U.S. patent application number 17/009127 was filed with the patent office on 2021-02-11 for power storage device.
This patent application is currently assigned to NEC Corporation. The applicant listed for this patent is NEC Corporation. Invention is credited to Hiroshi SASAKI, Kozo TATENO.
Application Number | 20210044129 17/009127 |
Document ID | / |
Family ID | 1000005181675 |
Filed Date | 2021-02-11 |
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United States Patent
Application |
20210044129 |
Kind Code |
A1 |
SASAKI; Hiroshi ; et
al. |
February 11, 2021 |
POWER STORAGE DEVICE
Abstract
A power storage device includes a plurality of series-connected
battery cells and a balance circuit board. The balance circuit
board includes: a heat-generating element (1121) that is provided
for each of the plurality of battery cells, and is connected with
the corresponding battery cell; and a first temperature sensor that
is arranged within a range sandwiched between heat-generating
elements positioned at both ends in an arrangement direction of a
plurality of heat-generating elements (1121).
Inventors: |
SASAKI; Hiroshi; (Tokyo,
JP) ; TATENO; Kozo; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NEC Corporation |
Tokyo |
|
JP |
|
|
Assignee: |
NEC Corporation
Tokyo
JP
|
Family ID: |
1000005181675 |
Appl. No.: |
17/009127 |
Filed: |
September 1, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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15575075 |
Nov 17, 2017 |
10797491 |
|
|
PCT/JP2016/065264 |
May 24, 2016 |
|
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17009127 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 2010/4271 20130101;
H01M 10/6571 20150401; H01M 10/615 20150401; H02J 7/0014 20130101;
G01K 7/22 20130101; H01M 10/486 20130101; G01K 1/14 20130101; H01M
10/637 20150401; H01M 10/633 20150401; H01M 10/4207 20130101; H02J
7/0016 20130101; H02J 7/0047 20130101 |
International
Class: |
H02J 7/00 20060101
H02J007/00; H01M 10/6571 20140101 H01M010/6571; G01K 7/22 20060101
G01K007/22; H01M 10/615 20140101 H01M010/615; H01M 10/48 20060101
H01M010/48; H01M 10/42 20060101 H01M010/42; H01M 10/637 20140101
H01M010/637; G01K 1/14 20060101 G01K001/14; H01M 10/633 20140101
H01M010/633 |
Foreign Application Data
Date |
Code |
Application Number |
May 25, 2015 |
JP |
2015-105596 |
Claims
1-10. (canceled)
11. A power storage device comprising a plurality of
series-connected battery cells and a circuit board, wherein the
circuit board includes: a plurality of heat-generating elements
connected with the plurality of series-connected battery cells; a
first temperature sensor provided at a position overlapping the
plurality of heat-generating elements in a plan view or in a
vicinity of the plurality of heat-generating elements; a first
region where the plurality of heat-generating elements are
provided; a second region where a second temperature sensor that is
different from the first temperature sensor is provided; and an
isolation region that separates the first region from the second
region, and the isolation region is a region of the circuit board
where no conductive pattern is provided.
12. The power storage device according to claim 11, wherein the
first temperature sensor is arranged at the center of the region
where the plurality of heat-generating elements are provided.
13. The power storage device according to claim 12, wherein the
first temperature sensor is arranged in a vicinity of the center of
the region where the plurality of heat-generating elements are
provided and in a position not overlapping with the plurality of
heating elements in the plan view.
14. The power storage device according to claim 11, wherein the
first temperature sensor is arranged at a location in the circuit
board where temperature is highest due to heat generation of the
plurality of heat-generating elements.
15. The power storage device according to claim 11, wherein the
circuit board includes a plurality of regions where the first
temperature sensor can be arranged in an arrangement direction of
the plurality of heat-generating elements, and the first
temperature sensor is arranged in a region, among the plurality of
regions, that is closest to a center where the plurality of
heat-generating elements are provided.
16. The power storage device according to claim 11, wherein the
circuit board is a substrate having a multilayer structure and the
first temperature sensor is arranged on wirings that connect the
plurality of heat-generating elements and the switch elements via
an insulator.
17. The power storage device according to claim 11, wherein the
first temperature sensor is arranged on a rear side of a face of
the circuit board on which the plurality of heat-generating
elements are arranged.
18. The power storage device according to claim 11, wherein the
isolation region includes a through-hole region that penetrates
through the circuit board.
19. The power storage device according to claim 11, further
comprising a second temperature sensor that is arranged outside the
circuit board.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a divisional application of U.S.
patent application Ser. No. 15/575,075, filed on Nov. 17, 2017
entitled "POWER STORAGE DEVICE," which is a national stage
application of International Application No. PCT/JP2016/065264
entitled "Power Storage Device" filed on May 24, 2016, which claims
priority to Japanese Patent Application No. 2015-105596 filed on
May 25, 2015, the disclosures of which are hereby incorporated by
reference in their entirety.
TECHNICAL FIELD
[0002] The present invention relates to a technique of controlling
a cell balance operation of a power storage device.
BACKGROUND ART
[0003] A power storage device configured by including a plurality
of battery cells such as lithium-ion batteries is equipped with a
balance circuit for equalizing voltages among the battery cells,
and performs circuit control for reducing a level difference in
cell voltages. There are a balance circuit that uses a passive
balance type and a balance circuit that uses an active balance
type. The balance circuit of a passive balance type operates to
equalize voltages among battery cells by connecting, to a bypassed
resistance circuit and the like, a battery cell having a relatively
high voltage, and discharging the battery cell alone.
[0004] An example of a technique relating to a balance circuit of a
passive balance type is disclosed in PTL 1 described below, for
example. PTL 1 described below discloses a power storage device
provided with a balance circuit of a passive balance type including
a resistor, and a temperature sensor, for each of a plurality of
power storage elements (battery cells). PTL 1 also discloses a
technique of controlling an ON/OFF state of a switch of each
balance circuit in such a way that a temperature of the resistor
detected by the temperature sensor is maintained at a maximum use
temperature during an operation of each balance circuit. In
addition, a technique of measuring a maximum temperature of a
surface of a heat-generating object is disclosed in PTL 2 described
below, for example.
CITATION LIST
Patent Literature
[PTL 1] Japanese Laid-open Patent Publication No. 2011-155751
[PTL 2] Japanese Laid-open Patent Publication No. 2009-300132
SUMMARY OF INVENTION
Technical Problem
[0005] In a balance operation of a balance circuit of a passive
balance type, a resistance circuit 1 and the like generate Joule
heat by consuming electric power. This heat becomes a factor of
decrease in reliability and service life of a battery cell
neighboring the balance circuit and other components. Thus, in
terms of reliability and service life of components of a balance
circuit, it is desirable that an operation of a balance circuit is
controlled based on a temperature of the balance circuit.
Accordingly, in order to accurately perform such control, a
technique of accurately detecting heat generation of a balance
circuit is desired.
[0006] An object of the present invention is to provide a technique
of accurately detecting heat generation of a balance circuit.
Solution to Problem
[0007] The present invention provides a power storage device
including a plurality of series-connected battery cells and a
circuit board, wherein the circuit board includes: a
heat-generating element that is provided for each of the plurality
of battery cells, and is connected with the corresponding battery
cell; and a first temperature sensor that is arranged within a
range sandwiched between the heat-generating elements positioned at
both ends in an arrangement direction of a plurality of the
heat-generating elements.
Advantageous Effects of Invention
[0008] The present invention enables to accurately detect heat
generation of a balance circuit.
BRIEF DESCRIPTION OF DRAWINGS
[0009] The above-described object and other objects, features and
advantages will be more apparent from the following preferred
example embodiments and the accompanying drawings.
