U.S. patent application number 13/315707 was filed with the patent office on 2012-03-29 for state of charge optimizing device and assembled battery system including same.
Invention is credited to Hiroya MURAO.
Application Number | 20120074911 13/315707 |
Document ID | / |
Family ID | 40199611 |
Filed Date | 2012-03-29 |
United States Patent
Application |
20120074911 |
Kind Code |
A1 |
MURAO; Hiroya |
March 29, 2012 |
STATE OF CHARGE OPTIMIZING DEVICE AND ASSEMBLED BATTERY SYSTEM
INCLUDING SAME
Abstract
A state of charge optimizing device according to the present
invention optimizes a state of charge of each of a plurality of
cells which are connected in series to form an assembled battery,
and conducts the optimization by discharging or charging a part or
all of the plurality of cells so that the differences between the
amount of charge after the optimization and the amount of charge in
a predetermined state of charge become uniform.
Inventors: |
MURAO; Hiroya; (Osaka,
JP) |
Family ID: |
40199611 |
Appl. No.: |
13/315707 |
Filed: |
December 9, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12237428 |
Sep 25, 2008 |
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13315707 |
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Current U.S.
Class: |
320/134 |
Current CPC
Class: |
H02J 7/0014 20130101;
Y02T 10/70 20130101; H02J 7/0016 20130101; Y02T 10/7055
20130101 |
Class at
Publication: |
320/134 |
International
Class: |
H02J 7/00 20060101
H02J007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 27, 2007 |
JP |
JP2007-251384 |
Claims
1. A state of charge optimizing device for optimizing a state of
charge of each cell of a plurality of cells which are connected in
series to form an assembled battery, wherein the device sets an
optimization target value in accordance with a full charging
capacity for each cell of a part or all of the plurality of cells,
and conducts optimization by conducting discharging or charging in
accordance with the set optimization target value.
2. The state of charge optimizing device according to claim 1,
wherein the optimization target value is an amount of charge, or a
value corresponding thereto, such that the difference between the
amount of charge after optimization and the amount of charge in a
predetermined state of charge is uniform among the plurality of
cells wherein the predetermined state of charge is set so that both
a discharge characteristic and a charge characteristic of the
assembled battery are favorable and well balanced.
3. The of charge optimizing device according to claim 1, wherein
the optimization target value is an amount of charge, or a value
corresponding thereto, such that the difference between the amount
of charge after optimization and the amount of charge in a
predetermined state of charge is uniform among the plurality of
cells, comprising: a charging and discharging unit capable of
charging and/or discharging each cell; an amount of charge
difference calculating unit calculating the difference between the
current amount of charge and the amount of charge in the
predetermined state of charge for at least one of the plurality of
cells; an optimization target value setting unit setting an
optimization target value in accordance with the amount of charge
difference calculated by the amount of charge difference
calculating unit for each cell of a part or all of the plurality of
cells; and an optimizing processing unit making the charging and
discharging unit conduct charging or discharging in accordance with
the set optimization target value for each cell of a part or all of
the plurality of cells when the optimization target value is
set.
4. The of charge optimizing device according to claim 3, wherein
the amount of charge difference calculating unit calculates the
difference between the current amount of charge and the amount of
charge in the predetermined state of charge for each of the cells
that form the assembled battery, the state of charge optimizing
device comprising: an identifying unit identifying a maximum value
and a minimum value from the amount of charge difference calculated
by the amount of charge difference calculating unit; a calculating
unit calculating the difference between the maximum value and the
minimum value identified by the identifying unit; and a
determination unit determining whether or not a value calculated by
the calculating unit is above a predetermined threshold, the
optimization target value setting unit setting the optimization
target value when the calculated value is determined to be above
the predetermined threshold by the determination unit.
5. An assembled battery system comprising an assembled battery that
includes a plurality of cells connected in series, and the state of
charge optimizing device according to claim 1.
6-9. (canceled)
Description
[0001] The priority application Number 2007-251384, upon which this
patent application is based, is hereby incorporated by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to devices optimizing the
states of charge of a plurality of cells that form an assembled
battery, and assembled battery systems including the devices.
[0004] 2. Description of Related Art
[0005] In recent years, an assembled battery has been widely used,
for example an assembled battery including a plurality of
lithium-ion secondary cells connected in series is used in a hybrid
vehicle as a power source. Discharge power of an assembled battery
is limited by a cell with the lowest state of charge (SOC) among a
plurality of cells that forms the assembled battery. Therefore,
performance of an assembled battery decreases due to the variation
of SOC of the plurality of cells that form the assembled
battery.
