U.S. patent application number 14/762635 was filed with the patent office on 2016-08-25 for apparatus and method for estimating power storage device degradation.
This patent application is currently assigned to Mitsubishi Electric Corporation. The applicant listed for this patent is Yuruki OKADA, Sho SHIRAGA, Toshihiro WADA, Shoji YOSHIOKA. Invention is credited to Yuruki OKADA, Sho SHIRAGA, Toshihiro WADA, Shoji YOSHIOKA.
Application Number | 20160245870 14/762635 |
Document ID | / |
Family ID | 51579460 |
Filed Date | 2016-08-25 |
United States Patent
Application |
20160245870 |
Kind Code |
A2 |
OKADA; Yuruki ; et
al. |
August 25, 2016 |
APPARATUS AND METHOD FOR ESTIMATING POWER STORAGE DEVICE
DEGRADATION
Abstract
Switches change the resistance value of a charge/discharge
circuit in a period from starting a discharging at an upper limit
voltage until the voltage reaches a lower limit voltage. An
electric charge estimator computes electric charge by
time-integrating current from a start of the discharging to an
arbitrarily determined time, and computes a relationship between
electric charge and voltage of a power storage device. An internal
resistance estimator computes internal resistance based on voltages
and currents of the storage device at times when resistance values
are different. An electric energy estimator computes a relationship
between electric charge and open voltage based on electric charge,
voltage, current and internal resistance of the storage device.
During charging or discharging of the storage device, the electric
energy estimator estimates the electric energy of the power storage
device based on the electric charge, the open voltage, the internal
resistance, and the charge/discharge current.
Inventors: |
OKADA; Yuruki; (Chiyoda-ku,
Tokyo, JP) ; SHIRAGA; Sho; (Chiyoda-ku, Tokyo,
JP) ; WADA; Toshihiro; (Chiyoda-ku, Tokyo, JP)
; YOSHIOKA; Shoji; (Chiyoda-ku, Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
OKADA; Yuruki
SHIRAGA; Sho
WADA; Toshihiro
YOSHIOKA; Shoji |
Chiyoda-ku, Tokyo
Chiyoda-ku, Tokyo
Chiyoda-ku, Tokyo
Chiyoda-ku, Tokyo |
|
JP
JP
JP
JP |
|
|
Assignee: |
Mitsubishi Electric
Corporation
Chiyoda-ku, Tokyo
OT
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20150369870 A1 |
December 24, 2015 |
|
|
Family ID: |
51579460 |
Appl. No.: |
14/762635 |
Filed: |
March 18, 2013 |
PCT Filed: |
March 18, 2013 |
PCT NO: |
PCT/JP2013/057717 PCKC 00 |
371 Date: |
July 22, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 10/44 20130101;
G01R 31/3842 20190101; Y02E 60/10 20130101; G01R 31/389 20190101;
G01R 31/392 20190101; H01M 10/48 20130101; G01R 31/3648
20130101 |
International
Class: |
G01R 31/36 20060101
G01R031/36 |
Claims
1. An apparatus for estimating power storage device degradation,
comprising: a charge/discharge circuit, including a resistor, that
is connected to a power storage device; a switch to switch an
electrical pathway of the charge/discharge circuit to change a
resistance value of the charge/discharge circuit; a voltage
detector to detect a voltage of the power storage device; a current
detector to detect a current flowing through the power storage
device; a circuit selector to select the switch such that a
resistance value of the charge/discharge circuit changes at least
once from starting a discharging of the power storage device in a
state in which the voltage is equal to or greater than a first
threshold value until the voltage becomes less than or equal to a
second threshold value, or from starting a charging of the power
storage device in a state in which the voltage is less than or
equal to a third threshold value until the voltage becomes equal to
or greater than a fourth threshold value; an electric charge
estimator to compute an electric charge by time-integrating the
current from a start time of the discharging or the charging to an
arbitrarily determined time, and compute a relationship between the
electric charge and the voltage; an internal resistance estimator
to compute an internal resistance of the power storage device,
based on the voltages and currents at times when resistance values
of the charge/discharge circuit are different since starting the
discharging or the charging; and an electric energy estimator to
compute a relationship between the electric charge and an open
voltage of the power storage device based on the relationship
between the electric charge and the voltage, the current, and the
internal resistance, and to estimate an electric energy of the
power storage device based on the relationship between the electric
charge and the open voltage, the internal resistance, and a current
flowing through the power storage device during discharging or
charging.
2. The apparatus for estimating power storage device degradation
according to claim 1, further comprising: a temperature detector to
detect a temperature of the power storage device, wherein the
internal resistance estimator computes a relationship between
temperature and internal resistance by interpolating based on
different values of the temperature and the internal resistance, or
corrects a predetermined relationship between temperature and
internal resistance based on the temperature and the internal
resistance, and the electric energy estimator corrects the internal
resistance based on a temperature of the power storage device
during discharging or charging and the computed relationship
between temperature and internal resistance or the corrected
relationship between temperature and internal resistance, and
estimates an electric energy of the power storage device based on a
relationship between the electric charge and an open voltage of the
power storage device, the corrected internal resistance, and a
current flowing through the power storage device during discharging
or charging.
