JP2020079723A - Secondary battery system - Google Patents

Abstract

To provide a secondary battery system capable of estimating a deterioration index with high accuracy while suppressing an amount of map data used to estimate the deterioration index.SOLUTION: The secondary battery system includes: a differential curve calculation unit 10 for charging and discharging an assembled battery 4 and calculating a differential curve V-dQ/dV showing a relationship between a battery voltage V of the assembled battery 4 and a differential value dQ/dV, which is a ratio of a change amount dQ of a battery capacity Q of the assembled battery 4 to a change amount dV of the battery voltage V; a characteristic point identifying unit 15 for identifying a characteristic point Pt of the differential curve V-dQ/dV that appears in a predetermined region of the battery voltage V; a data storage unit 13 storing a map showing a relationship between a voltage Vt of the characteristic point Pt in a state where charging and discharging of the assembled battery 4 is stopped and an SOH of the assembled battery 4; and an SOH estimation unit 16 for estimating the SOH of the assembled battery 4 based on the voltage Vt of the characteristic point Pt in the state where charging and discharging of the assembled battery 4 is stopped using the map stored in the data storage unit 13.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 indicating a deterioration degree of a secondary battery.

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

Therefore, by utilizing the fact that the shape of the differential curve having the differential characteristics with the battery capacity and the battery voltage at the time of charging/discharging the secondary battery as parameters varies according to the deterioration state of the secondary battery, the features that appear on the differential curve Various methods have been proposed for estimating the deterioration index of the secondary battery based on the transition of points, the amount of change, and the like.
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 that is the ratio of the change amount dQ of the battery capacity Q to the change amount dV of the battery voltage V is calculated. /dV is calculated, and the differential curve V-dQ/dV is calculated from the relationship between the differential value dQ/dV and the battery voltage V.

Then, from the voltage value of the characteristic point appearing on the differential curve V-dQ/dV within the range of the predetermined battery voltage V, more specifically, the voltage value of the maximum point which is the apex portion of the peak shape, it is a deterioration index of the secondary battery. We are looking for capacity reduction rate.
Further, in the secondary battery system described in Patent Document 2, from the characteristic points appearing in the differential curve V-dQ/dV, specifically, the differential value dQ/dV (maximum value) of the maximum point of the differential curve V-dQ/dV. Deterioration index of the secondary battery is obtained from.

JP, 2013-19709, A JP, 2014-139897, A

By the way, when the secondary battery is charged, the charging current may vary greatly depending on the capability of the charger, which is the power supply side, such as rapid charging and normal charging.
However, if the charging current is changed at the time of charging, the measured value of the charging voltage of the secondary battery changes, so that an estimation error may occur in the deterioration index. On the other hand, a map for estimating the deterioration index may be stored for each charging condition such as charging current, and the map may be selected and used according to the charging condition, but there are many map data to be stored. As a result, there are problems that the system resources are significantly consumed and the number of test steps required for storing the map data in advance is increased.

  The present invention has been made to solve such a problem, and an object thereof is to accurately estimate the deterioration index while suppressing the map data amount used for estimating the deterioration index. It is to provide a possible secondary battery system.

  In order to achieve the above object, the secondary battery system of the present invention is a charge/discharge control unit for controlling charge/discharge of a secondary battery, and the secondary battery is charged/discharged by the charge/discharge control unit. Differential curve V-dQ/dV showing the relationship between the battery voltage V of the secondary battery and the differential value 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 calculating unit, a characteristic point specifying unit that specifies a characteristic point of the differential curve V-dQ/dV that appears in a predetermined region of the battery voltage V, and a state in which charging/discharging of the secondary battery is stopped. In the storage unit that stores a map showing the relationship between the battery voltage of the characteristic point and the deterioration index of the secondary battery in, and using the map stored in the storage unit, charge and discharge of the secondary battery And a deterioration index estimation unit that estimates a deterioration index of the secondary battery based on the battery voltage at the characteristic point in a state where the battery is stopped.

Thereby, when estimating the deterioration index of the secondary battery, the influence of the charging/discharging of the secondary battery, specifically, the influence of the internal resistance and current value of the secondary battery on the voltage value is eliminated, and The deterioration index of the battery can be accurately estimated. Further, it is not necessary to prepare a map for estimating the deterioration index for each current value, and the map data can be reduced.
Further, preferably, the characteristic point is a point at which the differential value dQ/dV becomes a predetermined value.

