JP2019056595A - Secondary battery system - Google Patents

Abstract

To provide a secondary battery system capable of estimating deterioration index of a secondary battery with high precision.SOLUTION: The secondary battery system comprises: a differential curve calculation part 10 calculating differential curve V-dQ/dV indicative of the relation between cell voltage V of a battery pack 4 and a ratio dQ/dV of a variation amount dQ of the battery capacity Q to a variation amount dV of the cell voltage V of the battery pack 4; a feature point specification part 15 identifying, between a minimum point P1 and a maximum point P2 on a peak shape appearing in a range of a predetermined cell voltage in the differential curve V-dQ/dV, a feature point Ps in the differential curve V-dQ/dV in which variation amount of the differential value dQ/dV with respect to the cell voltage V is maximal; and an SOH estimation part 16 estimating, based on a variation amount maximum voltage value Vs as voltage value of the feature point Ps, an SOH as deterioration index of the battery pack 4.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a secondary battery system, and more particularly, to a secondary battery system having a function of estimating a deterioration index representing the degree of deterioration of a secondary battery.

  As a deterioration index representing the degree of deterioration of the secondary battery, SOH (State of Health), which is a ratio of the current full charge capacity to the full charge capacity at the time of a new battery, is widely known. The deterioration index SOH can be obtained, for example, by charging a secondary battery from a state where the remaining battery capacity is 0 to full charge and measuring the actual full charge capacity. However, in order to estimate the deterioration index, it is necessary to charge from the state where the remaining battery capacity is 0 to full charge, and there is a problem that the time required for the estimation becomes significantly longer.

Therefore, using the fact that the differential curve having the differential characteristics with the battery capacity and the battery voltage at the time of charging / discharging of the secondary battery as parameters is different depending on the deterioration state of the secondary battery, the feature that appears on the differential curve Various methods for estimating the degradation index of the secondary battery based on the transition of the points, the amount of change, and the like have been proposed.
For example, in the secondary battery system described in Patent Document 1, the battery capacity Q is calculated when the secondary battery is charged, and the differential value dQ which is the ratio of the change amount dQ of the battery capacity Q to the change amount dV of the battery voltage V. / dV is obtained, and the differential curve V-dQ / dV is calculated from the relationship between the differential value dQ / dV and the battery voltage V.

Then, it is a deterioration index of the secondary battery from the voltage value of the characteristic point appearing in the differential curve V-dQ / dV within the range of the predetermined battery voltage V, specifically, the voltage value of the maximum point which is the peak portion of the peak shape. The rate of capacity reduction is being sought.
On the other hand, in the secondary battery system described in Patent Document 2, the differential value dQ / dV is obtained when the secondary battery is discharged, and the deterioration index of the secondary battery is determined from the maximum value of the change amount of the differential value dQ / dV with respect to the voltage value. Seeking.

JP 2013-19709 A JP-A-2006-9659

However, in the secondary battery system in Patent Document 1, since the degradation index of the secondary battery is estimated from the voltage value at the maximum point of the differential curve V-dQ / dV, the voltage value at the maximum point is detected by noise or the like. When an error occurs, there is a possibility that an estimation error of a deterioration index is caused.
Also in the secondary battery system in Patent Document 2, there is a possibility that an error occurs in the amount of change in the differential value dQ / dV due to noise or the like, leading to an estimation error of the degradation index.

As described above, the secondary battery systems described in Patent Documents 1 and 2 are not sufficiently satisfactory with respect to the estimation accuracy of the deterioration index.
In particular, in a secondary battery mounted on an electric vehicle, since the deterioration state of the secondary battery affects the cruising range of the vehicle, it is required to enable estimation of a deterioration index with high accuracy even a little. ing.

  The present invention has been made to solve such problems, and an object of the present invention is to provide a secondary battery system capable of estimating a deterioration index of a secondary battery with high accuracy. .