3. A method for estimating power storage device degradation,
conducted by an apparatus for estimating power storage device
degradation that includes a charge/discharge circuit, including a
resistor, that is connected to a power storage device, and a switch
to switch an electrical pathway of the charge/discharge circuit to
change a resistance value of the charge/discharge circuit, the
method comprising: detecting a voltage of the power storage device;
detecting a current flowing through the power storage device;
switching the switch such that a resistance value of the
charge/discharge circuit changes at least once from starting a
discharging of the power storage device in a state in which the
voltage is equal to or greater than a first threshold value until
the voltage becomes less than or equal to a second threshold value,
or from starting a charging of the power storage device in a state
in which the voltage is less than or equal to a third threshold
value until the voltage becomes equal to or greater than a fourth
threshold value; computing an electric charge by time-integrating
the current from a start time of the discharging or the charging to
an arbitrarily determined time, and computing a relationship
between the electric charge and the voltage; computing an internal
resistance of the power storage device, based on the voltages and
currents at times when resistance values of the charge/discharge
circuit are different since starting the discharging or the
charging; and computing a relationship between the electric charge
and an open voltage of the power storage device based on the
relationship between the electric charge and the voltage, the
current, and the internal resistance, and estimating an electric
energy of the power storage device based on the relationship
between the electric charge and the open voltage, the internal
resistance, and a current flowing through the power storage device
during discharging or charging.
Description
TECHNICAL FIELD
[0001] The present disclosure relates to an apparatus and a method
for estimating power storage device degradation, which estimates
the electric energy of a power storage device.
BACKGROUND ART
[0002] To control the charging and discharging of a power storage
device, it is necessary to accurately assess the dischargeable
power and the chargeable power. In other words, it is necessary to
accurately assess the open voltage (open-circuit voltage), the
internal resistance, and the state of charge (SOC).
[0003] Directly measuring the state of charge of a power storage
device is difficult.
[0004] However, a degree of correlation between the SOC and the
open voltage of a power storage device has been recognized.
Accordingly, with the method of computing the SOC of a secondary
battery for an electric vehicle disclosed in Patent Literature 1,
the battery internal resistance of a secondary battery is computed
by multiplying a predetermined resistance value, a first resistance
ratio based on battery temperature, and a second resistance ratio
based on a given reference state of charge. Subsequently, the open
voltage is computed from the computed battery internal resistance
as well as the current and voltage of a battery during charging or
discharging, and the SOC of the battery is computed based on the
correlation of the SOC with the open voltage.
[0005] The remaining battery capacity detection apparatus disclosed
in Patent Literature 2 connects a load resistor to a secondary
battery to cause a constant current discharge, and based on the
voltage between the terminals immediately after starting the
constant current discharge and after a certain time elapses,
detects a polarization value dominated by internal mass movement or
a resistance value dominated by internal mass movement based on how
easily reactive matter inside the electrodes moves to a reaction
site in the secondary battery. Subsequently, the SOC of the
secondary battery is detected based on the polarization value
dominated by internal mass movement or the resistance value
dominated by internal mass movement.
[0006] The battery degradation measurement apparatus disclosed in
Patent Literature 3 computes the internal resistance of a battery
based on the battery voltages when different charging current
values are supplied, and computes a battery cell degradation ratio
based on the ratio against the internal resistance in an initial
state.
[0007] The battery degradation level estimation apparatus disclosed
in Patent Literature 4 uses relationship data obtained by
pre-measuring the relationship between the charge amount and the
open voltage value for each of different degradation levels, and
computes a degradation level of a battery based on an electric
charge of the battery computed by time-integrating a
charge/discharge current value detected with a current sensor.
CITATION LIST
Patent Literature
[0008] Patent Literature 1: Unexamined Japanese Patent Application
Kokai Publication No. 2000-258513
[0009] Patent Literature 2: Unexamined Japanese Patent Application
Kokai Publication No. 2007-017357
[0010] Patent Literature 3: Unexamined Japanese Patent Application
Kokai Publication No. 2008-123961
[0011] Patent Literature 4: Unexamined Japanese Patent Application
Kokai Publication No. 2012-057956
SUMMARY OF INVENTION
[0012] to change a resistance value of the charge/discharge
circuit. The voltage detector detects a voltage of the power
storage device. The current detector detects a current flowing
through the power storage device. The circuit selector switches the
switch so that a resistance value of the charge/discharge circuit
changes at least once from starting a discharging of the power
storage device in a state in which the voltage is equal to or
greater than a first threshold value until the voltage becomes less
than or equal to a second threshold value, or from starting a
charging of the power storage device in a state in which the
voltage is less than or equal to a third threshold value until the
voltage becomes equal to or greater than a fourth threshold value.
The electric charge estimator computes an electric charge by
time-integrating the current from a start time of the discharging
or the charging to an arbitrarily determined time, and computes a
relationship between the electric charge and the voltage. The
internal resistance estimator computes an internal resistance of
the power storage device, based on the voltages and currents at
times when resistance values of the charge/discharge circuit are
different since starting the discharging or the charging. The
electric energy estimator computes a relationship between the
electric charge and an open voltage of the power storage device
based on a relationship between the electric charge and the
voltage, the current, and the internal resistance, and estimates an
electric energy of the power storage device based on a relationship
between the electric charge and the open voltage, the internal
resistance, and a current flowing through the power storage device
during discharging or charging.
