JP2002010511A - Capacity adjusting method for battery pack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent misdecision of abnormality of cells, and to enable malfunction detection of a capacity adjusting function without providing a separate detection system, in capacity adjustment for a battery pack. SOLUTION: In a battery pack formed by connecting a plurality of modules each of which is composed of a plurality of cells in series, the average value Vamin of the voltages of the cells of a module having a minimum voltage is used as a target value Vg for capacity adjustment, and each cell is discharged by time which corresponds to its deviation from the target value. The voltage of a cell 12a which is not abnormal though its quantity of voltage decrease is relatively larger than the other many cells, approaches the same level as the voltages of the other cells, as shown in (a), (b), and (c) in order corresponding to the passage of time. When an open-circuit voltage lowers so largely as to exceed a first threshold Vd from the average value of the cell voltages of the minimum voltage module, the quantity of its voltage decrease can be decided as abnormal, and cells whose quantities of voltage decrease are abnormal can be clearly identified from those whose quantities of voltage decrease are normal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of adjusting the capacity of a battery pack for correcting variations in cell capacity of the battery pack.

[0002]

2. Description of the Related Art In a battery pack composed of a plurality of cells, the voltage of each cell varies with the use of the cell and the variation in the self-discharge current of the cell and the consumption current of a cell voltage detection circuit attached to the cell. It varies individually due to variations and the like. In a battery pack in which the battery capacity is in a certain proportional relationship with the open-circuit voltage, the variation in the open-circuit voltage itself results in the variation in the capacity of each cell. When charging the assembled battery, it is necessary to adjust the capacity according to the above-mentioned variation of each cell to make the capacity uniform.

Conventionally, for this capacity adjustment, a capacity adjustment discharge circuit is provided for each cell, and the average voltage of all cells of the assembled battery is set as a capacity adjustment target value. In some cases, a cell having a high voltage is discharged in accordance with a deviation from a capacity adjustment target value to approximate the average voltage of the assembled battery. Then, during the capacity adjustment, an abnormality determination level is set up and down by a predetermined value from the capacity adjustment target value as a reference, and the abnormality determination of the individual cell is performed based on whether or not the abnormality determination level is exceeded. Has become.

[0004]

However, in the above-described capacity adjustment method, when there is a cell which is not abnormal but has a relatively large voltage drop compared to a large number of other cells, the voltage drop is relatively small. There is a problem that a cell having a large value is erroneously determined to be abnormal. That is, since only cells whose voltage is higher than the average voltage of all cells of the capacity adjustment target value are discharged, the average voltage of all cells changes to a higher value as shown in FIG. The large filled cell Cx in the figure eventually falls below the abnormality determination level set to the lower Vd from the capacity adjustment target value.

FIG. 8 shows the voltage position of each cell by ○, and (a), (b), and (c) show the change of the cell voltage over time. In (a), cells Ca, Cb, and Cd higher than the capacity adjustment target value are discharged to a state of (b), and (c) shows a state after a further lapse of time. Since the cell Cx drops relatively more than the other cells,
Moving away from the average voltage of all cells.

Further, in the case where an abnormality in the capacity adjustment function occurs in any of the cells due to, for example, a failure in which the capacity adjustment discharge circuit for discharging the cell having a voltage higher than the capacity adjustment target value remains off. Since the voltage value of the cell may change while maintaining a predetermined deviation from the average voltage of all the cells, there is a problem that when the deviation is within Vd of the abnormality determination level width, an abnormality cannot be detected.

That is, since only the cells whose voltage is higher than the average voltage of all cells of the capacity adjustment target value are discharged, as shown in FIG. After that, the cells Ca and Cb higher than the capacity adjustment target value are discharged to be in the state of (b), and after the other cells are adjusted to the capacity adjustment target value while leaving the cell Cy as shown in (c), Cell C with abnormal capacity adjustment function
y changes while maintaining a predetermined deviation from the average voltage of all the cells. Therefore, a separate detection system for determining the ON / OFF failure of the capacity adjustment discharge circuit is required.

Accordingly, the present invention has been made in view of the above-mentioned conventional problems, and provides a method of adjusting the capacity of an assembled battery, in which erroneous determination of a cell abnormality is prevented, and abnormality detection of a capacity adjustment function is enabled without a separate detection system. The purpose is to do.

