U.S. patent application number 14/906968 was filed with the patent office on 2016-11-10 for apparatus and method for controlling power for secondary battery.
This patent application is currently assigned to LG CHEM, LTD.. The applicant listed for this patent is LG CHEM, LTD.. Invention is credited to Seung-Hun JUNG.
Application Number | 20160329612 14/906968 |
Document ID | / |
Family ID | 56126831 |
Filed Date | 2016-11-10 |
United States Patent
Application |
20160329612 |
Kind Code |
A1 |
JUNG; Seung-Hun |
November 10, 2016 |
APPARATUS AND METHOD FOR CONTROLLING POWER FOR SECONDARY
BATTERY
Abstract
A power control apparatus according to the present disclosure
includes a sensing unit configured to measure a temperature of a
battery cell, an outside air temperature around the battery cell
and a load current, an adjusting unit configured to adjust power
supplied from the battery cell to a load, and a control unit
configured to estimate a future temperature change of the battery
cell based on the temperature of the battery cell, the outside air
temperature around the cell and the load current measured by the
sensing unit, analyze the estimated future temperature change of
the cell, and control the adjusting unit to reduce the power
supplied from the battery cell to the load when the temperature of
the battery cell is estimated to increase above a limit temperature
for a preset reference time.
Inventors: |
JUNG; Seung-Hun; (Daejeon,
KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LG CHEM, LTD. |
Seoul |
|
KR |
|
|
Assignee: |
LG CHEM, LTD.
Seoul
KR
|
Family ID: |
56126831 |
Appl. No.: |
14/906968 |
Filed: |
July 22, 2015 |
PCT Filed: |
July 22, 2015 |
PCT NO: |
PCT/KR2015/007639 |
371 Date: |
January 22, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02J 7/00 20130101; H01M
2220/30 20130101; H01M 10/48 20130101; H01M 2220/20 20130101; H02J
7/0063 20130101; H02J 7/007 20130101; H02J 2007/0067 20130101; H01M
10/44 20130101; Y02E 60/10 20130101; H01M 2010/4271 20130101; H01M
2010/4278 20130101; H01M 10/443 20130101; H01M 10/425 20130101 |
International
Class: |
H01M 10/44 20060101
H01M010/44; H02J 7/00 20060101 H02J007/00; H01M 10/42 20060101
H01M010/42 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 19, 2014 |
KR |
10-2014-0184813 |
Claims
1. A power control apparatus comprising: a sensing unit configured
to measure a temperature of a battery cell, an outside air
temperature around the battery cell and a load current; an
adjusting unit configured to adjust power supplied from the battery
cell to a load; and a control unit configured to estimate a future
temperature change of the battery cell based on the temperature of
the battery cell, the outside air temperature around the cell and
the load current measured by the sensing unit, analyze the
estimated future temperature change of the cell, and control the
adjusting unit to reduce the power supplied from the battery cell
to the load when the temperature of the battery cell is estimated
to increase above a limit temperature for a preset reference
time.
2. The power control apparatus according to claim 1, wherein the
control unit estimates a future temperature change of the battery
cell by using the following equation: m C p T t = ( ( 1 - k ) I ) 2
R cell + ( T environment - T R th_environment ) ( Equation )
##EQU00002## m: battery cell mass (kg) C.sub.p: specific heat of
cell (J/kgK) T: cell temperature (.degree. C.) t: time k: derating
factor I: current (A) R.sub.cell: internal cell resistance
(.OMEGA.) T.sub.environment: outside air temperature around cell
(.degree. C.) R.sub.th.sub._.sub.environment: thermal resistance
between cell and environment (K/W).
3. The power control apparatus according to claim 2, wherein the
control unit analyzes the estimated future temperature change of
the battery cell, when the future temperature of the battery cell
is determined to converge, calculates a convergence time required
for the temperature of the battery cell to converge by using the
equation, and when the convergence temperature of the battery cell
is higher than or equal to the limit temperature and the
convergence time is less than or equal to the reference time,
controls the adjusting unit to reduce the power supplied from the
battery cell to the load.