[0010] FIG. 1 is a diagram conceptually illustrating a
configuration of a power storage device according to a first
example embodiment;
[0011] FIG. 2 is a schematic diagram representing a relationship
between an operation state of a balance circuit and heat generation
distribution in Y-Y' direction;
[0012] FIG. 3 is a schematic diagram representing a relationship
between an operation state of a balance circuit and heat generation
distribution in X-X' direction orthogonal to Y-Y' direction;
[0013] FIG. 4 is a diagram exemplifying a range for providing a
first temperature sensor;
[0014] FIG. 5 is a diagram illustrating a first placement example
of the first temperature sensor;
[0015] FIG. 6 is a diagram illustrating a second placement example
of the first temperature sensor;
[0016] FIG. 7 is a diagram illustrating a third placement example
of the first temperature sensor;
[0017] FIG. 8 is a diagram illustrating a fourth placement example
of the first temperature sensor;
[0018] FIG. 9 is a diagram illustrating a fifth placement example
of the first temperature sensor;
[0019] FIG. 10 is a diagram schematically illustrating a circuit
configuration example of the power storage device according to the
first example embodiment;
[0020] FIG. 11 is a diagram exemplifying a specific flow of a
balance operation of each channel in the power storage device in
FIG. 10;
[0021] FIG. 12 is a flowchart illustrating a flow of processing of
the balance operation in FIG. 11;
[0022] FIG. 13 is a flowchart illustrating a flow of processing of
a control unit transmitting a signal for notifying an abnormality
from a communication unit;
[0023] FIG. 14 is a diagram schematically illustrating another
circuit configuration example of the power storage device according
to the first example embodiment;
[0024] FIG. 15 is a diagram exemplifying a specific flow of a
balance operation of each channel in the power storage device in
FIG. 14;
[0025] FIG. 16 is a diagram exemplifying a specific flow of a
balance operation of each channel in the power storage device in
FIG. 14;
[0026] FIG. 17 is a flowchart illustrating a flow of processing of
the balance operation in FIG. 16;
[0027] FIG. 18 is a diagram conceptually illustrating a processing
configuration of a power storage device according to a second
example embodiment;
[0028] FIG. 19 is a diagram conceptually illustrating a circuit
configuration example of the power storage device according to the
second example embodiment; and
[0029] FIG. 20 is a flowchart illustrating a flow of a balance
operation in the power storage device in FIG. 19.
DESCRIPTION OF EMBODIMENTS
[0030] Example embodiments of the present invention will be
described below by using the drawings. Note that like components
are assigned with like reference numerals throughout all the
drawings, and description therefor will be omitted as
appropriate.
[0031] Note that components illustrated in each drawing are
implemented by an arbitrary combination of hardware and software,
mainly by a central processing unit (CPU) of an arbitrary computer,
a memory, a program loaded on a memory for implementing the
components in the drawing, a storage medium for storing the program
such as a hard disk, and an interface for network connection.
Accordingly, a method and a device for implementing the components
include various modification examples.
First Example Embodiment
Processing Configuration
[0032] FIG. 1 is a diagram conceptually illustrating a
configuration of a power storage device according to a first
example embodiment. As illustrated in FIG. 1, the power storage
device according to the present example embodiment includes a
battery string 3 of a plurality of series-connected battery modules
31, and a balance circuit board 1 that is connected with the
battery string 3 through a connector 2. The connector 2 includes an
electrode terminal and a cell temperature sensor terminal on a
battery cell 311 basis. Each of the battery modules 31 includes a
plurality of series-connected battery cells 311 (four battery cells
311 in an example in FIG. 1). As illustrated in FIG. 1, each of the
battery modules 31 may include a cell temperature sensor 312 that
measures a temperature of each battery cell 311.
[0033] The balance circuit board 1 includes a balance circuit block
11 and a control circuit block 12. The balance circuit block 11
includes a balance circuit 112 for equalizing voltages of the
battery cells 311, and a first temperature sensor 111 for measuring
a temperature of the balance circuit 112. The control circuit block
12 includes a control unit 121 for controlling an operation of the
balance circuit 112, and a communication unit 122 for communicating
with a not-illustrated external device and the like.
[0034] The balance circuit 112 is provided at least on a battery
module 31 basis. In the present example embodiment, the balance
circuit 112 is provided for each of the plurality of battery cells
311, and is connected with corresponding one of the battery cells
311. The balance circuit 112 may be a balance circuit of a
so-called passive balance type, or may be a balance circuit of a
so-called active balance type. Note that, in the following
respective example embodiments, a balance circuit of a passive
balance type will be described as an example. However, the present
invention is not limited to the balance circuit of the passive
balance type.
[0035] Herein, the passive balance type is a type in which, when
the plurality of battery cells 311 have a variation in voltage
(discharge capacity), voltages among the plurality of battery cells
are equalized by discharging a battery cell having a relatively
high voltage with a battery cell having a lowest voltage as a
reference. A balance circuit of the passive balance type includes a
resistive element for discharging each of battery cells, and a
switch element for controlling a balance operation by being
switched ON/OFF. On the other hand, an active balance type is a
type in which, when a plurality of battery cells have a variation
in voltage, voltages among the plurality of battery cells are
equalized by moving an electric charge from a battery cell having a
large capacity to a battery cell having a small capacity. A balance
circuit of the active balance type includes a capacitor or a
transformer for moving an electric charge among battery cells, and
a switch element for selecting a battery cell to be connected with
the capacitor or the transformer. The resistive element and the
transformer (inductor element) used in the balance circuit 112
mainly generate heat during a balance operation.
[0036] The first temperature sensor 111 is provided for every one
or more of the balance circuits 112, and measures a temperature of
a corresponding balance circuit 112. In addition, one or more first
temperature sensors 111 are provided for a corresponding balance
circuit 112. For example, one or more first temperature sensors 111
are provided for each of the balance circuits 112. When a width
between the balance circuits 112 is narrow and the like, it may be
difficult to provide the first temperature sensor 111 for every
balance circuit 112. In such a case, one or more first temperature
sensors 111 may be provided for every predetermined number of the
balance circuits 112 included in each battery module 31.
[0037] The first temperature sensor 111 becomes less responsive to
heat generated from a corresponding balance circuit 112 as the
first temperature sensor 111 is more distant from the balance
circuit 112. Thus, in terms of temperature measurement accuracy,
the first temperature sensor 111 is more preferably provided at a
position that is closer to the corresponding balance circuit 112. A
position where the first temperature sensor 111 is placed will be
described below.
[0038] FIG. 2 is a schematic diagram representing a relationship
between an operation state of a balance circuit and heat generation
distribution in Y-Y' direction. In an example in FIG. 2, eight
balance circuits 112 respectively including a heat-generating
element 1121 (a resistive element in the case of the passive
balance type) and a switch element 1122 are disposed. FIG. 2(a)
exemplifies temperature distribution in Y-Y' direction when the
balance circuits 112 of all channels perform balance operations.
Note that a channel (CH) means a set of one battery cell 311 and a
balance circuit 112 corresponding to the battery cell 311. In the
case of FIG. 2(a), a peak of temperature appears at a central part
since a heat dissipation performance at the central part is
inferior to that at an end part, and the temperature becomes lower
as coming closer to end part sides. FIG. 2(b) exemplifies
temperature distribution in YY' direction when the balance circuits
112 of upper-half channels perform balance operations. In the case
of FIG. 2(b), a peak of temperature appears at a central part of
the upper-half channels. FIG. 2(c) exemplifies heat generation
distribution in Y-Y' direction when every other one of the balance
circuits 112 performs a balance operation. In the case of FIG.
2(c), temperature is low at parts of channels where no balance
operation is performed, which results in wave-shaped temperature
distribution. In FIG. 2(c), peaks of temperature appear at two
points, which are between a third channel and a fourth channel from
the top, and between a fifth channel and a sixth channel from the
top. In this way, temperature distribution in Y-Y' direction
changes in response to an electrical conduction state of the
heat-generating element 1121, within a range sandwiched between the
heat-generating elements 1121 at both ends. Thus, providing the
first temperature sensor 111 in the range sandwiched between the
heat-generating elements 1121 at both ends in Y-Y' direction
facilitates detection of heat generated from the heat-generating
element 1121. Note that, among FIGS. 2(a) to (c), a highest
temperature in Y-Y' direction is detected in the case of FIG. 2(a)
in which the balance circuits 112 of all the channels operate. At
least one first temperature sensor 111 is ideally arranged in such
a way as to overlap a center of the range sandwiched between the
heat-generating elements 1121 at both ends in Y-Y' direction.
[0039] FIG. 3 is a schematic diagram representing a relationship
between an operation state of a balance circuit and heat generation
distribution in X-X' direction orthogonal to Y-Y' direction. The
switch element 1122 generally has small ON-resistance in comparison
with that of the heat-generating element 1121. Therefore, when the
heat-generating element 1121 is in an electrical conduction state,
a peak of temperature appears at a central part of the
heat-generating element 1121 in X-X' direction. Thus, the first
temperature sensor 111 is ideally arranged in such a way as to
overlap a center of the heat-generating element 1121 in X-X'
direction.
[0040] In addition, it can be predicted from FIGS. 2 and 3 that a
point that may reach a highest temperature on a plane of the
balance circuit board 1 (hereinafter, also written as a maximum
heat-generating point) is a point of intersection between a point
that reaches a highest temperature in Y-Y' direction and a point
that reaches a highest temperature in X-X' direction when all the
corresponding balance circuits 112 operate. Note that it is
possible to grasp the maximum heat-generating point also by
carrying out a test operation or simulation of the balance circuit
board 1 and measuring temperature distribution of the balance
circuit board 1 during a balance operation, for example.