[0009]

According to the present invention, a plurality of modules each having a plurality of cells connected in series are connected in series, and a discharge circuit is provided for each cell. A method of adjusting the capacity of an assembled battery, comprising: detecting the open-circuit voltage of each cell at predetermined time intervals, setting a cell voltage average value in a module having the lowest module voltage as a capacity adjustment target value, and a capacity adjustment target value and The adjustment discharge time is determined based on the open voltage of the cell, and the discharge of the cell is repeated for the adjustment discharge time.

According to a second aspect of the present invention, in addition to the configuration of the first aspect, a cell in which the difference between the cell voltage average value and the open circuit voltage exceeds a predetermined threshold value is determined to be abnormal. More specifically, the threshold value is a first threshold value applied to a cell having an open-circuit voltage lower than the cell voltage average value, and the difference between the cell voltage average value and the open-circuit voltage is determined. Is determined to be abnormal when the voltage exceeds a first threshold value. The invention according to claim 4 is applied to a cell having an open-circuit voltage whose threshold value is higher than the cell voltage average value. When the difference between the cell voltage average value and the open-circuit voltage exceeds the second threshold value, the cell is determined to be abnormal in the capacity adjustment function.

According to a fifth aspect of the present invention, the detection of the open-circuit voltage of the cell and the discharge for adjusting the capacity are performed in parallel for each module.

[0012]

According to the first aspect of the present invention, an adjusted discharge time determined based on the cell voltage average value of the module having the lowest module voltage as the capacity adjustment target value and each cell based on the open-circuit voltage and the capacity adjustment target value. Only the discharge, it is possible to approach the capacity adjustment target value only by the discharge, and the voltage of each cell is quickly equalized regardless of whether it is charging or discharging and without discharging the capacity more than necessary. The effect is that

According to the second aspect of the present invention, the abnormality of the cell can be determined based on the cell voltage average value and the threshold value. For example, the voltage of a cell that has a relatively large voltage drop but is not abnormal compared to a large number of other cells is determined by setting the average cell voltage of the module having the lowest module voltage as the overall capacity adjustment target value. Since the voltage approaches the same level as the voltage of many cells, the open-circuit voltage decreases so as not to approach the level of many cells but to exceed the first threshold from the average value of the cell voltage. In such a case, it can be determined that the voltage drop amount is abnormal, and the cell having the normal voltage drop amount and the cell having the abnormal voltage drop amount can be clearly identified.

In the case where the open-circuit voltage becomes higher as the number of cells exceeds the second threshold value from the average value of the cell voltage while a large number of cells gather at the level of the capacity adjustment target value, It is possible to judge that the adjustment function is abnormal, and even if there is no separate detection system to judge the discharge circuit failure etc. of the capacity adjustment, the cells in which the capacity adjustment is functioning normally and the capacity adjustment function are in an abnormal state. A cell can be clearly identified.
This reduces the number of separate detection systems and simplifies the failure diagnosis program.

According to the fifth aspect of the present invention, since the detection and discharge of the cell voltage are performed in parallel for each module, the processing time is shortened and the capacity adjustment becomes smooth.

[0016]

Embodiments of the present invention will be described below with reference to embodiments. FIG. 1 is a diagram showing a configuration of a control device for a battery pack to which the capacity adjusting method of the embodiment is applied. The assembled battery 10 is configured by connecting n modules 11 in series, and each module 11 has m cells 12 connected in series. A capacity adjusting discharge circuit 14 is connected between both terminals of each cell 12. The capacity adjusting discharge circuit 14 includes a discharge resistor 15 and a switching circuit 16. In the figure, () of the module 11 () indicates the module number, and () of the cell 12 () indicates the cell number in the module.

In the module 11, both terminals of each cell 12 are further connected to a cell controller 18. The cell controller 18 includes a cell voltage detection circuit (not shown). Cell controller 18 of each module 11
Is connected by a communication line to a battery controller 20 having a charging unit therein. The battery controller 20 manages various information related to the assembled battery such as charge / discharge information of the assembled battery. Both terminals of the assembled battery are connected to the battery controller 20.
It is connected to the. In the drawing, only one connection between the two terminals of the cell and the cell controller 18 is shown, and the other connections are simply indicated by arrows.

The cell controller 18 sequentially controls the open voltage (cell voltage) Vc of each cell 12 in the module 11 during charging and discharging by the battery controller 20.
Is calculated, and a total voltage Vj (hereinafter, referred to as a module voltage) in each module is calculated. Battery controller 20
Then, the module voltage Vj is input from each module 11 and compared, and the module voltage Vj of the module having the lowest module voltage (lowest voltage module) is set as the module voltage minimum value VMIN. Then, the cell voltage average value Vamin in the lowest voltage module is obtained.

