JP2019075845A - Secondary battery system - Google Patents

Abstract

To suppress an excessive increase in the frequency of equalization processing. An ECU 100 executes first to fourth processing for each of target cells other than a reference cell. The first process is a process of calculating the SOC of the target cell using the relationship (equation (2)) that holds between the SOC of the reference cell, the full charge capacity of the reference cell, and the full charge capacity of the target cell. (S104). The second process is a process of calculating the OCV corresponding to the SOC calculated in the first process by referring to the SOC-OCV curve (S105). The third process is a process of measuring the OCV of the target cell (S106). The fourth process is a correction process for reflecting the influence of the deviation of the full charge capacity of the target cell with respect to the full charge capacity of the reference cell on the measured value of OCV by the third process (S107). The ECU 100 does not execute the equalization process when there is no cell whose corrected OCV measurement value exceeds the threshold value TH. [Selection diagram] Fig. 5

Description

  The present disclosure relates to a secondary battery system, and more particularly, to equalization processing in a secondary battery system including an assembled battery in which a plurality of cells are connected in series.

  BACKGROUND ART In recent years, a battery pack including a plurality of cells connected in series is mounted on an electric vehicle such as a hybrid vehicle or a car that is in widespread use. When charging and discharging of such a battery pack are repeated, variations may occur in SOC (: State Of Charge) and voltage of each cell. When charging the battery pack, the cell having the highest SOC and the highest voltage is a constraint, and charging of all cells is stopped to avoid overcharging of the cell. On the contrary, when discharging the battery pack, the cell having the lowest SOC and the lowest voltage is a constraint, and the discharge of all the cells is stopped to avoid the overdischarge of the cell. Therefore, if SOC and voltage variation between cells is large, the range in which the battery pack can be charged and discharged becomes narrow, and there is a possibility that the battery pack can not be used sufficiently. Therefore, "equalization processing" is performed to equalize the SOC and voltage of each cell.

  For example, Japanese Patent Laid-Open No. 2015-136268 (Patent Document 1) discloses equalization processing in the configuration of a battery pack in which a plurality of cells are connected in series. In this equalization process, the change amount of the open circuit voltage (OCV) with respect to the SOC of the cell is from a region where the change amount of the OCV with respect to the SOC is smaller than a predetermined amount in the correspondence relationship (SOC-OCV characteristic) between the SOC and the OCV. The equalization process is performed when it is detected that the region has moved to a larger area than the quantitative.

JP, 2015-136268, A

  For example, as disclosed in Patent Document 1, it is conceivable to use the OCV difference between cells to determine whether to execute equalization processing. In such a case, the inventor has found that even if the power stored in the cells is equal due to the difference in the full charge capacity between the cells (variation in the full charge capacity), the OCV difference between the cells (or We focused on the point that SOC difference may occur.

  Then, for example, the equalization process is executed in a region where the SOC of the battery pack is low, and even if the OCV difference is eliminated, if the battery pack is charged thereafter and the SOC becomes high, the OCV resulting from the variation of the full charge capacity A difference may occur (details will be described later). As a result, the equalization process is performed again, and the frequency of the equalization process may be excessively high.

  The present disclosure has been made to solve the above problems, and an object thereof is to excessively increase the frequency of equalization processing in a secondary battery system including a battery pack in which a plurality of cells are connected in series. To suppress

  According to one aspect of the present disclosure, a secondary battery system includes conduction of at least one of a battery assembly including a plurality of cells connected in series and a plurality of switching devices connected in parallel to the plurality of cells. Thus, an equalization apparatus configured to be able to execute equalization processing to equalize the SOCs of a plurality of cells such that the SOCs of the plurality of cells approach a target SOC, and a control apparatus that controls the equalization apparatus. The control device estimates the SOC of any one of the plurality of cells and executes the first to fourth processes for each of the target cells other than the reference cell. The first process is a process of calculating the SOC of the target cell using the relationship established between the target SOC, the SOC of the reference cell, the full charge capacity of the reference cell, and the full charge capacity of the target cell. The second process is a process of calculating the OCV corresponding to the SOC calculated by the first process by referring to the correspondence between the predetermined SOC and the OCV. The third process is a process of measuring the OCV of the target cell. In the fourth process, the difference between the calculated value of OCV in the second process and the measured value of OCV in the third process is calculated to calculate the difference between the fully charged capacity of the target cell and the fully charged capacity of the reference cell. This process is a process of performing correction to reflect the influence on the measured value of OCV by the third process. The control device does not execute the equalization process when there is no cell in which the measured value of OCV after the correction by the fourth process exceeds a predetermined threshold value.

