STATE EVALUATION APPARATUS OF SECONDARY BATTERY, STATE EVALUATION
METHOD OF SECONDARY BATTERY, AND COMPUTER-READABLE MEDIUM
STORING STATE EVALUATION PROGRAM OF SECONDARY BATTERY
FIELD
The embodiment discussed herein is related to a state evaluation apparatus
of a secondary battery, a state evaluation method of the secondary battery, and
computer-readable medium storing a state evaluation program of the secondary
battery.
BACKGROUND
A lot of technologies have been proposed in which a state of health (SOH)
that indicates evaluation of a state of a secondary battery (hereinafter referred to
as battery state) is estimated on the basis of a change in characteristics
(voltage, current, and temperature) of the battery (for example, see Japanese
Patent No. 4009537 and Japanese Patent No. 4548011). In the calculation of
the battery state, the temperature of the battery is an important parameter. In
these technologies, for example, temperature that is directly measured using a
thermometer, or the like that is installed outside the battery is used.
SUMMARY
The external temperature that is measured by the thermometer that is
installed outside the battery becomes an indication of the battery state.
However, in an electric vehicle, current that flows through the battery changes
rapidly in a short space of a time. In such an environment, in view of a heat
capacity of a material that constitutes the battery and a distance between the
inside and outside of the battery, a temperature change in an electrode portion
that includes an active material inside the battery is barely reflected in a
measurement value of the thermometer that is installed outside the battery.
Therefore, the battery state is calculated on the basis of the external temperature
of the battery, so that accuracy of the battery state is reduced.

Therefore, in the calculation of the battery state, it is desirable that
temperature of a portion inside the battery, in which actual deterioration occurs
(in particular, an electrode portion including the active material) is used. It is
desirable that the temperature of the portion inside the battery is directly
measured. However, in view of a structure, a technology, and cost of the battery,
it is not easy to install the thermometer (sensor) inside the battery and measure
the temperature inside the battery directly.
It is an object of the present embodiment to provide a state evaluation
apparatus of a secondary battery, which highly accurately calculates a battery
state of the secondary battery, a state evaluation method of the secondary
battery, and computer-readable medium storing a state evaluation program of
the secondary battery.
According to a first aspect of the embodiment, a state evaluation apparatus
of a secondary battery, the state evaluation apparatus includes at least one
processor configured to perform a process including calculating internal
resistance based on a measured voltage value and current value of the secondary
battery and calculating internal temperature of the secondary battery based on
the current value, the internal resistance, and measured external temperature of
the secondary battery and obtaining an amount of charge and discharge electric
charge of the secondary battery based on the current value, or obtaining a
charge state that indicates a charging rate of the secondary battery based on the
current value and the voltage value, and calculating a battery state that indicates
a state after deterioration of the secondary battery, based on the internal
temperature and at least one of the amount of charge and discharge electric
charge and the charge state.
BRIEF DESCRIPTION OF DRAWINGS
Fig. 1 is a diagram illustrating an example of a configuration of a state
evaluation apparatus 10 of a secondary battery according to an embodiment.
Fig. 2 is a diagram illustrating an example of the further detailed
configuration of the state evaluation apparatus 10 of the secondary battery

according to the embodiment.
Fig. 3 is a diagram illustrating the overview of the calculation process of the
battery state of the secondary battery in the calculation device 6-5 according to
the embodiment.
Fig. 4 is a diagram to explain the measurement interval of the current value,
the voltage value, and the surface temperature, and the calculation timing of the
internal temperature and the battery state in the embodiment.
Fig. 5 is a flowchart illustrating the calculation process of the battery state of
the secondary battery according to the embodiment.
Fig. 6 is a diagram to explain a calculation example of the internal resistance
in the embodiment.
Fig. 7 is a diagram to explain change in internal temperature based on a
temperature difference between the inside and outside of the secondary battery,
which the heat transfer is considered.
Fig. 8 is a diagram illustrating an example of the effect of SOC, which is given
to neglected deterioration.
DESCRIPTION OF EMBODIMENTS
The embodiments of the present invention are described below with
reference to the accompanying drawings. Here, it is intended that the technical
scope of the present invention is not limited to the embodiments but can cover
items described in the scope of claims and their equivalents.
Configuration of a State Evaluation Apparatus of a Secondary Battery
Fig. 1 is a diagram illustrating an example of a configuration of a state
evaluation apparatus 10 of a secondary battery according to an embodiment. In
Fig. 1, the state evaluation apparatus 10 of the secondary battery includes, for
example, a measurement device 6-4, a storage device 6-6, a calculation device
6-5, and an external input/output device 6-7. The measurement device 6-4 is a
device that measures a usage state and an environment parameter of a
secondary battery LB. The measured information is stored in the storage device
6-6. In addition, the calculation device 6-5 calculates a battery state of each of

the secondary batteries LB on the basis of the measurement value that is stored
the storage device 6-6. The calculated battery state is output, for example, to
an external device 6-8 through the external input/output device 6-7.
The secondary battery LB according to the embodiment is a rechargeable
battery and a repeatedly usable battery. As an example of the secondary
battery LB, there is a lithium ion the secondary battery. In addition, the battery
state in the embodiment is in a state after deterioration, and in the embodiment,
a state of an amount of electric charge that can be stored in the secondary
battery LB (hereinafter referred to as storage enabled electric charge amount) is
described. In the embodiment, the battery state is indicated, for example, by a
ratio of a storage enabled electric charge amount at present time to an initial
storage enabled electric charge amount.
Detailed Configuration of the State Evaluation Apparatus of the Secondary
Battery
Fig. 2 is a diagram illustrating an example of the further detailed
configuration of the state evaluation apparatus 10 of the secondary battery
according to the embodiment. The measurement device 6-4 measures a
voltage value, a current value, and an external temperature as a usage state and
an environment parameter of the secondary battery LB, and stores the values
and temperature in the storage device 6-6.
A voltmeter or a voltage sensor 6-1 is provided in order to allow the voltage
value of the secondary battery LB to be measured. In addition, when all of the
secondary batteries LB are connected to each other in series, an ammeter or a
current sensor 6-2 is provided on a current line that connects the batteries. In
addition, the current value of the secondary battery LB is measured by the
current sensor 6-2. On the other hand, when all of the secondary batteries LB
are connected to each other in parallel, a current value of the corresponding
secondary battery LB is measured by the ammeter or the current sensor 6-2 that
is provided for each parallel current line.
In addition, the external temperature is measured, for example, by providing
a thermometer or a temperature sensor 6-3 on the surface of the secondary

battery LB. In the embodiment, the external temperature indicates temperature
of the surface of the secondary battery LB or temperature in the vicinity of the
surface. In order to reduce an error in calculation of internal temperature,
which is described later, it is desirable that temperature of the surface of the
secondary battery LB is measured as the external temperature.
Generally, the measurement sensor outputs an analog signal. Therefore,
the measurement device 6-4 converts the output analog signal into a digital
signal by digital signal processing, or the like, and outputs the digital signal to the
calculation device 6-5. In addition, the digital signal is stored in the storage
device 6-6. The calculation device 6-5 performs various pieces of calculation on
the basis of the digital signal, and calculates a battery state of the secondary
battery LB.
The storage device 6-6 stores, for example, a program that is used to
execute the various pieces of calculation that is executed by the calculation
device 6-5, calculation result data, and the like in addition to digital signals of the
measured usage state and environment parameter. In addition, the external
input/output device 6-7 outputs, for example, the usage state, the environment
parameter, the calculation result data, and the like to the external device 6-8 and
obtains an instruction, data, and the like from the external device 6-8.
It is noted that the calculation device 6-5 may be connected to the storage
device 6-6 through a wire, and may be connected to the storage device 6-6
through radio. In addition, the calculation device 6-5 may be connected to a
storage device 6-9 in the external device 6-8 through the external input/output
device 6-7. It is noted that, for each of the devices in the state evaluation
apparatus 10 of Fig. 2, two or more may be provided depending on the type of
calculation, or the like.
The overview of a calculation process of the battery state in the embodiment
is described below with reference to the drawings.
Overview of the Calculation Process of the Battery State
Fig. 3 is a diagram illustrating the overview of the calculation process of the
battery state of the secondary battery in the calculation device 6-5 according to