Advantageous Effects of Invention
[0013] According to the present disclosure, it becomes possible to
improve the accuracy of estimating the electric energy of a power
storage device.
BRIEF DESCRIPTION OF DRAWINGS
[0014] FIG. 1 is a block diagram illustrating an example
configuration of an apparatus for estimating power storage device
degradation according to Embodiment 1 of the present
disclosure;
[0015] FIG. 2 is a diagram illustrating an example of changes in a
current flowing through a power storage device and in a voltage of
the power storage device according to Embodiment 1;
[0016] FIG. 3 is a diagram illustrating an example of computing
electric charge according to Embodiment 1;
[0017] FIG. 4 is a diagram illustrating an example of computing
electric charge according to Embodiment 1;
[0018] FIG. 5 is a diagram illustrating an example of a
relationship between electric charge and the voltage of the power
storage device, and a relationship between electric charge and an
internal resistance, according to Embodiment 1;
[0019] FIG. 6 is a diagram illustrating an example of estimating
the electric energy of the power storage device according to
Embodiment 1;
[0020] FIG. 7 is a flowchart illustrating an example of measurement
operations conducted by the apparatus for estimating power storage
device degradation according to Embodiment 1;
[0021] FIG. 8 is a flowchart illustrating an example of electric
energy estimation operations conducted by the apparatus for
estimating power storage device degradation according to Embodiment
1;
[0022] FIG. 9 is a block diagram illustrating a different example
configuration of the apparatus for estimating power storage device
degradation according to Embodiment 1;
[0023] FIG. 10 is a diagram illustrating a different example of
changes in a current flowing through the power storage device and
in the voltage of the power storage device according to Embodiment
1;
[0024] FIG. 11 is a block diagram illustrating an example
configuration of an apparatus for estimating power storage device
degradation according to Embodiment 2 of the present
disclosure;
[0025] FIG. 12 is a diagram illustrating an example of a
relationship between the temperature and internal resistance of the
power storage device according to Embodiment 2;
[0026] FIG. 13 is a diagram illustrating an example of a
relationship between the electric charge and internal resistance
according to Embodiment 2;
[0027] FIG. 14 is a flowchart illustrating an example of
measurement operations conducted by the apparatus for estimating
power storage device degradation according to Embodiment 2; and
[0028] FIG. 15 is a flowchart illustrating an example of electric
energy estimation operations conducted by the apparatus for
estimating power storage device degradation according to Embodiment
2.
DESCRIPTION OF EMBODIMENTS
[0029] Hereinafter, embodiments of the present disclosure are
described in detail and with reference to the drawings. Note that
in the drawings, the same signs are given to the same or similar
parts.
Embodiment 1
[0030] FIG. 1 is a block diagram illustrating an example
configuration of an apparatus for estimating power storage device
degradation according to Embodiment 1 of the present disclosure.
The apparatus for estimating power storage device degradation 1 is
provided with a voltage detector 11, a current detector 12, a
circuit selector 13, an electric charge estimator 14, an internal
resistance estimator 15, an electric energy estimator 16, resistors
R1 and R2, and switches S1 and S2. The power storage device 2 is a
secondary battery, for example, a nickel-metal hydride battery or a
lithium-ion battery. As the power storage device 2 is repeatedly
charged and discharged, the capacity of the power storage device 2
decreases due to degradation caused by the repeated charging and
discharging, and the amount of storable electric energy decreases.
The apparatus for estimating power storage device degradation 1
estimates degradation in the power storage device 2, or in other
words, estimates the electric energy of the power storage device 2.
power storage device 2 based on the voltages and currents at times
when the resistance values of the charge/discharge circuit 17 are
different. The electric energy estimator 16 computes the
relationship between the electric charge and the open voltage of
the power storage device 2 based on the relationship between the
electric charge and the voltage computed by the electric charge
estimator 14, the current, and the internal resistance.
[0031] Based on the values computed as discussed above, when
discharging or charging the power storage device 2, the electric
energy estimator 16 estimates the electric energy of the power
storage device 2 based on the relationship between the electric
charge and the open voltage of the power storage device 2, the
internal resistance, and the current when discharging or charging
the power storage device 2.
[0032] FIG. 2 is a diagram illustrating an example of changes in a
current flowing through the power storage device and in the voltage
of the power storage device according to Embodiment 1. The top part
illustrates the current, while the bottom part illustrates the
voltage. The horizontal axis is time, while the vertical axis of
the top part is current, and the vertical axis of the bottom part
is voltage. An example will be described for a case in which
discharging starts in a state in which the voltage is equal to or
greater than a first threshold value, and discharging continues
until the voltage becomes less than or equal to a second threshold
value. Note that the first threshold value and the second threshold
value may be arbitrarily determined. For example, an upper limit
voltage of the power storage device 2 is set to the first threshold
value, and a lower limit voltage of the power storage device 2 is
set to the second threshold value. Note that a discharge current is
expressed as positive. As illustrated in FIG. 2, the voltage
changes from an upper limit voltage V.sub.UL to a lower limit
voltage V.sub.LL.