[0041] When considering a component interval, a wiring interval, an
electrical insulation interval, and the like of electrical
components such as the heat-generating element 1121 and the first
temperature sensor 111, the first temperature sensor 111 cannot
always be provided at an ideal position with no error. The first
temperature sensor 111 needs to be provided as close as possible to
the maximum heat-generating point. As a specific example, when a
distance in Y-Y' direction between the heat-generating elements
1121 at both ends is denoted by W, a width in X-X' direction of
each heat-generating element 1121 is denoted by L, and a coordinate
of the maximum heat-generating point that is specified as described
in FIGS. 2 and 3 is denoted by (Wymax, Lxmax), a range for
providing the first temperature sensor 111 can be defined by the
following Expression 1 and Expression 2, for example.
[Mathematical 1]
Placement Range in Y-Y' Direction=Wymax.+-.0.3.times.W (Expression
1)
Placement Range in X-X' Direction=Lxmax.+-.0.3.times.L (Expression
2)
[0042] This can be illustrated as in FIG. 4. FIG. 4 is a diagram
exemplifying a range for providing the first temperature sensor
111. A range indicated by slanting lines is defined based on the
maximum heat-generating point (Wymax, Lxmax) that is specified as
described using FIGS. 2 and 3, the distance W between the balance
circuits 112 positioned at both ends, and the width L of the
balance circuit 112. The first temperature sensor 111 is provided
in such a way as to overlap the range indicated by the slanting
lines.
[0043] FIG. 5 is a diagram illustrating a first placement example
of the first temperature sensor 111. FIGS. 5(a), (b), and (c)
respectively illustrate a top view, a sectional view in Y-Y'
direction, and a sectional view in X-X' direction of the balance
circuit board 1 in the first placement example. As illustrated in
FIG. 5, for example, the first temperature sensor 111 can be
provided on the balance circuit board 1 on a face at rear side of a
face provided with the components (the heat-generating element 1121
and the like) of the balance circuit 112. In this case, restriction
on arrangement due to other components is reduced, and the first
temperature sensor 111 can be provided in such a way as to overlap
the maximum heat-generating point that is predicted as described in
FIGS. 2 and 3 or is specified by a test operation and the like.
[0044] FIG. 6 is a diagram illustrating a second placement example
of the first temperature sensor 111. FIGS. 6(a), (b), and (c)
respectively illustrate a top view, a sectional view in Y-Y'
direction, and a sectional view in X-X' direction of the balance
circuit board 1 in the second placement example. It is assumed in
the second placement example, a case in which a certain degree of a
space is present at a central part of eight balance circuits 112.
In this case, the first temperature sensor 111 can be provided in
the space at the central part, with a physical electrical
insulation interval. Also with such a configuration, it becomes
possible to provide the first temperature sensor 111 in such a way
as to overlap the maximum heat-generating point that is specified
as described in FIGS. 2 and 3. In addition, in the example in FIG.
6, the first temperature sensor 111 and the balance circuit 112 may
be configured to be insulated from each other by providing an
insulator between the first temperature sensor 111 and the balance
circuit 112.
[0045] FIG. 7 is a diagram illustrating a third placement example
of the first temperature sensor 111. FIGS. 7(a), (b), and (c)
respectively illustrate a top view, a sectional view in Y-Y'
direction, and a sectional view in X-X' direction of the balance
circuit board 1 in the third placement example. In the third
placement example, the first temperature sensor 111 is provided on
an upper face of the heat-generating element 1121 while being
covered with an insulator 1111 that is a coating film and the like
formed of an insulating material. Also with such a configuration,
it becomes possible to provide the first temperature sensor 111 in
such a way as to overlap the maximum heat-generating point that is
predicted as described in FIGS. 2 and 3 or is specified by a test
operation and the like.
[0046] FIG. 8 is a diagram illustrating a fourth placement example
of the first temperature sensor 111. FIGS. 8(a), (b), and (c)
respectively illustrate a top view, a sectional view in Y-Y'
direction, and a sectional view in X-X' direction of the balance
circuit board 1 in the fourth placement example. In the fourth
placement example, it is assumed that the balance circuit board 1
is a substrate having a multilayer structure. In such a balance
circuit board 1, as illustrated in FIG. 8, a wiring line 1123 to be
connected with the heat-generating element 1121 may be provided on
an inner layer. In this case, the first temperature sensor 111 may
be provided at a position overlapping the wiring line 1123 in a
planar view. In FIG. 8, the wiring line 1123 is connected to an end
part of three series-connected heat-generating elements 1121, and
the first temperature sensor 111 is arranged in such a way as to
overlap the wiring line 1123 in a planar view. The wiring line 1123
is a metal and has high thermal conductivity, which facilitates
transfer of heat from the heat-generating element 1121. Thus, heat
from the heat-generating element 1121 can be detected relatively
accurately by providing the first temperature sensor 111 right
above the wiring line 1123 in this way.
[0047] FIG. 9 is a diagram illustrating a fifth placement example
of the first temperature sensor 111. In the fifth placement
example, illustrated is a case where twelve balance circuits 112
are provided separately in three blocks, and there exist a
plurality of spaces in which the first temperature sensor 111 can
be arranged between the blocks in Y-Y' direction. In the present
drawings, it is assumed that circuit components of the middle block
are present at a center of a range sandwiched between the
heat-generating elements 1121 at both ends, and there is no space
for arranging the first temperature sensor 111. In this case, the
first temperature sensor 111 can be arranged in at least either a
space between the upper block and the middle block or a space
between the middle block and the lower block. Note that FIG. 9
illustrates an example in which the first temperature sensor 111 is
provided in the upper space. Although not illustrated, when five
blocks are aligned, the first temperature sensor 111 is preferably
provided in at least either a space between the second block and
the third block or a space between the third block and the fourth
block, since these spaces are closer to a center of a range
sandwiched between the heat-generating elements 1121 at both ends.
Without limitation thereto, the first temperature sensor 111 may be
provided in a space between the uppermost block and the second
block, or in a space between the fourth block and the lowermost
block.
[0048] Note that an arrangement position of the first temperature
sensor 111 is not limited to the examples illustrated in FIGS. 5 to
9. For example, a plurality of first temperature sensors 111 may be
provided across the entire balance circuit board 1, within a range
that is defined in consideration of heat generation distribution in
Y-Y' direction and X-X' direction. In addition, for example, in
FIGS. 6, 8, and 9, the first temperature sensor 111 may be provided
on a rear face, as illustrated in FIG. 5.
[0049] In addition, the first temperature sensor 111 becomes less
responsive to heat generated from a corresponding balance circuit
112 as the first temperature sensor 111 is more distant from the
balance circuit 112. Thus, in terms of temperature measurement
accuracy, the first temperature sensor 111 is more preferably
provided at a position that is closer to the corresponding balance
circuit 112. The first temperature sensor 111 can be mounted near a
surface of the balance circuit board 1 by using a thermistor
resistor, a semiconductor temperature sensor, a resistance
temperature detector (RTD), and the like as the first temperature
sensor 111. Accordingly, it becomes possible to arrange the first
temperature sensor 111 in proximity to the balance circuit 112 in a
direction perpendicular to a face of the balance circuit board 1,
and measure a temperature of the balance circuit 112 with high
accuracy.
[0050] The control unit 121 controls a balance operation of the
balance circuit 112 corresponding to each of the battery cells 311,
based on a voltage of each of the battery cells 311 and a
temperature (hereinafter, also written as a first measured
temperature) measured by the first temperature sensor 111.
[0051] A basic control of the balance circuit 112 performed by the
control unit 121 will be described. The control unit 121 acquires a
voltage of each of the battery cells 311 via a terminal (not
illustrated) of the connector 2 connected to each of the battery
cells 311, and specifies a battery cell 311 having a lowest voltage
(hereinafter, a lowest voltage cell) among the plurality of battery
cells 311. Then, the control unit 121 calculates, for each of the
battery cells 311 other than the lowest voltage cell, a voltage
difference .DELTA.VB from the lowest voltage cell. Then, the
control unit 121 actuates the balance circuit 112 corresponding to
the battery cell 311 whose voltage difference .DELTA.VB from the
lowest voltage cell is equal to or more than a voltage difference
that is a balance operation start condition (hereinafter, this
voltage difference will be written as ".DELTA.VB.sub.on"). The
voltage difference .DELTA.VB between the battery cell 311
corresponding to the balance circuit 112 and the lowest voltage
cell is reduced by actuating the balance circuit 112. Then, when
the voltage difference .DELTA.VB between the battery cell 311 and
the lowest voltage cell becomes equal to or less than a voltage
difference that is a balance operation end condition (hereinafter,
this voltage difference will be written as ".DELTA.VB.sub.off"),
the control unit 121 stops a balance operation of the balance
circuit 112 corresponding to the battery cell 311.