the embodiment. First, an internal resistance calculation unit 51 of the
calculation device 6-5 calculates internal resistance on the basis of the current
value and voltage value of the secondary battery, which are measured by the
measurement device 6-4. In addition, a battery internal temperature calculation
unit 52 calculates internal temperature to be estimated in the secondary battery,
on the basis of the calculated internal resistance and the current value and
surface temperature that are measured by the measurement device 6-4. In the
embodiment, the internal temperature indicates temperature of one of or
combination of an active material in a positive electrode and a negative electrode
of the secondary battery, and an electrolyte of the secondary battery.
The internal temperature that is calculated by the battery internal
temperature calculation unit 52 is used to calculate the battery state of the
secondary battery. In the embodiment, the battery state of the secondary
battery is calculated, for example, on the basis of neglected deterioration and
charge and discharge cycle deterioration. Therefore, an SOC calculation unit 53
calculates a charge state that indicates a charging rate of the secondary battery
(state of charge, hereinafter referred to as SOC). In addition, a deterioration
amount calculation unit 55 calculates a degree of neglected deterioration on the
basis of the internal temperature and the SOC. Alternatively, an amount of
charge and discharge electric charge calculation unit 54 calculates an electric
charge amount that is associated with charge and discharge of the secondary
battery (hereinafter referred to as the amount of charge and discharge electric
charge). In addition, the deterioration amount calculation unit 55 calculates a
degree of cycle deterioration on the basis of the internal temperature and the
amount of charge and discharge electric charge. A battery state calculation unit
56 calculates a battery state on the basis of the degree of neglected deterioration
and the degree of cycle deterioration.
However, the battery state calculation unit 56 may calculate the battery state
on the basis of one of the degree of neglected deterioration and the degree of
cycle deterioration. In this case, one of the SOC or the amount of charge and
discharge electric charge is calculated. However, the SOC calculation unit 53

may calculate the amount of charge and discharge electric charge in order to
calculate the SOC independently of the amount of charge and discharge electric
charge calculation unit 54. As described above, in the state evaluation
apparatus 10 according to the embodiment, the internal temperature of the
secondary battery is calculated. In addition, the state evaluation apparatus 10
highly accurately calculates a battery state using the calculated internal
temperature and the SOC or the amount of charge and discharge electric charge.
Measurement Interval and Calculation Timing
Here, an interval in which a current value, a voltage value, and surface
temperature are measured, and timing at which internal temperature and a
battery state of the secondary battery are calculated in the embodiment are
described.
Fig. 4 is a diagram to explain the measurement interval of the current value,
the voltage value, and the surface temperature, and the calculation timing of the
internal temperature and the battery state in the embodiment. In the
embodiment, the current value, the voltage value, and the surface temperature
are measured for each time period "t". In addition, the calculation device 6-5
can calculate the internal temperature and the battery state on the basis of the
measurement data for each of the time periods "t". In addition, in the
embodiment, "n" indicates a measurement round that is a target, and "n-1"
indicates a measurement round at a previous time. In addition, "α" indicates a
calculation round in which the battery state is calculated at the previous time
(calculation round "n-1" at the previous time of the battery state), "b" indicates a
calculation round "n" that is a calculation target of the battery state. For
example, the battery state in the calculation round "b" is calculated on the basis
of the SOC and the amount of charge and discharge electric charge in a time
period "tx" from the calculation round "α" to the calculation round "b".
In addition, the time period "t" that indicates a measurement interval can be
set at a value by which current change can be appropriately grasped. When the
secondary battery is mounted on an electric vehicle, for example, the time period
"t" is set at a range from one millisecond to 10 seconds. This is why current that

flows through the battery changes rapidly in a short space of a time. On the
other hand, when the secondary battery is mounted on a machine in which
current changes gradually, the time period "t" may be set, for example, at 10
seconds or more. In addition, as the time period "t" becomes short, an amount
of the measurement data increases. Therefore, the time period "t" may be set
on the basis of a balance with the data amount.
It is noted that the calculation of the battery state may not always be
performed for each of the time periods "t". For example, the internal
temperature is calculated for each of the time periods "t", and the battery state
may be calculated not for each of the time periods "t" but at timing of the
calculation round "b" after the calculation round "α" at the previous time through
the plurality of time periods "t".
The calculation process of the battery state of the secondary battery is
described in detail below.
Detailed Calculation Process of the Battery State
Fig. 5 is a flowchart illustrating the calculation process of the battery state of
the secondary battery according to the embodiment. Here, an electric charge
amount calculation step (S14) and an SOC calculation step (S15) may be
executed prior to an internal resistance calculation step (S12) and may be
executed between the internal resistance calculation step (S12) and a
temperature estimation step (S13). It is noted that, in this example, a case is
described in which a calculation process of the battery state of the single
secondary battery is executed. When the battery states of the plurality of
secondary batteries are calculated, for example, the state evaluation apparatus
10 may executes the calculation process of the battery state by a plurality rounds,
or the plurality of state evaluation apparatuses 10 may execute the calculation
process of the battery state in parallel.
In addition, a case is exemplified in which the calculation processes in the
steps in Fig. 5 are executed in the single calculation device 6-5 of the state
evaluation apparatus 10 according to the embodiment. However, the
embodiment is not limited to such a case. The calculation processes in the steps

may be executed in different calculation devices, and the calculation process in
the single step may be executed by a plurality of calculation devices.
First, a voltage value, a current value, and surface temperature of the
secondary battery are measured (S11). The measured values are converted
into digital signals by an A/D conversion unit and stored in the storage device 6-6.
After that, the calculation device 6-5 calculates internal resistance of the battery
(S12).
Calculation of the Internal Resistance
In the embodiment, the internal resistance is calculated, for example, on the
basis of the measured voltage value and current value. In particular, in the
embodiment, the internal resistance is calculated on the basis of information on a
plurality of sets of the measured voltage value and current value that are
measured for the single secondary battery. When the internal resistance is
calculated at the time of the measurement round "n", sets for the appropriate
number of rounds of the previous measurement rounds (n-1 round, n-2 round,
...) are selected for the measurement round "n". On the other hand, when the
internal resistance at the time of the measurement round "n" is calculated after
repeating the measurement as time goes on after the measurement round "n",
sets for the appropriate number of measurement rounds from the past to the
future (..., round "n-2", round "n-1", round "n", round "n+1", round "n+2",...)
using the measurement round "n" as a reference can be selected. The number
of sets is determined depending on the number of sets that can be used at the
time of the calculation, calculation accuracy of the internal resistance, and a time
that is desired for the calculation. The calculated internal resistance is stored in
the storage device 6-6 and read by a subsequent calculation process.
In addition, need for the execution of internal resistance calculation may be
determined on the basis of the SOC at that time. For example, when the SOC is
small, it is probable that the calculated internal resistance has an error.
Therefore, for example, when the SOC is small, it is determined that the
calculation process of the internal resistance is not executed in order to avoid an
error. In this case, for example, any of values of the internal resistance that has

