U.S. patent application number 14/768014 was filed with the patent office on 2015-12-24 for managing the charging of a battery.
This patent application is currently assigned to RENAULT s.a.s.. The applicant listed for this patent is RENAULT s.a.s.. Invention is credited to Daniel BOIRON, Ana-Lucia DRIEMEYER-FRANCO, Masato ORIGUCHI, Antoine SAINT-MARCOUX.
Application Number | 20150367744 14/768014 |
Document ID | / |
Family ID | 48521184 |
Filed Date | 2015-12-24 |
United States Patent
Application |
20150367744 |
Kind Code |
A1 |
SAINT-MARCOUX; Antoine ; et
al. |
December 24, 2015 |
MANAGING THE CHARGING OF A BATTERY
Abstract
The invention concerns a method for managing the charging of an
Li-ion battery on the basis of at least one parameter chosen from
the group consisting of the deterioration of the battery and cell
imbalance, comprising the following steps of receiving a signal
determining the end-of-charge voltage value of said battery, of
generating a control signal controlling the charging of said
battery, and of transmitting the control signal to a charger, the
control signal being generated such that the battery is charged on
the basis of the end-of-charge voltage value determined in step a),
said end-of-charge voltage value being increased on the basis of
the state of deterioration of said Li-ion battery until a limit
value is reached, in order to ensure a constant minimal level of
required energy in said Li-ion battery, for a predetermined
reference temperature.
Inventors: |
SAINT-MARCOUX; Antoine;
(Palaiseau, FR) ; ORIGUCHI; Masato; (Rambouillet,
FR) ; DRIEMEYER-FRANCO; Ana-Lucia;
(Montigny-le-Bretonneux, FR) ; BOIRON; Daniel;
(Voisins-le-Bretonneux, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
RENAULT s.a.s. |
Boulogne-Billancourt |
|
FR |
|
|
Assignee: |
RENAULT s.a.s.
Boulogne-Billancourt
FR
|
Family ID: |
48521184 |
Appl. No.: |
14/768014 |
Filed: |
February 13, 2014 |
PCT Filed: |
February 13, 2014 |
PCT NO: |
PCT/FR2014/050277 |
371 Date: |
August 26, 2015 |
Current U.S.
Class: |
320/162 |
Current CPC
Class: |
Y02T 90/14 20130101;
B60L 11/1857 20130101; B60L 58/16 20190201; G01R 31/392 20190101;
B60L 2240/545 20130101; B60L 58/13 20190201; B60L 58/24 20190201;
H02J 7/007 20130101; B60L 58/15 20190201; B60L 2240/549 20130101;
Y02E 60/10 20130101; H02J 7/0047 20130101; H01M 10/44 20130101;
Y02T 10/7072 20130101; B60L 58/14 20190201; H01M 10/0525 20130101;
H02J 2310/48 20200101; B60L 53/00 20190201; B60L 2240/547 20130101;
Y02T 10/70 20130101 |
International
Class: |
B60L 11/18 20060101
B60L011/18 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 14, 2013 |
FR |
1351264 |
Claims
1. A method for managing the charging of a Li-ion battery as a
function of at least one parameter chosen from the group comprising
the ageing of the battery and the cell unbalance representing the
difference between the state of charge of the cell exhibiting the
highest charge and the state of charge of the cell exhibiting the
lowest charge, comprising the following steps of: a) determining an
end-of-charge voltage value of said battery, b) generating a
control signal controlling the charging of said battery and of
transmitting the control signal to a charger, the control signal
being generated such that the battery is charged as a function of
the end of charge voltage value determined in step a), said
end-of-charge voltage value being increased as a function of the
state of ageing of said Li-ion battery until a limit value is
reached in order to ensure a constant minimum required energy level
in said Li-ion battery, for a predetermined reference
temperature.
2. The method as claimed in claim 1, comprising, prior to step a),
a step of generating and processing a signal of evaluation of the
state of ageing of the battery.
3. The method as claimed in claim 1, comprising, after step b), a
step of generating and processing an end-of-charge signal when the
maximum cell voltage value is greater than or equal to the
end-of-charge voltage value and when the authorized charging power
in the battery is less than or equal to the maximum authorized
end-of-charge power.
4. The method as claimed in claim 1, comprising, in step b), a step
c) of generating and processing a modulation signal of said
end-of-charge voltage increased as a function of the cell
unbalance.