[0052] Herein, the balance circuit 112 generates heat through a
balance operation. For example, a balance circuit of the passive
balance type includes a resistive element, and during execution of
a balance operation, discharge energy of the battery cell 311 is
consumed by the resistive element and the resistive element
generates heat accordingly. This heat generation of the resistive
element may cause a temperature of the balance circuit 112 to be
higher than that of the battery cell 311. For example, when a power
storage device is used, a temperature of the battery cell 311 is
about 40.degree. C. even after rising, whereas a temperature of the
balance circuit may rise up to approximately 85.degree. C. through
a balance operation. Then, this heat transfers to the battery cell
311 and other components within the power storage device via a
medium such as the balance circuit board 1 and thereby causes
temperature rise. This may adversely affect service life, operation
reliability, and the like of the battery cell 311 and the other
components.
[0053] In view of the above, when a temperature measured by the
first temperature sensor 111 provided for the balance circuit 112
(hereinafter, also written as a first measured temperature) is
equal to or more than an upper reference temperature, the control
unit 121 stops an operation of the balance circuit 112
corresponding to the first temperature sensor 111, regardless of
the voltage difference .DELTA.VB of the battery cell 311 relative
to the lowest voltage cell described above. When the balance
circuit 112 corresponding to the first temperature sensor 111 is
stopped because the first measured temperature measured by the
first temperature sensor 111 becomes the upper reference
temperature, heat generation of the balance circuit 112 calms down
and the first measured temperature begins to decrease. Then, when
the first measured temperature measured by the first temperature
sensor 111 becomes equal to or less than a lower reference
temperature that is lower than the upper reference temperature, the
control unit 121 restarts the operation of the balance circuit 112
corresponding to the first temperature sensor 111. The control unit
121 holds, for example, information indicating a correspondence
relationship between the first temperature sensor 111 and the
balance circuit 112 in a not-illustrated storage region in advance.
When there is the first temperature sensor 111 measuring a
temperature equal to or more than the upper reference temperature,
by using the information in the storage region, the control unit
121 identifies the balance circuit 112 of which a balance operation
is to be stopped. In addition, by using the information in the
storage region, the control unit 121 identifies the balance circuit
112 of which a balance operation is to be restarted, when there is
the first temperature sensor 111 measuring a temperature equal to
or more than the upper reference temperature and then the
temperature drops to measure a temperature equal to or less than
the lower reference temperature.
[0054] The upper reference temperature is a threshold temperature
at which an operation of the balance circuit 112 is to be stopped.
When the upper reference temperature is set lower, heat generation
of the balance circuit can be suppressed and the battery cell 311
and the components can be protected with higher accuracy.
Meanwhile, the balance circuit 112 is more frequently stopped, and
it may take a longer time for voltages of the battery cells 311 to
be equalized. The lower reference temperature is a threshold
temperature at which an operation of the balance circuit 112 is to
be restarted. When the lower reference temperature is set lower, a
temperature of the balance circuit 112 decreases sufficiently and
the battery cell 311 and the components can be protected with
higher accuracy. Meanwhile, a time for a balance operation to be
restarted is prolonged, and it takes a longer time for voltages of
the battery cells 311 to be equalized. The upper reference
temperature and the lower reference temperature are respectively
adjusted to appropriate values, based on uses, performance
requirements, and the like of a power storage device, for example,
and are set in a not-illustrated storage region such as a memory of
the control unit 121. For example, the upper reference temperature
and the lower reference temperature are set as 85.degree. C. and
80.degree. C., respectively, in the storage region of the control
unit 121. When a difference (temperature hysteresis) between the
upper reference temperature and the lower reference temperature is
5.degree. C. or more, a balance operation of each balance circuit
112 can be stably controlled. In addition, when a difference
between the upper reference temperature and the lower reference
temperature is, for example, 10.degree. C. or less, it is possible
to reduce an adverse effect caused by heat generation of the
balance circuit 112 and the plurality of battery cells 311 can be
balanced without taking a longer time. However, a range of the
difference is not limited to the range exemplified herein.
[0055] When an operation stop time of the balance circuit 112 due
to the first measured temperature becoming equal to or more than
the upper reference temperature exceeds a reference value per unit
time, or when an operation stop number-of-times of the balance
circuit 112 due to the first measured temperature becoming equal to
or more than the upper reference temperature exceeds a reference
number-of-times per unit time, the communication unit 122 outputs,
to outside, information capable of specifying the balance circuit
or a battery cell corresponding to the balance circuit.
[0056] Specifically, the control unit 121 holds, in a
not-illustrated storage region, an operation stop time of the
balance circuit 112 due to the first measured temperature becoming
equal to or more than the upper reference temperature, or an
operation stop number-of-times of the balance circuit 112 due to
the first measured temperature becoming equal to or more than the
upper reference temperature. Then, the control unit 121 calculates,
by using held information, the operation stop time of the balance
circuit 112 per unit time or the operation stop number-of-times of
the balance circuit 112 per unit time. Then, the control unit 121
determines whether or not there is the balance circuit 112 of which
the calculated operation stop time is equal to or more than a
preset reference value per unit time, or whether or not there is
the balance circuit 112 of which the calculated operation stop
number-of-times is equal to or more than a preset reference
number-of-times per unit time. For example, the control unit 121
determines whether or not the operation stop time per unit time of
the balance circuit 112 occupies half or more of the unit time, or
whether or not the balance circuit 112 has stopped operating for a
fixed number of times or more per unit time. When the operation
stop time per unit time is longer than a predetermined reference
value, or when the operation stop number-of-times per unit time is
large, there is a possibility of occurrence of an abnormality, such
as abnormal heat generation of the balance circuit 112 and failure
of the first temperature sensor 111. In view of this, when there is
the balance circuit 112 of which the operation stop time exceeds
the predetermined reference value or of which the operation stop
number-of-times exceeds a predetermined reference number-of-times,
the control unit 121 generates information capable of specifying
the balance circuit or the battery cell 311 corresponding to the
balance circuit 112, and causes the communication unit 122 to
output the information.
Circuit Configuration Example 1
[0057] A configuration of the power storage device according to the
present example embodiment will be described by using FIG. 10. FIG.
10 is a diagram schematically illustrating a circuit configuration
example of the power storage device according to the first example
embodiment. In the present figure, an example in which one first
temperature sensor 111 is provided for one balance circuit 112 is
illustrated.
[0058] As illustrated in FIG. 10, each of the battery cells 311
included in the battery module 31 is connected with a corresponding
balance circuit 112 through a terminal of the connector 2. The
balance circuit 112 is provided in the balance circuit block 11 of
the balance circuit board 1, and includes the heat-generating
element 1121 and the switch element 1122. In the case of a passive
balance type, the heat-generating element 1121 is a resistive
element that consumes discharge energy of the battery cell 311
corresponding to each of the balance circuits 112. Further, the
switch element 1122 is a switching transistor, a metal oxide
semiconductor field effect transistor (MOS-FET), and the like, for
example.
[0059] The control unit 121 is connected with each of the switch
elements 1122 through a control line. The control unit 121
transmits a control signal to each of the switch elements 1122
through the control line, and switches ON/OFF states of each switch
element 1122. When the switch element 1122 is switched to an ON
state by the control unit 121, the battery cell 311 and the balance
circuit 112 corresponding to the battery cell 311 forms a closed
loop, and a balance operation is executed. On the other hand, when
the switch element 1122 is switched to an OFF state by the control
unit 121, the closed loop formed by the battery cell 311 and the
balance circuit 112 corresponding to the battery cell 311 is
released, and the balance operation is stopped.
[0060] The control unit 121 controls ON/OFF states of the switch
element 1122 of each of the balance circuits 112, based on a
voltage difference between the plurality of battery cells 311 and a
temperature detected by each of the first temperature sensors
111.