[0006] Accordingly, a process to equalize the SOCs of the plurality
of cells of the battery is required. In a conventional equalizing
process, the voltages across the respective cells that form an
assembled battery (open-circuit voltages) are detected, and the
lowest value or the average value of the detected cell voltages is
used as a target value for the equalizing. Thus, electric discharge
is conducted on the cell whose voltage is above the target value
for equalizing, thereby equalizing the SOCs of the plurality of
cells that form the assembled battery.
[0007] For example, as shown in FIG. 10 in which three cells 1 to 3
form an assembled battery, when the SOC of the cell 1 is the lowest
before equalizing, the cells 2 and 3 are discharged to the SOC of
the cell 1, thereby equalizing the SOC of the cells 1 to 3.
[0008] However, the inventor of the present invention has
discovered in his research that the full charging capacities of the
plurality of cells that form the assembled battery vary due to the
variation as-manufactured, or the variation attributed to
temperature distribution when used, and therefore, the conventional
equalizing process cannot sufficiently elicit the performance of
the assembled battery.
[0009] For example, as shown in FIG. 11, in which three cells 1 to
3 having different full charging capacities form an assembled
battery, in the case where the cells 1 to 3 are equalized when the
SOC of the cells is approximately 70 percent, since the discharge
amounts per unit time of the cells 1 to 3 are uniform, when the SOC
of the cell 1 reaches 50 percent due to discharge of the assembled
battery after the equalization, the SOC of the cells 1 to 3
varies.
[0010] Also, in the case where the cells 1 to 3 are equalized when
the SOC of the cells is approximately 30 percent, since the charge
amounts per unit time of the cells 1 to 3 are uniform, when the SOC
of the cell 1 reaches 50 percent due to charge of the assembled
battery after the equalization, the SOCs of the cells 1 to 3
vary.
[0011] The discharge characteristic of the battery decreases as the
SOC decreases, and the charge characteristic decreases as the SOC
increases as shown in FIG. 12. Therefore, the higher performance of
the assembled battery can be obtained when the SOCs of the
plurality of cells are equalized with the SOC in which both the
discharge characteristic and charge characteristic are favourable
and well balanced, such as approximately 50 percent, rather than
with a high or low SOC.
[0012] With the conventional equalizing process, in the case where
the SOCs of a plurality of cells are equalized when the SOC is
approximately 70 percent as described above, for example, since the
SOCs of the cells vary when the SOC of the cells decreases to
around 50 percent due to discharge of the assembled battery after
the equalization, the performance of the assembled battery cannot
be sufficiently elicited.
[0013] Accordingly, the equalization with the SOC of the plurality
of cells of around 50 percent is considered. It is desirable to
equalize the assembled battery of a hybrid car or the like when the
car is stopped and the battery is not charged or discharged in
order to accurately measure the amount of charge. However, the
hybrid car or the like is not necessarily stopped when the SOC of
the assembled battery is around 50 percent. It is therefore
problematic to do the equalization when the car is stopped in that
the equalization is done very infrequently.
SUMMARY OF THE INVENTION
[0014] An object of the present invention is to provide a state of
charge optimizing device capable of sufficiently eliciting the
performance of an assembled battery that includes a plurality of
cells with different full charging capacities and an assembled
battery system including the device.
[0015] A state of charge optimizing device according to the present
invention is a device optimizing the state of charge of each of a
plurality of cells connected in series to form an assembled
battery, and the device sets an equalization target value in view
of the full charging capacity for each of a part or all of the
cells to equalize the battery by discharging or charging each of
the cells in accordance with the set equalization target value.
[0016] In particular, the equalization target value is set to the
amount of charge, or a value corresponding thereto, such that the
difference between the amount of charge after optimization and the
amount of charge in a predetermined state of charge is uniform
among the plurality of cells.
[0017] According to the state of charge optimizing device of the
present invention, after optimization, the difference between the
amount of charge at the time and the amount of charge in the
predetermined state of charge is uniform among the plurality of
cells that form an assembled battery. Therefore, when the assembled
battery is discharged or charged thereafter, the states of charge
of the plurality of cells will be uniform in the predetermined
state of charge. Here, the predetermined state of charge is set to
a state of charge in which both the discharge characteristic and
charge characteristic of the assembled battery are preferable and
well balanced, such as 40 to 60 percent to sufficiently elicit the
performance of the assembled battery.