[0033] Starting from a state in which the voltage is the upper
limit voltage V.sub.UL and the switches S1 and S2 are off, at time
T1, the switch S1 is switched on, and discharging of the power
storage device 2 starts. During the period from time T1 to time T2,
the current is I.sub.11, and the voltage decreases to V.sub.11 over
the period from time T1 to time T2. At time T2, the switch S2 is
additionally switched on, the current becomes I.sub.21, and the
voltage becomes V.sub.21. During the period from time T2 to time
T3, the current is I.sub.21, and the voltage decreases over the
period from time T2 to time T3. At time T3, the switch S2 is
switched off, the current becomes I.sub.12, and the voltage
increases to approximately V.sub.21. During the period from time T3
to time T4, the current is I.sub.12, and the voltage decreases to
V.sub.12 over the period from time T3 to time T4. At time T4, the
switch S2 is switched on, the current becomes I.sub.22, and the
voltage becomes V.sub.22. Starting from time T4, the voltage
detector 11 and the current detector 12 detect the voltage and the
current at arbitrarily determined intervals until the voltage
reaches the lower limit voltage.
[0034] The internal resistance estimator 15 computes the internal
resistance of the power storage device 2 based on the voltages and
currents at times when the resistance values of the
charge/discharge circuit 17 are mutually different, such as
immediately before and immediately after time T2, for example. The
internal resistance R.sub.B1 based on the voltage and the current
immediately before and immediately after time T2 is expressed as
R.sub.B1=|V.sub.11-V.sub.21|/|I.sub.11-I.sub.21|. Also, the
internal resistance R.sub.B2 based on the voltage and the current
immediately before and immediately after time T4 is expressed as
R.sub.B2=|V.sub.12-V.sub.22|/|I.sub.12-I.sub.12-I.sub.22|. Provided
that V.sub.1n is the voltage and I.sub.1n is the current
immediately before an arbitrary time at which the switches S1 and
S2 are switched, and V.sub.2n is the voltage and I.sub.2n is
current immediately after the arbitrary time, the internal
resistance R.sub.Bn based on the voltage and the current
immediately before and immediately after the arbitrary time is
expressed as R.sub.Bn=|V.sub.1n-V.sub.2n|/|I.sub.1n-I.sub.2n|.
[0035] FIGS. 3 and 4 are diagrams illustrating an example of
computing electric charge according to Embodiment 1. The electric
charge estimator 14 computes the electric charge by
time-integrating the current from time T1 when discharging started,
until time T2, for example. The electric charge Q.sub.1 computed
based on the current from time T1 to time T2 corresponds to the
area of the shaded part in FIG. 3. Also, the electric charge
estimator 14 computes the electric charge by time-integrating the
current from time T1 when discharging started, until time T4, for
example. The electric charge Q2 computed based on the current from
time T1 to time T4 corresponds to the area of the shaded part in
FIG. 4.
[0036] The electric charge estimator 14 associates the voltage
V.sub.11 immediately before time T2 with the electric charge
Q.sub.1 based on the current from time T1 to time T2, and
associates the voltage V.sub.12 immediately before time T4 with the
electric charge Q.sub.2 based on the current from time T1 to time
T4. The electric charge estimator 14 computes the electric charge
based on the current from the start time of discharging to an
arbitrarily determined time as discussed above, and computes the
relationship between the electric charge and the voltage. FIG. 5 is
a diagram illustrating an example of a relationship between
electric charge and the voltage of the power storage device, and
the relationship between electric charge and the internal
resistance, according to Embodiment 1. The solid-line graph in the
top part of FIG. 5 indicates the relationship between the electric
charge and the voltage. The electric charge estimator 14 computes a
relationship between electric charge and voltage like the
solid-line graph in the top part of FIG. 5, for example.
[0037] The electric charge based on the current from time T1 to
time T2 is Q.sub.1, and the electric charge based on the current
from time T1 to time T4 is Q.sub.2. Also, the internal resistance
based on the voltage and the current immediately before and
immediately after time T2 is R.sub.B1, and the internal resistance
based on the voltage and the current immediately before and
immediately after time T4 is R.sub.B2. Consequently, the
relationship between the internal resistance and the electric
charge is expressed like the bottom part of FIG. 5. If the internal
resistance estimator 15 conducts an interpolation process using as
a reference the internal resistance computed based on the voltage
and the current at predetermined timings, a relationship between
the electric charge and the internal resistance like the graph in
the bottom part of FIG. 5 is obtained, for example.
[0038] The electric energy estimator 16 computes the relationship
between the electric charge and the open voltage of the power
storage device 2 based on the relationship between the electric
charge and the voltage indicated by the solid line in the top part
of FIG. 5, the current, and the internal resistance. The open
voltage E.sub.1 of the power storage device 2 corresponding to the
electric charge Q.sub.1 is expressed as
E.sub.1=V.sub.11+I.sub.11R.sub.B1. Also, the open voltage E.sub.2
of the power storage device 2 corresponding to the electric charge
Q.sub.2 is expressed as E.sub.2=V.sub.12+I.sub.12R.sub.B2. Provided
that Q.sub.n, is the electric charge corresponding to the internal
resistance R.sub.Bn based on the voltage and the current
immediately before and immediately after an arbitrary time, the
open voltage E.sub.n of the power storage device 2 corresponding to
the electric charge Q.sub.n is expressed as
E.sub.n=V.sub.1n+I.sub.1nR.sub.Bn. The electric energy estimator 16
computes the open voltage with respect to the electric charge as
discussed above, and computes the relationship between the electric
charge and the open voltage of the power storage device 2 as
indicated by the dashed line in the top part of FIG. 5.