4. The power control apparatus according to claim 3, wherein the
control unit fails to proceed with power derating of the battery
cell when the convergence temperature of the battery cell is less
than the limit temperature or the convergence time exceeds the
reference time.
5. The power control apparatus according to claim 2, wherein the
control unit analyzes the estimated future temperature change of
the battery cell, when the future temperature of the battery cell
is determined to diverge, calculates a reach time required for the
battery cell to reach the limit temperature by using the equation,
and when the calculated reach time is less than or equal to the
reference time, controls the adjusting unit to reduce the power
supplied from the battery cell to the load.
6. The power control apparatus according to claim 5, wherein the
control unit fails to proceed with power derating of the battery
cell when the reach time exceeds the reference time.
7. The power control apparatus according to claim 2, wherein the
control unit calculates a derating factor allowing the temperature
of the battery cell to reach a predetermined level of the limit
temperature for the reference time by using the equation,
determines a power amount to reduce based on the derating factor,
and controls the adjusting unit.
8. A power control method comprising: measuring a temperature of a
battery cell, an outside air temperature around the battery cell
and a load current; estimating a future temperature change of the
battery cell based on the measured temperature of the battery cell,
outside air temperature around the cell and load current;
determining whether the temperature of the battery cell increases
above a limit temperature for a preset reference time, by analyzing
the estimated future temperature change of the battery cell; and
reducing output power of the battery cell when the temperature of
the battery cell is determined to increase above the limit
temperature for the reference time as a result of the
determination.
9. The power control method according to claim 8, wherein the
estimating comprises estimating a future temperature change of the
battery cell by using the following equation: m C p T t = ( ( 1 - k
) I ) 2 R cell + ( T environment - T R th_environment ) ( Equation
) ##EQU00003## m: battery cell mass (kg) C.sub.p: specific heat of
cell (J/kgK) T: cell temperature (.degree. C.) t: time k: derating
factor I: current (A) R.sub.cell: internal cell resistance
(.OMEGA.) T.sub.environment: outside air temperature around cell
(.degree. C.) R.sub.th.sub._.sub.environment: thermal resistance
between cell and environment (K/W).
10. The power control method according to claim 9, wherein the
determining comprises: determining whether a future temperature of
the battery cell converges or diverges based on the estimated
future temperature change of the battery cell; and calculating a
convergence time required for the temperature of the battery cell
to converge by using the equation when the future temperature of
the battery cell is determined to converge, and the reducing of
output power comprises reducing the output power of the battery
cell when the convergence temperature of the battery cell is higher
than or equal to the limit temperature and the convergence time is
less than or equal to the reference time.
11. The power control method according to claim 10, wherein the
reducing of output power comprises failing to proceed with output
power derating of the battery cell when the convergence temperature
of the battery cell is less than the limit temperature or the
convergence time exceeds the reference time.
12. The power control method according to claim 9, wherein the
determining comprises: determining whether a future temperature of
the battery cell converges or diverges based on the estimated
future temperature change of the battery cell; and calculating a
reach time required for the battery cell to reach the limit
temperature by using the equation when the future temperature of
the battery cell is determined to diverge, and the reducing of
output power comprises reducing the output power of the battery
cell when the reach time is less than or equal to the reference
time.
13. The power control method according to claim 12, wherein the
reducing of output power comprises failing to proceed with output
power derating of the battery cell when the reach time exceeds the
reference time.
14. The power control method according to claim 9, wherein the
reducing of output power comprises: calculating a derating factor
allowing the temperature of the battery cell to reach a
predetermined level of the limit temperature for the reference time
by using the equation; and determining a power amount to reduce
based on the calculated derating factor, and reducing the output
power of the battery cell based on the determined power amount to
reduce.