  According to the above configuration, in the fourth process, the measured value of the OCV in the third process is corrected to reflect the influence of the shift of the full charge capacity of the other target cells with respect to the full charge capacity of the reference cell. By performing such correction, it is possible to suppress an excessive increase in the frequency of equalization processing (details will be described later).

  According to the present disclosure, it is possible to suppress an excessive increase in the frequency of equalization processing in a secondary battery system provided with a battery pack in which a plurality of cells are connected in series.

FIG. 1 schematically shows an overall configuration of a vehicle equipped with a secondary battery system according to an embodiment of the present invention. It is a figure for demonstrating the structure of a secondary battery system in more detail. It is a figure for demonstrating the influence which the capacity | capacitance variation between cells gives to the determination of equalization | homogenization processing. It is a flowchart for demonstrating the equalization process in this Embodiment. FIG. 5 is a flowchart for explaining the OCV correction process (the process of S10) shown in FIG. 4 in more detail. It is a figure for demonstrating the process of S104-S109 in OCV correction | amendment processing.

  Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding portions are denoted by the same reference characters and description thereof will not be repeated.

  Hereinafter, a configuration in which the secondary battery system according to the present embodiment is mounted on an electric vehicle (EV: Electric Vehicle) will be described as an example. However, the secondary battery system according to the present embodiment is applicable not only to EVs, but also to general electric vehicles (hybrid vehicles, fuel cell vehicles, etc.) on which a traveling assembled battery is mounted. Furthermore, the application of the secondary battery system according to the present embodiment is not limited to vehicles, and may be stationary, for example.

Embodiment
<Overall Configuration of Vehicle>
FIG. 1 is a view schematically showing an overall configuration of a vehicle equipped with the secondary battery system according to the present embodiment. Referring to FIG. 1, a vehicle 9 is an electric vehicle and includes a secondary battery system 1. The secondary battery system 1 includes a battery assembly 10, a monitoring unit 20, an equalization unit 30, and an electronic control unit (ECU: Electronic Control Unit) 100. The secondary battery system 1 further includes a system main relay (SMR) 40, a power control unit (PCU) 50, and a motor generator 60.

  The battery assembly 10 includes a plurality of blocks 11 to 1N (see FIG. 2) connected in parallel to one another. Each block includes a plurality (M) of cells connected in series. In the present embodiment, each cell is a lithium ion secondary battery. However, the type of secondary battery is not particularly limited, and each cell may be another secondary battery such as a nickel hydrogen battery.

  The battery assembly 10 stores electric power for driving the motor generator 60 and supplies the electric power to the motor generator 60 through the PCU 50. Also, the battery pack 10 is charged by receiving the generated power through the PCU 50 when the motor generator 60 generates power.

  The monitoring unit 20 includes a voltage sensor 21 (voltage sensors 2111 to 211M described later), a current sensor 22 and a temperature sensor 23. The voltage sensor 21 detects the voltage of each cell included in the assembled battery 10. Current sensor 22 detects a current IB input / output to / from battery assembly 10. The temperature sensor 23 detects the temperature of the battery pack 10. Each sensor outputs the detection result to the ECU 100.

  An equalization unit (equalization device) 30 is provided to eliminate the imbalance (unbalance) of the SOC among the cells included in the battery pack 10. More specifically, in the battery assembly 10, the SOC among the cells may vary with time due to the variation in the self-discharge current among the cells, the variation in the current consumption of the voltage sensor 21, or the like. The equalization unit 30 discharges the corresponding cell (one or more cells) among the plurality of cells connected in series in the block in accordance with the control signal of the ECU 100 in order to eliminate the SOC unevenness. Detailed configurations of the battery assembly 10, the monitoring unit 20 and the equalization unit 30 will be described with reference to FIG. It should be noted that there is a correlation between SOC and OCV (Open Circuit Voltage) that the OCV monotonously increases with the increase of SOC, so the object of equalization may be OCV.

  The SMR 40 is electrically connected to a power line connecting the PCU 40 and the assembled battery 10. The SMR 40 switches between supply and shutoff of power between the PCU 40 and the battery assembly 10 in response to a control signal from the ECU 100.