The battery controller 12 determines a cell abnormality based on the cell voltage average value Vamin, and sets the cell abnormality as a capacity adjustment target value Vg. Then, an adjustment discharge time Tc corresponding to the deviation between the capacity adjustment target value Vg and the open voltage Vc of each cell 12 is calculated, and the capacity adjustment discharge circuit 14 is turned on for the adjustment discharge time Tc to obtain the capacity adjustment target value. A cell having a voltage higher than Vg is discharged. In the following, in order to indicate individual cells and modules, subscripts i (i = 1, 2, ---, m),
Description will be given with j (j = 1, 2, ---, n).

FIGS. 2 and 3 are flowcharts showing the flow of control of capacity adjustment in the cell controller and the battery controller. First, in step 101, in each cell controller 18j, a variable i for sequentially counting the cells 12ji in the module 11j is set to 1, and the process proceeds to the next step 102. In step 102, it is checked whether or not the variable i is equal to or less than m corresponding to the total number of cells 12ji in the module 11j. When the variable i is equal to or less than m, in step 103,
The open circuit voltage Vcji of the i-th cell 12ji is detected, and the variable i is increased by 1 in step 104.

The above steps are repeated while the variable i is equal to or less than m. When the Vcji detection of all cells in the module 11j is completed and the variable i exceeds m, steps 102 to 105 are executed.
Proceed to. In step 105, the detected open circuit voltage Vcj
The module voltages Vj in the module 11j are obtained by summing i. The battery controller 20 reads the module voltage Vj from each module 11j at predetermined time intervals. In step 106, the module voltage Vj of each module is compared to determine the module voltage Vj of the lowest voltage module as the module voltage minimum value VMIN. Subsequently, in step 107, the module voltage minimum value VMIN is divided by the number m of cells constituting the module 11, and the cell voltage average value Vami of the lowest voltage module is obtained.
Find n.

Thereafter, each cell controller 18j determines an abnormal cell using the average cell voltage Vamin calculated by the battery controller 20. First,
In step 108, the variable i is reset to 1, and in step 109, it is checked whether the variable i is equal to or less than m.

If the variable i is less than m, step 1
10, the open circuit voltage Vc of the i-th cell 12ji
It is checked whether the difference between ji and the cell voltage average value Vamin is 0 or less. If the difference is equal to or less than 0, the process proceeds to step 111, where it is checked whether the value obtained by inverting the difference is smaller than a predetermined voltage drop amount abnormality determination threshold value Vd as a first threshold value. If it is within the voltage drop amount abnormality determination threshold value Vd, the variable i is increased by 1 in step 115, and the process returns to step 109.

Cell voltage average value Vamin and open circuit voltage Vc
If the difference from ji is equal to or greater than the voltage drop abnormality determination threshold value Vd, a determination output indicating that the cell 12ji has a voltage drop amount abnormality is made to the battery controller 20 in step 112, and the process proceeds to step 115. The battery controller 20 displays the occurrence of an abnormal cell as necessary.

In the check in the previous step 110,
Open voltage Vcji of cell 12ji and average cell voltage Va
If the difference of min is not less than 0, the process proceeds to step 113. In step 113, the above difference is determined as a second threshold set in advance as the capacity adjustment function abnormality determination threshold V
It is checked whether it is smaller than e, and if it is within the capacity adjustment function abnormality determination threshold Ve, step 115
Proceed to. Cell open voltage Vcji and cell voltage average value Va
If the difference of min is equal to or greater than the capacity adjustment function abnormality determination threshold value Ve, the battery controller 2 outputs a determination output indicating that the cell 12ji is abnormal in the capacity adjustment function in step 114.
0, and then proceed to step 115. After step 115, the process returns to step 109, and the above steps are repeated until the variable i exceeds m.

When the variable i exceeds m, the process proceeds from step 109 to step 116 to adjust the capacity. First, at step 116, each cell controller 18j sets the cell voltage average value Vamin as a capacity adjustment target value Vg. Then, in step 117, the variable i is reset to 1 again, and in step 118, it is checked whether or not the variable i is equal to or less than m. If the variable i is equal to or less than m, the process proceeds to step 119, where the difference between the open circuit voltage Vcji of the i-th cell 12ji and the capacity adjustment target value Vg is multiplied by a predetermined adjustment coefficient α, and the capacity adjustment voltage Vaji
And Subsequently, in step 120, using a conversion table prepared in advance as shown in FIG. 4, the capacitance adjustment voltage amount Vaji is converted into an adjustment capacitance Cji (Ah) and calculated. The open-circuit voltage Vcji of the cell and the capacity adjustment target value V
When the difference of g is 0 or less, the conversion to the adjustment capacitance Cji is not performed.