[0061] The control unit 121 is connected to terminals of the
connector 2, and acquires a voltage of each of the battery cells
311 from a voltage between the terminals. The control unit 121
compares the acquired voltages of the battery cells 311, and
specifies a lowest voltage cell. Then, the control unit 121
calculates a voltage difference .DELTA.VB from the lowest voltage
cell for each of the battery cells 311 other than the lowest
voltage cell. Herein, when the voltage difference .DELTA.VB between
the lowest voltage cell and a certain battery cell 311 is
.DELTA.VB.sub.on, the control unit 121 transmits a control signal
for switching the switch element 1122 corresponding to the battery
cell 311 to an ON state. Accordingly, a balance operation by the
balance circuit 112 is executed. On the other hand, when the
voltage difference .DELTA.VB between the lowest voltage cell and
the certain battery cell 311 becomes equal to or less than
.DELTA.VB.sub.off by executing the balance operation, the control
unit 121 transmits a control signal for switching the switch
element 1122 corresponding to the battery cell 311 to an OFF state.
Accordingly, the balance operation by the balance circuit 112 is
stopped. A voltage difference between the battery cell 311 and the
lowest voltage cell is reduced as the heat-generating element 1121
consumes discharge energy of the battery cell 311 whose voltage
difference .DELTA.VB from the lowest voltage cell is equal to or
more than .DELTA.VB.sub.on. A voltage of each of the plurality of
battery cells 311 becomes close to a voltage of the lowest voltage
cell by performing a balance operation for each of the plurality of
battery cells 311 whose voltage difference .DELTA.VB from the
lowest voltage cell is equal to or more than .DELTA.VB.sub.on. As a
result, voltages of the plurality of battery cells 311 are
equalized.
[0062] In addition, the control unit 121 is connected with each of
the first temperature sensors 111 through a signal line. The
control unit 121 acquires an output voltage from each of the first
temperature sensors 111 and converts the output voltage into a
temperature (a first measured temperature). When the
heat-generating element 1121 generates heat through a balance
operation and the first measured temperature becomes equal to or
more than an upper reference temperature, the control unit 121
transmits a control signal for setting the switch element 1122 of
the balance circuit 112 corresponding to the first temperature
sensor 111 to an OFF state, regardless of the voltage difference
.DELTA.VB. Accordingly, a balance operation of the balance circuit
112 corresponding to the first temperature sensor 111 measuring a
temperature equal to or more than the upper reference temperature
is stopped. When heat generation of the heat-generating element
1121 calms down and the first measured temperature becomes equal to
or less than a lower reference temperature, the control unit 121
transmits a control signal for setting the switch element 1122 to
an ON state, and restarts the balance operation by the balance
circuit 112.
[0063] In addition, the control unit 121 holds, in a
not-illustrated storage region, a time for which each balance
circuit 112 stops operating, or the number of times each balance
circuit 112 stops operating. Then, the control unit 121 calculates
an operation stop time or an operation stop number-of-times per
unit time of each balance circuit 112 by using information held in
the storage region. Then, the control unit 121 determines whether
or not there is the balance circuit 112 of which the calculated
operation stop time per unit time is equal to or more than a
predetermined reference value, or the balance circuit 112 of which
the calculated operation stop number-of-times per unit time is
equal to or more than a predetermined reference number-of-times.
When there is the balance circuit 112 concerned, the control unit
121 generates information capable of specifying the balance circuit
112 or the battery cell 311 corresponding to the balance circuit
112, and outputs the information to a communicably connected
external monitoring device and the like, for example, via the
communication unit 122. Accordingly, the external monitoring device
can display the information transmitted from the communication unit
122 on a display, and an operator of the external monitoring device
is able to specify the balance circuit 112 or the battery cell 311
that seems to have an abnormality of some kind.
[0064] The control unit 121 includes, for example, a
not-illustrated storage region such as a read only memory (ROM) and
a random access memory (RAM), and stores programs for implementing
the above-described functions in the storage region. In addition,
the control unit 121 includes a not-illustrated central processing
unit (CPU), and implements the above-described functions by
executing the programs stored in the storage region by use of the
CPU.
[0065] Further, the control unit 121 may be configured to execute a
balance operation by monitoring a voltage difference between the
plurality of battery cells 311 all the times, or may be configured
to execute a balance operation only when charging.
[0066] Although not illustrated in FIG. 10, the plurality of
battery modules 31 are connected in series between an external
positive electrode terminal 4 and an external negative electrode
terminal 5 of the power storage device. The power storage device is
connected to a not-illustrated external device and a
not-illustrated external power supply through the external positive
electrode terminal 4 and the external negative electrode terminal
5, and performs discharging or charging.
[0067] An example of a balance operation in the power storage
device in FIG. 10 will be described by using FIG. 11.
[0068] Note that, in the following description, when a certain
channel has a voltage difference .DELTA.VB of equal to or more than
.DELTA.VB.sub.on, the control unit 121 executes a balance operation
at a predetermined balance frequency FBAL. The balance frequency
FBAL includes an ON period T.sub.on during which the switch element
1122 is in an ON state, and an OFF period T.sub.off during which
the switch element 1122 is in an OFF state. The ON period T.sub.on
and the OFF period T.sub.off are alternately repeated. The control
unit 121 can manage a lapse of these periods by using a timer, for
example.
[0069] FIG. 11 is a diagram exemplifying a specific flow of a
balance operation of each channel in the power storage device in
FIG. 10.
[0070] First, a voltage difference .DELTA.VB of CH1 reaches
.DELTA.VB.sub.on at time t1. Then, the control unit 121 sets the
switch element 1122 of CH1 to an ON state, and starts a balance
operation of CH1. Accordingly, the voltage difference .DELTA.VB of
CH1 begins to decrease. In addition, a first measured temperature
begins to rise due to heat generated from the heat-generating
element 1121 of CH1. Note that FIG. 11 illustrates a behavior of
the linearly rising first measured temperature, but, in fact, the
first measured temperature may exhibit various behaviors upon
receiving influence such as operation states of surrounding
channels.
[0071] Thereafter, the first measured temperature continues to
rise, and the first measured temperature reaches an upper reference
temperature TRU at time t2. Then, the control unit 121 sets the
switch element 1122 of CH1 corresponding to the first temperature
sensor 111 to an OFF state, and stops the balance operation of CH1.
Since the balance operation is stopped in CH1, heat generation of
the heat-generating element 1121 of CH1 calms down, and the first
measured temperature begins to decrease. Note that FIG. 11
illustrates a behavior of the linearly decreasing first measured
temperature, but in fact, the first measured temperature may
exhibit various behaviors upon receiving influence such as
operation states of surrounding channels. In addition, when the
balance operation of the balance circuit 112 is stopped, load
impedance is increased and voltage rebound occurs. As illustrated
in FIG. 11, a voltage of the battery cell 311 of CH1 exhibits an
upward tendency because of this voltage rebound.
[0072] Thereafter, the first measured temperature drops down to a
lower reference temperature TRL at time t3. Then, the control unit
121 determines whether a balance frequency FBAL of CH1
corresponding to the first temperature sensor 111 is an ON period
T.sub.on or an OFF period T.sub.off. The control unit 121 restarts
the balance operation of CH1 in the case of the ON period T.sub.on.
In an example in FIG. 11, since CH1 is in the ON period T.sub.on at
time t3, the control unit 121 sets the switch element 1122 of CH1
to an ON state, and the balance operation is restarted in CH1.
Consequently, the voltage difference .DELTA.VB of CH1 begins to
decrease again, and the first measured temperature begins to rise
again.
[0073] Thereafter, the predetermined ON period T.sub.on elapses at
time t4. The control unit 121 sets the switch element 1122 of CH1
to an OFF state with timing at which time elapsed after the balance
operation turned into the ON state reaches T.sub.on, and stops the
balance operation. Herein, although not illustrated, the control
unit 121 completes the balance operation of CH1 when the voltage
difference .DELTA.VB becomes equal to or less than
.DELTA.VB.sub.off during the ON period T.sub.on.
[0074] In addition, although not illustrated, the control unit 121
completes the balance operation of CH1 when the voltage difference
.DELTA.VB after occurrence of voltage rebound is equal to or less
than a predetermined threshold value (an intermediate value between
.DELTA.VB.sub.on and .DELTA.VB.sub.off, for example) at a time of
entering a next ON period T.sub.on after a lapse of the OFF period
T.sub.off. Note that in this case, a threshold value for completing
the balance operation is set to a desirable value according to a
use environment and the like of the power storage device. When the
voltage difference .DELTA.VB is more than the predetermined
threshold value, the control unit 121 continues the balance
operation of the channel in a next cycle.
[0075] FIG. 12 is a flowchart illustrating a flow of processing of
the balance operation in FIG. 11.
