FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10, rule 13)
“BATTERY MANAGEMENT SYSTEM AND METHOD
FOR OPTIMIZING INTERNAL RESISTANCE OF
BATTERY”
LG CHEM, LTD., of 128, Yeoui-daero, Yeongdeungpo-gu,
Seoul 07336, Republic of Korea
The following specification particularly describes the invention and the manner in
which it is to be performed.
TECHNICAL FIELD
The present disclosure relates to a battery management system and method for
optimizing an internal resistance of a battery.
The present application claims priority to Korean Patent Application No. 10-2017-
0146221 filed on November 3, 2017 in the Republic of Korea, the disclosures of which are
incorporated herein by reference.
BACKGROUND ART
Recently, as the demand for portable electronic products such as notebook
computers, video cameras, and mobile phones is rapidly increasing and the development of
electric vehicles, energy storage batteries, robots, satellites, and the like is being
regularized, studies on high performance batteries capable of repeated charge and
discharge have been actively conducted.
Currently available batteries include nickel-cadmium batteries, nickel-hydrogen
batteries, nickel-zinc batteries, and lithium batteries. Of these, lithium batteries have
almost no memory effect as compared with nickel-based batteries, and are thus free for
charge and discharge and have a very low self-discharge rate and a high energy density.
Due to these advantages, lithium batteries have attracted attention.
Since the life of the battery is reduced when the battery is over-discharged, it is
necessary to adaptively adjust the output power of the battery according to the state of the
battery while discharging the battery. In order to adjust the output power of the battery,
the process of determining the internal resistance of the battery must be preceded. To this
end, a conventional technique as disclosed in Patent Literature 1 records voltage data and
current data indicating voltage-current characteristics of a battery with respect to a specific
state of charge and a specific temperature through a preliminary experiment and calculates
an internal resistance corresponding to the specific state of charge and the specific
temperature by linearizing the voltage-current characteristics by using a data fitting
algorithm such as a least square method.
However, even when the state of charge and the temperature of the battery are
constant, the internal resistance of the battery may change depending on a magnitude of a
discharging current. Therefore, it is difficult to effectively prevent over-discharge of the
battery by the technique disclosed in Patent Literature 1 or the like.
(Patent Literature 1) Korean Patent Application Publication No. 10-2006-0052273
(published on May 19, 2006).
DISCLOSURE
Technical Problem
The present disclosure is designed to solve the problems of the related art, and
therefore the present disclosure is directed to providing a battery management system and
method for optimizing an internal resistance of a battery, which is defined by a voltagecurrent
characteristic profile corresponding to a specific state of charge and a specific
temperature, based on a discharging current of a battery.
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
Various embodiments of the present disclosure for achieving the above objectives
are as follows.
In one aspect of the present disclosure, there is provided a battery management
system for optimizing an internal resistance of a battery, including: a current measurement
unit configured to measure a discharging current of the battery; a memory configured to
store a plurality of voltage-current characteristic profiles; and a control unit operatively
connected to the current measurement unit and the memory and configured to determine a
reference profile from the plurality of voltage-current characteristic profiles based on a
state of charge and a temperature of the battery. The reference profile includes a start
point, an end point, and a plurality of intermediate points positioned between the start point
and the end point, The control unit is further configured to: determine an internal
resistance of the battery based on the start point and the end point; set one of the plurality
of intermediate points as a reference point; determine a reference resistance smaller than
the internal resistance based on the reference point and the end point; and determine an
optimum resistance larger than the internal resistance based on the discharging current, the
internal resistance, the reference resistance, and a predetermined discharge upper limit
current.
In addition, the control unit may be further configured to determine the internal
resistance by dividing a difference between a voltage of the start point and a voltage of the
end point by a current of the end point. The voltage of the start point may indicate an
open circuit voltage of the battery corresponding to the state of charge and the temperature
of the battery.
In addition, the current of the end point may be equal to the discharge upper limit
current.
In addition, the control unit may be further configured to determine the reference
resistance based on a voltage of the reference point, a current of the reference point, a
voltage of the end point, and a current of the end point.
In addition, the control unit may be further configured to determine the reference
resistance by using Equation 1:
.
In Equation 1, Iref is the current of the reference point, Vref is the voltage of the
reference point, Iend is the current of the end point, Vend is the voltage of the end point, and
Rref is the reference resistance.
In addition, the control unit may be further configured to determine the optimum
resistance by using Equation 2:
.
In Equation 2, Rint is the internal resistance, Idis is the discharging current, and Ropt
is the optimum resistance.
In addition, the control unit may be further configured to determine, as the
reference point, an intermediate point closest to the end point among the plurality of
intermediate points.
In another aspect of the present disclosure, there is also provided a battery pack
including the battery management system.
In another aspect of the present disclosure, there is also provided a method of
optimizing an internal resistance of a battery, including: determining a reference profile
from a plurality of voltage-current characteristic profiles based on a state of charge and a
temperature of the battery, the reference profile including a start point, an end point, and a
plurality of intermediate points positioned between the start point and the end point,
determining an internal resistance of the battery based on the start point and the end point;
setting one of the plurality of intermediate points as a reference point; determining a
reference resistance smaller than the internal resistance based on the reference point and
the end point; and determining an optimum resistance larger than the internal resistance
based on a discharging current, the internal resistance, the reference resistance, and a
predetermined discharge upper limit current of the battery.
Advantageous Effects
According to at least one of the embodiments of the present disclosure, an internal
resistance of a battery, which is defined by a voltage-current characteristic profile