As a result, the characteristic points can be easily specified, and the deterioration index of the secondary battery can be estimated when the differential value dQ/dV reaches a predetermined value, and the deterioration index estimation time can be shortened. be able to.
Preferably, the deterioration index estimating unit stops charging/discharging of the secondary battery when the charging/discharging control unit charges/discharges the secondary battery and the differential value dQ/dV reaches the predetermined value. The deterioration index of the secondary battery may be estimated by using the battery voltage of the secondary battery after a predetermined time as the battery voltage of the characteristic point.

This makes it possible to estimate the deterioration index of the secondary battery based on the battery voltage of the secondary battery after a lapse of a predetermined time after stopping the charging/discharging of the secondary battery. By avoiding this, the deterioration index of the secondary battery can be accurately estimated.
Preferably, a temperature detection unit that detects the temperature of the secondary battery is provided, and the deterioration index estimation unit is based on the battery voltage of the characteristic point and the temperature of the secondary battery, and a deterioration index of the secondary battery. Should be estimated.

  Thereby, the deterioration index of the secondary battery can be accurately estimated in a wide temperature range.

  According to the secondary battery system of the present invention, the deterioration index is estimated by eliminating the influence of charging/discharging of the secondary battery, so that the deterioration index of the secondary battery can be accurately estimated. Furthermore, it is possible to reduce the map data, suppress the consumption of system resources, and suppress the number of test steps for acquiring the map data.

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 a differential curve V-dQ/dV. It is a characteristic view which shows an example of the correlation of voltage Vt and SOH of an assembled battery. It is a flowchart which shows the estimation control procedure of SOH of an assembled battery. It is a characteristic view which shows an example of the differential curve V-dQ/dV during energization of an assembled battery. It is an example of a characteristic diagram obtained by subtracting the overvoltage IR from the differential curve V-dQ/dV when the assembled battery is unloaded.

An embodiment of a secondary battery system embodying the present invention will be described below.
FIG. 1 is a schematic configuration diagram showing a secondary battery system of the present embodiment. FIG. 2 is a characteristic diagram showing an example of the differential curve V-dQ/dV. In FIG. 2, the differential value dQ/dV is taken as the vertical axis and the battery voltage V is taken as the horizontal axis, and the differential curves V-dQ/dV for SOH 100%, 75%, and 64% are shown. FIG. 3 is a characteristic diagram showing an example of the correlation between the voltage Vt and the SOH of the battery pack 4. In FIG. 3, each temperature is displayed as a solid line or a broken line.

  The secondary battery system 1 of the present embodiment is installed in a rechargeable vehicle such as an electric vehicle or a plug-in hybrid vehicle, and supplies electric power to a traveling motor that is a power source for traveling. The secondary battery system 1 as a whole is composed of a main controller 2 for integrally controlling the entire battery 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 unit cells to achieve a desired battery capacity and output voltage. The assembled battery 4 of the present embodiment contains LiMn ₂ O ₄ and LiMO ₂ (M is a transition metal element containing at least one of Co, Ni, Al, Mn, and Fe) in the positive electrode plate. There is.

A voltage sensor 7, a current sensor 8 and a temperature sensor 9 (temperature detection unit) are connected to the assembled battery 4. The voltage sensor 7 detects the battery voltage V of the assembled battery 4, the current sensor 8 detects the input/output current I of the assembled battery 4, the temperature sensor 9 detects the battery temperature T of the assembled battery 4, and the detected information. Is input to the sub controller 5.
The sub-controller 5 is composed of 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 driving the charge/discharge control unit 6 to control charge/discharge of the assembled battery 4, and during charge/discharge control, the maximum allowable current or the maximum allowable voltage is determined according to the deterioration index of the assembled battery 4. Adjust. In the present embodiment, SOH (State of Health), which is the ratio of the current full charge capacity to the new full charge capacity, is used as the deterioration index of the assembled battery 4.

  Further, the sub-controller 5 includes a differential curve calculating unit 10 that calculates a differential curve necessary for estimating the SOH of the battery pack 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 which is the ratio of the variation dQ of the battery capacity Q to the variation 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 every predetermined time set appropriately when the assembled battery 4 is charged or discharged, and acquires the battery voltage V in synchronization with the battery capacity Q. The differential value dQ/dV, which 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 battery 4, is calculated. Then, a differential curve V-dQ/dV is calculated as a curve showing the relationship between the obtained differential value dQ/dV and the battery voltage V.

