteriorated state of the secondary battery with high accuracy and shorten the charge / discharge time for diagnosing the deteriorated state.

It is a functional block diagram of the diagnostic system of a secondary battery. It is a figure which shows the bench data schematically. It is a figure which shows an example of the charge / discharge curve of a lithium ion battery. It is a figure which shows an example of the differential characteristic of the charge / discharge curve of a lithium ion battery. It is a figure explaining the difference of the peak shape by the difference of C rate. It is a flowchart which shows the diagnostic process (diagnosis method) of a lithium ion battery.

Hereinafter, various embodiments will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are designated by the same reference numerals, and duplicate explanations for the same or corresponding parts will be omitted.

FIG. 1 is a functional block diagram of a secondary battery diagnostic system 10. The secondary battery in the present embodiment is, for example, a lithium ion battery for a vehicle, but may be another secondary battery. The secondary battery in this embodiment functions as, for example, a battery for driving a vehicle. In the present embodiment, the secondary battery will be described as a lithium ion battery that functions as a driving battery for a vehicle. More specifically, the secondary battery is a lithium ion battery using a graphite-based negative electrode.

First, the outline of the lithium ion battery diagnostic system 10 according to the present embodiment will be described with reference to FIGS. 2 to 5. The diagnostic system 10 is, for example, a function of a BMS (Battery Management System) that estimates and monitors the state of a lithium-ion battery that functions as a drive battery. The diagnostic system 10 is a system that non-destructively estimates the internal state of the lithium-ion battery, and specifically estimates the value of SOC (State Of Charge) that represents the remaining capacity of the lithium-ion battery. The diagnostic system 10 estimates the SOC value by a well-known technique based on the current, voltage, and surface temperature of the lithium-ion battery. Here, in order to estimate the SOC value with high accuracy, it is preferable that the deterioration state (SOH) of the lithium ion battery is taken into consideration (that is, the SOC value is corrected based on the SOH value). The diagnostic system 10 estimates the value of SOH and corrects the value of SOC with the value of SOH to estimate the value of SOC with high accuracy.

The diagnostic system 10 obtains a charge / discharge curve (see FIG. 3) of the lithium ion battery based on the current and voltage of the lithium ion battery measured at the time of charging / discharging, and further, a differential characteristic (differential curve) of the charge / discharge curve. , Fig. 4), and the deterioration state (SOH) of the lithium-ion battery is estimated based on the differential curve.

FIG. 3 is a diagram showing an example of a charge / discharge curve of a lithium ion battery. As shown in FIG. 3, the charge / discharge curve is derived based on the current and voltage of the lithium ion battery during charging and discharging, with the horizontal axis representing capacity (mAh) and the vertical axis representing voltage (V). .. FIG. 4 is a diagram showing an example of the differential characteristic (differential curve) of the charge / discharge curve of the lithium ion battery. As shown in FIG. 4, the differential curve is derived based on the charge / discharge curve with the horizontal axis representing the capacitance (SOC (%)) and the vertical axis representing dV / dQ (V is the voltage and Q is the capacitance). ..

As shown in FIG. 4, in the differential curve, peaks (locally convex portions in the curve) occur in both charging and discharging. That is, in the example of FIG. 4, two peaks P1 and P2 are generated on the charge curve, and two peaks P3 and P4 are generated on the discharge curve. Such peak information (peak shape and position) is important information for estimating the deterioration state of the lithium ion battery.

Specifically, the diagnostic system 10 records bench data (see FIG. 2) in which the differential curve of the charge / discharge curve is recorded for each combination of the temperature (specifically, the internal temperature), the deterioration state, and the C rate of the lithium ion battery. Is stored in advance, and the deteriorated state of the lithium ion battery is derived by collating the derived differential curve with the differential curve of the bench data. That is, the diagnostic system 10 identifies from the bench data the data in which the information on the temperature and C rate of the lithium ion battery, which is the charge / discharge condition related to the charge / discharge control, matches and the differential curve is similar, and the data. The deteriorated state of is regarded as the deteriorated state of the lithium-ion battery to be diagnosed. The C rate is the magnitude of the current when charging and discharging the battery, and is derived based on the current. The C rate indicates the speed of charge / discharge.