Description
TECHNICAL FIELD
[0001] The present application claims priority to Korean Patent
Application No. 10-2014-0184813 filed in the Republic of Korea on
Dec. 19, 2014, the disclosure of which is incorporated herein by
reference.
[0002] The present disclosure relates to an apparatus and method
for controlling power for a secondary battery, and more
particularly, to an apparatus and method for controlling power
whereby a future temperature of a secondary battery is estimated
and an output of the secondary battery is selectively reduced
according to a result of the estimation.
BACKGROUND ART
[0003] As opposed to a disposable primary battery, a secondary
battery is referred to as a rechargeable battery, and has a wide
range of applications including, for example, electronic devices,
such as mobile phones, laptop computers and camcorders, or electric
vehicles. Also, a secondary battery is being used as a source of
power of automobiles because it does not cause air pollution and
can be used for a long period of time.
[0004] However, a secondary battery has characteristics that the
temperature rises due to the generation of heat from the battery
during charging or discharging and the life reduces when exposed to
high temperature for a long term.
[0005] According to such characteristics, a secondary battery pack
mounted in a vehicle discharge heat generated from a battery using
a separately mounted cooling system to maintain the temperature of
the secondary battery below a predetermined temperature.
[0006] However, the method of additionally mounting the cooling
system becomes a factor that causes the cost of the secondary
battery pack to increase and has a problem with an increase in size
of a battery system.
DISCLOSURE
Technical Problem
[0007] To solve the problem of the related art, the present
disclosure is directed to providing an apparatus and method for
controlling power for a secondary battery to protect the secondary
battery from overheat through power control of the secondary
battery without mounting a separate cooling system.
[0008] Further, the present disclosure is directed to providing an
apparatus and method for controlling power for a secondary battery
whereby a temperature change of a secondary battery is estimated
and an overheat phenomenon of the secondary battery is prevented
according to a result of the estimation.
[0009] These and other objects and advantages of the present
disclosure may be understood from the following detailed
description and will become more fully apparent from the exemplary
embodiments of the present disclosure. Also, it will be easily
understood that the objects and advantages of the present
disclosure may be realized by the means shown in the appended
claims and combinations thereof.
Technical Solution
[0010] To achieve the above objects, a power control apparatus
according to one aspect of the present disclosure includes a
sensing unit configured to measure a temperature of a battery cell,
an outside air temperature around the battery cell and a load
current, an adjusting unit configured to adjust power supplied from
the battery cell to a load, and a control unit configured to
estimate a future temperature change of the battery cell based on
the temperature of the battery cell, the outside air temperature
around the cell and the load current measured by the sensing unit,
analyze the estimated future temperature change of the cell, and
control the adjusting unit to reduce the power supplied from the
battery cell to the load when the temperature of the battery cell
is estimated to increase above a limit temperature for a preset
reference time.
[0011] The control unit may estimate a future temperature change of
the battery cell by using Equation 1.
[0012] The control unit may analyze the estimated future
temperature change of the battery cell, when the future temperature
of the battery cell is determined to converge, calculate a
convergence time required for the temperature of the battery cell
to converge by using Equation 1, and when the convergence
temperature of the battery cell is higher than or equal to the
limit temperature and the convergence time is less than or equal to
the reference time, control the adjusting unit to reduce the power
supplied from the battery cell to the load.
[0013] On the other hand, the control unit may fail to proceed with
power derating of the battery cell when the convergence temperature
of the battery cell is less than the limit temperature or the
convergence time exceeds the reference time.
[0014] Also, the control unit may analyze the estimated future
temperature change of the battery cell, when the future temperature
of the battery cell is determined to diverge, calculate a reach
time required for the battery cell to reach the limit temperature
by using Equation 1, and when the calculated reach time is less
than or equal to the reference time, control the adjusting unit to
reduce the power supplied from the battery cell to the load.
[0015] The control unit may fail to proceed with power derating of
the battery cell when the reach time exceeds the reference
time.
