JP3921826B2 - Battery cell capacity adjustment method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an assembled battery used in an electric vehicle or the like, which corrects variation in capacity of each cell constituting the assembled battery, and always controls the battery so that the battery capacity can be fully used as a whole assembled battery. The present invention relates to a battery cell capacity adjustment method. The electric vehicle in this case is not limited to a vehicle that runs only with a secondary battery, but may be a so-called hybrid vehicle as long as the battery power is used for driving the vehicle.
[0002]
[Prior art]
As a battery for an electric vehicle, an assembled battery is used in which a plurality of single cells called cells (for example, 6 to 8) are connected in series to form one block, and a module having a required voltage is connected in series. . In such an assembled battery, when charging and discharging are repeated, a difference occurs in the capacity of each cell (the remaining capacity that can be used at that time) according to the characteristics of each cell. If this is left as it is, the capacity that can be used as the whole assembled battery is reduced, so that the power of the large capacity cell is discharged at an appropriate time (for example, when the vehicle is started, etc.), and the overall balance is controlled. There is a need.
[0003]
In a conventional electric vehicle, the adjustment capacity (adjustment capacity) for each cell in an area where the relationship between the capacity and the open circuit voltage (terminal voltage at zero current) shown in FIG. (Capacity to be discharged) is stored as one table (FIG. 6B) corresponding to the deviation from the average cell open voltage, and the discharge for the adjusted capacity is performed accordingly. For example, when the cell controller is activated, such as when the vehicle is started or when charging is started, the open voltage of each cell is detected, the average cell open voltage is calculated from those values, and the deviation from the average cell open voltage For cells that are larger than the specified value, refer to the adjustment capacity table above, find the adjustment capacity according to the deviation, and control the overall balance by discharging the capacity for that value. ing. According to the above method, since the relationship between the capacity and the open circuit voltage is used only in a linear region, the adjustment capacity table can be easily created and the adjustment capacity can be calculated in a simple manner by referring to the table. Can do.
[0004]
[Problems to be solved by the invention]
However, in the conventional method as described above, the adjustment capacity cannot be calculated in the area where the slope of the linear relationship between the capacity and the open-circuit voltage changes (area where the capacity is small). In the state, variation in capacity of each cell cannot be suppressed. Therefore, there is a problem that not only the capacity of the battery as a whole can not be fully used, but also the variation in the deterioration state of each cell may be promoted by the expansion of the voltage variation.
[0005]
The present invention has been made to solve the problems of the prior art as described above, and it is possible to carry out capacity adjustment suitable for the detected open circuit voltage in any region. An object of the present invention is to provide a method for adjusting the capacity of assembled battery cells.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is configured as described in the claims. That is, in the invention described in claim 1, when no input / output is made to the assembled battery, the open voltage of each cell of the assembled battery is detected, the average open voltage of all the cells is calculated, and then the open voltage of each cell is calculated. The deviation of the average open circuit voltage from the voltage exceeds a predetermined value, and a cell that requires capacity adjustment is identified by discharging, and the slope of the open circuit voltage relative to the cell capacity of the identified cell is approximately each capacity range becomes constant, determine the adjustment space required by the preset approximate adjustment capacity calculation equation fitting the deviation obtained by subtracting the average open circuit voltage from the open voltage consists formula, in the adjustment capacity for each cell specified above By discharging the corresponding electric power, the variation in the capacity of each cell is adjusted.
[0007]
For example, in a lithium ion secondary battery, the capacity-open-circuit voltage characteristic can be approximated by three straight lines in the usage range. Therefore, by setting the adjustment capacity calculation formula corresponding to each linear area, and calculating the adjustment capacity according to the deviation between the open voltage of each cell and the average open voltage using the corresponding adjustment capacity calculation formula Therefore, accurate capacity adjustment can be performed regardless of the region where the open-circuit voltage of the detected cell is. Note that other secondary batteries can be similarly controlled by setting an adjustment capacity table using characteristics corresponding to the secondary batteries.
[0008]
Further, in the invention according to claim 2, in the assembled battery cell capacity adjustment method according to claim 1, from the approximate expression set in advance for each capacity range in which the slope of the open circuit voltage with respect to the cell capacity becomes approximately constant. A deviation obtained by subtracting the average open-circuit voltage from the open-circuit voltage is selected from the above-mentioned open-circuit voltage, and the adjustment capacity calculation formula of the capacity range to which the open-circuit voltage of the specified cell belongs is selected. It is configured to so that determine the necessary adjustments capacity I'm fitting a.