[0039] Based on the values computed as discussed above, the
electric energy estimator 16 estimates the electric energy of the
power storage device 2 based on usage conditions when the power
storage device 2 is used. Electric energy estimation is described
below. An example will be described for a case of discharging the
power storage device 2 from a state in which the voltage of the
power storage device 2 is the upper limit voltage until the voltage
reaches the lower limit voltage, while keeping the discharge
current at a constant value I. The electric energy estimator 16
acquires the discharge current value I, and acquires the upper
limit voltage V.sub.UL' and the lower limit voltage V.sub.LL' of
the power storage device 2 during discharging. FIG. 6 is a diagram
illustrating an example of estimating the electric energy of the
power storage device according to Embodiment 1. The dashed-line
graph indicates the relationship between the electric charge and
the open voltage of the power storage device 2. Provided that the
discharge current is I, since a voltage drop occurs, the voltage
V.sub.1 of the power storage device 2 corresponding to the electric
charge Q.sub.1 is expressed as V.sub.1=E.sub.1-IR.sub.B1. Also, the
voltage V.sub.2 of the power storage device 2 corresponding to the
electric charge Q.sub.2 is expressed as
V.sub.2=E.sub.2-IR.sub.B2.
[0040] The voltage of the power storage device 2 corresponding to
the electric charge is computed similarly. For example, the voltage
V.sub.n of the power storage device 2 corresponding to the electric
charge Q.sub.n is expressed as V.sub.n=E.sub.n-IR.sub.Bn. As
discussed above, the electric energy estimator 16 computes the
relationship between the electric charge and the voltage of the
power storage device 2 during discharging when the discharge
current is kept at a constant value I, based on the relationship
between the electric charge and the open voltage of the power
storage device 2, the internal resistance, and the discharge
current I. The voltage of the power storage device 2 during
discharging when the discharge current is kept at a constant value
I changes like in the graph illustrated by the solid line in FIG.
6. Within the range determined by the upper limit voltage V.sub.UL'
and the lower limit voltage V.sub.LL', the electric energy
estimator 16 integrates the voltage of the power storage device 2
during discharging when the discharge current is kept at a fixed
value I that corresponds to the electric charge, and estimates the
electric energy (units: Wh) of the power storage device 2. The
electric energy of the power storage device 2 corresponds to the
area of the shaded part in FIG. 6.
[0041] Note that when charging the voltage of the power storage
device 2, the electric energy estimator 16 may estimate the
electric energy of the power storage device 2 according to the
charging conditions, similarly to the example discussed above.
[0042] Provided that the charge current is I, since I is negative
value, the voltage V.sub.I of the power storage device 2
corresponding to the electric charge Q.sub.1 is expressed as
V.sub.1=E.sub.1+IR.sub.B1. Also, the voltage V.sub.2 of the power
storage device 2 corresponding to the electric charge Q.sub.2 is
expressed as V.sub.2=E.sub.2+IR.sub.B2. Note that the range of the
integral may also be determined based on the electric charge.
[0043] According to the apparatus for estimating power storage
device degradation 1 according to Embodiment 1, the relationship
between electric charge and the open voltage is computed based on
the voltage and the current measured by the voltage detector 11 and
the current detector 12, and the electric energy of the power
storage device 2 may be estimated for individual discharging or
charging conditions, excluding the effects of a voltage drop caused
by internal resistance. Consequently, it becomes possible to
improve the accuracy of estimating the electric energy of the power
storage device 2.
[0044] FIG. 7 is a flowchart illustrating an example of measurement
operations conducted by the apparatus for estimating power storage
device degradation according to Embodiment 1. An example will be
described for a case in which discharging starts in a state in
which the voltage of the power storage device 2 is equal to or
greater than the first threshold value, and discharging is
conducted until the voltage of the power storage device 2 becomes
less than or equal to the second threshold value. Starting from a
state in which the voltage of the power storage device 2 has
reached the upper limit voltage and the switches S1 and S2 are off,
the switch S1 is switched on, and discharging of the power storage
device 2 starts (step S110). The voltage detector 11 detects the
voltage of the power storage device 2, and the current detector 12
detects the current flowing through the power storage device 2
(step S120). While the voltage has not reached the lower limit
voltage (step S130; N), the processing of step S120 is
repeated.
[0045] When the voltage reaches the lower limit voltage (step S130;
Y), the internal resistance estimator 15 computes the internal
resistance of the power storage device 2 based on the voltages and
currents at times when the resistance values of the
charge/discharge circuit 17 are mutually different (step S140). The
electric charge estimator 14 computes the electric charge by
time-integrating the current from the start time of discharging to
an arbitrarily determined time, and computes the relationship
between the electric charge and the voltage (step S150). The
electric energy estimator 16 computes the relationship between the
electric charge and the open voltage of the power storage device 2
based on the relationship between the electric charge and the
voltage, the current, and the internal resistance (step S160).
After the processing of step S160 is completed, the apparatus for
estimating power storage device degradation 1 ends the measurement
process. The internal resistance computation processing of step
S140 and the electric charge computation processing of step S150
are executed in an arbitrary order, and may also be processed in
parallel.