[0076] The control unit 121 specifies, based on a voltage between
the terminals of the connector 2, a lowest voltage cell from among
the plurality of battery cells 311, and calculates a voltage
difference .DELTA.VB between the lowest voltage cell and each of
the other battery cells 311 (S101). Then, the control unit 121
determines, for each of the battery cells 311, whether or not the
voltage difference .DELTA.VB between the battery cell 311 and the
lowest voltage cell is equal to or more than .DELTA.VB.sub.on that
is a balance operation start condition (S102). When the voltage
difference .DELTA.VB from the lowest voltage cell is less than
.DELTA.VB.sub.on (S102: NO), it is not necessary to execute a
balance operation in a channel of the battery cell 311. Thus, the
control unit 121 does not actuate the balance circuit 112 and ends
the processing. On the other hand, when the voltage difference
.DELTA.VB from the lowest voltage cell is equal to or more than
.DELTA.VB.sub.on (S102: YES), the control unit 121 starts a balance
operation of a channel of the battery cell 311 (S103).
[0077] The control unit 121 determines, for the channel performing
the balance operation, whether or not the voltage difference
.DELTA.VB from the lowest voltage cell becomes equal to or less
than .DELTA.VB.sub.off that is one of balance operation completion
conditions (S104). When the voltage difference .DELTA.VB from the
lowest voltage cell becomes equal to or less than .DELTA.VB.sub.off
through the balance operation (S104: YES), the control unit 121
completes the balance operation of the channel.
[0078] On the other hand, when the voltage difference .DELTA.VB
from the lowest voltage cell is not equal to or less than
.DELTA.VB.sub.off (S104: YES), the control unit 121 determines
whether or not a first measured temperature acquired from the
corresponding first temperature sensor 111 of the channel is equal
to or more than an upper reference temperature TRU (S105).
[0079] When the first measured temperature is less than the upper
reference temperature TRU (S105: NO), the control unit 121
determines whether a balance frequency FBAL of the channel is an ON
period T.sub.on or an OFF period T.sub.off (S106). When the balance
frequency FBAL is the ON period T.sub.on (S106: T.sub.on), the
above-described processing from S104 is repeated. On the other
hand, when the balance frequency FBAL is the OFF period T.sub.off
(S106: T.sub.off), the control unit 121 sets the switch element
1122 of the channel to an OFF state, and stops the balance
operation (S107). Then, after waiting until the OFF period
T.sub.off elapses, the control unit 121 determines whether or not
the voltage difference .DELTA.VB when a next cycle starts (at a
time when a next ON period T.sub.on starts) is equal to or less
than a predetermined threshold value (an intermediate value between
.DELTA.VB.sub.on and .DELTA.VB.sub.off, for example) (S108).
Herein, when the voltage difference .DELTA.VB is equal to or less
than the threshold value (S108: YES), the control unit 121
completes the balance operation of the channel. On the other hand,
when the voltage difference .DELTA.VB is more than the threshold
value (S108: NO), a balance operation of the next cycle is started
(S103).
[0080] On the other hand, when the first measured temperature is
equal to or more than the upper reference temperature TRU (S105:
YES), the control unit 121 stops the balance operation of the
channel (S109). Then, the control unit 121 holds a state in which
the balance operation of the channel is stopped until the first
measured temperature becomes equal to or less than a lower
reference temperature TRL (S110: NO). When the first measured
temperature becomes equal to or less than the lower reference
temperature TRL (S110: YES), the control unit 121 determines
whether a balance frequency FBAL of the channel is an ON period
T.sub.on or an OFF period T.sub.off (S111). When the balance
frequency FBAL is the ON period T.sub.on (S111: T.sub.on), the
control unit 121 restarts the balance operation of the channel
(S103). On the other hand, when the balance frequency FBAL is the
OFF period T.sup.off (S111: T.sub.off), the control unit 121
determines whether or not the voltage difference .DELTA.VB when a
next cycle starts (at a time when a next ON period T.sub.on starts)
is equal to or less than a predetermined threshold value (an
intermediate value between .DELTA.VB.sub.on and .DELTA.VB.sub.off,
for example) (S108). Herein, when the voltage difference .DELTA.VB
is equal to or less than the threshold value (S108: YES), the
control unit 121 completes the balance operation of the channel. On
the other hand, when the voltage difference .DELTA.VB is more than
the threshold value (S108: NO), a balance operation of the next
cycle is started (S103).
[0081] An operation of the control unit 121 transmitting a signal
for notifying an abnormality from the communication unit 122 will
be described by using FIG. 13. FIG. 13 is a flowchart illustrating
a flow of processing of the control unit 121 transmitting a signal
for notifying an abnormality from the communication unit 122.
[0082] The control unit 121 reads out an operation stop time or an
operation stop number-of-times of each of the balance circuits 112
held in a storage region (S201). Then, the control unit 121
calculates, for each of the balance circuits 112, an operation stop
time or an operation stop number-of-times per unit time (S202).
Then, the control unit 121 determines whether or not the calculated
operation stop time is equal to or more than a predetermined
reference value, or whether or not the calculated operation stop
number-of-times is equal to or more than a predetermined reference
number-of-times (S203). When there is the balance circuit 112
concerned as a result of determination in S203 (S203: YES), the
control unit 121 generates information capable of specifying the
balance circuit 112 or the battery cell 311 corresponding to the
balance circuit 112, and causes the communication unit 122 to
transmit the information toward an external monitoring device and
the like (S204).
Circuit Configuration Example 2
[0083] FIG. 14 is a diagram schematically illustrating another
circuit configuration example of the power storage device according
to the first example embodiment. As illustrated in FIG. 14, the
first temperature sensor 111 may be provided for the plurality of
balance circuits 112. In an example of the present figure, one
first temperature sensor 111 is provided for every one battery
module 31 (for every three balance circuits 112). Other
configurations are similar to those in FIG. 10.
[0084] An example of a balance operation in the power storage
device in FIG. 14 will be described by using FIG. 15.
[0085] FIG. 15 is a diagram exemplifying a specific flow of a
balance operation of each channel in the power storage device in
FIG. 14. Note that example in FIG. 15 exemplifies an operation when
a lowest voltage cell is present in another battery module 31 that
are not illustrated in FIG. 14.
[0086] First, a voltage difference .DELTA.VB between the battery
cell 311 of CH1 and the lowest voltage cell reaches
.DELTA.VB.sub.on at time t1. Then, the control unit 121 sets the
switch element 1122 of CH1 to an ON state, and starts a balance
operation of CH1. Accordingly, the voltage difference .DELTA.VB of
CH1 begins to decrease. In addition, a first measured temperature
begins to rise due to heat generated from the heat-generating
element 1121 of CH1.
[0087] Thereafter, a voltage difference .DELTA.VB between the
battery cell 311 of CH2 and the lowest voltage cell reaches
.DELTA.VB.sub.on at time t2. Then, the control unit 121 sets the
switch element 1122 of CH2 to an ON state, and starts a balance
operation of CH2. Accordingly, the voltage difference .DELTA.VB of
CH2 begins to decrease. In addition, a rise value per unit time of
the first measured temperature increases from time t2, due to heat
generated from the heat-generating elements 1121 of CH1 and
CH2.
[0088] Thereafter, a voltage difference .DELTA.VB between the
battery cell 311 of CH3 and the lowest voltage cell reaches
.DELTA.VB.sub.on at time t3. Then, the control unit 121 sets the
switch element 1122 of CH3 to an ON state, and starts a balance
operation of CH3. Accordingly, the voltage difference .DELTA.VB of
CH3 begins to decrease. In addition, a rate of rise of the first
measured temperature further increases from time t3, due to heat
generated from the heat-generating elements 1121 of all the
channels.
[0089] Thereafter, the first measured temperature continues to
rise, and the first measured temperature reaches an upper reference
temperature TRU at time t4. Then, the control unit 121 sets the
switch element 1122 of a channel (CH1, CH2, and CH3) executing a
balance operation among the channels corresponding to the first
temperature sensor 111 to an OFF state, and stops the balance
operation of the channel. Since the balance operation is stopped in
CH1, CH2, and CH3, heat generation of the heat-generating elements
1121 of the channels calms down, and the first measured temperature
begins to decrease.
[0090] Thereafter, the first measured temperature drops down to a
lower reference temperature TRL at time t5. Then, the control unit
121 restarts a balance operation of a channel of which a balance
frequency FBAL is an ON period T.sub.on among the channels (CH1,
CH2, and CH3) corresponding to the first temperature sensor 111. In
the example in
[0091] FIG. 15, all the channels are in the ON period T.sub.on.