[0018] In particular, the state of charge optimizing device of the
present invention comprises:
[0019] a charging and discharging unit capable of charging and/or
discharging each of the cells;
[0020] an amount of charge difference calculating unit calculating
the difference between the current amount of charge and the amount
of charge in the predetermined state of charge for at least one of
the plurality of cells;
[0021] an optimization target value setting unit setting an
optimization target value in accordance with the amount of charge
difference calculated by the amount of charge difference
calculating unit for each of a part or all of the plurality of
cells; and
[0022] an optimizing processing unit making the charge and
discharge unit conduct charging or discharging in accordance with
the set optimization target value for each of a part or all of the
plurality of cells when the optimization target value is set.
[0023] According to the particular configuration described above,
the optimization target value set for each of the cells is an
amount of charge, or a value corresponding thereto, close to the
amount of charge at the time. Therefore, the charge or discharge
amount can be small.
[0024] Also in particular, the optimization target value setting
unit sets the optimization target value for each of the cells other
than a reference cell which is the at least one cell of the
plurality of cells, and comprises:
[0025] a first processing unit adding the amount of charge
difference of the reference cell calculated by the amount of charge
difference calculating unit to the amount of charge in the
predetermined state of charge for each of the cells other than the
reference cell; and
[0026] a second processing unit setting the optimization target
value to the amount of charge calculated by the first processing
unit or a value corresponding thereto for each of the cells other
than the reference cell.
[0027] In the particular configuration described above, the
optimization target value is set to the amount of charge, or a
value corresponding thereto, obtained by adding the difference
between the amount of charge of the reference cell at the time and
the amount of charge in the predetermined state of charge to the
amount of charge in the predetermined state of charge for each of
the cells other than the reference cell of the plurality of cells
that form the assembled battery. Each of the cells other than the
reference cell is discharged or charged in accordance with the
optimization target value. As a result, the difference between the
amount of charge after optimization and the amount of charge in the
predetermined state of charge of each of the cells other than the
reference cell is the same as the difference between the amount of
charge and the amount of charge in the predetermined state of the
reference cell. Therefore, when the assembled battery is discharged
or charged thereafter, the states of charge of the plurality of
cells are uniform in the predetermined state of charge.
[0028] In particular, the value corresponding to the amount of
charge is a state of charge or a cell voltage. The second
processing unit of the optimization target value setting unit
converts the amount of charge calculated by the first processing
unit into a state of charge or a cell voltage, and then sets the
state of charge or the cell voltage obtained from the conversion as
the optimization target value.
[0029] In the particular configuration described above, the target
amount of charge calculated by the first processing unit is
converted into the state of charge or the cell voltage. Here, the
state of charge can be calculated by dividing the amount of charge
by the full charging capacity and then multiplying the result by
the value of 100. Also, the cell voltage and the state of charge
have a certain relationship, and therefore when the relationship
between the cell voltage and the state of charge is preliminary
defined, the cell voltage can be derived from the state of charge
in accordance with the relationship. After that, the state of
charge or the cell voltage obtained by the conversion described
above is set as the target optimization value.
[0030] More particularly, the amount of charge difference
calculating unit calculates the amount of charge difference by
subtracting the amount of charge in the predetermined state of
charge from the current amount of charge for each of the cells that
form the assembled battery. The optimization target value setting
unit specifies a cell with the smallest amount of charge difference
calculated by the amount of charge difference calculating unit as
the reference cell from the plurality of cells that form the
assembled battery.
[0031] According to the particular configuration described above,
the optimization target value set for each of the cells other than
the reference cell is an amount of charge, or a value corresponding
thereto, which is below the amount of charge at the time. Therefore
the optimization can be conducted only by discharging. Thus, only a
discharging means is required and the structure is simple compared
to a state of charge optimizing device equipped with both
discharging means and charging means.
[0032] Further particularly, the amount of charge difference
calculating unit calculates the difference between the current
amount of charge and the amount of charge in the predetermined
state of charge for each of the cells that form the assembled
battery, and the state of charge optimizing device comprises:
[0033] an identifying unit identifying a maximum value and a
minimum value from the amount of charge difference calculated by
the amount of charge difference calculating unit;
[0034] a calculating unit calculating the difference between the
maximum value and the minimum value identified by the identifying
unit; and
[0035] a determination unit determining whether or not a value
calculated by the calculating unit is above a predetermined
threshold,
[0036] the optimization target value setting unit setting the
optimization target value when the calculated value is determined
to be above the predetermined threshold by the determination
unit.
[0037] In the particular configuration described above, when the
variation range of the difference between the current amount of
charge and the amount of charge in the predetermined state of
charge among the plurality of cells that form the assembled battery
exceeds the predetermined threshold, the optimization target value
is set and the optimizing process is conducted.