[0016] The control unit may calculate a derating factor allowing
the temperature of the battery cell to reach a predetermined level
of the limit temperature for the reference time by using Equation
1, determine a power amount to reduce based on the derating factor,
and controls the adjusting unit.
[0017] To achieve the above objects, a power control method
according to another aspect of the present disclosure includes
measuring a temperature of a battery cell, an outside air
temperature around the battery cell and a load current, estimating
a future temperature change of the battery cell based on the
measured temperature of the battery cell, outside air temperature
around the cell and load current, determining whether the
temperature of the battery cell increases above a limit temperature
for a preset reference time, by analyzing the estimated future
temperature change of the battery cell, and reducing output power
of the battery cell when the temperature of the battery cell is
determined to increase above the limit temperature for the
reference time as a result of the determination.
Advantageous Effects
[0018] The present disclosure has an advantage in that output of a
secondary battery is controlled to maintain the temperature of the
secondary battery below the range of a limit temperature before
overheat of the secondary battery occurs, thereby preventing a
phenomenon in which the life and performance of the secondary
battery is degraded due to overheat.
[0019] Also, the present disclosure has an effect on the
maintenance of the temperature of the secondary battery below the
limit temperature without having a separate device such as a
cooling system.
[0020] Further, the present disclosure has an effect on the
accurate estimation of overheat of the secondary battery through a
temperature estimation algorithm.
DESCRIPTION OF THE DRAWINGS
[0021] The accompanying drawings illustrate preferred embodiments
of the present disclosure and, together with the foregoing
disclosure, serve to provide further understanding of the technical
spirit of the present disclosure. However, the present disclosure
is not to be construed as being limited to the drawings.
[0022] FIG. 1 is a diagram showing configuration of an apparatus
for controlling power for a secondary battery according to an
embodiment of the present disclosure.
[0023] FIG. 2 is a schematic flowchart showing a method for
controlling power for a secondary battery according to an
embodiment of the present disclosure.
[0024] FIG. 3 is a graph of simulation showing a temperature change
in a battery cell to which a method for controlling power according
to the present disclosure is applied and a temperature change in a
traditional battery cell.
DETAILED DESCRIPTION FOR PRACTICING THE INVENTION
[0025] Hereinafter, the present disclosure will be described in
detail. It should be understood that the terms used in the
specification and the appended claims should not be construed as
limited to general and dictionary meanings, but interpreted based
on the meanings and concepts corresponding to technical aspects of
the present disclosure on the basis of the principle that the
inventor is allowed to define terms appropriately for the best
explanation. Therefore, the description proposed herein is just a
preferable example for the purpose of illustrations only, not
intended to limit the scope of the disclosure, so it should be
understood that other equivalents and modifications could be made
thereto without departing from the spirit and scope of the
disclosure.
[0026] FIG. 1 is a diagram showing configuration of an apparatus
for controlling power for a secondary battery according to an
embodiment of the present disclosure.
[0027] As shown in FIG. 1, the apparatus for controlling power for
a secondary battery according to a preferred embodiment of the
present disclosure includes a battery cell 10, a load 20, a sensing
unit 30, an adjusting unit 40, and a control unit 50.
[0028] The battery cell 10 supplies power to the load 20. The
battery cell 10 includes at least one cell, and is not limited to a
particular type and includes rechargeable batteries, for example,
lithium ion batteries, lithium metal batteries, lithium polymer
batteries, nickel cadmium batteries, nickel hydrogen batteries,
nickel zinc batteries and lead storage batteries.
[0029] The load 20 is not limited to a particular type, and
includes portable electronic devices such as video cameras, mobile
phones, portable PCs, PMPs and MP3 players, motors for electric
vehicle or hybrid vehicle, and DC to DC converters.