5. The method as claimed in claim 4, characterized in that step a)
of determining the end-of-charge voltage value consists of
determining the cut-off voltage for the end-of-charge on the
maximum cell voltage and the cut-off voltage for the end-of-charge
on the minimum cell voltage as a function of the state of ageing of
the battery.
6. The method as claimed in claim 4, characterized in that it
comprises, after step c), a step of receiving and processing an
end-of-charge signal when the authorized charging power in the
battery is less than or equal to the maximum authorized
end-of-charge power and when the maximum cell voltage value is
greater than or equal to the end-of-charge cut-off voltage on the
maximum cell voltage or when the value of the minimum cell voltage
is greater than or equal to the end-of-charge cut-off voltage on
the minimum cell voltage.
7. A device for managing the charging of a Li-ion battery as a
function of at least one parameter chosen from the group consisting
of the ageing of the battery and the cell unbalance representing
the difference between the state of charge of the cell exhibiting
the highest charge and the state of charge of the cell exhibiting
the lowest charge, comprising, 1) means of determining an
end-of-charge voltage value of said battery, 2) processing means
arranged to generate a control signal for controlling the charging
of said battery, 3) means of transmitting the control signal to a
charger, characterized in that the processing means are arranged so
that the control signal is generated in such a way that the
charging of the battery is carried out as a function of the
determined end-of-charge voltage value, said end-of-charge voltage
value being increased as a function of the increasing state of
ageing of said Li-ion battery up to a limit value in order to
provide a constant minimum required energy level in said Li-ion
battery, for a predetermined reference temperature.
8. The device as claimed in claim 7, characterized in that it
furthermore comprises means of generating and processing a signal
of evaluation of the state of ageing of the battery and the means
of determining the end of charge voltage value are arranged to
determine the cut-off voltage for the end-of-charge on the maximum
cell voltage and the cut-off voltage for the end-of-charge on the
minimum cell voltage as a function of the state of ageing of the
battery.
9. A lithium-ion battery assembly comprising a lithium-ion battery
and a device for managing charging as claimed in claim 7.
10. A motor vehicle incorporating a lithium-ion battery assembly as
claimed in claim 9.
Description
[0001] The invention relates to the field of managing the charging
of a battery. An example of application of the invention can be
found in the automobile industry, notably for managing the charging
of a traction battery of an electric and/or hybrid vehicle. This
type of battery, notably of the lithium-ion type, comprises a
plurality of electric accumulators, or cells, including a
rechargeable electro-chemical system intended to supply a nominal
voltage. They are generally controlled by a battery control system
(BMS "Battery Management System") which is an electronic system for
controlling the state of the various elements or parameters of a
lithium battery, and notably of its constituent cells comprising a
negative electrode and a positive electrode.
[0002] A BMS system is an important element in all lithium
batteries or battery assemblies comprising a battery and a BMS
system. It monitors the state of various elements or parameters of
the battery, such as the total voltage or that of individual cells,
the temperature (average temperature, cooling liquid inlet
temperature, cooling liquid outlet temperature, or temperatures of
the individual cells) and the state of charge or the depth of
discharge. A BMS system allows the monitoring of data, such as the
maximum charging power and discharging power, the energy supplied
from the last charge or the last charging cycle, the total energy
used from the first use and the total operating time since the
first use.
[0003] A BMS system provides protection of the battery by
preventing it from operating outside of its typical operating
range, and provides protection notably against overcurrent,
overvoltage (during charging), undervoltage (during discharge) and
also, which is particularly important for Li-ion batteries, against
overheating and under-temperature.
[0004] In particular, the BMS system makes it possible to manage
the charging of the battery by indicating at all times what is the
maximum authorized power during charging and if the battery is
fully charged or not.
[0005] For this purpose, one of the predominant parameters is the
end-of-charge voltage or cut-off voltage, which can, for example,
be measured at the terminals of the battery. In fact, this voltage
is representative of the charge limit of the constituent cells of
the battery. In other words, it is the value which the maximum
voltage of each cell must reach at the end of charging in order to
decide that the charging is fully completed. In Li-ion battery
technology, the cut-off voltage can be between 2.5 V and 4.5 V,
preferably between 3.5 V and 4.2 V. Apart from the choice of the
end-of-charge voltage, the definition of a charging strategy takes
on great importance because it makes it possible to seek a
compromise between the durability of the battery and the charging
time. For the same given end-of-charge voltage, when the authorized
charging power is greatly limited, the durability is improved to
the detriment of the charging time and, when a high charging power
is authorized, the charging time is reduced to the detriment of the
durability.