Here, the diagnostic system 10 compares the shape and position of the peak of the differential curve when collating the derived differential curve with the differential curve of the tabletop data. Therefore, in order to derive the deterioration state (SOH) with high accuracy, it is necessary to acquire the peak of the differential curve in an appropriate shape. In this regard, when charging / discharging is performed at a relatively high C rate (that is, high current), the chemical structure of the secondary battery changes rapidly, the data sampling sensitivity of the charging / discharging curve is insufficient, and the peak is appropriate. Since there is a possibility that the shape cannot be obtained, it is preferable to charge and discharge at a relatively low C rate (that is, a low current) from the viewpoint of appropriately acquiring the shape and position of the peak. This is also clear from FIG. FIG. 5 is a diagram illustrating a difference in the peak shape of the differential curve of the discharge curve due to the difference in the C rate. As shown in FIG. 5, when charging / discharging is performed at a relatively low C rate, the two peaks P3 and P4 are properly acquired, whereas charging / discharging is performed at a relatively high rate. In this case, the shape of the peak has not been acquired. On the other hand, when charging / discharging is performed at a low C rate, there is a problem that the time required for charging / discharging becomes long and the dead time of the drive battery becomes long.

When performing charge / discharge control in order to solve the above-mentioned problem, the diagnostic system 10 estimates from the travel history of the vehicle, for example, in addition to the information on the temperature and C rate of the lithium ion battery as the charge / discharge conditions related to the charge / discharge control. Acquires the deteriorated state of the lithium-ion battery. By acquiring the temperature, deterioration state, and C rate information, the diagnostic system 10 can specify one differential curve (differential curve assumed from the charge / discharge conditions) from the bench data. Then, the diagnostic system 10 charges / discharges a low C rate charge / discharge region (for example, a peak portion) which is important for diagnosing the deterioration state of the lithium ion battery based on the specified differential curve. In addition to the determination, the other regions are determined to be high C rate charge / discharge regions in which charge / discharge is performed at a high C rate, and charge / discharge control of the secondary battery is performed according to the determined C rate. As a result, the region where the peak is expected to occur based on the tabletop data is charged and discharged at a low C rate, and the shape and position of the peak of the differential curve are appropriately acquired (that is, in the lithium ion battery). The deterioration state can be estimated with high accuracy), and the charge / discharge is performed at a high C rate in the non-peak region, which is not used for estimating the deterioration state of the secondary battery, and the charge / discharge time can be shortened. can.

In the following, the details of the function of the diagnostic system 10 of the lithium ion battery will be described with reference to FIG. As shown in FIG. 1, the diagnostic system 10 includes a storage unit 11, an acquisition unit 12, a specific unit 13, a charge / discharge rate determination unit 14, a charge / discharge control unit 15, and a battery state estimation unit 16. It is equipped with.

The storage unit 11 is a database that stores bench data (see FIG. 2) in which the differential curve of the charge / discharge curve of the lithium ion battery for each combination of the temperature, deterioration state, and C rate of the lithium ion battery is recorded. Such bench data is prepared in advance for each type of battery, for example.

As a process for determining the C rate (charge / discharge rate) in each region of the differential curve, the acquisition unit 12 determines the charge / discharge conditions related to the charge / discharge control of the lithium ion battery, such as temperature, deterioration state, and C rate. Get information. The temperature is the internal temperature of the lithium ion battery, and is derived according to, for example, the surface temperature of the lithium ion battery, the current detected by the current sensor 21 of the battery module 2, and the like. The deteriorated state is, for example, a deteriorated state of the lithium ion battery estimated from the traveling history of the vehicle. The C rate may be a predetermined value or may be derived according to the current detected by the current sensor 21.

Further, the acquisition unit 12 acquires the values of the current and the voltage detected at the time of charging or discharging as the processing at the time of charging / discharging. The acquisition unit 12 acquires the current value flowing through the lithium ion battery 22 from the current sensor 21 of the battery module 2 composed of the plurality of lithium ion batteries 22. Further, the acquisition unit 12 acquires the voltage value applied to the lithium ion battery 22 from the voltage sensor that measures the voltage between the terminals of the lithium ion battery 22 constituting the battery module 2.