  In order to achieve the above object, a secondary battery system of the present invention includes a charge / discharge control unit that controls charge / discharge of a secondary battery, a battery voltage V of the secondary battery, and a change amount dV of the battery voltage V. A differential curve calculation unit for calculating a differential curve V-dQ / dV indicating a relationship with dQ / dV which is a ratio of the change amount dQ of the battery capacity Q of the secondary battery, and a predetermined region of the battery voltage V, Based on the battery voltage at the feature point, the second order based on the feature point specifying unit that specifies the feature point at which the amount of change in the differential value dQ / dV with respect to the battery voltage V in the differential curve V-dQ / dV is maximum. And a degradation index estimating means for estimating a degradation index of the battery.

  According to the secondary battery system configured as described above, the differential curve calculation unit calculates the differential curve V-dQ / dV when the secondary battery is charged or discharged, and the feature point specifying unit calculates the predetermined battery voltage V. In the region, a feature point at which the amount of change in the differential value dQ / dV with respect to the battery voltage V in the differential curve V-dQ / dV is maximized, that is, a feature point at which the slope of the differential curve V-dQ / dV is maximized is specified. . Then, the degradation index estimation means estimates the degradation index of the secondary battery based on the battery voltage at this feature point.

In the present invention, the characteristic point at which the amount of change of the differential value dQ / dV with respect to the battery voltage V in the differential curve V-dQ / dV is specified is maximum, so the battery voltage at the peak of the differential curve V-dQ / dV is determined by noise or the like. Even if a detection error occurs, the feature point can be specified with high accuracy, and the estimation accuracy of the degradation index of the secondary battery can be improved.
As another aspect, the predetermined region of the battery voltage may be set to a predetermined value on the differential curve V-dQ / dV by causing the charge / discharge control unit to start charging the secondary battery from a charging state of a predetermined amount or less. A region between the minimum point and the maximum point in the peak shape appearing in order is preferable.

According to this aspect, the peak shape appearing on the differential curve V-dQ / dV is specified according to the type of active material used for the electrode plate of the secondary battery, and the feature point is specified in this peak shape. The estimation accuracy of the battery deterioration index can be further improved.
As another aspect, a temperature detection unit that detects the temperature of the secondary battery is provided, and the deterioration index estimation unit is configured to determine the second battery based on the battery voltage V at the feature point and the temperature of the secondary battery. It is preferable to estimate the deterioration index of the secondary battery.

  According to this aspect, it is possible to improve the estimation accuracy of the deterioration index of the secondary battery over a wide temperature range.

  According to the secondary battery system of the present invention, the deterioration index of the secondary battery can be estimated with high accuracy.

It is a schematic block diagram which shows the secondary battery system of embodiment of this invention. It is a characteristic view which shows an example of the differential curve V-dQ / dV in SOH100%. It is a characteristic view which shows an example of the differential curve V-dQ / dV in SOH86%. It is a characteristic view which shows an example of the differential curve V-dQ / dV in SOH73%. It is a characteristic view which shows an example of the differential curve V-dQ / dV in SOH62%. It is a characteristic view which shows an example of the relationship between the maximum value of the gradient in differential curve V-dQ / dV, and SOH. It is a characteristic view which shows the relationship between the variation | change_quantity maximum voltage value of the differential curve in this embodiment, and SOH.

Hereinafter, an embodiment of a secondary battery system embodying the present invention will be described.
FIG. 1 is a schematic configuration diagram showing a secondary battery system of the present embodiment.
The secondary battery system 1 of the present embodiment is mounted on an electric vehicle and supplies power to a travel motor that is a power source for travel. The secondary battery system 1 as a whole is composed of a main controller 2 that integrally controls the whole and a plurality of secondary battery modules 3 connected in parallel to the main controller 2.

The secondary battery module 3 includes an assembled battery 4 (secondary battery), a sub-controller 5 and a charge / discharge control unit 6.
The assembled battery 4 is configured by combining a plurality of single cells in order to achieve a desired battery capacity and output voltage. The assembled battery 4 of the present embodiment includes LiMn ₂ O ₄ and LiMO ₂ (M is a transition metal element including at least one of Co, Ni, Al, Mn, and Fe) in the positive electrode plate. Yes.