corresponding to a specific state of charge and a specific temperature, may be optimized
based on a discharging current of a battery.
According to at least one of the embodiments of the present disclosure, the
optimized internal resistance is used to adjust the output power of the battery, thereby
effectively preventing over-discharge of the battery as compared with the related art.
The effects of the present disclosure are not limited to the above-described effects,
and other effects not described herein may be clearly understood by those skilled in the art
from the description of the claims.
DESCRIPTION OF DRAWINGS
The accompanying drawings illustrate a preferred embodiment of the present
disclosure and together with the foregoing disclosure, serve to provide further
understanding of the technical features of the present disclosure, and thus, the present
disclosure is not construed as being limited to the drawing.
FIG. 1 is a diagram illustrating a functional configuration of a battery pack
according to an embodiment of the present disclosure.
FIG. 2 is a flowchart of a method for optimizing an internal resistance of a battery,
according to an embodiment of the present disclosure.
FIG. 3 is a graph showing an exemplary voltage-current characteristic profile
referred to in describing the method of FIG. 2.
FIG. 4 is a graph referred to in describing a difference between a discharge
limiting current determined based on the internal resistance described above with reference
to FIGS. 2 and 3 and a discharge limiting current determined based on an optimum
resistance.
MODE FOR DISCLOSURE
Hereinafter, preferred embodiments of the present disclosure will be described in
detail with reference to the accompanying drawings. Prior to the description, 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, it should be understood that various equivalents and alternatives can be
made at the time of filing the present disclosure since the descriptions of the specification
and the features shown in the drawings are no other than preferred embodiments without
reflecting all the technical ideas of the present disclosure.
However, in the following descriptions and the accompanying drawings,
descriptions of well-known functions or constructions will be omitted if they are
considered to unnecessarily obscure the gist of the present disclosure.
It should be understood that terms including ordinals, such as first, second, etc.,
are used for the purpose of distinguishing one of various components from the others, and
are not used to limit the components by such terms.
It should be understood that terms such as "comprise", "include", and "have",
when used herein, specify the presence of stated elements, but do not preclude the presence
or addition of one or more other elements. In addition, the terms "control unit" as used
herein represent a unit for processing at least one function or operation, which may be
implemented by hardware, software, or a combination thereof.
It should be understood that when a region is referred to as being "connected to" or
"coupled to" another region, it may be "directly" connected or coupled to the other region,
or may be "indirectly" connected or coupled to the other region, with intervening regions
being disposed therebetween.
FIG. 1 is a diagram illustrating a functional configuration of a battery pack 1
according to an embodiment of the present disclosure.
Referring to FIG. 1, the battery pack 1 includes a battery 10, a switch 20, and a
battery management system 100. The switch 20 is configured to be turned on and off in
response to a switching signal (for example, a pulse width modulation signal) from the
battery management system 100 so as to adjust a magnitude of a charging current and/or a
discharging current of the battery 10. Hereinafter, it is assumed that the discharging
current is measured as a positive value, and the charging current is measured as a negative
value.
The battery management system 100 is electrically connectable to the battery 10
and is configured to monitor and control the state of the battery 10. The battery
management system 100 includes a sensing unit 110, a memory 120, a control unit 130,
and a communication interface 140.
The sensing unit 110 includes a current measurement unit 111. The current
measurement unit 111 measures a current of the battery 10 at each predetermined cycle and
transmits a current signal indicating the measured current to the control unit 130. The
current measured while discharging the battery 10 may be referred to as a "discharging
current", and the current mesaured while charging the battery 10 may be referred to as a
"charging current". The control unit 130 may convert an analog current signal
transmitted from the current measurement unit 111 into digital current data.
The sensing unit 110 may further include a voltage measurement unit 112. The
voltage measurement unit 112 measures a voltage of the battery 10 at each predetermined
cycle and transmits a voltage signal indicating the measured voltage to the control unit 130.
The control unit 130 may convert an analog voltage signal transmitted from the voltage
measurement unit 112 into digital voltage data.
The sensing unit 110 may further include a temperature measurement unit 113.
The temperature measurement unit 113 measures a temperature of the battery 10 at each
predetermined cycle and transmits a temperature signal indicating the measured
temperature to the control unit 130. The control unit 130 may convert an analog
temperature signal transmitted from the temperature measurement unit 113 into digital
temperature data. The current measurement unit 111, the voltage measurement unit 112,
and the temperature measurement unit 113 may operate in synchronization with one
another.
The memory 120 is configured to store a plurality of voltage-current characteristic
profiles. Each of the voltage-current characteristic profiles includes a start point, an end
point, and a plurality of intermediate points. The start point indicates an open circuit
voltage (OCV) measured when a discharging current is 0 A. The end point indicates a
voltage measured at the time of pulse discharge by the same constant current as a discharge
upper limit current. Each of the intermediate points indicates a voltage measured at the
time of pulse discharge by a constant current that is larger than 0 A and less than the
discharge upper limit current.
Each of the voltage-current characteristic profiles may be associated with a
specific state of charge (SOC) and a specific temperature. For example, any one of the
plurality of voltage-current characteristic profiles may be associated with an SOC of 80%
and a temperature of -20°C, and another may be associated with an SOC of 80% and a
temperature of 25°C. It will be apparent to those skilled in the art that various voltagecurrent
characteristic profiles associated with different SOCs and temperatures may be
stored in the memory 120.
The memory 120 may additionally store data, commands, and software required
for the overall operation of the battery management system 100. The memory 120 may
include at least one storage medium selected from flash memory, hard disk, solid state disk
(SSD), silicon disk drive (SDD), multimedia card micro type memory, random access
memory (RAM), static random access memory (SRAM), read-only memory (ROM),