been calculated in the past is diverted or a value that is obtained on the basis of
an equation using a plurality of pieces of internal resistance that have been
calculated before is applied.
Fig. 6 is a diagram to explain a calculation example of the internal resistance
in the embodiment. In Fig. 6, the vertical axis indicates voltage, and the
horizontal axis indicates current. In Fig. 6, in order to calculate the internal
resistance of the secondary battery that is a target, the appropriate number of
sets of a voltage value and a current value is plotted. A straight line LR in Fig. 6
is an approximation straight line that is calculated on the basis of a
correspondence relationship of the plotted voltage values and current values. In
this example, the slope of the straight line LR indicates a value of the internal
resistance. The straight line LR is obtained, for example, by performing straight
line approximation by a data analysis method such as a least square method.
In the embodiment, for example, a calculation program that is used to obtain
the slope of approximation straight line on the basis of the sets of the voltage
values and current values is stored in the storage device 6-6 beforehand. In
addition, the calculation device 6-5 reads the information on the plurality of sets
of voltage values and current values and calculates the calculated slope of
approximation straight line as the internal resistance in accordance with the
calculation program. It is noted that the calculation program may be read out,
for example, from the external device 6-8 through the external input/output
device 6-7.
It is noted that a method of obtaining the internal resistance is not limited to
such a case. For example, the internal resistance may be obtained on the basis
of a plurality of voltage values that are obtained by causing pulsed short time
current that has a plurality of given current amounts to flow. In addition, the
plurality of different methods of calculating the internal resistance may be used
so as to be switched by the SOC at that time.
Calculation of the Internal Temperature
Returning to the flowchart of Fig. 5, the calculation device 6-5 calculates the
internal temperature in the secondary battery on the basis of the internal

resistance that is calculated in the step S12, the current value, and the surface
temperature of the secondary battery (S13). In the embodiment, the
calculation device 6-5 calculates the internal temperature of the secondary
battery on the basis of internal temperature change (heat generation
temperature) based on a heat amount in accordance with the measured current
value and internal temperature change (heat transfer temperature) based on
heat transfer due to a temperature difference between the inside and outside of
the battery. First, a calculation process of internal temperature change based
on a heat amount in accordance with the current value is described.
Calculation of the Internal Temperature Change Based on Heat Amount
First, the calculation device 6-5 calculates heat generation temperature on
the basis of the measured current value and the calculated internal resistance
(S131). The following equation 1 is a common equation that is used to calculate
Joule heat E (heat amount) depending on current. As represented in the
equation 1, the Joule heat E is a heat amount when a current value I flows
through an object of electrical resistance R, and is obtained by multiplying the
square of the current value I by the internal resistance R.
E =R*I2 (equation 1)
Therefore, the calculation device 6-5 calculates internal temperature change
based on a heat amount depending on the current value as heat generation
temperature, on the basis of the following equation 2. The left side of the
equation "ΔTHn-1□n" in the equation 2 represents internal temperature change
that is obtained on the basis of a heat amount that is generated in the time period
"t" from the measurement round "n-1" to the measurement round "n". In
addition, in the equation 2, "Rin-1" is internal resistance that is calculated on the
basis of measurement data of the measurement round "n-1" at the previous time,
and "Rin" is internal resistance that is calculated on the basis of measurement
data of the measurement round "n" at this time. Therefore, "{(Rin-i+Rin)/2}"
represents an average value of the internal resistance in the time period "t" at the
measurement round "n-1" and the measurement round "n". Similarly,
"{(In-1+In)/2}" represents an average value of current in the time period "t".

ΔTHn-1□n=α*{(Rin-1+Rin)/2}*{(In-1+In)/2}2*t (equation 2)
As described above, in the embodiment, the average value of values of the
measurement round "n-1" and the measurement round "n" is used for the
calculation process as a value in the time period "t" at the measurement round
"n". As described above, by using the average value in the period "t" even when
there is large variation in each of the values, an appropriate value for which the
variation amount is considered is used for the calculation. As a result, accuracy
of the calculated internal temperature and battery state becomes high. However,
the embodiment is not limited to such a case, and the values of the measurement
round "n-1" or the measurement round "n" may be directly used as a value in the
time period "t", depending on circumstances.
In the equation 2, the equation 1 is further multiplied by the time period "t"
and a coefficient "α". By multiplying the equation 1 by the time period "t", the
Joule heat is converted into a heat amount when current {(In-i+In)/2} flows
during the time period "t". In addition, the coefficient "α" is a value that is used
to convert a heat amount into temperature, and a value that reflects a heat
characteristic such as a heat capacity of the secondary battery. By multiplying
the heat amount by the coefficient "α", temperature that rises in accordance with
the heat amount when the current "{(In-1+In)/2}" temperature flows during the
time period "t", that is, internal temperature change is calculated.
It is noted that the coefficients "α" are different depending on a material and
a configuration of the secondary battery. Therefore, the coefficient "α" is a
value that is set on the basis of an experimental value beforehand. In addition,
in the secondary battery, an individual difference between characteristics occurs
depending on variation of the material and the manufacturing process.
Therefore, it is desirable that the coefficient "α" is further adjusted in accordance
with the individual difference. By setting the coefficient "α" at an appropriate
value, accuracy of the calculated internal temperature change is improved. This
means that accuracy of the battery state of the secondary battery, which is
calculated on the basis of the internal temperature is also improved.
In particular, when the secondary battery state that is calculated by the state

evaluation apparatus 10 according to the embodiment is different from a battery
state that is obtained by electrical measurement (charge and discharge
characteristic evaluation, terminal open voltage measurement, or the like)
(hereinafter, referred to as a measured battery state), it is indicated that one of
the factors is that the coefficient "α" is not set at the appropriate value. In
particular, for example, when the calculated battery state change is smaller than
an actual battery state change, it is indicated that one of the factors is that the
temperature change based on the heat amount is underestimated. This
indicates that, for example, the value of the coefficient "α" is smaller than the
appropriate value.
As described above, in a step S131, the internal temperature change
ΔTH n-1□ n based on the heat amount, that is, internal elevated temperature due to
heat is calculated. After that, secondly, the calculation device 6-5 calculates
internal temperature change based on heat transfer due to a temperature
difference between the inside and outside of the secondary battery (S132).
Calculation of the Internal Temperature Change Based on Heat Transfer due
to a Temperature Difference between the Inside and Outside of the Secondary
Battery
The following equation 3 is an equation that is used to calculate internal
temperature change based on heat transfer due to the temperature difference
between the inside and outside of the secondary battery. The left side of the
equation "ΔTTn-1□ n" in the equation 3 represents internal temperature change
based on heat transfer in the time period "t" from the measurement round "n-1"
to the measurement round "n". When the internal temperature of the battery is
higher than the surface temperature, the heat transfer from the inside to the
outside of the battery occurs. Therefore, the internal temperature change
"ΔTTn-1□ n" becomes a negative value. On the other hand, when the surface
temperature of the battery is higher than the internal temperature of the battery,
the heat transfer from the outside to the inside of the battery occurs. Therefore,
the internal temperature change "ΔTTn-1□ n" becomes a positive value. In the
equation 3, "{(Tsn-1+Tsn)/2}" is the average surface temperature in the time

period "t", and Tn-1 is the internal temperature that is calculated at the previous
time by the state evaluation apparatus 10 according to the embodiment.
ΔTTn-1□ n={(TSn-1+TSn)/2}-{(TSn-1+TSn)/2-(Tn-1+ΔTHn-1□ n/2)}*exp(-βt)-Tn-1
(equation 3)
First, the portion calculation formula
,,{(TSn-1+TSn)/2-(Tn-1+ΔTHn-1□ n/2)}*exp(-βt)" in the equation 3 is described.
The portion calculation formula is a temperature difference between the surface
temperature of the secondary battery and the internal temperature in which the
temperature change based on the heat amount is considered, and indicates a
temperature difference in which the heat transfer is considered. "ΔTHn-1□ n" in
the portion calculation formula represents internal temperature change based on
the heat amount depending on the current that is calculated in accordance with
the above-described equation 2, and "ΔTHn-1□ n/2" represents average internal
temperature change in the time period "t". By adding the internal temperature
change ΔTHn-1□ n/2 based on the heat amount in the time period "t" to the internal
temperature Tn-1 that is calculated at the previous time, internal temperature in
which the temperature change based on the heat amount is considered is
calculated.
Therefore, "{(Tsn-1+TSn)/2-(Tn-1+ΔTHn-1□ n/2)}" that is a part of the portion
calculation formula represents a temperature difference between the surface
temperature and the internal temperature in which the temperature change
based on the heat amount is considered. When the temperature difference is a
negative value, it is indicated the heated internal temperature is higher than the
surface temperature. On the other hand, when the temperature difference is a
positive value, it is indicated that the surface temperature is higher than the
heated internal temperature. This indicates, for example, a case in which the
secondary battery is provided in a high temperature environment.
In addition, by multiplying such a temperature difference
"{(TSn-1+TSn)/2-(T=+ΔTTn-1□ n/2)}" by "exp(-βt)", temperature difference in
which the heat transfer is considered is calculated. The temperature difference
between the inside and outside of the secondary battery has a characteristic in