  PCU 50 is controlled by ECU 100 to perform power conversion between battery assembly 10 and motor generator 60. PCU 50 is configured to include an inverter that receives electric power from assembled battery 10 to drive motor generator 60, a converter (both not shown) that adjust the level of DC voltage supplied to the inverter, and the like.

  Motor generator 60 is an AC motor, and is, for example, a permanent magnet synchronous motor including a rotor in which permanent magnets are embedded. Motor generator 60 is driven by an inverter included in PCU 50 to drive a drive shaft (not shown). Further, at the time of braking of the vehicle, motor generator 60 receives the rotational force of the drive wheels to generate electric power. The electric power generated by motor generator 60 is stored in battery assembly 10 through PCU 50.

  The ECU 100 includes a central processing unit (CPU) 100A, a memory (more specifically, a read only memory (ROM) and a random access memory (RAM)) 100B, and an input / output port (not shown) for inputting and outputting various signals. And is included. The ECU 100 controls the battery assembly 10 based on the signals received from the sensors of the monitoring unit 20 and the programs and maps (maps to be described later) stored in the memory 100B. The main control executed by the ECU 100 includes “equalization processing” of the battery pack 10. Details of these processes will be described later.

<Configuration of Secondary Battery System>
FIG. 2 is a diagram for explaining the configuration of the secondary battery system 1 in more detail. Referring to FIG. 2, in the battery assembly 10, a plurality (N) of blocks (also referred to as modules) are connected in parallel. In each block, a plurality (M) of cells are connected in series. M and N are natural numbers of 2 or more. However, it is not essential in the present disclosure that the battery pack includes blocks connected in parallel, and N may be 1. Since the configuration of N blocks is common, the configuration of block 11 will be representatively described below.

  The block 11 includes cells 111 to 11M. The block 11 is provided with M voltage sensors 211 1 to 211 M and M equalization circuits 311 to 31 M. Voltage sensor 2111 detects the voltage of cell 111, and outputs the detection result to ECU 100. Similarly, the other voltage sensors 2112 to 211M detect the voltage of the corresponding cell and output the detection result to the ECU 100.

  One current sensor 22 is provided for the entire assembled battery 10, and detects the current IB flowing through the entire assembled battery 10 (the sum of the currents flowing through the blocks 11 to 1N). However, a current sensor may be provided for each of the blocks 11 to 1N.

  The equalization circuit 311 is connected in parallel to the cell 111, and includes a bypass resistor R11 and a switching element (such as a transistor) Q11 as in a general equalization circuit. The same applies to the other equalization circuits 312 to 31M.

  The ECU 100 acquires voltages VB11 to VB1M of the cells 111 to 11M from the voltage sensors 2111 to 211M, respectively. Furthermore, the ECU 100 calculates the OCV from the voltage of the cell. Then, the ECU 100 compares the OCV among the cells 111 to 11M, and controls the equalization circuits 311 to 31M such that the corresponding cells are discharged such that the SOCs of all the cells 111 to 11M approach the target SOC. . This control is called "equalization processing". In FIG. 2, control signals of the equalization process are indicated by S11 to S1M. By performing the equalization process, it is possible to eliminate the SOC unevenness among the cells 111 to 11M.

<Influence of variation with full charge capacity>
In the secondary battery system 1 configured as described above, as described above, the OCV difference between cells is used to determine whether or not to execute equalization processing. More specifically, when there is a cell in which the OCV difference between the cells 111 to 11M is equal to or greater than a predetermined threshold TH, equalization processing is performed. On the other hand, when there is no cell in which the OCV difference between the cells 111 to 11M is equal to or greater than the threshold TH, in other words, equalization is performed if the OCV difference between all the cells 111 to 11M is less than the threshold TH. Processing is not performed.

  When such a criterion is used to determine whether the equalization process is performed or not, the inventor has found that the difference between the full charge capacity among the cells (so-called variation in full charge capacity) is It paid attention to the point that OCV difference may occur between cells after charge and discharge after equalization processing.

  FIG. 3 is a diagram for explaining the influence of variations in full charge capacity among cells on the determination of equalization processing. In FIG. 3, the horizontal axis indicates the amount of power (unit: Ah) stored in a certain cell (one of the cells 111 to 11 M), and the vertical axis indicates the OCV of the cell. A correspondence relationship between the OCV and the power amount of a certain cell A is indicated by a curve La. Further, the correspondence between the OCV and the electric energy of another cell B is indicated by a curve Lb.