[0006] One of the difficulties is due to the fact that for a
predetermined end-of-charge voltage (cut-off voltage), the energy
available for a user is not the same, principally in relation to
three factors: [0007] the temperature of the battery. Thus, the
lower the temperature of the battery becomes, the lower is the
amount of energy that can be discharged from this cut-off voltage,
because the internal resistances of the cells are higher; [0008]
the ageing of the battery. As the battery becomes more degraded
("poor state of health"), the lower becomes the amount of energy
that can be discharged at this cut-off voltage, because the
available capacity (in A.h) in the battery is limited. The state of
ageing of the battery is defined as being the ratio between the
capacity available in the battery between a zero charge state and a
maximum charge state at a time t, and the capacity available in the
battery between a zero charge state and a maximum charge state at
the start of the service life. Therefore the ratio is 100% at the
start of use of the battery. [0009] the cell unbalance, defined as
being the difference between the state of charge of the cell
exhibiting the highest charge and the state of charge of the cell
exhibiting the lowest charge. Thus, the greater the unbalance
becomes, the lower becomes the amount of energy that can be
discharged at this cut-off voltage, because the lowest cell will
reach its end of discharge voltage limit (minimum charge level)
much earlier than the other cells.
[0010] These factors compete against increasing the end-of-charge
voltage in order to make it possible to provide a sufficient energy
level to a user.
[0011] Conversely, the higher the end-of-charge voltage becomes,
the more the battery is used in an operating range where it
degrades rapidly. More energy is certainly available at the start
of the service life but, after several months or years, the ageing
of the battery will be accentuated in an unacceptable manner for
the user, and an increase of the end-of-charge voltage will not be
sufficient to compensate for the loss of capacity.
[0012] In terms of provision of services, the battery, comprising
the cells and the BMS system, must provide a minimum required
energy level, not only at the start of its service life but also
after a certain number of years.
[0013] A problem to be solved relative to the BMS system is the
definition of an end-of-charge strategy which makes it possible (i)
at the start of the service life, to provide a minimum required
energy level despite a cell unbalance on leaving the factory (or
production line) greater than foreseen because of the manufacturing
process and (ii), over the years of use of the vehicle, to fully
compensate for the loss of energy in the battery.
[0014] In order to provide a user with an energy level equal to or
slightly higher than the minimum required energy level, an accepted
solution consists of choosing an end-of-charge voltage which is
fixed and determined, in the following conditions: a reference
temperature fixed, for example at 25.degree. C., a given ageing
level of the battery, for example at the start of the service life,
a nominal level of unbalance, for example less than 3% of unbalance
between the most charged cell and the least charged cell.
[0015] On the other hand, in cases other than those mentioned
above, the energy effectively available to the user is lower than
what is expected.
[0016] Conversely, if the cell unbalance is substantially lower
than the nominal unbalance, which can also be the case on leaving
the factory, then there will be more energy available than is
strictly necessary. This is not desirable, because this amounts to
using the battery over a larger operating range than what is
necessary, which results in loss of capacity after several years of
use.
[0017] Numerous patents explicitly describe the principle of
CC-CV--Constant Current (CC) first, followed by charging whilst
regulating with respect to a reference voltage (CV), such as the
document WO2012 074406 A2, and which makes it possible to choose
different charging algorithms in the BMS system, as a function of
the conditions, such as the temperature, the electric mains (cost
of the current) and of the actual type of charger. This logic makes
it possible to charge the battery up to a desired energy level in
nominal conditions. However, it does not, by itself, make it
possible to manage all the causes of "dispersion", such as the cell
unbalance, the temperature of the battery, and the ageing of the
battery.
[0018] The aim of the invention is to solve at least one of the
above disadvantages. In particular, a purpose of the invention is
to propose a method of managing charging making it possible to
provide a minimum required energy level, whilst limiting the
degradation of the battery.