electrically erasable programmable read-only memory (EEPROM), and programmable
read-only memory (PROM).
The control unit 130 is operatively coupled to the sensing unit 110, the memory
120, and the communication interface 140. The control unit 130 may estimate the SOC
of the battery 10 based on the current signal, the voltage signal, and/or the temperature
signal, which is transmitted from the sensing unit 110. The control unit 130 may update
the SOC of the battery 10 at each predetermined cycle based on the current signal by using
ampere counting. Alternatively, the control unit 130 may update the SOC of the battery
10 at each predetermined cycle by using a method well known in the art, such as an
extended Kalman filter, in addition to the ampere counting.
The control unit 130 may determine the temperature of the battery 10 based on the
temperature signal transmitted from the sensing unit 110, and then determine a reference
profile from a plurality of voltage-current characteristic profiles based on the estimated
SOC and the determined temperature. The reference profile may be any one voltagecurrent
characteristic profile corresponding to the estimated SOC and the determined
temperature among the plurality of voltage-current characteristic profiles.
According to hardware implementation, the control unit 130 may be implemented
by using at least one selected from application specific integrated circuits (ASICs), digital
signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic
devices (PLDs), field programmable gate arrays (FPGAs), microprocessors, and electrical
units for performing other functions.
The communication interface 140 may be communicably connected to an external
device 2 such as an ECU of an electric vehicle. The communication interface 140 may
receive a command message from the external device 2 and provide the received command
message to the control unit 130. The command message may be a message requesting
activation of a specific function of the battery management system 100. The
communication interface 140 may transmit a notification message from the control unit
130 to the external device 2. The notification message may be a message for notifying
the external device 2 of the result of the function executed by the control unit 130.
FIG. 2 is a flowchart of a method for optimizing an internal resistance of a battery,
according to an embodiment of the present disclosure, and FIG. 3 is a graph showing an
exemplary voltage-current characteristic profile referred to in describing the method of
FIG. 2.
Referring to FIG. 2, in step S200, the control unit 130 measures a discharging
current Idis and a temperature of the battery 10 by using the sensing unit 110.
In step S210, the control unit 130 determines a reference profile from a plurality of
voltage-current characteristic profiles stored in the memory 120, based on an SOC (for
example, SOC 80%) of the battery 10 and the measured temperature (for example, 25°C).
In other words, the reference profile determined through step S210 is any one of the
plurality of voltage-current characteristic profiles corresponding to the SOC (for example,
SOC 80%) and the temperature (for example, 25°C) of the battery 10. In order to
determine the reference profile, prior to the execution of step S210, the control unit 130
may update the SOC and the temperature of the battery 10 to the latest values, respectively,
based on the current signal, the voltage signal, and/or the temperature signal from the
sensing unit 110
A voltage-current characteristic profile 300 illustrated in FIG. 3 is an example of
the reference profile determined in step S210, and may be associated with an SOC of 80%
and a temperature of 25°C among the plurality of voltage-current characteristic profiles
300 stored in the memory 120.
It is assumed that the voltage-current characteristic profile 300 includes a total of
five points, that is, a start point Pstart, intermediate points Pinter_1, Pinter_2, and Pinter_3, and an
end point Pend. As described above, the three intermediate points Pinter_1, Pinter_2, and
Pinter_3 are positioned between the start point Pstart and the end point Pend.
The voltage-current characteristic profile 300 may be defined by terminal voltages
Vstart, Vinter_1, Vinter_2, Vinter_3, and Vend of other batteries measured at the time when the
other batteries are repeatedly pulse-discharged with constant currents Istart, Iinter_1, Iinter_2,
Iinter_3, and Iend of different magnitudes for a predetermined time (for example, 10 sec) in a
condition that the SOCs and temperatures of the other batteries manufactured to have the
same electrochemical characteristics as those of the battery 10 are constantly maintained at
specific values. For example, Vinter_1 is a voltage measured when the other batteries are
discharged with Iinter_1 for 10 seconds in a condition that the SOCs and temperatures of the
other batteries are 80% and 25°C, Vinter_2 is a voltage measured when the other batteries are
discharged with Iinter_2 for 10 seconds in a condition that the SOCs and temperatures of the
other batteries are 80% and 25°C, Vinter_3 is a voltage measured when the other batteries are
discharged with Iinter_3 for 10 seconds in a condition that the SOCs and temperatures of the
other batteries are 80% and 25°C, and Vend is a voltage measured when the other batteries
are discharged with Iend for 10 seconds in a condition that the SOCs and temperatures of
the other batteries are 80% and 25°C.
It will be apparent that the voltage-current characteristic profile 300 may include
two or less intermediate points or four or more intermediate points different from the
intermediate points illustrated in FIG. 3.
Each point defining the voltage-current characteristic profile 300 is represented by
a pair of a single voltage and a single current. Specifically, the start point Pstart may be
represented by Pstart = (Vstart, Istart), the end point Pend may be represented by Pend = (Vend,
Iend), the intermediate point Pinter_1 may be represented by Pinter_1 = (Vinter_1, Iinter_1), the
intermediate point Pinter_2 may be represented by Pinter_2 = (Vinter_2, Iinter_2), and the
intermediate point Pinter_1 may be represented by Pinter_3 = (Vinter_3, Iinter_3). Vstart is a
voltage detected when the discharging current is Istart, Vinter_1 is a voltage detected when the
discharging current is Iinter_1, Vinter_2 is a voltage detected when the discharging current is
Iinter_2, Vinter_3 is a voltage detected when the discharging current is Iinter_3, and Vend is a
voltage detected when the discharging current is Iend.
Vocv = Vstart > Vinter_1 > Vinter_2 > Vinter_3 > Vend, and Istart < Iinter_1 < Iinter_2 < Iinter_3 <
Iend = Imax. Vocv indicates the OCV of the battery 10 at an SOC of 80% and a temperature
of 25°C. Imax indicates the discharge upper limit current and may be a value given for
preventing the battery 10 from being damaged by an overcurrent. The control unit 130
may control the discharging current of the battery 10 so that a current exceeding the
discharge upper limit current Imax does not flow through the battery 10.
In step S220, the control unit 130 determines the internal resistance Rint of the
battery 10 based on the start point Pstart and the end point Pend. Specifically, a straight line
passing through the start point Pstart and the end point Pend may be expressed by Equation 1
below.