[0038] An assembled battery system according to the present
invention comprises an assembled battery that includes a plurality
of cells connected in series, and a state of charge optimizing
device for optimizing the state of charge of each of the cells
forming the assembled battery, and adopts the state of charge
optimizing device of the present invention described above as the
state of charge optimizing device.
[0039] As described, according to the state of charge optimizing
device of the present invention and the assembled battery system
including the state of charge optimizing device, it is possible to
sufficiently elicit the performance of the assembled battery that
includes the plurality of cells with different full charging
capacities.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] FIG. 1 is a block diagram illustrating a configuration of a
battery system according to the present invention;
[0041] FIG. 2 is a graph which explains an optimizing process of
the present invention;
[0042] FIG. 3 is a graph which explains the effect of the
optimizing process of the present invention;
[0043] FIG. 4 is a flowchart showing the procedure of the
optimizing process of the present invention;
[0044] FIG. 5 is a flowchart showing the concrete procedure of a
determining process of necessity of the optimizing by a state of
charge optimizing device of the first embodiment;
[0045] FIG. 6 is a flowchart showing the concrete procedure of an
optimization target voltage value calculating process by the state
of charge optimizing device;
[0046] FIG. 7 is a graph which explains timing of conducting an
optimizing process in a state of charge optimizing device of the
second embodiment;
[0047] FIG. 8 is a flowchart showing the concrete procedure of a
determining process of necessity of the optimizing by the state of
charge optimizing device;
[0048] FIG. 9 is a flowchart showing the concrete procedure of an
optimization target voltage value calculating process by the state
of charge optimizing device;
[0049] FIG. 10 is a graph which explains a conventional equalizing
process;
[0050] FIG. 11 is a graph which explains a problem of the
conventional equalizing process; and
[0051] FIG. 12 is a graph showing a charge and discharge
characteristic of an assembled battery.
DETAILED DESCRIPTION OF THE INVENTION
[0052] The present invention implemented in a battery system of a
hybrid car is described below on the basis of two embodiments.
First Embodiment
[0053] As shown in FIG. 1, the battery system according to the
present invention comprises an assembled battery that includes a
plurality of cells 1 which are lithium-ion secondary cells and
connected in series (three cells in the example of the drawing),
and a state of charge optimizing device 2 for optimizing the state
of charge of the assembled battery. The electrical power can be
supplied to a load 3 from the assembled battery.
[0054] A discharge circuit 21 which includes a resistor R and a
switch SW connected to each other in series and a voltage measuring
circuit 22 which measures the voltage across each cell
(open-circuit voltage) are connected to both sides of each of the
cells 1.
[0055] Values measured by each of the voltage measuring circuits
are supplied to a control circuit 20 and the control circuit 20
calculates optimization target voltage values as described below
based on the measured values, and then controls discharging of each
of the discharge circuits 21 based on the calculated optimization
target voltage values and the values measured by the respective
voltage measuring circuits 22.
[0056] In the optimizing process by the state of charge optimizing
device 2, a reference cell is a cell with the smallest amount of
charge difference among the plurality of cells that form the
assembled battery. The amount of charge difference can be obtained
by subtracting the amount of charge in a predetermined SOC from the
amount of charge at the time. A target amount of charge is set for
each of the cells other than the reference cell by adding the
amount of charge difference of the reference cell to the amount of
charge in the predetermined SOC. And then the optimization is
conducted by discharging each of the cells other than the reference
cell by the discharge circuit 21. Here, the predetermined SOC is
set so that both the discharge characteristic and charge
characteristic are favorable and well balanced. It is set to 50
percent in this embodiment.
[0057] For example, as shown in FIG. 2, with the assembled battery
that includes three cells 1 to 3 having different full charging
capacities, among the amount of charge differences of the three
cells 1 to 3, .DELTA.Ah1, .DELTA.Ah2, and .DELTA.Ah3, when the cell
3 has the smallest amount of charge difference .DELTA.Ah3, the cell
3 is the reference cell. The target amounts of charge for the cell
1 and cell 2 are set to values DAh1 and DAh2 respectively, which
are obtained by adding the amount of charge difference .DELTA.Ah3
to the amounts of charge in the SOC of percent. And then, the
optimization is conducted by discharging the cell 1 and cell 2 to
the respective target amounts of charge. As a result, among the
cells 1 to 3, the difference between the amount of charge after the
optimizing process and the amount of charge when the SOC is 50
percent is uniform, whereby discharging of the assembled battery
thereafter makes the SOCs of cells 1 to 3 uniform at 50 percent.
When the assembled battery is further discharged or charged
thereafter, the SOC of the cell 3, which has the smallest full
charging capacity among the cells 1 to 3, will reach 0 percent or
100 percent the earliest.