[0019] The invention therefore relates to a method for managing the
charging of a Li-ion battery as a function of at least one
parameter chosen from the group comprising the ageing of the
battery and the cell unbalance representing the difference between
the state of charge of the cell exhibiting the highest charge and
the state of charge of the cell exhibiting the lowest charge,
comprising the following steps of: [0020] a) determining an
end-of-charge voltage value of said battery, [0021] b) generating a
control signal controlling the charging of said battery and of
transmitting the control signal to a charger, the control signal
being generated such that the battery is charged as a function of
the end-of-charge voltage value determined in step a), said
end-of-charge voltage value being increased as a function of the
state of ageing of said Li-ion battery until a limit value is
reached in order to ensure a constant minimum required energy level
in said Li-ion battery, for a predetermined reference
temperature.
[0022] According to the invention, it is therefore possible to
provide the user with a Li-ion battery offering a minimum required
energy level, for example of between 18 kWh and 22 kWh, moreover
being constant, for a given reference temperature, for example
25.degree. C., typically in the range 15.degree. C.-40.degree. C.
and advantageously to do this for the longest permitted period of
use, whilst avoiding the use of the battery in a voltage range that
is too wide resulting in its premature degradation. It is thus
possible to take into account the ageing of the battery and/or the
cell unbalance in order to vary the end-of-charge voltage in order
to ensure the minimum required energy level of the battery.
[0023] The more degraded the battery becomes ("poor state of
health"), the lower becomes the amount of energy that can be
discharged at this cut-off voltage, because the available capacity
(in A.h) in the battery is limited, and this is the reason why the
cut-off voltage must be increased and fixed for charging.
[0024] By way of example, at the start of the service life of the
battery or, in other words, for zero ageing or a 100% state of
health, the cut-off voltage can have a value equal to 4.08 V for
each of the constituent cells of the battery, it being possible to
increase this value and fix it for example at 4.11 V when the state
of health of the battery is about 88%, and for example fixed at
4.13 V when the state of health of the battery is between 80% and
65%.
[0025] The method of the invention can be used advantageously by a
BMS battery control system, which comprises a computer containing
instructions for determining the charging voltage of said battery
(step a)) and deciding to increase this value as a function of the
increasing state of ageing of the battery.
[0026] In the context of the invention, the term "signal", is
equally understood to be an electric, differential or other kind of
signal, such as an electromagnetic signal.
[0027] Step a) can advantageously comprise a step of generating a
signal for determining the end-of-charge voltage value of said
battery, said signal making it possible to determine the
end-of-charge voltage value.
[0028] The method can advantageously comprise, prior to step a), a
step of generating and processing a signal of evaluation of the
state of ageing of the battery.
[0029] This step can be implemented by several methods known to
those skilled in the art. It can be a matter of characterizing the
internal resistance of the battery or of estimating the total
available capacity in the battery. An example of a method is
described in WO 2007/004817A1.
[0030] Preferably, the method can comprise, after step b), a step
of generating and processing an end-of-charge signal when the
maximum cell voltage value V.sub.cell.sup.max=max(V.sub.cell.sup.i,
i .di-elect cons. 1 . . . N)) is greater than or equal to the
end-of-charge voltage value (V.sub.EndOfCharge.sup.cut-off) and
when the authorized charging power in the battery (PCHG) is less
than or equal to the maximum authorized end-of-charge power
(P.sub.EndOfCharge.sup.Threshold).
[0031] The end-of-charge can typically be signaled by an indicator
operating according to a Boolean system.
[0032] Typical values for the end-of-charge voltage can be between
4.08 and 4.15 V and for the maximum authorized end-of-charge power;
these values can be equal to 1 kW.
[0033] The importance of this aspect may not be so much due to the
fact that the voltage of the battery is higher than a threshold,
but that this is the case for a low current level (typically 2A).
This is the advantage of this double condition on the authorized
charging power and the maximum cell voltage. In fact, the objective
of a charging strategy is to ensure that the open circuit voltage
(OCV) is correctly at a desired voltage level. However, what is
measured is the cell voltage, which can differ from the open
circuit voltage for a cell i of the battery (OCV.sub.cell.sup.i) by
the expression: DCR.sub.cell.sup.iI.sub.Bat, where
DCR.sub.cell.sup.i is the internal resistance of the cell i (Ohm)
and I.sub.Bat is the value of the current that passes through the
battery (A).
[0034] Thus, the lower the authorized charging power becomes, the
lower the input current I.sub.Bat of the battery can become and,
consequently, the more the cell voltage V.sub.cell.sup.i can
advantageously be a good indicator of the OCV.sub.cell.sup.i.