[0046] FIG. 8 is a flowchart illustrating an example of electric
energy estimation operations conducted by the apparatus for
estimating power storage device degradation according to Embodiment
1. The electric energy estimator 16 acquires a charge/discharge
current, and acquires the upper limit voltage and the lower limit
voltage of the power storage device 2 during charging or
discharging (step S210). The electric energy estimator 16 computes
the relationship between the electric charge and the voltage of the
power storage device 2 during charging or discharging, based on the
relationship between the electric charge and the open voltage of
the power storage device 2, the internal resistance, and the
charge/discharge current (step S220). Within the range determined
by the upper limit voltage and the lower limit voltage, the
electric energy estimator 16 integrates the voltage of the power
storage device 2 during charging or discharging with respect to the
electric charge, and estimates the electric energy of the power
storage device 2 (step S230).
[0047] In the above example, the internal resistance and the
relationship between the electric charge and the open voltage are
computed based on the voltage and the current detected during
discharging of the power storage device 2, but the internal
resistance and the relationship between the electric charge and the
open voltage may also be computed based on the voltage and the
current detected during charging of the power storage device 2.
FIG. 9 is a block diagram illustrating a different example
configuration of the apparatus for estimating power storage device
degradation according to Embodiment 1. The power storage device 2
is charged by a charging apparatus 3. Operation of each component
of the apparatus for estimating power storage device degradation 1
illustrated in FIG. 9 is similar to that of the apparatus for
estimating power storage device degradation 1 illustrated in FIG.
1.
[0048] FIG. 10 is a diagram illustrating a different example of
changes in a current flowing through the power storage device and
in the voltage of the power storage device according to Embodiment
1. The top part illustrates the current, while the bottom part
illustrates the voltage. The horizontal axis is time, while the
vertical axis of the top part is current, and the vertical axis of
the bottom part is voltage. An example will be described for a case
in which charging starts in a state in which the voltage is less
than or equal to a third threshold value, and charging is conducted
until the voltage becomes equal to or greater than a fourth
threshold value. Note that the third threshold value and the fourth
threshold value may be arbitrarily determined. For example, a lower
limit voltage of the power storage device 2 is set to the third
threshold value, and an upper limit voltage of the power storage
device 2 is set to the fourth threshold value. Note that a charge
current is expressed as negative. As illustrated in FIG. 10, the
voltage changes from a lower limit voltage V.sub.LL to an upper
limit voltage V.sub.UL.
[0049] Starting from a state in which the voltage is the lower
limit voltage V.sub.LL and the switches S1 and S2 are off, at time
T1, the switch S1 is switched on, and charging of the power storage
device 2 starts. During the period from time T1 to time T2, the
current is -I.sub.11, and the voltage increases to V.sub.11 over
the period from time T1 to time T2. At time T2, the switch S2 is
additionally switched on, the current becomes -I.sub.21, and the
voltage becomes V.sub.21. During the period from time T2 to time
T3, the current is -I.sub.21, and the voltage increases over the
period from time T2 to time T3. At time T3, the switch S2 is
switched off, the current becomes -I.sub.12, and the voltage
decreases to approximately V.sub.21. During the period from time T3
to time T4, the current is -I.sub.12, and the voltage increases to
V.sub.12 over the period from time T3 to time T4. At time T4, the
switch S2 is switched on, the current becomes -I.sub.22, and the
voltage becomes V.sub.22. Starting from time T4, the voltage
detector 11 and the current detector 12 detect the voltage and the
current at arbitrarily determined intervals until the voltage
reaches the upper limit voltage.
[0050] Similarly to the discharging case discussed earlier, the
internal resistance estimator 15 computes the internal resistance
of the power storage device 2 based on the voltages and currents at
times when the resistance values of the charge/discharge circuit 17
are mutually different, such as immediately before and immediately
after time T2, for example, and the internal resistance estimator
15 computes the internal resistance of the power storage device 2
based on the voltage and the current immediately before and
immediately after time T4. The electric charge estimator 14
computes the electric charge by time-integrating the absolute value
of the current from time T1 when charging started, until time T2,
for example. Also, the electric charge estimator 14 computes the
electric charge by time-integrating the absolute value of the
current from time T1 when charging started, until time T4, for
example. Similarly to the discharging case discussed earlier, the
electric charge estimator 14 computes the relationship between the
electric charge and the voltage.
[0051] Similarly to the discharging case discussed earlier, the
electric energy estimator 16 computes the relationship between the
electric charge and the open voltage of the power storage device 2
based on the relationship between the electric charge and the
voltage, the current, and the internal resistance. Subsequently,
based on the computed values, the electric energy estimator 16
estimates the electric energy of the power storage device 2 based
on usage conditions when the power storage device 2 is used.
Similarly to the discharging case discussed earlier, the electric
energy of the power storage device 2 may also be estimated based on
values computed during charging of the power storage device 2.
[0052] As described above, according to the apparatus for
estimating power storage device degradation 1 in accordance with
Embodiment 1 of the present disclosure, it becomes possible to
improve the accuracy of estimating the electric energy of the power
storage device 2.