Further, in the invention according to claim 3 , when the calculation is performed using the plurality of adjustment capacity calculation expressions, the open circuit voltage of the cell to be adjusted is in the vicinity of the region where the characteristic changes, and the two regions When it is necessary to discharge by crotch, the adjustment capacity is calculated from each of the adjustment capacity calculation formulas corresponding to the two areas, and the sum of the two calculated values is used as the adjustment capacity. . In other words, when the calculation is simply performed using a plurality of arithmetic expressions having different characteristics, the adjustment capacity is determined by the characteristic with the steeper slope at the boundary where the characteristics change, and the value of the adjustment capacity is more than the actually required value. May also be smaller. Therefore, instead of selecting an arithmetic expression to be referenced only from the average open-circuit voltage, by calculating the adjustment capacity by referring to two arithmetic expressions simultaneously according to the open-circuit voltage of the cell, the calculation accuracy is increased and the frequency of adjustment is increased. It is possible to control in a direction to suppress deterioration without charging and discharging as much as possible.
[0009]
【The invention's effect】
According to the present invention, by setting a plurality of adjustment capacity calculation formulas according to changes in battery characteristics, capacity adjustment suitable for it can be performed even in the end-of-discharge region where operation has been impossible until now. Therefore, the capacity variation is quickly eliminated, and the effect that the battery capacity can always be sufficiently used as the whole assembled battery is obtained.
[0010]
Further, in the invention described in claim 3 , even if the cell open-circuit voltage has to be adjusted over the region where the battery characteristics change, the adjustment capacity is calculated from the adjustment capacity calculation formula. By using the sum as the adjustment capacity, the capacity can be adjusted with high accuracy. For this reason, the adjustment capacity is not estimated to be small by calculating with one characteristic, so the frequency of capacity adjustment is reduced, and the progress of deterioration corresponding to the number of times of charge / discharge of the battery can be delayed. .
In addition, the capacity cannot be adjusted in a state where the battery is repeatedly charged and discharged in the end-of-discharge region as in the conventional case, and the voltage variation of the cell is expanded, and the nonuniform deterioration is promoted by the voltage variation. There is an effect that the situation can be prevented.
[0011]
Further, by using the capacitive discharge circuit that comes with the battery pack normal to perform the discharging of each of the one cell, and the measurement of the numerical using a cell controller and the battery controller are provided as a battery control device Since the present invention can be realized only by changing the software without adding new hardware by performing the calculation, it can be implemented at low cost.
[0012]
The present invention is not limited to the assembled battery, but can be similarly applied to a module-unit battery system, and the same effect can be obtained.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic diagram showing an example of the configuration of a controller used in the capacity adjustment method of the present invention. The configuration of FIG. 1 is a controller that controls charging / discharging of an assembled battery of an electric vehicle. In this embodiment, the capacity of each cell is adjusted using an existing controller for controlling the assembled battery of an electric vehicle. is there.
[0014]
In FIG. 1, 1 is a cell (single cell), 2 is a resistor, 3 is a transistor, 4 is a battery temperature sensor installed for each module, and 5 is a control signal that performs calculations in accordance with various input signals. , A portion 6 surrounded by a broken line is a cell controller for controlling each cell in the module, 7 is a battery controller for controlling the entire assembled battery, and 8 is a voltage measurement line connected to each cell in the module. , 9 is a signal line to each transistor in the module, 10 is a communication line between the battery controller and each cell controller, a portion 11 surrounded by a broken line is a capacity discharge circuit, and 12 is a current flowing through the capacity discharge circuit 11 Signal line. Note that an adjustment capacity table, which will be described later, is stored in the battery controller 7.
[0015]
The arrows A and B at both ends of the cell 1 are connected in series to the front and rear cells (not shown) at this portion, and a plurality of cells form one module, and one cell controller 6 is provided for each module. Is provided. And the cell controller 6 of all the modules is connected with the battery controller 7 via the communication line 10, and charging / discharging of each cell is controlled. The capacitive discharge circuit 11 is configured by a series circuit of a resistor 2 and a transistor 3. Then, based on the terminal voltage of each cell detected via the voltage measurement line 8 of each cell, for example, when the cell is overcharged during battery charging, or when the cell is overvoltage with respect to another cell, etc. When the control unit 5 determines and turns on the transistor 3 of the cell via the signal line 9, a current flows from the cell via the resistor 2 to discharge the charge. In the present embodiment, control is performed so that the capacity of each cell is balanced by discharging the adjustment capacity using the capacity discharge circuit 11. Each value such as the open circuit voltage and the discharge current is measured by the cell controller 6 through the voltage measurement line 8 and the signal line 12, and the adjustment capacity corresponding thereto is calculated by the battery controller 7.
[0016]
In addition, although the battery characteristic shown in this Embodiment uses the thing of a lithium ion secondary battery, in the case of another secondary battery, by setting an adjustment capacity table using the characteristic corresponding to it, Similarly, control is possible.
[0017]
First, calculation of the adjustment capacity in the present embodiment will be described.