[0035] Moreover, the fixing of a condition on the maximum cell
voltage, instead of the minimum cell voltage or the average cell
voltage, can make it possible to ensure the control of the voltage
of all of the cells, and that none of them will exceed this
predefined threshold.
[0036] As long as the cell unbalance remains below the nominal
unbalance level, typically at most 20 mV, this cut-off voltage can
advantageously make it possible to ensure the constant minimum
required energy level for the user. On the other hand, if the cell
unbalance exceeds the nominal end-of-charge unbalance, then this
cut-off voltage cannot make it possible to ensure the constant
minimum required energy level for the user.
[0037] According to advantageous embodiments, the method can
furthermore comprise, in step b), a step c) of generating and
processing a modulation signal of said end-of-charge voltage as a
function of the cell unbalance.
[0038] In this case, managing the charging of the battery can
include not only the strategy mentioned above, but this management
can also take account of the cell unbalance.
[0039] According to this embodiment, step a) can advantageously
consist of determining the cut-off voltage for the end-of-charge on
the maximum cell voltage (V.sub.EndOfCharge.sup.cut-Off-MAX) and
the cut-off voltage for the end-of-charge on the minimum cell
voltage (V.sub.EndOfCharge.sup.cut-Off-MIN) as a function of the
state of ageing of the battery.
[0040] According to this embodiment, the method can advantageously
comprise, after step c), a step of receiving and processing an
end-of-charge signal when the authorized charging power in the
battery (PCHG) is less than or equal to the maximum authorized
end-of-charge power (P.sub.EndOfCharge) and when the maximum cell
voltage value (V.sub.cell.sup.max=max(V.sub.cell.sup.i, i .di-elect
cons. 1 . . . N)) is greater than or equal to the end-of-charge
cut-off voltage on the maximum cell voltage
(V.sub.EndOfCharge.sup.cut-Off-MAX) or when the value of the
minimum cell voltage (V.sub.cell.sup.min=min(V.sub.cell.sup.i, i
.di-elect cons. 1 . . . N)) is greater than or equal to the
end-of-charge cut-off voltage on the minimum cell voltage
(V.sub.EndOfCharge.sup.cut-Off-MIN).
[0041] Insofar as it is the lowest cell voltage which is limiting
in order to ensure the minimum required energy level in the
battery, it can be necessary for the minimum cell voltage to be
greater than (or equal to) a predetermined threshold. However, in
order to endure optimum durability of the battery, it is usually
appropriate to stop charging as soon as the maximum cell voltage
exceeds another additional threshold, such as defined above.
[0042] The authorized charging power can be calculated in several
ways known to those skilled in the art.
[0043] By way of non-limitina example. the followina variables are
defined:
P CHG 1 = { V cell Cut - off - MAX - max ( OCV cell i , i
.epsilon.1 N ) } max ( DCR cell i , i .epsilon. 1 N ) V cell Cut -
off - MAX N ##EQU00001## P CHG 2 = { V cell Cut - off - MIN - min (
OCV cell i , i .epsilon.1 N ) } max ( DCR cell i , i .epsilon. 1 N
) V cell Cut - off - MIN N ##EQU00001.2##
[0044] According to a first example, the authorized charging power
is calculated by the following formula:
PCHG=min{P.sub.CHG.sup.1, P.sub.CHG.sup.2.}
[0045] According to a second example, the authorized charging power
is limited as soon as the maximum cell voltage V.sub.cell.sup.max
is greater than or equal to a voltage threshold. This voltage
threshold can for example be equal to
V lim = V cell Cut - off - MIN + V cell Cut - off - MIN 2
##EQU00002##
[0046] In practice, it is for example possible to determine the
authorized charging power by the following formula:
PCHG = { min { P CHG 1 , P CHG 2 } , ifV cell max .ltoreq. V lim
0.5 .times. min { P CHG 1 , P CHG 2 } , ifV cell max > V lim
##EQU00003##
[0047] The advantage of the last two examples of power and of
voltages is that the latter can make it possible to retain the
durability of the cell by limiting the authorized charging power a
little more as soon as the maximum cell voltage exceeds the cut-off
voltage V.sub.lim.
[0048] According to this embodiment, when the cell unbalance is
less than the nominal cell unbalance, typically at most 20 mV, it
is possible to provide the constant minimum required energy level,
whilst reducing the maximum end-of-charge cell voltage, that is to
say that this value of said voltage can be at the value of said
voltage obtained when only the ageing threshold is taken into
account.