[0030] The sensing unit 30 includes a first temperature sensor 31
to measure the temperature of the battery cell 10, a second
temperature sensor 32 to measure the outside air temperature around
the battery cell, and a current sensor 33 to measure an electric
current of the load 20. The first temperature sensor 31
periodically measures the temperature of the battery cell 10 and
transmits the same to the control unit 50. Also, the second
temperature sensor 32 periodically measures the outside air
temperature around the battery cell and transmits the same to the
control unit 50. Also, the current sensor 33 periodically measures
an electric current in the load 20 and transmits the same to the
control unit 50.
[0031] The adjusting unit 40 adjusts the amount of the power
supplied from the battery cell 10 to the load 20 under the control
of the control unit 50. The adjusting unit 40 may include a
variable element which changes the voltage level supplied from the
battery cell 10, and the control unit 50 may control the power
supply from the battery cell 10 by controlling the variable element
included in the adjusting unit 40.
[0032] The control unit 50 estimates a temperature change of the
battery cell 10 based on sensing data obtained from the sensing
unit 30, determines whether to derate the power supply from the
battery cell 10 based on the temperature change, and when power
derating is determined, controls the adjusting unit 40 to derate
the power supply from the battery cell 10. Specifically, the
control unit 50 estimates a future temperature change of the
battery cell 10 over time by substituting data sensed through the
sensing unit 30 to the following Equation 1, and determines whether
the future temperature of the battery cell 10 diverges or converges
based on a temperature change trend.
m C p T t = ( ( 1 - k ) I ) 2 R cell + ( T environment - T R
th_environment ) ( Equation 1 ) ##EQU00001##
[0033] m: battery cell mass (kg)
[0034] C.sub.p: specific heat of cell (J/kgK)
[0035] T: cell temperature (.degree. C.)
[0036] t: time
[0037] k: derating factor
[0038] I: current (A)
[0039] R.sub.cell: internal cell resistance (.OMEGA.)
[0040] T.sub.environment: outside air temperature around cell
(.degree. C.)
[0041] R.sub.th.sub._.sub.environment: thermal resistance between
cell and environment (K/W)
[0042] The Equation 1 is an energy balance equation, and the
battery cell mass (m), the specific heat of cell (C.sub.p), the
internal cell resistance (R.sub.cell), and the thermal resistance
between cell and environment (R.sub.th.sub._.sub.environment) may
be preset. Also, the derating factor (k) is initially set to `0`,
and has a value of from `0` to `1`. On the other hand, the internal
cell resistance (R.sub.cell) may be also identified through a
measured value. That is, the control unit 50 may also measure the
current and voltage of the battery cell 10 using a sensor (not
shown) which measures the current and voltage of the battery cell
10, and measure the internal cell resistance (R.sub.cell) based on
the measured current and voltage.
[0043] The control unit 50 identifies a temperature change (dT) of
the battery cell 10 vs time change (dt) by substituting the
temperature values and current values received from each of the
first temperature sensor 31, the second temperature sensor 32, and
the current sensor 33 to Equation 1, and estimates a future
temperature change trend of the battery cell 10.
[0044] The control unit 50 determines whether the future
temperature of the battery cell 10 diverges or converges by
analyzing the estimated future temperature change trend. When the
future temperature of the battery cell 10 diverges, the control
unit 50 calculates a limit temperature reach time
(.DELTA.t.sub.limit) required to reach a limit temperature
(T.sub.limit) preset using Equation 1. Further, when the limit
temperature reach time (.DELTA.t.sub.limit) exceeds a preset
reference time (.DELTA.t.sub.ref), the control unit 50 does not
proceed with power derating of the battery cell 10. In contrast,
when the limit temperature reach time (.DELTA.t.sub.limit) is less
than or equal to the reference time (.DELTA.t.sub.ref), the control
unit 50 calculates a derating factor (k) allowing the temperature
of the battery cell 10 to only increase up to a predetermined level
(e.g., 99%) of the limit temperature (T.sub.limit) during the
reference time (.DELTA.t.sub.ref) and controls the adjusting unit
40 to derate the power supply from the battery cell 10 based on the
derating factor (k). In this instance, the control unit 50
determines a power amount of the battery cell 10 to reduce, in
proportion to the calculated dimension of the derating factor (k),
and controls the adjusting unit 40 to deduct the determined power
amount from the output power. For example, when the derating factor
(k) is calculated as `0.9`, the control unit 50 may control the
adjusting unit 40 such that the output of the battery cell 10 is at
the level of 10% as compared to the very previous batter cell
output, and when the derating factor (k) is calculated as `0.8`,
the control unit 50 may control the adjusting unit 40 such that the
output of the battery cell 10 is at the level of 20% as compared to
the very previous batter cell output.