V = Vocv − RintI
The internal resistance Rint is a solution of simultaneous equations in which the
voltages and currents of the start point Pstart and the end point Pend are respectively
substituted into V and I of Equation 1, and the control unit 130 may determine the internal
resistance Rint by using Equation 2 below.

Alternatively, the internal resistance Rint may be a value prestored in the memory
120 for the voltage-current characteristic profile 300. In this case, the control unit 130
may read the internal resistance Rint from the memory 120 instead of executing step S220.
In step S230, the control unit 130 determines a reference point Pref from the
reference profile 300. The reference point Pref may be any one of the intermediate points
Pinter_1, Pinter_2, and Pinter_3 included in the voltage-current characteristic profile 300. When
k = 1, 2, and 3, the control unit 130 calculates a slope of a straight line
passing through the intermediate point Pinter_k and the end point Pend, and set, as the
reference point Pref, one intermediate point at which the absolute value of the calculated
slope becomes the smallest. In the case of
as in the voltage-current characteristic
profile 300 of FIG. 3, the control unit 130 may set Pinter_3 as the reference point Pref.
Alternatively, the control unit 130 may set, as the reference point Pref, the
intermediate point Pinter_3 closest to the end point Pend among the intermediate points Pinter_1,
Pinter_2, and Pinter_3.
In step S240, the control unit 130 determines the reference resistance Rref smaller
than the internal resistance Rint based on the reference point Pref and the end point Pend.
Specifically, a straight line passing through the reference point Pref and the end
point Pend may be expressed by Equation 3 below.