FIG. 4 is a characteristic diagram showing characteristics of battery capacity and open-circuit voltage in a lithium ion secondary battery. As shown in FIG. 4, the characteristics of capacity and open circuit voltage are approximated by a line graph composed of three straight lines. The open circuit voltages at which this characteristic changes are V1 and V2.
[0018]
FIG. 5 is a diagram showing regions of the battery characteristics shown in FIG. 4 and respective adjustment capacity calculation formulas corresponding thereto. That is, from the higher cell open circuit voltage, Cc = a1 · ΔV (1) equation Cc = a2 · ΔV (2) equation Cc = a3 · ΔV (3) equation. However, Cc is an adjustment capacity (Ah), and ΔV is a deviation (V) between each cell open voltage and an average open voltage (average value of open voltages of each cell). Further, a1, a2, and a3 are constants, which are values determined from the battery characteristics and represent the slope of the voltage with respect to the capacity.
[0019]
Next, application of each of the adjustment capacity calculation formulas will be described.
When the open voltage Vc (n) (where n is a cell number) of each cell is detected when the cell controller (C / C) is activated (for example, when an ignition switch of an electric vehicle is turned on), Average open circuit voltage Vc ave is calculated. And Vc (n) of each cell and average open circuit voltage Vc Deviation ΔVc (n) from ave is calculated by the following equation.
ΔVc (n) = Vc (n) −Vc ave
When the detected value of Vc (n) is equal to or smaller than a preset deviation allowable value ΔVcmax, that is, ΔVc (n) ≦ ΔVcmax
If it is, the cell variation is determined to be less than the allowable value, and the capacity adjustment is not performed. on the other hand,
ΔVc (n)> ΔVcmax
If there is a cell to be adjusted, the adjustment capacity Cc is further calculated for the cell according to the following conditions, and the capacity adjustment is performed.
[0020]
(1) Vc If ave ≧ V1, this is the average open circuit voltage Vc This is the case where ave is in a range larger than V1 in FIG. 5. In this case, the adjustment capacity calculation formula is the formula (1), and ΔVc (n) is substituted for ΔV to calculate the adjustment capacity. Then, the calculated adjustment capacity Cc is discharged using the capacity discharge circuit 11.
[0021]
(2) V1> Vc If ave ≧ V2 and V1 ≧ Vc (n), this is the average open circuit voltage Vc This is the case where ave is between V1 and V2 in FIG. 5, and the open circuit voltage Vc (n) of the cell is V1 or less. In this case, formula (2) is used as the adjustment capacity calculation formula, ΔVc (n) is substituted for ΔV to calculate the adjustment capacity, and the calculated adjustment capacity Cc is calculated using the capacity discharge circuit 11. Discharge.
[0022]
(3) V2> Vc If ave and V2 ≧ Vc (n), this is the average open circuit voltage Vc This is the case where ave is smaller than V2 in FIG. 5, and the open circuit voltage Vc (n) of the cell is V2 or less. In this case, the adjustment capacity calculation formula is the formula (3), and ΔVc (n) is substituted for ΔV to calculate the adjustment capacity, and the calculated adjustment capacity Cc is calculated using the capacity discharge circuit 11. Discharge.
[0023]
(4) V1> Vc If ave ≧ V2 and Vc (n)> V1, this is the average open circuit voltage Vc The range of ave is the same as (2) above, but the case where the open circuit voltage Vc (n) of the cell is larger than V1, that is, the vicinity of the bending point of V1 is the operating point. In this case, first,
ΔVc (n) 1 = Vc (n) −V1
The adjustment capacity Cc1 according to the above is calculated from the equation (1), and ΔVc (n) 2 = V1−Vc. ave
The adjustment capacity Cc2 corresponding to the above is calculated from the formula (2),
Cc = Cc1 + Cc2
Is the adjusted capacity, and is discharged using the capacity discharge circuit 11.
[0024]
(5) V2> Vc If ave and Vc (n)> V2, this is the average open circuit voltage Vc Although ave is the same as (3) above, the open voltage Vc (n) is larger than V2, that is, the operating point is near the bending point of V2. In this case, first,
ΔVc (n) 3 = Vc (n) −V2
The adjustment capacity Cc3 according to the above is calculated from the equation (2),
ΔVc (n) 4 = V2−Vc ave
The adjustment capacity Cc4 according to the above is calculated from the equation (3),
Cc = Cc3 + Cc4
Is the adjusted capacity, and is discharged using the capacity discharge circuit 11.
[0025]
It should be noted that the absolute value of ΔVc (n) is a predetermined value ΔVc determined in advance. If it is greater than fail, that is, if the deviation between the open circuit voltage and the average open circuit voltage of a certain cell is abnormally large, it is determined that the cell is abnormal and capacity adjustment is prohibited for that cell. At the same time, a warning prompting replacement is output.