A voltage sensor 7, a current sensor 8, and a temperature sensor 9 (temperature detection unit) are connected to the assembled battery 4. The battery voltage V of the assembled battery 4 is detected by the voltage sensor 7, the input / output current I of the assembled battery 4 is detected by the current sensor 8, the temperature T of the assembled battery 4 is detected by the temperature sensor 9, and the detected information is Input to the sub-controller 5.
The sub-controller 5 includes an input / output device (not shown), a storage device (ROM, RAM, etc.) used for storing control programs and control maps, a central processing unit (CPU), a timer counter, and the like. The sub-controller 5 has a function of controlling the charge / discharge of the battery pack 4 by driving the charge / discharge control unit 6. During charge / discharge control, the maximum allowable current and the maximum allowable voltage are determined according to the deterioration index of the battery pack 4. Adjust. In this embodiment, SOH (State of Health) that is a ratio of the current full charge capacity to the full charge capacity at the time of a new article is used as a deterioration index of the assembled battery 4.

  The sub-controller 5 includes a differential curve calculation unit 10 that calculates a differential curve necessary for estimating the SOH of the assembled battery 4. In this embodiment, V-dQ / dV is used as the differential curve. The differential curve V-dQ / dV is the relationship between the battery voltage V of the assembled battery 4 and the differential value dQ / dV that is the ratio of the change amount dQ of the battery capacity Q to the change amount dV of the battery voltage V of the assembled battery 4. Is shown.

  The differential curve calculation unit 10 sequentially calculates the battery capacity Q of the assembled battery 4 at predetermined time intervals when the assembled battery 4 is charged or discharged, acquires the battery voltage V in synchronization with this, and acquires the battery voltage of the assembled battery 4. A differential value dQ / dV that is a ratio of the change amount dQ of the battery capacity Q to the change amount dV of the voltage V is calculated. Then, a differential curve V-dQ / dV is calculated as a curve indicating the relationship between the obtained differential value dQ / dV and the battery voltage V.

  FIG. 2 is a characteristic diagram showing an example of the differential curve V-dQ / dV. In FIG. 2, a differential curve V-dQ / dV is represented with the differential value dQ / dV as the vertical axis and the battery voltage V as the horizontal axis. As the assembled battery 4 is charged or discharged, the battery voltage V increases or decreases with the state of charge (SOC) of the assembled battery 4, and the differential value dQ / dV changes accordingly. As shown in -5, inflection points (for example, P1 and P2 described later) appear on the differential curve V-dQ / dV.

The differential curve calculation unit 10 outputs the calculated differential curve V-dQ / dV and the temperature T detected by the temperature sensor 9 (hereinafter referred to as actual measurement data) to the main controller 2. Which feature point on the differential curve V-dQ / dV is specified for the estimation of SOH and how it is estimated is a feature of the present invention, and its method will be described in detail later.
The sub-controller 5 calculates the SOC of the assembled battery 4 by accumulating the input / output current I accompanying charging / discharging of the assembled battery 4 every predetermined time, and outputs the information to the main controller 2.

On the other hand, the main controller 2, like the sub-controller 5, is an input / output device (not shown), a storage device (ROM, RAM, etc.) for storing control programs and control maps, a central processing unit (CPU), a timer counter, etc. It is composed of
The main controller 2 includes an input / output unit 12, a data storage unit 13, a feature point specification unit 15, an SOH estimation unit 16 (degradation index estimation unit), and a charge / discharge command unit 17.

The data storage unit 13 stores actual measurement data input from the sub-controller 5 of each secondary battery module 3 via the input / output unit 12. The data storage unit 13 stores in advance data indicating the correlation between specific feature points on the differential curve V-dQ / dV and the SOH of the assembled battery 4 (hereinafter referred to as reference data) for each temperature range. ing.
The reference data creation process is as follows.

First, a deterioration test of the assembled battery 4 having the same standard as the assembled battery 4 of the present embodiment is performed, and charging / discharging of the unused assembled battery 4 is repeated to gradually deteriorate the life limit. In each SOH in the deterioration process, the assembled battery 4 is charged and discharged under a plurality of different temperature ranges.
Then, similarly to the processing of the differential curve calculation unit 10 described above, the differential value dQ / dV is calculated based on the battery voltage V and the battery capacity Q obtained by charging / discharging, and the relationship between the battery voltage V and the differential value dQ / dV. Is calculated, and then the position (V, dQ / dV) of a specific feature point appearing on the differential curve V-dQ / dV is obtained. As a result, the correlation between the specific feature point and the SOH of the assembled battery 4 is determined for each temperature range, and is stored in advance in the data storage unit 13 as common reference data for each secondary battery module 3.