In the next step 121, an adjustment time Tcji (h) corresponding to the adjustment capacity Cji is calculated. The adjustment time is obtained by the following equation. Tcji = Cji / Id Here, Id is a current value flowing through the capacity adjusting discharge circuit 14ji of the cell, and is determined by the open voltage of the cell and the impedance of the capacity adjusting discharge circuit. In step 122, the capacity adjustment discharge circuit 14ji of the cell is turned on for the adjustment time Tcji to discharge the cell voltage (open circuit voltage Vcji) to match the capacity adjustment target value Vg. Then, after increasing the variable i by 1 in step 123, the process returns to step 118. When the difference between the open-circuit voltage Vcji of the cell and the capacity adjustment target value Vg is 0 or less, conversion to the adjustment capacity Cji is not performed as described above, and the capacity adjustment discharge circuit remains off and is not discharged. Step 119 and the subsequent steps are repeated, and when the variable i exceeds m, the control ends.

The transition of the voltage of each cell by the above-described capacity adjustment control is shown in, for example, FIG. First, assuming that the cell voltage of each module is distributed as shown in (a) at the start of control, the average cell voltage Vamin of the lowest voltage module (minimum module voltage VMIN) is set as the capacity adjustment target value Vg. Cells having a voltage higher than the capacity adjustment target value Vg are discharged for an adjustment time according to the voltage difference from Vg. Thus, after adjustment by discharge,
As shown in (b), most of the cell voltages are near the average value level of all the cells.

Here, assuming that the filled cell 12a in the above (a) is not abnormal but has a relatively large voltage drop amount compared to many other cells, as shown in (b). Only the filled cell 12a has dropped to a lower voltage than many other cells.

In the state (b), the module including the filled cell 12a whose voltage has been lowered to a voltage lower than the other cells is the lowest voltage module. In the next adjustment, the cell voltage average value Vamin 'of this lowest voltage module is reduced. The capacity adjustment target value Vg is set. Then, similarly to the above, cells having voltages higher than the capacity adjustment target value Vg
The discharge is performed for an adjustment time according to the voltage difference from g. Thereafter, since the voltage of the solid-filled cell 12a is relatively larger than that of many other cells, the average value of the cell voltage of the module including the cell 12a is set as the capacity adjustment target value Vg. Each time the adjustment is repeated, the voltage of the filled cell 12a approaches the same level as many other cells. Therefore, the filled cell 12
Since the voltage of “a” approaches the cell voltage average value serving as a criterion for cell abnormality determination, the cell 12a, which has a relatively large voltage drop compared to many other cells but is not abnormal, is erroneously determined to be abnormal. Is avoided.

On the other hand, if the voltage drop amount of the solid cell 12b shown in FIG. 6A is abnormal, even if a module not including the cell becomes the lowest voltage module at first, (b) ) Is the lowest voltage module, and the cell voltage average value Vamin ′ of this lowest voltage module is set as the capacity adjustment target value Vg in the next adjustment. However, while discharging cells of a higher voltage toward the capacity adjustment target value Vg, the voltage of the solid cell 12b continues to decrease, so that after discharging each cell, the same module is charged with the lowest voltage. Even if it ’s a module,
Eventually, as shown in (c), the cell voltage average value Vami
The difference between n ″ and the voltage of the cell 12b exceeds the voltage drop abnormality determination threshold value Vd. Thus, it is reliably detected that the voltage drop is abnormal.

Next, for the filled cell 12c shown in FIG. 7A, for example, when a failure of the capacity adjusting discharge circuit 14 occurs and the capacity adjusting function becomes abnormal, any one of the modules has the lowest voltage. As a module, the cell voltage average value Vamin is set as a capacity adjustment target value Vg,
When cells having higher voltages are respectively discharged for a predetermined adjustment time, the voltages of a large number of cells are aligned at substantially the same level as shown in (b), but only the solid cells 12c are left behind because they are not discharged. .

Similarly, when the cell voltage average value Vamin 'of the lowest voltage module in the state (b) is set as the capacity adjustment target value Vg and the adjustment is further repeated, the average voltage of the other cells except the solid cell 12c becomes The difference between the solid-filled cell 12c and the average cell voltage value of the lowest voltage module increases. Thus (c)
As shown in the figure, the difference between the voltage of the cell 12c and the cell voltage average value Vamin "is the capacity adjustment function abnormality determination threshold Ve.
If it exceeds, it is detected that the capacity adjustment function is abnormal.