[0026]
Further, by previously storing the relationship between each arithmetic expression and the deviation as an adjustment capacity table in the battery controller 7, the adjustment capacity value corresponding to the deviation can be immediately read out.
Moreover, you may comprise so that the value correct | amended according to battery temperature may be used for said open circuit voltage, average open circuit voltage, etc.
FIG. 2 and FIG. 3 are flowcharts showing the above-described calculation process, and both figures are connected at the points (A) and (B).
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an example of a configuration of a controller used in a capacity adjustment method of the present invention.
FIG. 2 is a part of a flowchart showing an adjustment capacity calculation process;
FIG. 3 is another part of the flowchart showing the calculation process of the adjustment capacity.
FIG. 4 is a characteristic diagram showing characteristics of battery capacity and open-circuit voltage in a lithium ion secondary battery.
FIG. 5 is a diagram showing regions of battery characteristics shown in FIG. 4 and respective adjustment capacity calculation formulas corresponding thereto.
6A and 6B are diagrams for explaining a conventional adjustment method, in which FIG. 6A is a characteristic diagram showing a relationship between a capacity and an open circuit voltage, and FIG. 6B is a diagram illustrating an adjustment capacity for each cell from an average cell open circuit voltage; The figure which shows the table matched with the deviation.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Cell (single cell) 2 ... Resistor 3 ... Transistor 4 ... Battery temperature sensor 5 ... Control part 6 ... Cell controller 7 ... Battery controller 8 ... Voltage measurement line 9 ... Signal line 10 ... Communication line 11 ... Capacity discharge circuit 12 ... Signal lines for detecting current

Claims (4)

A method for adjusting the capacity of the cell in an assembled battery in which a plurality of modules each composed of a plurality of cells are connected,
Detects the open circuit voltage of each cell of the assembled battery when no input / output is made to the assembled battery,
Next , calculate the average open circuit voltage of all cells from the detected value ,
Next, the deviation obtained by subtracting the average open circuit voltage from the open circuit voltage of each cell exceeds a predetermined value to specify a cell that needs capacity adjustment ,
Necessary by the adjustment capacity calculation formula that applies a deviation obtained by subtracting the average open-circuit voltage from the open-circuit voltage for each capacity range in which the slope of the open-circuit voltage with respect to the cell capacity of the specified cell is approximately constant. Seeking the correct adjustment capacity ,
An assembled battery cell capacity adjustment method, wherein a variation in capacity of each cell is adjusted by discharging power corresponding to the adjustment capacity for each specified cell. In the assembled battery cell capacity adjustment method according to claim 1,
  Of the adjustment capacity calculation formula consisting of an approximate expression set in advance for each capacity range in which the slope of the open circuit voltage with respect to the cell capacity is approximately constant, the adjustment of the capacity range to which the average open circuit voltage and the open circuit voltage of the specified cell belong Select the capacity calculation formula, and apply the deviation obtained by subtracting the average open-circuit voltage from the open-circuit voltage to the adjustment capacity calculation formula.
  An assembled battery cell capacity adjustment method, wherein a variation in capacity of each cell is adjusted by discharging power corresponding to the adjustment capacity for each of the specified cells. In the assembled battery cell capacity adjustment method according to claim 1 or 2,
The capacity range in which the slope of the open-circuit voltage with respect to the cell capacity to which the open-circuit voltage of the specified cell belongs is approximately constant is different from the capacity range to which the average open-circuit voltage belongs when considered as the voltage of the specified cell. In the meantime, when there is a voltage value in which the slope of the approximately constant open-circuit voltage changes and the voltage of the specified cell is larger than the average open-circuit voltage ,
Apply the deviation obtained by subtracting the voltage whose slope changes from the voltage of the specified cell to the adjustment capacity calculation formula of the capacity range to which the open voltage of the specified cell belongs to calculate the first adjustment capacity and specify the average open voltage The second adjustment capacity is calculated by applying a deviation obtained by subtracting the average open-circuit voltage from the voltage whose slope changes to the adjustment capacity calculation formula of the capacity range to which the average open-circuit voltage belongs when the voltage is regarded as the cell voltage. The sum of 1 and the second adjustment capacity is the adjustment capacity necessary for the specified cell ,
An assembled battery cell capacity adjustment method, wherein a variation in capacity of each cell is adjusted by discharging power corresponding to the adjustment capacity for each specified cell . In the assembled battery cell capacity adjustment method according to any one of claims 1 to 3 ,
When a cell is detected in which the absolute value of the deviation obtained by subtracting the average open circuit voltage from the open circuit voltage of each cell exceeds a predetermined value, the capacity adjustment of that cell is prohibited and a warning prompting replacement is output. battery pack cell capacity adjusting how to characterized in that.

Images