[0058] FIG. 4 shows the procedure of the optimizing process
conducted by the control circuit 20 of the state of charge
optimizing device 2 when the ignition switch of a hybrid car is set
to OFF. When the ignition switch is set to OFF first, in step S1,
the control circuit 20 measures the open-circuit voltage of each of
the cells that form the assembled battery after a predetermined
period such as one hour. And then in step S2, it determines whether
or not it is necessary to conduct the optimizing process. The
particular procedure of the determining process in step S2 is to be
described later. Subsequently in step S3, the control circuit 20
determines whether or not the optimizing process is determined to
be necessary in step S2 and when it determines NO, the process
returns to step S1.
[0059] In contrast, when it is determined that conducting the
optimizing process is necessary and therefore determined YES in
step S3, the control circuit 20 calculates an optimization target
voltage in step S4, and then in step S5, starts discharging a cell
with a voltage above the optimization target voltage calculated in
step S4. The particular procedure of the optimization target
voltage calculation process in step S4 is to be described
later.
[0060] Subsequently in step S6, after a predetermined period, such
as 30 minutes, the control circuit 20 measures the open-circuit
voltage of each of the cells that form the assembled battery, and
then in step S7, it terminates discharging the cell whose
open-circuit voltage reaches the optimization target voltage
calculated in step S4. Next, in step S8, it determines whether or
not it has terminated discharging all the cells with a voltage
above the optimization target voltage. When it determines NO, the
process returns to step S6. When it terminates discharging all the
cells thereafter, it determines YES in step S8 and terminates the
procedure.
[0061] FIG. 5 shows the concrete procedure of the determining
process of necessity of optimization in step S2 described above. In
the description below, the predetermined SOC is indicated as N
percent and referred to as a reference SOC.
[0062] In the determining process, after initializing a cell number
i to 0 in step S11, the control circuit 20 estimates the current
SOC[i] of the cell with the cell number i from the open-circuit
voltage thereof. Here, the SOC can be estimated from the
open-circuit voltage by referring to a table stored in a memory,
which shows the relationship between the open-circuit voltage and
SOC.
[0063] Next in step S13, for the cell with the cell number i, the
amount of charge difference .DELTA.Ah[i] between the current amount
of charge and the amount of charge in the reference SOC (=N
percent) is calculated from the full charging capacity Q[i] and the
SOC[i] estimated in step S12 by using the formula 1 below.
.DELTA.Ah[i]=Q[i].times.(SOC[i]-N) Formula 1
[0064] Subsequently in step S14, the cell number is increased by
one, and then in step S15, the control circuit 20 determines
whether or not the cell number i conforms to the number of cells n
that form the assembled battery. When it determines NO, the process
returns to step S12 and the procedure described above is
repeated.
[0065] Thereafter, when the amount of charge difference
.DELTA.Ah[i] between the current amount of charge and the amount of
charge in the reference SOC (=N percent) is calculated for all the
cells that form the assembled battery, the control circuit 20
determines YES in step S15, and then in step S16, identifies the
minimum value min .DELTA.Ah and the maximum value max .DELTA.Ah
from among the amount of charge differences .DELTA.Ah[i] calculated
for all the cells that form the assembled battery.
[0066] Subsequently in step S17, the control circuit 20 determines
whether or not the difference between the minimum value min
.DELTA.Ah and the maximum value max .DELTA.Ah is above a
predetermined threshold value X. When it determines NO, it
determines that it is not necessary to conduct the optimizing
process in step S18, and terminates the procedure described above,
while when it determines YES, it determines that it is necessary to
conduct the optimizing process in step S19 and terminates the
procedure described above.
[0067] According to the procedure described above, when the SOCs of
the plurality of cells that form the assembled battery vary a great
deal and the difference between the minimum value min .DELTA.Ah and
the maximum value max .DELTA.Ah calculated for the plurality of
cells is above a predetermined threshold value X, it is determined
that the optimizing process is necessary.
[0068] FIG. 6 shows the concrete procedure of the optimization
target voltage value calculating process in step S4 of FIG. 4. In
this calculating process, first in step S21, the control circuit 20
specifies a cell from among the plurality of cells that form the
assembled battery as a reference cell, and sets the cell number of
the reference cell to the reference cell number K. Here, the cell
with the smallest amount of charge difference .DELTA.Ah[i]
calculated in step S13 of FIG. 5 is specified as the reference
cell.
[0069] Next, after initializing the cell number i to 0 in step S22
of FIG. 6, the control circuit 20 determines whether or not the
cell number i conforms to the reference cell number K in step S23.