The specific unit 13 identifies a differential curve that matches the charge / discharge conditions acquired by the acquisition unit 12 from each differential curve of the bench data stored in the storage unit 11. That is, the specifying unit 13 specifies the differential curve of the bench data in which the charge / discharge conditions acquired by the acquisition unit 12 and the temperature, the deterioration state, and the C rate all match (or are closest to each other).

The charge / discharge rate determination unit 14 charges / discharges at a relatively low C rate in a charge / discharge region, which is important for diagnosing the deterioration state of the lithium ion battery, based on the differential curve specified by the specific unit 13. The charge / discharge region is determined, and the other regions are determined to be high C rate charge / discharge regions that charge / discharge at a higher C rate than the low C rate charge / discharge region. Specifically, the charge / discharge rate determination unit 14 identifies a peak portion in the differential curve specified by the specific unit 13, and determines the peak portion in the low C rate charge / discharge region. The charge / discharge rate determination unit 14 specifically determines the above-mentioned low C rate and high C rate using the C rate acquired by the acquisition unit 12 as a reference C rate. The low C rate is a C rate at which the shape and position of the peak can be appropriately acquired at least on the differential curve.

The charge / discharge control unit 15 controls the charge / discharge of the lithium ion battery according to the C rate determined by the charge / discharge speed determination unit 14. That is, the charge / discharge control unit 15 charges / discharges at a low C rate in the region designated by the charge / discharge speed determination unit 14 as the low C rate charge / discharge region, specifically, the region where the peak portion appears. While controlling the charge / discharge operation, the area designated as the high C rate charge / discharge region by the charge / discharge speed determination unit 14, specifically, the region where the peak portion does not appear is charged so that the charge / discharge is performed at the high C rate. Control the discharge operation.

The battery state estimation unit 16 derives a charge / discharge curve and a differential curve of the charge / discharge curve based on the current value and the voltage value acquired by the acquisition unit 12 at the time of charging / discharging, and derives the temperature and C rate information and the derivation. Identify the tabletop data (data included in the tabletop data) where the differential curve and information (peak information) match. Then, the battery state estimation unit 16 estimates the deterioration state of the specified bench data as the deterioration state of the lithium ion battery to be diagnosed. The battery state estimation unit 16 further corrects the SOC value according to the deterioration state (SOH value), thereby estimating the SOC value with high accuracy.

Next, the diagnostic process (diagnosis method) of the lithium ion battery according to the present embodiment will be described with reference to FIG. FIG. 6 is a flowchart showing a diagnostic process (diagnosis method) of the lithium ion battery, and more specifically, a flowchart showing an estimation process of a deterioration state by charge control of the lithium ion battery.

As shown in FIG. 6, in the diagnostic system 10, the charging condition is first acquired (step S1). The charging condition is information on the temperature, deterioration state, and C rate of the lithium ion battery. Subsequently, the diagnostic system 10 identifies a differential curve that matches the acquired charging conditions from each differential curve of the stored bench data (step S2).

Subsequently, the diagnostic system 10 determines the charging speed (C rate) in each region of the differential curve based on the specified differential curve (step S3). Specifically, the diagnostic system 10 determines the peak portion as a low C rate charging region for charging at a relatively low C rate based on the specified differential curve, and sets the other regions as a lower C rate charging region than the low C rate charging region. It is determined to be a high C rate charging region for charging at a high C rate.

Subsequently, the diagnostic system 10 controls the charging of the lithium ion battery according to the determined C rate (step S4). That is, the diagnostic system 10 controls the charging operation so that charging is performed at a low C rate in the region where the peak portion appears, and charging is performed at a high C rate in the region where the peak portion does not appear. Control the charging operation.

Subsequently, the diagnostic system 10 derives a charging curve and a differential curve of the charging curve based on the current value and the voltage value acquired at the time of charging, and acquires peak information (step S5). Then, the diagnostic system 10 estimates the deterioration state of the lithium ion battery to be diagnosed based on the peak information and the like by referring to the bench data (step S6).