  As the battery voltage V increases or decreases with the charging rate (SOC: State of Charge) of the battery pack 4 as the battery pack 4 is charged or discharged, and the differential value dQ/dV changes accordingly, for example, as shown in FIG. As shown in, a peak shape appears on the differential curve V-dQ/dV in a predetermined range of the battery voltage V (for example, near 3.85V to 4.05V). In addition, the range of the battery voltage V including the low voltage side inclined portion at this peak is defined as a specific voltage section Vr. This specific voltage section Vr corresponds to a predetermined region of the battery voltage V in the present invention.

The differential curve calculation unit 10 outputs the calculated differential curve V-dQ/dV and the battery temperature T detected by the temperature sensor 9 (hereinafter, referred to as actual measurement data) to the main controller 2.
The sub-controller 5 calculates the SOC of the battery pack 4 by integrating the input/output current I associated with the charging/discharging of the battery pack 4 at each set predetermined time, and outputs the information to the main controller 2.

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

From the differential curve V-dQ/dV calculated by the differential curve calculating unit 10, the feature point identifying unit 15 determines that the differential value dQ/dV is within the specific voltage section Vr at the specified value a (for example, 60, which is the predetermined value of the present invention). The point on the differential curve V-dQ/dV (corresponding to) is defined as the characteristic point Pt.
The data storage unit 13 stores the actual measurement data input from the sub-controller 5 of each secondary battery module 3 via the input/output unit 12. In the data storage unit 13, data indicating the correlation between the voltage Vt of the specific feature point Pt on the differential curve V-dQ/dV and the SOH of the battery pack 4 in advance by a test (hereinafter referred to as reference data). ) Is stored for each temperature range. For example, as shown in FIG. 3, the reference data has a relationship such that SOH decreases as the voltage Vt of the characteristic point Pt increases for each temperature range.

The process of creating the reference data is as follows, and the test is performed at a factory or the like.
First, a deterioration test of the assembled battery 4 having the same standard as that of the assembled battery 4 of the present embodiment is performed, and the unused assembled battery 4 is repeatedly charged and discharged to gradually deteriorate to 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, in the differential curve calculation unit 10, a differential value dQ/dV is calculated based on the battery voltage V and the battery capacity Q obtained by charging/discharging, and a differential curve V indicating the relationship between the battery voltage V and the differential value dQ/dV. -Calculate dQ/dV. Further, the characteristic point identifying unit 15 obtains the voltage Vt of the characteristic point Pt at which the differential value dQ/dV in the differential curve V-dQ/dV becomes the specified value a.

In particular, in this embodiment, the voltage Vt, the input/output current (current It), and the internal resistance R of the assembled battery 4 when the differential value dQ/dV reaches the specified value a are acquired for each SOH and temperature. Then, the no-load voltage V0 at the time of estimation is calculated from the voltage Vt, the current It and the internal resistance R by the following formula (1).
V0=Vt-It*R (1)
Then, the data storage unit 13 preliminarily sets the correlation between the no-load voltage V0 and the SOH of the assembled battery 4 as common reference data (map data) of each secondary battery module 3 for each temperature range. Remember.

  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 the reference data with the actually measured data to determine the current SOH of the 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 from the reference data of each SOH corresponding to the temperature range, the characteristic point that is the same or closest to the position of the specific characteristic point of the actual measurement data. Select the reference data that has, and consider the SOH of the reference data as the estimated value. The characteristic point Pt in the present embodiment is a graph showing the relationship between the battery voltage V and the differential value dQ/dV, the line L where the differential value dQ/dV is the predetermined value a, and the measured differential curve V-dQ/ It is the intersection with dV.

It is not necessary for the actual measurement data at this time to calculate the entire area of the differential curve V-dQ/dV, and if the differential value dQ/dV can be found to be the predetermined value a, the characteristic point Pt can be identified and then extended. SOH can be estimated. The present invention also includes the case where such a partial differential curve V-dQ/dV is calculated.
Since the reference data cannot be specified between each SOH and each temperature range, 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 or the like estimated by the SOH estimation unit 16. For example, with respect to the secondary battery module 3 in which SOH less than the predetermined value is estimated, a command for limiting the maximum allowable current and the maximum allowable voltage during charging/discharging is output. By the charge/discharge control by the sub-controller 5 based on this command, the assembled battery 4 which has deteriorated can be protected.