[0045] On the other hand, when the temperature of the battery cell
10 is estimated as converging, the control unit 50 calculates a
convergence time (.DELTA.t.sub.sat) required for the battery cell
10 to reach a convergence temperature (T.sub.sat) by using Equation
1. Further, when the convergence temperature (T.sub.sat) is higher
than or equal to the preset limit temperature (T.sub.limit), and
the convergence time (.DELTA.t.sub.sat) is less than or equal to
the preset reference time (.DELTA.t.sub.ref), the control unit 50
calculates a derating factor (k) allowing the convergence
temperature (T.sub.sat) to only reach as much as a predetermined
level (e.g., 99%) of the limit temperature (T.sub.limit) during the
reference time (.DELTA.t.sub.ref) through Equation 1, and controls
the adjusting unit 40 to reduce the output of the battery cell 10
based on the derating factor (k). In contrast, when the convergence
temperature (T.sub.sat) is less than the limit temperature
(T.sub.limit) or the convergence time (.DELTA.t.sub.sat) exceeds
the reference time (.DELTA.t.sub.ref), the control unit 50 does not
proceed with power derating of the battery cell 10.
[0046] On the other hand, the control unit 50 may be implemented as
a microprocessor which executes a code programmed to embody a
method for controlling power for a secondary battery according to
the present disclosure. Alternatively, the control unit 50 may be
implemented as a semiconductor chip in which a control flow of a
method for controlling power for a secondary battery according to
the present disclosure is embodied as a logic circuit. However, the
present disclosure is not limited thereto.
[0047] Also, the apparatus for controlling power for a secondary
battery according to the present disclosure may be used in
combination with a battery pack driving apparatus which receives
power from the batter pack. For example, the present disclosure may
be used in various types of electronic products which receive power
from batteries, such as laptop computers, mobile phones, and
personal mobile multimedia players. As another example, the present
disclosure may be used in combination with various types of
battery-powered devices such as electric vehicle, hybrid vehicle,
and e-bike. Also, the apparatus for controlling power for a
secondary battery according to the present disclosure may be used
in a battery management system (BMS) which controls the
charge/discharge of the battery pack and protects the battery pack
from overcharge or overdischarge.
[0048] FIG. 2 is a schematic flowchart showing a method for
controlling power for a secondary battery according to an
embodiment of the present disclosure.
[0049] Referring to FIG. 2, the control unit 50 collects sensing
information of the secondary battery at a predetermined cycle using
the sensing unit 30 (S201). That is, the control unit 50 collects
the temperature of the battery cell 10 using the first temperature
sensor 31 of the sensing unit 30, the outside air temperature
around the battery cell 10 using the second temperature sensor 32,
and the electric current in the load 20 using the current sensor
33.
[0050] Subsequently, the control unit 50 estimates a future
temperature change trend of the battery cell by substituting the
collected sensing information (i.e., the battery cell temperature,
the outside air temperature, and the load current) to Equation 1
(S203). Additionally, the control unit 50 identifies a temperature
change (dT) of the battery cell 10 vs time change (dt) by
substituting the battery cell temperature, the outside air
temperature, and the current collected at the predetermined cycle
through the sensing unit 30 to Equation 1, and estimates a future
temperature change trend of the battery cell 10.