[0049] Moreover, if the cell unbalance is greater than the nominal
unbalance, without however exceeding
(V.sub.EndOfCharge.sup.cut-Off-Charge-V.sub.EndOfCharge.sup.cut-Off-MIN),
then it is possible to ensure the constant minimum required energy
level in the battery. In particular, this solution makes it
possible to manage the cell unbalance which could appear on leaving
the factory.
[0050] In the case where the cell unbalance exceeds
(V.sub.EndOfCharge.sup.cut-Off-Charge-V.sub.EndOfCharge.sup.cut-Off-Charg-
e), it is in any case impossible to provide the minimum required
energy level.
[0051] The advantages of this embodiment are as follows. It can
make it possible, on the one hand, to ensure, over the first years
of use, typically 0-3 years, the constant minimum required energy
level, for the user of the battery, as long as the cell unbalance
remains below the nominal unbalance and, on the other hand, to
limit the degradation of the battery at the start of the service
life by limiting its range of use.
[0052] By way of non-limiting examples according to the prior art
and according to the invention, the following values,
V.sub.EndOfCharge.sup.cut-Off=4.08V and the nominal cell
unbalance=20 mV, are considered for a 100% state of health of the
battery (new battery).
[0053] In other words, V.sub.EndOfCharge.sup.cut-Off, has been
fixed to ensure 22 kWh of energy available in the battery, for a
nominal unbalance of 20 mV, that is to say:
V.sub.cell.sup.min=4.06V.
[0054] V.sub.EndOfCharge.sup.cut-Off-MAX=4.10V and V
.sub.EndOfCharge.sup.cut-Of-MIN=4.06V are also considered.
[0055] a) if the cell unbalance is such that: .DELTA.V.sub.cell=10
m V, then:
[0056] According to the prior art, the charging of the battery is
stopped at V.sub.cell.sup.max=4.08V (and V.sub.cell.sup.min=4.07V).
The user will have more than 22 kWh of available energy and the
battery will have been uselessly overcharged.
[0057] According to the invention, the charging of the battery is
stopped at V.sub.cell.sup.max=4.07V (and V.sub.cell.sup.min=4.06V).
There will be exactly 22 kWh of available power, whilst limiting
the maximum cell voltage.
[0058] b) If the cell unbalance is such that: .DELTA.V.sub.cell=40
m V , then:
[0059] According to the prior art, the charging of the battery is
stopped at V.sub.cell.sup.max=4.08V (and V.sub.cell.sup.min=4.04V).
The user will not have 22 kWh.
[0060] According to the invention, the charging of the battery is
stopped at V.sub.cell.sup.max=4.10V (and V.sub.cell.sup.min=4.06V).
There will be exactly 22 kWh of available power, without however
fixing too high a value of maximum cell voltage.
[0061] In the context of the invention, the Li-ion battery is in no
way limited, and can preferably be a battery where the lithium
remains in an ionic state due to the use of an insertion compound
both in the negative electrode, generally graphite, and in the
positive electrode, able to be cobalt oxide, magnesium oxide or
iron phosphate. Among Li-ion batteries it is possible to mention
the so-called "lithium metal-polymer" and "lithium-air" batteries.
The Li-ion batteries of the invention can be applied in various
technological fields, such as motor vehicles, computers or telecoms
and can be adapted to onboard or non-onboard systems.
[0062] The method of the invention can be used by any type of
charger known to those skilled in the art, notably available
commercially, and the chargers are in no way limited.
[0063] The invention also relates to a device for managing the
charging of a Li-ion battery as a function of at least one
parameter chosen from the group consisting of the ageing of the
battery and the cell unbalance representing the difference between
the state of charge of the cell exhibiting the highest charge and
the state of charge of the cell exhibiting the lowest charge,
comprising, [0064] means of determining an end-of-charge voltage
value of said battery, [0065] processing means arranged to generate
a control signal for controlling the charging of said battery,
[0066] means of transmitting the control signal to a charger,
characterized in that the processing means are arranged so that the
control signal is generated in such a way that the charging of the
battery is carried out as a function of the determined
end-of-charge voltage value, said end-of-charge voltage value being
increased as a function of the increasing state of ageing of said
Li-ion battery up to a limit value in order to provide a constant
minimum required energy level in said Li-ion battery, for a
predetermined reference temperature.
[0067] Such a device can in particular be adapted for the use of
the above method with the different variants.