Further, the charge/discharge command unit 17 displays a message prompting a vehicle inspection on the display unit 18 provided in the driver's seat when SOH which is shorter than the life limit is estimated in any of the secondary battery modules 3. As a result, the vehicle is inspected by a sales company or the like, and the battery pack 4 is replaced if necessary.
In the above description, for the entire assembled battery 4 of each secondary battery module 3, the detection process of the battery voltage V, the input/output current I and the temperature T, the calculation process of the differential curve V-dQ/dV, the SOH Although the estimation process is performed, the estimation process is not limited to this. For example, each process may be performed for each unit cell that constitutes 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 have to be present 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.

Next, a method of estimating the SOH of the battery pack 4 executed by the main controller 2 will be described in detail with reference to FIG.
FIG. 4 is a flowchart showing the SOH estimation control procedure of the battery pack 4.
In the present embodiment, the SOH of each assembled battery 4 is estimated when the assembled battery 4 is charged. The SOH estimation control shown in FIG. 4 can be performed when the battery pack 4 is charged from a state where the voltage of the battery pack 4 is less than the specific voltage section.

First, in step S10, the charge/discharge control unit 6 starts charging the assembled battery 4. Then, the process proceeds to step S20.
In step S20, the current differential value dQ/dV is input from the differential curve calculation unit 10 and it is determined whether the differential value dQ/dV is equal to or greater than the specified value a. Since this control is started from the state where the differential value dQ/dV is less than the specified value a, in this step, it is determined whether or not the differential value dQ/dV has been reached. If the differential value dQ/dV is greater than or equal to the specified value a, the process proceeds to step S30. If the differential value dQ/dV is less than the specified value a, step S20 is repeated.

In step S30, the battery voltage V, the input/output current I, and the temperature T are detected by the sensors 7, 8, and 9. That is, in this step, the voltage Vt, the current It, and the temperature T when the differential value dQ/dV reaches the specified value a are acquired. Then, the process proceeds to step S40.
In step S40, charging of the assembled battery 4 is stopped. Then, the process proceeds to step S50.
In step S50, it is determined whether or not the elapsed time after stopping the charging in step S40 has exceeded a predetermined time t1 (for example, 10 seconds). The predetermined time t1 corresponds to the predetermined time of the present invention.
If the elapsed time after stopping the charging is the predetermined time t1 or more, the process proceeds to step S60. When the elapsed time after stopping the charging is less than the predetermined time t1, step S50 is repeated.

In step S60, the voltage sensor 7 detects the voltage value Vb of the battery pack. Then, the process proceeds to step S70.
In step S70, the internal resistance value R of the battery pack 4 is calculated. As shown in the following formula (2),
The internal resistance value R is a value obtained by dividing the difference ΔV (=Vt−Vb) between the voltage Vt detected in step S30 and the voltage value Vb detected in step S60 by the current It detected in step S30. is there.

R=ΔV/It (2)
Then, the process proceeds to step S80.
In step S80, the overvoltage IR of the battery pack 4 is calculated. Specifically, the current It detected in step S30 is multiplied by the internal resistance R calculated in step S70. Then, the process proceeds to step S90.

In step S90, the no-load voltage V0 is calculated. Specifically, the no-load voltage V0 is obtained by subtracting the overvoltage IR calculated in step S80 from the voltage Vt detected in step S30. Then, the process proceeds to step S100.
In step S100, the no-load voltage V0 calculated in step S90 and the temperature T detected in step S30 are used to indicate the correlation between the no-load voltage V0 stored in the data storage unit 13 and the SOH of the battery pack 4. The SOH of the battery pack 4 is obtained using the map. Then, the process proceeds to step S110.

In step S110, charging is restarted. Then, this routine is finished.
As described above, in the present embodiment, it is assumed that the differential value dQ/dV is the specified value a as the characteristic point Pt of the differential curve V-dQ/dV, and based on the voltage Vt at the specified value a. Since the SOH is estimated, the SOH can be accurately estimated by utilizing the relationship between the SOH and the voltage Vt having a strong correlation.

  However, as shown in FIG. 5, the peak position of the differential curve V-dQ/dV changes depending on the charging current value flowing in the assembled battery 4. Specifically, as the charging current value flowing in the battery pack 4 increases, the voltage rises due to the internal resistance of the battery pack 4, and the differential curve V-dQ/dV peaks on the high voltage side (right side in FIG. 5). The value moves. Therefore, if SOH is estimated during charging, an error may occur depending on the charging current value.