Embodiment 2
[0053] FIG. 11 is a block diagram illustrating an example
configuration of the apparatus for estimating power storage device
degradation according to Embodiment 2 of the present disclosure.
The apparatus for estimating power storage device degradation 1
according to Embodiment 2 is additionally provided with a
temperature detector 18, in addition to the configuration of the
apparatus for estimating power storage device degradation 1
according to Embodiment 1. Operations of the apparatus for
estimating power storage device degradation 1 that differ from
Embodiment 1 will be described.
[0054] The temperature detector 18 detects the surface temperature
of the power storage device 2, or estimates the internal
temperature of the power storage device 2, at arbitrarily
determined times. The temperature detector or temperature
estimation uses arbitrary technology of the related art. The
temperature detector 18 detects the surface temperature of the
power storage device 2 at times in conjunction with the computation
of the internal resistance, for example. When the voltage and the
current changes as in FIG. 2, the temperature detector 18 detects
the surface temperature of the power storage device 2 at time T2,
for example.
[0055] The internal resistance estimator 15 computes the internal
resistance similarly to Embodiment 1. The computation of the
internal resistance is conducted under conditions in which the
temperature differs, and the relationship between the temperature
detected by the temperature detector 18 and the internal resistance
is computed. FIG. 12 is a diagram illustrating an example of a
relationship between the temperature and internal resistance of the
power storage device according to Embodiment 2. The internal
resistance estimator 15 obtains the internal resistance at
respective temperatures, as indicated by the black circles in FIG.
12. The internal resistance estimator 15 interpolates the obtained
internal resistance values, and computes a relationship between
temperature and internal resistance as illustrated by the
solid-line graph in FIG. 12.
[0056] Alternatively, the internal resistance estimator 15 corrects
a predetermined relationship between temperature and internal
resistance based on the temperature detected by the temperature
detector 18 and the internal resistance computed similarly to
Embodiment 1. As illustrated by the dashed-line graph in FIG. 12,
the internal resistance estimator 15 stores a predetermined
relationship between temperature and internal resistance. Based on
the difference R.sub.D between the internal resistance computed
based on the voltage and the current when the temperature detected
by the temperature detector 18 is Th1, and an internal resistance
based on the predetermined relationship between temperature and
internal resistance, the internal resistance estimator 15 corrects
the predetermined relationship between temperature and internal
resistance, and obtains a relationship between temperature and
internal resistance as illustrated by the solid-line graph in FIG.
12.
[0057] Based on the values computed as discussed above, the
electric energy estimator 16 estimates the electric energy of the
power storage device 2 based on usage conditions when the power
storage device 2 is used. Electric energy estimation is described
below. The electric energy estimator 16 corrects the internal
resistance based on the temperature of the power storage device 2
when discharging or charging, and the computed relationship between
temperature and internal resistance, or the corrected relationship
between temperature and internal resistance. An example will be
described for a case of discharging the power storage device 2 from
a state in which the voltage of the power storage device 2 is the
upper limit voltage until the voltage reaches the lower limit
voltage, while keeping the discharge current at a constant value I.
Provided that Th2 is the temperature when discharging started, the
internal resistance is R.sub.B1', as indicated by the computed
relationship between temperature and internal resistance or the
corrected relationship between temperature and internal resistance
illustrated in FIG. 12.
[0058] FIG. 13 is a diagram illustrating an example of a
relationship between the electric charge and internal resistance
according to Embodiment 2. Based on the temperature Th2 when
discharging started and the computed relationship between
temperature and internal resistance or the corrected relationship
between temperature and internal resistance illustrated in FIG. 12,
the electric energy estimator 16 corrects the relationship between
the electric charge and the internal resistance indicated by the
dashed line in FIG. 13, and computes the relationship between the
electric charge and the internal resistance indicated by the solid
line in FIG. 13. Similarly to Embodiment 1, the electric energy
estimator 16 acquires the discharge current value I, and acquires
the upper limit voltage V.sub.UL'and the lower limit voltage
V.sub.LL' of the power storage device 2 during discharging.
Provided that the discharge current is I, since a voltage drop
occurs, the voltage V.sub.I of the power storage device 2
corresponding to the electric charge Q.sub.1 is expressed as
V.sub.1=E.sub.1-IR.sub.B1'. Also, the voltage V.sub.2 of the power
storage device 2 corresponding to the electric charge Q.sub.2 is
expressed as V.sub.2=E.sub.2-IR.sub.B2'. As illustrated in FIG. 13,
R.sub.B1' and R.sub.B2' are the internal resistance corrected based
on the temperature when discharging started. Note that the
temperature is not limited to the temperature when discharging
started, and the relationship between the electric charge and the
internal resistance may also be corrected based on the temperature
after an arbitrarily determined fixed time elapses since the start
of discharging, or an average value of the temperature over a fixed
time since the start of discharging.
[0059] As discussed above, the electric energy estimator 16
computes the relationship between the electric charge and the
voltage of the power storage device 2 during discharging when the
discharge current is kept at a constant value I, based on the
relationship between the electric charge and the open voltage of
the power storage device 2, the internal resistance corrected based
on the temperature when discharging started, and the discharge
current I. Similarly to Embodiment 1, within the range determined
by the upper limit voltage V.sub.UL' and the lower limit voltage
V.sub.LL', the electric energy estimator 16 integrates the voltage
of the power storage device 2 during discharging when the discharge
current is kept at a fixed value I that corresponds to the electric
charge, and estimates the electric energy of the power storage
device 2.