When it determines NO, the process proceeds to step S24 and the
control circuit 20 calculates the optimization target amount of
charge D.DELTA.Ah[i] for the cell with the cell number i from the
full charging capacity Q[i], the reference SOC (=N percent) and the
amount of charge difference .DELTA.Ah[K] of the reference cell by
using the formula 2 below. Here, (Q[i].times.N/100) in the formula
2 below is the amount of charge in the reference SOC.
.DELTA.DAh[i]=Q[i].times.N/100+.DELTA.Ah[K] Formula 2
[0070] Subsequently in step S25, the control circuit 20 converts
the optimization target amount of charge .DELTA.DAh[i] calculated
for the cell with the cell number i in step S24 into the SOC by
using the formula 3 below.
DSOC[i]=.DELTA.DAh[i]/Q[i] Formula 3
[0071] Next in step S26, the control circuit 20 converts the
optimization target SOC calculated for the cell with the cell
number i in step S25 into a voltage value, and then the process
proceeds to step S27. Here, the SOC can be converted into the
voltage value by referring to a table stored in a memory, which
shows the relationship between the SOC and the voltage value.
[0072] In addition, when the cell number i conforms to the cell
number K and therefore it is determined YES in step S23, the
process proceeds to step S27, bypassing steps 24 to 26.
[0073] After the cell number i is increased by one in step S27, the
control circuit 20 determines whether or not the cell number i
conforms to the number of cells n that form the assembled battery
in step S28. When it determines NO, the process returns to step S23
and the procedure described above is repeated.
[0074] When the optimization target voltage value is calculated for
all of the plurality of cells that form the assembled battery other
than the reference cell, the control circuit 20 determines YES in
step S28 and terminates the procedure.
[0075] According to the state of charge optimizing device 2 of the
present invention, when the assembled battery is discharged or
charged after the optimizing process as described above, the SOCs
of the plurality of cells that form the assembled battery is
uniform at 50 percent, where both the discharge characteristic and
charge characteristic are favorable and well balanced. When the
assembled battery is further discharged or charged thereafter, the
cell with the smallest full charging capacity will reach 0 percent
or 100 percent the earliest among the plurality of cells, thereby
obtaining the maximum charging and discharging capacity of the
assembled battery. Therefore, it is possible to maximally elicit
the performance of the assembled battery that includes the
plurality of cells having different full charging capacities.
[0076] Also, according to the state of charge optimizing device of
the present invention, it is possible to conduct the optimizing
process regardless of the SOCs of the plurality of cells that form
the assembled battery.
[0077] Further, among the plurality of cells that form the
assembled battery, the cell with the smallest amount of charge
difference, which is obtained by subtracting the amount of charge
when the SOC is 50 percent from the amount of charge at the time,
is specified as the reference cell. Therefore, the optimization
target amount of charge calculated for each of the cells other than
the reference cell is below the amount of charge at the time,
whereby the optimizing process can be conducted by only
discharging. Accordingly, only the discharge circuit 21 is
required, and the configuration is simple compared to a state of
charge optimizing device with both the discharge circuit and charge
circuit.
Second Embodiment
[0078] While the state of charge optimizing device of the first
embodiment is to conduct the optimizing process when the SOCs of
the plurality of cells that form the assembled battery vary a great
deal, the state of charge optimizing device of this embodiment is
to conduct the optimizing process when the amount of charge of a
cell of the plurality of cells that form the assembled battery
falls below or exceeds a lower limit and an upper limit which are
determined in accordance with the amount of charge of the cell with
the smallest full charging capacity.
[0079] The configuration of the state of charge optimizing device
in this embodiment is the same as that in the first embodiment
except for the control circuit. Therefore, the description thereof
is omitted. Also, the overall procedure of the optimizing process
conducted by the control circuit of this embodiment is the same as
the procedure described in the first embodiment shown in FIG. 4.
Therefore, the description thereof is omitted.
[0080] The charging and discharging capacity of the assembled
battery is determined by the cell with the smallest full charging
capacity among the plurality of cells that form the assembled
battery. In other words, in the case of charging the assembled
battery, the maximum charging capacity is obtained when the SOC of
the cell with the smallest full charging capacity reaches 100
percent the earliest, and in the case of discharging the assembled
battery, the maximum discharging capacity is obtained when the SOC
of the cell with the smallest full charging capacity reaches 0
percent the earliest.
[0081] In order for the SOC of the cell with the smallest full
charging capacity to reach 0 percent or 100 percent the earliest,
the amount of charge of the cells other than this cell should be
within a range with a lower limit which is the amount of charge of
the cell with the smallest full charging capacity and an upper
limit which is the amount of charge obtained by adding the
difference of the full charging capacities between the cell with
the smallest full charging capacity and each of the cells other
than this cell to the amount of charge of the cell with the
smallest full charging capacity.