[0051] Subsequently, the control unit 50 determines whether the
future temperature of the battery cell 10 converges on a particular
temperature or continues to diverge by analyzing the estimated
temperature change trend (S205).
[0052] Subsequently, when the future temperature of the battery
cell 10 is determined to converge (NO at S205), the control unit 50
identifies a convergence temperature (T.sub.sat) on which the
battery cell 10 converges from the estimated future temperature
change trend, and calculates a convergence time (.DELTA.t.sub.sat)
required to reach the convergence temperature (T.sub.sat) by
applying the convergence temperature (T.sub.sat) to Equation 1
(S207). In this instance, the control unit 50 may substitute the
sensing information (cell temperature, outside air temperature, and
load current) identified at S201 to Equation 1, or may re-collect
sensing information (cell temperature, outside air temperature, and
load current) using the sensing unit 30 and substitute the
re-collected sensing information to Equation 1. Also, the control
unit 50 may measure the current and voltage of the battery cell 10
using a sensor (not shown) which measures the current and voltage
of the battery cell 10, measure an internal cell resistance
(R.sub.cell) based on the measured current and voltage, and
substitute the measured internal cell resistance (R.sub.cell) to
Equation 1.
[0053] Subsequently, the control unit 50 compares the convergence
temperature (T.sub.sat) to a preset limit temperature (T.sub.limit)
to determine whether the convergence temperature (T.sub.sat) is
less than the limit temperature (T.sub.limit) (S209). Subsequently,
when the convergence temperature (T.sub.sat) is higher than or
equal to the limit temperature (T.sub.limit) (NO at S209), the
control unit 50 compares the convergence time (.DELTA.t.sub.sat) to
a preset reference time (.DELTA.t.sub.ref) to determine whether the
convergence time (.DELTA.t.sub.sat) exceeds the reference time
(.DELTA.t.sub.ref) (S211). Also, when the convergence time
(.DELTA.t.sub.sat) does not exceed the referenced time
(.DELTA.t.sub.ref) as a result of the determination (NO at S211),
the control unit 50 calculates a derating factor (k) allowing the
convergence temperature (T.sub.sat) to only reach a predetermined
level (e.g., 99%) of the limit temperature (T.sub.limit) through
Equation 1 to reduce the output power of the battery cell 10
(S213). In this instance, the control unit 50 calculates the
derating factor (k) by applying the convergence time
(.DELTA.t.sub.sat) and the convergence temperature (T.sub.sat) to
Equation 1.
[0054] Subsequently, the control unit 50 determines a power amount
to reduce, in proportion to the calculated derating factor (k)
value, and controls the adjusting unit 40 to deduct a power amount
as much as the power amount to reduce from the power supply, and
finally to reduce the power supplied from the battery cell 10 to
the load 20 (S215). That is, when the convergence temperature
(T.sub.sat) is higher than or equal to the limit temperature
(T.sub.limit) and the convergence time (.DELTA.t.sub.sat) does not
exceed the reference time (.DELTA.t.sub.ref) as a result of
determination at S209 and S211, the control unit 50 estimates that
overheat above the limit temperature occurs within the reference
time (.DELTA.t.sub.ref), and controls the adjusting unit 40 based
on the calculated derating factor (k) to reduce the output of the
battery cell 10 beforehand, thereby preventing the battery cell 10
from overheating.
[0055] On the other hand, at S205, when the temperature of the
battery cell 10 is determined to diverge (YES at S205), the control
unit 50 calculates the time (.DELTA.t.sub.limit) required for the
temperature of the battery cell 10 to reach the preset limit
temperature (T.sub.limit) through Equation 1 (S217). That is, the
control unit 50 calculates a time change (dt) by substituting the
limit temperature (T.sub.limit) to Equation 1, and calculates a
limit temperature reach time (.DELTA.t.sub.limit) required to reach
the limit temperature based on the calculated time change (dt). In
this instance, the control unit 50 may substitute the sensing
information (cell temperature, outside air temperature, and load
current) identified at S201 to Equation 1, or may re-collect
sensing information (cell temperature, outside air temperature, and
load current) using the sensing unit 30 and substitute the
re-collected sensing information to Equation 1.