which the temperature difference exponentially decreases using a Napier's
constant as a base for the time period "t". When the internal temperature is
higher than the surface temperature of the battery, heat amount that occurs
inside the battery due to the current is transferred to the outside of the battery.
The internal temperature is reduced due to the heat transfer from the inside to
the outside of the battery, and the temperature difference between the inside and
outside of the battery exponentially decreases. That is, the temperature
difference becomes zero ultimately, and the internal temperature becomes the
same as the surface temperature. However, in the surface temperature at that
time, surface temperature change in the time period "t" is considered, and
"(Tsn-1+TSn)/2" is obtained. As described above, by multiplying the temperature
difference by "exp(-βt)", a temperature difference in which a change
characteristic of the heat transfer based on the time period "t" is reflected is
calculated.
A coefficient "β" is a coefficient that indicates a moving speed of a heat
amount in which a heat characteristic such as a heat capacity of the battery is
reflected. The coefficient "β" is set by an experimental value beforehand. In
addition, because an individual difference between characteristics occurs
depending on variation of the material and the manufacturing process, it is
desirable that the coefficient "β" is adjusted in accordance with the individual
difference. In addition, similar to the coefficient "α", by setting the coefficient
"β" appropriately, accuracy of calculated internal temperature change is improved.
Therefore, accuracy of a battery state of the secondary battery, which is
calculated on the basis of the internal temperature, is also improved.
When the battery state that is calculated in the state evaluation apparatus 10
and the actual battery state are different in the embodiment, it is indicated that
one of the factors is that the coefficient "β" is not set at an appropriate value.
For example, when the calculated battery state change is smaller than the actual
battery state change, temperature reduction due to heat transfer is
overestimated. This indicates the value of the coefficient "β" is larger than the
appropriate value.

As described above, by the portion calculation formula
"{(Tsn-1+TSn)/2-(Tn-1+ΔTHn-1□n/2)}*exp(-βt)" in the equation 3, a temperature
difference between the surface temperature and the internal temperature, in
which the temperature change based on the heat amount is considered, that is, a
temperature difference in which the heat transfer is considered is calculated.
When the internal temperature is higher than the external temperature in the
secondary battery, the calculated temperature difference becomes a negative
value, and when the internal temperature is lower than the external temperature
in the secondary battery, the calculated temperature difference becomes a
positive value. In addition, in the equation 3, by further subtracting the
calculated temperature difference from the surface temperature {(Tsn-i+Tsn)/2},
internal temperature based on the temperature difference between the inside
and outside of the secondary battery, in which the heat transfer is considered is
calculated.
Fig. 7 is a diagram to explain change in internal temperature based on a
temperature difference between the inside and outside of the secondary battery,
which the heat transfer is considered. In Fig. 7, the horizontal axis indicates the
time period "t", and the vertical axis indicates internal temperature. In addition,
a curve LT indicates internal temperature that is calculated by the calculation
formula "{(Tsn-1+TSn)/2}-{(TSn-1+Tsn)/2-(Tn-1+ΔTHn-1□n/2}*exp(-βt)". In this
example, a case is described in which the internal temperature of the secondary
battery is higher than the external surface temperature. Therefore, as
illustrated in the curve LT in Fig. 7, the internal temperature is reduced as the
time period "t" becomes long because the battery internal temperature is
transferred to the outside. In addition, as described above, the temperature
difference between the inside and outside of the battery exponentially decreases
as time continues.
For example, when it is assumed that "time period t=0" is set, "exp(-(3t)=l"
is obtained, so that the internal temperature in Fig. 7 becomes
"(Tn-1+ΔTHn-1□n/2)". That is, the internal temperature when the time period "t"
does not elapses at all is apparently regarded as temperature that is obtained by

adding the elevated temperature "ΔTHn-1□n/2" based on the heat amount to the
internal temperature "Tn-1" at the previous time. This is why the rise of the
internal temperature by "ΔTHn-1□n" during the time period "t" is considered. On
the other hand, for example, when "time period t=oo" is set, "exp(-(βt)=0" is
obtained, so that the internal temperature that is the calculation result becomes
"{(Tsn-i+Tsn)/2}". This indicates that the internal temperature is apparently
intended to be close to the external temperature "{(TSn-1+Tsn)/2}" as the time
period "t" becomes long. This is why change of the surface temperature from
"Tsn-1" to "Tsn" during the time period "t" is considered.
In addition, in the equation 3, the internal temperature "Tn-i" at the previous
time is further subtracted from the internal temperature that is calculated by the
calculation formula ,,{(TSn-1+TSn)/2}-{(TSn-1+Tsn)/2-(Tn-1+ΔTHn-1□n/2)}*exp(-(βt),,
that is represented by the curve LT in Fig. 7. As a result, temperature change
"ΔTTn-1□n" from the previous time of the internal temperature based on the
temperature difference between the surface temperature and the internal
temperature in which the temperature change based on the heat amount is
considered, that is, the temperature difference in which the heat transfer is
considered. As described above, internal temperature change based on the
heat transfer between the inside and outside of the secondary battery is
calculated.
Addition of the Internal Temperature Change
In addition, the following equation 4 is an equation that is used to calculate
internal temperature of the measurement round "n". The left side of the
equation "Tn" in the equation 4 indicates internal temperature of the
measurement round "n". In the equation 4, by adding internal temperature
change in the time period "t" at this time, that is, internal temperature change
"ΔTHn-1□n" based on the heat amount (S131) and internal temperature change
"ΔTTn-1□n" based on the heat transfer due to the temperature difference between
the inside and outside of the secondary battery (S132) to the internal
temperature "Tn-1" at the previous time, internal temperature "Tn" of the
measurement round "n" is calculated. For example, when the internal

temperature is higher than the temperature of the surface portion in the battery,
internal temperature change "ΔTTn-1□n" based on the heat transfer becomes a
negative value. In this case, it is indicated that the internal temperature change
"ΔTTn-1□n" that rises due to generation of heat and the internal temperature
change "ΔTTn-1□n" that is reduced due to the heat transfer are combined to each
other.
Tn=Tn-1+ATHn-1□n+ΔTTn-1□n (equation 4)
As described above, by using the internal temperature change based on the
internal Joule heat of the secondary battery, which is obtained on the basis of the
current value and the internal resistance and internal temperature change based
on the heat transfer due to the temperature difference between the inside and
outside of the secondary battery, the internal temperature is calculated. The
calculated internal temperature "Tn" is used to calculate the battery state of the
measurement round "n".
It is noted that, in a case in which there are a plurality of parts in which
deterioration occurs in the secondary battery, the battery state may be calculated
for each of the parts. In this case, for example, the internal temperature is also
calculated for each of the parts. In the calculation of the internal temperature, it
is desirable that the coefficient "α" and the coefficient "β" that are used for the
equations are set for each of the parts.
After that, in the steps of the second half of the flowchart in Fig. 5 (S14 to
S17), the battery state of the secondary battery is calculated using the calculated
internal temperature. As described above, in the embodiment, the battery state
indicates a deterioration state of a storage enabled electric charge amount, and is
calculated on the basis of one of or both of a degree of deterioration due to
charge and discharge cycle (hereinafter, referred to as cycle deterioration) and a
degree of deterioration due to neglect (hereinafter, referred to as neglected
deterioration).
Calculation of a Amount of Charge and Discharge Electric Charge
In the embodiment, in order to obtain the degree of the cycle deterioration,
for example, an amount of charge and discharge electric charge that indicates an