This embodiment is constructed as described above. In the battery pack 10 constructed by connecting a plurality of modules including a plurality of cells 12 in series, the average value of the cell voltage of the lowest voltage module is set to the capacity adjustment target value. Vg, the capacity adjustment discharge circuit 14 of each cell is turned on for an adjustment discharge time Tc corresponding to the deviation between the capacity adjustment target value Vg and the open voltage of the cell, thereby discharging cells having a voltage larger than the capacity adjustment target value Vg. Therefore, the voltage of each cell is quickly uniformed regardless of whether charging or discharging. At this time, the capacity is adjusted within the normal range of the capacity variation without discharging the capacity more than necessary.

Further, when the deviation between the cell voltage average value of the lowest voltage module and the voltage of each cell exceeds a predetermined threshold value, it is determined that there is an abnormality.
A cell that has a relatively large voltage drop but is not abnormal compared to many other cells is prevented from being erroneously determined to be abnormal, and the capacity adjustment function becomes abnormal due to a failure of the capacity adjustment discharge circuit or the like. The cell is reliably detected.

Further, since a cell controller is provided for each module, and cell voltage detection and discharge controlled by the capacity adjusting discharge circuit are executed in parallel with other modules, the overall processing time is reduced. As a result, the control flow can be repeated in a short time, and the frequency of the capacitance adjustment increases, so that the change of each cell voltage becomes smooth.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a control device for a battery pack according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a flow of control of capacity adjustment according to the embodiment.

FIG. 3 is a flowchart illustrating a flow of control of capacity adjustment according to the embodiment.

FIG. 4 is a diagram showing a conversion table between a capacitance adjustment voltage amount and an adjustment capacitance.

FIG. 5 is a diagram showing a transition of the voltage of each cell by the capacity adjustment control.

FIG. 6 is a diagram showing a change in the voltage of a cell when there is a voltage drop amount abnormality;

FIG. 7 is a diagram showing a change in cell voltage when a capacity adjustment function is abnormal.

FIG. 8 is a diagram showing a change in cell voltage in a conventional example.

FIG. 9 is a diagram showing a transition of a voltage of a cell when a capacity adjustment function is abnormal in the conventional example.

[Description of Signs] 10 battery pack 11 module 12 cell 14 capacity adjustment discharge circuit (discharge circuit) 15 discharge resistor 16 transistor 18 cell controller 20 battery controller

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5G003 AA01 BA03 CA12 CB07 CC04 EA02 5H030 AA04 AA06 AS20 BB01 BB21 BB26 FF41 FF43 FF44 FF52

Claims (5)

[Claims] 1. A method for adjusting the capacity of an assembled battery comprising a plurality of modules connected in series and having a plurality of modules connected in series, and a discharge circuit for each cell, comprising: The open-circuit voltage of each cell is detected, the cell voltage average value of the module having the lowest module voltage is set as the capacity adjustment target value, and the adjustment discharge time is determined based on the capacity adjustment target value and the cell open-circuit voltage. A method of adjusting the capacity of a battery pack, comprising repeating the discharging of the cell for a time. 2. A method for adjusting the capacity of a battery pack comprising a plurality of modules connected in series and having a plurality of cells connected in series, and a discharge circuit for each cell, comprising: The open-circuit voltage of each cell is detected, the cell voltage average value of the module having the lowest module voltage is set as the capacity adjustment target value, and the adjustment discharge time is determined based on the capacity adjustment target value and the cell open-circuit voltage. A method of adjusting the capacity of a battery pack, comprising repeating the discharging of the cell for a period of time and determining that a cell in which the difference between the cell voltage average value and the open circuit voltage exceeds a predetermined threshold value is abnormal. 3. The threshold value is a first threshold value applied to a cell having an open voltage lower than the cell voltage average value, and a difference between the cell voltage average value and the open voltage is a first threshold. 3. The method according to claim 2, wherein when the value exceeds the value, it is determined that the voltage of the cell is abnormal. 4. The threshold value is a second threshold value applied to cells having an open voltage higher than the cell voltage average, and a difference between the cell voltage average and the open voltage is a second threshold. 4. The method according to claim 2, wherein when the value exceeds the value, the cell is determined to have a capacity adjustment function abnormality. 5. The capacity of an assembled battery according to claim 1, wherein the detection of the open-circuit voltage of the cells and the discharge for adjusting the capacity are performed in parallel for each module. Adjustment method.