V = Vnew − RrefI
In Equation 3, Vnew is a voltage of a point at which a straight line having a slope of
-Rref and passing through the reference point Pref meets a V axis as illustrated in FIG. 3.
The voltage Vnew and the reference resistance Rref are two solutions of
simultaneous equations in which the voltages and currents of the reference point Pref and
the end point Pend are respectively substituted into V and I of Equation 3, and the control
unit 130 may determine the reference resistance Rref by using Equation 4 below.

As in the above example, when the reference point Pref is the intermediate point
Pinter_3, Vref = Vinter_3 and Iref = Iinter_3 in Equation 4.
Alternatively, the reference resistance Rref may be a value previously stored in the
memory 120 for the voltage-current characteristic profile 300. In this case, the control
unit 130 may read the reference resistance Rref from the memory 120 instead of executing
steps S230 and S240.
Referring to FIG. 3, since the intermediate points Pinter_1, Pinter_2, and Pinter_3 are
positioned below the straight line passing the start point Pstart and the end point Pend, it will
be readily understood by those skilled in the art that the reference resistance Rref is less
than the internal resistance Rint.
In step S250, the control unit 130 determines an optimum resistance Ropt based on
the measured discharging current Idis, the internal resistance Rint, the reference resistance
Rref, and the discharge upper limit current Imax. In this case, the optimum resistance Ropt is
larger than the internal resistance Rint. If the optimum resistance Ropt determined in step
S250 is equal to or smaller than the internal resistance Rint, the control unit 130 may
determine that an error has occurred during execution of at least one of steps S200 to S250
and may return to step S210.
If the voltage Vend and the current Iend of the end point Pend are respectively
substituted into V and I of Equation 1, it may be expressed by Equation 5 below.