Finally, the operation and effect of the diagnostic system of the lithium ion battery according to the present embodiment will be described.

The lithium ion battery diagnostic system 10 according to the present embodiment includes a storage unit 11 that stores a differential curve of the charge / discharge curve of the lithium ion battery for each combination of temperature, deterioration state, and C rate, and charge / discharge of the lithium ion battery. As charge / discharge conditions related to control, charge / discharge conditions acquired by the acquisition unit 12 from the acquisition unit 12 that acquires temperature, deterioration state, and C rate information and each differential curve stored in the storage unit 11. Based on the specific unit 13 that specifies the differential curve that matches the above and the differential curve specified by the specific unit 13, charge / discharge at a relatively low C rate for the charge / discharge region that is important for diagnosing the deterioration state of the lithium ion battery. The charge / discharge rate determination unit 14 determines the low C rate charge / discharge region for performing charge / discharge, and determines the other regions as the high C rate charge / discharge region for charging / discharging at a higher C rate than the low C rate charge / discharge region. A charge / discharge control unit 15 that controls charge / discharge of the lithium ion battery according to the C rate determined by the charge / discharge rate determination unit 14 is provided.

In the diagnostic system 10 according to the present invention, from the differential curve of the charge / discharge curve which is the tabletop data stored in advance, the differential that matches the charge / discharge conditions (temperature, deterioration state, and C rate) related to the charge / discharge control. The curve is identified. Then, in the diagnostic system 10 according to the present embodiment, based on the specified differential curve, the region important in the diagnosis of the deteriorated state is determined to be the low C rate charge / discharge region, and the other regions are determined to be the high C rate charge / discharge region. The charge / discharge control of the lithium ion battery is performed according to the determined C rate. According to such a configuration, based on the tabletop data prepared in advance, charge / discharge is performed at a low C rate for an important region in the diagnosis of the deterioration state to obtain an accurate charge / discharge curve, and other parts are obtained. For the region, charging / discharging can be performed at a high C rate to quickly obtain a charging / discharging curve. As described above, according to the diagnostic system 10 according to the present embodiment, it is possible to diagnose the deteriorated state of the lithium ion battery with high accuracy and shorten the charge / discharge time for diagnosing the deteriorated state.

The charge / discharge rate determination unit 14 may specify a peak location in the differential curve specified by the specific unit 13, and determine the peak location in the low C rate charge / discharge region. Information on the peak location (position, shape, etc.) on the differential curve is important information for diagnosing the deterioration state of the lithium ion battery. Therefore, since the peak portion in the differential curve is determined in the low C rate charge / discharge region, the deterioration state of the lithium ion battery can be diagnosed with higher accuracy.

10 ... diagnostic system, 11 ... storage unit, 12 ... acquisition unit, 13 ... specific unit, 14 ... charge / discharge speed determination unit, 15 ... charge / discharge control unit.

Claims (2)

A storage unit that stores the differential curve of the charge / discharge curve of the secondary battery for each combination of temperature, deterioration state, and C rate,
As charge / discharge conditions related to charge / discharge control of the secondary battery, an acquisition unit that acquires temperature, deterioration state, and C rate information, and an acquisition unit.
From each of the differential curves stored in the storage unit, a specific unit that specifies the differential curve that matches the charge / discharge conditions acquired by the acquisition unit, and a specific unit.
Based on the differential curve specified by the specific unit, the charge / discharge region, which is important for diagnosing the deterioration state of the secondary battery, is determined to be a low C rate charge / discharge region in which charge / discharge is performed at a relatively low C rate. , A charge / discharge rate determining unit that determines the other regions as high C rate charge / discharge regions that charge / discharge at a higher C rate than the low C rate charge / discharge regions.
A secondary battery diagnostic system including a charge / discharge control unit that controls charge / discharge of the secondary battery according to a C rate determined by the charge / discharge speed determination unit. The diagnostic system according to claim 1, wherein the charge / discharge rate determining unit identifies a peak portion in the differential curve specified by the specific portion, and determines the peak portion in the low C rate charge / discharge region.

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