[0082] For example, in the case where the assembled battery
includes three cells 1 to 3 as shown in FIG. 7, the amount of
charge of the cell 1 should be within the range which is the amount
of charge of the cell 3 Ah3 or above, and the amount of charge Aho1
or below, which is obtained by adding the difference a1 between the
full charging capacities of the cell 1 and cell 3 to the amount of
charge of the cell 3 Ah3. The amount of charge of the cell 2 should
be within the range which is the amount of charge of the cell 3 Ah3
or above, and the amount of charge Aho2 or below, which is obtained
by adding the difference a2 between the full charging capacities of
the cell 2 and cell 3 to the amount of charge of the cell 3
Ah3.
[0083] Accordingly, in the state of charge optimizing device of
this embodiment, the optimizing process is conducted when the
amount of charge of any of the plurality of cells that form the
assembled battery deviates the range described above.
[0084] FIG. 8 shows the concrete procedure of a determining process
of necessity of optimization conducted by the control circuit of
this embodiment. In this determining process, first in step S31,
the cell number i is initialized to zero, and then the current
SOC[i] of the cell is estimated from the open-circuit voltage of
the cell with the cell number i in step S32. Here, the SOC can be
estimated by referring to a table stored in a memory, which shows
the relationship between the open-circuit voltage and the SOC.
[0085] Next in step S33, for the cell with the cell number i, the
current amount of charge Ah[i] is calculated from the full charging
capacity Q[i] and the SOC[i] estimated in step S32, by using the
formula 4 below.
Ah[i]=Q[i].times.SOC[i]/100 Formula 4
[0086] Subsequently in step S34, the cell number i is increased by
one, and the control circuit determines whether or not the cell
number i conforms to the number of cells n that form the assembled
battery in step S35. When it determines NO, the process returns to
step S32 and the procedure described above is repeated.
[0087] After that, when the current amounts of charge Ah[i] of all
the cells that form the assembled battery are calculated, it
determines YES in step S35, and next in step S36, identifies the
minimum value minq from among the calculated current amounts of
charge of all the cells that form the assembled battery.
[0088] Subsequently in step S37, it determines whether or not the
minimum value minq identified in step S36 is below the current
amount of charge of the cell with the smallest full charging
capacity, Ah[J] (J is the cell number of the cell with the smallest
full charging capacity). When it determines YES, it determines that
the optimizing process is necessary in step S38 and terminates the
procedure.
[0089] When the minimum value minq is the current amount of charge
of the cell with the smallest full charging capacity Ah[J] or above
and therefore it determines NO in step S37, it initializes the cell
number i to zero in step S39, and then in step S40, it determines
whether or not the current amount of charge of the cell with the
cell number i Ah[i] is above the upper limit which is obtained by
adding the difference between the full charging capacities of the
cell with the cell number i and the cell with the smallest full
charging capacity (Q[i]-Q[J]) to the current amount of charge of
the cell with the smallest full charging capacity Ah[J]. When it
determines NO, the cell number i is increased by one in step S42,
and then it determines whether or not the cell number i conforms to
the number of cells n in step S43. When it determines NO, the
process returns to step S40 and the procedure described above is
repeated.
[0090] During repeating the procedure described above, when it
determines YES in step S40, it determines that the optimizing
process is necessary in step S41 and terminates the procedure.
[0091] In contrast, when it determines NO in step S40 for all the
cells that form the assembled battery, finally it determines YES in
step S43 and then in step S44, it determines that the optimizing
process is not necessary and terminates the procedure.
[0092] In accordance with the procedure described above, in the
case where the amount of charge of any of the plurality of cells
that form the assembled battery is below the lower limit, or above
the upper limit, the control circuit determines that optimizing
process is necessary.
[0093] In contrast, in the case where the amount of charge of none
of the plurality of cells that form the assembled battery is below
the lower limit, or above the upper limit, the control circuit
determines that optimizing process is not necessary.
[0094] FIG. 9 shows the concrete procedure of an optimization
target voltage value calculating process conducted by the control
circuit of this embodiment. In this calculating process, after
initializing the cell number i to zero in step S51, the control
circuit, in step S52, calculates the amount of charge difference
.DELTA.Ah[i] between the current amount of charge and the amount of
charge in the reference SOC (=N percent) from the full charging
capacity Q[i] and the SOC[i] estimated in step S32 of FIG. 8, by
using the formula 1 stated above.