  Referring to FIG. 3, as a result of the equalization processing being performed in the low SOC region, a state in which the amount of power stored in cell A and the amount of power stored in cell B are both substantially equal at Ah1 An example will be described.

  When the battery pack 10 is charged after execution of the equalization processing, since all the cells 111 to 11M in the block 11 are connected in series, substantially equal power is charged to all the cells 111 to 11M. Here, it is assumed that the degree of progress of deterioration differs between the cell A and the cell B, and the cell A is more deteriorated than the cell B. Therefore, the full charge capacity of the cell A is smaller than the full charge capacity of the cell B. Then, when the amount of power stored in cell A and the amount of power stored in cell B both reach Ah2, the SOC of cell A and the SOC of cell B will be different. As an example, the SOC of the cell A is 85%, whereas the SOC of the cell B is 80%. Since there is a correspondence relationship (monotonically increasing relationship) between the OCV of the cell and the SOC, the OCV of cell A is higher than the OCV of cell B, and an OCV difference occurs. If the OCV difference is larger than the threshold value TH, the equalization process is performed again on the assembled battery 10 after charging. In this way, an unnecessary equalization process is actually performed, and the frequency of the equalization process may be excessively high.

  Therefore, in the present embodiment, a configuration is adopted in which OCV correction processing is performed prior to the determination of execution / non-execution of equalization processing based on OCV. As described in detail below, the OCV correction process can correct the influence of variations in full charge capacity among cells.

<Equilibrium processing flow>
FIG. 4 is a flowchart for explaining the equalization process in the present embodiment. This flowchart is called from the main routine and executed when a predetermined condition is satisfied or whenever a predetermined operation cycle elapses. Although each step (hereinafter abbreviated as S) of this flowchart is basically realized by software processing by ECU 100, it may be realized by hardware processing by an electronic circuit fabricated in ECU 100.

  Referring to FIGS. 2 and 4, in S <b> 10, ECU 100 executes “OCV correction processing” on each of cells 111 to 11 </ b> M in block 11. This process will be described in detail in FIG. 5 and FIG.

  In S20, when there is a cell in which the corrected OCV (ΔOCVc (i) described later) is equal to or larger than the threshold TH (YES in S20), the ECU 100 advances the process to S30 and executes the equalization process. More specifically, for the equalization circuit connected in parallel to the cell in which ΔOCVc (i) is equal to or higher than the threshold TH, the switching elements in the equalization circuit are made conductive.

  On the other hand, when there is no cell in which ΔOCVc (i) is equal to or greater than threshold TH, that is, when ΔOCVc (i) is smaller than threshold TH for all cells (NO in S20), ECU 100 equally Do not execute the conversion process and return the process to the main routine.

  FIG. 5 is a flowchart for explaining the OCV correction process (the process of S10) shown in FIG. 4 in more detail. With reference to FIGS. 2 and 5, in S101, ECU 100 calculates the full charge capacity of all cells 111 to 11M. As the method of calculating the full charge capacity is known, detailed description will not be repeated. Hereinafter, the full charge capacity of the i-th cell (i is a natural number from 1 to M) is described as C (i).

In the OCV correction process in the present embodiment, any one of the cells 111 to 11M in the block 11 is selected as a reference. Since any cell can be selected, the case where the cell 111 is selected as a reference will be described as an example for simplification of the description below. In S102, the ECU 100 sets the full charge capacity C (1) of the cell 111 as a "reference capacity" C _REF . Further, the ECU 100 estimates the SOC of the cell 111, and sets the estimated SOC as a "reference SOC" S _REF .

In S103, the ECU 100 sets a "target SOC" S _TAG , which is a target SOC of all cells (a target value for approaching the SOC by the equalization processing), if the equalization processing is temporarily performed. Among the SOCs of all the cells 111 to 11M, the target SOC (S _TAG ) is to ensure the longest possible EV travel distance (the distance that the vehicle 9 can travel with the power stored in the battery pack 10). Although it is less than the lowest SOC, it is preferable to set a high SOC to some extent.

  The subsequent processes of S104 to S107 are executed for each of the target cells (cells 112 to 11M) other than the reference cell (cell 111). Here, the case where a series of processes of S104 to S107 are executed for the cell 112 will be described as an example. After execution of the process on the first target cell 112, a series of processes are similarly performed on the remaining cells 113 to 11M.