Vend = Vocv − RintIend
If the voltage Vend and the current Iend of the end point Pend are respectively
substituted into V and I of Equation 3, it may be expressed by Equation 6 below.

Vend = Vnew − RrefIend
If Equation 6 is summarized with respect to Vnew, it may be expressed by Equation
7 below.

Vnew = Vend + RrefIend
If Vocv − IendRint of Equation 5 is substituted into in Vend of Equation 7, it may be
expressed by Equation 8 below.

Vnew = (Vocv − RintIend) + IendRref = Vocv − (Rint − Rref)Iend
In FIG. 3, Pdis is a discharge point positioned on a straight line passing the
reference point Pref and the end point Pend. The current of the discharge point Pdis is the
discharging current Idis. Therefore, from Equation 3, the voltage Vdis of the discharge
point Pdis may be expressed by Equation 9 below.

Vdis = Vnew −RrefIdis
when 'Vocv − (Rint − Rref)Iend' of Equation 8 is substituted into Vnew of Equation 9, it
may be expressed by Equation 10 below.

Vdis = Vocv − (Rint − Rref)Iend − RrefIdis
A straight line passing through the start point Pstart and the discharge point Pdis may
be expressed by Equation 11 below.

V = Vocv − RoptI
The optimum resistance Ropt indicates a slope of a straight line passing between
the start point Pstart and the discharge point Pdis. If the voltage Vdis and the current Idis of
the discharge point Pdis are respectively substituted into V and I of Equation 11, it may be
expressed by Equation 12 below.

when 'Vocv − (Rint − Rref)Iend − RrefIdis' of Equation 10 is substituted into Vdis of
Equation 12, it may be expressed by Equation 13 below.

The control unit 130 may determine the optimum resistance Ropt by using Equation
13. That is, the control unit 130 may determine the optimum resistance Ropt by
substituting Rint, Rref, Idis, and Iend obtained in steps S210 to S240 into Equation 13.
As described above, since Rint is larger than Rref, Ropt is larger than Rint.
Therefore, when the output power is controlled while discharging the battery 10 by using
Ropt, the over-discharge of the battery 10 may be effectively prevented, as compared with
the method of controlling the output power at the time of discharging the battery 10 by
using Rint.
FIG. 4 is a graph referred to in describing a difference between a discharge
limiting current determined based on the internal resistance described above with reference
to FIGS. 2 and 3 and a discharge limiting current determined based on the optimum
resistance.
Referring to FIG. 4, a polarization voltage ΔVpola may be generated in the battery
at a time point when the discharging current Idis is measured, according to a use state
thereof. The control unit 130 can determine the polarization voltage ΔVpola by using a
known data fitting method such as a least square algorithm.
When the polarization voltage ΔVpola is generated, the voltage-current
characteristic profile 300 illustrated in FIG. 3 may be modified to be shifted by ΔVpola
along the V axis as illustrated in FIG. 4. Accordingly, the start point Pstart is shifted to
Pstart_pola, and the end point Pend is shifted to Pend_pola. In this case, Pstart_pola = (Vocv −
ΔVpola, 0) and Pend_pola = (Vend − ΔVpola, Imax). Although not separately illustrated, the
intermediate points Pinter_1, Pinter_2, and Pinter_3 in FIG. 3 are also shifted by ΔVpola along the
V axis.
In order to reflect the polarization voltage ΔVpola, Equation 1 may be changed to
Equation 14 below and Equation 11 may be changed to Equation 15 below.

V = (Vocv − ΔVpola) − RintI

V = (Vocv − ΔVpola) − RoptI
In order to prevent the over-discharge of the battery 10, it is preferable to
determine the discharge limiting current for the battery 10 in consideration of the
polarization voltage ΔVpola.
A discharge limiting current Ilimit_1 based on the internal resistance Rint may be
determined by using Equation 16 below related to Equation 14.

On the other hand, the control unit 130 may determine a discharge limiting current
Ilimit_2 based on the optimum resistance Ropt by using Equation 17 below related to
Equation 15.