[0095] Subsequently, after increasing the cell number i by one in
step S53, the control circuit determines whether or not the cell
number i conforms to the number of cells n that form the assembled
battery in step S54. When it determines NO, the process returns to
step S52 and the procedure described above is repeated.
[0096] Thereafter, when the amount of charge difference
.DELTA.Ah[i] between the current amount of charge and the amount of
charge in the reference SOC (=N percent) is calculated for all the
cells that form the assembled battery, it determines YES in step
S54 and the process proceeds to step S55.
[0097] And then, by conducting the procedure from steps S55 to S62,
the optimization target voltage value is calculated for all the
cells that form the assembled battery other than the reference
cell. Here, the procedure from steps S55 to S62 is the same as that
from steps S21 to S28 shown in FIG. 6 and conducted by the control
circuit of the first embodiment. Therefore the description thereof
is omitted.
[0098] In accordance with the state of charge optimizing device of
this embodiment, since the optimizing process is conducted with the
timing described above, it is possible to prevent the SOCs of the
cells other than the cell with the smallest full charging capacity
from reaching 0 percent or 100 percent the earliest. Also, as in
the first embodiment, when the assembled battery is discharged or
charged after the optimizing process, all the SOCs of the plurality
of cells become 50 percent. When the assembled battery is further
discharged or charged thereafter, the SOC of the cell with the
smallest full charging capacity reaches 0 percent or 100 percent
the earliest, thereby eliciting the performance of the assembled
battery maximally.
[0099] In addition, in the embodiments above, the optimizing
process is conducted based on the optimization target voltage value
converted from the optimization target amount of charge. However,
it is also possible to adopt the configuration in which the
optimizing process is conducted based on the optimization target
amount of charge, or the configuration in which the optimizing
process is conducted based on the optimization target SOC.
[0100] Also, in the embodiments above, the optimization is
conducted by discharging each cell until the cell voltage becomes
equivalent to the optimization target voltage value in a state
where the ignition switch of a hybrid car is set to OFF. However,
it is also possible to adopt a configuration in which the
optimization is conducted during charging and discharging the
assembled battery. In such a configuration, an integration value of
the charging or discharging amount since the target value is set is
referred to as P (when it is charging, P>0, and when it is
discharging, P<0), and the optimization target amount of charge
DAh is kept modified using the formula (DAh+P). Accordingly
discharging or charging is conducted until the amount of charge, or
the value corresponding thereto, of each cell becomes the
optimization target amount of charge or the value corresponding
thereto.
[0101] Further, in the embodiments above, the optimization is
conducted by only discharging the assembled battery, specifying a
cell with the smallest the value as the reference cell. Here, the
value is obtained by subtracting the amount of charge when the SOC
is 50 percent from the amount of charge at the time. However, it is
also possible to adopt the configuration in which the optimization
is conducted by only charging the assembled battery, specifying a
cell with the greatest value as the reference cell, or the
configuration in which optimization is conducted by discharging and
charging the assembled battery, specifying a cell other than the
cells with the smallest and greatest values as the reference cell.
The values here are obtained in the same manner as described
above.
[0102] In the embodiments above, for each of the cells other than
the reference cell, the optimization target amount of charge is
calculated by adding the difference between the current amount of
charge and the amount of charge in the predetermined SOC to the
amount of charge in the predetermined SOC. However, it is possible
to obtain the optimization target amount of charge by calculating
the difference between the current amount of charge and the amount
of charge in the predetermined SOC for all the cells that form the
assembled battery, and then calculating the average value of the
calculated differences to be added to the amount of charge in the
predetermined SOC for each of the cells.
[0103] Also, in the embodiments above, the predetermined SOC is set
to 50 percent. However, it is not limited to 50 percent, and it is
possible to set the SOC to any value which can sufficiently elicit
the performance of the assembled battery depending on the
configuration or characteristic of the assembled battery. For
example, with the state of charge optimizing device of the
assembled battery in which discharging should be stopped at X1
percent (X1>0) and charging should be stopped at X2 percent
(X2<100), the predetermined SOC (=N percent) is set to the value
obtained by calculating with the formula 5 below.
N=(X1+X2)/2 Formula 5
[0104] Still further, in the embodiments above, each cell is
discharged separately. However, it is also possible to adopt a
configuration in which the optimization target value is set for a
plurality of cells which are one module, and charging and/or
discharging is conducted for every module to conduct the
optimization. In a state of charge optimizing device for an
assembled battery that includes many cells, adopting such a
configuration can realize a small circuit size.
[0105] Furthermore, the state of charge optimizing device of the
present invention can be used for not only the assembled battery
comprising lithium ion secondary cells, but also other kinds of
assembled batteries.
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