amount of electric charge that is charged and discharged to and from the
secondary battery is used. Therefore, the calculation device 6-5 calculates the
amount of charge and discharge electric charge (S14). A deterioration degree
at the time of charging and a deterioration degree at the time of discharging are
calculated so as to be distinguishable. Therefore, as an amount of charge and
discharge electric charge of the measurement round "n", an electric charge
amount "Cc" at the time of charging and an electric charge amount "CD" at the
time of discharging are calculated so as to be distinguishable.
The following equation 5 is an equation that is used to calculate the amount
of charge and discharge electric charge. The left side of the equation "Cn" in the
equation 5 indicates an electric charge amount in the time period "t". In
addition, "{(In-i+In)/2}" represents an average current value in the time period
"t". In addition, by multiplying the average current value by the time period "t",
electric charge amount "Cn" in the time period "t" is approximately calculated.
When polarities of "In-i" and "In" are the same depending on the connection
direction of the ammeter, that is, here, when the electric charge amount "Cn" is a
positive value, it is indicated that the electric charge amount "Cn" is an electric
charge amount "Cnc" at the time of charging. In addition, when the electric
charge amount "Cn" is a negative value, it is indicated that the electric charge
amount Cn is an electric charge amount "CnD" at the time of discharging.
Cn=(In-i+In)*t/2 (equation 5)
On the other hand, when the polarities of "In-i" and "In" are different, it is
indicated that both of the charging and discharging occur during the time period
"t". For example, when "In-i" is a negative value and "In" is a positive value,
each electric charge amount is obtained on the basis of the equation 5'.
CnD=In-i*t/2 (equation 5')
Cnc=in*t/2 (equation 5')
In addition, when "In-i" is a positive value and "In" is a negative value, each of the
electric charge amounts is obtained on the basis of the equation 5".
CnD=In*t/2 (equation 5")
Cnc=In-i*t/2 (equation 5")

In addition, in order to calculate a deterioration amount, the electric charge
amounts "Cn" in each of the time periods "t" from the calculation round "α" of the
battery state at the previous time to the calculation round "b" that is a target (the
electric charge amount "Cc" at the time of charging and the electric charge
amount "CD" at the time of discharging) become cumulatively combined. The
following equation 6 indicates the total of the electric charge amounts "Cn" from
the calculation round "α" at the previous time to the target calculation round "b".
It is noted that, as described above, the electric charge amount "Cc" at the time
of charging and the electric charge amount "CD" at the time of discharging are
combined so as to be distinguishable. In addition, the calculated electric charge
amounts are stored in the storage device 6-6 and read out by the calculation
device 6-5 as appropriate.

(equation 6)
It is noted that, in the embodiment, a degree of cycle deterioration is set as
a calculation target. Therefore, the calculation device 6-5 obtains the amount of
charge and discharge electric charge. However, the calculation of the amount of
charge and discharge electric charge is not need when the degree of cycle
deterioration is not calculated. In addition, the calculation method of the
amount of charge and discharge electric charge is not limited to such an example.
The amount of charge and discharge electric charge may be calculated, for
example, by converting the electric charge amount in accordance with
information on transmutation of the SOC.
Calculation of the SOC
After that, the calculation device 6-5 calculates an SOC of the secondary
battery in order to calculate a degree of neglected deterioration (S15). The SOC
indicates, for example, a ratio of a charge state using a storage enabled capacity
of initial performance of the secondary battery as a parameter. The SOC may be
used for the above-described calculation step of internal resistance (S12). In

this case, it is desirable that the calculation of the SOC is performed prior to the
calculation of the internal resistance. As described above, it is desirable that the
order of the calculation is determined by considering subsequent calculation for
which the result of the above-described calculation is used.
Fig. 8 is a diagram illustrating an example of the effect of SOC, which is given
to neglected deterioration. Fig. 8 is quoted from NEDO, Annual Report 2004,
"Technological development of lithium battery for FCVs and HEVs". In Fig. 8,
the horizontal axis indicates an aging time (day), and the vertical axis indicates a
degree of a storage enabled electric charge amount as a degree of neglected
deterioration. Curves 8a to 8e in Fig. 8 indicate transmutation of deterioration
degrees in cases of SOC 20% to SOC 80%. In particular, the curve 8a indicates
a decrease degree of the storage enabled electric charge amount, that is, a
degree of neglected deterioration in SOC 20%, the curve 8b indicates a degree of
neglected deterioration in SOC 35%, the curve 8c indicates a degree of neglected
deterioration SOC 50%, the curve 8d indicates a degree of neglected
deterioration in SOC 65%, and the curve 8e indicates a degree of neglected
deterioration SOC 80%. In Fig. 8, the degree of neglected deterioration of SOC
80% illustrated in curve 8e is greater than the degree of neglected deterioration
of SOC 20% illustrated in the curve 8a. As described above, the degree of
neglected deterioration is affected by the SOC. Therefore, in the calculation of
the neglected deterioration, the SOC is calculated.
Various methods of calculating an SOC are discussed (for example, Japanese
Patent 3919604). In addition, the characteristic of a secondary battery that is
mounted on an electric vehicle is different from the characteristic of the
secondary battery to which a common method of calculating an SOC is applied.
Due to the difference of characteristics, when the common calculation method is
used, it is probable that an error occurs in the SOC. Therefore, for example, in a
case of a lithium ion battery that is mounted on an electric vehicle, the SOC is
calculated by applying an appropriate battery characteristic model to a method
using a Kalman filter. For example, the basic concept of the method using the
Kalman filter is discussed in P. Lurkens, W. Steffens, Ladezustandsschatzung von

BleibatterienmitHilfe des Kalman-Filters, etzArchiv, vol. 8, No. 7, July 1986, pp.
231-236.
In addition, the application of the battery characteristic model is discussed in
the papers such as "Domenico Di Domenico et al., 17th IEEE International
Conference on Control Applications Part of 2008 IEEE Multi-conference on
Systems and Control, p702, 2008", "Zhiwei He et al., Image and Signal
Processing, 2009. CISP '09. 2nd International Congress on, pl42, 2009", JieXuet
al., Image and Signal Processing, 2009. CISP '09. 2nd International Congress on,
2009", "Carmelo Speltino et al., 2010 American Control Conference, p5050,
2010", and "Mori W. Yatsui et al., Vehicle Power and Propulsion Conference
(VPPC), 2011.
For example, the calculation device 6-5 according to the embodiment
calculates an SOC on the basis of the method using the Kalman filter and stores
the SOC in the storage device 6-6. In addition, the SOC includes a characteristic
that is changed on the basis of temperature of the secondary battery, and has, for
example, a tendency to increase as the temperature increases. Therefore, the
calculated SOC is corrected on the basis of the temperature. In particular, when
the internal temperature increases, the SOC is corrected so as to be increased on
the basis of a measured value, or the like. At this time, as original temperature
to be corrected, the internal temperature that is calculated in step S13 may be
used. By using the internal temperature for the correction of the SOC, accuracy
of the correction is improved, and accuracy of the calculated battery state is also
improved.
It is noted that, in the embodiment, the degree of neglected deterioration is
set as a calculation target. Therefore, the calculation device 6-5 calculates an
SOC. However, the calculation of the SOC is not need when the degree of
neglected deterioration is not calculated. In addition, the calculation method of
the SOC is not limited to the method of using the Kalman filter.
Calculation of the Deterioration Degree
Next, the calculation device 6-5 calculates a deterioration degree of a
storage enabled electric charge amount using the internal temperature, the