[0068] The processing means can comprise a processor core or CPU
(Central Processing Unit), a processor or other means.
[0069] The transmission means can for example comprise an output
pin, an output port or other means.
[0070] Advantageously, the device can furthermore comprise means
of: [0071] generating a signal for determining the end-of-charge
voltage value of said battery, said signal making it possible to
carry out the determination of the end-of-charge voltage value;
[0072] generating and processing a signal of evaluation of the
state of ageing of the battery, [0073] generating and processing an
end-of-charge signal when the maximum value of the cell voltage is
greater than or equal to the end-of-charge voltage value and when
the authorized charging power in the battery is less than or equal
to the maximum authorized end-of-charge power, [0074] generating
and processing a modulation signal of said end-of-charge voltage
increased as a function of the cell unbalance. [0075] receiving and
processing an end-of-charge signal when the authorized charging
power in the battery is less than or equal to the maximum
authorized end-of-charge power and when the maximum cell voltage
value is greater than or equal to the cut-off voltage for the
end-of-charge on the maximum cell voltage or when the value of the
minimum cell voltage is greater than or equal to the cut-off
voltage for the end-of-charge on the minimum cell voltage.
[0076] Advantageously, the means of determining the end-of-charge
voltage value of said battery can be arranged to determine the
cut-off voltage for the end-of-charge on the maximum cell voltage
and the cut-off voltage for the end-of-charge on the minimum cell
voltage as a function of the state of ageing of the battery.
[0077] According to another aspect, the invention relates to a
computer program comprising instructions for carrying out the steps
of the method of the invention, when these instructions are
executed by a processor.
[0078] Advantageously, this computer program can be stored in a
memory of the device for managing charging.
[0079] The invention also relates to a lithium-ion battery assembly
comprising a lithium-ion battery and a device for managing the
charging of the battery, such as described above.
[0080] The invention also relates to a motor vehicle incorporating
a lithium-ion battery and the device for managing charging and/or a
battery assembly, such as described above.
[0081] The invention is illustrated by the following figures and
the non-limiting examples, in which:
[0082] FIG. 1 shows an example of a graph illustrating the
end-of-charge voltage, as a function of the state of health of the
Li-ion battery exhibiting a minimum energy level of 22 kWh,
according to one embodiment,
[0083] FIG. 2 shows an example of a graph illustrating the
end-of-charge voltage, here consisting of
(V.sub.EndOFCharge.sup.cut-Off-MAX) and (as a function of
Oigh:.sub.g.sup.ie.sup.N) the state of health of the battery and of
the cell unbalance, according to another embodiment of the
invention, and
[0084] FIG. 3 shows an example of a motor vehicle comprising a
traction battery assembly, according to one embodiment.
[0085] FIG. 1 shows a graph illustrating the end-of-charge voltage,
as a function of the state of health of the Li-ion battery
exhibiting a minimum energy level of 22 kWh, according to an
embodiment of the invention. This graph was established thanks to
the BMS system incorporating appropriate known software.
[0086] The state of health (SOHQ) of the battery was previously
determined using a computing device in the BMS system, according to
conventional methods known to those skilled in the art. The cut-off
voltage for a 100% state of health has a value of 4.08 V for each
of the constituent cells of the battery.
[0087] FIG. 1 shows that the older the battery becomes, the more it
is appropriate to increase the end-of-charge voltage in order to
compensate for the loss of capacity of the battery. In other words,
the end-of-charge voltage value is increased as a function of the
increasing state of ageing of the battery.
[0088] FIG. 2 shows a graph illustrating the end-of-charge voltage,
here consisting of the cut-off voltage for the end-of-charge on the
maximum cell voltage and the cut-off voltage for the end-of-charge
on the minimum cell voltage as a function of the state of health
(SOHQ) of the battery, as a function, on the one hand, of the state
of health of the Li-ion battery, exhibiting a minimum energy level
of 22 kWh, and, on the other hand, of the cell unbalance, according
to another embodiment of the invention. The values of FIG. 1 have
been added in a dotted line. This graph was established using the
BMS system incorporating appropriate and commercially available
software.
[0089] Referring to FIG. 3, a motor vehicle 10 comprises a traction
battery assembly 11, which can be charged by means of a charger
(not shown), for example a charging terminal connected to the
electrical supply system.
[0090] The battery 12 can for example be a lithium ion battery.