  The SOH estimation unit 16 reads the reference data of each secondary battery module 3 stored in the data storage unit 13 and sequentially compares it with the actually measured data, and determines the SOH of the current assembled battery 4 for each secondary battery module 3. presume. Specifically, the temperature range is specified based on the battery temperature T of the actual measurement data, and the feature point that is the closest or closest to the position of the specific feature point of the actual measurement data from the reference data of each SOH corresponding to the temperature range Is selected, and the SOH of the reference data is regarded as an estimated value. As will be described later, the comparison of the feature points in the present embodiment uses the point having the largest slope of the differential curve in the region between the two peak values (minimum point P1 and maximum point P2) as an index.

The actual measurement data at this time does not need to calculate the entire region of the differential curve V-dQ / dV. If the region includes the region between the peak values (P1, P2), the feature point is specified and extended. Can estimate SOH. The deterioration index estimation means of the present invention includes a case where such a partial differential curve V-dQ / dV is calculated.
In addition, since reference data cannot be specified between each SOH and between temperature ranges, the reference data may be calculated by interpolation processing.

  The charge / discharge command unit 17 outputs a charge / discharge control command to the sub-controller 5 of each secondary battery module 3 via the input / output unit 12 based on the SOH estimated by the SOH estimation unit 16. For example, a command for limiting the maximum allowable current and the maximum allowable voltage at the time of charging / discharging is output to the secondary battery module 3 in which SOH less than a predetermined value is estimated. By the charge / discharge control by the sub-controller 5 based on this command, the assembled battery 4 having deteriorated can be protected.

The charge / discharge command unit 17 displays a message for prompting vehicle inspection on the display unit 18 provided in the driver's seat when, for example, SOH below the life limit is estimated in any of the secondary battery modules 3. As a result, vehicle inspection is performed at a sales company or the like, and the assembled battery 4 is replaced as necessary.
In the above description, for the entire assembled battery 4 of each secondary battery module 3, the battery voltage V, the input / output current I and the temperature T are detected, the differential curve V-dQ / dV is calculated, the SOH is calculated. Although the estimation process is performed, the present invention is not limited to this. For example, each process may be performed for each unit cell constituting the assembled battery 4 or each process may be performed for each unit cell group including a plurality of unit cells. Further, the differential curve calculation unit 10, the data storage unit 13, the feature point identification unit 15, and the SOH estimation unit 16 do not necessarily exist in the main controller 2 or the sub controller 5, and these processes are performed by software of an external PC or the like. May be.

  In the assembled battery 4 of the present embodiment, for example, the differential curve V-dQ / dV shown in FIG. 2 is obtained when the SOH is 100% and the battery temperature is 25 ° C., and a plurality of appearing on the differential curve V-dQ / dV. Among the feature points, a feature point Ps having the largest slope of the differential curve V-dQ / dV in a region between two peak values (minimum point P1 and maximum point P2) as a feature point suitable for estimation of SOH. Selected.

2 to 5 are examples of V-dQ / dV based on actual measurement values when charging is performed from a completely discharged state in each SOH at a battery temperature of 25 ° C. 2 shows SOH 100%, FIG. 3 shows SOH 86%, FIG. 4 shows SOH 73%, and FIG. 5 shows SOH 62%.
The feature point Ps selected in the present embodiment is the minimum point P1 that is the inflection point of the base portion in the upward peak shape that appears second in the differential curve V-dQ / dV after starting charging from the fully discharged state and the maximum point. It is selected from the region between the points P2, that is, the rising region of the upward peak shape that appears second. In this region, the point where the slope of the differential curve is maximum, that is, the point where the change amount of the differential value dQ / dV with respect to the battery voltage V is maximum is defined as the feature point Ps.