amount of charge and discharge electric charge, and the SOC (S16). The
deterioration degree of the storage enabled electric charge amount in the
embodiment is based on deterioration degrees due to neglected deterioration
and cycle deterioration. However, as described above, the deterioration degree
of the storage enabled electric charge amount may be based on only one of the
degreed of neglected deterioration and cycle deterioration.
Calculation of the Neglected Deterioration Degree
First, the calculation device 6-5 calculates a neglected deterioration amount
as the degree of neglected deterioration (S161). The neglected deterioration
amount is calculated, for example, on the basis of temperature and SOC of the
secondary battery. In the embodiment, calculated internal temperature is used
as the temperature of the secondary battery.
The following equation 7 indicates a neglected deterioration function DH that
is used to calculate a neglected deterioration amount using a cumulative
deterioration amount "IΣn-1", the internal temperature "Tn", and an SOC "SOCn"
as a parameter. Here, the cumulative deterioration amount "ΣDn-1" is the total
(sum) of the neglected deterioration amount and the cycle deterioration amount
up to the measurement round "n-1" that is the calculation round "α" at the
previous time. The neglected deterioration function "DH" is stored in the storage
device 6-6, and read out from the calculation device 6-5, as appropriate. The
neglected deterioration amount depends on, for example, the temperature and
the SOC. As an example, the neglected deterioration amount has a tendency to
increase when the internal temperature is high. In addition, as described above
in Fig. 8, as an example, the neglected deterioration amount has a tendency to
increase when the SOC is high. In addition, for example, the neglected
deterioration amount varies depending on the cumulative deterioration amount
"ΣDn-1". For example, the neglected deterioration amount has a tendency to
increase when the cumulative deterioration amount "ΣDn-1" is small and has a
tendency to decrease when the cumulative deterioration amount "ΣDn-1" is large.
As described above, the deterioration degree of the storage enabled electric
charge amount due to neglected deterioration deteriorates depending on the

internal temperature and the charge state and depends on the sum of the
deterioration degrees. The neglected deterioration function "DH" is calculated
beforehand, for example, on the basis of an experiment, or the like in which the
cumulative deterioration amount, the internal temperature, and the SOC are
changed depending on the type of the secondary battery.
DH (ΣDn-1, T„, SOCn) (equation 7)
After that, a neglected deterioration amount from the calculation round "α"
of the battery state at the previous time to the calculation round "b" that is a
target is calculated on the basis of the following equation 8. In particular, a
deterioration amount at the time of calculation is obtained by cumulatively
combining neglected deterioration amounts based on the internal temperature
and the change state for each of the time periods "t". In the equation 8, for
example, the neglected deterioration amount in the calculation round "α" at the
previous time is represented as "DH(ΣDa-1, Ta, SOCa)*t", and a neglected
deterioration amount in a calculation round "a+1" is represented as "DH(ΣDa, Ta+1,
SOCa+1)*t". In addition, the neglected deterioration amount in the calculation
round "b" that is a target is represented as "DH(ΣDb-1, Tb/ SOCb)*t". In addition,
by combining the neglected deterioration amounts in the time periods "t" from
the calculation round "α" to the calculation round "b", the total neglected
deterioration amount from the calculation round "α" at the previous time to the
calculation round "b" that is a target is calculated.

(equation 8)
It is noted that, in this example, the degree of neglected deterioration is
obtained as the neglected deterioration amount, and the embodiment is not
limited to such an example. The degree of neglected deterioration may be
calculated as a neglected deterioration rate. In this case, by obtaining a
neglected deterioration rate in the time period "t" and multiplying the neglected

deterioration rates of the respective time periods "t" to each other, the total
neglected deterioration rate from the calculation round "α" at the previous time to
the calculation round "b" that is a target is calculated.
Calculation of the Cycle Deterioration
After that, the calculation device 6-5 calculates a cycle deterioration amount
as the degree of cycle deterioration (S162). The cycle deterioration amount is
calculated, for example, on the basis of the temperature of the secondary battery
and the amount of charge and discharge electric charges "Cc" and "CD". In the
embodiment, the internal temperature is calculated as the temperature of the
secondary battery is used. In addition, the cycle deterioration amounts at the
time of charging and at the time of discharging are calculated so as to be
distinguishable.
The following equation 9 indicates a cycle deterioration function "Dc" that is
used to calculate a cycle deterioration amount at the time of charging, using the
cumulative deterioration amount "ΣDn-i", the internal temperature "Tn", and a
charge electric charge amount "Ccn" as a parameter. Similarly, a cumulative
deterioration amount "ΣDn-1" indicates the total (sum) of the neglected
deterioration amount and the cycle deterioration amount up to the measurement
round "n-1" that is the calculation round "α" at the previous time.
Dc (ΣDn-1, Tn, Ccn) (equation 9)
In addition, the following equation 10 indicates a cycle deterioration function
"DD" that is used to calculate a cycle deterioration amount at the time of
discharging, using the cumulative deterioration amount ΣDn-i", the internal
temperature "Tn", and a discharge electric charge amount "CDn" as a parameter.
DD (ΣDn-1, Tn, CDn) (equation 10)
The cycle deterioration amount depends on, for example, the temperature
and the amount of charge and discharge electric charge. As an example, the
cycle deterioration amount has a tendency to increase as the internal
temperature decreases, and has a tendency to increase as the amount of charge
and discharge electric charge increases. In addition, for example, the cycle
deterioration amount varies depending on the cumulative deterioration amount

"ΣDn-1". For example, the cycle deterioration amount has a tendency to increase
when the cumulative deterioration amount "ΣDn-1" is small and has a tendency to
decrease when the cumulative deterioration amount "ΣDn-1" is large.
As described above, the deterioration degree of the storage enabled electric
charge amount due to the cycle deterioration deteriorates depending on the
internal temperature and the amount of charge and discharge electric charge and
depends on the sum of the deterioration degrees. Each of the cycle
deterioration functions is obtained beforehand, for example, on the basis of an
experiment, or the like in which the cumulative deterioration amount, the internal
temperature, the amount of charge and discharge electric charge, and the speed
of charge and discharge are changed depending on the type, or the like of the
secondary battery. In addition, each of the cycle deterioration functions is
stored in the storage device 6-6 and is used so as to be read out from the
calculation device 6-5, as appropriate.
After that, a cycle deterioration amount from the calculation round "α" of the
battery state at the previous time to the calculation round "b" that is a target is
calculated on the basis of the following equation 11. In particular, a
deterioration amount at the time of calculation is obtained by cumulatively
combining cycle deterioration amounts based on the internal temperature and
the amount of charge and discharge electric charge for the time periods "t". In
the equation 11, for example, the cycle deterioration amount in the calculation
round "α" at the previous time is represented as "{Dc(ΣDa-1, Ta, Cca)+DD(ΣDa-1, Ta,
CDa)}*t", a cycle deterioration amount in the calculation round "a+1" is
represented as "{Dc(ΣDa, Ta+1, Cca+1)+DD(ZDa, Ta+1, CDa+1)}*t". In addition, a
cycle deterioration amount in the calculation round "b" that is a target is
represented as "{Dc(ΣDb-1, Tb, Ccb)+DD(ΣDb-1, Tb, CDb)}*t". In addition, by
combining cycle deterioration amounts in the time periods "t" from the
calculation round "α" to the calculation round "b", the total cycle deterioration
amount from the calculation round "α" at the previous time to the calculation
round "b" that is a target is calculated.


(equation 11)
It is noted that, in this example, the degree of cycle deterioration is obtained
as the cycle deterioration amount, and the embodiment is not limited to such an
example. The degree of cycle deterioration may be calculated as a cycle
deterioration rate. In this case, a cycle deterioration rate in the time period "t" is
obtained, and the total cycle deterioration rate from the calculation round "α" at
the previous time to the calculation round "b" that is a target is calculated by
multiplying the cycle deterioration rates in the respective time periods "t" to each
other. It is noted that, a speed of charge and discharge may be used as a
parameter at the time of calculation of the cycle deterioration amount.
As described above, in accordance with the steps S161 and 162, the
neglected deterioration amount and the cycle deterioration amount from the
calculation round "α" of the battery state at the previous time to the calculation
round "b" that is a target are calculated. That is, each of the deterioration
amounts of the battery state at the time of calculating is calculated. Each of the
deterioration amounts in the embodiment is calculated using not the external
temperature but the internal temperature, thereby realizing high accuracy as
compared to a method using the external temperature.
Calculation of the Total Deterioration Degree
In addition, the calculation device 6-5 calculates the total deterioration
amount "ΔQa□b" of a storage enabled electric charge amount in accordance with
the following equation 12 (S163). The equation 12 is an equation to calculate
the total deterioration amount "ΔQa□b" from the calculation round "α" to the
calculation round "b" by combining the neglected deterioration amounts and
combining the cycle deterioration amounts from the calculation round "α" to the
calculation round "b". It is noted that, when a neglected deterioration rate and

a cycle deterioration rate are calculated, the total deterioration rate is calculated
by multiplying the neglected deterioration rate and the cycle deterioration rate
each other. In addition, when the battery state is calculated on the basis of one
of the neglected deterioration and the cycle deterioration, the calculation device
6-5 regards the corresponding deterioration amount as the total deterioration
amount.