  Therefore, in this embodiment, the SOH of the assembled battery is estimated based on the voltage value of the characteristic point in the no-load state. FIG. 6 shows an example of the differential curve V-dQ/dV when the overvoltage IR is subtracted at the time of low power or large current, and it is regarded as a no-load state. As shown in FIG. 6, in the no-load state, the differential curve V-dQ/dV is substantially the same as the differential curve V-dQ/dV at low power or high current.

Therefore, in the present embodiment, when estimating the SOH of the battery pack 4, the effect of charging the battery pack 4, more specifically, the voltage value (Vt) of the internal resistance (R) of the battery pack 4 and the current value (It). ), the SOH of the battery pack 4 can be estimated accurately.
Further, by storing a map for estimating SOH from the no-load voltage V0, it is not necessary to easily prepare a map for estimating SOH from the voltage Vt of the characteristic point Pt for each current value. Data can be reduced. As a result, the consumption of system resources is suppressed, and map data indicating the relationship between the voltage Vt at the characteristic point Pt and SOH (actually, map data indicating the relationship between the no-load voltage V0 and SOH), that is, the reference data. It is possible to suppress the number of test steps for storing the value.

  Further, since the differential value dQ/dV is the point at which the differential value dQ/dV becomes the specified value a as the characteristic point of the differential curve V-dQ/dV, the characteristic point Pt can be easily specified and the differential value dQ/dV is specified. It becomes possible to estimate the SOH of the assembled battery 4 near the time when the value becomes a, specifically, after a predetermined time t1 has elapsed from the time when the differential value dQ/dV became the specified value a), and the assembled battery 4 was fully charged. It becomes possible to estimate the SOH before setting, and the estimation time of the SOH can be shortened.

Further, in the present embodiment, not only the battery voltage V and the input/output current I but also the temperature T is detected and the SOH is estimated from the map stored for each temperature. Therefore, the estimation accuracy of the SOH is improved in a wide temperature range. Can be made
Although the description of the embodiment has been completed, the aspects of the present invention are not limited to this embodiment. For example, in the above embodiment, the SOH is estimated during charging, but the SOH may be estimated during discharging.

Further, in the above embodiment, the point where the differential value dQ/dV becomes the specified value a in the differential curve V-dQ/dV is set as the characteristic point Pt, and the SOH is estimated from the battery voltage V. The feature point Pt may be a point other than the point where the differential value dQ/dV becomes the specified value a, such as the peak, inflection point, and maximum point of the differential curve V-dQ/dV in the range.
Further, in the present embodiment, the present invention has been embodied as the secondary battery system 1 mounted in a vehicle such as an electric vehicle, but the present invention is not limited to the vehicle, and may be used in, for example, a factory or a store. It may be embodied in a stationary secondary battery system used.

4 battery pack (secondary battery)
6 Charge/discharge control section 9 Temperature sensor (temperature detection section)
10 differential curve calculation unit 13 data storage unit (storage unit)
15 Feature Point Identification Section 16 SOH Estimation Section (Degradation Index Estimation Section)

Claims (4)

A charge/discharge control unit for controlling charge/discharge of the secondary battery,
The charging/discharging control unit charges/discharges the secondary battery to obtain a ratio of a battery voltage V of the secondary battery and a change amount dQ of the battery capacity Q of the secondary battery to a change amount dV of the battery voltage V. A differential curve calculating unit for calculating a differential curve V-dQ/dV showing a relationship with a certain differential value dQ/dV,
A characteristic point specifying unit that specifies a characteristic point of the differential curve V-dQ/dV that appears in a predetermined region of the battery voltage V;
A storage unit that stores a map showing the relationship between the battery voltage of the characteristic point and the deterioration index of the secondary battery in a state where charging/discharging of the secondary battery is stopped,
Degradation index estimation for estimating a degradation index of the secondary battery based on the battery voltage at the characteristic point in a state where charging/discharging of the secondary battery is stopped using the map stored in the storage unit. And a secondary battery system.   The secondary battery system according to claim 1, wherein the characteristic point is a point at which the differential value dQ/dV becomes a predetermined value.   When the charge/discharge control unit charges/discharges the secondary battery and the differential value dQ/dV reaches the predetermined value, the deterioration index estimation unit stops the charge/discharge of the secondary battery and a predetermined time elapses. The secondary battery system according to claim 2, wherein a deterioration index of the secondary battery is estimated based on a battery voltage of the secondary battery afterwards. A temperature detector for detecting the temperature of the secondary battery,
4. The deterioration index estimation unit estimates the deterioration index of the secondary battery based on the battery voltage at the characteristic point and the temperature of the secondary battery. The secondary battery system according to.

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