Thus, the control unit 121 sets the switch elements 1122 of all the
channels to an ON state, and a balance operation is restarted in
all the channels. Consequently, the voltage difference of each
channel begins to decrease again, and the first measured
temperature begins to rise again.
[0092] Thereafter, the voltage difference .DELTA.VB between the
battery cell 311 of CH1 and the lowest voltage cell reaches
.DELTA.VB.sub.off at time t6. Then, the control unit 121 sets the
switch element 1122 of CH1 to an OFF state before time t7 at which
the ON period T.sub.on of CH1 ends, and completes the balance
operation of CH1. Since the cell balance operation is executed in
only CH2 and CH3 from time t6, the first measured temperature
decreases.
[0093] Thereafter, the ON period T.sub.on ends in CH2 and CH3
respectively at time t8 and time t9. Then, the control unit 121
sets the switch element 1122 of CH2 to an OFF state at time t8, and
stops the balance operation of CH2. The control unit 121 also sets
the switch element 1122 of CH3 to an OFF state at time t9, and
stops the balance operation of CH3.
[0094] In addition, as described in FIG. 11, the control unit 121
completes the balance operation in CH2 and CH3 when the voltage
difference .DELTA.VB, after occurrence of voltage rebound, is equal
to or less than a predetermined threshold value (an intermediate
value between .DELTA.VB.sub.on and .DELTA.VB.sub.off, for example)
at a time of entering a next ON period T.sub.on after a lapse of
the OFF period T.sub.off. When the voltage difference .DELTA.VB
between the battery cell 311 of each channel and the lowest voltage
cell is more than the predetermined threshold value, the control
unit 121 continues the balance operation of the channel in a next
cycle.
[0095] The flow of the balance operation of the power storage
device in FIG. 15 is similar to that in the flowchart illustrated
in FIG. 12, except for the following point.
[0096] When the determination in S105 indicates that the first
measured temperature is equal to or more than the upper reference
temperature TRU (S105: YES), the control unit 121 stops the balance
operations of all the channels (CH1, CH2, and CH3 in the example in
FIG. 14) corresponding to the first temperature sensor 111 (S109).
Then, the control unit 121 holds a state in which the balance
operations of the channels are stopped until the first measured
temperature becomes equal to or less than the lower reference
temperature TRL (S110: NO). When the determination in S110
indicates that the first measured temperature drops down to the
lower reference temperature TRL (S110: YES), the control unit 121
determines, for each of the channels stopped in S109, whether a
balance frequency is an ON period T.sub.on or an OFF period
T.sub.off (S111). Then, the control unit 121 restarts a balance
operation for a channel of which the balance frequency is the ON
period T.sub.on (S103), and performs determination in S108 for a
channel of which the balance frequency is the OFF period
T.sub.off.
[0097] Another example of a balance operation in the power storage
device in FIG. 14 will be described by using FIG. 16. FIG. 16 is a
diagram exemplifying a specific flow of a balance operation of each
channel in the power storage device in FIG. 14. The present example
is different from the case of FIG. 15 in that each channel does not
have a frequency of a balance operation (a balance frequency
FBAL).
[0098] A flow from time t1 to time t6 in FIG. 16 is similar to that
in the case of FIG. 15. In the present example, since the balance
frequency FBAL is absent, the control unit 121 continues a balance
operation of each channel until a voltage difference .DELTA.VB from
a lowest voltage cell becomes .DELTA.VB.sub.off, except for a
period of time from when a first measured temperature becomes an
upper reference temperature TRU to when the first measured
temperature drops to a lower reference temperature TRL (from time
t4 to time t5). In the example in FIG. 16, the voltage difference
.DELTA.VB between the battery cell 311 of CH2 and the lowest
voltage cell becomes .DELTA.VB.sub.off at time t7, and the control
unit 121 completes the balance operation of CH2 at time t7.
Although not illustrated, the control unit 121 also completes the
balance operation of CH3 when the voltage difference .DELTA.VB
between the battery cell 311 of CH3 and the lowest voltage cell
becomes .DELTA.VB.sub.off.
[0099] FIG. 17 is a flowchart illustrating a flow of processing of
the balance operation in FIG. 16. The flowchart in FIG. 17 is
different from the flowchart in FIG. 12 in that processing relating
to a balance frequency FBAL is absent.
[0100] A flow of processing from S101 to S105 is similar to that in
the flowchart in FIG. 12.
[0101] When the first measured temperature is less than the upper
reference temperature TRU (S105: NO), processing from S104 is
repeated. On the other hand, when the first measured temperature is
equal to or more than the upper reference temperature TRU (S105:
YES), the control unit 121 stops the balance operations of all the
channels (CH1, CH2, and CH3 in the example in FIG. 14)
corresponding to the first temperature sensor 111 (S109). Then, the
control unit 121 holds a state in which the balance operations of
the channels are stopped until the first measured temperature
becomes equal to or less than the lower reference temperature TRL
(S110: NO). When the determination in S110 indicates that the first
measured temperature drops down to the lower reference temperature
TRL (S110: YES), the control unit 121 restarts the balance
operation of each channel (S103).
Operation and Effect of First Example Embodiment
[0102] In the present example embodiment, as above, an operation of
the balance circuit 112 that generates heat through a balance
operation is controlled by a measured temperature of the first
temperature sensor 111 corresponding to the balance circuit.
Specifically, when a temperature that is measured by the first
temperature sensor 111 corresponding to a certain balance circuit
112 becomes equal to or more than an upper reference temperature, a
balance operation of the balance circuit 112 is stopped. This
prevents the balance circuit 112 from generating heat to a fixed
temperature or more, and enables to prevent decrease in service
life of the battery cell 311 neighboring the balance circuit 112 as
well as decrease in service life and operation reliability of
components in a power storage device due to heat. In addition, the
present example embodiment maintains a state in which the balance
operation of the balance circuit 112 is stopped until a measured
temperature of the first temperature sensor 111 drops to a lower
reference temperature after the operation of the balance circuit
112 is stopped. This allows the heat-generated balance circuit 112
to cool down, and enables to prevent decrease in service life of
the battery cell 311 as well as decrease in service life and
operation reliability of components in a power storage device due
to heat.
Second Example Embodiment
[0103] The present example embodiment is similar to the
configuration of the first example embodiment, except that a power
storage device further includes a second temperature sensor 13.
Processing Configuration
[0104] FIG. 18 is a diagram conceptually illustrating a processing
configuration of a power storage device according to a second
example embodiment. As illustrated in FIG. 18, a balance circuit
board 1 further includes a second temperature sensor 13. Unlike a
first temperature sensor 111, the second temperature sensor 13 is
provided for measuring an ambient temperature. Thus, the second
temperature sensor 13 is provided at a position more distant from
the balance circuit 112 than the first temperature sensor 111 is,
so as not to be influenced by heat generation of each of balance
circuits 112. A range not influenced by heat generated from the
balance circuit 112 depends on a parameter such as a dimension of a
balance circuit block 11, a thickness and thermal resistance of the
balance circuit board 1, and layout of the balance circuit 112. For
example, when the balance circuit board 1 is a printed circuit
board (PCB) having a thickness of 1.6 cm and the balance circuit
block 11 has a dimension of 10 cm square, the second temperature
sensor 13 is provided at a position distant by 10 cm or more from
an edge portion of the balance circuit block 11, for example. In
addition, a range not influenced by heat generated from the balance
circuit 112 can be grasped by carrying out a test operation or
simulation of the balance circuit board 1 and measuring temperature
distribution of the balance circuit board 1, for example.
Accordingly, a position of the second temperature sensor 13 can be
determined by using a result of the measurement.
[0105] The balance circuit board 1 preferably includes an isolation
region that is a region for separating a region where the plurality
of balance circuits 112 each including a heat-generating element
1121 as a main heat source are provided from a region where the
second temperature sensor 13 is provided, and that is a region
where no conductive pattern is provided. The conductive pattern is
metal and generally has a higher thermal conductivity than that of
a base material of the balance circuit board 1. Thus, the
conductive pattern-free isolation region interposed between the
region where the balance circuits 112 are provided and the region
where the second temperature sensor 13 is provided can prevent heat
from transferring to the second temperature sensor 13 through the
balance circuit board 1. As a result, the second temperature sensor
13 can accurately measure an ambient temperature.
[0106] The second temperature sensor 13 may also be provided
outside the balance circuit board 1, instead of on the balance
circuit board 1. For example, the second temperature sensor 13 may
be provided on a housing face of the power storage device, or may
be provided in midair away from the balance circuit board 1 by a
fixed distance or more, by means of a wire, a binding material, and
the like. The second temperature sensor 13 may use a thermistor
resistor, a semiconductor temperature sensor, an RTD, and the like,
similarly to the first temperature sensor 111.