[0056] Subsequently, the control unit 50 identifies whether the
calculated limit temperature reach time (.DELTA.t.sub.limit)
exceeds the preset reference time (.DELTA.t.sub.ref) (S219), and
when the limit temperature reach time does not exceed the reference
time, calculates a derating factor (k) allowing the temperature
from the battery cell 10 to only increase up to a predetermined
level (e.g., 99%) of the limit temperature (T.sub.limit) for the
reference time (.DELTA.t.sub.ref) through Equation 1 (S213). In
this instance, the control unit 50 calculates the derating factor
(k) by applying the limit temperature reach time
(.DELTA.t.sub.limit) and the limit temperature (T.sub.limit) to
Equation 1.
[0057] Subsequently, the control unit 50 determines a power amount
to reduce, in proportion to the calculated derating factor (k)
value, and controls the adjusting unit 40 to deduct a power amount
as much as the power amount to reduce from the output power, and
finally to reduce the power supplied from the battery cell 10 to
the load 20 (S215).
[0058] On the other hand, when the convergence temperature
(T.sub.sat) is less than the preset limit temperature (T.sub.limit)
at S209, when the convergence time (.DELTA.t.sub.sat) exceeds the
reference time (.DELTA.t.sub.ref) at S211, or when the limit
temperature reach time (.DELTA.t.sub.limit) exceeds the reference
time (.DELTA.t.sub.ref) at S219, the control unit 50 does not
proceed with output power derating of the battery cell 10 (S221).
In this instance, the derating factor (k) is continuously set as
the previous value (i.e., 0).
[0059] FIG. 2 illustrates a process corresponding to one cycle, and
the process according to FIG. 2 may be performed at a predetermined
interval of time.
[0060] FIG. 3 is a graph of simulation showing a temperature change
in a battery cell to which the method for controlling power
according to the present disclosure is applied and a temperature
change in a traditional battery cell.
[0061] In the simulation according to FIG. 3, the initial cell
temperature is set to 52.degree. C., outside air temperature is set
to 50.degree. C., and the reference time (.DELTA..sub.ref) is set
to 7,200 s.
[0062] Referring to FIG. 3, the reference numeral 310 in FIG. 3
indicates a graph showing a temperature change of a traditional
battery cell, and it can be seen that the battery cell is
overheated beyond the limit temperature (i.e., 80.degree. C.). In
contrast, the reference numeral 320 in FIG. 3 indicates a graph
showing a temperature change in a battery cell to which the method
for controlling power according to the present disclosure is
applied, and it can be seen that the temperature of the battery
cell is maintained less than the limit temperature (i.e.,
80.degree. C.) dissimilar to the traditional battery cell.
[0063] As described in the foregoing, the present disclosure
controls the output of the battery cell 10 to maintain the
temperature of the battery cell 10 below the limit temperature
before overheat of the secondary battery occurs, thereby preventing
a phenomenon in which the life and performance of the secondary
battery is degraded due to overheat. Also, the present disclosure
maintains the temperature of the secondary battery below a
predetermined temperature without having a separate device such as
a cooling system, thereby reducing the production cost of the
battery pack. Further, the present disclosure accurately estimates
overheat of the secondary battery through a temperature estimation
algorithm, not experimental data.
[0064] While the present disclosure has been hereinabove described
with respect to a limited number of embodiments and drawings, the
present disclosure is not limited thereto, and various
modifications and changes may be made by those skilled in the art
within the technical aspect of the present disclosure and the scope
of the appended claims and equivalents thereto.
* * * * *