(equation 12)
It is noted that, in the embodiment, as the calculation of the deterioration
degree (deterioration amount, deterioration rate, and the like), the method using
the deterioration function is described, and the embodiment is not limited to such
a method. For example, a table of a deterioration amount in accordance with a
parameter value such as internal temperature is prepared beforehand, and a
deterioration amount may be obtained on the basis of the table. In addition, as
another method of calculating a deterioration degree, for example, a method
using an electric charge amount is discussed in Japanese Patent 3919604, and
the like, a method using an electric charge amount and battery terminal open
voltage is discussed in Japanese Unexamined Patent Application Publication No.
2004-170231, and the like, and a method using discharge depth (SOC) and
temperature is discussed in Japanese Patent 4009537, and the like.
Calculation of the Battery State
In addition, the calculation device 6-5 calculates a battery state of the
secondary battery on the basis of the calculated deterioration amount of the
storage enabled electric charge amount (S17). For example, first, the
calculation device 6-5 calculates a storage enabled electric charge amount "Qb" in
the calculation round "b" in accordance with the following equation 13. In the
step S16, a deterioration amount "ΔQaΔ□b" of a storage enabled electric charge

amount from the calculation round "α" at the previous time to the calculation
round "b" that is a target is calculated. Therefore, by subtracting the
deterioration amount "ΔQa□ b" that is calculated in step S16, from the calculated
storage enabled electric charge amount "Qa" in the calculation round "α" at the
previous time in accordance with the equation 13, a storage enabled electric
charge amount "Qb" in the calculation round "b" that is a target is calculated.
Qb=Qa-AQanb (equation 13)
In addition, the calculation device 6-5 calculates a ratio "RQ" of the storage
enabled electric charge amount in the measurement round "b" to an initial
storage enabled electric charge amount of the battery as a battery state of
secondary battery in accordance with the following equation 14. In particular, in
the equation 14, the ratio "RQ" is calculated by dividing the storage enabled
electric charge amount "Qb" in the measurement round "b", which is calculated
by the equation 13 by the initial storage enabled electric charge amount "Qo" of
the secondary battery.
RQ=Qb/Q0 (equation 14)
In the embodiment, as the battery state that is a calculation target, a
deterioration degree of the charge enabled electric charge amount is calculated.
Alternatively, as the battery state that is a calculation target, a deterioration
degree based on the internal resistance may be calculated. The battery state
based on the internal resistance is obtained in accordance with the following
equation 15. In the equation 15, internal resistance "Rib" is internal resistance
that is calculated in the measurement round "b", and internal resistance "Rio" is
initial internal resistance of the secondary battery. In the equation 15, by
dividing the internal resistance "Rib" in the measurement round "b" by the initial
internal resistance "Ri0", a deterioration state "RRi" based on the internal
resistance is calculated as the battery state.
RRi=Rib/Rio (equation 15)
It is noted that, the value of the internal resistance that is calculated in the
step S12 in the flowchart of Fig. 5 may be corrected on the basis of the internal
temperature in the embodiment. In this case, for example, the plots of the

voltage value and the current value, which are illustrated in Fig. 6 are corrected
on the basis of the internal temperature. For example, the internal resistance
has a tendency to decrease as the temperature increases. Therefore, for
example, the plot of the voltage value and the current value when the internal
temperature is high is corrected so that the internal resistance is reduced. As a
result, accuracy of the internal resistance is improved, and accuracy of the
calculated battery state (deterioration state based on the internal resistance) is
also improved.
As described above, the state evaluation apparatus 10 of the secondary
battery according to the embodiment calculates internal resistance on the basis
of the measured voltage value and current value of the secondary battery, and
calculates the internal temperature of the secondary battery on the basis of the
current value, the internal resistance, and the measured external temperature of
the secondary battery. In addition, the state evaluation apparatus 10 obtains a
charge state that indicates an amount of charge and discharge electric charge of
the secondary battery based on the current value or a charging rate of the
secondary battery based on the current value and the voltage value, and
calculates a battery state that indicates a state after deterioration of the
secondary battery, on the basis of at least one of the amount of charge and
discharge electric charge and the charge state, and the internal temperature.
As described above, the state evaluation apparatus 10 according to the
embodiment calculates battery internal temperature to be estimated and can
calculate a battery state highly accurately.
In particular, when a battery state of a secondary battery that is mounted on
an electric vehicle is calculated, current in the secondary battery varies greatly.
For example, when the electric vehicle is traveling, it is assumed that large
current of 100A or more flows in a short space of a time within a unit of one
second. At this time, temperature rise of about 10°C or more is predicted inside
of the secondary battery. On the other hand, a rapid temperature rise of the
surface of the secondary battery when the current flows barely occurs on the
basis of the heat capacity, the shape, and the dimension. Therefore, when a

battery state is calculated using the surface temperature based on the
thermometer that is installed outside the battery, for example, by using the
surface temperature that is different from the internal temperature of the battery
by 10°C or more, the error between the calculated battery state and the actual
battery state becomes large. The estimated life of the secondary battery that is
used for the electric vehicle is, for example, about five years to 10 years.
Therefore, it is probable that there is a problem that the error between the
battery states becomes large.
As described above, when the secondary battery is mounted in an
environment in which current is changed rapidly in a short space of a time, a
difference between the internal temperature and the surface temperature of the
battery becomes large easily. Therefore, the state evaluation apparatus 10
according to the embodiment calculates internal temperature using first internal
temperature change based on internal Joule heat of the secondary battery, which
is obtained on the basis of the current value and the internal resistance, and
second internal temperature change based on the heat transfer due to the
temperature difference between the inside and outside of the secondary battery.
As described above, by considering the rise of the internal temperature based on
the Joule heat, and decrease in the internal temperature (when the external
temperature of the battery is lower than the internal temperature) or increase in
the internal temperature (when the external temperature of the battery is higher
than the internal temperature) based on the heat transfer due to the temperature
difference between the inside and outside of the secondary battery, the internal
temperature can be calculated. As a result, the internal temperature to be
estimated can be calculated on the basis of the current value, the external
temperature, and the internal resistance based on the current value and voltage
value.
In addition, the state evaluation apparatus 10 obtains the first internal
temperature change by multiplying a product of the square of the current value
and the internal resistance by a set coefficient. As a result, the first internal
temperature change can be highly accurately calculated on the basis of a