In S104, the ECU 100 calculates S _CMP (2) as the “compare SOC” used to compare the OCV with the reference cell (cell 111) for the cell 112. More specifically, S _CMP (2) is calculated as follows.

  FIG. 6 is a diagram for explaining the processing of S104 to S109 in the OCV correction processing. In FIG. 6, the horizontal axis indicates cell numbers i (i = 1 to M) in the block 11. The vertical axis represents the SOC of the cell, the OCV of the cell, the ΔOCV (ΔOCV calculated at S107) before the process of S109, and the ΔOCVc after the process of S109, in order from the top.

Referring to FIG. 6A, here, in order to perform comparison using a reference cell, cell 111 which is a reference cell and a cell which is a target cell until each SOC reaches a target SOC (S _TAG ) It is assumed that the state 112 is discharged.

  It is assumed that the amount of discharge power from the cell 112 and the amount of discharge power from the cell 111 are equal. As described above, when the amounts of discharged electric power are equal, the fact that the SOC change amount associated with the discharge is relatively large means that the full charge capacity is relatively small. Therefore, the SOC change amount ΔS (2) of the cell 112 when discharged until the SOC reaches the target SOC and the SOC change amount ΔS (1) of the cell 111 when discharged until the SOC reaches the target SOC The ratio (ΔS (2): ΔS (1)) is equal to the ratio of the reciprocal of the full charge capacity C (2) of the cell 112 to the inverse of the full charge capacity of the cell 111. As an example, when ΔS (2) = 4% and ΔS (1) = 5%, the full charge capacity of the cell 112 is larger than that of the cell 111, and the full charge capacity C (2) of the cell 112 The ratio of the full charge capacity of the cell 111 to that of the cell 111 is 5: 4.

This is more generally expressed as the following formula (1). That is, the difference (S _CMP (2)-S _TAG ) between the comparison SOC S _CMP (2) and the target SOC _STAG, and the difference between the reference SOC S _REF and the target SOC S _TAG (S The ratio to _REF -S _TAG ) is equal to the ratio of 1 / C (2) to 1 / C _REF .
(S _CMP (2)-S _TAG ): (S _REF- S _TAG ) = 1 / C (2): 1 / C _REF
... (1)

The following equation (2) is obtained by modifying the equation (1). The comparison SOC (S _CMP (2)) is calculated by substituting the parameters calculated in S101 to S103 into the equation (2).
S _CMP (2) = S _TAG − (S _TAG −S _REF ) × C (2) / C _REF
... (2)

The comparison SOC (S _CMP (2)) of the cell 112 refers to the reference SOC (S _REF ), and takes into consideration the influence of the variation of the full charge capacity of the cell 112 on the reference capacity C _REF . Is a value obtained by calculating the SOC of From the equation (2), S _CMP (2) is performed using only the target SOC (S _TAG ) and the parameters (S _REF and C _REF ) on the cell 111 as a reference other than the full charge capacity C (2) of the cell 112. It can be seen that) is represented. Therefore, by comparing the comparison SOCs between the cells 112 to 11M, it is possible to compare the SOC deviation due to the influence of the variation of the full charge capacity of the cells 112 to 11M with respect to the reference capacity C _REF .

5 and 6B, in S105, ECU 100 calculates in S104 by referring to a map (not shown) indicating an SOC-OCV curve stored in advance in memory 100B. The OCV _CMP (2) is calculated as a “compare OCV” that is an OCV corresponding to the comparison SOC (S _CMP (2)). The OCV _REF is similarly calculated from the SOC _REF for the reference cell 111.

Furthermore, the ECU 100 measures the OCV of the cell 112 using the voltage sensor 2112 and the current sensor 22 (S106). The OCV of the cell 112 measured in this manner is referred to as "measurement OCV" and is described as OCV _MSR (2). The measured OCV can be determined, for example, from the voltage measurement value after the charge / discharge state of the assembled battery 10 continues and the polarization is eliminated.

Referring to FIGS. 5 and 6C, in S107, ECU 100 performs the comparison OCV (OCV _CMP (2)) calculated in S105 and the measured OCV (OCV _MSR (2) measured in S106. The difference with the above is calculated according to the following equation (3).
ΔOCV (2) = OCV _CMP (2)-OCV _MSR (2) (3)

  This difference is the difference between the OCV (comparison OCV) in consideration of the effect of the variation in the full charge capacity and the measured OCV (measured OCV), and the actual value of the OCV is considered in the effect of the variation in the full charge capacity It is understood that it is corrected by the ideal value. This shift is referred to as "OCV shift", and the OCV shift of the i-th cell is described as "ΔOCV (i)".