It has been confirmed that peaks such as the minimum point P1 and the maximum point P2 in the differential curve V-dQ / dV shift to the high voltage side as the deterioration progresses, as shown in FIGS. This is considered to be caused by the increase in internal resistance and the deterioration of the positive electrode and the negative electrode accompanying the deterioration of the secondary battery.
Here, the inventor measured a plurality of differential curves V-dQ / dV and actual SOH for the assembled battery 4. FIG. 6 is a graph showing the relationship between the maximum value of the change amount of the differential value dQ / dV with respect to the battery voltage V, that is, the maximum value of the slope of the differential curve V-dQ / dV and the actual SOH. In FIG. 6, □ is the region between the minimum point P1 and the maximum point P2, and ◇ is the entire charge, specifically the region from the fully discharged state to the fully charged state.

As shown in FIG. 6, the correlation between the maximum value of the slope of the differential curve V-dQ / dV and SOH is not observed in the region between the minimum point P1 and the maximum point P2, and is also observed in the entire charging. There wasn't. Therefore, it is difficult to accurately estimate SOH from the maximum value of the change amount of the differential value dQ / dV with respect to the battery voltage V.
Therefore, in the present embodiment, in the region between the minimum point P1 and the maximum point P2, based on the voltage value of the feature point Ps at which the slope of the differential curve V-dQ / dV is maximum, in other words, the differential curve V The SOH is estimated based on the maximum change amount voltage value Vs that is the voltage value of the feature point Ps at which the change amount of the differential value dQ / dV with respect to the battery voltage V at −dQ / dV is maximum.

Specifically, the charge / discharge command unit 17 charges the assembled battery 4 via the charge / discharge control unit 6 from a fully discharged state or a charged state equal to or less than a predetermined amount close to complete discharge. Then, the differential curve calculation unit 10 calculates the differential curve V-dQ / dV. A filter may be used when calculating the differential curve V-dQ / dV.
The feature point specifying unit 15 first specifies the minimum point P1 and the maximum point P2. When specifying the minimum point P1 and the maximum point P2, charging is started as described above, and the minimum point P1 and the maximum point P2 in the upward peak shape that appears second in the differential curve V-dQ / dV are as follows. do it. Next, in the region between the minimum point P1 and the maximum point P2, that is, in the region between the minimum point P1 that is the rising start point and the maximum point P2 that is the rising end point in the second peak shape from the start of charging, the differentiation is performed. A point having the largest slope of the curve V-dQ / dV, that is, a point having the largest change amount of the differential value dQ / dV with respect to the battery voltage V is specified as the feature point Ps.

  The SOH estimating unit 16 reads out reference data based on the battery temperature input from the temperature sensor 9 from the reference data stored in advance in the data storage unit 13, and uses the reference data as a voltage value of the feature point Ps. SOH is estimated on the basis of a certain change amount maximum voltage value Vs. Since this battery temperature is expected to change during charging, the battery temperature is detected and stored together with the detection of the battery voltage V during charging, and the battery temperature at the maximum variation voltage value Vs is used. That's fine.

FIG. 7 is a characteristic diagram showing a result of measuring a plurality of relations between the maximum variation voltage value Vs and SOH in the present embodiment. In FIG. 7, □ points are when the battery temperature is 0 ° C., and ◇ points are when the battery temperature is 25 ° C.
As shown in FIG. 7, the correlation between the maximum change amount voltage value Vs and the SOH is strongly expressed. Therefore, the SOH can be accurately estimated from the change maximum voltage value Vs. In the present embodiment, the correlation strongly appears in a relatively wide range such as SOH 85% to 59% especially at a battery temperature of 0 ° C., and accurate estimation of SOH is possible within this range.

Further, when the battery temperature is 0 ° C. and 25 ° C., the difference in the correlation between the change maximum voltage value Vs and the SOH is small. Therefore, for example, in the temperature range between 0 ° C. and 25 ° C., the reference data can be collected, the memory capacity in the data storage unit 13 can be reduced, and the calculation load when the SOH estimation unit 16 estimates the SOH. Can be suppressed.
In this embodiment, since SOH is estimated from a voltage value, SOH can be estimated with high accuracy using the relationship between a voltage value having a strong correlation with SOH.