Since Ropt is larger than Rint, Ilimit_2 is smaller than Ilimit_1. Therefore, when Ilimit_2
instead of Ilimit_1 is determined as the discharge limiting current of the battery 10, the
amount of voltage drop of the battery 10 is reduced by the magnitude corresponding to
(Ilimit_1 − Ilimit_2), thereby effectively preventing the over-discharge of the battery 10.
The control unit 130 may adjust a duty cycle of the switching signal output to the
switch 20 so that a discharging current exceeding the determined discharge limiting current
Ilimit_2 does not flow.
The above-described embodiments of the present disclosure are not implemented
only by the devices and methods and may be implemented by the program for realizing the
functions corresponding to the configuration of the embodiments of the present disclosure
or the recording medium having recorded thereon the program. These implementations
can be easily achieved by those skilled in the art from the description of the embodiments
described above.
While the present disclosure has been shown and described with reference to
certain preferred embodiments thereof, but the present disclosure is not limited thereto. It
should be understood by those skilled in the art that various changes and modifications can
be made without departing from the spirit of the present disclosure as defined by the
appended claims and their equivalents.
In addition, it should be understood by those skilled in the art that since various
changes and modifications can be made without departing from the spirit of the present
disclosure, the present disclosure is not limited to the above-described embodiments and
the accompanying drawings, and all or some of the embodiments may be selectively
combined so that various modifications can be made.

1: battery pack
10: battery
20: switch
100: battery management system
110: sensing unit
120: memory
130: control unit
140: communication interface

WHAT IS CLAIMED IS:
1. A battery management system for optimizing an internal resistance of a
battery, the battery management system comprising:
a current measurement unit configured to measure a discharging current of the
battery;a memory configured to store a plurality of voltage-current characteristic profiles;
and
a control unit operatively connected to the current measurement unit and the
memory and configured to determine a reference profile from the plurality of voltagecurrent
characteristic profiles based on a state of charge and a temperature of the battery,
the reference profile including a start point, an end point, and a plurality of intermediate
points positioned between the start point and the end point,
wherein the control unit is further configured to:determine an internal resistance of the battery based on the start point and the end
point;set one of the plurality of intermediate points as a reference point;
determine a reference resistance smaller than the internal resistance based on the
reference point and the end point; and
determine an optimum resistance larger than the internal resistance based on the
discharging current, the internal resistance, the reference resistance, and a predetermined
discharge upper limit current.
2. The battery management system of claim 1, wherein the control unit is
further configured to determine the internal resistance by dividing a difference between a
voltage of the start point and a voltage of the end point by a current of the end point, and
the voltage of the start point indicates an open circuit voltage of the battery
corresponding to the state of charge and the temperature of the battery.
3. The battery management system of claim 2, wherein the current of the end
point is equal to the discharge upper limit current.
4. The battery management system of claim 1, wherein the control unit is
further configured to determine the reference resistance based on a voltage of the reference
point, a current of the reference point, a voltage of the end point, and a current of the end
point.
5. The battery management system of claim 4, wherein the control unit is
further configured to determine the reference resistance by using Equation 1:
(Iref is the current of the reference point, Vref is the voltage of the reference point,
Iend is the current of the end point, Vend is the voltage of the end point, and Rref is the
reference resistance).
6. The battery management system of claim 5, wherein the control unit is
further configured to determine the optimum resistance by using Equation 2:
(Rint is the internal resistance, Idis is the discharging current, and Ropt is the
optimum resistance).
7. The battery management system of claim 1, wherein the control unit is
further configured to determine, as the reference point, an intermediate point closest to the
end point among the plurality of intermediate points.
8. A battery pack comprising the battery management system of any one of
claims 1 to 7.
9. A method of optimizing an internal resistance of a battery, the method
comprising:
determining a reference profile from a plurality of voltage-current characteristic
profiles based on a state of charge and a temperature of the battery, the reference profile
including a start point, an end point, and a plurality of intermediate points positioned
between the start point and the end point,
determining an internal resistance of the battery based on the start point and the
end point;
setting one of the plurality of intermediate points as a reference point;
determining a reference resistance smaller than the internal resistance based on the
reference point and the end point; and
determining an optimum resistance larger than the internal resistance based on a
discharging current, the internal resistance, the reference resistance, and a predetermined
discharge upper limit current of the battery.