  In addition, the process of S104-S107 is respectively corresponded to the "1st process"-"4th process" concerning this indication.

  In S108, the ECU 100 completes the calculation of the OCV deviation ΔOCV (i) (i = 2 to M) for all cells other than the cell selected as the reference (all cells 112 to 11 M other than the cell 111 in this example). It is determined whether it has been done. If the calculation of the OCV deviation ΔOCV (i) is not completed for all cells (NO in S108), the process returns to S104, and the processes of S104 to S107 are executed again for the next cell. .

When the calculation of the OCV deviation ΔOCV (i) is completed for all cells (YES in S108), the ECU 100 advances the process to S109 and executes the conversion process of the OCV deviation ΔOCV calculated in S107. More specifically, as shown in the following equation (4), for each of the cells 111 to 11M, the difference between the OCV deviation ΔOCV (i) of the cell and the minimum value of the OCV deviation of all the cells is calculated. This difference is described as "ΔOC Vc (i)".
ΔOCVc (i) = ΔOCV (i) −min (ΔOCV (i)) (4)

  As shown in FIG. 6C, .DELTA.OCV.DELTA. (I) before execution of the process of S109 is 0 in the cell 111 as a reference, but other cells 112 to 11M can take various positive and negative values.

  Therefore, the ΔOCV (i) of each cell is subtracted the ΔOCV (5) of the fifth cell in the example shown in FIG. 6 (C) from the minimum value of ΔOCV (i), as shown in FIG. 6 (D). As shown, ΔOCVc (i) of all cells is 0 or more (0 or a positive value). Thus, while ΔOCVc (i) and the threshold value TH are compared in the process of S20 of FIG. 4, a positive value can be set as the threshold value TH, and the negative value ΔOCVc (i) can be set. There is no need to consider, and the comparison operation is simplified. However, the process of S109 is not essential, and may be compared with another threshold value (not limited to a positive value) of ΔOCV (i) of each cell.

As described above, according to the present embodiment, the processing between S104 and S107 of the OCV correction processing makes it possible to obtain an inter-cell relationship based on the full charge capacity (reference capacitance C _REF ) of the cell 111 which is the reference cell. It is possible to correct the influence of the variation of the full charge capacity. This prevents the equalization process from being performed again after the execution of the equalization process, so that an excessive increase in the frequency of the equalization process can be suppressed.

  It should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present disclosure is indicated not by the description of the embodiments described above but by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

  Reference Signs List 1 secondary battery system, 10 assembled batteries, 11 to 11 N blocks, 111 to 11 M cells, 20 monitoring units, 21, 2111 to 211 M voltage sensors, 22 current sensors, 23 temperature sensors, 30 equalization units, 40 SMR, 50 PCUs 60 motor generator, 311 to 31 M equalization circuit, R11 to R1 M bypass resistance, Q11 to Q1 M switching element, 100 ECU, 100 A CPU, 100 B memory, 9 vehicles.

Claims (1)

An assembled battery including a plurality of cells connected in series;
By conducting at least one of the plurality of switching elements connected in parallel to the plurality of cells, the SOCs of the plurality of cells are equalized so that the SOCs of the plurality of cells approach the target SOC. An equalization device configured to be able to execute an equalization process
A control device for controlling the equalization device;
The control device estimates the SOC of any one of the plurality of cells, and executes the first to fourth processes for each of the target cells other than the reference cell.
The first process calculates the SOC of the target cell using a relationship established between the target SOC, the SOC of the reference cell, the full charge capacity of the reference cell, and the full charge capacity of the target cell. Processing,
The second process is a process of calculating an OCV corresponding to the SOC calculated by the first process by referring to a correspondence between a predetermined SOC and an OCV.
The third process is a process of measuring the OCV of the target cell,
In the fourth process, the difference between the calculated value of OCV by the second process and the measured value of OCV by the third process is calculated to obtain the fullness of the target cell with respect to the full charge capacity of the reference cell. A process of performing correction to reflect the influence of the deviation of the charge capacity on the measured value of OCV by the third process,
The said control apparatus is a secondary battery system which does not perform the said equalization process, when the measured value of OCV after correction | amendment by the said 4th process does not exceed a predetermined | prescribed threshold value.

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