[0060] Note that when charging the voltage of the power storage
device 2, the electric energy estimator 16 may estimate the
electric energy of the power storage device 2 according to the
charging conditions, similarly to the example discussed above.
According to the apparatus for estimating power storage device
degradation 1 in accordance with Embodiment 2, the relationship
between electric charge and open voltage is computed based on the
voltage and the current measured by the voltage detector 11 and the
current detector 12, and the electric energy of the power storage
device 2 may be estimated for individual discharging or charging
conditions, excluding the effects of a voltage drop caused by
internal resistance that varies according to the temperature of the
power storage device 2. Consequently, it becomes possible to
improve the accuracy of estimating the electric energy of the power
storage device 2.
[0061] FIG. 14 is a flowchart illustrating an example of
measurement operations conducted by the apparatus for estimating
degradation in the power storage device according to Embodiment 2.
Steps S110 to S160 are similar to the processing of steps S110 to
S160 conducted by the apparatus for estimating power storage device
degradation 1 according to Embodiment 1 illustrated in FIG. 7. The
internal resistance estimator 15 computes a relationship between
the temperature detected by the temperature detector 18 and the
internal resistance computed similarly to Embodiment 1, or
alternatively, corrects a predetermined relationship between
temperature and internal resistance based on the temperature
detected by the temperature detector 18 and the internal resistance
computed similarly to Embodiment 1 (step S170).
[0062] FIG. 15 is a flowchart illustrating an example of electric
energy estimation operations conducted by the apparatus for
estimating degradation in the power storage device according to
Embodiment 2. The electric energy estimator 16 corrects the
relationship between the electric charge and the internal
resistance based on the temperature when discharging started, and
the computed relationship between temperature and internal
resistance or the corrected relationship between temperature and
internal resistance (step S201). The processing of step S210 is
similar to the operations conducted by the apparatus for estimating
power storage device degradation 1 according to Embodiment 1
illustrated in FIG. 8. The electric energy estimator 16 computes
the relationship between the electric charge and the voltage of the
power storage device 2 during charging or discharging, based on the
relationship between the electric charge and the open voltage of
the power storage device 2, the internal resistance corrected based
on the temperature when discharging started, and the
charge/discharge current (step S221). The processing of step S230
is similar to the operations conducted by the apparatus for
estimating power storage device degradation 1 according to
Embodiment 1 illustrated in FIG. 8.
[0063] As described above, according to the apparatus for
estimating power storage device degradation 1 in accordance with
Embodiment 2 of the present disclosure, it becomes possible to
improve the accuracy of estimating the electric energy of the power
storage device 2.
[0064] An embodiment of the present disclosure is not limited to
the foregoing embodiments. The configuration of the
charge/discharge circuit 17 is not limited to the configuration of
FIG. 1, and an arbitrary circuit able to modify the resistance
value of the charge/discharge circuit 17 may be used. The
resistance values of the resistors R1 and R2 are arbitrary values
determined in conjunction with the scale of the power storage
device 2. The power storage device 2 is provided with a single cell
or multiple cells. Also, the switching times and sequence of the
switches S1 and S2 are arbitrary, and not limited to the foregoing
embodiments.
[0065] In the foregoing embodiments, the electric charge estimator
14 uses Ah as the units of electric charge, but the units of
electric charge are not limited to Ah, and a unit matched to the
charge/discharge rate of the power storage device 2 may be used.
For example, if the internal resistance of the power storage device
2 is extremely small and the charge/discharge rate is comparatively
high, a measurement time of several hours is not required, and thus
As or Amin may be used. The circuit selector 13 may also be
configured to switch the switches S1 and S2 at times when the
electric charge computed by the electric charge estimator 14
reaches an arbitrarily determined threshold value.
[0066] If the power storage device 2 drives a vehicle an electric
railcar, an automobile, or the like, the electric energy of the
power storage device 2 may be computed daily by utilizing a parked
time of several hours at night, for example. Consequently, the
daily degree of degradation in the power storage device 2 may be
assessed accurately.
[0067] In the foregoing embodiments, various modifications are
possible within the scope of the spirit of the present disclosure.
The foregoing embodiments are for the purpose of describing the
present disclosure, and are not intended to limit the scope of the
present disclosure. The scope of the present disclosure is
indicated by the attached claims rather than the embodiments.
Various modifications made within the scope of the claims and their
equivalents are to be included in the scope of the present
disclosure.
INDUSTRIAL APPLICABILITY
[0068] The present disclosure may be suitably adopted in an
apparatus for estimating power storage device degradation, which
estimates the electric energy of a power storage device.
REFERENCE SIGNS LIST
[0069] 1 apparatus for estimating power storage device
degradation
[0070] 2 power storage device
[0071] 3 charging apparatus
[0072] 11 voltage detector
[0073] 12 current detector
[0074] 13 circuit selector
[0075] 14 electric charge estimator
[0076] 15 internal resistance estimator
[0077] 16 electric energy estimator
[0078] 17 charge/discharge circuit
[0079] 18 temperature detector
[0080] R1, R2 resistor
[0081] S1, S2 switch
* * * * *