  In particular, in the present embodiment, the SOH is not estimated based on the peak value (maximum value) of the differential value dQ / dV as in Patent Document 1, but the voltage at which the change amount of the differential value dQ / dV becomes the maximum value. SOH is estimated based on the value (variation maximum voltage value Vs). For example, as shown in FIG. 5, when noise is generated at the peak of the differential value dQ / dV in the differential curve V-dQ / dV, the peak value of the differential value dQ / dV may vary. Therefore, if the SOH is estimated based on the voltage value at the peak value of the differential value dQ / dV, the accuracy may decrease. On the other hand, the point at which the amount of change in the differential value dQ / dV that is the middle of the peak shape is maximum is not easily affected by noise. Therefore, as in the present embodiment, the point where the amount of change in the differential value dQ / dV becomes the maximum value, that is, the point that is the middle of the peak shape that is hardly affected by noise, is used as a feature point, and the voltage value (maximum change amount) By estimating the SOH based on the voltage value Vs), the SOH can be estimated with high accuracy.

Further, in the present embodiment, charging is started from a fully discharged state or a charged state equal to or less than a predetermined amount, and between the minimum point P1 and the maximum point P2 in the peak shape that appears second in the differential curve V-dQ / dV. The feature point Ps is specified in the region, and this specifies the feature point using a peak shape that clearly appears among a plurality of peak shapes appearing in each SOH as shown in FIGS.
The assembled battery 4 of this embodiment includes, for example, LiMn ₂ O ₄ and LiMO ₂ (M is a transition metal element containing at least one of Co, Ni, Al, Mn, and Fe) as an active material on a positive electrode plate. Among them, the characteristic that is considered to appear due to LiMn ₂ O ₄ appears as the second clear peak shape from the start of charging on the differential curve V-dQ / dV, and the characteristics of the middle in this clear peak shape By using the points as indices, it is possible to estimate with high accuracy.

  It should be noted that the characteristic point Ps in the region between the minimum point P1 and the maximum point P2 in the peak shape that appears second in the differential curve V-dQ / dV after starting from the fully discharged state or the charged state below the predetermined amount. Instead, the voltage value range in which the peak shape appears in the differential curve V-dQ / dV is confirmed in advance, the minimum point P1 and the maximum point P2 are specified in the voltage value range, and the region between them The maximum variation voltage value Vs may be specified by

In the present embodiment, since the SOH is estimated based on not only the maximum change voltage value Vs but also the battery temperature, the SOH estimation accuracy can be improved over a wide temperature range.
This is the end of the description of the embodiment, but the aspect of the present invention is not limited to this embodiment. For example, in the above-described embodiment, the secondary battery system 1 mounted on an electric vehicle is embodied, but the present invention is not limited to a vehicle. For example, the stationary battery system 1 used in a factory or a store is used. A secondary battery system may be embodied.

4 Battery pack (secondary battery)
9 Temperature sensor (temperature detector)
DESCRIPTION OF SYMBOLS 10 Differential curve calculation part 13 Data storage part 15 Feature point specific | specification part 16 SOH estimation part (degradation parameter | index estimation part)
17 Charge / Discharge command section

Claims (3)

A charge / discharge control unit for controlling charge / discharge of the secondary battery;
A differential curve V-dQ / dV indicating the relationship between the battery voltage V of the secondary battery and dQ / dV, which is the ratio of the change amount dQ of the battery capacity Q of the secondary battery to the change amount dV of the battery voltage V, A differential curve calculation unit for calculating,
A feature point specifying unit for specifying a feature point at which a change amount of the differential value dQ / dV with respect to the battery voltage V in the differential curve V-dQ / dV is maximum in a predetermined region of the battery voltage V;
A deterioration index estimating means for estimating a deterioration index of the secondary battery based on the battery voltage of the feature point;
A secondary battery system comprising:   The predetermined region of the battery voltage V is a peak that appears in a predetermined order on the differential curve V-dQ / dV when the charge / discharge control unit starts charging the secondary battery from a charging state of a predetermined amount or less. The secondary battery system according to claim 1, wherein the secondary battery system is a region between a minimum point and a maximum point in the shape. A temperature detection unit for detecting the temperature of the secondary battery;
3. The secondary battery according to claim 1, wherein the deterioration index estimating unit estimates a deterioration index of the secondary battery based on a battery voltage at the feature point and a temperature of the secondary battery. Battery system.

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