characteristic of the secondary battery that is a target. In addition, the state
evaluation apparatus 10 obtains the second internal temperature change on the
basis of a characteristic in which a temperature difference between the inside and
outside of the secondary battery exponentially varies for a time using the Napier's
constant as a base. As a result, the second internal temperature change can be
highly accurately calculated on the basis of the characteristic in which the
temperature difference exponentially decreases for a time.
In addition, the state evaluation apparatus 10 of the secondary battery
according to the embodiment calculates, for each set time period, internal
temperature on the basis of a voltage value, a current value, and external
temperature that are measured for each of the set time periods. In addition, the
state evaluation apparatus 10 of the secondary battery calculates internal
temperature in the set time period at this time (measurement round "n" in the
embodiment) by adding the internal temperature change that is calculated in the
set time period at this time to the internal temperature that is calculated in the
set time period at the previous time (measurement round "n-1" in the
embodiment). As a result, the internal temperature of the calculation target
round is calculated using the internal temperature at the previous time as the
original, so that the internal temperature can be calculated further highly
accurately.
As described above, in the state evaluation apparatus 10 according to the
embodiment, internal temperature in which the error with actual internal
temperature is small can be calculated, and accuracy of the calculated battery
state is improved. It is noted that the error between the actual internal
temperature and the internal temperature that is calculated by the state
evaluation apparatus 10 according to the embodiment can be dealt with by
appropriately adjusting the coefficient "α" and the coefficient "(3" that are used to
calculate the internal temperature. As a result, the error between the actual
internal temperature and the calculated internal temperature becomes small, and
accuracy of the battery state is improved.
In addition, the internal temperature that is calculated by the state

evaluation apparatus 10 according to the embodiment indicates temperature of
one of or the combination of the active material in the positive electrode and the
negative electrode of the secondary battery, and the electrolyte of the secondary
battery. For example, in the lithium ion the secondary battery, deterioration of
the battery state occurs when lithium ion that can be generated is reduced.
Therefore, it is desirable that the battery state is calculated on the basis of
temperature (internal temperature) of the active material in the positive
electrode and the negative electrode and the electrolyte inside the battery, which
are portions in which the deterioration occurs. The state evaluation apparatus
10 according to the embodiment estimates and calculates the temperature of one
of or the combination of the active material in the positive electrode and the
negative electrode of the secondary battery and the electrolyte of the secondary
battery, so that the battery state can be calculation highly accurately.
It is noted that the state evaluation processing of the secondary battery
according to the embodiment may be stored in a computer-readable storage
medium as a program and executed by reading the program by a computer.

CLAIMS
1. A state evaluation apparatus (10) of a secondary battery (LB), the
state evaluation apparatus comprising:
at least one processor configured to perform a process including:
calculating (51) internal resistance (Ri) based on a measured
voltage value and current value (I) of the secondary battery;
calculating (52) internal temperature of the secondary battery
(Tn) based on the current value, the internal resistance, and measured external
temperature of the secondary battery (Ts);
obtaining (53,54) an amount of charge and discharge electric
charge of the secondary battery (Σ Cn based on the current value, or obtaining
a charge state (SOC) that indicates a charging rate of the secondary battery
based on the current value and the voltage value; and
calculating (55,56) a battery state (RQ) that indicates a state
after deterioration of the secondary battery, based on the internal temperature
and at least one of the amount of charge and discharge electric charge and the
charge state.
2. The state evaluation apparatus of the secondary battery, according
to claim 1, wherein
in the calculating of the internal temperature, the internal temperature is
calculated using first internal temperature change (equation 2) based on internal
Joule heat of the secondary battery, which is obtained based on the current value
and the internal resistance, and second internal temperature change (equation 3)
based on heat transfer due to a temperature difference between the inside and
outside of the secondary battery.
3. The state evaluation apparatus of the secondary battery, according
to claim 2, wherein
the first internal temperature change is obtained by multiplying a product
of a square of the current value and the internal resistance by a set coefficient

(α).
4. The state evaluation apparatus of the secondary battery, according
to claim 2, wherein
the second internal temperature change is obtained based on a
characteristic in which the temperature difference between the inside and outside
of the secondary battery exponentially varies for a time using a Napier's constant
as a base.
5. The state evaluation apparatus of the secondary battery, according
to claim 2, wherein
in the calculating of the internal temperature, the internal temperature is,
for each set time period (t), calculated based on the voltage value, the current
value, and the external temperature that are measured for each of the set time
periods, and calculates the internal temperature in the set time period at this time
by adding internal temperature change that is calculated in the set time period at
this time to the internal temperature (Tn-1) that is calculated in the set time
period at a previous time.
6. The state evaluation apparatus of the secondary battery, according
to claim 1, wherein
the charge state is obtained based on the internal temperature using a
Kalman filter.
7. The state evaluation apparatus of the secondary battery, according to
claim 1, wherein
the battery state of the secondary battery is one of or both of a first
battery state that indicates a deterioration degree of a storage enabled electric
charge amount of the secondary battery, which deteriorates depending on the
internal temperature and the charge state and depends on a sum of deterioration
degrees, and a second battery state that indicates a deterioration degree of a

storage enabled electric charge amount of the secondary battery, which
deteriorates depending on the internal temperature and the amount of charge
and discharge electric charge and depends on the sum of the deterioration
degrees.
8. The state evaluation apparatus of the secondary battery, according
to claim 7, wherein
the first battery state indicates a total of the deterioration degrees of the
storage enabled electric charge amount based on the internal temperature that is
calculated for each set time period and the charge state in the set time period,
and
the second battery state indicates a total of the deterioration degrees of
the storage enabled electric charge amount based on the internal temperature
that is calculated for each of the set time periods and the amount of charge and
discharge electric charge in the set time period.
9. The state evaluation apparatus of the secondary battery, according
to claim 7, wherein
The deterioration degree of the storage enabled electric charge amount
in the secondary battery is represented as a ratio of a storage enabled electric
charge amount at the time of calculation to an initial storage enabled electric
charge amount of the secondary battery (Q 0).
10. The state evaluation apparatus of the secondary battery, according
to claim 1, wherein
the internal temperature is temperature of one of or combination of an
active material in a positive electrode and negative electrode of the secondary
battery, and an electrolyte of the secondary battery.
11. The state evaluation apparatus of the secondary battery, according
to claim 1, wherein

the external temperature is one of temperature of a surface of the
secondary battery and a temperature near the surface.
12. The state evaluation apparatus of the secondary battery, according
to claim 1, wherein
the calculated internal resistance is corrected depending on the internal
temperature calculated at the previous time.
13. A state evaluation method of a secondary battery, the state
evaluation method comprising:
calculating internal resistance based on a measured voltage value and
current value of the secondary battery;
calculating internal temperature of the secondary battery based on the
current value, the internal resistance, and measured external temperature of the
secondary battery;
obtaining an amount of charge and discharge electric charge of the
secondary battery based on the current value, or obtaining a charge state that
indicates a charging rate of the secondary battery based on the current value and
the voltage value; and
calculating a battery state of the secondary battery based on the internal
temperature and at least one of the amount of charge and discharge electric
charge and the charge state.
14. The state evaluation method of a secondary battery, according to
claim 13, wherein
in the calculation of the internal temperature, the internal temperature is
calculated using first internal temperature change based on internal Joule heat of
the secondary battery, which is obtained based on the current value and the
internal resistance, and second internal temperature change based on heat
transfer due to a temperature difference between the inside and outside of the
secondary battery.

15. A computer-readable state evaluation program of a secondary
battery, which causes a computer to executes state evaluation processing of the
secondary battery, the state evaluation processing comprising:
calculating internal resistance based on a measured voltage value and
current value of the secondary battery;
calculating internal temperature of the secondary battery based on the
current value, the internal resistance, and measured external temperature of the
secondary battery;
obtaining an amount of charge and discharge electric charge of the
secondary battery based on the current value, or obtaining a charge state that
indicates a charging rate of the secondary battery based on the current value and
the voltage value; and
calculating a battery state of the secondary battery based on the internal
temperature and at least one of the amount of charge and discharge electric
charge and the charge state.

ABSTRACT

A state evaluation apparatus of a secondary battery, the state evaluation
apparatus includes at least one processor configured to perform a process
including calculating internal resistance based on a measured voltage value and
current value of the secondary battery and calculating internal temperature of
the secondary battery and obtaining an amount of charge and discharge electric
charge of the secondary battery based on the current value, or obtaining a
charge state that indicates a charging rate of the secondary battery based on the
current value and the voltage value, and calculating a battery state that indicates
a state after deterioration of the secondary battery, based on the internal
temperature and at least one of the amount of charge and discharge electric
charge and the charge state.