[0107] In a control unit 121 according to the present example
embodiment, the control unit 121 controls a balance operation of
each of the balance circuits 112, by using a difference temperature
between a first measured temperature measured by the first
temperature sensor 111 and a temperature measured by the second
temperature sensor 13 (hereinafter, written as a second measured
temperature), instead of using the first measured temperature.
Since the difference temperature is a parameter different from the
first measured temperature, the control unit 121 holds an upper
reference temperature and a lower reference temperature (a second
upper reference temperature and a second lower reference
temperature) for the difference temperature, separately from an
upper reference temperature and a lower reference temperature (a
first upper reference temperature and a first lower reference
temperature) that are set for the first measured temperature. The
control unit 121 calculates the difference temperature between the
first measured temperature and the second measured temperature.
When the difference temperature is equal to or more than the second
upper reference temperature, the control unit 121 stops the
operation of the balance circuit 112 corresponding to the first
temperature sensor 111. When the balance circuit 112 is stopped,
heat generation of the balance circuit 112 calms down, and the
first measured temperature begins to decrease. Then, the control
unit 121 restarts the operation of the balance circuit 112
corresponding to the first temperature sensor 111 when the
difference temperature between the first measured temperature
measured by the first temperature sensor 111 and the second
measured temperature measured by the second temperature sensor 13
becomes equal to or less than the second lower reference
temperature that is lower than the second upper reference
temperature.
[0108] Depending on an ambient temperature, the first measured
temperature (an absolute temperature) measured by the first
temperature sensor 111 may become equal to or more than the first
upper reference temperature even when the difference temperature
(in other words, a relative temperature relative to the ambient
temperature) does not reach the second upper reference temperature.
In this case, the balance circuit 112 has a possibility of
continuing the balance operation while being in a state at the
first upper reference temperature or more (in other words, a high
temperature state that may possibly affect the neighboring battery
cell 311 and other components adversely). In order to avoid
continuing the operation of the balance circuit 112 in such a
state, the control unit 121 may stop the operation of the balance
circuit corresponding to the first temperature sensor 111 when the
first measured temperature of the first temperature sensor 111 is
equal to or more than the first upper reference temperature,
regardless of the difference temperature. In this case, similarly
to the first example embodiment, the control unit 121 maintains a
state in which the corresponding balance circuit 112 is stopped
until the first measured temperature becomes equal to or less than
the first lower reference temperature.
[0109] Similarly to the first example embodiment, the control unit
121 according to the present example embodiment also stores
programs for implementing the above-described functions of the
present example embodiment in, for example, a not-illustrated
storage region such as a ROM and a RAM. Further, the control unit
121 according to the present example embodiment implements the
functions of the present example embodiment by executing the
programs stored in the storage region by use of a not-illustrated
CPU.
Circuit Configuration Example
[0110] FIG. 19 is a diagram conceptually illustrating a circuit
configuration example of the power storage device according to the
second example embodiment.
[0111] In the example in FIG. 19, the plurality of balance circuits
112, the first temperature sensor 111 corresponding to each balance
circuit 112, and the second temperature sensor 13 are provided on
the balance circuit board 1. Then, the balance circuit board 1
includes, in an isolation region 14 between the balance circuit 112
and the second temperature sensor 13, a through-hole region 141
that penetrates through the balance circuit board 1. Since the
through-hole region 141 includes no conductive pattern, the
through-hole region 141 serves a role of preventing heat from
transferring from the balance circuit to the second temperature
sensor 13 through the balance circuit board 1. Accordingly, even in
such a case of being unable to assure a sufficient distance for
preventing reception of heat generated from the balance circuit
112, the through-hole region 141 reduces heat transferring from the
balance circuit 112, and the second temperature sensor 13 can
accurately measure an ambient temperature.
[0112] FIG. 20 is a flowchart illustrating a flow of a balance
operation in the power storage device in FIG. 19. The flowchart in
FIG. 20 is based on the flowchart in FIG. 12, and is similar to the
flowchart in FIG. 15 except for processing of S301 and S302. In the
following, the processing of S301 and S302 will be mainly
described.
[0113] When the voltage difference .DELTA.VB from the lowest
voltage cell is not equal to or less than .DELTA.VB.sub.off (S104:
YES) after starting a balance operation (S103), the control unit
121 determines whether or not a difference temperature that is
calculated by using a first measured temperature measured by the
first temperature sensor 111 and a second measured temperature
measured by the second temperature sensor 13 is equal to or more
than a second upper reference temperature TRU', or whether or not
the first measured temperature is equal to or more than a first
upper reference temperature TRU (S301). When the difference
temperature is equal to or more than the second upper reference
temperature TRU', or when the first measured temperature is equal
to or more than the first upper reference temperature TRU (S301:
YES), the control unit 121 stops a balance operation of a channel
corresponding to the first temperature sensor 111 (S109). When a
balance operation is stopped because the difference temperature
becomes equal to or more than the second upper reference
temperature TRU', the control unit 121 maintains a state in which
the balance operation is stopped until the difference temperature
becomes equal to or less than a second lower reference temperature
TRL' (S302: NO). Alternatively, when a balance operation is stopped
because the first measured temperature becomes equal to or more
than the first upper reference temperature TRU, the control unit
121 maintains a state in which the balance operation is stopped
until the first measured temperature becomes equal to or less than
a first lower reference temperature TRL (S302: NO). When the first
measured temperature decreases because the balance operation is
stopped and the difference temperature becomes equal to or less
than the second lower reference temperature TRL', or when the first
measured temperature becomes equal to or less than the first lower
reference temperature TRL (S302: YES), the control unit 121
restarts the balance operation (S103) when a balance frequency of
the channel is an ON period T.sub.on (S111: T.sub.on).
Operation and Effect of Second Example Embodiment
[0114] In the present example embodiment, as above, an operation of
each of the balance circuits 112 is controlled by a difference
temperature that is obtained by subtracting an ambient temperature
measured by the second temperature sensor 13 from a temperature
measured by the first temperature sensor 111. This makes it
possible to control each of the balance circuits 112 by using heat
generated in each balance circuit 112 as a parameter.
[0115] As above, the example embodiments of the present invention
have been described with reference to the drawings. However, these
are examples of the present invention, and various configurations
other than the above may be also employed.
[0116] For example, the control unit 121 may change the first upper
reference temperature or the second upper reference temperature in
accordance with magnitude of a variation in voltage between a
plurality of battery cells. For example, the control unit 121 may
be configured to add, to the first upper reference temperature or
the second upper reference temperature held in advance, a
correction value that takes a larger value for the larger voltage
difference .DELTA.VB between each battery cell 311 and the lowest
voltage cell. Accordingly, when the voltage difference .DELTA.VB is
large, in other words, when a balance between a certain battery
cell 311 and the lowest voltage cell is largely disrupted, the
first upper reference temperature or the second upper reference
temperature is increased. Therefore, a balance operation of the
balance circuit 112 corresponding to the battery cell 311 becomes
less likely to be stopped. As a result, when a balance between the
battery cells is largely disrupted, it becomes possible to equalize
voltages of the plurality of battery cells 311 in a shorter
time.
[0117] In addition, since the plurality of battery cells 311 are
connected in series, it is possible that a balance operation rather
lower discharge energy especially in the case of a passive balance
type. In view of this, in the case where a balance operation is
performed when charging the battery cell 311, the control unit 121
may use a first upper reference temperature or a second upper
reference temperature that is higher than the temperature when
discharging the battery cell 311. In this case, the control unit
121 holds in advance, in a not-illustrated storage region, a first
upper reference temperature or a second upper reference temperature
at the time of charging, and a first upper reference temperature or
a second upper reference temperature at the time of discharging
that is lower than the first upper reference temperature or the
second upper reference temperature at the time of charging, for
example. Such a configuration reduces time for performing a balance
operation when charging, and can prevent discharge energy of a
power storage device from decreasing.
[0118] In addition, in the plurality of flowcharts used in the
above description, a plurality of steps (processes) are described
in order, but execution order of the steps to be executed in each
of the example embodiments is not limited to the order of the
description. In each of the example embodiments, the order of the
illustrated steps may be changed as far as the change does not
detract from contents. The above-described example embodiments may
also be combined as far as contents do not conflict with each
other.
[0119] This application is based upon and claims the benefit of
priority from Japanese Patent Application No. 2015-105596, filed on
May 25, 2015, the disclosure of which is incorporated herein in its
entirety.
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