[0091] The charger can for example be a fast charging terminal
supplying a DC current to the battery assembly 11 of the vehicle
10.
[0092] The battery assembly 11 can integrate a device for managing
the charging 13, for example a battery control system of the BMS
type, which comprises a computer program comprising instructions
for determining the charging voltage value of said battery and
deciding to proceed with an increase of this value as a function of
the state of ageing of the battery up to a limit value making it
possible to provide a constant minimum required level at a
temperature of 20.degree. C. for example.
[0093] The device for managing charging 13 comprises means of
generating and receiving a signal of determination of the
end-of-charge voltage value of said battery, (not shown), for
example an input pin electrically connected to sensors (not shown)
of the motor vehicle 10.
[0094] The device 13 comprises processing means (not shown)
arranged to generate a control signal controlling the charging of
said battery and in order that the control signal is generated such
that the charging of the battery is carried out as a function of
the end-of-charge voltage value determined in the preceding step,
said end-of-charge voltage value being increased as a function of
the state of ageing of said Li-ion battery up to a limit value in
order to provide a constant minimum required energy level in said
Li-ion battery, for a reference temperature of, for example,
20.degree. C.
[0095] These processing means are in this case the core of a
processor.
[0096] The device 13 comprises means of transmitting the signal
(not shown) to a charger, which are in this case for example an
output pin.
EXAMPLE
[0097] This example shows the managing of the charging of a Li-ion
battery for providing 22 kWh of energy available in the battery
which is constant for a temperature of 25.degree. C.
[0098] The following values are considered:
V.sub.EndOfCharge.sup.cut-Off=4.08V and the nominal cell
unbalance=20 mV, the state of health of the battery being 100% (new
battery).
[0099] In other words, V.sub.EndOfCharge.sup.cut-Off has been fixed
in order to ensure 22 kWh of energy available in the battery, for a
nominal unbalance of 20 mV, that is to say:
V.sub.cell.sup.min=4.06V.
[0100] The following is also considered:
V.sub.EndOfCharge.sup.cut-Of-MAX=4.10V and
V.sub.EndOfCharge.sup.cut-Of-MIN=4.06V.
[0101] a) If the cell unbalance is such that: .DELTA.V.sub.cell=10
mV, then:
[0102] According to the prior art, the charging of the battery will
be stopped at V.sub.cell.sup.max=4.08V (and
V.sub.cell.sup.min=4.07V). The user will have more than 22 kWh of
available energy and the battery will have been uselessly
overcharged.
[0103] According to the invention, the charging of the battery will
be stopped at V.sub.cell.sup.max=4.07V (and
V.sub.cell.sup.min=4.06V). There will be exactly 22 kWh of
available energy, whilst limiting the maximum cell voltage.
[0104] b) If the cell unbalance is such that: .DELTA.V.sub.cell=20
m V , then:
[0105] According to the prior art, the charging of the battery will
be stopped at V.sub.cell.sup.max=4.08V (and
V.sub.cell.sup.min=4.06V).
[0106] According to the invention, the charging of the battery will
be stopped at V.sub.cell.sup.max=4.08V (and
V.sub.cell.sup.min=4.06V).
[0107] The two results are identical.
[0108] c) If the cell unbalance is such that: .DELTA.V.sub.cell=40
mV, then:
[0109] According to the prior art, the charging of the battery will
be stopped at V.sub.cell.sup.max=4.08V (and
V.sub.cell.sup.min=4.04V). The user will not benefit from an
available energy of 22 kWh, which will be lower.
[0110] According to the invention, the charging of the battery will
be stopped at V.sub.cell.sup.max=4.10V (and
V.sub.cell.sup.min=4.06V). There will be exactly 22 kWh of
available energy in the battery, without however fixing too high a
value of maximum cell voltage.
[0111] d) If the cell unbalance is such that .DELTA.V.sub.cell=50
mV, then:
[0112] According to the prior art, the charging of the battery will
be stopped at V.sub.cell.sup.max=4.08V (and
V.sub.cell.sup.min=4.03V). The user will not benefit from an
available energy of 22 kWh, which will be lower.
[0113] According to the invention, the charging of the battery will
be stopped at V.sub.cell.sup.max=4.10V (and
V.sub.cell.sup.min=4.06V). There will be a little less than 22 kWh
of energy available in the battery, without however fixing too high
a value of maximum cell voltage.
* * * * *